JP6789794B2 - Dispersion solution of metal particles - Google Patents

Description

The present invention relates to a dispersion solution of metal particles used for joining an electronic component (adhesive body) such as a semiconductor package or a semiconductor chip to another adherend such as a substrate or an electrode.

In recent years, the increase in power consumption, modularization, high integration, and high reliability of electronic components such as semiconductor chips have been rapidly progressing. Mounting devices equipped with such electronic components need to set a high upper limit of the usable current density in order to realize high power consumption, high integration, etc., and when the current density becomes high, the electronic components As a result of the increase in the amount of heat generated, the operating temperature tends to rise and become high. Conventionally, high-temperature lead solder that can withstand high-temperature use has been used as a die bond material or the like. However, in recent years, the use of high-temperature lead solder has tended to be regulated due to environmental problems. Therefore, as a new die bond material that can withstand high-temperature use, the temperature is lower than that of bulk metal without using lead. Attention has been focused on bonding with a conductive paste containing metal nanoparticles, which enables bonding under conditions.

As a bonding method using a conductive paste containing metal nanoparticles, for example, a paste for heat bonding or a plate-shaped molded body containing metal particles is prepared, and the molded body is heated and sintered under pressure. A method of joining an electronic component (for example, a semiconductor chip) to a substrate or the like is known.

In Patent Document 1, a pre-drying film is formed on a substrate by applying a silver paste on the substrate and heating the substrate, and the pre-drying film is pre-pressurized to flatten the surface of the pre-drying film. A method of joining an electronic component to a substrate via a silver bonding layer by arranging the electronic component on the surface of the pre-dried film and then heating the electronic component while applying pressure is disclosed.

Further, in Patent Document 2, cracks are described in order to prevent cracks from occurring at the time of solvent removal after adding 1,3-propanediol as a drying inhibitor to a dispersion liquid in which metal particles are dispersed in a solvent. A method of forming a metal wiring (conductor pattern) by ejecting ink droplets generated by adding a polyglycerin compound having a polyglycerin skeleton as an inhibitor onto a substrate is disclosed.

Japanese Unexamined Patent Publication No. 2014-213325 JP-A-2009-37880

In the method of joining electronic components disclosed in Patent Document 1, a metal paste (silver paste) containing metal particles (silver particles) is applied onto a substrate and heated to perform pre-drying. However, in the state after the pre-drying, a part of the solvent has evaporated and the bonding between the metal particles has not started yet, and the metal paste is in a semi-dried state after the pre-drying. The particles exist in a separated state, and have the drawback of being unstable and easily peeling off. Further, when sintering, pressure is applied to bond the chips, but the peripheral portion of the chip is a non-pressurized portion, and there is a drawback that it is unstable and easily peeled off even after pressure-heat bonding.

In particular, when printed (coated) on a ceramic circuit board such as a power semiconductor module, the peeled metal particles fall between the circuits and move to unexpected parts on the surface of the circuit board. There is a problem that the circuit is short-circuited, the resin adhesion is lowered in the resin sealing process of the subsequent process, and the clean room is contaminated.

Further, in Patent Document 2, the drying temperature after ejecting ink droplets onto a substrate (ceramic green sheet) is as low as 60 ° C., and polyglycerin as a crack inhibitor uses a polymer chain of silver colloids. Since the colloids are only connected to each other during drying to prevent cracks during drying, metal particles are likely to fall off from the substrate after drying, and the above-mentioned Patent Document 1 There was a similar problem as.

An object of the present invention is that metal particles are less likely to fall off in a paste-like state after drying before sintering, preventing short circuits and adhesion of foreign substances, and forming a bonding layer having excellent sintering characteristics. , Provide a dispersion solution of metal particles.

As a result of diligent research by the present inventors, the following findings were obtained.
Copper is used as an organic dispersion medium (S) of a dispersion solution of metal particles (P), for example, metal particles (P1) containing copper nanoparticles (P1), using a trivalent alcohol containing about 50% by mass, for example, glycerin. When a nanopaste was prepared and this copper nanopaste was printed on a substrate, the printed paste would flow out under pressure if pressure was applied as it was, so the copper was dried so that the copper concentration was between 87 and 93% by mass. .. At this time, it was clarified that by raising the temperature at which the copper nanopaste is dried higher than before, the bonding force between the particles becomes stronger even at the same drying concentration, and the particles can be prevented from falling off. The reason for this is that the copper nanoparticles have a surface modified with a compound (A2) having an amide group, for example, PVP (polyvinylpyrrolidone) to form an organic protective film (F1), and the PVP and glycerin are used. It is considered that the reaction produces a gelling substance, whereby the metal particles (P) are in close contact with the substrate. The copper nanoparticles (P1) can exist even if a part of the PVP that modifies the surface reacts, but in the case of colloid, the reaction occurs even if the surrounding modifier is not PVP or PVP. If a part of the particles is lost, the electrical balance will be lost and the particles will become unstable, which is considered unfavorable.

It was also found that the higher the drying temperature, the more the reaction between glycerin and PVP progresses, so that the amount of residual solvent decreases and the sintering tends to be insufficient at the time of sintering. Therefore, the present inventors adopt a configuration in which a conventionally used solvent (for example, glycerin) and a solvent having a higher polymer than this solvent (for example, polyglycerin) are used in combination as the organic dispersion medium (S). As a result, the solvent could be prevented from evaporating even if the solvent was dried at a higher temperature (preliminary before sintering), and good sintering characteristics could be obtained even in the subsequent sintering.

However, as the reducing substance, a substance having a hydroxy group is preferable, but a substance having a hydroxy group and a polymer (mannitol, etc.) is a solid at around room temperature, and also has a melting point and a boiling point. It is not suitable as a heat-bonding material because it is not practical at a high and practical mounting temperature of around 200 to 300 ° C. On the other hand, a polyhydric alcohol having four or more hydroxy groups in one molecule (for example, polyglycerin) is a liquid at room temperature, decomposes at a practical mounting temperature of 300 ° C. or lower, and is a trivalent alcohol (for example, glycerin). ) Etc., so it is suitable as a heat bonding material. Therefore, as the polymer solvent, it is preferable to use a polyhydric alcohol (for example, polyglycerin) having 4 or more hydroxy groups in one molecule. Further, as the polyglycerin, a polyglycerin having a linear structure is particularly preferable to a polyglycerin having a cyclic structure. This is because polyglycerin having a cyclic structure may become hydrophobic.

However, when the concentration of polyglycerin in the organic dispersion medium (S) is increased, for example, when the organic dispersion medium (S) consists only of polyglycerin, there is no glycerin that reacts with PVP, so that the metal particles (S) Sufficient adhesion between P) and the substrate cannot be obtained.

In addition, polyglycerin has 3 to 40 dimers depending on the degree of polymerization, but as the degree of polymerization increases, the decomposition temperature increases, the residual amount of solvent in the sintered body increases, and the electrical resistance of the sintered body increases. Since it becomes high, there is a tendency that sufficient conductivity cannot be obtained.

Therefore, in the present invention, the bond between the metal particles (P) is a compound (A2) having a trihydric alcohol (A1a) such as glycerin and an amide group such as PVP modifying the copper nanoparticles (P1). ) Is obtained by reacting with), and the drying temperature is raised to strengthen the bond, making it difficult for metal particles to fall off in the pasty state after drying before sintering, and trihydric alcohol. In order to solve the drawback that the decomposition of (A1a) progresses and the sinterability deteriorates, the organic dispersion medium (S) is mixed with a trihydric alcohol (A1a) in one molecule such as polyglycerin having a high decomposition temperature. By using a polyhydric alcohol (A1b) having four or more groups in combination, it is possible to form a bonding layer having good conductivity and sinterability after sintering, and the present invention has been completed. It was.

Further, regarding the detachment of the non-pressurized portion around the chip of the bonding, it was clarified that the copper nanoparticles were bonded to the substrate and the detachment was suppressed by oxidizing the copper nanoparticles.

That is, the gist structure of the present invention is as follows.
(1) A dispersion solution of metal particles composed of metal particles (P) containing copper nanoparticles (P1) having an average primary particle diameter of 2 nm to 500 nm and an organic dispersion medium (S), wherein the copper nanoparticles. (P1) has a surface modified with a compound (A2) having an amide group, and the organic dispersion medium (S) has a trihydric alcohol (A1a) and four or more hydroxy groups in one molecule. A dispersion solution of metal particles, which comprises a polyhydric alcohol (A1b).
(2) The above-mentioned (1), wherein the ratio of the polyhydric alcohol (A1b) to the trihydric alcohol (A1a) and the polyhydric alcohol (A1b) is 2% by weight or more. A dispersion solution of metal particles.
(3) The dispersion solution of metal particles according to (1) or (2) above, wherein the trihydric alcohol (A1a) is glycerin and the polyhydric alcohol (A1b) is polyglycerin.
(4) The dispersion solution of metal particles according to any one of (1) to (3) above, wherein the polyhydric alcohol (A1b) is a hexamer or less polyglycerin.
(5) The dispersion solution of metal particles according to any one of (1) to (4) above, wherein the compound (A2) having an amide group is polyvinylpyrrolidone.
(6) The dispersion solvent for metal particles according to any one of (1) to (5) above, wherein the copper nanoparticles (P1) have an degree of oxidation of 0.10 or more and 4.0 or less. ..

According to the present invention, metal particles are less likely to fall off in a paste-like state after drying before sintering, preventing short circuits and adhesion of foreign substances, and having good conductivity and sinterability after sintering. It has become possible to provide a dispersion solution of metal particles capable of forming a bonding layer comprising the above.

FIG. 1 is an X-ray diffraction chart shown as an example for explaining a method of calculating the degree of oxidation of copper nanoparticles.

Next, embodiments of the present invention will be described in detail below.
The dispersion solution of metal particles according to the present invention is a dispersion solution of metal particles composed of metal particles (P) containing copper nanoparticles (P1) having an average primary particle diameter of 2 nm to 500 nm and an organic dispersion medium (S). The copper nanoparticles (P1) have a surface modified with a compound (A2) having an amide group, and the organic dispersion medium (S) is contained in one molecule with a trihydric alcohol (A1a). It contains a polyhydric alcohol (A1b) having 4 or more hydroxy groups.

[1] Dispersion solution of metal particles (1) Metal particles (P)
The metal particles (P) need to have sinterability. Further, the metal particles (P) are composed of only copper nanoparticles (P1) having an average primary particle diameter of 2 to 500 nm, and in addition to the copper nanoparticles (P1), an average primary particle diameter of 0.5 μm. It may be configured as a mixed particle in which metal fine particles (P2) exceeding 50 μm or less are mixed.

(A) Copper nanoparticles (P1)
The copper nanoparticles (P1) are not particularly limited as long as the average particle size of the primary particles is copper fine particles of 2 nm to 500 nm. If the average particle size of the primary particles of copper nanoparticles (P1) is less than 2 nm, it is difficult to manufacture. On the other hand, if the average particle size of the primary particles exceeds 500 nm, the melting point does not decrease during sintering, and sintering is performed. This is because the sex deteriorates. As unavoidable impurities in copper nanoparticles, boron (B), calcium (Ca), iron (Fe), potassium (K), sodium (Na), nickel (Ni), lead (Pb), strontium (Sr), Zinc (Zn), chromium (Cr), magnesium (Mg), silicon (Si), and phosphorus (P) may be contained in an amount of about 30 ppm or less each.

Here, the "primary particle diameter" means the diameter of the primary particles of the individual metal particles constituting the secondary particles. This primary particle size can be measured using an electron microscope (SEM (scanning electron microscope)). In the present invention, using an SEM (manufactured by Hitachi High-Technologies Corporation, device name "SU8020"), an SEM image was acquired by observing at an accelerating voltage of 3 kV and a magnification of 200,000 times. Then, 20 arbitrary particles were selected from the image, the particle size was measured, and the average was calculated to obtain the average particle size. Further, the "average primary particle diameter" means the number average particle diameter of the primary particles.

Further, the copper nanoparticles (P1) used in the dispersion solution of the present invention need to have a surface modified by the compound (A2) having an amide group, and the surface side portion constituting the copper nanoparticles (P1). In, an organic protective film (F1) containing an amide group is formed on at least a part of the surface of the copper nanoparticles (P1).

The thickness of the organic protective film (F1) is preferably 0.1 to 5% by mass in terms of the mass ratio of the entire copper nanoparticles (P1). If the mass ratio is less than 0.1% by mass, the thickness of the organic protective film (F1) tends to be too thin, and the effect of preventing the aggregation of copper nanoparticles (P1) in the dispersion solution tends not to be recognized. Further, if the mass ratio exceeds 5% by mass, the thickness of the organic protective film tends to be too thick and the sinterability tends to be inferior. Since it is difficult to directly measure the thickness of the organic protective film, a carbon / sulfur concentration analyzer was used.

The carbon / sulfur concentration analyzer heats the sample in oxygen to a high temperature state and extracts the contained carbon in the state of carbon dioxide. The concentration of the extracted carbon dioxide is measured by a carbon dioxide detector, the amount of carbon is obtained from the integrated concentration, and the amount of carbon contained in the sample is calculated. If the weight of the initial sample is known, the carbon concentration of the sample can be determined. The method for producing the copper nanoparticles (P1) with the organic protective film (F1) is not particularly limited, and a known method can be used. As an example of the method for producing copper nanoparticles (P1) with an organic protective film (polymer dispersant), the method described in Examples of JP-A-2011-074476 can be mentioned.

Moreover, it is preferable that the copper nanoparticles (P1) are oxidized. This is because when the copper nanoparticles are oxidized, the bondability between the metal particles after heat drying (before sintering) tends to be further improved. It is not clear why the oxidation of the copper nanoparticles improves the bondability between the metal particles after heat drying (before sintering), but probably, when the copper nanoparticles are oxidized, the copper nanoparticles (P1) Along with the decomposition of the compound (A2) having an amide group that modifies the surface, glycerin in the organic dispersion medium is oxidized and changed to acetaldehyde and formaldehyde, and acetaldehyde and formaldehyde are further oxidized and changed to formic acid and acetic acid. It is presumed that formic acid and acetic acid produced by these oxidation reactions exert an action of cleaning the surface of the base material to be bonded, thereby improving the adhesion of metal particles to the substrate. The copper nanoparticles (P1) preferably have an oxidation degree of 0.10 or more and 4.0 or less. If the degree of oxidation is less than 0.10, the effect of cleaning the surface of the base material is not sufficient, so that the effect of improving the bondability between the metal particles after heating and drying cannot be sufficiently obtained, and the degree of oxidation is 4. If it exceeds .0, oxides are likely to remain on the surface of the copper nanoparticles after heat-drying or sintering, and the adhesion of the metal particles to the substrate after heat-drying (before sintering) is lowered and the metal particles are baked. This is because there is a tendency that a decrease in conductivity is observed after firing. The degree of oxidation was defined as follows. First, the X-ray diffraction of the copper nanoparticles, and the peak intensity of Cu 2 [Theta] comes into the vicinity of 43 °, 2 [Theta] peak intensities of Cu 2 _O exiting the vicinity of 36.5 ° was measured, peaks from these peak intensities The intensity ratio (peak intensity of Cu ₂ O / peak intensity of Cu) was calculated, and this peak intensity ratio was defined as the degree of oxidation. As an example, an X-ray diffraction chart of copper nanoparticles having an oxidation degree of 0.46 is shown in FIG.
Further, the method for oxidizing the copper nanoparticles is not particularly limited, and examples thereof include a method in which the copper nanoparticles are immersed in an acetic acid solution and the degree of oxidation is adjusted by changing the immersion time.

(B) Metal fine particles (P2)
The metal fine particles (P2) have an average particle diameter of 0.5 μm to 50 μm of the primary particles, and are used when the metal particles (P) are formed as mixed particles with copper nanoparticles (P1). The metal fine particles (P2) are not particularly limited, but gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), tungsten (W), nickel (Ni), and iron. From (Fe), Cobalt (Co), Tantal (Ta), Bismus (Bi), Lead (Pb), Indium (In), Tin (Sn), Zinc (Zn), Titanium (Ti), and Aluminum (Al) One or more fine particles of choice can be used, with copper being particularly preferred.

When copper nanoparticles (P1) having an average primary particle diameter of 2 nm to 500 nm and metal fine particles (P2) having an average primary particle diameter of more than 0.5 μm and 50 μm or less coexist, the copper nanoparticles (P2) are interspersed with each other. P1) intervenes in an appropriate dispersed state, and free movement of copper nanoparticles (P1) can be effectively suppressed during heat treatment, and the dispersibility and stability of the copper nanoparticles (P1) described above can be effectively suppressed. As a result, it becomes possible to form a porous body having a more uniform particle size and pores by heating and firing (stituting).

The average primary particle size of the metal fine particles (P2) is preferably more than 0.5 μm and 50 μm or less. If the average primary particle size of the metal fine particles (P2) is 0.5 μm or less, the effect of adding the metal fine particles (P2) is not exhibited, and if it exceeds 50 μm, firing may become difficult. The "average primary particle size" is defined as a particle size having a cumulative frequency of 50% as measured by a laser diffraction type particle size distribution meter.

(2) Organic dispersion medium (S)
The organic dispersion medium (S) contains a trihydric alcohol (A1a) and a polyhydric alcohol (A1b) having four or more hydroxy groups in one molecule, and modifies the surface of copper nanoparticles (P1). A compound (A2) having an amide group for this purpose is further contained. In addition, the organic dispersion medium (S) is one or more polyhydric alcohols (A1c), amine compounds (A3), low, which have two or more hydroxy groups in one molecule, as other organic solvents. A boiling point organic solvent (A4) or the like can be contained.

(A) Trivalent alcohol (A1a)
Examples of the trihydric alcohol include glycerin (glycerol), 1,1,1-trishydroxymethylethane, 1,2,6-hexanetriol, 1,2,3-hexanetriol, and 1,2,4-butanetriol. It can contain one or more selected from the above, and glycerin is particularly preferable.

(B) A polyhydric alcohol (A1b) having 4 or more hydroxy groups in one molecule.
The polyhydric alcohol (A1b) having 4 or more hydroxy groups in one molecule is formed by binding, for example, by dehydration condensation of a trihydric alcohol (A1a), and polyglycerin is particularly preferable, and particularly 6 amounts. It is more preferably below the body. This is because if the degree of polymerization of glycerin is too large, the decomposition temperature rises, and organic substances remain in the film even after sintering, and the electrical resistivity tends to rise. Considering the sinterability of the heat bonding material (M), the ratio of the polyhydric alcohol (A1b) to the trihydric alcohol (A1a) and the polyhydric alcohol (A1b) is 2% by weight or more. It is more preferable that the organic dispersion medium (S) contains 40% by weight or more. Further, as the polyglycerin, a polyglycerin having a linear structure is particularly preferable to a polyglycerin having a cyclic structure. This is because polyglycerin having a cyclic structure may become hydrophobic.

(C) One or more polyhydric alcohols (A1c) having two or more hydroxy groups in one molecule
As one kind or two or more kinds of polyhydric alcohols (A1) having two or more hydroxy groups in one molecule, ethyleneglycol, diethyleneglycol, which has two or more hydroxy groups in one molecule, 1,2-Propanediol, 1,3-propanediol, 1,2-butanjiol, 1,3-butanjiol, 1,4-butanjiol, 2-butene-1,4- Diol, 2,3-butanjiol, pentaneol, hexanediol, octanediol, glycerin (glycerol), 1,1,1-trishydroxymethylethane, 2-ethyl-2-hydroxymethyl-1,3 -Propanediol, 1,2,6-hexanetriol, 1,2,3-hexanetriol, 1,2,4-butanetriol, traytoll, erythritol, pentaerythritol, pentitol, 1- Propanol, 2-propanol, 2-butanol, 2-methyl2-propanol, xylitol, ribitol, arabitol, hexitol, mannitol, sorbitol, zulcitol, glycerin aldehyde, dioxyacetone, treose, elittlerose, erythrose, arabinose, ribose, Ribroth, xylose, xylulose, lyxose, glucose, fructose, mannose, idose, sorbose, growth, talose, tagatos, galactose, allose, altrose, lactos, isomaltos, glucoheptose, heptose , Maltotriol, lacturose, and trehalose, which may be selected from one or more.

Since these alcohols have reducing properties, the surface of the metal particles (P) is reduced, and further heat treatment causes the polyvalent alcohol (A1) to continuously evaporate, and the liquid and vapor thereof are present. When reduced and fired in an atmosphere, sintering of metal fine particles (P) is promoted.

(D) Compound having an amide group (A2)
Examples of the compound (A2) having an amide group include N-methylacetamide, N-methylformamide, N-methylpropanamide, formamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N, N-dimethylformamide, 1-methyl-2-pyrrolidone, hexamethylphosphorictriamide, 2-pyrrolidone, alkyl-2-pyrrolidone, ε-caprolactam, and acetamide, polyvinylpyrrolidone, polyacrylamide, and N-vinyl-2- One or more selected from pyrrolidones can be exemplified. The compound (A2) having an amide group is used as an organic protective film (F1) that covers the surface of metal particles. The compound (A2) having an amide group can be blended in an organic dispersion medium (S) in an amount of 10% by mass to 80% by mass. Of these, polyvinylpyrrolidone is preferable.

(E) Amine compound (A3)
The amine compound (A3) is selected from aliphatic primary amines, aliphatic secondary amines, aliphatic tertiary amines, aliphatic unsaturated amines, alicyclic amines, aromatic amines, and alkanol amines. One or more amine compounds are mentioned, and specific examples thereof include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, di-n-propylamine, and tri-n-propylamine. , N-butylamine, di-n-butylamine, tri-n-butylamine, t-propylamine, t-butylamine, ethylenediamine, propylenediamine, tetramethylenediamine, tetramethylpropylenedimine, pentamethyldiethylenetriamine, mono-n-octylamine , Mono-2 ethylhexylamine, di-n-octylamine, di-2ethylhexylamine, tri-n-octylamine, tri-2ethylhexylamine, triisobutylamine, trihexylamine, triisooctylamine, triisononylamine , Triphenylamine, dimethylcoconatamine, dimethyloctylamine, dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dimethylbehenylamine, dilaurylmonomethylamine, diisopropylethylamine, methanolamine, Dimethanolamine, trimethanolamine, ethanolamine, diethanolamine, triethanolamine, propanolamine, isopropanolamine, diisopropanolamine, triisopropanolamine, butanolamine, N-methylethanolamine, N-methyldiethanolamine, N, N-dimethyl Among ethanolamine, N-ethylethanolamine, N-ethyldiethanolamine, N, N-diethylethanolamine, Nn-butylethanolamine, Nn-butyldiethanolamine, and 2- (2-aminoethoxy) ethanol One or more selected species can be mentioned. The amine compound (A3) can be blended in the organic dispersion medium (S) in an amount of 0.3 to 30% by mass.

(F) Low boiling point organic solvent (A4)
The low boiling point organic solvent (A4) is an organic solvent having a boiling point at normal pressure of 60 to 120 ° C. (the boiling point means the boiling point at normal pressure; the same applies hereinafter) and has a relatively low boiling point. The low boiling point organic solvent (A4) is preferably one or more selected from alcohols, ethers, and ketones having one hydroxyl group in the molecule.

Examples of the alcohol having one hydroxyl group in the molecule include methanol (64.7 ° C.), ethanol (78.0 ° C.), 1-propanol (97.15 ° C.), 2-propanol (82.4 ° C.), and the like. One or more selected from 2-butanol (100 ° C.) and 2-methyl2-propanol (83 ° C.) can be exemplified. Examples of the ether include diethyl ether (35 ° C.), methylpropyl ether (31 ° C.), dipropyl ether (89 ° C.), diisopropyl ether (68 ° C.), methyl-t-butyl ether (55.3 ° C.), and t-amyl. One or more selected from methyl ether (85 ° C.), divinyl ether (28.5 ° C.), ethyl vinyl ether (36 ° C.), and allyl ether (94 ° C.) can be exemplified. Further, as the ketone, one or more selected from acetone (56.5 ° C.), methyl ethyl ketone (79.5 ° C.), and diethyl ketone (100 ° C.) can be exemplified.

By containing the organic solvent (A4) which is a low boiling point organic solvent in the organic dispersion medium (S), the viscosity of the organic dispersion medium (S) can be adjusted and the accuracy of pattern formation can be improved. The content ratio of the low boiling point organic solvent (A4) in the organic dispersion medium (S) is preferably about 1% by mass to 30% by mass.

[2] Method for Producing a Bonded Structure Next, an example of the manufacturing method for a bonded structure suitable for manufacturing using a dispersion solution of metal particles according to the present invention will be described below.
The method for producing the bonded structure is a first step of arranging a dispersion solution of metal particles between a first adherend and a second adherend using the above-mentioned dispersion solution of metal particles, and the dispersion thereof. It includes a second step of drying the solution to obtain a heat-bonded material and a third step of sintering the heat-bonded material, and the drying temperature in the second step is in the range of 140 to 170 ° C. As a method for manufacturing a bonded structure, for example, a heat-bonded material can be placed between a semiconductor chip (first adherend) and a substrate (second adherend), and then the object to be processed can be pressed in a vacuum. It can be done by introducing it into the device. When the heat-bonding material is a paste-like material, a bonding structure can be manufactured by forming a bonding layer after sintering by using a coating method or a printing method on one or both of the surfaces to be bonded.

(1) First step In the first step, metal particles are formed between a first adherend, for example, an electronic component such as a semiconductor package or a semiconductor chip, and a second adherend, for example, a substrate or an electrode. This is a step for arranging the dispersion solution.

In the dispersion solution of metal particles used to form the heat bonding material (M), the ratio (mass ratio) of the organic dispersion medium (S) / metal particles (P) is stable in consideration of patterning and sinterability. 10/90 to 70/30 is desirable in order to obtain the desired bonding force, but the ratio depends on whether a sheet-shaped heat-bonded molded body (T1) or a heat-bonded paste (T2) is selected. It is determined.

If the ratio of the organic dispersion medium (S) / metal fine particles (P) is less than 10/90, the metal particles (P) remain in powder form when the heat bonding material (M) is formed. It tends to be present in and is impossible to make into a paste. Further, if the amount of the organic dispersion medium is more than 70/30, the shape is not stable after printing, and printing tends to be impossible. This ratio is preferably 20/80 to 60/40.

The dispersion solution of the metal particles can be obtained by dispersing the metal particles (P) in the organic dispersion medium (S) using a known mixer, kneader or the like. The coating thickness of the dispersion solution of the metal particles for forming the heat bonding material (M) is not particularly limited, but is preferably in the range of, for example, 50 to 200 μm.

(2) Second Step The second step is a step of (preliminarily) drying the dispersion solution to form a heat-bonded material after the first step.

The heat-bonding material (M) is a sheet-shaped heat-bonding molded product (T1) or a heat-bonding paste (T2) in which metal particles (P) are dispersed in an organic dispersion medium (S). ) Can be. Further, as the heat bonding material (M), a patterned product made of the heat bonding material (M) can be arranged on the surface to be bonded (for example, the surface of a copper plate). In this case, when the semiconductor chip (K) is placed on the patterned product and the metal particles (P) are heated within the temperature range for sintering, the trivalent alcohol (A1a) forms the surface of the copper nanoparticles (P1). It is reduced and activated, and sintering of metal particles (P) is promoted. As a result, the electrode and the substrate can be electrically and mechanically bonded to each other as in the case of using a paste-like material containing nano-sized metal fine particles. When the heat bonding material (M) is heat-sintered, the organic dispersion medium (S) is removed by decomposition, evaporation, or the like.

The organic dispersion medium (S) contains a low molecular weight trihydric alcohol (A1a) and a high molecular weight polyhydric alcohol (A1b). In this way, by using two types of alcohols having different molecular weights, the high molecular weight polyhydric alcohol (A1b) remains even if the drying temperature is raised, so that the reducing property is maintained and the main sintering can be performed. In the meantime, good sintering properties can be obtained.

The drying method is not particularly limited, and may be performed in, for example, a drying furnace. In the present invention, the drying temperature is preferably 140 to 170 ° C. If the drying temperature is less than 140 ° C, evaporation of the solvent can be prevented, but sufficient sintering characteristics tend not to be obtained in the subsequent sintering, and if it exceeds 170 ° C, evaporation of the solvent tends to occur. This is because the amount is large and the adhesion between the metal particles after drying and the substrate tends to be poor. The drying time may be any time as long as the copper concentration in the heat-bonded material (M) formed after drying can be adjusted to 87 to 93% by mass, and is not particularly limited, but is, for example, 30. It is preferably about 60 minutes. The dry atmosphere may be an atmospheric atmosphere, an atmosphere containing 21% by volume or less of oxygen together with an inert gas (argon, helium, nitrogen, etc.), or a vacuum atmosphere.

(3) Third Step In the third step, a heat-bonding material composed of a sheet-shaped heat-bonding molded body (T1) or a heat-bonding paste (T2) is sintered, and adherends are joined to each other. This is a step of forming a bonded structure having a bonded layer.

As a sintering method, for example, the object to be processed is sandwiched between a press plate having a built-in heater, and then evacuated to sufficiently reduce the pressure. At this time, since the pressure corresponding to the atmospheric pressure is applied to the absolute pressure, the pressure is applied by hydraulic pressure or pneumatic pressure at a gauge pressure in consideration of the pressure. The heating (sintering) temperature is preferably about 190 to 400 ° C., and the heating holding time is preferably about 10 minutes to 120 minutes.

Then, if necessary, annealing treatment may be performed at a temperature of 190 to 400 ° C. for about 1 hour to 30 hours in an atmosphere, an inert atmosphere, or a reducing atmosphere such as hydrogen. By this annealing treatment, strain and residual stress in the joint layer are removed, and reliability is further improved.

According to the above method for manufacturing a bonded structure, the heat bonding material 1 is sintered to form a bonding layer made of a sintered body of copper nanopaste, and a semiconductor device (bonding structure) in which a substrate and a semiconductor chip are bonded by the bonding layer. Body) can be obtained. In this way, the metal particles in the heat bonding material (M) are heated by heating the substrate and the heat bonding material, and the heat bonding material and the semiconductor chip in contact with each other under no pressure or pressure. (P) is sintered to form a porous bonding layer, and the substrate and the semiconductor chip are bonded to each other.

The thickness of the bonding layer (L) formed by this method is preferably in the range of 5 to 500 μm. This is because if the thickness is less than 5 μm, the paste thickness becomes thinner than the unevenness of the semiconductor chip (K), some parts are not covered with the paste, and the bonding reliability tends to decrease. On the other hand, if the thickness exceeds 500 μm, the thermal resistance becomes too large, which is not preferable. Therefore, the thickness of the bonding layer (L) in the present embodiment is preferably a numerical value within the range of 5 to 500 μm.

Embodiments of the present invention will be described in more detail based on the following examples. The present invention is not limited to these examples.

(Examples 1 to 17 and Comparative Examples 1 and 2)
(1) Copper nanoparticles (P1)
As the copper nanoparticles (P1), copper nanoparticles with an organic protective film were used.
Copper nanoparticles with an organic protective film were produced by the following procedure according to the method described in Examples of JP-A-2011-074476. First, as a raw material for copper nanoparticles (P1) in an aqueous solution prepared by dissolving 10 g of polyvinylpyrrolidone (PVP, number average molecular weight of about 3500), which is a polymer dispersant and a raw material for an organic protective film, in 799.3 ml of distilled water. 29.268 g of cupric hydroxide (Cu (OH) ₂ ) having a particle size range of 0.1 to 100 μm was added. Next, the liquid temperature was adjusted to 20 ° C., and 20.73 ml of an aqueous solution containing 150 mmol of sodium borohydride and 480 mmol of sodium hydroxide was added dropwise while stirring in a nitrogen gas atmosphere, and then the reduction reaction was carried out with good stirring for 45 minutes. went. The reduction reaction was terminated when the generation of hydrogen gas from the reaction system was completed. By the above reduction reaction, an aqueous solution of copper nanoparticles (P1) in which at least a part of copper nanoparticles (P1) covered with an organic protective film (polymer dispersant) was dispersed in the aqueous solution was obtained. Then, 66 ml of chloroform as an extractant is added to this aqueous solution to precipitate copper nanoparticles (P1), and then solid-liquid separation is performed by centrifugation, methanol is added and stirred, and then solid-liquid is further centrifuged. Separation was performed and the particles were washed. Then, after washing several times, copper nanoparticles (P1) with an organic protective film were obtained. When the thickness of the organic protective film (F1) was measured using a carbon / sulfur concentration analyzer as the mass ratio of carbon to the entire copper nanoparticles (P1), the carbon concentration was 0.6% by mass. .. The average primary particle diameter of the copper nanoparticles (P1) was 50 nm. An SEM image was acquired by observing with an SEM (manufactured by Hitachi High-Technologies Corporation, device name "SU8020") at an accelerating voltage of 3 kV and a magnification of 200,000 times. Then, 20 arbitrary primary particles were selected from the image and the particle size was measured, and the average value calculated from the measured values of those particle sizes was used as the average primary particle size.

Regarding the oxidation of copper nanoparticles, immersion treatment was performed at 40 ° C. for 1 to 3 hours in a 1 volume% acetic acid solution, and when the oxidation time was 1 hour, the degree of oxidation was 1.1 and the oxidation time was 2. The time was 3.9 and the oxidation time was 4.5 at 3 hours. In Example 14, the copper nanoparticles were heated in 100% hydrogen at 200 ° C. for 1 hour to reduce the copper nanoparticles. As a result, the degree of oxidation was 0.06. The degree of oxidation was defined as follows. First, X-ray diffraction of the copper nanoparticles (see FIG. 1), was measured and the peak intensity of Cu 2 [Theta] comes into the vicinity of 43 °, 2 [Theta] peak intensities of Cu 2 _O exiting the vicinity of 36.5 °, these The peak intensity ratio (peak intensity of Cu ₂ O / peak intensity of Cu) was calculated from the peak intensity of, and this peak intensity ratio was defined as the degree of oxidation.

(2) Preparation of dispersion solution of metal particles (P) The dispersion solution of metal particles (P) is an organic dispersion in which glycerin and a polyglycerin hexamer (a molecule in which 6 glycerins are connected) are mixed in the ratio shown in Table 1. It was prepared by sufficiently mixing 50 g of metal particles (P) composed of copper nanoparticles (P1) having an average primary particle diameter of 50 nm and an organic protective film with 50 g of the medium (S) in a dairy pot.

(3) Evaluation Method The peelability of the heat-bonded material (paste) formed from the dispersion solution of the metal particles (P) was evaluated using a dicing tape (FC2016 manufactured by Furukawa Electric Co., Ltd.). For the evaluation sample, copper nanopaste is printed on a 10 cm square oxygen-free copper plate at 5 cm square, and dried at the drying temperature shown in Table 1 (preliminary before sintering). A dicing tape cut to a width of 1 cm and a length of 10 cm is attached there.

Then, this sample was fixed in a tensile tester, a peel test was performed at room temperature, and the peel strength (N / cm ² ) was measured. In this test, when the peel strength is 2 N / cm ² or more, the adhesive strength is sufficiently high, and the metal particles (P) do not fall off from the substrate (oxygen-free copper plate) and have excellent adhesion. and "◎" as is, also, the peel strength is 1.5 N / cm ² or more, the case is less than 2N / cm ^2, no practical problem, after drying (before sintering), metal particles (P) Is marked with "○" as a level having good adhesion without falling off from the substrate (oxygen-free copper plate), and if the peel strength is less than 1.5 N / cm ² , a problem may occur in practical use. Because there is, it was evaluated as "x".

Regarding the bondability between the metal particles after drying (before sintering), the sample printed on the substrate and pre-dried at the drying temperature shown in Table 1 was observed with a microscope in a 1 mm square area, and cracks were dried. ) Is 14 or less, it is regarded as a level where the bondability between metal particles is excellent, and it is marked as “◎”, and the number of dry cracks (cracks) is 15 or more and 20 or less. Is marked with “○” as the bondability between the metal particles is good, and “×” is given as the bondability between the metal particles is poor when the number of dry cracks (cracks) is 21 or more. Was evaluated as.

Regarding conductivity, the above-mentioned dispersion solution (copper nanopaste) was printed (coated) on a 3 cm square glass plate in a 2 cm region with a thickness of 100 μm, and pre-drying in the second step was performed at the drying temperature shown in Table 1. After that, heat treatment (sintering) was performed at 300 ° C. for 60 minutes in a nitrogen atmosphere. The volume resistivity (Ωcm) of the sample was determined by the four-probe method and evaluated from the value of the reciprocal. Regarding the conductivity, when the volume resistivity is 1 × 10 ^-4 Ωcm or less, it is regarded as “◎” as the level of excellent conductivity, and the volume resistivity exceeds 1 × 10 ^-4 Ωcm and 1 × 10 ^When it is ^-3 Ωcm or less, the conductivity is good and it is a level that does not cause any problem in practical use, and it is marked as “○”, and when the volume resistivity exceeds 1 × 10 ^-3 Ωcm, the conductivity is It was evaluated as "x" as an inferior level.

Furthermore, as a comprehensive evaluation of these, the case where all of the above three performances are evaluated as "◎" is regarded as "excellent", and the case where all the above three performances are "○" or more and do not correspond to the above "excellent". Was evaluated as "possible", and when even one of the above performances had "x", it was evaluated as "impossible" because there is a possibility of causing a problem in practical use.

By the above method, a combination of various glycerins shown in Table 1 and polyglycerin composed of trimers to 40-mer (a molecule in which 3 to 40 glycerins are connected) was tested at the drying temperature shown in Table 1. Was done. In each case, the copper concentration in the heat-bonded material was adjusted to 87 to 93% by mass. The results are shown in Table 1.

From the results shown in Table 1, all of Examples 1 to 17 in which the composition of the organic dispersion medium (S) is within the appropriate range of the present invention are the characteristics after drying (before sintering), and the peel strength is 1. It is 5 N / cm ² or more, the number of dry cracks generated is 20 or less, and the volume resistivity, which is a characteristic after sintering, is 1 × 10 ^-3 Ω cm or less, both of which are practically acceptable levels. Is. Comparing the results of performance evaluation in Examples 1 to 17, both Example 8 using 10-mer polyglycerin and Example 9 using 40-mer polyglycerin were sintered. Later, the evaluation of conductivity is "○", and in Example 10 in which the drying temperature in the second step is as low as 130 ° C., the evaluation of the adhesion of the metal particles to the substrate after drying is "○". Further, in Example 13 in which the drying temperature in the second step was as high as 180 ° C., the evaluation of the bondability between the metal particles after drying and the conductivity after sintering were both “◯”, and further, In Example 14 in which the degree of oxidation of the copper nanoparticles was less than 0.10, the evaluation of the bondability between the metal particles after drying was "○", and the degree of oxidation of the copper nanoparticles exceeded 4.0. In Example 17, the evaluation of the bondability between the metal particles after drying and the conductivity after sintering was "◯". On the other hand, in Examples 1 to 7, 11, 12, 15 and 16, the peel strength is 2.0 N / cm ² or more and the number of dry cracks is increased, which is a characteristic after drying (before sintering). The number was 14 or less, and the volume resistivity, which is a characteristic after sintering, was 1 × 10 ^-4 Ωcm or less, and all the characteristic evaluations were “⊚”.

On the other hand, in Comparative Example 1, which does not contain polyglycerin in the organic dispersion medium (S) and is outside the appropriate range of the present invention, many drying cracks after drying occur and the volume resistivity is large. , It is inferior in conductivity and fails as a comprehensive evaluation. Further, in Comparative Example 2 in which the organic dispersion medium (S) does not contain glycerin and is outside the appropriate range of the present invention, the peel strength after drying is low, and the metal particles (P) fall off from the substrate before sintering. It is in a state where it is easy to do, and it fails as a comprehensive evaluation.

According to the present invention, metal particles are less likely to fall off in a paste-like state after drying before sintering, preventing short circuits and adhesion of foreign substances, and forming a bonding layer having excellent sintering characteristics. , It has become possible to provide a dispersion solution of metal particles.

Claims (5)

A dispersion solution of metal particles composed of metal particles (P) containing copper nanoparticles (P1) having an average primary particle diameter of 2 nm to 500 nm and an organic dispersion medium (S).
The copper nanoparticles (P1) have a surface modified with a compound (A2) having an amide group.
The organic dispersion medium (S) contains a trihydric alcohol (A1a) and a polyhydric alcohol (A1b) having four or more hydroxy groups in one molecule.
A dispersion solution of metal particles, wherein the polyhydric alcohol (A1b) is a hexamer or less polyglycerin. The dispersion of metal particles according to claim 1, wherein the ratio of the polyhydric alcohol (A1b) to the trihydric alcohol (A1a) and the polyhydric alcohol (A1b) is 2% by weight or more. solution. The dispersion solution of metal particles according to claim 1 or 2, wherein the trihydric alcohol (A1a) is glycerin. The dispersion solution of metal particles according to any one of claims 1 to 3, wherein the compound (A2) having an amide group is polyvinylpyrrolidone. Dispersion solvent solution of metal particles according to any one of claims 1 to 4 oxidation degree is 0.10 to 4.0 of the copper nano-particles (P1).

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