JP2015193009A - Metal joint material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal joint material excellent in conductivity of a joint whose joint strength after sintering is strong, in which the thickness of the joint can be control to be small.SOLUTION: A metal joint material includes (A) metal particles and (B) an organic solvent whose boiling point is 243-275°C, and vapor pressure at 25°C is 0.010-4.0 Pa, the metal particles consisting of first metal particles whose particle size distribution of an average primary particle diameter is in the range of 100-6000 nm, and second metal particles whose particle size distribution of an average primary particle diameter is in the range of 0.5-10 μm.

Description

  The present invention uses a metal bonding material containing metal particles and an organic solvent, more specifically, a known printing method such as a screen printing method or an ink jet printing method on a substrate, or a known ejection method such as a dispenser method. The present invention relates to a metal bonding material capable of bonding an electronic component onto the substrate by heat treatment at a low temperature (for example, about 200 ° C.) by coating.

  In the field of mounting electronic components on a substrate, lead-free solder, for example, tin-silver solder, tin-copper solder, tin-silver-copper solder is mainly used for electrical joining (Patent Document 1). . However, lead-free solder has a high melting point, and the mounting temperature is as high as 250 ° C. or higher. Therefore, the electronic component or the substrate may be thermally damaged, and it cannot be applied to all the electronic components and the substrate. Therefore, when using a substrate with poor heat resistance, such as PET, or when it must be bonded at a low temperature due to the heat resistance problem of the module, etc., bismuth and indium alloys that can be electrically bonded at a relatively low temperature Was used. However, bismuth has a problem in bonding strength and alloy brittleness, and an indium alloy has a problem in that it is expensive.

  On the other hand, silver paste that can be electrically joined at a relatively low temperature is used for mounting electronic components and modules that are unsuitable for soldering in terms of heat resistance, in order to prevent an increase in conduction resistance. Addition of a low melting point metal, a conductive filler, or metal nanoparticles to the silver paste is performed. Since metal nanoparticles have a large specific surface area and high reaction activity, they have the characteristic of low-temperature sintering that fuses at a low temperature compared to metal bulk. For example, in the case of silver nanoparticles, it is known that a fusion-bonding phenomenon occurs by heat treatment at about 200 ° C., which is much lower than the original melting point of 964 ° C., and exhibits the same level of conductivity as a metal bulk. However, there is a problem that conductivity and bonding strength are insufficient.

  In recent years, in order to prevent thermal damage due to heat generated by electronic components, there is a demand for a bonding material that not only causes a fusion bonding phenomenon by heat treatment at about 200 ° C. but also has high heat dissipation. Therefore, a metal bonding material in which an organic solvent such as saturated hydrocarbon having a cyclic structure is added to metal particles such as silver particles which are high heat dissipation materials is used, and the metal bonding material is sintered by heat treatment at about 200 ° C. In some cases, electronic components are mounted on a substrate.

  However, even with the metal bonding material, the bonding strength is still insufficient. Furthermore, with the above metal bonding material, it is difficult to control the thickness of the metal bonding material thinly during application, so heat released from electronic components and heat during sintering are likely to accumulate at the bonded portion, and heat dissipation is improved. There was a problem that it was not enough.

JP 2013-258399 A

  An object of this invention is to provide the metal joining material which is excellent in the electroconductivity of a junction part, has high joint strength after sintering, and can control the thickness of a junction part thinly in view of the said situation.

  An aspect of the present invention is a metal bonding material containing (A) metal particles and (B) an organic solvent having a boiling point of 243 ° C. to 275 ° C. and a vapor pressure of 25 ° C. of 0.010 Pa to 4.0 Pa. is there.

  An aspect of the present invention is the metal bonding material in which the organic solvent (B) is a glycol ether type. The “glycol ether type” means a chemical structure having a structure in which glycol is dehydrated and condensed as a main skeleton.

  In the aspect of the present invention, the (A) metal particles have (A1) first metal particles having an average primary particle size particle size distribution in the range of 100 nm to 6000 nm and (A2) an average primary particle size particle size distribution of 0. A metal bonding material comprising second metal particles in the range of 5 μm to 10 μm.

  An aspect of the present invention is a metal bonding material in which the (A1) first metal particles and the (A2) second metal particles are silver, a silver alloy, or copper coated with silver or a silver alloy.

  An aspect of the present invention is a metal bonding material in which (A1) the mass of the first metal particles: (A2) the mass of the second metal particles is 3: 7 to 7: 3.

  An embodiment of the present invention is a metal bonding material further comprising (C) a dispersant.

  An aspect of the present invention is an electronic component assembly in which an electronic component is mounted on a substrate using the metal bonding material.

  The electronic component is an electronic component assembly that is an LED element or a power device.

  According to the aspect of the present invention, the metal bonding material is blended with an organic solvent having a boiling point of 243 ° C. to 275 ° C. and a vapor pressure of 25 ° C. of 0.010 Pa to 4.0 Pa. Instead, the joint strength is excellent, and the thickness of the joint can be controlled thin. This is because the organic solvent does not volatilize over a long period of time not only when applied to a substrate or the like performed at room temperature, but bonds the electronic component and the substrate by a heat treatment of about 200 ° C. In this case, since the applied metal bonding material volatilizes smoothly, a good bonding strength can be obtained. Further, when a predetermined load is applied when the electronic component is mounted on the substrate, the bonding portion is desired. This is probably because the thickness can be adjusted. Therefore, the metal bonding material of the present invention is less likely to volatilize at the time of application and after application even at a small application amount, so that the junction can be made to have a desired thickness.

  According to the aspect of the present invention, when the organic solvent is a glycol ether, conductivity is further improved.

  According to an aspect of the present invention, (A) the metal particles are (A1) the first primary metal particles having an average primary particle size distribution in the range of 100 nm to 6000 nm and (A2) the average primary particle size distribution is By comprising the second metal particles in the range of 0.5 μm to 10 μm, the fusion bonding phenomenon occurs by heat treatment at about 200 ° C. with surely having mechanical bonding strength.

  According to the aspect of the present invention, since (C) the dispersant is further contained, separation of the metal particles and the organic solvent in the metal bonding material can be prevented, so that the metal bonding material is clogged at the discharge port of the coating apparatus. And uneven application amount can be suppressed. Accordingly, it is possible to perform fine and fine coating (for example, a size of about 100 μm to 200 μm) with high accuracy.

It is a figure explaining the temperature profile of the substrate surface which is a test piece.

  Next, the metal bonding material of the present invention will be described. The metal bonding material of the present invention contains (A) metal particles and (B) an organic solvent having a boiling point of 243 ° C. to 275 ° C. and a vapor pressure of 25 ° C. of 0.010 Pa to 4.0 Pa.

(A) Metal particles The metal particles are not particularly limited in terms of type and particle diameter as long as the particles are conductive powder. As a metal seed | species, the metal simple substance used for solder, such as gold | metal | money, silver, copper, platinum, palladium, nickel, bismuth, lead, indium, tin, zinc, titanium, aluminum, and antimony, and the said metal seed | species are contained, for example. Mention may be made of metal alloys. Among the above metal species, silver, a silver alloy, or copper coated with silver or a silver alloy is preferable from the viewpoint of conductivity and high heat dissipation. The said metal may be used individually and may be used in mixture of 2 or more types.

  The particle diameter of the metal particles is, for example, an average primary particle diameter of 10 nm to 10 μm, and since the specific surface area is large and the reaction activity on the particle surface is high, the electronic component is boarded at a heating temperature much lower than the original melting point of the metal. It is preferable to include metal particles having an average primary particle size of nano-order (that is, an average primary particle size of 10 nm or more and less than 1000 μm) from the point of being able to be electrically bonded to the metal, and good mechanical bonding strength by suppressing generation of voids. (A1) first metal particles having an average primary particle size distribution in the range of 100 nm to 6000 nm and (A2) particles having an average primary particle size distribution in the range of 0.5 μm to 10 μm. Particularly preferred are metal particles comprising 2 metal particles.

  In addition, the maximum peak primary particle diameter of each of the (A1) first metal particles and the (A2) second metal particles is not particularly limited. From the viewpoint of obtaining an excellent metal joint, (A1) the maximum peak primary particle diameter of the first metal particles is preferably 200 nm to 800 nm, and (A2) the maximum peak primary particle diameter of the second metal particles is 500 nm to 2200 nm is preferable. Further, (A1) Mass of the first metal particles: (A2) The mass of the second metal particles is not particularly limited, but it is 3: 7 from the viewpoint of forming a high-density joint by widening the particle size distribution. ~ 7: 3 is preferred.

  Further, the blending ratio of the metal particles as the component (A) can be appropriately selected. For example, the lower limit is 80% by mass in the metal bonding material from the viewpoint of obtaining a bonded portion having good conductivity. It is preferably included, and 90% by mass is particularly preferable. On the other hand, the upper limit of the blending ratio is preferably 96% by weight, particularly preferably 95% by weight, from the viewpoint of blending the organic solvent which is the component (B).

(B) Organic solvent having boiling points of 243 ° C. to 275 ° C. and 25 ° C. of vapor pressure of 0.010 Pa to 4.0 Pa Boiling points of 243 ° C. to 275 ° C. and vapor pressure of 25 ° C. of 0.010 Pa to 4.0 Pa By blending a certain organic solvent, when the metal bonding material of the present invention is used for bonding between metals, the bonding strength is excellent, and the thickness of the bonded portion can be controlled to be thin. The thickness of the bonded portion can be controlled thinly because the organic solvent is less likely to volatilize at room temperature (for example, 25 ° C.), so that the metal bonding material is applied after applying the metal bonding material to the substrate or the like performed at room temperature. This is presumably because the paste can be maintained at room temperature for a long time, and the applied metal bonding material can be adjusted to a desired thickness by applying a predetermined load when an electronic component or the like is mounted on a substrate. Further, the bonding strength is excellent when the heat treatment (for example, about 200 ° C.) is performed in a state where the metal bonding material is maintained in a paste state when bonding an electronic component or the like to the substrate. This is thought to be due to volatilization smoothly.

Examples of the organic solvent include compounds having a hydroxyl group, an ester bond, and / or an ether structure. Specific examples of the organic solvent include diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, and diethylene glycol monoethyl hexyl ether. C ₉ -C ₁₄ acyclic aliphatic monoalcohols such as C ₈ -C ₁₄ glycol ethers, such as nonan-1-ol, dodecan-1-ol, tetradecan-1-ol, etc., pentanediol, C ₅ -C ₇ straight chain aliphatic dialcohols such as hexanediol and heptanediol, etc., having branched chains such as 2-ethyl-1,3-hexanediol and 2,5-dimethyl-2,5-hexanediol C ₆ -C ₉ aliphatic dialcohols acyclic and the like. In addition, examples of the compound having no hydroxyl group include esters such as diethylene glycol monobutyl ether acetate and esters of the above glycol ethers with acrylic acid or methacrylic acid. These compounds may be used alone or in combination of two or more.

  The blending ratio of the organic solvent having a boiling point of 243 ° C. to 275 ° C. and a vapor pressure of 25 ° C. of 0.010 Pa to 4.0 Pa can be selected as appropriate. For example, the lower limit value provides good bonding strength. From the viewpoint, it is preferable that 2.0% by mass is contained in the metal bonding material, and 4.0% by mass is particularly preferable. On the other hand, the upper limit of the blending ratio is preferably 20% by mass, particularly preferably 10% by mass, from the viewpoint of preventing a decrease in bonding strength.

(C) Dispersant In this invention, you may mix | blend (C) a dispersant as needed. By blending the dispersion medium, separation of the metal particles and the organic solvent in the metal bonding material can be prevented, so that clogging of the metal bonding material at the discharge port of the coating apparatus and uneven application amount can be suppressed.

  The dispersing agent is not particularly limited, and examples thereof include acrylic alcohols, methacrylic copolymers, sugar alcohols such as sorbitol, and fluorine. Among these, a fluorine-based dispersant is preferable because it is excellent in preventing separation between metal particles and an organic solvent and can maintain low-temperature sinterability of the metal bonding material.

  Further, among the fluorine-based dispersants, the separation of the metal particles and the organic solvent is surely prevented, and even in a fine discharge device with a nozzle diameter of 100 to 200 μm such as a dispenser, clogging in the nozzle is prevented, and the minute amount is small. From the point that the coating amount of metal particles can be made uniform even with the supply amount, the following general formula (I)

(Wherein R ¹ , R ² , R ³ , and R ⁴ each independently represent F, CF ₃ , C ₂ CF ₅ , and C ₃ F ₇ ), the above general formula ( A compound having a main skeleton of an oligomer of the compound represented by I) or an oligomer of the compound represented by the general formula (I) is preferable, and the compound represented by the general formula (I) is hexafluoropropene or Hexafluoropropene trimer is particularly preferred. The “compound oligomer represented by the general formula (I)” means a polymer in which 2 to 100 compounds represented by the general formula (I) are bonded. These compounds may be used alone or in combination of two or more.

  The mixing ratio of the dispersing agent can be selected as appropriate. For example, the lower limit value is 0.3% by mass in the metal bonding material from the viewpoint of suppressing clogging of the metal bonding material and uneven application amount. It is preferably 0.4% by mass. On the other hand, the upper limit of the blending ratio is preferably 2.0% by mass, and particularly preferably 1.0% by mass from the viewpoint of preventing a decrease in bonding strength.

  In the metal bonding material of the present invention, a conventional additive may be appropriately blended depending on the application. Examples of the additive include a gloss imparting agent, a metal corrosion inhibitor, a stabilizer, a fluidity improver, a thickener, a viscosity modifier, a moisturizer, an antifoaming agent, a disinfectant, and a filler. . These additives may be used alone or in combination of two or more.

  Next, the manufacturing method of the metal joining material of this invention is demonstrated. The method for producing the metal bonding material of the present invention is not particularly limited. For example, after the above-mentioned components (A) and (B) and other components are blended at a predetermined ratio as required, three at room temperature are mixed. It can be produced by kneading or mixing with a kneading means such as a roll, a ball mill or a sand mill, or a stirring means such as a super mixer or a planetary mixer.

  Next, application examples of the metal bonding material of the present invention will be described. The metal bonding material of the present invention can be widely used as a material for metal bonding between parts, for example, a high-brightness LED that is required to be mounted at a low temperature of 200 ° C. or lower and to reduce the thickness of the bonding portion. Can be used as a conductive bonding material for electrically and physically bonding an electronic component to a wiring board, such as a material for mounting the substrate on a substrate or a material for bonding a power device to the substrate.

  Next, usage examples of the metal bonding material of the present invention will be described. When the metal bonding material of the present invention is used as a conductive bonding material, for example, a predetermined amount of the metal bonding material of the present invention is applied to a position where an electronic component (semiconductor, etc.) on the substrate is bonded. After placing the electronic component on the material, the electronic component is bonded onto the substrate by baking. The method for applying the metal bonding material is not particularly limited, and examples thereof include a screen printing method, a dispenser method, and an ink jet method. The application amount of the metal bonding material can be selected as appropriate, and for example, it is applied with a thickness of 1 to 20 μm and a width of 100 to 1000 μm. The firing temperature is not particularly limited as long as the metal particles are fused to each other and sintered. For example, the metal particles include metal particles having an average primary particle diameter of nano-order, and the metal species is copper. Or in the case of silver, it is 180-230 degreeC, Preferably it is 190-210 degreeC. Moreover, baking time can be selected suitably and is 30 to 120 minutes, for example.

  Next, the metal bonding material of the present invention will be described in more detail using examples. However, the metal bonding material of the present invention is not limited to the embodiments shown below.

Examples 1-6, Comparative Examples 1-5
Each component shown in the following Table 1 is blended in the blending ratio shown in the following Table 1, mixed and dispersed by three rolls, and used in Examples 1 to 6 and Comparative Examples 1 to 5 in a paste-like metal joint. The material was prepared. And the prepared metal joining material was apply | coated to the board | substrate as follows, and the test piece was produced. In addition, the numerical value of the mixture ratio in Table 1 shows a mass part, and the "-" part of a mixture ratio means 0 mass part.

Firing conditions Firing: 200 ° C., 60 min, heating rate 0.8 ° C./min
The substrate surface temperature was baked with the reflow simulator “SMT Scope SK-5000” manufactured by Sanyo Seiko under the temperature condition of the profile shown in FIG.

Evaluation (1) Volume resistivity On the slide glass, the paste of the metal bonding material prepared as described above was applied in the form of a thin film by screen printing on an area of 5 cm × 1 cm using a 50 μm-thick metal mask, and the above firing was performed. The thin film was fired under the conditions, and the obtained fired thin film was subjected to a four-probe method according to JIS K 7194, and “Lorestar GP” manufactured by Mitsubishi Chemical Analytech Co., Ltd. Was measured.

(2) Joint shear strength Using a Nordson EFD dispenser device “DISPENSER ULTIMUS V 100PSI” on a 10 mm × 10 mm × 1 mm thick Au / Ni plated Cu substrate degreased with ethyl acetate, the diameter is 150 to 250 μm, and the mass is 8 A metal bonding material was applied (discharged) to ˜12 μg, and a 1 mm × 1 mm Au / Ni plated Si dummy chip was mounted using a chip mounter “YV100Xg” manufactured by YAMAHA. Next, after firing under the above firing conditions, the shear strength was measured at a rate of 83.3 μm / sec (5 mm / min) using a bond tester “DAGE4000” manufactured by Nordson DAGE.
The results were evaluated in three stages: ◯: chip shear strength of 40 MPa or more, Δ: chip shear strength of 20 MPa or more and less than 40 MPa, and X: chip shear strength of less than 20 MPa.

(3) Bonding shear strength after drying in the air (drying property)
After applying (discharging) the metal bonding material in (2) above and before mounting the dummy chip, it is left for 1 hour in an environment of 25 ° C. and 55% humidity, and then the same process as in (2) above Then, the shear strength was measured in the same manner as in the above (2) for the sample that was mounted with a dummy chip and fired.
The results were evaluated in three stages: ◯: chip shear strength of 40 MPa or more, Δ: chip shear strength of 20 MPa or more and less than 40 MPa, and X: chip shear strength of less than 20 MPa.

(4) Separability About 2 g of metal bonding material was measured in a 10 cc glass bottle, centrifuged at 2000 rpm for 1 min, and it was visually confirmed whether solid-liquid separation had occurred.
The results are as follows: ○: no liquid floating is observed, no separation occurs, Δ: liquid is floating on the surface, x: liquid is separated so that the liquid that floats when it is tilted 3 Rated by stage.

(5) Bonding thickness A test piece produced in the same manner as in (3) above was sealed with an epoxy resin, and a cross-section was obtained by mechanical polishing, followed by JEOL FE-SEM “JSM-7001F”. The joining portion was observed and the thickness of the metal joining material was measured.
The results were evaluated in three stages: ◯: junction thickness of 10 ± 2 μm, Δ: junction thickness of 13 to 40 μm, and x: junction thickness of more than 40 μm.

(6) Time for maintaining initial characteristics (drying time)
In the item (3), the time during which the metal bonding material can maintain the initial paste state was visually observed.

  Each evaluation result about Examples 1-6 and Comparative Examples 1-5 is shown in the following Table 1. The boiling point of the organic solvent used in the examples and the vapor pressure at 25 ° C. are shown in Table 2 below.

  As shown in Tables 1 and 2, in Examples 1 to 6 using an organic solvent having a boiling point of 243 ° C. to 272 ° C. and a vapor pressure of 0.013 Pa to 3.9 Pa at 25 ° C., the value of volume resistivity is Reduced to 5.0 Ω · cm or less, that is, the bonding thickness can be reduced to 10 ± 2 μm without impairing conductivity, and the time that the metal bonding material can maintain the initial paste state is 1 hour or more. After that, the paste state could be maintained for a long time. Furthermore, in Examples 1 to 6, in which the bonding thickness and the time during which the initial characteristics can be maintained (drying time) are good, both the bonding shear strength and the bonding shear strength after being left in the atmosphere are as good as 40 MPa or more, and firing immediately after coating. However, in any case, the bonded portion excellent in mechanical strength could be formed even after baking after application.

  From Example 1 and Example 3, when a glycol ether system is used as an organic solvent having a boiling point of 243 ° C. to 272 ° C. and a vapor pressure of 25 ° C. of 0.013 Pa to 3.9 Pa, the conductivity tends to be further improved. there were. Further, from Examples 1 to 5 and Example 6, when a fluorine-based dispersant whose main skeleton is hexafluoropropene is used as the (C) dispersant, solid-liquid separation further occurs in the metal bonding material. And good dispersibility was obtained.

  On the other hand, when an organic solvent other than an organic solvent having a boiling point of 243 ° C. to 272 ° C. and a vapor pressure of 0.013 Pa to 3.9 Pa is used from Comparative Examples 1 to 5, the junction thickness is 13 μm or more. As a result, the time during which the initial characteristics can be maintained (drying time) has also been shortened to 30 minutes or less. Further, in Comparative Examples 1 to 5, the shear strength, particularly the joint shear strength after being left in the air, was lowered to less than 40 MPa. Further, from Comparative Example 5, when a sorbitol-based dispersant was used, it was possible to prevent the occurrence of solid-liquid separation in the metal bonding material, and good dispersibility was obtained, but the bonding thickness exceeded 40 μm and the initial characteristics were improved. The time that can be maintained (drying time) was also 10 minutes or less, and both the joint shear strength and the joint shear strength after being left in the air were reduced to less than 20 MPa.

  The metal bonding material of the present invention has excellent bonding portion conductivity and high bonding strength after sintering. Therefore, it is widely used as a bonding agent for bonding between metals, for example, to substrates of semiconductor components such as LED elements and power devices. In addition, the metal bonding material of the present invention can control the thickness of the bonding portion to be thin, so that mounting of a high-luminance LED element that requires high heat dissipation at the bonding portion with the substrate is possible. Available in the field.

Claims (8)

  A metal bonding material comprising (A) metal particles and (B) an organic solvent having a boiling point of 243 ° C. to 275 ° C. and a vapor pressure of 25 ° C. of 0.010 Pa to 4.0 Pa.   The metal bonding material according to claim 1, wherein the organic solvent (B) is a glycol ether type.   The (A) metal particles are (A1) first metal particles having an average primary particle size distribution in a range of 100 nm to 6000 nm and (A2) a particle size distribution of an average primary particle size in a range of 0.5 μm to 10 μm. The metal bonding material according to claim 1, wherein the metal bonding material comprises the second metal particles.   The metal bonding material according to claim 3, wherein the (A1) first metal particles and the (A2) second metal particles are silver, a silver alloy, or copper coated with silver or a silver alloy.   The metal bonding material according to claim 3 or 4, wherein (A1) the mass of the first metal particles: the mass of the (A2) second metal particles is 3: 7 to 7: 3.   The metal bonding material according to claim 1, further comprising (C) a dispersant.   An electronic component assembly in which an electronic component is mounted on a substrate using the metal bonding material according to any one of claims 1 to 6.   The electronic component assembly according to claim 7, wherein the electronic component is an LED element or a power device.

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