JP3345961B2 - Low-temperature diffusion bonding method of copper or copper alloy and method of manufacturing conductive paste and multilayer wiring board using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining copper or a copper alloy widely used in the field of metal processing and the electronics industry, a conductive paste applying the principle, and a multilayer wiring board manufactured by the same principle. It is about the method.

[0002]

2. Description of the Related Art Conventionally, copper and its alloys have been widely used in the industrial field. Many techniques have long been used to join two or more members when processing these metals, but brazing represented by soldering is widely performed as a general joining method. Have been made also ultrasonic connection as a special example in the microelectronics field, if attempted generally electrically connected with a reliable connection by soldering or brazing was the only one .

On the other hand, a multilayer wiring board is used in various electric circuits. Multilayer wiring boards are classified into two types according to the method of manufacturing via holes for connecting wiring layers. One is a method of forming a conductive film in a via hole by plating, and the other is a method of forming a via hole with a conductive paste.

[0004] The method of using the conductive paste is further classified into two types, one of which uses a conductive paste composed of a noble metal powder and a binder resin, which are usually known as a silver through-hole wiring board. The other uses a conductive paste that uses metal powder and solder powder as conductive elements.In this case, heating melts the solder and combines the metal powder to form a conductive path. is there.

[0005]

However, since the connection using solder uses different metals such as lead and tin, corrosion may occur depending on the use environment and the formation of an intermetallic compound may occur, so that the connection portion may not be formed. There is a problem that it is fragile and cracks easily occur due to repeated stress and the like. Although connection by ultrasonic waves does not include the above-mentioned problems, it can obtain only a very small connection area and is difficult to apply to general use.
An object of the present invention is to provide a novel method for connecting copper or copper alloy with excellent reliability.

On the other hand, in the production of a multilayer wiring board, a via hole formed by plating has excellent conductivity and reliability because the conductive layer is made of metallic copper, but requires many man-hours for production.
Further, a pollution treatment facility for a plating waste liquid and a substrate cleaning liquid is required, and the manufacturing cost is high. On the other hand, via holes (silver through holes) made of conductive paste have a simple manufacturing process and low cost, but have high through-hole conduction resistance, exhibit non-ohmic properties that increase conduction resistance especially in low current regions, and have a limited use range. Was limited. Further, although the method using metal powder and solder powder can be expected to achieve ohmic connection by metal conduction, the connection is brittle and easily broken by a heat shock test or the like, and is not practically used.

Therefore, another object of the present invention is to provide a multilayer wiring board having a novel concept applying the above-described novel connection principle of copper or a copper alloy, and a conductive paste used therefor.

[0008]

As a means for solving the above-mentioned problems, the present invention relates to a method for joining a metal having at least one of copper and a copper alloy, the method comprising: After forming either an oxide film remover coating layer or a conductive paste layer containing copper or its alloy powder and an oxide film remover as main components, the joining surfaces are overlapped, and heated and pressed to 170 ° C. or more. It is characterized by joining.

Further, the method for manufacturing a multilayer wiring board according to the present invention is characterized in that a noble metal is inserted into a hole formed in a predetermined portion of the insulating adhesive layer.
After imprinting a conductive paste mainly composed of a conductive powder of copper or an alloy thereof and an oxide layer remover, the oxide film is removed by hot pressing at a temperature of 170 ° C. or more.
Between the surface of the copper foil and the conductive powder
The bonding is performed by diffusion of copper atoms . Further, in the multilayer substrate according to the present invention, holes formed in the insulating adhesive layer are filled with a conductive paste containing conductive particles and an oxide film remover, and the insulating adhesive layer is made of copper foil so as to cover the holes. Between the surface of the copper foil from which the oxide film has been removed
The conductive powder is electrically connected to the conductive powder by diffusion bonding of copper atoms at a bonding interface .

Another feature of the present invention is that the oxidized layer removing agent is a polymer or an oligomer containing a carboxylic acid or carboxyl group in the structure. Still another feature of the present invention is to use an oxide layer removing agent in a binder resin of the conductive paste.

[0011]

When joining metals having at least one of copper or a copper alloy, a noble metal thin film layer, an oxide film remover coating layer, or copper or its alloy powder and an oxide film remover are applied to the joining surface of the copper or copper alloy metal. After forming any one of the conductive paste layers mainly composed of
By heating and pressurizing to 70 ° C. or more, copper atoms on the bonding surface diffuse to the surface of the opposing metal, and bonding is performed.

Further, according to the above principle, after a predetermined portion of the insulating adhesive layer, that is, a via hole portion, is printed with a conductive paste mainly composed of a conductive powder of noble metal, copper or an alloy thereof and an oxide film remover, By heating and manufacturing at a temperature of 170 ° C. or higher, the upper and lower copper foils sandwiching the insulating adhesive layer and the conductive powder in the conductive paste are joined by metal bonding by diffusion of metal atoms, and the conductive paste is produced at the time of manufacturing. However, the upper and lower copper foils are completely electrically connected. For this reason, despite the fact that it can be manufactured at a low cost in the same way as a conventional silver through-hole substrate, the connection resistance does not increase even in a low current region as in the case of the via hole formed by plating, and can be used in all circuits. A wiring board is obtained.

[0013]

Embodiments of the present invention will be described below.

As the copper or copper alloy used in the present invention, general copper or its alloy such as electrolytic copper, rolled copper, bronze, brass, beryllium copper, and gunmetal can be used. These may have any shape such as a plate shape, a foil shape, a line shape, a bar shape, and the like. These metals are plated with a noble metal after removing the oxide film on the surface.

Various means are known for removing an oxide film as a pretreatment for plating. For example, required properties of materials such as etching with acid, mechanical polishing, heating in a reducing atmosphere,
Although it can be arbitrarily selected depending on the shape, it is desirable to select a balanced process in consideration of the next process of the noble metal plating process. In other words, when the plating step is performed by a wet method, the oxide film is preferably removed by wet etching.
When the plating process is performed by a dry process such as vacuum deposition, CVD, or sputtering, it is preferable that the oxide film is also removed by the dry process.

Therefore, it is preferable that a continuous film such as a copper foil is continuously formed by a wet method. In the case of a small piece such as a single component, a reducing atmosphere furnace may be used.

Following the removal of the oxide film, a thin noble metal plating is performed. The purpose of the noble metal plating is to prevent surface oxidation of copper or copper alloy and not to hinder the diffusion of copper during bonding.

That is, although nickel plating, which is generally practiced, prevents surface oxidation, it also impedes the diffusion of copper at the same time. Therefore, a copper or copper alloy having a surface coated with a base metal such as nickel is used as in the present invention. Cannot be joined at very low temperatures. In other words, the features of the present invention can be realized only by adopting a noble metal plating on a clean copper surface. Therefore, a thin noble metal plating film is sufficient. For example, as shown in the following specific examples, a thickness of 100 mm is sufficient for the purpose. In general, there is no problem even if the noble metal layer is thick, but it does not make much sense because it only increases the process cost. Further, when used in an electric circuit, a large amount of silver may lead to a decrease in reliability. Therefore, it is desirable that the noble metal plating layer has a minimum necessary thickness, and may be set in accordance with the use conditions of the product.

Various methods of noble metal plating are known, and various methods can be selected according to the shape of the object to be plated. For example, in the case of a continuous copper foil or the like, it is efficient and easy to manage by electroplating. On the other hand, in the case of a single component or the like, adopting the electroless plating method can obtain a uniform plating film thickness without depending on the shape.
Furthermore, a vacuum evaporation method, a CVD method, a sputtering method, or the like can be adopted as long as the film is a continuous film.

The noble metals used for plating include gold,
Silver, platinum, palladium, rhodium and the like can be mentioned, but use of gold or silver is desirable in view of economy and the like. However, after silver plating, if stored in a room for a long period of time, sulfuration occurs, so it is desirable to avoid long-term storage in an open system until bonding after silver plating.

When applying an oxide film removing agent instead of plating and joining, if the oxide film of copper or copper alloy to be joined is thick, it is desirable to remove the oxide film in advance. Various means are known for removing the oxide film as a pretreatment. For example, it can be arbitrarily selected according to the required characteristics and shape of the material, such as etching with an acid, mechanical polishing, and heating in a reducing atmosphere. Even if the oxide film is removed, an extremely thin oxide film exists because the copper or copper alloy is rapidly oxidized in air.

As the oxide film removing agent applied to the copper or copper alloy surface, it is desirable to use a polymer or an oligomer containing a carboxylic acid or a carboxyl group in the structure. Examples of these are straight-chain or side-chain saturated fatty acids such as caproic acid, enanthic acid, caprylic acid, 2-ethylhexanoic acid and stearic acid, oleic acid, linoleic acid,
Examples include unsaturated fatty acids such as linolenic acid, carboxylic acids such as abietic acid, succinic acid, and malonic acid, polyacrylic acid, alkyd resins, and terminal carboxypolybutadiene. Incidentally, the oxide film removing agent described in the present specification, the surface oxidized copper or noble metal surface changes to a metal state,
Or a substance to be kept.

These oxide film removing agents can be applied directly or after dissolving in a solvent or the like. In addition to the above, activators conventionally used for soldering fluxes, such as dimethylamine hydrochloride, can also be used as an oxide film remover, but when these inorganic activators are used, they are removed by washing after bonding. It is necessary to.

The temperature required for joining must be at least 170 ° C. or higher. If the temperature is lower than this, diffusion of copper does not occur and bonding cannot be performed. Although there is no particular upper limit on the temperature, copper or an alloy thereof is generally susceptible to a change in characteristics due to oxidation or high temperature. As a matter of course, the higher the bonding temperature, the shorter the bonding time. Furthermore, combined use of ultrasonic waves is effective if conditions permit.

Since the pressure required for the present invention is merely for bringing the surfaces of the joining portions close to each other, an extremely high pressure is not necessary. It is desirable to make the surface roughness of the surface as small as possible. However, even when the surface roughness is poor, copper or a copper alloy having low elasticity is plastically deformed by pressurization, so that bonding can be performed. Furthermore, by joining a highly ductile metal such as gold or silver between copper or a copper alloy to be joined at the time of joining, joining strength can be increased at a low joining pressure.

The present invention can be used not only for bonding the above-mentioned plate members but also for a resin-based conductive paste using copper or its alloy powder as a conductive material. That is, a resin having the properties of the oxide film remover is used as a binder resin of the conductive paste, or an oxide film remover is added to the binder resin, and after the paste is applied, the paste is heated and pressed while applying pressure. Thereby, the copper or the alloy powder thereof in the paste can be bonded to each other to form a conductive path. As the binder resin, a generally used thermoplastic resin or thermosetting resin can be used. Since the conductive path obtained here is based on metal bonding, it exhibits ohmic properties, and the resistance does not increase even with a very small current. Further, the above-mentioned conductive paste can be used not only for electrical purposes but also as an auxiliary agent for joining copper. That is, when the surface roughness of copper or its alloy to be joined is poor, it can be used as a filler for concave portions on the surface.

As the conductive powder used in the present invention, gold,
Silver, copper and their alloy powders can be used. Although noble metals other than these can be used, they have high conduction resistance, are expensive, and have little meaning. These powders are usually supplied to the market in the form of spheres, flakes, resins, and the like. However, in the present invention, the use of spherical conductive powders is most convenient because the pressing pressure described below can be reduced. In addition, the spherical shape described here does not need to be a perfect true sphere, but indicates a non-plate-like shape including a polyhedron.

As the oxide film remover, an activator conventionally used in soldering or the like can be used. However, considering long-term reliability, an organic activator having a slower activity than an inorganic activator can be used. Oligomers or polymers containing a carboxylic acid or carboxyl group in the structure are preferred. Examples of these are straight-chain or side-chain saturated fatty acids such as propionic acid, caproic acid, enanthic acid, caprylic acid, 2-ethylhexanoic acid and stearic acid, and unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid. And carboxylic acids such as abietic acid, succinic acid, malonic acid, aspartic acid and ascorbic acid or aminocarboxylic acids and derivatives thereof, polyacrylic acid, acrylic acid copolymers, alkyd resins, polybutadiene derivatives, etc. And an oligomer or polymer having a carboxyl group.

When an activator having a low boiling point such as a lower fatty acid is used, as shown in Example 1, after the activator acts upon the production of a substrate to form a conductive path, it is used during soldering or during normal use. In order not to adversely affect the conduction reliability, it is desirable to use a resin material such as an epoxy resin which reacts with these activators to give a stable compound.

The manufacture of the multilayer wiring board according to the present invention will be described below with reference to the drawings. In FIG. 1A, the conductive paste 3 is printed using a squeegee 4 or the like into a hole 2 formed in a predetermined portion of the insulating adhesive layer 1, and two copper foils 5 are formed as shown in FIG. Fig. 1 (c)
And hot pressing at a temperature of 170 ° C. or higher. Thus double-sided copper-clad plate 7 forming a conductive path (via hole) 6 necessary portion shown in FIG. 2 (a) can be formed. The double-sided copper-clad board 7 can be formed into a double-sided wiring board 8 shown in FIG. Since the conductive powder in the via hole 6 obtained here is bonded by metal bonding as described above, the conductive resistance is low, and the conductive powder in the via hole is also metal bonded to both surfaces of the copper foil. Similar to the via hole manufactured by the method, the resistance does not increase even in a low current region, and a double-sided wiring board excellent in reliability can be obtained.

The plurality of double-sided wiring boards 8 thus obtained,
As shown in FIGS. 3 (a) and 3 (b), 8 ′ and 8 ″ are heated and pressed together with the plurality of insulating adhesive layers 9 and 9 ′ on which the conductive paste is imprinted, thereby forming four to six layers. A multi-layer wiring board can be easily formed by increasing the number of double-sided wiring boards and insulating adhesive layers during hot pressing.
Naturally, a multi-layer wiring board can be formed.

The technique of imprinting a conductive paste having the above-described material composition into a hole provided in a predetermined portion of the insulating adhesive layer includes a method using screen printing, a method using pins, laminating a release film, and attaching the release film together. A known method such as a method in which a hole is formed, the image is directly imprinted, and the post-release film is peeled off can be employed.

Referring to the method using a release film, FIG.
This will be described with reference to FIG. In FIG. 4 (a), first, a release film 10 is bonded to the insulating adhesive layer 1, and then a via hole 2 is formed in a predetermined place along with the release film 10. A conductive paste 3 is placed on the via hole 2 with a squeegee 4.
Imprint using such as. Subsequently, as shown in FIG. 4B, the release film 10 is peeled off, so that the conductive paste 3 is provided at a predetermined location and no conductive substance is present on the surface of the insulating adhesive layer. An insulating adhesive layer 1 can be obtained.

When copper powder is used as the conductive material of the conductive paste 3, even if the surface of the insulating adhesive layer is contaminated with the conductive paste 3, the copper powder is removed by etching. There is no need to use a release film.

The insulating adhesive layer in which the conductive paste is imprinted on a predetermined portion is dried, if necessary, by a solvent, and then sandwiched between two pieces of copper foil and heated and pressed to produce a double-sided board. The production of a multilayer board having four or more layers can be performed by repeating the above-mentioned hot press operation.

The temperature required for the hot press is 170 ° C. or higher,
Preferably it is 180 ° C. or higher. At a temperature lower than 170 ° C., the diffusion of the metal in the paste does not occur, and the metal in the conductive paste does not bond to each other. Or an increase in the resistance value occurs.

The pressure required for pressing varies depending on the metal material used as a conductor in the paste. That is, gold,
A highly ductile material such as silver is joined at a relatively low pressure, whereas a conductor that is relatively difficult to deform, such as copper or an alloy thereof, is preferably joined at a higher pressure.

Although the present invention has been described above, the above-mentioned conductive paste can be used not only for electrical applications but also generally as an auxiliary agent for joining a noble metal, copper or an alloy thereof. That is, when the surface roughness of a noble metal, copper, or an alloy thereof to be joined is poor, the above-mentioned conductive paste can be used as a filler for a concave portion on the surface.

(Example 1) Thickness 0.5 preliminarily degreased
The surface of a copper plate having a thickness of 2.5 mm was soft-etched with a sulfuric acid-hydrogen peroxide aqueous solution, washed with water, and then silver-plated on the surface by an electroplating method. A commercially available non-cyanide silver plating solution was used as the plating solution, and a silver plate was used as the anode, and silver plating was performed at a current density of 0.5 A / dm ² at 500 °. As a result, the surface of the copper plate became silver-white.

After the silver plating, the copper plate washed with water and dried
Two sheets are stacked and sandwiched between hard chrome plated steel sheets.
I did it. Press conditions are 180 ° C, 30 minutes, 300kg /
cm ^TwoAnd As a result, the two copper plates are firmly joined
Was. The silver plated surface of the copper plate that was in contact with air during pressing
Because it is oxidized and colored, at the above press temperature
It was confirmed that copper diffusion occurred through the silver-plated surface.
Was. Shearing with a tensile tester to achieve joint strength
As a result of measuring the separation strength, the joining strength was 400 to 500.
kg / cm^Twoshowed that.

For comparison, a copper plate was soft-etched, washed with water, dried, and two sheets were stacked and heated and pressed under the above conditions.
No bonding occurred. Further, for comparison, the silver-plated copper plate and the copper plate which had been soft-etched and washed with water but not subjected to silver plating were overlapped and heated and pressed under the above-mentioned conditions, but joining was still impossible.

From the above results, it was confirmed that the copper plates were joined for the first time by the method of the present invention in which thin silver-plated copper plates were stacked and heated and pressed.

Example 2 Silver plating was performed on a smooth surface of an 18 μm copper foil in the same manner as in Example 1. The plating thickness was 100 °. This copper foil was overlaid on the silver-plated copper plate of Example 1 and heated and pressed under the conditions of Example 1. However, the pressure was 750 kg / cm ² . In addition, 1m from the top of the copper foil
m copper plates were stacked so that pressure was applied evenly to the foil.
Also in this case, the copper foil was bonded to the silver-plated copper plate, but was not bonded to the copper plate installed for equalizing.

As a result of the pressing, the copper foil was firmly bonded to the copper plate, and a peeling test of T peeling was performed. However, the copper foil was cut and the bonding strength could not be measured accurately.

Example 3 An epoxy resin (epichlorohydrin-bisphenol Α type with an epoxy equivalent of 180) containing no curing agent was applied to the surface of the silver-plated copper plate obtained in Example 1 in order to see the effect of surface contamination. Then, it was heated and pressed under the conditions of Example 1. As a result, the same strong bonding as in Example 1 was obtained. From this result, it was confirmed that even if a resin component or the like adhered to the surface, it did not hinder the joining.

Example 4 A silver plate having a thickness of 0.5 mm and the thin silver-plated copper plate manufactured in Example 1 were overlaid and pressed under the conditions of Example 1. Also in this case, a strong joint was obtained as in Example 1. At this time, diffusion of copper was observed from the edge of the copper plate on the surface of the silver plate in contact with copper to the surface of the silver plate at about 0.5 mm, and copper atoms diffused inside silver and contributed to the bonding. I understood. Further, when the interface between silver and copper was examined with a wavelength dispersive x-ray microanalyzer (XMA), FIG.
As shown in the figure, it was confirmed that silver and copper were diffused into the metal of the other party over several μm.

Example 5 In Example 1, when the heating press temperature was set to 170 ° C. and the time was set to 1 hour, the copper plates were joined to each other. there were.

Example 6 When the silver plating thickness was set to 100 ° in Example 1, the same strong bonding as in Example 1 was obtained. From this result, it was found that the thickness of silver may be extremely thin.

(Example 7) A phosphor bronze plate having a thickness of 0.2 mm was plated with 500 ° silver in the same manner as in Example 1. Laminate this plated phosphor bronze plate, 180 ° C, 30 minutes, 2000kg / c
When pressed under the conditions of m ^2, the phosphor bronze plate was joined. However, the joint strength was weak, and the joint peeled off when bent. Then, when the joining temperature was set to 220 ° C., strong joining was obtained, and the elasticity of the phosphor bronze was not impaired.

Example 8 Gold plating was performed on a copper foil of a printed wiring board. The plating thickness was 200 mm. On the other hand, after the solder plating layer of the lead wire of the QFP package IC connected to the wiring board was removed by etching, the lead wire was plated with copper and further plated with silver. The plating thickness was 5 μ and 500 °, respectively. After arranging the lead wire of the above IC on a predetermined wiring board, hold down the lead wire with a jig,
After heating at 220 ° C. for 1 minute, the lead wire was firmly connected to the wiring board.

When a circuit based on the actual connection and a circuit based on the conventional solder were subjected to a thermal cycle test, the circuit according to the present example showed a service life twice or more that of the circuit based on the solder joint. As a matter of course, the circuit made of solder was broken by heating at 200 ° C., whereas the circuit according to the present example showed no abnormality at 200 ° C.

Example 9 The surface of a rolled copper plate having a thickness of 2 mm was polished with # 1200 sandpaper, washed with water and dried, and then a 5% acetone solution of abietic acid was applied and dried to prepare a treated copper plate. Two sheets of the above treated copper sheets are stacked and 180
The copper plate was joined by hot pressing at 380 kg / cm ² for 30 minutes. A tensile test piece was cut out from the bonded copper plate thus obtained, and a shear tensile test was performed. As a result, the shear tensile strength was 240 to 260 kg / cm ^2, and it was found that the joint was firmly joined.

For comparison, the above-mentioned rolled copper sheet was polished with # 1200 sandpaper, washed with water, dried, and then two sheets were stacked and heated and pressed under the above-mentioned conditions, but no joining occurred.

From the above results, it was confirmed that the copper plates were joined for the first time by the method of the present invention, in which a 5% acetone solution of abietic acid was applied to the surface of the copper plate and heated and pressed.

(Example 10) The treated copper plate of Example 1 was overlaid on a silver plate having a thickness of 2 mm, and heated and pressed under the same conditions as in Example 9. As a result, both the plates were firmly joined, and as a result of the tensile test, the shear tensile strength was 540 to 660 k.
g / cm ² .

When the vicinity of the joined interface was examined with a wavelength-dispersive x-ray microanalyzer (XMA), it was confirmed that silver and copper were diffused over several μm into the other metal as shown in FIG. Was. FIG. 7 shows an XMA analysis result of the interface when the heating press conditions were 240 ° C. and 30 minutes.

(Example 11) A tip of a copper round bar having a diameter of 10 mm was shaved to a diameter of 5 mm, and a flat portion of the tip was finished smoothly, and then an abietic acid solution was applied and dried. Then, the round bars were abutted, and heated and pressed with a silver plate having a thickness of 0.5 mm between flat portions having a diameter of 5 mm. Pressing conditions were 680 kg / cm ² and 195 ° C. for 30 minutes.
When the tensile test of the obtained round bar was performed,
It showed a breaking strength of 30 kg / cm ² , and it was found that it was joined very firmly.

(Example 12) After coating an abietic acid solution on the surface of a copper plate, a gold wire having a diameter of 1 mm was overlapped and pressed on a hot plate at 195 ° C for 15 minutes. As a result, the gold wire was bonded on the copper plate. A part of the gold wire was peeled off, and a peeling test was performed at right angles to a copper plate. As a result, it was found that the peeling strength was 4.0 kg / mm, and that the bonding was firmly performed.

Example 13 In Example 1, β-lauryl N-lauroyl aspartate was used as the activator instead of abietic acid. In this case, when the copper plate was heated and the activator was sprinkled and melted on the surface, strong bonding was obtained as in Example 1.

Example 14 A polymer was prepared by adding 0.5% of benzoyl peroxide to acrylic acid monomer and heating and stirring at 60 ° C. A solution prepared by dissolving this polymer in water to form a 5% solution was used as an activator instead of the abietic acid solution of Example 1. Also in this case, strong bonding was obtained as in Example 1.

(Example 15) In Example 1, when the heating press temperature was 170 ° C. and the time was 1 hour, the copper plates were joined to each other. there were.

Example 16 75 g of spherical copper powder (crystal copper, trade name of Tanaka Kikinzoku Co., Ltd.) having a diameter of 4 to 5 μm and 25 g of rosin were dispersed and dissolved in 35 g of cellosolve acetate to produce a conductive paste. 0.5mm in diameter when this paste is cut into the specified part of glass-epoxy prepreg
Was printed in the through-holes, sandwiched between both sides with a copper foil of 35 μm, and heated and pressed to produce a double-sided wiring board having a thickness of 0.5 mm. The pressing conditions were 180 ° C. for 30 minutes at a pressure of 150 kg / cm ² .

After pressing, the wiring substrate was etched into a predetermined pattern, and the DC resistance of the through hole was measured. As a result, the resistance value per through hole was 1 mΩ or less, and this value was maintained in the current range from high current to 10 μA.

On the other hand, the through-hole resistance value of the ordinary through-hole wiring board used for comparison is 10 mΩ,
When the current value became 10 mA or less, the resistance increased.

From these results, it can be seen that the copper bonding method according to the present invention is a very effective conductive path forming method.

Example 17 A conductive paste was prepared by dispersing 75 g of sprayed copper powder having a diameter of 2 to 15 μm and 7.5 g of dimethylolpropionic acid in 15 g of an epichlorohydrin-bisphenol A type epoxy resin (epoxy equivalent: 180). did. This paste was imprinted into a through-hole with a diameter of 0.5 mm opened in a predetermined portion of a glass-epoxy prepreg, and was hot-pressed with 35 μm copper foil from both sides to produce a double-sided wiring board with a thickness of 0.5 mm. . The pressing conditions were 180 ° C. for 30 minutes at a pressure of 150 kg / cm ² .

After the manufactured wiring board was pressed, the wiring board was etched into a predetermined pattern, and the DC resistance of the through hole was measured. As a result, the resistance value per through hole is 0.
<1 mΩ, which was maintained in the current range from high current to 10 μA.

Further, when the substrate was subjected to a heat cycle test at 260 ° C. and 25 ° C., no abnormality was found in the resistance value after 100 tests.

On the other hand, the through-hole resistance value of the ordinary through-hole wiring board used for comparison is 10 mΩ,
When the current value became 10 mA or less, an increase in the resistance value was observed. Furthermore, the resistance value of the ordinary through-hole wiring board showed a change of 20% or more in 100 heat cycle tests.

From the results, it was confirmed that the upper and lower copper foils of the double-sided wiring board according to the present invention were completely electrically connected.

(Example 18) A hole having a diameter of 0.5 mm was formed in a predetermined portion of the two double-sided wiring boards obtained in Example 1, and an epoxy prepreg filled with the conductive paste manufactured in Example 1 was sandwiched between the two. A four-layer wiring board was manufactured by hot pressing.
The electrical connection of the four-layer wiring board obtained here is also stable and low in resistance as in the first embodiment, and is a multilayer wiring excellent in electrical connectivity only by a simple heating press operation as in this embodiment. It has been demonstrated that boards can be manufactured.

Example 19 75 g of sprayed copper powder having a diameter of 2 to 15 μm and 25 g of rosin were added to cellosolve acetate 25.
g to prepare a conductive paste. This paste was applied to a 0.5 mm diameter through-hole formed in a predetermined portion of a glass-epoxy prepreg. After drying the solvent, the paste was sandwiched between both sides with a 35 μm copper foil and hot-pressed to a thickness of 0.5 mm. A double-sided wiring board was manufactured. The pressing conditions were 180 ° C. for 30 minutes at a pressure of 150 kg / cm ² .

After pressing, the wiring substrate was etched into a predetermined pattern, and the DC resistance of the through hole was measured. As a result, the resistance value per through hole was 0.1 mΩ or less, and this value was maintained in the current range from high current to 10 μA.

(Example 20) A double-sided substrate was manufactured by using a conductive paste in which spherical silver powder having a diameter of 1 µm was used instead of the sprayed copper powder in Example 1. In this example, the pressing pressure was 50 kg / cm ² and the temperature was 190 ° C. Also in this case, a double-sided board excellent in reliability and conductivity was obtained. Observation of the through-hole part of this double-sided board revealed that the silver powder was integrated into a silver pillar, and that silver and copper were mutually diffused and integrated at the interface between the copper foil and the silver pillar. I understood.

Example 21 A styrene-maleic acid (1: 1) copolymer resin was used in Example 1 in place of dimethylolpropionic acid and epichlorohydrin-bisphenol A type epoxy resin. In this case, methyl ethyl ketone was used as a solvent for the conductive paste. Also in this example, a double-sided wiring board having good electrical connectivity was obtained.

Example 22 In Example 1, a double-sided substrate having good electrical connectivity was obtained also in the case where N-stearoyl aspartic acid monostearyl ester was used in place of dimethylolpropionic acid.

(Example 23) A double-sided board was manufactured in the same manner as in Example 1 except that the pressing temperature was 170 ° C and the pressing time was 1 hour. The conduction resistance of this double-sided board was the same as that of Example 1, but the disconnection occurred in 20 heat cycle tests. From this result, it was found that the lower limit of the pressing temperature was 170 ° C.

[0078]

As described in the above embodiments, the joining method of copper or copper alloy according to the present invention enables joining at a low temperature exceeding conventional common sense. Despite the simple manufacturing method similar to the conventional silver through-hole wiring board, the manufacturing method can produce a wiring board showing very excellent conductivity similar to the plating method. The effect is great.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a method for manufacturing a double-sided wiring board according to an embodiment of the present invention.

FIG. 2 is a perspective view of a double-sided wiring board manufactured by a manufacturing method according to an embodiment of the present invention.

FIG. 3 is a conceptual diagram showing a manufacturing process of a multilayer wiring board according to an embodiment of the present invention.

FIG. 4 is a conceptual diagram showing one method of imprinting a conductive paste into holes of an insulating adhesive layer.

FIG. 5 is a diagram showing diffusion of copper atoms into a silver plate according to an example of the present invention.

FIG. 6 is a view showing diffusion of copper atoms into a silver plate according to the example.

FIG. 7 is a view showing diffusion of copper atoms into a silver plate according to the example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating adhesive layer 2 Hole 3 Conductive paste 4 Squeegee 5, 5 'copper foil 6 Conduction path 7 Double-sided copper bonding board 8 Double-sided wiring board

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI H05K 1/09 H05K 1/09 A 3/32 3/32 C 3/40 3/40 K (56) References JP-A-Showa 55 -55600 (JP, A) JP-A-2-66803 (JP, A) JP-A-4-96293 (JP, A) JP-A-4-159797 (JP, A) (58) Fields investigated (Int. . ^7, DB name) H05K 3/46 B23K 20/00 H01B 1/22 H05K 1/09 H05K 3/32 H05K 3/40

Claims (17)

(57) [Claims] 1. A method for removing a noble metal thin film layer and an oxide film removing agent from a bonding surface of a metal of copper or copper alloy when bonding the bonding surface of a metal of at least one of copper or copper alloy by diffusion of copper atoms at the bonding interface. After forming either a coating layer or a conductive paste layer containing copper or its alloy powder and an oxide film remover as main components, the joining surfaces are overlapped, and
A low-temperature diffusion bonding method for copper or a copper alloy, wherein the bonding is performed by heating and pressing at a temperature of 0 ° C. or higher. 2. One of the joining surfaces is made of copper or an alloy thereof having an oxide film remover coating layer formed thereon, and the other joining surface is made of a metal having a noble metal or an alloy thin film layer thereof.
A low-temperature diffusion bonding method for copper or a copper alloy according to the above. 3. The method according to claim 1, wherein the oxide film removing agent is a polymer or an oligomer containing a carboxylic acid or a carboxyl group in the structure. 4. A conductive paste for low-temperature diffusion bonding, comprising a noble metal, copper or an alloy powder thereof, an oxide film remover and, if necessary, a binder resin. 5. The conductive paste for low-temperature diffusion bonding according to claim 4, wherein the oxide film removing agent is a polymer or an oligomer containing a carboxylic acid or a carboxyl group in the structure. 6. The conductive paste for low-temperature diffusion bonding according to claim 4, wherein the shape of the noble metal, copper or its alloy powder is spherical. 7. The conductive paste for low-temperature diffusion bonding according to claim 4, wherein the oxide film removing agent is a binder resin. 8. In the production of a multilayer wiring board produced by sandwiching an insulating adhesive layer between two or more copper foils and heating and pressing, a noble metal, copper or copper is inserted into a hole formed in a predetermined portion of the insulating adhesive layer. After imprinting a conductive paste mainly composed of a conductive powder of the alloy and an oxide film remover,
Copper from which oxide film has been removed by hot pressing at a temperature of 0 ° C or higher
Copper atoms at the joining interface between the surface of the foil and the conductive powder
For manufacturing a multilayer wiring board to be joined by diffusion of a metal. 9. The method for manufacturing a multilayer wiring board according to claim 8, wherein the shape of the noble metal, copper or its alloy powder is spherical. 10. The method according to claim 8, wherein the oxide film removing agent is a polymer or an oligomer containing a carboxylic acid or a carboxyl group in the structure. 11. The method according to claim 8, wherein the binder resin of the conductive paste is an oxide film remover. 12. A method in which the insulating adhesive layer is previously scissored with a release film, holes are formed, a conductive paste is printed on the release film, and then the release film is peeled off. The method for manufacturing a multilayer wiring board according to claim 8, wherein 13. A conductive particle is formed in a hole formed in an insulating adhesive layer.
Filled conductive paste containing a child and an oxide film removing agent, wherein the insulating adhesive layer sandwiched between the copper foil so as to cover the hole, acid
The surface of the copper foil from which the oxide film has been removed is joined to the conductive powder.
A multilayer wiring board electrically connected by diffusion bonding of copper atoms at an interface . 14. The conductive powder in the conductive paste is a noble metal,
2. A copper or alloy powder thereof.
3. The multilayer wiring board according to 3. 15. The multilayer wiring board according to claim 14, wherein the shape of the noble metal, copper or its alloy powder is spherical. 16. The multilayer wiring board according to claim 13, wherein the binder resin of the conductive paste contains an oxide film removing agent. 17. The multilayer wiring board according to claim 16, wherein the oxide film removing agent is a polymer or an oligomer containing a carboxylic acid or a carboxyl group in the structure.