JP2018049939A - Bonding material and bonded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonding material capable of forming a bonding layer having high relaxation ability against thermal stress and excellent bonding reliability.SOLUTION: The bonding material includes: at least one inorganic particle selected from a group consisting of metal particles and metal oxide particles; resin particles in which at least one functional group selected from a group consisting of carboxyl group, mercapto group, sulfide group, and amino group is introduced on a surface; metal-coated resin particles including a metal coating layer formed on surfaces of the resin particles; and a solvent.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bonding material that can be used, for example, when a semiconductor element is mounted on an insulated circuit board or the like, and a bonded body bonded using the bonding material.

A semiconductor device such as an LED or a power module has a structure in which a semiconductor element is bonded on a circuit layer made of a conductive material.
In power semiconductor elements for large power control used to control wind power generation, electric vehicles, hybrid vehicles, etc., the amount of heat generated is large. Therefore, for example, AlN (aluminum nitride), Al A power module substrate comprising a ceramic substrate made of ₂ O ₃ (alumina) and the like, and a circuit layer formed by disposing a metal having excellent conductivity on one surface of the ceramic substrate, Widely used in the past.
In addition, as a power joule substrate, a substrate having a metal layer formed on the other surface of a ceramic substrate is also provided.

  Here, as a bonding material for bonding a semiconductor element on a circuit layer, a paste-like bonding material containing fine inorganic particles and a solvent is known. As the inorganic particles, metal particles such as gold, silver, copper, tin and nickel or metal oxide particles such as silver oxide, copper oxide, tin oxide and nickel oxide are used. In the bonding material including the inorganic particles, the objects to be bonded are bonded by a sintered body obtained by sintering the inorganic particles.

  For example, Patent Document 1 discloses a metal coating in which metal fine particles made of a first metal and resin particles having a particle diameter larger than the metal fine particles are coated with a second metal that can be sintered with the first metal. A bonding material including resin particles as an aggregate is disclosed. In the bonding material disclosed in Patent Document 1, metal-coated resin particles are present in a bonding layer (sintered metal particles) formed by sintering the bonding material, and the elastic modulus of the bonding layer is lowered. By suppressing the thermal stress applied to the bonding layer during the heat cycle, the reliability of the bonding layer is improved.

JP 2011-198674 A

By the way, recently, higher output of power semiconductor elements and the like has been promoted, and accordingly, the amount of heat generated by the power module tends to increase. For this reason, a more severe heat cycle is applied to the joint between the circuit layer and the power semiconductor element, and a bonding material that is superior in bonding reliability with respect to the heat cycle is required compared to the conventional case. ing.
The bonding layer formed by sintering the bonding material disclosed in Patent Document 1 is high in the metal fine particles (first metal) and the coated metal (second metal) covering the metal-coated resin particles. Bonded with adhesive force. However, since the adhesive force between the resin particles and the coated metal is low, when severe heat cycles are applied, the resin particles and the coated metal are separated from each other, and the ability to relax thermal stress cannot be fully exhibited. Further, the peeled portion becomes a starting point of the crack in the bonding layer, and there is a possibility that the bonding reliability is lowered.

  The present invention has been made in view of the above circumstances, and is a bonding material capable of forming a bonding layer having a high ability to relax against thermal stress and having excellent bonding reliability, and a bonded body bonded using this bonding material. The purpose is to provide.

  In order to solve the above-described problems, the bonding material of the present invention includes at least one inorganic particle selected from the group consisting of metal particles and metal oxide particles, and a group consisting of a carboxyl group, a mercapto group, a sulfide group, and an amino group. It is characterized by having a resin particle in which at least one functional group selected from the surface is introduced, a metal-coated resin particle including a metal coating layer formed on the surface of the resin particle, and a solvent. .

  According to the bonding material of this configuration, the functional group such as carboxyl group, mercapto group, sulfide group, and amino group introduced on the surface of the resin particle serving as the core of the metal-coated resin particle and the metal coating layer are chemically adsorbed. Therefore, the adhesive force between the resin particles and the metal coating layer is increased. For this reason, the bonding layer formed by sintering this bonding material is difficult to peel off the resin particles and the metal coating layer even when a severe heat cycle is applied, and maintains high mitigation ability against thermal stress. Is less likely to occur.

  The joined body of the present invention is a joined body in which the first member and the second member are joined via a joining layer, and the joining layer is selected from the group consisting of metal particles and metal oxide particles. A sintered body of at least one inorganic particle, resin particles having on the surface thereof at least one functional group selected from the group consisting of a carboxyl group, a mercapto group, a sulfide group and an amino group, and formed on the surface of the resin particle. And metal-coated resin particles including a metal-coated layer.

  According to the bonded body of this configuration, the metal-coated resin particles contained in the bonding layer have high adhesion between the resin particles and the metal coating layer. It is difficult to peel off from the metal coating layer, high relaxation ability against thermal stress is maintained, and cracks are hardly generated. For this reason, the joining reliability of the first member and the second member is excellent.

  According to the present invention, it is possible to provide a bonding material capable of forming a bonding layer having high relaxation ability against thermal stress and excellent bonding reliability, and a bonded body bonded using this bonding material.

It is a schematic cross section which shows the metal-coated resin particle contained in the joining material which is embodiment of this invention. It is sectional drawing which shows the conjugate | zygote (power module) using the joining material which is embodiment of this invention. FIG. 3 is an enlarged schematic cross-sectional view showing a bonding layer in FIG. 2.

  Hereinafter, a bonding material according to an embodiment of the present invention and a bonded body using the bonding material will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

<Bonding material>
First, the structure of the bonding material which is one embodiment of the present invention will be described. The bonding material of the present embodiment is roughly configured to include inorganic particles, metal-coated resin particles, and a solvent. The bonding material may further contain an additive.
When the bonding material of this embodiment is heated, the inorganic particles are sintered to form a bonding layer. By forming a bonding layer on the portion to be bonded, the first member and the second member can be bonded to form a bonded body.

(Inorganic particles)
As the inorganic particles, at least one particle selected from the group consisting of metal particles and metal oxide particles is used.
The metal particles used as the inorganic particles are preferably particles made of gold, silver, copper, tin, nickel, or an alloy of these metals. In this case, when the bonding material is sintered, a sintered body (bonding layer) of inorganic particles excellent in conductivity and thermal conductivity is generated, so that the heat applied to the bonding layer is easily released to the outside. It is difficult to accumulate in the bonding layer. For this reason, the bonding layer formed by sintering this bonding material maintains a high relaxation ability against thermal stress even when a severe heat cycle is applied, and cracks are less likely to occur.

  The metal oxide particles used as the inorganic particles are preferably silver oxide particles, copper oxide particles, tin oxide particles, or nickel oxide particles. When metal oxide particles are used, it is preferable to sinter the bonding material in a reducing atmosphere or a reduced state in which a reducing substance is contained in the bonding material. When sintered in such a reduced state, some or all of the metal oxide particles are reduced, and a sintered body (bonding layer) excellent in conductivity and thermal conductivity is generated. The applied heat is easily released to the outside and is not easily accumulated in the bonding layer.

  The inorganic particles can be used alone or in combination. Moreover, you may use it combining a metal particle and a metal oxide particle.

  The average particle diameter of the inorganic particles is determined by a desired sintering speed when forming the bonding layer, strength after sintering, porosity, and the like, and is preferably in the range of 5 nm to 10 μm. The bonding material may include a plurality of types of inorganic substances having different average particle diameters, but the inorganic particles preferably include 30% by mass or more of particles having an average particle diameter of 10 nm to 1 μm.

The average particle diameter of the inorganic particles can be measured, for example, by the following method.
When the average particle size of inorganic particles is expected to be 500 nm or more, a dispersion obtained by dispersing inorganic particles in alcohol such as ethanol using ultrasonic waves is dropped onto a grid such as copper and dried. An observation sample is obtained. The diameter (particle diameter) of 300 particles of this observation sample is measured at a magnification of 5000 using a transmission electron microscope (TEM). Next, an average value of the measured particle diameters is calculated to obtain an average particle diameter.
On the other hand, when the average particle size of the inorganic particles is expected to be less than 500 nm, the software (product name :) is used by using a scanning electron microscope (for example, “SU-8000” manufactured by Hitachi High-Technologies Corporation) instead of TEM. The particle size of 300 particles is measured at a magnification of 50000 times using a PC SEM or the like. Next, an average value of particle diameters measured in the same manner as described above is calculated to obtain an average particle diameter.

  The shape of the inorganic particles is selected depending on the desired rheological properties of the bonding material.For example, a perfect spherical particle, a particle having an almost spherical shape such as an ellipse, a particle having a slight unevenness on the surface, a flat particle, Scalpel-like particles, rod-like particles, and the like are included.

(Metal-coated resin particles)
As shown in FIG. 1, the metal-coated resin particles 10 include resin particles 11 and a metal coating layer 13 formed on the surface of the resin particles 11. The resin particle 11 has at least one functional group 12 selected from the group consisting of a carboxyl group, a mercapto group, a sulfide group, and an amino group on the surface. The metal-coated resin particles 10 have a high adhesive force between the resin particles 11 and the metal coating layer 13 because the functional groups 12 and the metal coating layer 13 are chemically adsorbed.

  The introduction of the functional group 12 on the surface of the resin particle 11 means that, for example, argon sputtering or FIB is used until the metal coating layer 13 of the metal-coated resin particle 10 has a thickness capable of analyzing the functional group 12. After thinning, it can be confirmed by analyzing organic components using X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary ion mass spectrometry (TOF-SIMS).

  Although it does not specifically limit as the resin particle 11, Specifically, an acrylic resin particle, a styrene resin particle, a phenol resin particle, a silicone resin particle, a silicone rubber particle, a polyimide resin particle, a fluorine rubber particle etc. are mentioned, for example.

The average particle diameter of the resin particles 11 is preferably 0.5 to 40 μm. The particle size distribution of the resin particles varies depending on the desired rheological properties of the bonding material, and the particle size distribution is preferably broad within a certain range in order to impart thixotropic properties to the bonding material.
By setting the average particle size of the resin particles 11 to 0.5 μm or more, aggregation is less likely to occur in the production process of the metal-coated particles and the particles after production, and the stress relaxation effect when the bonded body is obtained is increased. Moreover, by making the average particle diameter of the resin particles 11 be 40 μm or less, it becomes easy to apply the bonding material to various coating and printing methods.

  The average particle diameter of the resin particles 11 is measured by the following method. First, using a scanning electron microscope (for example, “SU-1500” manufactured by Hitachi High-Technologies Corporation), software (product name: PC SEM, etc.) with a magnification of 5000 times (diameter of 300 particles) Diameter). Next, an average value of the measured particle diameters is calculated to obtain an average particle diameter.

The metal coating layer 13 is preferably a layer made of gold, silver, copper, palladium, platinum, tin, nickel, or an alloy of these metals. Since these metals and alloys have excellent affinity with the functional groups 12 on the surface of the resin particles 11, the adhesion between the metal coating layer 13 and the resin particles 11 is enhanced by using these metals and alloys. Can do.
The thickness of the metal coating layer 13 is preferably in the range of 5 nm to 10 μm. The metal coating layer 13 may be a single layer or a plurality of layers. If the thickness of the metal coating layer 13 becomes too thin, the surface energy of the metal coating layer 13 becomes high, which tends to cause aggregation and metal diffusion with surrounding inorganic particles or metal coating particles, and storage in the bonding material. Stability may deteriorate. On the other hand, when the thickness of the metal coating layer 13 becomes too thick, the surface energy of the metal coating layer 13 is lowered, and the sinterability of the bonding material may be impaired.

The metal-coated resin particles 10 can be produced, for example, by the following method.
First, the resin particles 11 are subjected to surface cleaning with an alkaline cleaning liquid and then washed with water. Thereafter, the resin particles 11 are dispersed in water or an organic solvent, and then a surface modifier is introduced into the resin particle dispersion to introduce functional groups 12 on the surface of the resin particles 11. If necessary, heat treatment or UV irradiation may be performed as a post-treatment.

As the surface modifier, for example, when introducing carboxyl groups on the surface of the resin particles 11, potassium permanganate solution, carboxyl group-containing silane coupling agent, α-hydroxy fatty acid such as glycolic acid, thioglycolic acid Α-thiohydroxy fatty acid and salts thereof, and solutions containing them can be used. For example, when introducing a mercapto group, a mercapto group-containing silane coupling agent, alkanethiols such as dodecanethiol, sulfanylalkyldiols such as dithiothreitol and dithioerythritol, triazinethiol, thioacetic acid and salts thereof are used. be able to. For example, when a sulfide group is introduced, an alkyl disulfide compound such as a sulfide group-containing silane coupling agent or octadecyl disulfide, or all thiols when an unsaturated bond has been previously introduced into the resin particle 11 is used. it can. For example, when introducing an amino group, an amino group-containing silane coupling agent, aliphatic amines such as hexylamine, diamines such as hexamethylenediamine, O- (diphenylphosphinyl) hydroxylamine such as Gabriel reagent, etc. Nucleophilic aminating agents and electrophilic aminating agents can be used. The amino group here includes a substituted amino group.
When introducing functional groups 12 using these surface modifiers, substances with highly reactive functional groups such as epoxy groups and amine groups, alkyl halides, and trace amounts of acids and bases are used in combination as auxiliary agents. May be.

  Next, the metal coating layer 13 is formed on the surface of the resin particle 11 into which the functional group 12 is introduced. As a method of forming the metal coating layer 13, an electroless plating method can be used.

For example, as a method for forming the silver coating layer, the following method can be used.
First, the resin particles 11 into which a functional group is introduced are added to an aqueous solution of a tin compound and stirred. Thereafter, the resin particles 11 are separated by filtration and washed with water. Thereby, a tin adsorption layer made of a tin compound is provided on the surface of the resin particle 11.

Here, as the tin compound, stannous chloride, stannous fluoride, stannous bromide, stannous iodide, or the like can be used. When using stannous chloride, the content of stannous chloride in the aqueous solution of the tin compound is preferably ³⁰ to 100 g / dm ³ . If the content of stannous chloride is 30 g / dm ³ or more, it is easy to form a uniform tin adsorption layer. Moreover, it is easy to suppress the amount of inevitable impurities in stannous chloride as the content of stannous chloride is 100 g / dm ³ or less. Note that stannous chloride can be contained in an aqueous solution of a tin compound until saturation.

Moreover, it is preferable that the aqueous solution of a tin compound contains 0.5-2 cm < ³ > of hydrochloric acid with respect to 1 g of stannous chloride. When the amount of hydrochloric acid is 0.5 cm ³ or more, the solubility of stannous chloride can be improved and the hydrolysis of tin can be suppressed. When the amount of hydrochloric acid is 2 cm ³ or less, the pH of the aqueous solution of the tin compound does not become too low, so that tin can be efficiently adsorbed to the resin particles 11. Furthermore, the aqueous solution of the tin compound may contain a palladium salt. As the palladium salt, palladium chloride can be used. Palladium is deposited on the surface of the tin adsorption layer as a catalyst.

Moreover, 20-45 degreeC may be sufficient as the temperature of the aqueous solution of a tin compound, 20-35 degreeC is preferable, 25-35 degreeC is more preferable, and 27-35 degreeC is the most preferable.
By setting the temperature of the aqueous solution of the tin compound to 20 ° C. or higher, the activity of the aqueous solution can be suppressed and the tin compound can be sufficiently adhered to the resin particles 11. On the other hand, by setting the temperature of the aqueous solution of the tin compound to 45 ° C. or less, the oxidation of the tin compound can be suppressed, the aqueous solution is stabilized, and the tin compound can be sufficiently adhered to the resin particles 11. By attaching a tin compound to the resin particles 11 with an aqueous solution at 20 to 45 ° C., suitable crystals can be obtained even for the resin particles 11 made of an acrylic resin, a styrene resin, a silicone resin, or the like having low adhesion to silver. Small diameter silver crystal particles can be deposited. For this reason, the silver coating layer excellent in adhesiveness / denseness can be formed. Furthermore, since the silver coating layer is excellent in adhesion and denseness, the resistance value in the compression direction when 10% of the particle diameter is compressed in one direction can be reduced.

  Moreover, although stirring time is suitably determined by the temperature of the aqueous solution of a tin compound and content of a tin compound, 0.5 to 24 hours are preferable.

  Next, a silver coating layer is formed on the surface of the tin adsorption layer by electroless plating. As the electroless plating method, (1) a method in which resin particles 11 provided with a tin adsorption layer are immersed in an aqueous solution containing a complexing agent, a reducing agent, etc., and a silver salt aqueous solution is dropped, (2) a silver salt, A method of immersing the resin particles 11 provided with a tin adsorption layer in an aqueous solution containing a complexing agent and dropping the reducing agent aqueous solution, (3) tin adsorption to an aqueous solution containing a silver salt, a complexing agent, a reducing agent, etc. A method in which the resin particles 11 provided with a layer are immersed and a caustic aqueous solution is dropped.

  Here, as the silver salt, silver nitrate or silver nitrate dissolved in nitric acid can be used. Complexing agents include salts such as ammonia, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, nitrotriacetic acid, triethylenetetraamminehexaacetic acid, sodium thiosulfate, succinate, succinimide, citrate or iodide salt Can be used. As the reducing agent, formalin, glucose, imidazole, Rochelle salt (sodium potassium tartrate), hydrazine and its derivatives, hydroquinone, L-ascorbic acid or formic acid can be used. As the reducing agent, formaldehyde is preferable, a mixture of two or more reducing agents including at least formaldehyde is more preferable, and a mixture of reducing agent including formaldehyde and glucose is most preferable.

  In the case of forming a gold coating layer, examples of the gold salt include gold cyanide and its salt, gold chloride, chloroauric acid, gold sulfite and its salt, gold thiosulfate and its salt, and the like. Examples of complexing agents for gold salts include cyanide, ammonia, thiosulfate, thiourea, Rochelle salt, ethylenediamine, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetate, triethylenetetraamminehexaacetic acid, citrate, and the like. It is done. As the reducing agent, hydrazine and its salt, borohydride, phosphinate, glycine, dimethylamine borane, formaldehyde and the like can be used.

  When forming the copper coating layer, examples of the copper salt include monovalent or divalent copper sulfate, copper chloride, copper nitrate, copper hydroxide, copper sulfamate, copper carbonate, copper oxide, and hydrates thereof. . Of these, divalent copper sulfate and copper chloride are preferred. Examples of the complexing agent include Rochelle salt, ethylenediamine, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, triethylenetetraamminehexaacetic acid, imidazole, and imidazole derivatives. Examples of the reducing agent include formaldehyde, hydrazine and derivatives thereof, divalent cobalt salt, and divalent chromium salt. As the reducing agent, formaldehyde is preferred because of its strong reducing power. As stabilizers, sodium cyanide, potassium cyanide, potassium thiocyanide, 2,2′-bipyridyl, 2,2′-dipyridine, sodium gluconate, 2,2′-biquinoline, dithizone, diphenylcarbazide, nicotinic acid, thio Urea or the like may be added.

  In the case of forming the palladium coating layer, palladium chloride, palladium nitrate, palladium sulfate, tetraammine palladium salt, palladium acetate, or the like can be used as the palladium salt. Further, ammonia, ethanolamine, methylamine, dimethylamine, methylenediamine, ethylenediamine, tetramethylenediamine, diethylenetriamine, or EDTA salt can be used as the complexing agent for the palladium salt. As the reducing agent, formic acid, hypophosphite, hydrazine, or the like can be used.

  In the case of forming a platinum coating layer, platinum sulfate, platinum chloride, dinitrodiaminoplatinum, dinitrodiammine platinum, hexaammineplatinum, sodium hexahydroxyplatinate, etc. can be used as the platinum salt. Further, ammonia, chloride ion-containing salt, ethylenediamine, ethyleneamine, piperidine and the like can be used as the platinum salt complexing agent. As the reducing agent, sodium borohydride, hydrazine and its hydrate, hydrazine sulfate, dimethylamine borane and the like can be used.

  In the case of forming a tin coating layer, tin chloride, tin sulfate, tin nitrate and hydrate salts thereof can be used as tin salts, and these salts can be used in both divalent and tetravalent forms. It is preferable to use a divalent salt. As the complexing agent of tin salt, citric acid and its salt, acetic acid and its salt, benzenesulfonic acid, ethylenediaminetetraacetic acid tetrasodium, nitrilo 3-acetic acid and the like can be used. As the reducing agent, titanium chloride, tin salt (as a disproportionation reagent) and the like can be used.

  When the nickel coating layer is formed, nickel sulfate, nickel carbonate, nickel chloride, nickel nitrate, nickel citrate, nickel sulfamate, or the like can be used as the nickel salt. Nickel salt complexing agents include lactic acid, propionic acid, acetic acid and salts thereof, succinic acid and salts thereof, malic acid and salts thereof, citric acid and salts thereof, maleic acid and salts thereof, malonic acid and salts thereof, tartaric acid And salts thereof, ethylenediamine, ethyleneamine, piperidine, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, triethylenetetraamminehexaacetic acid and the like can be used. As the reducing agent, sodium tetrahydroborate, dimethylamine borane, phosphinic acid salt or the like can be used, and boric acid or a lead compound may be added as an additive.

(solvent)
As the solvent, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-butyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, Ether alcohol solvents such as dipropylene glycol monobutyl ether and tripropylene glycol monomethyl ether and their acetate solvents, ethylene hydrocarbon, propylene glycol, terpineol, mineral spirits, aromatic hydrocarbon solvents such as toluene, fats such as dodecane, etc. Group hydrocarbon solvents, formic acid, dimethylformamide, N-methyl 2-pyrrolidone, dimethyl sulfoxide, diacetone alcohol, dimethylacetamide, .gamma.-butyrolactone. These solvents are determined by a desired volatilization rate, additives, and compatibility with a protective layer on the surface of the particles in the bonding material. Further, when metal oxide particles are contained in the bonding material, it is preferable to select a reducing solvent such as alcohol. These solvents can be used alone or in combination of two or more.

(Additive)
Additives can be mixed in the bonding material as long as conductivity, adhesion, and shape retention are not impaired. Examples of the additive include a silane coupling agent, a titanium coupling agent, a thickener, a dispersant, a flame retardant, an antifoaming agent, a reducing agent, a sintering accelerator, and an antioxidant.

<Manufacturing method of bonding material>
Next, the manufacturing method of the bonding material of this embodiment will be described in detail.
The joining material of this embodiment can be manufactured by mixing inorganic particles, metal-coated resin particles, a solvent, and additives as necessary, and kneading them with a three-roll mill or the like.
The inorganic particles and the metal-coated resin particles in the bonding material are preferably 10:90 to 90:10 by volume ratio. When the content ratio of the metal-coated resin particles is less than this range, the resin content in the joined body becomes insufficient, and the stress relaxation property may be impaired. On the other hand, when the content ratio of the metal-coated resin particles exceeds this range, the bonding strength may be impaired due to insufficient components having bonding strength. The content of the solvent is adjusted according to the desired viscosity of the bonding material, and is preferably 5 to 30% by mass with respect to the bonding material. When the content is less than 5% by mass, the fluidity of the bonding material is impaired, and there is a possibility that the material becomes unsuitable for dispensing or printing. When the content exceeds 30% by mass, the viscosity is unnecessarily lowered, and the particles may be easily precipitated and separated. The addition amount of the additive is adjusted according to the desired physical properties of the bonding material, and is preferably 0.001 to 5% by mass with respect to the bonding material. If the amount added is less than 0.001% by mass, desired physical properties may not be obtained. If the amount added is more than 5% by mass, defects such as inhibiting the sintering of the joining material may occur during the production of the joined body. There is.

<Joint body (power module)>
Next, a power module as an example of a joined body using the joining material according to the present embodiment will be described with reference to FIGS. 2 and 3.
FIG. 2 is a cross-sectional view showing a joined body (power module) using a joining material according to an embodiment of the present invention. FIG. 3 is an enlarged schematic cross-sectional view showing the bonding layer of FIG.

  The power module 20 includes a power module substrate 30 on which a circuit layer 32 is disposed, a semiconductor element 50 bonded to the surface of the circuit layer 32 via a bonding layer 40, and a cooler 70.

The power module substrate 30 includes a ceramic substrate 31 constituting an insulating layer, a circuit layer 32 disposed on one surface of the ceramic substrate 31 (upper surface in FIG. 2), and the other surface of the ceramic substrate 31 (FIG. 2 and a metal layer 33 disposed on the lower surface.
The ceramic substrate 31 prevents electrical connection between the circuit layer 32 and the metal layer 33, and is made of highly insulating AlN (aluminum nitride). Further, the thickness of the ceramic substrate 31 is set in a range of 0.2 to 1.5 mm, and in this embodiment, is set to 0.635 mm.

  The circuit layer 32 is formed by bonding a conductive metal plate to one surface of the ceramic substrate 31. In the present embodiment, the circuit layer 32 is formed by joining an aluminum plate made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99 mass% or more to the ceramic substrate 31. On the surface of the aluminum plate forming the circuit layer 32, a metal thin film having a high affinity with the bonding material may be formed. Gold, silver, copper, and nickel can be mentioned as a metal with high affinity with a joining material. In addition, as a method for forming these metal thin films, a normal film forming method such as a plating method or a sputtering method can be used.

  The metal layer 33 is formed by bonding a metal plate to the other surface of the ceramic substrate 31. In the present embodiment, the metal layer 33 is formed by joining an aluminum plate made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99 mass% or more, like the circuit layer 32, to the ceramic substrate 31. Has been.

  The semiconductor element 50 is mainly used by dicing a silicon wafer on which fine lines are formed into a rectangle. A thin metal film having a high affinity with the bonding material may be formed on the bonding surface of the semiconductor element 50. Gold, silver, copper, and nickel can be mentioned as a metal with high affinity with a joining material. In addition, as a method for forming these metal thin films, a normal film forming method such as a plating method or a sputtering method can be used.

  The cooler 70 is for cooling the power module substrate 30 described above, and the top plate portion 71 to be joined to the power module substrate 30 and the top plate portion 71 are suspended downward. The heat dissipating fins 72 and a flow path 73 for circulating a cooling medium (for example, cooling water) are provided. The cooler 70 (top plate portion 71) is preferably made of a material having good thermal conductivity, and is made of A6063 (aluminum alloy) in the present embodiment.

  In the present embodiment, a buffer layer 60 made of aluminum, an aluminum alloy, or a composite material containing aluminum (for example, AlSiC) is provided between the top plate 71 of the cooler 70 and the metal layer 33. Yes.

In the power module 20 illustrated in FIG. 2, the bonding layer 40 is formed between the circuit layer 32 and the semiconductor element 50 using the bonding material according to the present embodiment described above.
As shown in FIG. 3, the bonding layer 40 includes a sintered body 41 of inorganic particles and metal-coated resin particles 10. As the inorganic particles, at least one particle selected from the group consisting of metal particles and metal oxide particles is used. The metal-coated resin particle 10 includes a resin particle 11 having at least one functional group selected from the group consisting of a carboxyl group, a mercapto group, a sulfide group, and an amino group on the surface, and a metal coating formed on the surface of the resin particle 11. Layer 13. A part or all of the metal coating layer 13 of the metal-coated resin particles 10 is sintered with the sintered body 41 of inorganic particles. The sintered body 41 of inorganic particles is sintered with the inorganic particles and their reduced bodies, the metal coating layer 13 of the metal-coated resin particles 10, and the semiconductor element 50 and the circuit layer 32.

  The bonding layer 40 is formed by applying the bonding material according to the present embodiment on the surface of the circuit layer 32 with a thickness of 10 to 100 μm using a dispenser or a screen printer, and then laminating the semiconductor elements 50, and the temperature is 100 to 300 ° C. The circuit layer 32 and the semiconductor element 50 are bonded to each other by firing under conditions of a holding time of 0.1 to 2.0 hours.

  According to the bonding material of the present embodiment configured as described above, a carboxyl group, a mercapto group, a sulfide group, an amino group, and the like introduced on the surface of the resin particle 11 serving as the nucleus of the metal-coated resin particle 10. Since the functional group 12 and the metal coating layer 13 are chemically adsorbed, the adhesive force between the resin particles and the metal coating layer 13 is increased.

  Moreover, according to the power module 20 (joined body) which is this embodiment, since the joining layer 40 is formed using the joining material which is this embodiment, the circuit layer 32 and the semiconductor element 50 are joined. Even when this power module 20 is subjected to a heat cycle, the bonding layer 40 maintains a high mitigation capability against thermal stress, and cracks are less likely to occur. Therefore, the bonding between the semiconductor element 50 and the power module substrate 30 is difficult. Excellent bonding reliability.

The embodiment of the present invention has been described in detail above, but the specific configuration is not limited to this embodiment, and includes a design and the like within a range not departing from the gist of the present invention.
For example, the objects to be joined are not limited to semiconductor elements, and any first member and second member may be joined using the joining material described above to form a joined body.
In the present embodiment, the power module is described as an example of the joined body, but the present invention is not limited to this, and other semiconductor devices such as LEDs may be used.

Moreover, although demonstrated as what comprised the circuit layer with aluminum, it is not limited to this, You may be comprised with other electrically-conductive materials, such as copper.
Furthermore, the ceramic substrate made of AlN has been described as an example of the insulating layer, but the present invention is not limited to this, and the insulating layer is made of other insulators such as Al ₂ O ₃ , Si ₃ N ₄ , and insulating resin. May be.

  Hereinafter, although the effect of the present invention is explained in detail using an example and a comparative example, the present invention is not limited to the following example.

[Invention Example 1]
<Preparation of bonding material>
(1) Production of silver-coated resin particles 20 g of silicone resin particles having an average particle diameter of 2.0 μm were subjected to surface cleaning with an alkali cleaning solution, washed with water and filtered, and then dispersed in an ethanol solution. 1 g of a mercapto group-containing silane coupling agent (KBM403, Shin-Etsu Chemical Co., Ltd.) is added to the resulting dispersion, followed by washing with water and filtering again to introduce mercapto groups on the surface of the resin particles to obtain mercapto group-introduced resin particles. It was.
In addition, it confirmed that the mercapto group was introduce | transduced into the resin particle surface by analyzing the resin particle surface by TOF-SIMS.

  Next, 15 g of stannous chloride and 15 mL of 35% hydrochloric acid were diluted to 500 mL with water using a 500 mL volumetric flask and kept at 25 ° C. To this aqueous solution, 10 g of mercapto group-introduced resin particles were added and stirred for 1 hour. Thereafter, the mercapto group-introduced resin particles were separated by filtration and washed with water. This provided the tin adsorption layer on the surface of the mercapto group-introduced resin particles.

  Next, 250 g of ethylenediaminetetraacetic acid tetrasodium (complexing agent), 100 g of sodium hydroxide and 200 mL of formalin (reducing agent) were dissolved in 5 L of water to prepare an aqueous solution containing the complexing agent and the reducing agent. In addition, 63 g of silver nitrate, 65 mL of 25% ammonia water, and 400 mL of water were mixed to prepare an aqueous solution containing silver nitrate.

  Next, the mercapto group-introduced resin particles provided with a tin adsorption layer were immersed in an aqueous solution containing a complexing agent and a reducing agent. Thereafter, while stirring the aqueous solution, an aqueous solution containing silver nitrate was dropped, and the mercapto group-introduced resin particles provided with the tin adsorption layer were coated with silver to produce silver-coated resin particles having a silver content of 80% by mass. Thereafter, the silver-coated resin particles were washed with water and dried. The layer thickness of the silver coating layer of the obtained silver-coated resin particles was measured by the following method. The results are shown in Table 1.

(Method for measuring the thickness of the silver coating layer)
100 silver-coated resin particles were embedded in an epoxy resin and cut, and the cut surface was polished. And the cut surface was observed with the transmission electron microscope (TEM), the layer thickness of the silver coating layer of each silver coating resin particle was measured, and the average of the layer thickness was computed.

(2) Preparation of bonding material 20 g of the silver-coated resin particles prepared in (1), 5.0 g of silver oxide particles, 5.0 g of ethylene glycol, and 0.5 g of a carboxylic acid-based dispersant were bubble-milled. Mix in Taro (Sinky Corporation). The obtained mixture was kneaded with a three-roll mill (EXAKT) to obtain a paste-like bonding material.

<Reliability test>
A reliability test was performed on the manufactured bonding material. Specifically, first, on a smooth silver plate made of silver having a purity of 99.9% or more, the produced bonding material was printed using a 1 mm square, 50 μm thick mask to form a printed film, A 1 mm square silicon substrate plated with silver with a thickness of 300 nm was allowed to stand on the printed film to obtain a test piece before heating. This pre-heating test piece was heated in a radiant heating furnace at 300 ° C. for 15 minutes in a state where a pressure of 3 MPa was applied, and this was used as a test piece. Next, this test piece was subjected to 500 cycles of the thermal cycle test in the range of −45 ° C. to 150 ° C. using a thermal cycle tester. The joining rate was evaluated for the test pieces before and after the cycle test. The evaluation results are shown in Table 1 together with the components of the bonding material.

The evaluation of the bonding rate was performed by observing the bonding interface of the test piece before and after the thermal cycle test with an ultrasonic flaw detection image and measuring the bonding area and the peeling area by image analysis. The joining rate (unit:%) was determined by the following formula.
Bonding ratio before cooling cycle test = bonding area before cooling cycle test / area of silicon substrate × 100
Bonding rate after cooling cycle test = (bonding area before cooling cycle test−peeling area after cooling cycle test) / bonding area before cooling cycle test × 100

[Invention Example 2]
In the production of (1) silver-coated resin particles in Invention Example 1, 20 g of acrylic resin particles having an average particle size of 3.0 μm were used instead of silicone resin particles, and the surface of the acrylic resin particles was washed with an alkaline cleaning liquid. After washing with water and filtering, it was dispersed in an ethanol solution. 1 g of a sulfide group-containing silane coupling agent (KBE846, Shin-Etsu Chemical Co., Ltd.) was added to the obtained dispersion, washed again with water and filtered to introduce sulfide groups on the surface of the resin particles. Silver-coated resin particles were produced in the same manner as in Invention Example 1, except that a silver coating layer was formed so that the silver content was 70% by mass with respect to the obtained sulfide group-introduced resin particles. Next, in the preparation of the bonding material of Example 1 of the present invention (2), in the same manner as in Example 1 of the present invention, except that 5.0 g of silver particles having an average particle diameter of 100 nm were used instead of the silver oxide particles, A reliability test was performed on the manufactured bonding material. The results of this reliability test are shown in Table 1 together with the components of the bonding material.

[Invention Example 3]
In production of (1) silver-coated resin particles in Invention Example 1, 20 g of styrene resin particles having an average particle diameter of 1.0 μm were used in place of silicone resin particles, and the styrene resin particles were used with a surfactant and an alkaline cleaning solution. The surface was washed, washed with water and filtered, and then dispersed again in water. To the obtained dispersion, a potassium permanganate solution (strongly acidic) was added so that the concentration was 0.5%, and the mixture was stirred for 30 minutes while being kept at 40 ° C., and the carboxyl group was converted to a styrene resin by surface oxidation. It was introduced on the particle surface. Next, in the preparation of the bonding material of Example 1 of the present invention (2), in the same manner as in Example 1 of the present invention, except that 5.0 g of silver particles having an average particle diameter of 50 nm were used instead of the silver oxide particles, A reliability test was performed on the manufactured bonding material. The results of this reliability test are shown in Table 1 together with the components of the bonding material.

[Invention Example 4]
In the production of (1) silver-coated resin particles of Example 1 of the present invention, 20 g of silicone rubber particles having an average particle size of 30.0 μm were used in place of the silicone resin particles, and the silicone rubber particles were used with a surfactant and an alkaline cleaning solution. The surface was washed, washed with water and filtered, and then dried in the atmosphere at 60 ° C. The dried particles were irradiated with plasma for 15 minutes in an air plasma device for powder to activate the resin particles, and then dispersed in an ethanol solution. 1 g of amino group-containing silane coupling agent (KBM903, Shin-Etsu Chemical Co., Ltd.) was added to the obtained dispersion, and the amino groups were introduced to the resin particle surfaces by washing and filtering again. Silver-coated resin particles were obtained in the same manner as in Example 1 except that the silver coating layer was formed so that the silver content was 50% by mass with respect to the obtained amino group-introduced resin particles.

  Next, in (2) preparation of the bonding material of Invention Example 1, 20 g of the silver-coated resin particles produced as described above, 4.2 g of silver oxide particles having an average particle diameter of 100 nm, 2-butoxy-ethoxyethanol, and 6. After mixing 0 g and 0.5 g of an amine-based dispersant with Foaming Netaro (Sinky), a paste-like bonding material was obtained by kneading with a three-roll mill (EXAKT). About the produced joining material, it carried out similarly to this invention example 1, and performed the reliability test. The results of this reliability test are shown in Table 1 together with the components of the bonding material.

[Invention Example 5]
<Preparation of bonding material>
(1) Preparation of copper-coated resin particles 20 g of silicone resin particles having an average particle diameter of 2.0 μm were subjected to surface cleaning with an alkali cleaning solution, washed with water and filtered, and then redispersed in an ethanol solution. 1 g of a mercapto group-containing silane coupling agent (KBM403, Shin-Etsu Chemical Co., Ltd.) was added to this dispersion, followed by washing with water and filtering again to introduce mercapto groups on the surface of the resin particles. This was redispersed in water to give a 3 L slurry. While stirring this slurry at a rotation speed of 500 rpm, 0.3 g of palladium chloride, 20 g of stannous chloride and 200 g of hydrochloric acid (concentration 35% by mass) are added to this slurry and kept at 30 ° C. for 15 minutes in a water bath. Then, the slurry was washed with water. This provided the tin palladium adsorption layer to which the palladium catalyst was provided on the surface of the mercapto group-introduced resin particles.

  Next, silicone resin particles provided with a tin-palladium adsorption layer were dispersed in ion-exchanged water to prepare a slurry. 200 mL of formaldehyde (concentration: 37% by mass) as a reducing agent and 100 mg of polyethylene glycol as a surfactant were added to this slurry, and the temperature was raised to 50 ° C. in a water bath while stirring. Further, 230 g of copper sulfate pentahydrate as a copper salt, 500 g of sodium ethylenediaminetetraacetate as a complexing agent, and 50 mg of sodium cyanide as a stabilizing agent were stirred and dissolved in 600 g of ion-exchanged water to prepare a copper plating solution. The copper plating solution was dropped into the heated slurry, and copper coated resin particles were obtained by performing copper plating on the silicone resin particles provided with a tin-palladium adsorption layer.

(2) Preparation of bonding material 18 g of the copper-coated resin particles prepared in (1), 3.5 g of silver oxide particles having an average particle diameter of 50 nm, 2.5 g of ethylene glycol, 1.0 g of formic acid, and a carboxylic acid series 0.5 g of a dispersant was mixed with Foamer Nitaro (Sinky Corporation). The obtained mixture was kneaded with a three-roll mill (EXAKT) to obtain a paste-like bonding material.

  About the produced joining material, it carried out similarly to this invention example 1, and performed the reliability test. The results of this reliability test are shown in Table 1 together with the components of the bonding material.

[Comparative Example 1]
In the production of (1) silver-coated resin particles of Invention Example 1, the present invention except that no mercapto group-containing silane coupling agent was added to the dispersion and no mercapto group was introduced on the surface of the silicone resin particles. In the same manner as in Invention Example 1, a joining material was produced, and a reliability test of the produced joining material was performed. The results of this reliability test are shown in Table 1 together with the components of the bonding material.

  It was confirmed that the bonding materials of Examples 1 to 5 of the present invention manufactured using resin particles having a specific functional group introduced on the surface maintained a good bonding rate even after the thermal cycle test. On the other hand, since the bonding material of Comparative Example 1 produced using resin particles in which a specific functional group is not introduced on the surface has low adhesive force between the resin particles and the silver coating layer, stress relaxation is achieved. Not enough, the joining rate after the thermal cycle test was less than 60%.

DESCRIPTION OF SYMBOLS 10 Metal-coated resin particle 11 Resin particle 12 Functional group 13 Metal coating layer 20 Power module 30 Power module substrate 31 Ceramic substrate 32 Circuit layer 33 Metal layer 40 Bonding layer 41 Sintered body of inorganic particles 50 Semiconductor element 60 Buffer layer 70 Cooling Unit 71 Top plate part 72 Radiating fin 73 Flow path

Claims (2)

At least one inorganic particle selected from the group consisting of metal particles and metal oxide particles;
Metal coating comprising resin particles having at least one functional group selected from the group consisting of a carboxyl group, mercapto group, sulfide group and amino group introduced on the surface, and a metal coating layer formed on the surface of the resin particles Resin particles,
And a solvent. A joined body in which the first member and the second member are joined via a joining layer,
The bonding layer is a sintered body of at least one inorganic particle selected from the group consisting of metal particles and metal oxide particles;
Metal-coated resin particles comprising resin particles having on the surface at least one functional group selected from the group consisting of a carboxyl group, a mercapto group, a sulfide group and an amino group, and a metal coating layer formed on the surface of the resin particles And a joined body characterized by comprising:

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