JP2011058041A - Silver-copper based mixed powder and joining method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material which can exhibit joining strength at a level equal to that of a silver nanoparticle single substance and further has excellent migration resistance. <P>SOLUTION: The silver-copper based mixed powder contains a power composed of silver based fine particles containing organic components and copper based fine particles containing organic components, wherein the average particle diameter of the powder composed of the silver based fine particles is ≤50 nm, and the average particle diameter of the powder composed of the copper based fine particles is ≥50 nm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a silver-copper mixed powder and a bonding method using the same.

  Metal nanoparticles are ultrafine particles with a particle size of 1 to several hundreds of nanometers, and atoms existing on the surface are extremely unstable, so that they spontaneously cause fusion between particles and become coarse. It has been. Therefore, metal nanoparticles are usually stabilized by covering the surface with an organic protecting group. Unlike bulk metals, metal nanoparticles exhibit unique physical properties such as low melting point and low temperature sinterability, and are used as conductive pastes for wiring formation and bonding as engineering applications.

Metal nanoparticles are often classified by synthetic methods. The synthesis method of metal nanoparticles is a physical method of pulverizing bulk metal to obtain particles, and generating zero-valent metal atoms from precursors such as metal salts and metal complexes, and aggregating them to obtain nanoparticles There are two major categories: chemical methods. The pulverization method, which is one of the physical methods, is a method of obtaining metal nanoparticles by grinding a metal using an apparatus such as a ball mill. However, particles obtained by this method have a wide particle size distribution, and it is difficult to obtain particles having a size of several hundred nm or less. On the other hand, as chemical methods, 1) a method of synthesizing metal nanoparticles by heating a reaction gas with a CO ₂ laser called a laser synthesis method, and 2) a metal salt solution called a spray pyrolysis method is sprayed in a high temperature atmosphere. There are a method for obtaining metal nanoparticles by instantaneous evaporation and thermal decomposition of the solution, and 3) a method for obtaining metal nanoparticles by a reduction reaction from a metal salt solution called a reduction method. There are drawbacks.

  On the other hand, in order to solve the problems of the existing method for synthesizing metal nanoparticles, the present inventors have been able to synthesize metal nanoparticles simply by heating the metal complex as a metal source without solvent. The method has been developed first (Patent Document 1, Patent Document 2, etc.). The greatest feature of this thermal decomposition control method is the simplicity of heating without solvent, and therefore, mass synthesis is possible. Furthermore, it has been found that by adding an organic compound or the like having a mild reducing property to the reaction system, the reaction conditions become mild, and the particle diameter and shape, the design of the surface protective layer, and the like can be made.

  Industrial application of such metal nanoparticles has been actively studied in various fields, and one of them is a bonding process using metal nanoparticles. In particular, a joining process using silver has been actively studied, and it has been reported that joining strength comparable to that of lead-tin solder or the like can be obtained (Non-Patent Document 1, Non-Patent Document 2, etc.).

JP 2007-63579 A JP 2007-63580 A

E. Ide, S. Angata ,, A. Hirose, K. F. Kobayashi, Acta Mater, 53 (2005) 2385. Eiichi Ide, Shinji Angata, Akio Hirose, Shinjiro Kobayashi, “Joint Process Using Silver Nanoparticles—Examination of Bondability with Cu—“ Mate 2004 ”, Yokohama, (Feb., 2004) 213.

  However, although silver is excellent in terms of bonding strength, etc., in addition to the problem of high cost, migration that shortens the path between electrodes by silver ionization and reprecipitation outside the circuit when used under high humidity. It is regarded as a problem that this phenomenon is very likely to occur. On the other hand, even in the conventional techniques as described above, a specific technique that can exhibit good migration resistance as well as excellent bonding strength is not disclosed in particular.

  Therefore, a main object of the present invention is to provide a material that can exhibit a bonding strength equivalent to that of a single silver nanoparticle and is excellent in migration resistance.

  As a result of intensive studies in view of the problems of the prior art, the present inventor applies a mixed powder containing a powder composed of silver-based fine particles containing an organic component and a powder composed of copper-based fine particles containing an organic component. The inventors have found that the above object can be achieved, and have completed the present invention.

That is, the present invention relates to the following silver-copper mixed powder and a bonding method using the same.
1. A mixed powder comprising a powder composed of silver-based fine particles containing an organic component and a powder composed of copper-based fine particles containing an organic component, wherein the average particle diameter of the powder composed of the silver-based fine particles is 50 nm or less, and the copper-based powder A silver-copper-based mixed powder characterized in that an average particle size of powder composed of fine particles is 50 nm or more.
2. The total amount of powder consisting of the silver-based fine particles and the total amount of powder consisting of the copper-based fine particles is 100 to 60 parts by weight. Item 2. The silver-copper mixed powder according to Item 1, which is 40 parts by weight.
3. Item 2. The silver-copper mixed powder according to Item 1, wherein the metal content of the silver-based fine particles is 60 to 98% by weight.
4). Item 2. The silver-copper mixed powder according to Item 1, wherein the copper-based fine particles have a metal content of 80 to 99% by weight.
5. Item 2. The silver-copper mixed powder according to Item 1, wherein the copper-based fine particles and / or the silver-based fine particles are obtained by heat-treating a starting material containing a metal salt in the presence of an amine compound.
6). Item 2. The silver-copper mixed powder according to Item 1, which is used for bonding.
7). A paste comprising the silver-copper mixed powder according to item 1 and at least one of a solvent and a viscosity adjusting resin.
8). The joining method including the process of heating at 150-400 degreeC, after interposing the silver-copper type mixed powder of said claim | item 1 or the paste containing it between two members which should be joined.

  The silver-copper-based mixed powder of the present invention is used in combination of copper-based fine particles having a relatively large particle diameter and silver-based fine particles having a relatively small particle diameter on the premise that fine particles containing an organic component are used. Therefore, it is possible to exhibit the same bonding strength as that of a single silver nanoparticle and to improve the migration resistance, which was a drawback of the single silver nanoparticle.

  Further, compared to the case of using silver nanoparticles alone, a part thereof can be replaced with relatively inexpensive copper fine particles, which is advantageous in terms of cost.

  The silver-copper mixed powder of the present invention having such features can be suitably used particularly as a bonding material. For example, it can be widely used for various applications of electronic materials (printed wiring, conductive materials, optical elements, etc.) and structural materials (far infrared materials, composite film forming materials, etc.). In particular, the mixed powder of the present invention can be suitably used for wiring formation that requires migration resistance or for joining instead of high-temperature solder.

It is a figure which shows the shape and arrangement | positioning method of the sample piece (member) used for the joining test. Fig.1 (a) shows the shape and size of each member, and the joining method of both members. FIG.1 (b) is a figure which shows a state when performing a shear test to a conjugate | zygote. It is a graph which shows the relationship between content of silver type powder as joining material, and joining strength. It is a figure which shows the SEM photograph of the torn surface after the shear test in each joined body. It is a figure which shows the SIM photograph of the joining layer cross section of each joined body. It is a figure which shows the sample external appearance after the migration test of each electrode.

1. Silver-copper mixed powder The silver-copper mixed powder of the present invention (the present powder) is a mixed powder containing a powder composed of silver-based fine particles containing an organic component and a powder composed of copper-based fine particles containing an organic component. The average particle size of the powder composed of the silver-based fine particles is 50 nm or less, and the average particle size of the powder composed of the copper-based fine particles is 50 nm or more.

  Silver-based fine particles contain an organic component. Although the kind of this organic component is not specifically limited, It is preferable that it is normally comprised from the organic compound used as a starting material, or its thermal decomposition product. In this case, the content of the organic component is not limited, but it is preferable to adjust the metal content of the silver-based fine particles to usually 60 to 98% by weight, particularly 75 to 95% by weight.

  The average particle size of the powder composed of silver-based fine particles (silver-based powder) is usually 50 nm or less, preferably 5 to 40 nm, more preferably 5 to 30 nm. By setting within this range, high bonding strength and good migration resistance can be obtained.

  The copper-based fine particles contain an organic component. Although the kind of this organic component is not specifically limited, Usually, it is preferable to be comprised from the organic compound used as a starting material, or its thermal decomposition product. In this case, the content of the organic component is not limited, but it is preferably adjusted so that the metal content of the copper-based fine particles is usually 70 to 99% by weight, particularly 80 to 99% by weight.

  The average particle diameter of the powder (copper powder) composed of copper-based fine particles is usually 50 nm or more, particularly 200 to 600 nm, more preferably 400 to 500 nm. By setting it within this range, high bonding strength and good migration resistance can be obtained.

  The content ratio of the silver-based powder and the copper-based powder in the powder of the present invention can be appropriately set according to the use of the powder of the present invention, but generally 100 parts by weight in total of the silver-based powder and the copper-based powder. On the other hand, the powder composed of the silver-based fine particles is 40 to 60 parts by weight (especially 45 to 55 parts by weight), and the powder composed of the copper-based fine particles is 60 to 40 parts by weight (particularly 55 to 45 parts by weight). It is preferable to do. By setting within such a range, it is possible to obtain good migration resistance with higher joint strength.

  Moreover, in this invention powder, the other component may be contained in the range which does not inhibit the effect of this invention. For example, the content of other components is preferably 15% by weight or less.

  The relationship between the average particle size of the silver-based powder and the average particle size of the copper-based powder may be as long as the average particle size of the silver-based powder is smaller as described above. It is desirable to set the average particle diameter of the system powder to 2 times or more, particularly 10 times or more, and further 50 times or more. The upper limit in this case is not limited, but may be about 100 times.

  Known or commercially available silver-based powders and copper-based powders of the present invention can be used. Moreover, what was manufactured with the well-known synthesis | combining method can also be used. The synthesis method may be any of a liquid phase method, a solid phase method, and a gas phase method.

  In the present invention, for example, a material obtained by heat-treating a starting material containing a metal salt in the presence of an amine compound can be preferably used. This method will be described below as a representative example.

  Examples of metal salts (Ag salts or Cu salts) include inorganic acid salts such as nitrates, chlorides, carbonates and sulfates; organic acid salts such as stearates and myristates, and metal complexes (complex salts). Can also be used. In particular, in the present invention, at least one metal salt (Ag salt or Cu salt) of (1) metal carbonate, (2) fatty acid salt, and (3) metal complex can be preferably used.

As the fatty acid salt, R ¹ —COOH or HOOC—R ¹ —COOH (where R ¹ represents a hydrocarbon group having 7 or more carbon atoms (particularly 7 to 17) which may have a substituent. ) Or HOOC-R ² —COOH (wherein R ² represents a hydrocarbon group having 3 or more carbon atoms and optionally having a substituent), a metal salt of a fatty acid is preferred. The hydrocarbon groups R ¹ and R ² may be either saturated or unsaturated.

Moreover, as a metal complex, the metal complex containing a carboxylate ligand is preferable. As such a metal complex, a monodentate ligand or OOC represented by R ¹ COO (where R ¹ represents a hydrocarbon group having 7 or more carbon atoms and optionally having a substituent). Any of bidentate ligands (including chelate ligands) represented by —R ² —COO (where R ² represents a hydrocarbon group) may be used. In the case of a monodentate ligand, a linear alkyl group is preferred. In the case of a bidentate ligand, a linear methylene group is preferred. The hydrocarbon group R ¹ preferably has 7 to 30 carbon atoms, and more preferably has 7 to 17 carbon atoms. The hydrocarbon group R ² may be any of a saturated hydrocarbon group such as a methylene group; and an unsaturated hydrocarbon group such as a phenyl group, a propylene group, and a vinylene group. The number of carbon atoms of the hydrocarbon group R ² is not limited, but is preferably about 6 to 12.

  As long as the metal complex has a carboxylate ligand, the metal complex may have another ligand such as a phosphine ligand.

As the metal complex in the present invention, for example, the following complex a) can be preferably used.
a) M (R ¹ R ² R ³ P) (O ₂ CR ′) (M represents Ag or Cu. R ^{1 to} R ³ and R ′ are the same as or different from each other, and represent a cyclohexyl group, phenyl, Group or an alkyl group having 1 to 30 carbon atoms, which may have a substituent.)
Examples of the substituent in a) include a methyl group, an ethyl group, a propyl group, a sulfone group, an OH group, a nitro group, an amino group, a halogen group (Cl, Br, etc.), a methoxy group, and an ethoxy group. . The position and number of substituents are not particularly limited.
Among these, a metal complex represented by M (PPh ₃ ) (O ₂ CC _n H _{2n + 1} ) (wherein M represents Ag or Cu, Ph represents a phenyl group, and n represents 7 to 17). It can be used suitably.

  Moreover, in this invention, another component can also be made to contain in a starting material as needed. For example, a fatty acid or a salt thereof can be added. Preferably, as the fatty acid, the same fatty acid as that in the fatty acid salt can be used. For example, when copper octoate is used as the metal salt, octanoic acid can be suitably used. The content and the like can be appropriately set according to the type of starting material used.

  In the production method of the present invention, the starting material containing the metal component as described above is heat-treated in the presence of an amine compound. In particular, in the present invention, a starting material containing a metal component and an amine may be charged into a reaction vessel and heat-treated without using an organic solvent. When the amine is solid, the starting material containing the metal component and the amine may be heat-treated while being solid.

  The kind of the amine compound is not particularly limited even if it is any of primary amine, secondary amine, and tertiary amine.

As the primary amine, those represented by the general formula RNH ₂ (where R represents a hydrocarbon group having 8 or more carbon atoms) are particularly preferred. For example, octylamine _C 8 _H 17 NH _2, laurylamine _C 12 _H 25 NH _2, stearylamine _C 18 _H 37 NH ₂ and the like.

The secondary amine is particularly represented by the general formula R ¹ R ² NH (wherein R ¹ and R ² are the same or different from each other and represent a hydrocarbon group having 2 to 8 carbon atoms). Is preferred. For example, diethylamine _{(C 2 H 5) 2 NH} , dihexylamine _{(C 6 H 13) 2 NH} , dioctylamine _{(C 8 H 17)} 2 NH, and the like.

The tertiary amine is particularly represented by the general formula R ¹ R ² R ³ N (wherein R ^{1 to} R ³ are the same or different from each other and represent a hydrocarbon group having 2 to 8 carbon atoms). Are preferred. Examples thereof include triethylamine (C ₂ H ₅ ) ₃ N, tripropylamine (C ₃ H ₇ ) ₃ N, trioctylamine (C ₈ H ₁₇ ) ₃ N, and the like.

  The usage-amount of an amine compound will not be specifically limited if it is equimolar or more with the starting material containing a metal component. Therefore, an excessive amount may be used as necessary. The amine compound can also be used after being dissolved or dispersed in a suitable organic solvent in advance.

  The heat treatment temperature is not particularly limited as long as the metal salt reacts with the amine compound to obtain predetermined metal nanoparticles, and can be appropriately determined according to the type of metal salt and amine compound used. In general, the temperature may be set in a range of 50 ° C. or higher, and in particular, the temperature may be set to a temperature range above the temperature at which the mixture of the starting material and the amine compound finally becomes liquid and below the boiling point of the amine compound. preferable. That is, the formation of metal nanoparticles composed of a substance containing at least one of P, N, and O can be more effectively advanced by heat treatment at a temperature equal to or higher than the temperature at which the mixture finally becomes a molten state. it can.

  The heat treatment time may be appropriately set according to the type of starting material to be used, the heat treatment temperature, etc., but is usually about 1 to 10 hours, preferably 3 to 8 hours.

  The heat treatment atmosphere may be any of an oxidizing atmosphere, air, reducing atmosphere, inert gas, and the like, and can be appropriately set according to, for example, the metal species of the metal salt. Moreover, as said inert gas, what is necessary is just to use inert gas, such as nitrogen, a carbon dioxide, argon, helium, for example.

  After the heat treatment is completed, purification is performed as necessary. As a purification method, a known purification method can be applied, and for example, washing, centrifugation, membrane purification, solvent extraction and the like may be performed.

  The mixed powder of the present invention can be obtained by uniformly mixing the thus obtained silver-based powder and copper-based powder. That is, the mixed powder of the present invention can be produced by mixing a powder composed of silver-based fine particles containing at least an organic component and copper-based fine particles containing an organic component. The mixing method may be dry mixing, or wet mixing using a solvent or the like shown below.

  Although this invention powder can be used for various uses like the conventional metal nanoparticle, it can be used suitably especially for joining. For example, it can be suitably used for joining metals (for example, copper-based metal-copper-based metal, silver-based metal-copper-based metal, etc.). More specifically, an electrical junction region can be suitably formed using the powder of the present invention or a paste containing the powder. Thereby, two circuits can be joined. The joining method is, for example, 2. It can carry out according to the method of.

  The present invention includes a paste containing the silver-copper mixed powder according to the present invention and at least one of a solvent and a viscosity adjusting resin. The solvent is not particularly limited. For example, terpene solvents, ketone solvents, alcohol solvents, ester solvents, ether solvents, aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, cellosolve solvents, carbitol solvents. A solvent etc. are mentioned. More specifically, organic solvents such as terpineol, methyl ethyl ketone, acetone, isopropanol, butyl carbitol, decane, undecane, tetradecane, benzene, toluene, hexane, diethyl ether, and kerosene can be exemplified. Further, the viscosity adjusting resin is not limited. For example, a thermosetting resin such as a phenol resin, a melamine resin, or an alkyd resin, a thermoplastic resin such as a phenoxy resin or an acrylic resin, a curing agent curable resin such as an epoxy resin, or the like. Can be used. When used as a paste, the solid content of the silver-copper mixed powder can be appropriately set within a range of about 20 to 90% by weight.

2. Bonding method The bonding method of the present invention includes a step of heat-treating at 150 to 400 ° C. after interposing the silver-copper mixed powder according to the present invention or a paste containing the same between two members to be bonded. It is.

  Examples of the silver-copper mixed powder or the paste containing the same include the above 1. The powder or paste described in the above can be used.

  Examples of members to be joined include metals (including alloys and intermetallic compounds), ceramics, plastics, composite materials thereof, and the like. In the present invention, metals (joining metals) are particularly used. preferable. Further, the shape of the member is not particularly limited as long as these powders or pastes can be appropriately disposed between the members.

  The silver-copper mixed powder or a paste containing the same is interposed between members to be joined. The amount of the silver-copper-based mixed powder or the paste containing it is not particularly limited, and may be set as appropriate so as to be an amount that can be uniformly interposed over the entire bonding surface. In addition, when using the paste containing a solvent, after interposing a paste between members, it is preferable to implement the pre-processing for evaporating one part or all part of the solvent prior to heat processing. Examples of the pretreatment method include a method of heating at about 100 to 150 ° C.

  Next, heat treatment is performed at 150 to 400 ° C. The heat treatment temperature can be appropriately set according to, for example, the type of mixed powder to be used, the desired bonding strength, the material of the member, and the like. The heat treatment atmosphere is not particularly limited, and for example, the heat treatment atmosphere can be performed in any of an oxidizing atmosphere, air, reducing atmosphere, and inert gas. Moreover, when heat-processing, it is desirable to heat-process, pressing the members which should be joined. As a pressure in that case, it can set suitably, for example within the range of about 5-20 MPa. The heat treatment time can be appropriately set according to the heat treatment temperature or the like, but it is usually sufficient to be about 1 to 60 minutes. In this way, it is possible to obtain a joined body in which the fired body of the powder of the present invention is interposed between the members.

  The features of the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to the examples.

The physical properties of the fine particles (powder) of the present invention were measured and analyzed by the following method.
(1) Qualitative analysis The metal component was identified by powder X-ray diffraction analysis using a powerful X-ray diffractometer "RINT 2500V" (manufactured by Rigaku Corporation).
(2) Average particle diameter Measured with a transmission electron microscope (TEM) “JEM-2100” (manufactured by JEOL Ltd.), an arithmetic average value of the diameters of 100 arbitrarily selected particles was obtained, and the average particle diameter was obtained from the value. It was.
(3) Content of metal component The content was determined by TG / DTA analysis using a thermal analyzer “SSC / 5200” (Seiko Electronics Co., Ltd.).
(4) Analysis of organic component etc. Confirmation of P (phosphorus component), N (nitrogen component) and O (oxygen component) in metal nanoparticles is performed by X-ray photoelectron spectrum apparatus “ESCA-700” (manufactured by ULVAC-PHI), FT-IR apparatus “GX I-RO” (manufactured by PerkinElmer) was used. The organic component was confirmed using an FT-NMR apparatus “JNM-EX270” (manufactured by JEOL Ltd.) and a GC / MS (gas chromatograph mass spectrometer) apparatus “5973Network MSD” (manufactured by Hewlett-Packard Company).

Example 1
(1) Preparation of silver-based powder and copper-based powder (1-1) Preparation of silver-based powder 1 Silver carbonate (41.4 g) and octylamine (40.7 g) were added to a Pyrex (registered trademark) three-necked flask. The solid was placed and gradually heated to 100 ° C. in the atmosphere. After maintaining at 100 ° C. for 4 hours, the mixture was allowed to cool to 70 ° C., washed with methanol several times, and the produced powder was filtered off with a Kiriyama funnel and dried under reduced pressure to obtain a silver-based powder. The obtained powder had an average particle size of 7.9 nm and a metal content of 72% by weight.

(1-2) Preparation of Copper-Based Powder 1 Copper octanoate (1.75 g) and trioctylamine (3.57 g) were placed in a Pyrex (registered trademark) three-necked flask as a solid, and 160 under a nitrogen atmosphere. Heated gradually to ° C. After maintaining at 160 ° C. for 16 hours, the mixture was allowed to cool to 70 ° C., washed with methanol several times, and the produced powder was filtered off with a Kiriyama funnel and dried under reduced pressure to obtain a copper-based powder. The obtained powder had an average particle size of 4.6 nm and a metal content of 82.6% by weight.

(1-3) Preparation of Copper-Based Powder 2 Copper octoate (3.54 g) and trioctylamine (1.90 g) were placed in a Pyrex (registered trademark) three-necked flask as a solid, and 160 under a nitrogen atmosphere. Heated gradually to ° C. After maintaining at 160 ° C. for 24 hours, the mixture was allowed to cool to 70 ° C., washed with methanol several times, and the produced powder was filtered off with a Kiriyama funnel and dried under reduced pressure to obtain a copper-based powder. The obtained powder had an average particle size of 63.6 nm and a metal content of 91.0% by weight.

(1-4) Preparation of Copper-Based Powder 3 Copper octoate (3.54 g) and trioctylamine (1.90 g) are placed in a Pyrex (registered trademark) three-necked flask as a solid, and 180 in a nitrogen atmosphere. Heated gradually to ° C. After maintaining at 180 ° C. for 5 hours, the mixture was allowed to cool to 70 ° C., methanol was added and washed several times, and the resulting powder was filtered with a Kiriyama funnel and dried under reduced pressure to obtain a copper-based powder. The average particle size of the obtained powder was 498.0 nm, and the metal content was 98.4% by weight.

(2) Preparation of Paste The powder obtained in (1) above was dispersed in terpineol to prepare pastes each having a solid content concentration of about 70% by weight. In each test example described later, the paste was mixed and used so that the silver-based powder and the copper-based powder had a predetermined blending ratio.

Test example 1
Each mixed powder was prepared so that the content ratio of the silver-based powder 1 to the copper-based powder 3 was in the range of 10 to 70 mass% (10%, 30%, 50%, 70%). A joining test was carried out. For comparison, the same test was conducted on the copper powder 3 alone and the silver powder 1 alone.

  The shape of a joining test piece made of oxygen-free copper used in the joining test is shown in FIG. The joint surface of each test piece was finished by lathe processing so that Rmax = 3.2S, and after ultrasonic cleaning in acetone and pickling in hydrochloric acid, it was subjected to water washing and drying, and then subjected to the test. . A fixed amount of the metal nanoparticle paste was applied to the joining surface of the larger disk specimen, and the joining specimen was adjusted so that the paste spread over the entire joining surface while being lightly pressed by overlapping the smaller specimen. After holding the test piece at 150 ° C. for 5 minutes, a bonding test in the atmosphere was performed at a bonding temperature (heat treatment temperature) of 250 to 350 ° C. In joining, no pressure was applied from the beginning, and after holding at 150 ° C. for 5 minutes, pressure was applied at a pressure of 10 MPa. Immediately after the test, the test piece was taken out of the apparatus and air-cooled.

  Each joint joint obtained by the joint test was subjected to a shear test using an Instron universal material testing machine as shown in FIG. In FIG. 2, the relationship between the content rate of silver type powder and joining strength is shown. In FIG. 2, the ● marks indicate the results of the heat treatment temperature 350 ° C., the ■ marks indicate the heat treatment temperature 300 ° C., and the triangles indicate the heat treatment temperature 250 ° C.

  As apparent from the results of FIG. 2, since the average particle diameter of the copper-based powder 3 is relatively large, only the copper-based powder 3 alone has a shear strength of 153 N (joining conditions of a heat treatment temperature of 350 ° C. and a pressure of 10 MPa). 7.8 MPa). On the other hand, in the case of the mixed powder containing 50 mass% of the silver-based powder 1 in the copper-based powder 3, the shear strength increases to 1010 N (51.5 MPa) under the same joining conditions, and the case of the silver-based powder 1 alone and Almost the same value was shown. That is, it turns out that high joint strength is obtained by using together the copper-type powder which has an average particle diameter 60 to 70 times the average particle diameter of silver-type powder.

  The decomposition end temperature of the organic protective layer (organic component) of the copper-based powder 3 in a nitrogen atmosphere measured by TG / DTA is about 350 ° C., and the decrease in shear strength at 300 ° C. or lower is It is thought that this is due to the residual. Thus, it turns out that it can join with higher intensity | strength by heat-processing at the decomposition | disassembly completion temperature of the organic component of copper-type powder (in the above cases, for example, 340-360 degreeC vicinity). In addition, from this, it can be expected that the temperature of the bonding process can be lowered by lowering the decomposition temperature of the organic component.

  In FIG. 3, the SEM photograph of the torn surface after a shear test is shown about the test piece joined using various metal nanoparticle paste. Test pieces exhibiting high shear strength of 1000 N (51.0 MPa) or more (joined using silver powder 1 alone (Ag), joined using mixed powder containing 50 mass% silver powder 1 (Ag) Elongated dimples were clearly observed on the fracture surface of Cu5Ag5)). On the other hand, the fracture surface of the test piece (Cu) joined only with the copper-based powder 3 is accompanied by a large number of voids, and it is observed that the firing between the particles of the copper-based powder 3 hardly proceeds. It was done.

  Further, a cross-section of the bonding layer (using copper powder 3 alone (Cu), using a mixed powder containing 50 mass% silver powder 1 (Cu5Ag5)) using FIB is prepared, and SIM (Scanning Ion Microscopy) image was observed. The result is shown in FIG. Large and small voids are confirmed in the bonding layer fired using the copper-based powder 3 alone (Cu). On the other hand, when the mixed powder is used (Cu5Ag5), it is understood that a very dense bonding layer can be obtained although slight peeling is observed at the interface with the material to be bonded.

Test example 2
The migration resistance of the powder of the present invention was examined. Screen printing is performed with a paste using silver powder 1 alone and a mixed powder containing 50 mass% of silver powder 1, and after printing the counter electrode, it is dried at 150 ° C. for 5 minutes, and then held at 350 ° C. for 5 minutes for firing. I let you. Next, migration resistance was evaluated by the water drop method. Specifically, water was dropped between the electrodes, and the time from when the voltage (3 to 6 V) was applied to when the electrodes were short-circuited was measured and evaluated.

  As a result, for comparison, in the case of a silver electrode made of silver-based powder 1 alone, the time from application of a voltage of 3 V to short-circuiting was 4 minutes and 27 seconds. On the other hand, in the case of an electrode made of a paste using a mixed powder containing 50 mass% of the silver-based powder 1 in the copper-based powder 3, no change was observed in the electrode even after 15 minutes. In addition, a voltage of 3 V was applied for 15 minutes and then the voltage was changed to 6 V and held for 10 minutes. However, significant migration from the electrode could not be confirmed. FIG. 5 shows a photograph of each sample after the evaluation of migration resistance characteristics. It can be seen that the silver electrode (Ag) is short-circuited due to migration.

Claims (8)

A mixed powder comprising a powder composed of silver-based fine particles containing an organic component and a powder composed of copper-based fine particles containing an organic component, wherein the average particle diameter of the powder composed of the silver-based fine particles is 50 nm or less, and the copper-based powder A silver-copper-based mixed powder characterized in that an average particle size of powder composed of fine particles is 50 nm or more. The total amount of powder consisting of the silver-based fine particles and the total amount of powder consisting of the copper-based fine particles is 100 to 60 parts by weight. The silver-copper mixed powder according to claim 1, which is 40 parts by weight. The silver-copper mixed powder according to claim 1, wherein the metal content of the silver-based fine particles is 60 to 98% by weight. The silver-copper mixed powder according to claim 1, wherein the metal content of the copper-based fine particles is 80 to 99% by weight. The silver-copper mixed powder according to claim 1, wherein the copper-based fine particles and / or the silver-based fine particles are obtained by heat-treating a starting material containing a metal salt in the presence of an amine compound. The silver-copper mixed powder according to claim 1, which is used for bonding. A paste comprising the silver-copper mixed powder according to claim 1 and at least one of a solvent and a viscosity adjusting resin. The joining method including the process of heating at 150-400 degreeC after interposing the silver-copper type mixed powder of Claim 1 or the paste containing it between two members which should be joined.