阅读说明：本技术 一种预成型焊料及其制备方法 (Preformed solder and preparation method thereof ) 是由 贺会军 赵朝辉 *** 张敬国 朱捷 林卓贤 张江松 张焕鹍 卢茂成 卢彩涛 张 于 2019-08-27 设计创作，主要内容包括：本发明涉及一种预成型焊料及其制备方法。一种预成型焊料,包括预成型金属基体和包覆于所述基体外表面的纳米颗粒膜；所述纳米颗粒膜主要含纳米金属颗粒,并且所述纳米金属颗粒的熔点低于所述金属基体的熔点。本发明降低了焊料烧结过程中溶剂挥发形成的孔隙率,降低了导热损失,提高了焊接可靠性。(The invention relates to a preformed solder and a preparation method thereof. A preformed solder comprises a preformed metal matrix and a nanoparticle film coated on the outer surface of the matrix; the nanoparticle film contains mainly metal nanoparticles, and the melting point of the metal nanoparticles is lower than that of the metal matrix. The invention reduces the porosity formed by solvent volatilization in the solder sintering process, reduces the heat conduction loss and improves the welding reliability.)

1. A preformed solder is characterized by comprising a preformed metal matrix and a nanoparticle film coated on the outer surface of the matrix; the nanoparticulate membrane mainly contains nanoparticulate, and the melting point of the nanoparticulate is lower than the melting point of the preformed metal matrix.

2. The solder preform of claim 1, wherein the nano-metal particles are nano-copper particles or nano-silver particles.

3. The solder preform of claim 1, wherein the material of the pre-formed metal matrix is silver, nickel, copper-based metal;

preferably, the preformed metal matrix is in the form of a sheet, strip or cylinder.

4. The solder preform of any of claims 1-3, wherein the nanoparticle film further comprises a modifier comprising at least one of a dispersant, a resin, and an organic acid;

the dispersant is preferably at least one of hydrogenated castor oil and polyamide;

the resin is preferably at least one of rosin and modified rosin, more preferably at least one of hydrogenated rosin and polymerized rosin;

the organic acid is preferably a solid organic acid, more preferably at least one of succinic acid, adipic acid, glutaric acid, salicylic acid and pimelic acid;

preferably, the weight ratio of the dispersant, the resin and the organic acid is 1-5: 5-15: 2 to 6.

5. The solder preform of claim 1, wherein the nano-metal particles have a particle size of 300nm or less.

6. A method of making a solder preform as claimed in claims 1 to 5, characterised in that it comprises the steps of:

coating slurry containing nano metal particles on the surface of a preformed metal matrix, and then drying to form a nano particle film;

when the nanoparticle film contains a modifier, it is added in its entirety to the slurry.

7. The method according to claim 6, wherein the slurry further contains an organic solvent, preferably at least one of alcohol, ketone and ester, preferably at least one of ethanol, isopropanol, acetone and ethyl acetate.

8. The method of claim 7, wherein the concentration of the nano-metal particles in the slurry is 40-90 wt.%.

9. The production method according to claim 7, wherein when the slurry contains the dispersant, the resin, and the organic acid, the weight ratio of the organic solvent to the dispersant to the resin to the organic acid is 74 to 92: 1-5: 5-15: 2 to 6.

10. The method for preparing according to claim 7, wherein the slurry is obtained by: all raw materials of the slurry are sheared and mixed, and the shearing speed is more than 6000 rpm.

Technical Field

The invention relates to the field of materials, in particular to a preformed solder and a preparation method thereof.

Background

The power semiconductor device IGBT is a core technology in applications such as rail transit, smart grid, aerospace, electric vehicle, new energy equipment, and industrial fields, and is called a "CPU" of a power electronic device. In recent years, with the progress of the IGBT towards intellectualization and miniaturization, the power density of the device is gradually increased, and the heat flux of the device during operation is also increased. If the heat cannot be rapidly discharged, the junction temperature of the semiconductor chip can rapidly rise, permanent damage can be caused to the power semiconductor device, and the power semiconductor device can fail.

The connection of the IGBT module chip is to realize the interconnection of the power semiconductor chip and the substrate through the connecting material, and the connecting layer of the chip and the substrate is the most important ring for providing necessary functions of heat dissipation, electric conduction, and mechanical support. At present, materials commonly used for the connecting layer comprise Sn-based soldering paste or soldering lug, and nano silver paste is required to be used for products with high temperature resistance requirements. Sn-based solders such as Sn-Ag and Sn-Ag-Cu have melting points of less than 300 ℃ and cannot be used in high-power devices and high-temperature environments. The volatilization of the solvent of the nano silver slurry in the sintering process can form pores in the sintering layer, thereby greatly reducing the heat conductivity of the sintering layer and causing hidden danger to the reliability of the product.

Disclosure of Invention

The first purpose of the invention is to provide a preformed solder, which reduces the porosity formed by solvent volatilization in the sintering process of the solder, reduces the heat conduction loss and improves the welding reliability.

The second purpose of the present invention is to provide a method for preparing the solder preform, which can modify the conventional metal solder through a simple process to achieve the effect of improving the thermal conductivity.

In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

a preformed solder comprises a preformed metal matrix and a nanoparticle film coated on the outer surface of the matrix; the nanoparticulate membrane mainly contains nanoparticulate, and the melting point of the nanoparticulate is lower than the melting point of the preformed metal matrix.

The invention adds a layer of nano-particle film on the surface of the preformed metal matrix, and can achieve the following technical effects:

the nano-particle film is pre-baked and coated on the pre-formed surface, so that a compact particle film can be obtained, and compared with the existing nano-silver slurry, the porosity formed during welding (or sintering) is low, the heat conduction loss is less, and the welding reliability is higher.

The preformed metal matrix of the present invention may be any simple metal or alloy suitable for use in a solder. Since the metal matrix is mainly used as the core material of the preformed solder and is the main heat conducting medium, it is preferable to use a metal with a high melting point, such as (Ag, Ni, Cu), to meet the requirements of the IGBT for use in high power and high temperature environments. If the solder is used for other purposes, a suitable metal substrate is selected as required. The application of the solder preform is not limited, and the solder preform can be used not only as a connection layer in an IGBT, but also as an encapsulation layer, a heat conduction layer, and the like of other electronic devices or optical elements.

The preforming in the invention refers to the shape of the metal matrix which is preformed in advance, and refers to the shape of the solder for standby, namely the preformed metal matrix is coated by the nano-particle film and then is directly used without changing the size or the shape through the procedures of cutting and the like.

The nano metal particles described in the present invention may be any metal as long as it satisfies a melting point lower than that of the metal matrix. The metal type of the metal matrix is the same as or different from that of the nano metal particles, and when the metal type of the metal matrix is the same as that of the nano metal particles, the melting point of the nano metal particles is lower than that of the metal matrix inevitably due to the nano effect. In terms of material availability, cost, and the like, the nano metal particles are preferably nano Cu particles or nano Ag particles.

The preformed metal matrix is in a sheet shape, a strip shape, a column shape or other irregular shapes, so that the nano metal particles can be coated and attached conveniently.

The particle size of the nano metal particles is preferably less than or equal to 300 nm.

The nanoparticle film preferably further contains at least one of a dispersant, a resin, and an organic acid. The dispersing agent can uniformly disperse the nano metal particles and avoid agglomeration. The resin can be uniformly coated on the surface of the nano-particles, so that the nano-particles can be dispersed and protected, and the long-term storage of the solder at normal temperature can be ensured. The organic acid can remove oxide layers on the surfaces of the nano particles and the substrate in the process of sintering the solder.

The dispersant is preferably at least one of hydrogenated castor oil and polyamide.

The resin is preferably at least one of rosin and modified rosin, and is preferably at least one of hydrogenated rosin and polymerized rosin.

The organic acid is preferably a solid organic acid, preferably at least one of succinic acid, adipic acid, glutaric acid, salicylic acid and pimelic acid, such as succinic acid, adipic acid, glutaric acid, salicylic acid or pimelic acid, or a mixture of adipic acid and glutaric acid, or a mixture of succinic acid and glutaric acid, or the like.

Preferably, the weight ratio of the dispersant, the resin and the organic acid is 1-5: 5-15: 2 to 6.

The invention also provides a preparation method of the preformed solder, which comprises the following steps:

coating slurry containing nano metal particles on the surface of a preformed metal matrix, and then drying to form a nano particle film; when the nanoparticle film contains a modifier, it is added in its entirety to the slurry.

The method mainly relates to two procedures of coating and drying, and does not need complex or expensive equipment.

The slurry for coating of the invention at least contains an organic solvent to dilute the nanoparticles; if the organic vehicle contains a modifier, the organic solvent also serves to dissolve the modifier.

The organic solvent is preferably at least one of alcohol, ketone and ester, mainly lower alcohol, ketone and ester, more preferably at least one of ethanol, isopropanol, acetone and ethyl acetate, such as ethanol, isopropanol, acetone or ethyl acetate, or a mixture of ethanol and acetone, or a mixture of isopropanol and ethyl acetate, or a mixture of ethanol and ethyl acetate; the above mixing refers to mixing in any proportion.

The concentration of the nano-metal particles in the slurry according to the present invention is determined according to the requirements of fluidity, film compactness, cost, etc., and considering the above, any value in the range of 40-90 wt.% is preferred, such as 40 wt.%, 45 wt.%, 50 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, 70 wt.%, 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.%, etc.

Preferably, when the slurry contains a dispersant, a resin and an organic acid, the weight ratio of the organic solvent, the dispersant, the resin and the organic acid is preferably 74-92: 1-5: 5-15: 2-6, preferably 82-92: 1-4: 5-10: 2-4, for example 74:5:15:6, 76:3:15:6, 80:5:9:6, 89:2.5:5:1.5, 92:1:5:2, 80:4:10:4, and the like.

The metal substrate may also be cleaned prior to the coating.

Preferably, the drying is drying until the organic solvent is removed. For ethanol, isopropanol, acetone and ethyl acetate, the temperatures typically required are: 50-80 ℃.

Preferably, the slurry is obtained by: all raw materials of the slurry are sheared and mixed, and the shearing speed is more than 6000 rpm.

In summary, compared with the prior art, the invention achieves the following technical effects:

(1) the solder of the invention takes a metal matrix as a core and nano metal particles as a film, and simultaneously realizes the purposes of sintering at low melting point and stable connection at high temperature: the characteristic of low melting point of the nano particles is utilized, sintering interconnection at low temperature can be realized, and the formed sintering layer has high melting point of metal and can meet the use requirements of an IGBT (insulated gate bipolar translator) in high-power and high-temperature environments;

(2) the nano-particle film is pre-baked and coated on the pre-formed surface, so that a compact particle film can be obtained, and compared with the existing nano-silver slurry, the porosity formed during welding (or sintering) is low, the heat conduction loss is less, and the welding reliability is higher.

(3) The dispersant added in the nano-particle film is beneficial to the uniformity of the quality and performance of the solder;

(4) the resin added in the nano-particle film plays a role in protecting and fixing the nano-metal particles;

(5) the organic acid added into the nano-particle film can assist in removing an oxide layer of a welded interface;

(6) the slurry coated on the surface of the metal matrix is dried before application, which is beneficial to improving the density of the nano-particles on the matrix.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.