JP2015104748A - Copper material bonding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive copper material bonding method capable of forming bonded parts high in reliability and excellent in mechanical properties even at a low bonding temperature by using a bonding composition easy to handle and excellent in long-term stability and by reducing voids and residual organic components in bonded layers.SOLUTION: Provided is a copper material bonding method including: a step of interposing a bonding composition consisting of a nanoporous metal material containing metallic nanoparticles arrayed in three dimensions and having a mean particle size of 5 to 500 nm between a first bonding target copper material and a second bonding target copper material; and a step of heating the bonding composition interposed between the first bonding target copper material and the second bonding target copper material at 50 to 400°C, and pressing the first bonding target copper material and the second bonding target copper material.

Description

  The present invention relates to a low-temperature bonding method for copper materials, more specifically, using a bonding composition that is easy to handle and excellent in long-term stability, and has high reliability and reduced voids and residual organic components in the bonding layer. The present invention relates to an inexpensive method for joining copper materials, which enables formation of a joint having mechanical properties even at a low joining temperature.

  Conventionally, in order to mechanically and / or electrically and / or thermally bond metal parts and metal parts represented by copper materials and copper-coated parts, solder, conductive adhesive, silver paste and An anisotropic conductive film or the like is used.

  Especially, the adhesive agent, paste, and film containing the conductive filler which consists of solder and a metal are used for joining the part which needs an electrical connection. Furthermore, since metals generally have high thermal conductivity, adhesives, pastes, and films containing these solders and conductive fillers may be used to increase heat dissipation.

  On the other hand, for example, when a high-luminance lighting device or a light-emitting device is manufactured using a light-emitting element such as an LED, or a semiconductor device is manufactured using a semiconductor element that operates at a high temperature and is called a power device. In some cases, the amount of heat generation tends to increase. Attempts have been made to improve the efficiency of devices and elements to reduce heat generation. However, at present, sufficient results have not been achieved, and the operating temperature of devices and elements has risen.

  Further, from the viewpoint of preventing device damage during bonding, there is a demand for a bonding material that can ensure sufficient bonding strength at a low bonding temperature (for example, 350 ° C. or lower). Therefore, the bonding material for bonding devices and elements is required to have heat resistance that can withstand the increase in operating temperature due to the operation of the device after bonding and maintain sufficient bonding strength as the bonding temperature decreases. However, there are many cases where conventional bonding materials are not sufficient. For example, solder joins members through a process of heating the metal to the melting point or higher (reflow process). Generally, the melting point is inherent to the composition, so heating (joining) when trying to increase the heat-resistant temperature. The temperature will rise.

  Furthermore, when several layers of elements and substrates are bonded using solder, it is necessary to go through the heating process for the number of layers to be overlapped. In order to prevent melting of the already bonded portion, the solder used for the next bonding It is necessary to lower the melting point (joining temperature) of the solder, and the number of types of solder composition is required by the number of layers to be overlaid, which makes handling complicated.

  On the other hand, in the conductive adhesive, silver paste and anisotropic conductive film, the members are joined together by using thermosetting such as epoxy resin contained, but when the use temperature of the obtained device or element rises, the resin component May decompose and deteriorate. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2008-63688) proposes fine particles that are used as a main material of a bonding material so that higher bonding strength can be obtained when bonded members are bonded to each other. The problem of decomposition and deterioration of the resin component at the time of use temperature rise has not been solved.

  Conventionally, solder containing lead has been used as high-temperature solder used at high operating temperatures. Since lead is toxic, the trend toward solder-free solder is remarkable. Since there is no other good alternative material for high-temperature solder, lead solder is still used, but from the viewpoint of environmental problems, a bonding material that does not use lead is eagerly desired.

  In recent years, as an alternative material for high-temperature solder, a bonding material using metal nanoparticles centered on noble metals such as silver and gold has been developed (for example, Patent Document 2: JP 2012-046779 A). However, since metal nanoparticles are not only expensive, but also easily aggregate at room temperature, in order to maintain a dispersed state for a long period of time, the surface of the metal nanoparticles is coated with an organic layer, and a suitable dispersant for the solvent. Need to be added.

  The bonding layer formed by sintering metal nanoparticles has superior characteristics compared to conventional solders, such as having a heat resistance temperature corresponding to the melting point of the metal, while the organic layer and the dispersing agent are bonded at the sintering stage. There is a problem that voids are formed. In addition, there is an unavoidable problem that the bonding temperature depends on the decomposition temperature of the organic layer and the dispersant.

JP 2008-63688 A JP 2012-046779 A

  In view of the above situation, the object of the present invention is to use a bonding composition that is easy to handle and excellent in long-term stability, and has high reliability and mechanical properties by reducing voids and residual organic components in the bonding layer. It is an object of the present invention to provide an inexpensive method for joining copper materials, which enables formation of a joining portion having a low temperature even at a low joining temperature.

  As a result of earnest research on the bonding composition to achieve the above object, the present inventor uses a bonding composition containing a nanoporous metal material in which metal nanoparticles are arranged three-dimensionally. It has been found that it is extremely effective in achieving the above object, and has reached the present invention.

That is, the present invention
A bonding composition containing a nanoporous metal material including metal nanoparticles having a three-dimensionally arranged average particle diameter of 5 to 500 nm is obtained by combining a first bonded copper material and a second bonded copper material. Interposing the process,
While heating the said composition for joining interposed between said 1st to-be-joined copper material and said 2nd to-be-joined copper material to 50-350 degreeC, said 1st to-be-joined copper material and said 1st And a step of pressurizing a second copper material to be joined.

  In the present invention, it is necessary to use an organic coating layer, a dispersant and the like in order to ensure dispersibility of the metal nanoparticles by using a nanoporous metal material in which metal nanoparticles are three-dimensionally arranged. Therefore, voids and residual organic substances in the bonding layer can be greatly reduced.

  In the copper material joining method of the present invention, it is preferable that the joining composition is composed only of the nanoporous metal material. By using only a nanoporous metal material that does not require the use of an organic solvent or a dispersant as the bonding composition, the organic layer, the dispersant, etc. remain in the bonding layer during the sintering stage, and voids are formed. Can be effectively solved. In addition, the inevitable problem of the joining method using metal nanoparticles, in which the joining temperature depends on the decomposition temperature of the organic layer and the dispersant or the like, can be solved.

  Moreover, in the joining method of this invention, it is preferable that the said nanoporous metal material is a nanoporous metal sheet formed by decomponent corrosion of a metal material (metal foil or metal plate). Although it is extremely difficult to arrange individually generated metal nanoparticles in three dimensions, a nanoporous metal sheet can be easily obtained by using decomponent corrosion of a metal material (metal foil or metal plate). Can do. Moreover, if a nanoporous metal material is a sheet form, it can arrange | position easily between to-be-joined copper materials.

  Here, the decomponent corrosion is based on the selective dissolution of alloy elements using an appropriate corrosive solution. Reported by Erlebacher et al., Nature, 410 (2001), 40, and a nanoporous metal sheet formed using this technique is preferably used in the joining method of the present invention.

Especially, in the joining method of this invention, it is preferable that the metal material which performs a decomponent corrosion is a binary system alloy, and it is more preferable that it is an Au-Ag alloy. By decomponent corrosion of the binary alloy, one of the elements is mainly dissolved and removed, and a nanoporous metal material composed of metal nanoparticles mainly composed of the other element can be efficiently obtained. Moreover, the nanoporous metal material mainly composed of gold (Au) can be efficiently obtained by decomponent corrosion of the Au—Ag alloy with, for example, nitric acid (HNO ₃ ).

  Moreover, in the joining method of this invention, it is preferable that the said nanoporous metal material is the nanoporous metal powder obtained by grind | pulverizing the said nanoporous metal sheet. By making the nanoporous metal material into a powder form, it is possible to easily dispose the bonding composition according to the surfaces to be bonded having various sizes and shapes.

  According to the present invention, a bonding composition that is easy to handle and excellent in long-term stability is used, and formation of a joint having high reliability and mechanical properties is low by reducing voids and residual organic components in the bonding layer. It is possible to provide an inexpensive copper bonding method that is possible even at a bonding temperature.

It is a schematic sectional drawing of a power module. It is a SEM photograph of the Au-Ag alloy sheet which gave decomponent corrosion for 1 hour. It is a SEM photograph of the Au-Ag alloy sheet which gave decomponent corrosion for 2 hours. It is a SEM photograph of the Au-Ag alloy sheet which gave decomponent corrosion for 3 hours. It is a SEM photograph of the Au-Ag alloy sheet which gave decomponent corrosion for 4 hours. It is a SEM photograph of the Au-Ag alloy sheet which gave decomponent corrosion for 5 hours. It is a SEM photograph of the Au-Ag alloy sheet which gave decomponent corrosion for 10 hours. It is a SEM photograph of the nanoporous metal sheet kept at a high temperature at 100 ° C. It is a SEM photograph of the nanoporous metal sheet kept at a high temperature at 150 ° C. It is a SEM photograph of the nanoporous metal sheet kept at a high temperature at 200 ° C. It is a SEM photograph of the nanoporous metal sheet kept at a high temperature at 250 ° C. It is an XPS narrow scan spectrum of Au4f of a nanoporous metal sheet. It is an XPS narrow scan spectrum of Ag3d of a nanoporous metal sheet. It is the shape and arrangement | positioning figure of a joining test piece which consists of a silicon | silicone (Si) board | substrate used for the joining test. It is a graph which shows the tensile strength of the joint joint obtained using the nanoporous metal sheet. It is the shape of the joining test piece which consists of oxygen-free copper used for the joining test. It is a graph which shows the shear strength of the joint joint obtained using the nanoporous metal sheet. It is an external appearance photograph of nanoporous metal powder.

  Hereinafter, a preferred embodiment of a copper material joining method using the nanoporous metal material of the present invention will be described in detail. In addition, in the following description, only one embodiment of the present invention is shown, and the present invention is not limited by these, and redundant description may be omitted.

(1) Joining composition The joining composition of this embodiment is characterized by containing a nanoporous metal material, and contains an organic solvent, a dispersing agent, etc. as needed. These components will be described below.

(1-1) Nanoporous metal material The nanoporous metal material used in the bonding composition of the present embodiment is a nanoporous material in which metal nanoparticles having an average particle diameter of 5 to 500 nm are three-dimensionally arranged. A metal material is preferable, and a nanoporous metal material in which metal nanoparticles having an average particle diameter of 10 to 50 nm are three-dimensionally arranged is more preferable. Metal nanoparticles generally have poor stability and dispersibility, and it is necessary to coat the surface with organic matter, etc., but the metal nanoparticles are arranged in a three-dimensional manner without using the coating or the like for a long time. Stability and dispersibility can be ensured.

  In addition, by setting the average particle size of the metal nanoparticles constituting the nanoporous metal material to 5 to 500 nm, the metal nanoparticles can express the low-temperature firing function inherently and can be heated at about 50 to 400 ° C. Even if it exists, sintering of metal nanoparticles can be advanced. When decomponent corrosion is applied to a metal material, it is easy to obtain a nanoporous metal material having an average particle size of metal nanoparticles of 5 nm or more. When the average particle size of metal nanoparticles is 500 nm or less, the low-temperature firing function is exhibited. Easy to be. In addition, by setting the average particle diameter of the metal nanoparticles to 10 to 50 nm, both the stability of the metal nanoparticles and the low-temperature sintering function can be achieved at a high level. The average particle diameter of the metal nanoparticles can be measured from an electron micrograph, for example, and can be calculated from the electron micrograph using an image processing apparatus. In addition, the average particle diameter of the metal nanoparticle which comprises a nanoporous metal material means the average value of the shortest diameter, when the metal nanoparticle is flat.

  The nanoporous metal material is preferably a nanoporous metal sheet formed by decomponent corrosion of a metal material (metal foil or metal plate). Although it is extremely difficult to arrange individually generated metal nanoparticles in three dimensions, a nanoporous metal sheet can be easily obtained by using decomponent corrosion of a metal material (metal foil or metal plate). Can do. Moreover, if a nanoporous metal material is a sheet form, it can arrange | position easily between to-be-joined copper materials.

As described above, decomponent corrosion uses selective dissolution of alloy elements using an appropriate corrosive solution, and the corrosive solution depends on the metal material to be treated and the shape of the target nanoporous metal material. May be selected as appropriate. As the corrosive liquid, for example, HF, HCl, NaOH, HNO ₃ , H ₂ SO ₄ , citric acid, H ₂ SO ₄ + MnSO ₄ , (NH 4) ₂ SO ₄ + MnSO ₄ , AgNO ₃ or the like can be used.

  Decomponent corrosion does not need to be applied to all of the metal material, and is preferably applied only to the vicinity of the surface. As long as at least the surface vicinity of the metal material in contact with the copper material to be joined has a nanoporous structure, it has a low-temperature firing function, so that a good joint can be obtained. In this case, firing of the metal nanoparticles is unnecessary inside the metal material that has not been subjected to decomponent corrosion, and bonding can be achieved extremely efficiently.

In the joining method of the present invention, the metal material subjected to decomponent corrosion is preferably a binary alloy, more preferably an Au—Ag alloy. By decomponent corrosion of the binary alloy, one of the elements is mainly dissolved and removed, and a nanoporous metal material composed of metal nanoparticles mainly composed of the other element can be efficiently obtained. A nanoporous metal material mainly composed of gold (Au) can be efficiently obtained by decomponent corrosion of the Au—Ag alloy with nitric acid (HNO ₃ ), for example.

  In addition, as a metal material that can obtain a nanoporous metal material by decomponent corrosion, Au-Ag-Pt, Au-Cu, Au-Zn, Au-Al, Ag-Al, Ag-Zn, Cu-Al Cu-Mg, Cu-Mn, Cu-Zn, Pt-Cu, Pt-Si, Pt-Al, Pt-Zn, Pd-Ag, Pt-Co, Pd-Al, Pd-Ni-P, Ni-Al Ni-Cu etc. can be illustrated. Here, the nanoporous material Au is obtained by decomponent corrosion such as Au-Ag-Pt, Au-Cu, Au-Zn, and Au-Al, and the nanoporous material Ag is obtained by decomponent corrosion such as Ag-Al and Ag-Zn. The material is made of nanoporous Cu material by decomponent corrosion such as Cu—Al, Cu—Mg, Cu—Mn and Cu—Zn, and Pt—Cu, Pt—Si, Pt—Al, Pt—Zn, Pd—Ag. And Pt-Co, etc. to remove nanoporous Pt material, Pd-Al and Pd-Ni-P, etc., to remove nanoporous Pd material, Ni-Al, Ni-Cu, etc. Each nanoporous Ni material can be obtained by corrosion.

  The nanoporous metal material is preferably in the form of a sheet. By using the sheet shape, when only the nanoporous metal material is used as the bonding composition, it can be easily arranged between the bonded copper materials. On the other hand, the nanoporous metal material may be powdery, and the powdered nanoporous metal material can be used as it is as a bonding composition. Furthermore, it can be suitably used as a paste-like bonding composition by dispersing a powdery nanoporous metal material in an organic solvent. In addition, powdery nanoporous metal material can be easily obtained by completely decomponent corrosion of the metal material with a corrosive solution to which ultrasonic waves are applied, or by pulverizing the sheet-like nanoporous metal material. Can do.

(1-2) Others Various organic solvents can be used as the organic solvent used in the bonding composition of the present embodiment as long as the effects of the present invention are not impaired. Examples of the organic solvent include terpene solvents, ketone solvents, alcohol solvents, ester solvents, ether solvents, aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, cellosolve solvents, carbitol solvents, and the like. Is 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 used.

  In addition to the components described above, the bonding composition of the present embodiment is provided with functions such as appropriate viscosity, adhesion, drying properties, and printability according to the intended use within a range that does not impair the effects of the present invention. In order to do so, a dispersion medium, for example, an oligomer component that serves as a binder, a resin component, an organic solvent (a part of the solid content may be dissolved or dispersed), a surfactant, a thickener, or a surface tension. You may add arbitrary components, such as a regulator. Such optional components are not particularly limited.

  As the dispersion medium of the optional components, various types can be used as long as the effects of the present invention are not impaired, and examples thereof include hydrocarbons and alcohols.

  Examples of the hydrocarbon include aliphatic hydrocarbons, cyclic hydrocarbons and alicyclic hydrocarbons, and each may be used alone or in combination of two or more.

  Examples of the aliphatic hydrocarbon include saturated or unsaturated aliphatic hydrocarbons such as tetradecane, octadecane, heptamethylnonane, tetramethylpentadecane, hexane, heptane, octane, nonane, decane, tridecane, methylpentane, normal paraffin, and isoparaffin. Is mentioned.

  Examples of the cyclic hydrocarbon include toluene and xylene.

  Furthermore, as the alicyclic hydrocarbon, for example, limonene, dipentene, terpinene, terpinene (also referred to as terpinene), nesol, sinene, orange flavor, terpinolene, terpinolene (also referred to as terpinolene), ferrandrene, mentadiene, teleben, Examples thereof include dihydrocymene, moslen, isoterpinene, isoterpinene (also referred to as isoterpinene), clitomen, kautssin, cajeptene, oilimene, pinene, turpentine, menthane, pinane, terpene, and cyclohexane.

  Alcohol is a compound containing one or more OH groups in the molecular structure, and examples thereof include aliphatic alcohols, cyclic alcohols and alicyclic alcohols, and each may be used alone or in combination of two or more. Also good. Moreover, a part of OH group may be induced | guided | derived to the acetoxy group etc. in the range which does not impair the effect of this invention.

Examples of the aliphatic alcohol include heptanol, octanol (1-octanol, 2-octanol, 3-octanol, etc.), decanol (1-decanol, etc.), lauryl alcohol, tetradecyl alcohol, cetyl alcohol, 2-ethyl-1- Examples thereof include saturated or unsaturated C _6-30 aliphatic alcohols such as hexanol, octadecyl alcohol, hexadecenol and oleyl alcohol.

  Examples of the cyclic alcohol include cresol and eugenol.

  Further, as the alicyclic alcohol, for example, cycloalkanol such as cyclohexanol, terpineol (including α, β, γ isomers, or any mixture thereof), terpene alcohol such as dihydroterpineol (monoterpene alcohol etc. ), Dihydroterpineol, myrtenol, sobrerol, menthol, carveol, perillyl alcohol, pinocarveol, sobrerol, berbenol and the like.

  The content when the dispersion medium is contained in the bonding composition of the present embodiment may be adjusted according to desired properties such as viscosity, and the content of the dispersion medium in the bonding composition is 1 to 30 mass. % Is preferred. If content of a dispersion medium is 1-30 mass%, the effect of adjusting a viscosity in the range which is easy to use as a joining composition can be acquired. A more preferable content of the dispersion medium is 1 to 20% by mass, and a more preferable content is 1 to 15% by mass.

  Examples of the resin component include polyester resins, polyurethane resins such as blocked isocyanate, polyacrylate resins, polyacrylamide resins, polyether resins, melamine resins, and terpene resins. May be used alone or in combination of two or more.

  As the organic solvent, except for those mentioned as the above dispersion medium, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, 2-propyl alcohol, 1,3-propanediol, 1,2-propanediol, 1 , 4-butanediol, 1,2,6-hexanetriol, 1-ethoxy-2-propanol, 2-butoxyethanol, ethylene glycol, diethylene glycol, triethylene glycol, weight average molecular weight in the range of 200 to 1,000 Polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol having a weight average molecular weight in the range of 300 to 1,000, N, N-dimethylformamide, dimethyl sulfoxide, N- Chill-2-pyrrolidone, N, N- dimethylacetamide, glycerin, or acetone and the like may be used each of which alone or in combination of two or more.

  Examples of the thickener include clay minerals such as clay, bentonite or hectorite, for example, emulsions such as polyester emulsion resins, acrylic emulsion resins, polyurethane emulsion resins or blocked isocyanates, methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose. , Cellulose derivatives such as hydroxypropylcellulose and hydroxypropylmethylcellulose, polysaccharides such as xanthan gum and guar gum, and the like. These may be used alone or in combination of two or more.

  Moreover, you may add surfactant different from the said organic component. In a multi-component solvent-based metal colloidal dispersion, roughness of the coating surface and uneven solid content are likely to occur due to differences in volatilization rate during drying. By adding a surfactant to the bonding composition of the present embodiment, these disadvantages can be suppressed, and a bonding composition that can form a uniform conductive film is obtained.

  The surfactant that can be used in the present embodiment is not particularly limited, and any of an anionic surfactant, a cationic surfactant, and a nonionic surfactant can be used, for example, an alkylbenzene sulfonate. A quaternary ammonium salt etc. are mentioned. Since the effect can be obtained with a small addition amount, a fluorosurfactant is preferable.

  In addition, it is easy to adjust the method of adjusting the amount of organic components in a predetermined range by heating. Moreover, you may carry out by adjusting the quantity of the organic component added when producing nanoporous metal powder. Heating can be performed with an oven or an evaporator, and may be performed under reduced pressure. When performed under normal pressure, it can be performed in air or in an inert atmosphere. Furthermore, amines (and carboxylic acids) can be added later for fine adjustment of the amount of organic components.

  The viscosity of the bonding composition of the present embodiment may be adjusted as long as the solid content does not impair the effects of the present invention. For example, the viscosity may be in the range of 0.01 to 5000 Pa · S. A viscosity range of 1 to 1000 Pa · S is more preferable, and a viscosity range of 1 to 100 Pa · S is particularly preferable. By setting it as the said viscosity range, a wide method is applicable as a method of apply | coating the composition for joining to a to-be-joined copper material.

  The viscosity is adjusted by adjusting the particle size of the nanoporous metal powder, adjusting the organic content, adjusting the addition amount of the dispersion medium and other components, adjusting the blending ratio of each component, and adding a thickener. be able to. The viscosity of the metal bonding composition can be measured, for example, with a cone plate viscometer (for example, Rheometer MCR301 manufactured by Anton Paar).

  The joining composition used in the joining method of the present invention can be obtained by uniformly mixing the above-mentioned nanoporous metal powder, organic solvent, and the like by various conventionally known methods. The mixing method may be dry mixing, or wet mixing using a solvent or the like.

(2) Joining method If the composition for metal joining of this embodiment is used, high joining strength can be obtained in the joining of the copper members accompanied by heating. That is, the bonding composition application step of interposing the metal bonding composition between the first bonded copper member and the second bonded copper member by application or arrangement, and the first bonded copper member, A bonding step in which the bonding composition applied or disposed between the second bonded copper member is baked and bonded to a desired temperature (for example, 400 ° C. or less, preferably 150 to 300 ° C.). Thus, the first bonded copper member and the second bonded copper member can be bonded. At this time, the intervening bonding composition may be heated by heating one or both of the first bonded copper material and the second bonded copper material.

  In addition, during this heating, by applying a pressure of about 0.5 to 30 MPa in the direction of sandwiching the first bonded copper material and the second bonded copper material from the outside, a strong bonded portion can be obtained. Can be obtained. In addition, when firing, the temperature can be raised or lowered stepwise. Furthermore, it is also possible to apply a surfactant or a surface activator to the surface of the member to be joined in advance.

  As a result of intensive studies, the inventor has obtained the first bonded copper by using the metal bonding composition of the present embodiment described above as the metal bonding composition in the metal bonding composition coating step. It discovered that a member and the 2nd to-be-joined copper member can be joined more reliably with high joining strength (a joined body is obtained).

  Here, from the viewpoint of long-term stability of the metal bonding composition and reduction of voids and residual organic components in the bonding layer, only the nanoporous metal material in sheet form or powder form is bonded to the first object. Most preferably, it is placed between the copper member and the second copper member to be joined, and fired and bonded at a desired temperature (for example, 400 ° C. or lower, preferably 150 to 300 ° C.) while applying pressure.

  The “application” of the metal bonding composition of the present embodiment is a concept including the case where the metal bonding composition is applied in the form of a plane and the case where the composition is applied (drawn) in a linear form. The shape of the coating film made of the composition for metal bonding before being applied and fired by heating can be made into a desired shape. Therefore, in the joined body of the present embodiment after firing by heating, the metal joining composition is a concept including both a planar joining layer and a linear joining layer, and these planar joining layer and linear The bonding layer may be continuous or discontinuous, and may include a continuous portion and a discontinuous portion.

  As a 1st to-be-joined copper member and a 2nd to-be-joined copper member which can be used in this embodiment, if the composition for metal joining can be apply | coated or arrange | positioned and it can bake by heating and can join. The copper member is not particularly limited, but is preferably a copper member having heat resistance that is not damaged by the temperature at the time of joining.

  In addition, the to-be-joined copper member may coat | cover copper by various methods, such as plating and vapor deposition, to base materials other than copper. Examples of such a base material include polyesters such as polyamide (PA), polyimide (PI), polyamideimide (PAI), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polycarbonate. (PC), polyethersulfone (PES), vinyl resin, fluororesin, liquid crystal polymer, ceramics, glass, or metal other than copper can be used.

  The bonded copper member may have various shapes such as a plate shape or a strip shape, and may be rigid or flexible. The thickness of the substrate can also be selected as appropriate. A copper member that has been subjected to a surface treatment such as a hydrophilization treatment may be used in order to improve adhesiveness or adhesion, or for other purposes.

  The bonding method of the present invention can also be suitably used when bonding a semiconductor element in a power module as shown in FIG. 1 to a heat dissipation substrate. In this case, it is preferable that the surfaces to be bonded of the heat dissipation substrate and the semiconductor element are copper.

  In the process of applying the metal bonding composition to the copper member to be bonded, various methods can be used. For example, as described above, dipping, screen printing, spraying, bar coating, spin coating The ink jet method, the dispenser method, the pin transfer method, the brush application method, the casting method, the flexo method, the gravure method, the syringe method, and the like can be appropriately selected and used.

  The coated film after coating as described above is baked by heating to a temperature of 350 ° C. or less, for example, within a range that does not damage the copper member to be bonded, and the bonded body of this embodiment can be obtained. In the present embodiment, as described above, since the metal bonding composition of the present embodiment is used, a bonding layer having excellent adhesion to a copper member to be bonded is obtained, and a stronger bonding strength is obtained. It is definitely obtained.

  In this embodiment, when the metal bonding composition includes a binder component, the binder component is also sintered from the viewpoint of improving the strength of the bonding layer and improving the bonding strength between the bonded copper members, In some cases, the binder component may be mainly used to adjust the viscosity of the bonding composition for application to various printing methods, and the binder condition may be controlled to remove all of the binder component.

  The method for performing the baking is not particularly limited. For example, the temperature of the metal bonding composition applied, drawn or arranged on the bonded copper member using a conventionally known oven or the like is, for example, 350 ° C. It can join by baking so that it may become the following. The lower limit of the firing temperature is not necessarily limited, and is preferably a temperature at which the bonded copper members can be bonded to each other and does not impair the effects of the present invention. Here, in the metal bonding composition after firing, it is better that the residual amount of the organic matter is small in terms of obtaining as high a bonding strength as possible, but a part of the organic matter remains within the range not impairing the effect of the present invention. It does not matter.

  According to the metal bonding composition used in the bonding method of the present invention, it is possible to realize a bond having a bonding layer that exhibits high conductivity even by firing at a low temperature of, for example, about 50 to 250 ° C. Even if the copper members to be joined are weak, they can be joined. Further, the firing time is not particularly limited, and may be any firing time that can be bonded according to the firing temperature.

  In this embodiment, in order to further improve the adhesion between the bonded copper member and the bonding layer, the surface treatment of the bonded copper member may be performed. Examples of the surface treatment method include a method of performing dry treatment such as corona treatment, plasma treatment, UV treatment, and electron beam treatment, and a method of previously providing a primer layer and a conductive paste receiving layer on a substrate.

  The atmosphere in the bonding step is not particularly limited, and can be performed in the air, under an inert gas atmosphere, under reduced pressure, or the like.

  As mentioned above, although typical embodiment of this invention was described, this invention is not limited only to these. For example, nanoparticles other than the nanoporous metal material can be appropriately added to the bonding composition and used.

  Hereinafter, although the joining method using the nanoporous metal material of the present invention will be further described in Examples, the present invention is not limited to these Examples.

Example 1
An Au-Ag alloy sheet (Au: 50 mass%, Ag: 50 mass%) with a thickness of about 100 μm was used as the metal material, and a nanoporous metal sheet was produced by decomponent corrosion. Specifically, after polishing the surface of the Au—Ag alloy sheet with abrasive paper, it is immersed in 60% nitric acid (HNO ₃ ) with application of ultrasonic waves to etch Ag in the vicinity of the surface, and mainly gold (Au). A nanoporous metal sheet having a nanoporous structure constituted by the following was obtained. Here, the immersion time was 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 10 hours, and the sample after immersion was washed pure.

  In FIGS. 2-7, the scanning electron microscope (SEM) photograph of the Au-Ag alloy sheet | seat of immersion time 1 hour-10 hours is shown, respectively. It can be confirmed that the surface of the Au-Ag alloy sheet after the immersion treatment (decomponent corrosion) has a nanoporous structure in which metal nanoparticles are arranged three-dimensionally. The average particle diameter of the metal nanoparticles forming the nanoporous structure was measured from the SEM photograph. When the immersion time was 1 hour and 2 hours, the decomponent corrosion was insufficient and the metal nanoparticles were not clearly formed. When the immersion time was 3 hours, it was 5.5 nm, when the immersion time was 4 hours, 7.5 nm, when the immersion time was 5 hours, it was 8.8 nm, and when the immersion time was 10 hours, it was 14.2 nm. The scanning electron microscope used was an ultra-high resolution analytical scanning electron microscope SU-70 manufactured by Hitachi High-Tech.

  A nanoporous metal sheet (average particle diameter of metal nanoparticles: 5.5 nm) obtained with a 3-hour immersion time was kept at a high temperature for 30 minutes to evaluate a low-temperature sintering function. The holding temperatures were 100 ° C., 150 ° C., 200 ° C., and 250 ° C. 8 to 11 show SEM photographs of the surface of the nanoporous metal sheet held at a high temperature of 100 ° C to 250 ° C. Even when the holding temperature is as low as 250 ° C. or lower, it can be confirmed that the sintering of the metal nanoparticles proceeds and the pores are reduced. In particular, when the holding temperature is 250 ° C., a dense sintered body is obtained. As the scanning electron microscope, an ultra-high resolution analytical scanning electron microscope SU-70 manufactured by Hitachi High-Tech Co., Ltd. was used.

  In order to evaluate the composition near the surface of the nanoporous metal sheet, an Au-Ag alloy sheet before decomponent corrosion, an Au-Ag alloy sheet after decomponent corrosion (immersion time 3 hours), and decomponent corrosion (immersion time) After 3 hours), XPS measurement was performed on the Au—Ag alloy sheet subjected to the above-mentioned various high temperature holdings. 12 and 13 show the narrow scan spectrum and the Ag3d narrow scan spectrum of Au4f, respectively. Compared with the Au-Ag alloy sheet before decomponent corrosion, the Au-Ag alloy sheet after decomponent corrosion has a significantly larger peak intensity of Au4f, and the surface of the nanoporous metal sheet is mainly made of gold (Au). It turns out that it is comprised with the metal nanoparticle used as a component.

  As for the peak of Ag3d, the peak intensity is significantly smaller in the Au-Ag alloy sheet after decomponent corrosion compared to the Au-Ag alloy sheet before decomponent corrosion, and the result is also near the surface of the nanoporous metal sheet. Suggests that it is composed of metal nanoparticles mainly composed of gold (Au). Here, the peak intensity of Ag3d increases as the high temperature holding time increases. This is a result of diffusion of silver (Ag) from the inside to the surface of the Au—Ag alloy sheet by holding at a high temperature. For XPS measurement, JPS-9010TR manufactured by JEOL Ltd. was used, and measurement was performed with a combination of Mg-Kα (1253.6 eV) and a monochromator.

  FIG. 14 shows the shape of a bonding test piece made of a silicon (Si) substrate used in the bonding test. Nanoporous material obtained by decomponent corrosion (immersion time 3 hours) between the materials to be bonded, which is obtained by depositing copper (Cu) on the surface of a 1 cm × 1 cm × 525 μm silicon (Si) substrate A body metal sheet was arranged to prepare a joining test piece. The test piece was subjected to a bonding test at a bonding temperature of 250 ° C. and a reduced pressure of 3 kPa. When joining, pressurization was performed at a pressure of 8 MPa, and the joining time was 20 minutes. Note that immediately after the test, the test piece was taken out of the apparatus and air-cooled.

  About the joint 1 obtained by the joining test, the tensile test was done and the joining strength was calculated | required. The obtained tensile strength is shown in FIG. Three bonded joints were prepared, and a tensile test was performed on each bonded joint to obtain an average value. In the tensile test, in the test piece shown in FIG. 14, a dedicated jig is fixed to each of the upper and lower silicon (Si) substrates via the bonding interface, and in a direction substantially perpendicular to the bonding interface with respect to the jig. A load was applied.

<< Example 2 >>
A bonded joint 2 was obtained in the same manner as in Example 1 except that the bonding temperature was 200 ° C. The tensile strength obtained in the same manner as in Example 1 is shown in FIG.

Example 3
A bonded joint 3 was obtained in the same manner as in Example 1 except that the bonding temperature was 150 ° C. The tensile strength obtained in the same manner as in Example 1 is shown in FIG.

Example 4
A bonded joint 4 was obtained in the same manner as in Example 1 except that the bonding temperature was 100 ° C. The tensile strength obtained in the same manner as in Example 1 is shown in FIG.

Example 5
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 nanoporous metal sheet obtained by decomponent corrosion (immersion time: 4 hours) was placed on the joining surface of the larger disc test piece, and the smaller test piece was stacked to prepare a joining test piece. The test piece was subjected to a bonding test at a bonding temperature of 350 ° C. to obtain a bonded joint 5. When joining, pressurization was performed at a pressure of 20 MPa, the joining time was 30 minutes, and the joining atmosphere was air. Note that immediately after the test, the test piece was taken out of the apparatus and air-cooled.

  About the joining joint 1 obtained by the joining test, the shear test (shear rate 1.0mm / min, shear height 200micrometer) was done using the bond tester, and joining strength was calculated | required. The obtained shear strength is shown in FIG. Three bonded joints were prepared, and a shear test was performed on each bonded joint to obtain an average value.

Example 6
A bonded joint 6 was obtained in the same manner as in Example 5 except that the bonding temperature was 300 ° C. The shear strength obtained in the same manner as in Example 1 is shown in FIG.

Example 7
A bonded joint 7 was obtained in the same manner as in Example 5 except that the bonding temperature was 250 ° C. The shear strength obtained in the same manner as in Example 1 is shown in FIG.

Example 8
Using a Au-Ag alloy sheet (Au: 25 mass%, Ag: 75 mass%) with a thickness of about 100 μm as the metal material, nanoporous metal powder was produced by decomponent corrosion. Specifically, after polishing the surface of the Au—Ag alloy sheet with abrasive paper, it is immersed in 60% nitric acid (HNO ₃ ) with application of ultrasonic waves to etch Ag in the vicinity of the surface, and mainly gold (Au). Demineralization corrosion was performed until a nanoporous metal powder having a nanoporous structure composed of: The nanoporous metal powder was washed and dried, and then used as a bonding composition. An appearance photograph of the obtained nanoporous metal powder is shown in FIG.

  A joint joint 8 was obtained in the same manner as in Example 3 except that nanoporous metal powder was used instead of the nanoporous metal sheet. When the tensile strength was measured in the same manner as in Example 1, a value of 2.5 MPa was obtained.

Example 9
A bonded joint 9 was obtained in the same manner as in Example 8 except that the bonding temperature was 100 ° C. When the tensile strength was measured in the same manner as in Example 1, a value of 1.2 MPa was obtained.

Example 10
A bonded joint 10 was obtained in the same manner as in Example 8 except that the bonding temperature was 50 ° C. When the tensile strength was measured in the same manner as in Example 1, a value of 0.45 MPa was obtained.

≪Comparative example 1≫
A comparative joint 1 was obtained in the same manner as in Example 1 except that the nanoporous metal sheet was not disposed on the surface to be joined. The tensile strength obtained in the same manner as in Example 1 is shown in FIG.

«Comparative example 2»
Comparative joint 1 was obtained in the same manner as in Example 2 except that the nanoporous metal sheet was not disposed on the surface to be joined. The tensile strength obtained in the same manner as in Example 1 is shown in FIG.

«Comparative Example 3»
A comparative joint 3 was obtained in the same manner as in Example 3 except that the nanoporous metal sheet was not disposed on the surface to be joined. Measurement of tensile strength was attempted in the same manner as in Example 1, but the strength was too low to obtain a value.

<< Comparative Example 4 >>
A comparative joint 4 was obtained in the same manner as in Example 4 except that the nanoporous metal sheet was not disposed on the surface to be joined. Measurement of tensile strength was attempted in the same manner as in Example 1, but the strength was too low to obtain a value.

<< Comparative Example 5 >>
A comparative joint 5 was obtained in the same manner as in Example 5 except that the surface of a joining test piece made of oxygen-free copper was plated with Au. A shear test obtained in the same manner as in Example 5 is shown in FIG.

<< Comparative Example 6 >>
Comparative joint 6 was obtained in the same manner as in Comparative Example 5 except that the joining temperature was 300 ° C. A shear test obtained in the same manner as in Example 5 is shown in FIG.

<< Comparative Example 7 >>
Comparative joint 7 was obtained in the same manner as Comparative Example 5 except that the joining temperature was 250 ° C. A shear test obtained in the same manner as in Example 5 is shown in FIG.

  As shown in FIG. 15, the bonded joints 1 to 4 exhibit higher tensile strength than the comparative joints 1 to 4 at all bonding temperatures. In particular, at a bonding temperature of 250 ° C., the bonded joint 1 exhibits a remarkably high tensile strength of about 5 MPa.

  Moreover, as shown in FIG. 17, the joint joints 5-7 have favorable shear strength, and the shear strength of the joint joint 5 obtained at the joining temperature of 350 ° C. has reached about 25 MPa. Furthermore, compared with the comparative joints 5 to 7 to be Au—Au joints, the joint joints 5 to 7 to be Cu—Cu joints have high shear strength, and the joining method of the present invention is a Cu—Cu joint. It can be seen that it can be suitably used.

In addition, regarding the joints 8 to 10 obtained using the nanoporous metal powder, a good joint is obtained despite the extremely low joining temperature.

Claims (6)

A bonding composition containing a nanoporous metal material including metal nanoparticles having a three-dimensionally arranged average particle diameter of 5 to 500 nm is obtained by combining a first bonded copper material and a second bonded copper material. Interposing the process,
While heating the said composition for joining interposed between said 1st to-be-joined copper material and said 2nd to-be-joined copper material to 50-400 degreeC, said 1st to-be-joined copper material and said 1st Including a step of pressurizing the second bonded copper material,
A method for joining copper materials. The bonding composition is composed of only the nanoporous metal material;
The method for joining copper materials according to claim 1. The nanoporous metal material is a nanoporous metal sheet formed by decomponent corrosion of a metal material,
The copper material joining method according to claim 1 or 2. The metal material is a binary alloy;
The method for joining copper materials according to claim 3. The binary alloy is an Au-Ag alloy;
The method for joining copper materials according to claim 4. The nanoporous metal material is a nanoporous metal powder;
The method for joining copper materials according to claim 1, wherein: