Active metal soldering paste and its preparation method

Abstract

This invention discloses an active metal brazing paste and its preparation method. The active metal brazing paste is characterized by comprising brazing powder and a binder, wherein the binder component accounts for 8-20% by mass. The brazing powder comprises the following components by mass percentage: 10-30% nano-silver powder; 60-80% silver-copper alloy powder; 5-10% aluminum-silicon alloy powder / titanium-aluminum alloy powder; 2-5% titanium hydride powder. The binder comprises the following components by mass fraction: 75-90% solvent; 5-10% thickener; 2-4% surfactant; 1-2% dispersant; 2-5% thixotropic agent. Compared with the prior art, the active metal brazing paste of this invention has the following beneficial effects: the ceramic copper-clad laminate prepared by the active metal brazing paste has high connection reliability and excellent resistance to thermal cycling.

Description

Technical Field

[0001] This invention relates to the field of ceramic copper-clad laminate technology, specifically to active metal solder paste and its preparation method. Background Technology

[0002] In the prior art:

[0003] Application publication number CN104409425A discloses a high thermal conductivity silicon nitride ceramic copper-clad laminate and its preparation method, relating to the field of copper-clad laminate manufacturing technology. It can achieve bonding with thick copper substrates; its thermal conductivity is 3-4 times that of alumina ceramic substrates, significantly improving the heat dissipation performance of the substrate; the active copper bonding process used has higher interfacial bonding strength, fewer voids, and higher reliability compared to direct copper cladding. Therefore, it features high strength, high thermal conductivity, and high reliability.

[0004] Application publication number CN114394838A discloses a high-breakdown-strength high-frequency copper-clad substrate and its preparation method. The silicon nitride ceramic copper-clad substrate incorporates polystyrene-modified BaTiO3 and is doped with neodymium oxide to promote the phase transition of barium titanate nanoparticles, contributing to superior dielectric and breakdown performance. Simultaneously, it is modified with Eu2O3, a filler with high breakdown strength, to mitigate the reduction in breakdown strength caused by the doping of high-dielectric-constant fillers. The ceramic substrate coated with active metal solder paste is placed in a malic acid reaction solution, where malic acid chemically etches the active metal solder, inhibiting the formation of oxides on the solder surface and thus improving solderability with the ceramic.

[0005] As IGBT modules develop towards higher voltage and higher power, the requirements for the heat dissipation capacity and reliability of IGBT module packaging materials are also increasing. However, the coefficients of thermal expansion of ceramic and copper foil differ significantly. After the connection is completed, a large residual stress will be generated at the sealing interface. Furthermore, the thermal cycling of the ceramic copper-clad laminate during use will further lead to the accumulation of residual stress, resulting in a decrease in the bonding strength and resistance to thermal cycling of the copper-clad laminate.

[0006] In summary, this invention provides an active metal solder paste and its preparation method. Applying this active metal solder paste to ceramic substrates can solve the problems of low connection reliability and poor resistance to thermal cycling in current ceramic copper-clad laminates. Summary of the Invention

[0007] The purpose of this invention is to provide an active metal solder paste and its preparation method. The active metal solder paste prepared by this method is applied to the structure of copper-clad ceramic, forming a copper-ceramic substrate-copper "sandwich" structure. The copper-clad ceramic board prepared by the active metal solder paste of this invention has low void ratio, high peel strength, and in the thermal shock test, the copper layer does not separate after 5000 cycles of thermal cycling at a temperature of -50 to 150°C, with high and low temperature holding for 30 minutes each and a conversion time of 15 seconds.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] An active metal brazing paste includes brazing powder and a binder, wherein the binder component accounts for 8-20% by mass;

[0010] in,

[0011] The brazing powder comprises the following components by weight percentage: 10-30% nano silver powder; 60-80% silver-copper alloy powder; 5-10% aluminum-silicon alloy powder / titanium-aluminum alloy powder; and 2-5% titanium hydride powder.

[0012] The binder comprises the following components by mass fraction: 75-90% solvent; 5-10% thickener; 2-4% surfactant; 1-2% dispersant; and 2-5% thixotropic agent.

[0013] As a further improvement to this solution, the solvent is any one or more of terpineol, diethylene glycol butyl ether, and diethylene glycol butyl ether acetate.

[0014] As a further improvement to this solution, the thickener is ethyl cellulose, modified rosin resin, etc.

[0015] As a further improvement to this solution, the surfactant is a fatty alcohol polyoxyethylene ether.

[0016] As a further improvement to this scheme, the dispersant is tributyl phosphate.

[0017] As a further improvement to this solution, the thixotropic agent is modified hydrogenated castor oil.

[0018] As a further improvement to this solution, the nano silver powder, silver-copper alloy powder, aluminum-silicon alloy powder / titanium-aluminum alloy powder, and titanium hydride powder are all spherical powders.

[0019] The nano silver powder has a particle size of 50-100 nm, the silver-copper alloy powder has a particle size of 5-20 μm, the aluminum-silicon alloy powder / titanium-aluminum alloy powder has a particle size of 5-20 μm, and the titanium hydride powder has a particle size of 5-10 μm.

[0020] A method for preparing an active metal brazing ceramic copper-clad laminate includes the following preparation steps:

[0021] S1 material cleaning

[0022] The ceramic substrate and oxygen-free copper foil are gradually subjected to acid washing, alcohol washing, and water washing, and then dried with a fan for later use.

[0023] S2 Printed Soldering Paste

[0024] The prepared active metal solder paste according to any one of claims 1 to 7 is printed on both sides of a ceramic substrate using screen printing technology, wherein the solder paste is composed of solder powder and binder, wherein the binder component accounts for 8 to 20%.

[0025] S3 Solvent Drying

[0026] The S2-printed ceramic substrate is placed in a drying oven to remove organic solvents.

[0027] S4 Vacuum Sintering

[0028] The copper foil and the ceramic substrate obtained in S3 are bonded together on both sides to form a copper-ceramic substrate-copper "sandwich" structure. The structure is then placed in a vacuum furnace for sintering to obtain a ceramic copper-clad laminate.

[0029] As a further improvement to this solution, the process conditions for cleaning the materials described in S1 are as follows: The ceramic substrate is cleaned in 10% nitric acid for 30 minutes, then ultrasonically cleaned in ethanol for 10 minutes, followed by rinsing with water for 2 minutes and drying with a fan. The copper foil is cleaned in 10% sulfuric acid for 30 minutes, then ultrasonically cleaned in ethanol for 10 minutes, followed by rinsing with water for 2 minutes and drying with a fan.

[0030] As a further improvement to this scheme, the preparation method of the active metal brazing paste in S2 is to mix the brazing powder and binder evenly, and then roll them through a three-roll mill to obtain a paste.

[0031] As a further improvement to this solution, the solvent drying process conditions described in S3 are: drying temperature of 100℃ and drying time of 12min.

[0032] As a further improvement to this scheme, the vacuum sintering process conditions described in S4 are: sintering temperature of 800–830℃ and vacuum degree of 10. -4 ~10 -2 Pa.

[0033] The active metal brazing ceramic copper-clad laminate prepared by this invention has the following advantages compared with the prior art:

[0034] 1. This invention introduces nano-silver powder with a high specific surface area. It has high surface energy, high sintering activity, and requires significantly less internal energy to melt. When using silver-copper-titanium active metal brazing paste for sealing, titanium has a greater affinity for copper than silver, resulting in a large portion of titanium existing in the copper-rich phase. However, titanium in the copper-rich phase typically does not wet the ceramic substrate during brazing. The addition of nano-silver powder promotes the release of titanium from the copper-rich phase, thereby increasing the activity of the silver-copper-titanium active metal brazing paste, resulting in a denser sintered structure and reducing interfacial porosity.

[0035] 2. The aluminum-silicon alloy powder / titanium-aluminum alloy powder introduced in this invention does not consume the active elements in the brazing filler metal and is uniformly distributed in the brazing layer, which is beneficial to the interfacial reaction during the brazing process and plays a role in dispersion strengthening. Since the coefficients of thermal expansion of ceramic and copper foil differ significantly, a large residual stress will be generated at the sealing interface after the connection is completed. Adding functionally graded materials such as aluminum-silicon alloy powder / titanium-aluminum alloy powder between the two creates a coordinated gradient of thermal expansion coefficients between the ceramic-active metal brazing layer-copper, improving the bonding strength of the copper-clad laminate.

[0036] 3. As one of the most important process parameters in brazing, brazing temperature directly affects the interfacial reaction between the filler metal and the base material, thus affecting the joint strength. High brazing temperatures lead to excessively vigorous reactions between the filler metal and the base material, resulting in a coarse interfacial layer and a decrease in the mechanical properties of the joint. The sintering temperature of this invention is 50–80°C lower than conventional sintering temperatures. This allows the active element titanium to diffuse fully, continuously accumulate on the ceramic surface, and react with the base material to form a dense and continuous reaction layer, improving the connection reliability of the copper-clad laminate. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described below in conjunction with embodiments 1 to 8:

[0038] Examples 1, 2, and the comparative examples present four different modified material formulations. The raw materials used in each example, including micron-sized silver powder and other powders, were supplied by Zhongke Yannuo (Beijing) Technology Co., Ltd.

[0039] In this embodiment, the thickness of the brazing layer is represented by the wet weight. The brazing is applied evenly during the printing process, and the thickness of the active metal brazing paste 30 is controlled to be 3 μm.

[0040] The copper foil 10 has dimensions of 136×188 mm and a thickness of 0.30 mm.

[0041] Example 1

[0042] S1 material cleaning

[0043] The silicon nitride ceramic substrate was cleaned in 10% nitric acid for 30 minutes, then ultrasonically cleaned in ethanol for 10 minutes, followed by rinsing with water for 2 minutes and drying with a fan. The copper foil was cleaned in 10% sulfuric acid for 30 minutes, then ultrasonically cleaned in ethanol for 10 minutes, followed by rinsing with water for 2 minutes and drying with a fan.

[0044] S2 Printed Soldering Paste

[0045] Weigh 20 wt% nano silver powder, 70 wt% silver-copper alloy powder, 7 wt% aluminum-silicon alloy powder, and 3 wt% titanium hydrogenation powder, and mix them evenly in a container to prepare brazing powder. Weigh 52 wt% terpineol, 20 wt% diethylene glycol butyl ether, and 15 wt% diethylene glycol butyl ether acetate separately and mix them as a solvent. Heat to 70°C, then add 4 wt% ethyl cellulose and 2 wt% modified rosin resin and stir evenly until completely dissolved. Cool to 55°C, then add 2.5 wt% fatty alcohol polyoxyethylene ether, 1.5 wt% tributyl phosphate, and 3 wt% modified hydrogenated castor oil and stir evenly. Allow to cool. Mix the prepared brazing powder with a binder evenly to obtain active metal brazing paste. Use screen printing technology to print the prepared active metal brazing paste onto a silicon nitride ceramic substrate on both sides.

[0046] S3 Solvent Drying

[0047] After the solder paste was printed, the silicon nitride ceramic substrate was placed in a drying oven to remove the organic solvent. The drying temperature was 100℃ and the drying time was 12 minutes.

[0048] S4 Vacuum Sintering

[0049] A copper-ceramic substrate-copper "sandwich" structure was formed by double-sided lamination of copper foil and dried silicon nitride ceramic substrate, followed by sintering in a vacuum furnace at a temperature of 800℃ and a vacuum degree of 10. -4 Pa yielded a silicon nitride ceramic copper-clad laminate.

[0050] Example 2

[0051] S1 material cleaning

[0052] The aluminum nitride ceramic substrate was cleaned in 10% nitric acid for 30 minutes, then ultrasonically cleaned in ethanol for 10 minutes, followed by rinsing with water for 2 minutes and drying with a fan. The copper foil was cleaned in 10% sulfuric acid for 30 minutes, then ultrasonically cleaned in ethanol for 10 minutes, followed by rinsing with water for 2 minutes and drying with a fan.

[0053] S2 Printed Soldering Paste

[0054] Weigh 18 wt% nano silver powder, 70 wt% silver-copper alloy powder, 8 wt% titanium-aluminum alloy powder, and 4 wt% titanium hydrogenation powder, and mix them evenly in a container to prepare brazing powder. Weigh 52 wt% terpineol, 20 wt% diethylene glycol butyl ether, and 15 wt% diethylene glycol butyl ether acetate separately and mix them as a solvent. Heat to 70°C, then add 4 wt% ethyl cellulose and 2 wt% modified rosin resin and stir evenly until completely dissolved. Cool to 55°C, then add 2.5 wt% fatty alcohol polyoxyethylene ether, 1.5 wt% tributyl phosphate, and 3 wt% modified hydrogenated castor oil and stir evenly. Allow to cool. Mix the prepared brazing powder with the binder evenly to obtain active metal brazing paste. Use screen printing technology to print the prepared active metal brazing paste onto an aluminum nitride ceramic substrate on both sides.

[0055] S3 Solvent Drying

[0056] After the solder paste was printed, the aluminum nitride ceramic substrate was placed in a drying oven to remove the organic solvent. The drying temperature was 100℃ and the drying time was 12 minutes.

[0057] S4 Vacuum Sintering

[0058] Copper foil was laminated to both sides of a dried aluminum nitride ceramic substrate to form a copper-ceramic substrate-copper "sandwich" structure, which was then sintered in a vacuum furnace at a temperature of 820℃ and a vacuum degree of 10. -4 Pa yielded aluminum nitride ceramic copper-clad laminate.

[0059] Comparative Example 1

[0060] The difference between Comparative Example 1 and Example 1 is that nano silver powder is replaced with micron silver powder, wherein the particle size of the micron silver powder is 5-20 μm.

[0061] S2: In the preparation of brazing powder, 20wt% nano silver powder is replaced with 20wt% micron silver powder (particle size 5-20μm), and mixed evenly with 70wt% silver-copper alloy powder, 7wt% aluminum-silicon alloy powder and 3wt% titanium hydride powder in a container to obtain brazing powder.

[0062] All other reagents and conditions were the same as in Example 1.

[0063] Comparative Example 2

[0064] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not contain aluminum-silicon alloy powder.

[0065] S2: In the preparation of brazing powder, 7wt% of aluminum-silicon alloy powder is removed, and 20wt% of nano silver powder, 77wt% of silver-copper alloy powder and 3wt% of titanium hydride powder are weighed, placed in a container and mixed evenly to obtain brazing powder.

[0066] All other reagents and conditions were the same as in Example 1.

[0067] Comparative Example 3

[0068] The difference between Comparative Example 3 and Example 1 is that the sintering temperature is 890°C.

[0069] S4 involves double-layering copper foil with a dried silicon nitride ceramic substrate to form a copper-ceramic substrate-copper "sandwich" structure, followed by sintering in a vacuum furnace at a temperature of 890°C and a vacuum degree of 10. -4 Pa yielded a silicon nitride ceramic copper-clad laminate.

[0070] All other reagents and conditions were the same as in Example 1.

[0071] The silicon nitride ceramic copper-clad laminate prepared above was tested for void ratio, 90° peel strength and thermal shock resistance.

[0072] The test conditions are as follows:

[0073] Void ratio: Measured according to the requirements of JB / T8931-1999, using an ultrasonic microscope (SAT) for C-scan.

[0074] 90° Peel Strength: Measured according to the requirements of IPC-TM6502.4.8. Select peel strength testing equipment, the copper line etching width of the sample is 3mm, and apply a uniform upward pulling force of 90 degrees at a speed of 70mm / min. Record the force when the copper foil is peeled from the ceramic substrate.

[0075] Thermal shock resistance test: Measured according to the requirements of GB / T2423.22-2012, with a thermal cycling temperature of -50 to 150℃, and high and low temperatures held for 30 minutes each, with a transition time of 15 seconds.

[0076] The test data is shown in Table 1:

[0077]

[0078] Table 1 Sample Test Data

[0079] As can be seen from the test results in Table 1, the silicon nitride ceramic copper-clad laminate prepared by the present invention has low void ratio, high peel strength, and good resistance to thermal shock. In the thermal shock test, the copper layer does not separate after 5000 cycles with a thermal cycling temperature of -50 to 150°C, a high and low temperature holding time of 30 min, a switching time of 15 s, and a thermal shock resistance of 15 s.

[0080] Comparative Example 4

[0081] The difference between Comparative Example 4 and Example 2 is that the nano silver powder is replaced with micron silver powder (particle size 5-20 μm).

[0082] In the preparation of S2 brazing powder, 18wt% nano silver powder is replaced with 18wt% micron silver powder (particle size 5-20μm), and mixed evenly with 70wt% silver-copper alloy powder, 8wt% titanium-aluminum alloy powder and 4wt% titanium hydride powder in a container to obtain brazing powder.

[0083] All other reagents and conditions were the same as in Example 2.

[0084] Comparative Example 5

[0085] The difference between Comparative Example 5 and Example 2 is that titanium-aluminum alloy powder is not added.

[0086] In the preparation of S2 brazing powder, 8 wt% of titanium-aluminum alloy powder is removed, and 18 wt% of nano silver powder, 78 wt% of silver-copper alloy powder, and 4 wt% of titanium hydride powder are weighed, placed in a container, and mixed evenly to obtain brazing powder.

[0087] All other reagents and conditions were the same as in Example 2.

[0088] Comparative Example 6

[0089] The difference between Comparative Example 6 and Example 2 is that the sintering temperature is changed to 880°C.

[0090] S4 involves double-layering copper foil with a dried silicon nitride ceramic substrate to form a copper-ceramic substrate-copper "sandwich" structure, followed by sintering in a vacuum furnace at 880°C and a vacuum degree of 10. -4 Pa yielded aluminum nitride ceramic copper-clad laminate.

[0091] All other reagents and conditions were the same as in Example 2.

[0092] The porosity, 90° peel strength, and thermal shock resistance of the aluminum nitride ceramic copper-clad laminate prepared above were tested. The test data are shown in Table 2.

[0093]

[0094]

[0095] Table 2 Sample Test Data

[0096] As can be seen from the test results in Table 2, the aluminum nitride ceramic copper-clad laminate prepared by the present invention has low void ratio, high peel strength, and no separation of copper layer after 1200 cycles of thermal shock with a temperature range of -50 to 150°C, a high and low temperature holding time of 30 min, a switching time of 15 s, and a thermal shock resistance test.

[0097] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent modifications made using the present invention are within the patent protection scope of the present invention.

Claims

1. An active metal soldering paste, characterized in that, It includes brazing powder and binder, wherein the binder component accounts for 8-20% by mass; in, Brazing powder, comprising the following components by weight percentage: Nano silver powder 10-30%; Silver-copper alloy powder 60-80%; Titanium-aluminum alloy powder 8~10%; 2-5% titanium hydride powder; The binder comprises the following components by mass fraction: 75-90% solvent; 5-10% thickener; 2-4% surfactant; 1-2% dispersant; and 2-5% thixotropic agent.

2. The active metal soldering paste according to claim 1, characterized in that, The solvent is any one or more of terpineol, diethylene glycol butyl ether, and diethylene glycol butyl ether acetate.

3. The active metal soldering paste according to claim 1, characterized in that, The thickener is any one or more of ethyl cellulose and modified rosin resin.

4. The active metal soldering paste according to claim 1, characterized in that, The surfactant is a fatty alcohol polyoxyethylene ether.

5. The active metal soldering paste according to claim 1, characterized in that, The dispersant is tributyl phosphate.

6. The active metal soldering paste according to claim 1, characterized in that, The thixotropic agent is modified hydrogenated castor oil.

7. The active metal soldering paste according to claim 1, characterized in that, The nano silver powder, silver-copper alloy powder, titanium-aluminum alloy powder, and titanium hydride powder are all spherical powders. The nano-silver powder has a particle size of 50–100 nm, the silver-copper alloy powder has a particle size of 5–20 μm, the titanium-aluminum alloy powder has a particle size of 5–20 μm, and the titanium hydride powder has a particle size of 5–10 μm.

8. A method for preparing the active metal soldering paste according to any one of claims 1 to 7, characterized in that, The brazing paste is composed of brazing powder and binder, wherein the binder accounts for 8-20% by mass. The preparation method of active metal brazing paste is as follows: the brazing powder and binder are stirred evenly at room temperature, and then rolled by a three-roll mill to obtain active metal brazing paste.

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