JP2017103180A - Copper paste non-pressure conjugation, conjugation, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper paste for non-pressure conjugation capable of providing sufficient conjugation strength even when member having different thermal expansion rate are conjugated each other with no pressure.SOLUTION: There is provided a copper paste for non-pressure conjugation containing a metal particle and a dispersant, wherein the metal particle contains a submicro copper particle having volume average particle diameter of 0.01 μm to 0.8 μm and a micro copper particle having volume average particle diameter of 2.0 μm to 50 μm and the dispersant contains a solvent having the boiling point of 300°C or more and content of the solvent having the boiling point of 300°C or more is 2 mass% or more based on total mass of the copper paste for non-pressure conjugation.SELECTED DRAWING: None

Description

  The present invention relates to a copper paste for pressureless bonding, a bonded body using the same, and a semiconductor device.

  When manufacturing a semiconductor device, various bonding materials are used for bonding a semiconductor element and a lead frame (support member). Among semiconductor devices, high melting point lead solder has been used as a bonding material for bonding power semiconductors, LSIs, and the like that are operated at a high temperature of 150 ° C. or higher. In recent years, due to the increase in capacity and space saving of semiconductor elements, the operating temperature has increased to near the melting point of high melting point lead solder, and it has become difficult to ensure connection reliability. On the other hand, with the strengthening of RoHS regulations, a bonding material not containing lead is required.

  So far, joining of semiconductor elements using materials other than lead solder has been studied. For example, Patent Document 1 below proposes a technique for sintering silver nanoparticles to form a sintered silver layer. It is known that such sintered silver has high connection reliability with respect to the power cycle (Non-Patent Document 1).

  As another material, a technique for sintering a copper particle to form a sintered copper layer has also been proposed. For example, Patent Document 2 below discloses a bonding material containing copper nanoparticles and copper microparticles or copper submicroparticles, or both, and also describes that this bonding material can bond members without pressure. Has been.

Japanese Patent No. 4247800 JP 2014-167145 A

R. Khazaka, L .; Mendizabal, D.M. Henry: J.H. ElecTron. Mater, 43 (7), 2014, 2459-2466

  Since the method described in Patent Document 1 requires densification of the sintered silver layer in order to obtain high connection reliability, a thermocompression process involving pressurization is required. When performing a thermocompression bonding process involving pressurization, there are problems such as a decrease in production efficiency and a decrease in yield. Furthermore, when silver nanoparticles are used, a significant increase in material cost due to silver becomes a problem.

  Although the method described in Patent Document 2 performs sintering without applying pressure, it is still not sufficient for practical use in the following points. That is, the copper nanoparticles need to be modified with a protective agent to suppress oxidation and improve dispersibility. However, since copper nanoparticles have a large specific surface area, in a bonding material mainly composed of copper nanoparticles, The amount of the surface protective agent tends to increase. In addition, the amount of the dispersion medium tends to increase in order to ensure dispersibility. Therefore, the bonding material described in Patent Document 2 has a large proportion of the surface protective agent or the dispersion medium for supply stability such as storage or coating, and the volume shrinkage during sintering tends to be large. Moreover, the density after sintering tends to decrease, and it is difficult to ensure the strength of the sintered body.

  Further, the non-pressure joining using the joining material is performed well when the materials of the members to be joined are equal or close to each other, but the joining force is increased when the materials of the members to be joined are different. It is easy to drop greatly. According to the study by the present inventors, for example, when a copper plate having copper on the deposition surface and a copper block having nickel on the deposition surface are joined, a copper plate having copper on the deposition surface, and a deposition surface It was found that the bonding strength of the latter may be greatly reduced depending on the composition of the copper paste for bonding under pressureless sintering conditions. That is, when a member having a different coefficient of thermal expansion, such as a copper block and a silicon chip, is bonded with no pressure, bonding failure may occur.

  An object of the present invention is to provide a pressure-free bonding copper paste that can obtain sufficient bonding strength even when members having different thermal expansion coefficients are bonded without pressure. It is another object of the present invention to provide a joined body and a semiconductor device using a pressure-free joining copper paste, and a method for producing them.

  In order to solve the above problems, the present inventors have conducted the following investigation. First, in the joining with the joining copper paste, after the dispersion medium is volatilized at the time of the drying process at the time of joining or the temperature rise in the sintering process, a deposit of dried copper-based particles is left. The dried copper-based particle deposits are in a very fragile state because there is no bonding force such as cohesive force of the dispersion medium between the particles. At this time, if the materials of the members to be joined are different, the shear force due to the difference in thermal expansion coefficient between the members to be joined due to the temperature difference between the room temperature and the drying process temperature, or the temperature difference between the room temperature and the sintering process temperature. It is considered that the deposit layer of the copper-based particles can be easily peeled off. If the member is positively pressurized in the sintering process, the delamination will be crushed and the sintered product of the copper-based particle deposit will be joined to the member. May remain detached. From the viewpoint of suppressing such separation, as a result of studies to control the state of deposits at the time of temperature rise, by using a specific solvent at a specific ratio as a dispersion medium, members having different thermal expansion coefficients can be used. It has been found that sufficient bonding strength can be obtained even when bonding is performed under pressure, and the present invention has been completed.

  The present invention is a non-pressure bonding copper paste containing metal particles and a dispersion medium, wherein the metal particles have a volume average particle diameter of 0.01 μm or more and 0.8 μm or less, and a volume average A copper paste for pressure-free joining, comprising a micro copper particle having a particle size of 2.0 μm or more and 50 μm or less, a dispersion medium containing a solvent having a boiling point of 300 ° C. or more, and a content of the solvent having a boiling point of 300 ° C. or more A copper paste for pressureless bonding, which is 2% by mass or more based on the total mass of

  In this specification, “non-pressurized” means a state in which a pressure of 0.01 MPa or less is received in addition to the self-weight of the members to be joined or the self-weight.

  The present invention is also a non-pressure bonding copper paste containing metal particles and a dispersion medium, wherein the metal particles have a volume average particle diameter of 0.01 μm or more and 0.8 μm or less, and a volume of sub-micro copper particles. Non-pressure bonding copper containing a copper particle having a mean particle size of 2.0 μm or more and 50 μm or less, a dispersion medium containing a solvent having a boiling point of 300 ° C. or more, and a solvent having a boiling point of 300 ° C. or more. There is provided a copper paste for pressureless bonding that is 8% by volume or more based on the total capacity of the paste.

  According to the copper paste for pressureless bonding of the present invention, sufficient bonding strength can be obtained even when members having different thermal expansion coefficients are bonded with no pressure. The present inventors infer the reason why such an effect is obtained as follows. That is, when the dispersion medium contains a specific amount of a solvent having a boiling point of 300 ° C. or higher, a predetermined amount of the solvent having a boiling point of 300 ° C. or higher may remain in the copper paste between the members in the temperature rising process during bonding. It is considered possible. This residual solvent gives the copper paste flexibility and adhesion, so that even when shearing force due to the difference in thermal expansion coefficient is applied, the copper paste between the members can be deformed and followed, It is thought that it was able to join without peeling.

  In the present invention, the solvent having a boiling point of 300 ° C. or higher may have at least one group selected from the group consisting of a hydroxy group, an ether group, and an ester group. When the pressure-free bonding copper paste includes such a solvent, a surface treatment agent having a Hansen solubility parameter such as an organic acid, an organic amine, a hydroxyl group-containing polymer, or polyvinylpyrrolidone can be used.

  The copper paste for pressureless bonding of the present invention is sintered when the copper paste for pressureless bonding existing between two members is heated at a temperature of 250 ° C. or higher and lower than 350 ° C. Then, a metal bond may be formed, and the two members may be joined with a die shear strength of 10 MPa or more and a thermal conductivity of 100 W / (m · K) or more. With such a pressure-free bonding copper paste, sufficient bonding strength is easily obtained when members having different coefficients of thermal expansion are bonded.

  The copper paste for pressureless bonding of the present invention is a pressureless bonding when the content of the solvent having a boiling point of 300 ° C. or higher remaining when the temperature is raised from 25 ° C. to 300 ° C. is raised to 300 ° C. It may be 1% by mass or more based on the mass of the composite copper paste. In this case, it is easy to maintain the flexibility of the copper paste composition for pressureless bonding, and when bonding members having different coefficients of thermal expansion, the copper paste for pressureless bonding easily deforms and follows the member. Therefore, it tends to be easy to improve the bonding strength.

  The present invention also provides the first member, the second member having a coefficient of thermal expansion different from that of the first member, and the non-pressure bonding copper paste for joining the first member and the second member. And a sintered body.

  According to the joined body of the present invention, even when the members having different coefficients of thermal expansion are joined together by the sintered body of the copper paste for pressureless joining, the members are joined with sufficient joining strength. It can become the joined body.

  The present invention also includes a first member, a copper paste for pressureless bonding, and a second member having a thermal expansion coefficient different from that of the first member on the side in which the weight of the first member acts. A step of preparing a laminate that is sequentially laminated and sintering a copper paste for pressureless bonding in a state of receiving the weight of the first member or the weight of the first member and a pressure of 0.01 MPa or less. The manufacturing method of a joined body provided with this is provided.

  According to the method for manufacturing a joined body of the present invention, even when the members having different coefficients of thermal expansion are used, the members are joined with a sufficient joining force by using the copper paste for pressureless joining of the present invention. Thus, it is possible to manufacture a bonded body having excellent connection reliability.

  The present invention also provides the first member, the second member having a coefficient of thermal expansion different from that of the first member, and the non-pressure bonding copper paste for joining the first member and the second member. A semiconductor device, wherein at least one of the first member and the second member is a semiconductor element.

  According to the method for manufacturing a semiconductor device of the present invention, by using the copper paste for pressureless bonding of the present invention, the members are sufficient even if the members constituting the semiconductor device have different coefficients of thermal expansion. It is possible to manufacture a semiconductor device that is bonded with an appropriate bonding force and has excellent connection reliability.

  The present invention can provide a pressure-free bonding copper paste that can obtain sufficient bonding strength even when members having different thermal expansion coefficients are bonded without pressure. The present invention can further provide a bonded body and a semiconductor device using a copper paste for pressureless bonding, and a method for producing them.

It is a schematic cross section which shows an example of the joined body manufactured using the copper paste for non-pressure joining of this embodiment. It is a schematic cross section which shows an example of the semiconductor device manufactured using the copper paste for pressureless joining of this embodiment. FIG. 3 is a view showing an SEM image of a cross section of a bonding sample of Example 1. 6 is a view showing an SEM image of a cross section of a bonded sample of Comparative Example 1. It is a figure which shows about the relationship between the ratio for which the solvent which has a boiling point of 300 degreeC or more accounts for the copper paste for non-pressure joining, and die shear strength. It is a figure shown about the relationship between the boiling point of a dispersion medium, and die shear strength.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments.

<Copper paste for pressureless bonding>
The pressureless bonding copper paste of the present embodiment is a pressureless bonding copper paste including metal particles and a dispersion medium, and the metal particles include sub-micro copper particles and micro copper particles.

(Metal particles)
Examples of the metal particles according to the present embodiment include sub-micro copper particles, micro-copper particles, and other metal particles other than these copper particles.

(Sub-micro copper particles)
The sub-micro copper particles may be copper particles having sinterability in a temperature range of 250 ° C. or higher and 350 ° C. or lower. Examples of the sub-micro copper particles include those containing copper particles having a particle size of 0.01 μm or more and 0.8 μm or less. For example, copper particles of a copper particle having a volume average particle size of 0.01 μm or more and 0.8 μm or less Can be used. If the volume average particle diameter of the sub-micro copper particles is 0.01 μm or more, effects such as suppression of the synthesis cost of the sub-micro copper particles, good dispersibility, and suppression of the use amount of the surface treatment agent are easily obtained. If the volume average particle diameter of the sub-micro copper particles is 0.8 μm or less, an effect that the sinterability of the sub-micro copper particles is excellent is easily obtained. From the standpoint of further exerting the above effects, the upper limit of the volume average particle diameter of the sub-micro copper particles may be 0.6 μm or less, may be 0.5 μm or less, and may be 0.4 μm or less. Also good. In addition, the lower limit of the volume average particle size of the sub-micro copper particles may be 0.02 μm or more, 0.05 μm or more, or 0.1 μm or more. The volume average particle size of the sub-micro copper particles may be, for example, from 0.01 μm to 0.5 μm, from 0.12 μm to 0.8 μm, and from 0.15 μm to 0.8 μm. It may be 0.15 μm or more, 0.6 μm or less, 0.2 μm or more and 0.5 μm or less, or 0.3 μm or more and 0.45 μm or less.

  In the present specification, the volume average particle diameter means 50% volume average particle diameter. When determining the volume average particle size of copper particles, light scattering is performed by dispersing copper particles as raw materials or dry copper particles from which volatile components have been removed from pressure-free bonding copper paste in a dispersion medium using a dispersant. It can be determined by a method of measuring with a method particle size distribution measuring device (for example, a Shimadzu nano particle size distribution measuring device (SALD-7500 nano, manufactured by Shimadzu Corporation)). When using a light scattering particle size distribution analyzer, hexane, toluene, α-terpineol, 4-methyl-1,3-dioxolan-2-one, or the like can be used as a dispersion medium.

  The content of the sub-micro copper particles may be 20% by mass or more and 90% by mass or less, 30% by mass or more and 90% by mass or less, or 35% by mass or more based on the total mass of the metal particles. 85 mass% or less may be sufficient, and 40 mass% or more and 80 mass% or less may be sufficient. If the content of the sub-micro copper particles is within the above range, it becomes easy to secure the bonding strength of the joined body produced by sintering the copper paste for pressureless bonding, and the copper paste for pressureless bonding is used as a semiconductor. When used for joining elements, semiconductor devices tend to exhibit good die shear strength and connection reliability.

  The content of the sub-micro copper particles is preferably 20% by mass or more and 90% by mass or less based on the total mass of the sub-micro copper particles and the mass of the micro-copper particles. If the content of the sub-micro copper particles is 20% by mass or more, the space between the micro-copper particles can be sufficiently filled, and the joining strength of the joined body produced by sintering the pressure-free joining copper paste. When the copper paste for pressureless bonding is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. If the content of the sub-micro copper particles is 90% by mass or less, volume shrinkage when sintering the copper paste for pressureless bonding can be sufficiently suppressed. Therefore, it is produced by sintering the copper paste for pressureless bonding. It is easy to ensure the bonding strength of the bonded body, and when the non-pressure bonding copper paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of further achieving the above effects, the content of the sub-micro copper particles may be 30% by mass or more and 85% by mass or less based on the total mass of the sub-micro copper particles and the mass of the micro-copper particles. 35 mass% or more and 85 mass% or less may be sufficient, and 40 mass% or more and 80 mass% or less may be sufficient.

  The shape of the sub-micro copper particles is not particularly limited. Examples of the shape of the sub-micro copper particles include a spherical shape, a lump shape, a needle shape, a flake shape, a substantially spherical shape, and an aggregate thereof. From the viewpoints of dispersibility and filling properties, the shape of the sub-micro copper particles may be spherical, substantially spherical, or flaky. From the viewpoint of combustibility, dispersibility, miscibility with flaky microparticles, etc., Alternatively, it may be approximately spherical. In the present specification, the “flakes” include flat shapes such as plates and scales.

  The sub-micro copper particles may have an aspect ratio of 5 or less or 3 or less from the viewpoints of dispersibility, filling properties, and miscibility with the flaky micro particles. In this specification, “aspect ratio” indicates the long side / thickness of a particle. The measurement of the long side and thickness of the particle can be obtained, for example, from the SEM image of the particle.

  The sub-micro copper particles may be treated with a specific surface treatment agent. Examples of the specific surface treatment agent include organic acids having 2 to 18 carbon atoms. Examples of the organic acid having 2 to 18 carbon atoms include acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, caprylic acid, methylheptanoic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid, and methyloctane. Acid, ethylheptanoic acid, propylhexanoic acid, capric acid, methylnonanoic acid, ethyloctanoic acid, propylheptanoic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanoic acid, lauric acid, methylundecane Acid, ethyldecanoic acid, propylnonanoic acid, butyloctanoic acid, pentylheptanoic acid, tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyldodecane Acid, propylundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid, methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, Ethyltetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, heptadecanoic acid, octadecanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentyl Cyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid , Saturated fatty acids such as nonylcyclohexanecarboxylic acid; octenoic acid, nonenoic acid, methylnonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, sabienoic acid, Unsaturated fatty acids such as oleic acid, vaccenic acid, linoleic acid, linolenic acid, linolenic acid; terephthalic acid, pyromellitic acid, o-phenoxybenzoic acid, methylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, butylbenzoic acid, pentyl Examples thereof include aromatic carboxylic acids such as benzoic acid, hexyl benzoic acid, heptyl benzoic acid, octyl benzoic acid, and nonyl benzoic acid. An organic acid may be used individually by 1 type, and may be used in combination of 2 or more type. By combining such an organic acid and the sub-micro copper particles, the dispersibility of the sub-micro copper particles and the detachability of the organic acid during sintering tend to be compatible.

The treatment amount of the surface treatment agent may be an amount that adheres to a monomolecular layer to a trimolecular layer on the surface of the sub-micro copper particles. This amount depends on the number of molecular layers (n) attached to the surface of the sub-micro copper particles, the specific surface area (A _p ) (unit m ² / g) of the sub-micro copper particles, and the molecular weight (M _s ) of the surface treatment agent ( (Unit g / mol), minimum covering area (S _S ) (unit m ² / piece) of surface treatment agent, and Avogadro's number (N _A ) (6.02 × 10 ²³ pieces). Specifically, the treatment amount of the surface treatment agent is the treatment amount of the surface treatment agent (% by mass) = {(n · A _p · M _s ) / (S _S · N _A + n · A _p · M _s )} * Calculated according to the equation of 100%.

The specific surface area of the sub-micro copper particles can be calculated by measuring the dried sub-micro copper particles by the BET specific surface area measurement method. Minimum coverage of the surface treatment agent, if the surface treatment agent is a straight-chain saturated fatty acids, is 2.05 × ¹⁰ -19 ^m 2/1 molecule. In the case of other surface treatment agents, for example, calculation from a molecular model, or “Chemistry and Education” (Akihiro Ueda, Juno Inafuku, Mori Kaoru, 40 (2), 1992, p114-117) It can be measured by the method described. An example of the method for quantifying the surface treatment agent is shown. The surface treatment agent can be identified by a thermal desorption gas / gas chromatograph mass spectrometer of a dry powder obtained by removing the dispersion medium from the non-pressure bonding copper paste, and thereby the carbon number and molecular weight of the surface treatment agent can be determined. The carbon content of the surface treatment agent can be analyzed by carbon content analysis. Examples of the carbon analysis method include a high frequency induction furnace combustion / infrared absorption method. The amount of the surface treatment agent can be calculated by the above formula from the carbon number, molecular weight, and carbon content ratio of the identified surface treatment agent.

  The treatment amount of the surface treatment agent may be 0.07% by mass or more and 2.1% by mass or less, may be 0.10% by mass or more and 1.6% by mass or less, and may be 0.2% by mass. It may be 1.1% by mass or less.

  Since the above-mentioned sub-micro copper particles have good sinterability, there are problems such as expensive synthesis cost, poor dispersibility, and decrease in volume shrinkage after sintering, which are mainly seen in bonding materials using copper nanoparticles. Can be reduced.

  As the sub-micro copper particles according to the present embodiment, commercially available ones can be used. Examples of commercially available sub-microparticles include CH-0200 (Mitsui Metal Mining Co., Ltd., volume average particle size 0.36 μm), HT-14 (Mitsui Metal Mining Co., Ltd., volume average particle size 0.41 μm). ), CT-500 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.72 μm), Tn-Cu100 (manufactured by Taiyo Nissan Co., Ltd., volume average particle size 0.12 μm).

(Micro copper particles)
As the micro copper particles, copper particles having a particle size of 2.0 μm or more and 50 μm or less can be used. For example, copper particles having a volume average particle size of 2.0 μm or more and 50 μm or less can be used. If the volume average particle size of the micro copper particles is within the above range, the volume shrinkage and void generation when the copper paste for pressureless bonding is sintered can be sufficiently reduced, and the copper paste for pressureless bonding is sintered. It becomes easy to ensure the bonding strength of the bonded body manufactured by the above-mentioned method, and when the pressure-free bonding copper paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of further exerting the above effects, the volume average particle diameter of the micro copper particles may be 2 μm or more and 20 μm or less, 2 μm or more and 10 μm or less, or 3 μm or more and 20 μm or less, It may be 3 μm or more and 10 μm or less.

  The content of the micro copper particles may be 10% by mass to 90% by mass, 15% by mass to 65% by mass, or 20% by mass to 60% by mass based on the total mass of the metal particles. The mass% or less may be sufficient. If the content of the micro copper particles is within the above range, it becomes easy to secure the bonding strength of the joined body produced by sintering the copper paste for pressureless bonding, and the copper paste for pressureless bonding is used as a semiconductor. When used for joining elements, semiconductor devices tend to exhibit good die shear strength and connection reliability.

  The total of the content of the sub-micro copper particles and the content of the micro-copper particles can be 80% by mass or more based on the total mass of the metal particles. If the sum of the content of the sub-micro copper particles and the content of the micro-copper particles is within the above range, the volume shrinkage when sintering the copper paste for pressureless bonding can be sufficiently reduced, and the copper paste for pressureless bonding It becomes easy to ensure the joining strength of the joined body manufactured by sintering the material. When the pressure-free bonding copper paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the standpoint of further exerting the above effects, the total content of the sub-micro copper particles and the content of the micro-copper particles may be 90% by mass or more based on the total mass of the metal particles, and 95% by mass. The above may be sufficient and 100 mass% may be sufficient.

  The shape of the micro copper particles is not particularly limited. Examples of the shape of the micro copper particles include a spherical shape, a lump shape, a needle shape, a flake shape, a substantially spherical shape, and an aggregate thereof. Among these, the shape of the micro copper particles is preferably a flake shape. By using the flake-shaped micro copper particles, the micro copper particles in the pressure-free bonding copper paste are oriented substantially parallel to the bonding surface, thereby sintering the pressure-free bonding copper paste. Volume shrinkage can be suppressed, and it becomes easy to ensure the bonding strength of the bonded body manufactured by sintering the pressure-free bonding copper paste. When the pressure-free bonding copper paste is used for bonding semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the standpoint of further achieving the above effects, the flaky micro copper particles may have an aspect ratio of 4 or more, or 6 or more.

  In the micro copper particles, the presence or absence of the treatment with the surface treatment agent is not particularly limited. From the viewpoint of dispersion stability and oxidation resistance, the micro copper particles may be treated with a surface treatment agent. The surface treatment agent may be removed at the time of joining. Examples of such surface treatment agents include aliphatic carboxylic acids such as dodecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, arachidic acid, linoleic acid, linolenic acid, oleic acid; terephthalic acid, pyromellitic acid, o- Aromatic carboxylic acids such as phenoxybenzoic acid; aliphatic alcohols such as cetyl alcohol, stearyl alcohol, isobornylcyclohexanol, tetraethylene glycol; aromatic alcohols such as p-phenylphenol; octylamine, dodecylamine, stearylamine, etc. Alkylamines; aliphatic nitriles such as stearonitrile and decanonitrile; silane coupling agents such as alkylalkoxysilanes; high content of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, silicone oligomers, etc. Treating material and the like. A surface treating agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  The treatment amount of the surface treatment agent may be a monomolecular layer or more on the particle surface. The treatment amount of such a surface treatment agent varies depending on the specific surface area of the micro copper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent. The treatment amount of the surface treatment agent is usually 0.001% by mass or more. The specific surface area of the micro copper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent can be calculated by the method described above.

  When preparing a copper paste for pressureless bonding only from the above-mentioned sub-micro copper particles, the volume shrinkage and sintering shrinkage that accompany the drying of the dispersion medium are large, and therefore, the copper paste for joining is easily peeled off from the adherend surface during sintering In addition, it is difficult to obtain sufficient die shear strength and connection reliability in the joining of semiconductor elements and the like. When preparing a copper paste for pressureless bonding only from the micro copper particles, the sintering temperature tends to increase and a sintering step of 400 ° C. or more tends to be required. By using the sub-micro copper particles and the micro-copper particles in combination, volume shrinkage when the pressure-free bonding copper paste is sintered is suppressed, and the bonded body can have sufficient bonding strength. When the pressure-free bonding copper paste is used for bonding of semiconductor elements, an effect that the semiconductor device exhibits good die shear strength and connection reliability can be obtained.

  What is marketed can be used as micro copper particles concerning this embodiment. Examples of commercially available microparticles include MA-C025KFD (Mitsui Metals Mining Co., Ltd., volume average particle size 7.5 μm), 3L3 (Fukuda Metal Foil Powder Co., Ltd., volume average particle size 8.0 μm). 1110F (Mitsui Metals Mining Co., Ltd., volume average particle size 3.8 μm), HWQ 3.0 μm (Fukuda Metal Foil Powder Co., Ltd., volume average particle size 3.0 μm).

(Other metal particles other than the above copper particles)
The metal particles may include other metal particles other than the sub-micro copper particles and the micro-copper particles, and may include, for example, particles of copper nanoparticles, nickel, silver, gold, palladium, platinum, and the like. . Other metal particles other than the copper particles may have a volume average particle size of 0.01 μm or more and 10 μm or less, 0.01 μm or more and 5 μm or less, or 0.05 μm or more and 3 μm or less. . When other metal particles are contained, the content thereof may be less than 20% by mass or less than 10% by mass based on the total mass of the metal particles from the viewpoint of obtaining sufficient bondability. May be. Other metal particles may not be included. The shape of other metal particles is not particularly limited.

  When metal particles other than copper particles are included, a sintered body in which multiple types of metals are dissolved or dispersed can be obtained, so that mechanical properties such as yield stress and fatigue strength of the sintered body are improved, and connection is achieved. Reliability is easy to improve. Moreover, the sintered compact of the copper paste for pressureless joining can have sufficient joining strength with respect to a specific adherend by adding a multiple types of metal particle. When the pressure-free bonding copper paste is used for bonding semiconductor elements, the die shear strength and connection reliability of the semiconductor device are likely to be improved.

(Dispersion medium)
The dispersion medium includes a solvent having a boiling point of 300 ° C. or higher. As the boiling point of the solvent having a boiling point of 300 ° C. or higher, from the viewpoint that when pressing the copper paste for pressureless bonding, the sintering and densification are not hindered and the bonding temperature is quickly evaporated and removed. May be 300 ° C. or higher and 450 ° C. or lower, 305 ° C. or higher and 400 ° C. or lower, or 310 ° C. or higher and 380 ° C. or higher.

  For the solvent having a boiling point of 300 ° C. or higher, it is preferable to select a structure having a high affinity for the metal particle surface in order to improve the dispersibility of the contained metal particles. When the metal particles are surface-treated with a surface treatment agent containing an alkyl group, it is preferable to select a solvent having an alkyl group. Examples of the solvent having a boiling point of 300 ° C. or higher include isobornyl cyclohexanol (MTPH, manufactured by Nippon Terpene Co., Ltd.), butyl stearate, Exepal BS (manufactured by Kao Corporation), stearyl stearate, Exepal SS (manufactured by Kao Corporation). ), 2-ethylhexyl stearate, Exepal EH-S (manufactured by Kao), isotridecyl stearate, Exepal TD-S (manufactured by Kao), isooctadecanol, fine oxocol 180 (manufactured by Nissan Chemical Co., Ltd.), fine oxo Coal 180T (manufactured by Nissan Chemical Co., Ltd.), 2-hexyldecanol, fine oxocol 1600 (manufactured by Nissan Chemical Co., Ltd.), tributyrin, tetraethylene glycol, heptadecane, octadecane, nonadecane, eicosane, heneicosane, docosane, methylheptadecane, tride Silcyclohexane, tetradecylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, undecylbenzene, dodecylbenzene, tetradecylbenzene, tridecylbenzene, pentadecylbenzene, hexadecylbenzene, heptadecylbenzene, nonylnaphthalene, diphenylpropane, octanoic acid Octyl, methyl myristate, ethyl myristate, methyl linoleate, methyl stearate, triethylene glycol bis (2-ethylhexanoic acid), tributyl citrate, pentylphenol, dibutyl sebacate, oleyl alcohol, cetyl alcohol, methoxyphenethyl alcohol Benzylphenol, hexadeconitrile, heptadeconitrile, benzyl benzoate, cinmethylin, etc. That.

As the solvent having a boiling point of 300 ° C. or higher, a solvent having a Hansen solubility parameter close to that of the surface treatment agent is preferably selected from the viewpoint of improving dispersibility. As a surface treatment agent, an organic acid, an organic amine, a hydroxyl group-containing polymer, polyvinyl pyrrolidone and the like are easy to handle. It preferably has a seed group. The Hansen solubility parameter can be searched from, for example, the end document database of the following published document, or can be searched / calculated by the database and simulation integrated software HSPiP.
Published literature: “HANSEN SOLUBILITY PARAMETERS: A USER'S HANDBOOK” (CRC Press, 1999)

  Content of the solvent which has a boiling point of 300 degreeC or more can be 2 mass% or more on the basis of the total mass of the copper paste for pressureless joining. The content of the solvent having a boiling point of 300 ° C. or higher may be 2.2% by mass or more, or 2.4% by mass or more based on the total mass of the copper paste for pressureless bonding. When the content of the solvent having a boiling point of 300 ° C. or higher is within the above range, a certain amount of solvent remains in the pressure-free bonding copper paste when the pressure-free bonding copper paste of this embodiment is sintered. The flexibility and adhesion of the copper paste between the members can be easily maintained, and even when the members used for bonding have different coefficients of thermal expansion, they tend to be bonded without peeling. The upper limit of the content of the solvent having a boiling point of 300 ° C. or higher is not particularly limited. From the viewpoint that the time until the dispersion medium is removed at the sintering temperature can be suppressed and the sintering time can be shortened, even if it is 9% by mass or less based on the total mass of the copper paste for pressureless bonding Good.

  Moreover, in the copper paste for pressureless bonding of the present embodiment, the content of the solvent having a boiling point of 300 ° C. or more may be 8% by volume or more based on the total capacity of the copper paste for pressureless bonding, It may be 17% by volume or more, or 23% by volume or more. When the content of the solvent having a boiling point of 300 ° C. or higher is within the above range, a certain amount of solvent remains in the pressure-free bonding copper paste when the pressure-free bonding copper paste of this embodiment is sintered. The flexibility and adhesion of the copper paste between the members can be easily maintained, and even when the members used for bonding have different coefficients of thermal expansion, they tend to be bonded without peeling. The upper limit of the content of the solvent having a boiling point of 300 ° C. or higher is not particularly limited. From the viewpoint that the time until the dispersion medium is removed at the sintering temperature can be suppressed and the sintering time can be shortened, even if it is 60% by volume or less based on the total capacity of the copper paste for pressureless bonding Good.

  The dispersion medium may contain a solvent having a boiling point of less than 300 ° C. Examples of the solvent having a boiling point of less than 300 ° C. include α-terpineol, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, 4-methyl-1,3-dioxolan-2-one, diethylene glycol monobutyl ether and the like. A solvent having a boiling point of less than 300 ° C. can be easily removed in a drying step or a temperature rising step prior to the sintering step. A dispersion medium may be used individually by 1 type from the solvent which has a boiling point of 300 degreeC or more, and the solvent which has a boiling point of less than 300 degreeC, and may be used in combination of 2 or more type.

  The content of the dispersion medium may be 5 to 50 parts by mass with 100 parts by mass of the total mass of the metal particles. If the content of the dispersion medium is within the above range, the pressure-free joining copper paste can be adjusted to a more appropriate viscosity, and it is difficult to inhibit sintering of the copper particles.

  The content of the solvent having a boiling point of 300 ° C. or higher in the dispersion medium may be 20% by mass or more and 100% by mass or less based on the total mass of the dispersion medium. If the content of the solvent having a boiling point of 300 ° C. or higher in the dispersion medium is within the above range, it is easy to ensure the content of the solvent having a boiling point of 300 ° C. or higher with respect to the total mass of the copper paste for pressureless bonding.

  The kind of the dispersion medium contained in the copper paste composition for pressureless bonding can be analyzed by, for example, high-temperature desorption gas gas chromatography-mass spectrometry and TOF-SIMS. As another analysis method, the supernatant obtained by separating the particle components by centrifugation may be identified by ordinary organic analysis, for example, FT-IR, NMR, liquid chromatograph, and combinations thereof. The ratio of the type of dispersion medium can be quantified by liquid chromatography, NMR, or the like.

(Additive)
If necessary, the copper paste for pressureless bonding includes a nonionic surfactant, a wetting improver such as a fluorosurfactant; an antifoaming agent such as silicone oil; an ion trapping agent such as an inorganic ion exchanger, and the like. You may add suitably.

  The pressure-free bonding copper paste of this embodiment is obtained when the content of the solvent having a boiling point of 300 ° C. or higher remaining when the paste is heated from 25 ° C. to 300 ° C. is heated to 300 ° C. It is preferably 1% by mass or more based on the mass of the copper paste for pressureless bonding. The heating rate can be 9.2 (° C./min). In this case, it becomes easy to maintain the flexibility of the copper paste between the members, and even when the shearing force due to the difference in the thermal expansion coefficient is applied when the members having different thermal expansion coefficients are joined together, the copper paste However, since it can be deformed / followed with respect to the member, it tends to be firmly joined. The upper limit of the content of the solvent having a boiling point of 300 ° C. or higher that remains when the paste is heated from 25 ° C. to 300 ° C. is not particularly limited until the dispersion medium is removed at the sintering temperature. 9 mass% or less may be sufficient from a viewpoint that time can be restrained and sintering time can be shortened.

  The pressure-free bonding copper paste of this embodiment can have sufficient flexibility at the time of bonding, so the pressure-free bonding copper paste existing between two members is heated at a temperature of 250 ° C. or higher and lower than 350 ° C. Then, the micro copper particles and the sub-micro copper particles are sintered to form a metal bond, and the two members can be bonded with a die shear strength of 10 MPa or more and a thermal conductivity of 100 W / (m · K) or more. .

  As one aspect of the copper paste for pressureless bonding of the present embodiment, the metal particles are sub-micro copper particles having a volume average particle diameter of 0.01 μm or more and 0.8 μm or less, and a volume average particle diameter of 2.0 μm. The content of the solvent containing the micro copper particles having a boiling point of 300 ° C. or higher, including the micro copper particles of 50 μm or less, and having a boiling point of 300 ° C. or higher is based on the total mass of the copper paste for pressureless bonding An example of the copper paste for pressureless bonding is 2% by mass or more.

  Examples of the pressureless bonding copper paste include sub-micro copper particles having a volume average particle diameter of 0.01 μm to 0.8 μm, micro copper particles having a volume average particle diameter of 2.0 μm to 50 μm, and 300 A dispersion medium containing a solvent having a boiling point of not lower than ° C. and other components as necessary, and the amount of the solvent having a boiling point of not lower than 300 ° C. is the total mass of the copper paste for pressureless bonding. As a reference | standard, what is 2 mass% or more is mentioned.

  Even in paste-like compositions in which sub-micro copper particles having sinterability and micro-copper particles having a reinforcing effect are mixed with a dispersion medium having a normal boiling point of less than 300 ° C., the coefficient of thermal expansion is remarkable between members to be joined. If there is no difference, it can be bonded with high strength (for example, see the die shear strength for the Ni-plated Cu plate of Comparative Example 1 in Table 1). However, when such a paste-like composition is used for joining members having different coefficients of thermal expansion, the joining force tends to be greatly reduced (for example, die shear strength with respect to the Ni-plated Si chip of Comparative Example 1 in Table 1). See). The cause of the decrease in the bonding force is that if the boiling point of the dispersion medium is lower than the bonding temperature, the dispersion medium evaporates during the heating process, and the paste-like composition becomes a brittle composition that dries before reaching the bonding temperature. It is possible to end up. In this state, when thermal stress acts on each member having a different coefficient of thermal expansion, the dried and brittle composition cannot follow the member and peels off or cracks, so that it is considered that the joining force decreases as a result.

  By including a solvent having a boiling point of 300 ° C. or higher at which the dispersion medium can remain at the bonding temperature, the solvent having a boiling point of 300 ° C. or higher, preferably 1% by mass or higher, is contained in the non-pressure bonding copper paste in the temperature rising process. Since it can remain, flexibility and adhesion can be given to the pressure-free bonding copper paste. Therefore, even when thermal stress is applied to each member having a different coefficient of thermal expansion at the time of joining, the copper paste for pressureless joining is deformed and followed, and the members can be joined without peeling.

(Preparation of pressureless copper paste)
The copper paste for pressureless bonding can be prepared by mixing the above-mentioned sub-micro copper particles, micro-copper particles, other metal particles, and any additive in a solvent having a boiling point of 300 ° C. or higher as a dispersion medium. it can. You may perform a stirring process after mixing of each component. The copper paste for pressureless bonding may adjust the maximum particle size of the dispersion by classification operation. At this time, the maximum particle size of the dispersion liquid can be 20 μm or less, and can also be 10 μm or less.

  The copper paste for pressureless bonding is prepared by mixing sub-micro copper particles, a surface treatment agent, and a solvent having a boiling point of 300 ° C. or higher, which is a dispersion medium, and performing dispersion treatment to prepare a dispersion of sub-micro copper particles. Furthermore, micro copper particles, other metal particles, and optional additives may be mixed. By setting it as such a procedure, the dispersibility of a sub micro copper particle improves, a miscibility with a micro copper particle improves, and the performance of the copper paste for pressureless joining can be improved more. Aggregates may be removed from the sub-micro copper particle dispersion by classification.

  The stirring treatment can be performed using a stirrer. Examples of the stirrer include, for example, Ishikawa stirrer, Silverson stirrer, cavitation stirrer, rotation / revolution stirrer, ultra-thin high-speed rotary disperser, ultrasonic disperser, reika machine, twin-screw kneader, bead mill, ball mill, three Examples thereof include a roll mill, a homomixer, a planetary mixer, an ultra-high pressure type disperser, and a thin layer shear disperser.

  Classification operation can be performed using filtration, natural sedimentation, and centrifugation, for example. Examples of the filter for filtration include a water comb, a metal mesh, a metal filter, and a nylon mesh.

  Examples of the dispersion treatment include a thin layer shear disperser, a bead mill, an ultrasonic homogenizer, a high shear mixer, a narrow gap three-roll mill, a wet super atomizer, a supersonic jet mill, and an ultra high pressure homogenizer.

  The copper paste for pressureless bonding may be adjusted to a viscosity suitable for each printing / coating method when molding. As the viscosity of the copper paste for pressureless bonding, for example, the Casson viscosity at 25 ° C. may be 0.05 Pa · s or more and 2.0 Pa · s or less, and 0.06 Pa · s or more and 1.0 Pa · s or less. There may be.

<Joint and semiconductor device>
Hereinafter, preferred embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  FIG. 1 is a schematic cross-sectional view showing an example of a joined body manufactured using the pressure-free joining copper paste of the present embodiment. The joined body 100 of the present embodiment includes the first member 2, the second member 3 having a coefficient of thermal expansion different from that of the first member, and the first member and the second member. And a sintered body 1 of a copper paste for pressure bonding.

  As the first member 2 and the second member 3, for example, semiconductor elements such as IGBT, diode, Schottky barrier diode, MOS-FET, thyristor, logic, sensor, analog integrated circuit, LED, semiconductor laser, transmitter, etc. , A lead frame, a ceramic substrate with a metal plate (for example, DBC), a substrate for mounting a semiconductor element such as an LED package, a power supply member such as a copper ribbon, a metal block, and a terminal, a radiator plate, and a water-cooled plate.

  The 1st member 2 and the 2nd member 3 may contain the metal in the surfaces 4a and 4b which contact the sintered compact of the copper paste for pressureless joining. Examples of the metal include copper, nickel, silver, gold, palladium, platinum, lead, tin, and cobalt. A metal may be used individually by 1 type and may be used in combination of 2 or more type. Further, the surface in contact with the sintered body may be an alloy containing the above metal. Examples of the metal used for the alloy include zinc, manganese, aluminum, beryllium, titanium, chromium, iron, and molybdenum in addition to the above metals. Examples of the member containing metal on the surface in contact with the sintered body include, for example, a member having various metal plating, a wire, a chip having metal plating, a heat spreader, a ceramic substrate to which a metal plate is attached, and a lead frame having various metal plating. Or the lead frame which consists of various metals, a copper plate, and copper foil are mentioned.

  The die shear strength of the joined body may be 10 MPa or more, 15 MPa or more, 20 MPa or more, or 30 MPa from the viewpoint of sufficiently joining the first member and the second member. It may be the above. The die shear strength can be measured using a universal bond tester (4000 series, manufactured by DAGE) or the like.

  The thermal conductivity of the sintered body of the copper paste for pressureless bonding may be 100 W / (m · K) or more, and 120 W / (m · K) from the viewpoint of heat dissipation and connection reliability at high temperatures. ) Or higher, or 150 W / (m · K) or higher. The thermal conductivity can be calculated from the thermal diffusivity, specific heat capacity, and density of the sintered body of the copper paste for pressureless bonding.

  The difference in coefficient of thermal expansion between the first member and the second member may be 2 ppm to 30 ppm, 3 ppm to 23 ppm, or 5 ppm to 15 ppm.

  Next, the manufacturing method of the joined body using the copper paste for pressureless joining of this embodiment is demonstrated.

  The manufacturing method of the joined body using the non-pressure bonding copper paste of the present embodiment includes the first member, the non-pressure bonding copper paste, and the first member on the side in which the weight of the first member acts. A laminate in which a second member having a coefficient of thermal expansion different from that of the member is laminated in this order is prepared, and the non-pressure bonding copper paste is used for the weight of the first member or the weight of the first member and the weight of the first member. A step of sintering under a pressure of 01 MPa or less. The direction in which the weight of the first member works can also be said to be the direction in which gravity works.

  The laminate is prepared by, for example, providing the pressure-free bonding copper paste of the present embodiment on a necessary portion of the second member and then placing the first member on the pressure-free bonding copper paste. Can do.

  As a method for providing the pressure-free bonding copper paste of the present embodiment on a necessary portion of the second member, any method may be used as long as the pressure-free bonding copper paste is deposited. Examples of such methods include screen printing, transfer printing, offset printing, jet printing, dispenser, jet dispenser, needle dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, intaglio printing, gravure printing. Printing, stencil printing, soft lithography, bar coating, applicator, particle deposition method, spray coater, spin coater, dip coater, electrodeposition coating, and the like can be used. The thickness of the copper paste for pressureless bonding may be 1 μm or more and 1000 μm or less, 10 μm or more and 500 μm or less, 50 μm or more and 200 μm or less, or 10 μm or more and 3000 μm or less, It may be 15 μm or more and 500 μm or less, 20 μm or more and 300 μm or less, 5 μm or more and 500 μm or less, 10 μm or more and 250 μm or less, or 15 μm or more and 150 μm or less.

  The pressure-free bonding copper paste provided on the second member may be appropriately dried from the viewpoint of suppressing flow and void generation during sintering. The gas atmosphere at the time of drying may be air, an oxygen-free atmosphere such as nitrogen or a rare gas, or a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying at room temperature, drying by heating, or drying under reduced pressure. For heat drying or reduced pressure drying, for example, hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic A heating device, a heater heating device, a steam heating furnace, a hot plate press device, or the like can be used. The drying temperature and time may be appropriately adjusted according to the type and amount of the dispersion medium used. As the drying temperature and time, for example, the drying may be performed at 50 ° C. or higher and 180 ° C. or lower for 1 minute or longer and 120 minutes or shorter.

  Examples of the method for arranging the first member on the non-pressure bonding copper paste include a chip mounter, a flip chip bonder, a carbon or ceramic positioning jig.

  The laminated body is heat treated to sinter the copper paste for pressureless bonding. For the heat treatment, for example, hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic heating device, A heater heating device, a steam heating furnace, or the like can be used.

  The gas atmosphere at the time of sintering may be an oxygen-free atmosphere from the viewpoint of suppressing oxidation of the sintered body, the first member, and the second member. The gas atmosphere at the time of sintering may be a reducing atmosphere from the viewpoint of removing the surface oxide of the copper particles of the copper paste for pressureless bonding. Examples of the oxygen-free atmosphere include introduction of oxygen-free gas such as nitrogen and rare gas, or under vacuum. Examples of the reducing atmosphere include pure hydrogen gas, hydrogen and nitrogen mixed gas typified by forming gas, nitrogen containing formic acid gas, hydrogen and rare gas mixed gas, and rare gas containing formic acid gas. Can be mentioned.

  The maximum temperature reached during the heat treatment may be 250 ° C. or higher and 450 ° C. or lower, from the viewpoint of reducing thermal damage to the first member and the second member and improving the yield, and may be 250 ° C. or higher and 400 ° C. or lower. Or 250 ° C. or more and 350 ° C. or less. If the ultimate temperature is 200 ° C. or higher, the sintering tends to proceed sufficiently when the ultimate temperature holding time is 60 minutes or less.

  The maximum temperature holding time may be 1 minute or more and 60 minutes or less, or 1 minute or more and less than 40 minutes from the viewpoint of sufficiently volatilizing the dispersion medium and improving the yield. More than 30 minutes may be sufficient.

  By using the copper paste for pressureless bonding of the present embodiment, the bonded body can have a sufficient bonding strength even when bonding without pressure is performed when the laminate is sintered. That is, only the weight of the first member laminated on the copper paste for pressureless bonding, or in addition to the weight of the first member, 0.01 MPa or less, preferably 0.005 MPa or less is sufficient. Bonding strength can be obtained. If the pressure applied during the sintering is within the above range, a special pressurizing device is not required, and the void reduction, die shear strength and connection reliability can be further improved without impairing the yield. Examples of the method in which the pressure-free bonding copper paste receives a pressure of 0.01 MPa or less include a method of placing a weight on the first member.

  In the joined body, at least one of the first member and the second member may be a semiconductor element. Examples of the semiconductor element include a power module including a diode, a rectifier, a thyristor, a MOS gate driver, a power switch, a power MOSFET, an IGBT, a Schottky diode, and a fast recovery diode, a transmitter, an amplifier, and an LED module. In such a case, the joined body is a semiconductor device. The obtained semiconductor device can have sufficient die shear strength and connection reliability.

In the semiconductor device, the difference in thermal expansion coefficient between the first member and the second member may be 2 ppm to 30 ppm, or 3 ppm to 23 ppm. It may be 5 ppm to 15 ppm.

  FIG. 2 is a schematic cross-sectional view showing an example of a semiconductor device manufactured using the pressure-free bonding copper paste of the present embodiment. A semiconductor device 110 shown in FIG. 2 includes a semiconductor element 8 connected on a lead frame 5a via a sintered body 1 of a copper paste for pressureless bonding according to the present embodiment, and a mold resin 7 for molding them. Consists of. The semiconductor element 8 is connected to the lead frame 5 b through the wire 6.

  Examples of the semiconductor device manufactured using the pressure-free bonding copper paste of this embodiment include a diode, a rectifier, a thyristor, a MOS gate driver, a power switch, a power MOSFET, an IGBT, a Schottky diode, and a fast recovery diode. Power module, transmitter, amplifier, high-intensity LED module, semiconductor laser module, logic, sensor, and the like.

  The semiconductor device can be manufactured in the same manner as the above-described manufacturing method of the joined body. That is, the method for manufacturing a semiconductor device uses a semiconductor element for at least one of the first member and the second member, and the first member and the non-pressure-bonding side in the direction in which the weight of the first member acts. Prepare a laminate in which the copper paste and the second member are laminated in this order, and apply the non-pressure bonding copper paste to the weight of the first member or the weight of the first member and the pressure of 0.01 MPa or less. A step of sintering in the received state. For example, a step of providing a pressure-free bonding copper paste on the lead frame 5a and placing and heating the semiconductor element 8 can be mentioned. The obtained semiconductor device can have sufficient die shear strength and connection reliability even when bonding is performed without applying pressure. The semiconductor device of the present embodiment has a sufficient bonding strength, and has a copper sintered body having a high thermal conductivity and a high melting point, thereby having a sufficient die shear strength, excellent connection reliability, and a power cycle. It can be excellent in tolerance.

[Example 1]
(Preparation of pressureless copper paste)
15.84 g (52.8% by mass) of CH-0200 (50% volume average particle size 0.36 μm, manufactured by Mitsui Kinzoku Co., Ltd.) as sub-micro copper particles, isobornylcyclohexanol as a solvent having a boiling point of 300 ° C. or higher 3.6 g (12% by mass) of a boiling point of 308 ° C. (hereinafter abbreviated as MTPH) was weighed and mixed in an automatic mortar for 5 minutes. Furthermore, this mixture was subjected to a dispersion treatment at 19.6 kHz, 600 W for 10 minutes using an ultrasonic homogenizer (US-600, manufactured by Nippon Seiki Co., Ltd.).

  After the dispersion-treated mixture was transferred to a plastic bottle, MA-C025KFD (50% volume average particle size 5 μm, manufactured by Mitsui Kinzoku Co., Ltd.) was weighed and added as micro copper particles at 2000 rpm. A copper paste for non-pressure bonding was obtained by applying to a stirrer manufactured by Shinky Corporation (Awatori Netaro ARE-310) under reduced pressure for 2 minutes.

(Solid content measurement)
The pressureless bonding copper paste was taken into the magnetic crucible, and the weight of the pressureless bonding copper paste was obtained from the difference between the weight of the magnetic crucible and the weight of the magnetic crucible containing the pressureless bonding copper paste. A magnetic crucible containing a copper paste for pressureless bonding was placed in a muffle furnace heated to 600 ° C. and treated for 1 hour. From the difference between the weight of the crucible after the treatment and the tare weight of the magnetic crucible, the weight of the nonvolatile content of the copper paste for pressureless bonding was obtained. The solid content (mass%) of the copper paste for pressureless bonding was calculated from the following equation.
Solid content (mass%) of copper paste for pressureless bonding = {(weight of non-volatile content of copper paste for pressureless bonding) / (weight of copper paste for pressureless bonding before heating)} × 100

(Measurement of residual solvent ratio)
When the temperature was raised from room temperature (25 ° C.) to 300 ° C., the ratio of the dispersion medium (residual solvent ratio) remaining in the pressure-free bonding copper paste was measured. After measuring the mass of the copper plate and the chip, a copper paste for pressureless bonding was printed on the copper plate, and the chip was mounted thereon to obtain a laminate. At this stage, the mass of the laminate was measured. The laminate was heated in an oven under nitrogen from 25 ° C. to 300 ° C. in 30 minutes, and then the laminate was taken out and rapidly cooled on a brass block. The mass of the laminated body after cooling was measured and taken as the mass when reaching 300 ° C. The residual solvent ratio when reaching 300 ° C. was calculated from the following formula.

(Preparation of bonded sample for die shear strength test)
(Joint sample using Si chip)
Using a 75 μm thick stainless steel mask having a 3 × 3 mm ² square opening and a squeegee, a pressure-free bonding copper paste was stencil-printed on a copper plate of size 25 × 20 × 3 mm thick. For non-pressure bonding of Si chip (coated surface nickel) with titanium / nickel sputtered in this order on the entire bonding surface of 400 μm thickness and size 3 × 3 mm on printed matter of copper paste for pressureless bonding The chip was placed in contact with the copper paste composition, and the chip was lightly pressed with tweezers to adhere the nickel surface and the copper paste for pressureless bonding. This was installed in a tubular furnace, the inside was replaced with argon gas, hydrogen was then introduced, and sintering was performed under conditions of a temperature increase of 30 minutes, 300 ° C., and 10 minutes. Then, hydrogen was stopped, it cooled to 50 degrees C or less under argon stream, and the joining sample was taken out in the air.

(Joint sample using Cu plate)
A bonded sample was produced in the same manner as described above except that a Cu plate (nickel to be deposited) having a thickness of 250 μm and a size of 2 × 2 mm and plated with nickel was used.

(Die shear strength test)
The joint strength of the die shear strength sample was evaluated by die shear strength. Using a universal bond tester (4000 series, manufactured by Daisy Japan Co., Ltd.) equipped with a DS-100 load cell, press the Si chip or Cu plate in the horizontal direction at a measurement speed of 5 mm / min and a measurement height of 50 μm. The die shear strength was measured. A die shear strength of 20 MPa or more was considered good bonding.

[Comparative Example 1]
A copper paste for pressureless bonding was obtained in the same manner as in Example 1 except that 9.0 parts by mass of α-terpineol (boiling point 220 ° C.) was used without using isobornylcyclohexanol. The die shear strength was measured in the same manner as in Example 1 except that this pressureless bonding copper paste was used. The results are shown in Table 1.

  The sample of Example 1 in which part of the dispersion medium was MTPH having a boiling point of 308 ° C. showed a good die shear strength of 31 MPa with respect to the Si chip. On the other hand, in the sample of Comparative Example 1 using the non-pressure bonding copper paste containing no solvent having a boiling point of 300 ° C. or higher, the die shear strength with respect to the Si chip was 9 MPa, resulting in poor bonding.

  When the residual solvent ratio was measured, in Example 1, 1.2% by mass of the solvent remained even when 300 ° C. was reached. This is 10% by volume in volume, and the residual solvent does not add flexibility and adhesion enough to absorb the displacement applied to the copper paste for pressureless bonding due to the difference in thermal expansion coefficient between the copper plate and the Si chip. It is thought that it was given to the copper paste for pressure bonding. On the other hand, in Comparative Example 1, the remaining solvent when reaching 300 ° C. was 0.3% by mass, and the volume was 3% by volume. Therefore, in the copper paste for pressureless bonding of Comparative Example 1, there is not enough solvent between the particles, and the copper paste for pressureless bonding peels off from the chip due to the displacement due to the difference in thermal expansion coefficient and the die shear strength decreases. Conceivable.

  A cross-sectional SEM image of the Si chip / die bond layer interface of the die bond portion where the copper substrate and the Si chip were joined was observed. The test sample used for the observation of the SEM image was the one prepared in (Preparation of a die shear strength test bonded sample). A cross-sectional SEM image of Example 1 is shown in FIG. 3, and a cross-sectional SEM image of Comparative Example 1 is shown in FIG. In the sample of Example 1, the silicon chip 9 having the Ti / Ni plating layer 10 and the sintered body 11 of the copper paste for pressureless bonding were bonded satisfactorily. On the other hand, in the sample of Comparative Example 1, since a peeled portion (crack) 12 was generated between the silicon chip 9 having the Ti / Ni plating layer 10 and the sintered body 11 of the copper paste for pressureless bonding, It was. This is a displacement due to the difference in coefficient of thermal expansion between the copper substrate and the Si chip, and is considered to have peeled off at the Si chip / die bond layer interface before bonding.

[Examples 2 to 5, Comparative Example 2]
(Preparation of copper paste composition)
As a solvent having a boiling point of 300 ° C. or higher, isobornylcyclohexanol (boiling point 308 ° C., hereinafter abbreviated as MTPH) and α-terpineol (boiling point 220 ° C.) as other solvents were mixed according to the ratio in Table 2. There, 10.56 g (35.2 mass%) of MA-C025KFD (50% volume average particle size 5 μm, manufactured by Mitsui Kinzoku Co., Ltd.) as micro copper particles, and CH-0200 (50% volume average particle) as sub-micro copper particles. 15.84 g (52.8% by mass) of 0.36 μm in diameter (manufactured by Mitsui Kinzoku Co., Ltd.) was weighed and mixed for 5 minutes in an automatic mortar. After the mixture was transferred to a plastic bottle, a copper paste composition for pressureless bonding was obtained by applying it to a stirrer manufactured by Shinky Corporation (Awatori Netaro ARE-310) under reduced pressure at 2000 rpm for 2 minutes.

(Die shear test sample preparation)
In the same manner as in Example 1, a joining sample (Si) using a Si chip in which titanium / nickel was sputtered in this order on the entire joining surface having a size of 3 × 3 mm was produced. Further, a joined sample (copper plate) joined in the same manner as in Example 1 was prepared using a copper plate having a size of 2 × 2 mm and plated with nickel. The die shear strength of each bonded sample was measured in the same manner as in Example 1. The results are shown in Table 2 and FIG.

[Example 6]
A copper paste for pressureless bonding was prepared in the same manner as in Example 1 except that tributyrin (boiling point 310 ° C.) was used as a solvent having a boiling point of 300 ° C. or higher. A bonding sample (Si) using a Si chip in which titanium / nickel was sputtered in this order over the entire bonding surface of size 3 × 3 mm in the same manner as in Example 1 except that this pressureless bonding copper paste was used. The die shear strength was measured. As a result, the die shear strength was as good as 20 MPa.

[Example 7]
A copper paste for pressureless bonding was used in the same manner as in Example 1 except that fine oxocol 180 (isooctadecanol, boiling point 302 ° C., manufactured by Nissan Chemical Industries, Ltd.) was used as a solvent having a boiling point of 300 ° C. or higher. Prepared. A bonding sample (Si) using a Si chip in which titanium / nickel was sputtered in this order over the entire bonding surface of size 3 × 3 mm in the same manner as in Example 1 except that this pressureless bonding copper paste was used. The die shear strength was measured. As a result, the die shear strength was a good value of 23 MPa.

[Example 8]
A copper paste for pressureless bonding was prepared in the same manner as in Example 1 except that butyl stearate (boiling point 343 ° C.) was used as a solvent having a boiling point of 300 ° C. or higher. A bonding sample (Si) using a Si chip in which titanium / nickel was sputtered in this order over the entire bonding surface of size 3 × 3 mm in the same manner as in Example 1 except that this pressureless bonding copper paste was used. The die shear strength was measured. As a result, the die shear strength was a favorable value of 25 MPa.

[Example 9]
A copper paste for pressureless bonding was prepared in the same manner as in Example 1 except that octyl octoate (boiling point 311 ° C.) was used as the solvent composition having a boiling point of 300 ° C. or higher. A bonding sample (Si) using a Si chip in which titanium / nickel was sputtered in this order over the entire bonding surface of size 3 × 3 mm in the same manner as in Example 1 except that this pressureless bonding copper paste was used. The die shear strength was measured. As a result, the die shear strength was a good value of 26 MPa.

[Comparative Example 3]
A copper paste for pressureless bonding was prepared in the same manner as in Example 1 except that diethylene glycol monobutyl ether (boiling point: 230 ° C., hereinafter abbreviated as DEGBE) was used as the dispersion medium. A bonding sample (Si) using a Si chip in which titanium / nickel was sputtered in this order over the entire bonding surface of size 3 × 3 mm in the same manner as in Example 1 except that this pressureless bonding copper paste was used. The die shear strength was measured. As a result, the die shear strength was 6 MPa, and it was determined that the connection was poor.

[Comparative Example 4]
A copper paste for pressureless bonding was prepared in the same manner as in Example 1 except that diethylene glycol monobutyl ether acetate (boiling point 247 ° C., hereinafter abbreviated as BDGAC) was used as the dispersion medium. A bonding sample (Si) using a Si chip in which titanium / nickel was sputtered in this order over the entire bonding surface of size 3 × 3 mm in the same manner as in Example 1 except that this pressureless bonding copper paste was used. The die shear strength was measured. As a result, the die shear strength was 5 MPa, and it was determined that the connection was poor.

  Table 3 shows the results of Examples 6 to 9 and Comparative Examples 3 and 4. In FIG. 6, the die shear strength of the joining sample (Si) using the copper paste for pressureless joining in Examples 1, 6, 7, 8, and 9 and Comparative Examples 1, 3, and 4 is plotted against the boiling point of the solvent. did. In Examples using a solvent having a boiling point of 300 ° C. or higher, good die shear strength of 20 MPa or higher was obtained. On the other hand, in the comparative examples using a solvent having a boiling point lower than 300 ° C., all had low die shear strength of 9 MPa or less, resulting in poor bonding.

DESCRIPTION OF SYMBOLS 1 ... Sintered body of copper paste for pressureless joining, 2 ... 1st member, 3 ... 2nd member, 5a, 5b ... Lead frame, 6 ... Wire, 7 ... Mold resin, 8 ... Semiconductor element, 9 ... Silicon chip, 10... Ti / Ni plating layer, 11... Sintered body of copper paste for pressureless bonding, 12.

Claims (8)

A copper paste for pressureless bonding comprising metal particles and a dispersion medium,
The metal particles include sub-micro copper particles having a volume average particle size of 0.01 μm or more and 0.8 μm or less, and micro copper particles having a volume average particle size of 2.0 μm or more and 50 μm or less,
The dispersion medium contains a solvent having a boiling point of 300 ° C. or higher, and the content of the solvent having a boiling point of 300 ° C. or higher is 2% by mass or more based on the total mass of the pressure-free bonding copper paste. Copper paste for pressureless bonding. A copper paste for pressureless bonding comprising metal particles and a dispersion medium,
The metal particles include sub-micro copper particles having a volume average particle size of 0.01 μm or more and 0.8 μm or less, and micro copper particles having a volume average particle size of 2.0 μm or more and 50 μm or less,
The dispersion medium contains a solvent having a boiling point of 300 ° C. or higher, and the content of the solvent having a boiling point of 300 ° C. or higher is 8% by volume or more based on the total capacity of the copper paste for pressureless bonding. Copper paste for pressureless bonding.   The copper paste for pressureless bonding according to claim 1 or 2, wherein the solvent having a boiling point of 300 ° C or higher has at least one group selected from the group consisting of a hydroxy group, an ether group, and an ester group.   When the copper paste for pressureless bonding existing between two members is heated at a temperature of 250 ° C. or higher and lower than 350 ° C., the micro copper particles and the sub-micro copper particles are sintered to form a metal bond, The copper paste for pressureless joining according to any one of claims 1 to 3, wherein the two members are joined with a die shear strength of 10 MPa or more and a thermal conductivity of 100 W / (m · K) or more.   The content of the solvent having a boiling point of 300 ° C. or more remaining when the temperature is raised from 25 ° C. to 300 ° C. is based on the mass of the copper paste for pressureless bonding when the temperature is raised to 300 ° C. The copper paste for pressureless bonding according to any one of claims 1 to 4, wherein the copper paste is mass% or more.   The first member, a second member having a coefficient of thermal expansion different from that of the first member, and the first member and the second member are joined together. And a sintered body of the copper paste for pressureless bonding described in 1.   The first member, the copper paste for pressureless bonding according to any one of claims 1 to 5, and a coefficient of thermal expansion different from that of the first member on a side in which the weight of the first member acts. Prepared a laminate in which this second member is laminated in this order, the copper paste for pressureless bonding, the weight of the first member, or the weight of the first member and 0.01 MPa or less A method for manufacturing a joined body, comprising a step of sintering under pressure. The first member, a second member having a coefficient of thermal expansion different from that of the first member, and the first member and the second member are joined together. And a sintered body of the copper paste for pressureless bonding described in
A semiconductor device, wherein at least one of the first member and the second member is a semiconductor element.