Connection process of copper clad ceramic and oxygen-free copper foil of IGBT module

Abstract

The application discloses a connecting process of a copper-clad plate ceramic and an oxygen-free copper foil of an IGBT module, the copper-clad plate ceramic is a ceramic substrate, a patterned active metal brazing layer, a metal film and a low-temperature metal brazing layer are sequentially connected between the upper surface of the ceramic substrate and the lower surface of the oxygen-free copper foil in the order from close to far to the ceramic substrate, and the application has the characteristics of effectively reducing residual stress and good connection stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic copper clad plate, in particular to a connection process of a ceramic copper clad plate and oxygen-free copper foil of an IGBT module with good connection stability. BACKGROUND

[0002] The high-power insulated gate bipolar transistor (IGBT) module is used as a switch in a static converter for generating a sinusoidal current by pulse width modulation. The IGBT module is suitable for conversion systems with a direct voltage of 600 V or more, such as alternating current motors, inverters, switching power supplies, lighting circuits, traction drives, etc., and has the advantages of small driving power and low on-voltage drop.

[0003] The connection between the ceramic copper clad plate and the electronic package in the IGBT module is prone to failure. Thermal fatigue occurs in the multi-layer package structure of the IGBT module due to temperature changes and the mismatch between the coefficients of thermal expansion (CTE). Statistical data shows that more than 55% of IGBT module failures are caused by temperature changes.

[0004] The main production methods of ceramic copper clad plates at present are active metal brazing, surface metallization and direct copper cladding. The above methods all need to form a bonding layer at high temperature, which will generate a large amount of residual stress, which greatly affects the mechanical properties of the copper clad plate.

[0005] During use, the copper clad plate is subjected to cyclic loading due to repeated heating and cooling of the IGBT module, and internal stress causes cracks or even cracking at the connection between the ceramic and the oxygen-free copper foil.

[0006] In order to reduce internal stress, some studies have proposed methods such as introducing a transition metal layer or adding low-expansion particles to the brazing material to relieve internal stress. However, the above methods will increase the thickness of the connection layer, affect the cooling effect, and also reduce the service life of the IGBT module. SUMMARY

[0007] The purpose of the present application is to solve the problem of cracks at the connection between the ceramic copper clad plate and the oxygen-free copper foil of the IGBT module, and to provide a connection process of a ceramic copper clad plate and oxygen-free copper foil of an IGBT module with good connection stability.

[0008] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0009] A connection process of a ceramic copper clad plate and oxygen-free copper foil of an IGBT module, the ceramic copper clad plate being a ceramic substrate, a patterned active metal brazing layer, a metal thin film and a low-temperature metal brazing layer being sequentially connected from near to far to the ceramic substrate between the upper surface of the ceramic substrate and the lower surface of the oxygen-free copper foil; comprising the following steps:

[0010] Step 1, cleaning the ceramic substrate:

[0011] Put the ceramic substrate after surface polishing into a beaker containing acetone solution, place the beaker in an ultrasonic cleaner for 15-20 min, rinse the ceramic substrate with anhydrous ethanol, and then blow dry the ceramic substrate;

[0012] Step 2, making a patterned active metal brazing layer on the ceramic substrate:

[0013] Place the patterned screen template on the upper surface of the ceramic substrate, coat the active metal brazing filler on the patterned screen template, and the active metal brazing filler forms a regular distribution of dot-shaped brazing layer on the ceramic substrate through the holes of the patterned screen template, then remove the patterned screen template;

[0014] Put the ceramic substrate into a vacuum heat treatment furnace, melt the dot-shaped brazing layer to fix it to the ceramic substrate, and form a patterned active metal brazing layer on the ceramic substrate;

[0015] The patterned active metal brazing layer is an island-shaped non-connected structure, and the difference in thermal expansion coefficient between the ceramic substrate and the traditional continuous brazing layer during high-temperature cooling to room temperature will cause a large residual stress. The island-shaped structure greatly reduces the residual stress due to its discontinuous nature, and provides sufficient longitudinal connection force for the later connection of the ceramic substrate and the oxygen-free copper foil.

[0016] Step 3, put the ceramic substrate into the sputtering chamber of the magnetron sputtering instrument to form a 0.5-3 μm metal film on the surface of the patterned active metal brazing layer;

[0017] The working temperature of magnetron sputtering to generate metal film is low, which avoids the generation of large residual stress and provides sufficient transverse connection force for the later connection of the ceramic substrate and the oxygen-free copper foil.

[0018] Step 4, making a low-temperature metal brazing layer on the surface of the metal film:

[0019] Place the patterned screen template on the upper surface of the metal film, coat the low-temperature metal brazing filler on the patterned screen template, and the low-temperature metal brazing filler forms a low-temperature metal brazing filler layer on the metal film through the holes of the patterned screen template, then remove the patterned screen template, and place the oxygen-free copper foil on the surface of the low-temperature metal brazing filler layer;

[0020] Put the ceramic substrate into a vacuum heat treatment furnace, melt the low-temperature metal brazing filler layer to form a low-temperature metal brazing layer, and the low-temperature metal brazing layer is fixedly connected with the oxygen-free copper foil and the patterned active metal brazing layer, respectively.

[0021] The low-temperature brazing technology effectively avoids the large residual stress generated in the cooling process of high-temperature brazing, and can realize the good connection between the ceramic substrate and the oxygen-free copper foil based on the patterned active metal brazing layer and the magnetron sputtering coating.

[0022] Therefore, the application effectively avoids the problem of high residual stress in the traditional ceramic copper-clad plate production mode by adopting the process of patterned active metal brazing layer+magnetron sputtering coating+low-temperature brazing, realizes the connection mode of low residual stress, achieves the purpose of good connection between the ceramic copper-clad plate and the oxygen-free copper foil, and improves the service life of the ceramic copper-clad plate.

[0023] Preferably, the ceramic substrate is made of any one of AlN, Al2O3, Si3N4, B4C, and SiC;

[0024] The patterned active metal brazing layer is made of Ag 72 -Cu 28 alloy powder, one or more active metal powders of Ti, Zr, and Hf, and an organic binder.

[0025] Preferably, the Ag 72 -Cu 28 alloy powder has a particle diameter of 0.1-100 μm;

[0026] The active metal powder has a particle diameter of 0.5-100 μm.

[0027] Preferably, the organic binder is composed of a solvent, a thickening agent, a dispersing agent, an antioxidant, a thixotropic agent, and a corrosion inhibitor;

[0028] The solvent is selected from two or more of glycol-based solvents, alcohol-based solvents, trichloroethylene, diethylene glycol butyl ether, turpentine, and esters, and multiple low-boiling-point solvents are used to prevent the concentration of solvent volatilization to generate pores;

[0029] The thickening agent is selected from one or more of acrylic resin, hydroxyethyl cellulose, terpineol, methyl cellulose, ethyl cellulose, polypropylene glycol, and polyethylene glycol, so that the binder has a certain viscosity and prevents the occurrence of sagging after application;

[0030] The dispersing agent is selected from one or more of fish oil, stearic acid, ethanolamine, fish oil, methyl amyl alcohol, and cetyl trimethyl ammonium bromide, so that the metal particles are uniformly dispersed in the binder;

[0031] The antioxidant is selected from one or more of adipic acid, salicylic acid, citric acid, oxalic acid, glutaric acid, and azelaic acid, and the use of organic weak acid has a protective effect on the metal powder without corroding the metal powder;

[0032] Thixotropic agent is selected from one or more of polyamide wax, hydrogenated castor oil, fumed silica, polyurea, which makes hydrogen bond breakage and easy to spread when screen printing;

[0033] Corrosion inhibitor is selected from one or more of benzotriazole, mercaptobenzothiazole, methylbenzothiazole, phosphonic acid, phosphonic carboxylic acid, and mercaptobenzothiazole, which makes metal powder not easy to lose electrons through physical adsorption by electrostatic attraction and van der Waals force and chemical adsorption based on electron sharing of metal and polar groups;

[0034] The mass fraction ratio of the solvent, thickening agent, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder is:

[0035] (80-140) : (2-20) : (2-20) : (2-20) : (2-10) : (1-4).

[0036] The binder with the above components and proportions is not concentrated when heated and volatilized, has no residue, is not easy to produce defects, has a good protective effect on metal powder, and has good viscosity and thixotropy when screen printing.

[0037] As preferred, the Ag in the patterned active metal brazing layer 72 -Cu 28 The mass fraction ratio of the alloy powder and the active metal powder is (47.5-49) : (1-2.5).

[0038] The mass fraction ratio of the active metal powder in the patterned active metal brazing layer and the organic binder is (8-9) : (1-2).

[0039] As preferred, the metal thin film in step 3 is made by magnetron sputtering of any one of Au, Ag, and Cu target materials, or the metal thin film is made by magnetron sputtering of at least two of Au, Ag, and Cu target materials at the same time.

[0040] As preferred, the low-temperature metal brazing layer uses low-temperature metal brazing filler including one or more of Ag, Pb, Bi, In, Cd, Sn, Zn, and Cu metal elements, and the low-temperature metal brazing filler is in paste or foil shape.

[0041] As preferred, the oxygen-free copper foil has an oxygen content of not more than 0.003% and a total impurity content of not more than 0.05%, and the thickness of the oxygen-free copper foil is 50-600 μm.

[0042] As preferred, the fixing connection of the point-shaped brazing layer to the ceramic substrate after melting and the formation of the patterned active metal brazing layer on the ceramic substrate include the following specific steps:

[0043] The vacuum heat treatment furnace is vacuumed to 5x10-4 Pa-2x10 -3 Pa, the temperature in the vacuum heat treatment furnace is increased to 750-770℃ at a rate of 5-10℃ / min, and kept for 15-30min, then the temperature in the vacuum heat treatment furnace is increased to 870-930℃ at a rate of 3-5℃ / min, and kept for 5-15min, then the temperature in the vacuum heat treatment furnace is decreased to below 500-600℃ at a rate of 3-5℃ / min, and then the furnace is cooled down.

[0044] Therefore, the present application has the following beneficial effects: by adopting the process of patterned active metal brazing layer + magnetron sputtering + low-temperature brazing, the problem of high residual stress in the traditional production mode of ceramic copper-clad plate can be effectively avoided, a low-residual-stress connection mode is realized, the purpose of good connection of ceramic and oxygen-free copper foil is achieved, and the service life of the ceramic copper-clad plate is improved. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a process flowchart of the present application;

[0046] Figure 2 is a structural schematic view of the ceramic substrate of the present application.

[0047] In the figure: ceramic substrate 1, acetone solution 2, patterned silk screen template 3, patterned active metal brazing layer 4, magnetron sputtering target material atom 5, metal thin film 6, oxygen-free copper foil 7. DETAILED DESCRIPTION

[0048] The present application will be further described below in combination with the drawings and specific embodiments.

[0049] Example 1

[0050] As shown in the embodiments shown in Figure 1 , Figure 2 , the present application is a connection process of ceramic and oxygen-free copper foil of a copper-clad plate of an IGBT module, the ceramic copper-clad plate is a ceramic substrate 1, and a patterned active metal brazing layer 4, a metal thin film 6 and a low-temperature metal brazing layer are sequentially connected in order from near to far to the ceramic substrate between the upper surface of the ceramic substrate and the lower surface of the oxygen-free copper foil 7; comprising the following steps:

[0051] Step 1, cleaning the ceramic substrate:

[0052] The ceramic substrate after surface polishing treatment is placed in a beaker containing acetone solution 2, the beaker is placed in an ultrasonic cleaner for cleaning for 20min, the ceramic substrate is rinsed with anhydrous ethanol, and then the ceramic substrate is blown dry;

[0053] Step 2, making a patterned active metal brazing layer on the ceramic substrate:

[0054] The patterned screen template 3 is placed on the upper surface of the ceramic substrate, active metal brazing material is coated on the patterned screen template, the active metal brazing material forms a regularly distributed dot-shaped brazing layer on the ceramic substrate through each hole of the patterned screen template, the shape and thickness of the dot-shaped brazing layer are controlled through the patterned screen template, the thickness is controlled at 20-150 μm, and then the patterned screen template is removed;

[0055] The ceramic substrate is made of AlN material;

[0056] The patterned active metal brazing layer is made of Ag 72 -Cu 28 The alloy powder, the Zr and Hf active metal powder, and the organic binder are mixed to form. Ag 72 -Cu 28 The particle diameter of the alloy powder is 60 μm, and the particle diameter of the active metal powder is 80 μm.

[0057] The organic binder is composed of a solvent, a thickening agent, a dispersing agent, an antioxidant, a thixotropic agent, and a corrosion inhibitor;

[0058] The mass fraction ratio of the solvent, the thickening agent, the dispersing agent, the antioxidant, the thixotropic agent, and the corrosion inhibitor in the organic binder is 80:20:2:2:2:4.

[0059] Ag 72 -Cu 28 The mass fraction ratio of the alloy powder and the active metal powder is 47.5:1;

[0060] The mass fraction ratio of the active metal powder and the organic binder in the patterned active metal brazing layer is 9:1.

[0061] The ceramic substrate is placed in a vacuum heat treatment furnace, the dot-shaped brazing layer is melted to be fixedly connected with the ceramic substrate, and the patterned active metal brazing layer is formed on the ceramic substrate;

[0062] The vacuum heat treatment furnace is vacuumized to 5×10 -4 Pa, the vacuum heat treatment furnace is heated to 770℃ at a speed of 5℃ / min, is kept for 15 min, is heated to 870℃ at a heating rate of 3℃ / min, is kept for 5 min, is then decreased to below 600℃ at a rate of 3℃ / min, and is then cooled with the furnace.

[0063] Step 3, the ceramic substrate is placed in a sputtering chamber of a magnetron sputtering instrument, a Cu metal target to be plated is fixed on a target seat in the sputtering chamber of the magnetron sputtering instrument, the sputtering chamber is vacuumized to 2.0×10 -3Pa, the temperature of the ceramic substrate on the sample turntable is raised to 300℃ by heating the substrate to transfer heat, argon is introduced into the sputtering chamber, the argon flow is controlled to be 30sccm, the bias voltage is adjusted to 500V, the Cu metal target is pre-sputtered for 40min to remove the oxide layer and stains on the surface of the Cu target, and the purity and quality of the thin film are ensured.

[0064] The substrate bias is adjusted to 80V, the argon flow is controlled to be 25sccm, the pressure in the sputtering chamber is raised to 2.0Pa, the voltage of the target seat with the Cu metal target is raised to 300V to produce glow discharge, the argon is ionized to produce argon ions, the argon ions bombard the Cu metal target to cause the Cu target to sputter Cu atoms; the working pressure in the sputtering chamber is adjusted to 0.8Pa, and pre-sputtering is performed for 10min; after the pre-sputtering process, the self-rotation speed of the sample turntable is controlled to be 8r / min, the voltage and current of the target seat with the Cu metal target are adjusted to make the power reach 250W, and sputtering is continued for 50min to form a Cu metal thin film with a thickness of 0.5μm-3μm on the surface of the patterned active metal brazing layer;

[0065] Step 4: making a low-temperature metal brazing layer on the surface of the metal thin film:

[0066] The patterned screen template is placed on the surface of the metal thin film, and AuSn 20 The low-temperature metal brazing material passes through each hole of the patterned screen template to form a low-temperature metal brazing layer on the metal thin film, and the shape and thickness of the low-temperature metal brazing layer are controlled by the patterned screen template, and the thickness is controlled to be 10μm-100μm, and then the patterned screen template is removed, and the oxygen-free copper foil is placed on the surface of the low-temperature metal brazing layer.

[0067] The oxygen-free copper foil has an oxygen content of not more than 0.003%, and a total impurity content of not more than 0.05%; the thickness of the oxygen-free copper foil is 50μm-600μm.

[0068] The ceramic substrate is placed in a vacuum heat treatment furnace, and the low-temperature metal brazing layer is melted to form a low-temperature metal brazing layer, and the low-temperature metal brazing layer is fixedly connected with the oxygen-free copper foil and the patterned active metal brazing layer, respectively.

[0069] The ceramic substrate is placed in a vacuum heat treatment furnace, and the vacuum is extracted to reach 2×10 -3 Pa, the temperature of the ceramic substrate on the sample turntable is raised to 300℃ by heating the substrate to transfer heat, argon is introduced into the sputtering chamber, the argon flow is controlled to be 30sccm, the bias voltage is adjusted to 500V, the Cu metal target is pre-sputtered for 40min to remove the oxide layer and stains on the surface of the Cu target, and the purity and quality of the thin film are ensured.

[0070] The patterned active metal brazing layer, the metal film, the low-temperature metal brazing layer, and the oxygen-free copper foil can also be located on both sides of the ceramic substrate.

[0071] Example 2

[0072] In Example 2, the mass fraction ratio of the solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder is 140:2:20:20:10:1.

[0073] Ag 72 -Cu 28 The mass fraction ratio of the alloy powder and the active metal powder is 49:2.5.

[0074] The mass fraction ratio of the active metal powder and the organic binder in the patterned active metal brazing layer is 8:2.

[0075] The low-temperature metal brazing material is Pb 93.5 Sn5Ag 1.5 The other contents of Example 2 are the same as those in Example 1.

[0076] Example 3

[0077] In Example 3, the mass fraction ratio of the solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder is 90:10:11:15:8:2.

[0078] Ag 72 -Cu 28 The mass fraction ratio of the alloy powder and the active metal powder is 48:2.

[0079] The mass fraction ratio of the active metal powder and the organic binder in the patterned active metal brazing layer is 7:1.5.

[0080] The low-temperature metal brazing material is AuSn 20 The other contents of Example 3 are the same as those in Example 1.

[0081] Example 4

[0082] In Example 4, the mass fraction ratio of the solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder is 110:5:8:12:7:2.

[0083] Ag 72 -Cu 28 The mass fraction ratio of the alloy powder and the active metal powder is 48.5:2.

[0084] The mass fraction ratio of the active metal powder and the organic binder in the patterned active metal brazing layer is 8.7:1.3.

[0085] Low temperature metal solder is Pb 93.5 Sn5Ag 1.5 The other contents of Example 4 are the same as those in Example 1.

[0086] Performance test:

[0087] According to the recommended test method of rigid copper-clad laminate for printed circuits in GB_T4722-2017, the mechanical performance of the final ceramic copper-clad plate is detected in terms of pull-off strength, and a nano indentation tester is used to detect the surface of the copper foil of the ceramic copper-clad plate. The indentation depth of the sample after brazing and the original oxygen-free copper foil is compared, combined with the hardness data of the oxygen-free copper foil, and the residual stress is calculated through the Suresh model.

[0088] Table 1 pull-off strength and residual stress of ceramic copper-clad plate in different connection modes

[0089]

[0090] Through the analysis of the data in Table 1, it can be seen that the ceramic copper-clad plate connected by the present application has higher pull-off strength and lower residual stress than the ceramic copper-clad plate prepared by the traditional active metal brazing process.

[0091] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for joining a copper clad ceramic and an oxygen-free copper foil of an IGBT module, characterized by, The copper-clad plate ceramic is a ceramic substrate, and a patterned active metal brazing layer, a metal film and a low-temperature metal brazing layer are sequentially connected between the upper surface of the ceramic substrate and the lower surface of the oxygen-free copper foil in order from the ceramic substrate to the far end. Step 1, cleaning the ceramic substrate: After the ceramic substrate is subjected to surface polishing treatment, it is placed in a beaker containing an acetone solution, and the beaker is placed in an ultrasonic cleaner for 15-20 minutes. The ceramic substrate is then rinsed with anhydrous ethanol and dried. Step 2, making a patterned active metal brazing layer on the ceramic substrate: Place the patterned screen template on the upper surface of the ceramic substrate, apply active metal brazing material on the patterned screen template, and the active metal brazing material will form a regular distribution of dot-shaped brazing layer on the ceramic substrate through the holes of the patterned screen template. Then remove the patterned screen template. Place the ceramic substrate in a vacuum heat treatment furnace to melt the dot-shaped brazing layer and fix it to the ceramic substrate, forming a patterned active metal brazing layer on the ceramic substrate. Step 3, place the ceramic substrate in the sputtering chamber of the magnetron sputtering instrument to form a 0.5-3 μm metal film on the upper surface of the patterned active metal brazing layer. Step 4, making a low-temperature metal brazing layer on the upper surface of the metal film: Place the patterned screen template on the upper surface of the metal film, apply low-temperature metal brazing material on the patterned screen template, and the low-temperature metal brazing material will form a low-temperature metal brazing layer on the metal film through the holes of the patterned screen template. Then remove the patterned screen template and place the oxygen-free copper foil on the upper surface of the low-temperature metal brazing layer. Place the ceramic substrate in a vacuum heat treatment furnace to melt the low-temperature metal brazing layer and form a low-temperature metal brazing layer, which is fixedly connected to the oxygen-free copper foil and the patterned active metal brazing layer, respectively. The ceramic substrate is made of any one of AlN, Al2O3, Si3N4, B4C, SiC; The patterned active metal brazing layer employs Ag 72 -Cu 28 alloy powder, one or more active metal powders of Ti, Zr, Hf, and an organic binder The organic binder is composed of solvent, thickening agent, dispersant, antioxidant, thixotropic agent and corrosion inhibitor; The mass fraction ratio of the solvent, thickening agent, dispersant, antioxidant, thixotropic agent and corrosion inhibitor in the organic binder is: （80-140）：（2-20）：（2-20）：（2-20）：（2-10）：（1-4）； The process for connecting the copper-clad plate ceramic and the oxygen-free copper foil of the IGBT module includes the following steps: The vacuum heat treatment furnace is vacuumed to 5x10 -4 Pa-2x10 -3 Pa, the temperature in the vacuum heat treatment furnace is raised to 750-770°C at a rate of 5-10°C / min, and held for 15-30 min, then raised to 870-930°C at a rate of 3-5°C / min, held for 5-15 min, then lowered to below 500-600°C at a rate of 3-5°C / min, and then cooled with the furnace.

2. The process for connecting the copper-clad plate ceramic and the oxygen-free copper foil of the IGBT module according to claim 1, characterized in that, The Ag 72 -Cu 28 The particle diameter of the alloy powder is 0.1 μm - 100 μm; The particle diameter of the active metal powder is 0.5-100 μm.

3. The process for connecting the copper-clad plate ceramic and the oxygen-free copper foil of the IGBT module according to claim 1, characterized in that, Ag in the patterned active metal brazing layer 72 -Cu 28 The mass fraction ratio of the alloy powder to the active metal powder is (47.5-49):(1-2.5); The mass fraction ratio of the active metal powder to the organic binder in the patterned active metal brazing layer is (8-9):(1-2).

4. The process for connecting the copper-clad plate ceramic and the oxygen-free copper foil of the IGBT module according to claim 1, characterized in that, The metal film in step 3 is made of any one of Au, Ag, Cu target material by magnetron sputtering, or the metal film is made of at least two kinds of Au, Ag, Cu target material by magnetron sputtering at the same time.

5. The ceramic and oxygen-free copper foil connecting process of the copper-clad plate of the IGBT module according to claim 1, characterized in that, The low-temperature metal brazing layer adopts low-temperature metal brazing filler including one or more metal elements of Ag, Pb, Bi, In, Cd, Sn, Zn and Cu, and the low-temperature metal brazing filler is in paste or foil shape.

6. The ceramic and oxygen-free copper foil connecting process of the copper-clad plate of the IGBT module according to claim 1, characterized in that, The oxygen-free copper foil is a copper foil with the oxygen content not more than 0.003% and the total impurity content not more than 0.05%, and the thickness of the oxygen-free copper foil is 50-600 μm.

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