A film copper sheet for chip front copper electrode interconnection and a preparation method and application thereof

Abstract

The application provides a film copper sheet for chip front copper electrode interconnection and a preparation method and application thereof. The preparation method of the film copper sheet comprises the following steps: S1, pretreating and single-sided metallization treating a bare copper sheet to obtain a copper sheet with a single-sided metallization layer; S2, coating a metal solder paste on the single-sided metallization layer of the copper sheet, and then drying in an inert or reducing atmosphere to obtain a copper sheet with a metal solder film; and S3, applying a temporary adhesive to part of the point positions of the metal solder film of the copper sheet to obtain a film copper sheet for chip front copper electrode interconnection. The application can provide sufficient temporary adhesion between the film copper sheet and the chip during the transfer and sintering processes, and the temporary adhesive can be organically inter-dissolved with the metal solder paste during the sintering process, so that the problems of organic pollution and reduction of bonding area are solved.

Description

Technical Field

[0001] This invention relates to the field of power device packaging technology, and in particular to a coated copper sheet for interconnecting copper electrodes on the front side of a chip, its preparation method, and its application. Background Technology

[0002] Third-generation wide-bandgap semiconductors, especially those represented by silicon nitride (SiC) and gallium nitride (GaN), exhibit excellent operating characteristics such as high power density, high junction temperature, and high frequency. However, as a packaging structure providing critical electrical connections, the wire bonding on the top of the chip faces complex and demanding operating conditions, making it difficult to ensure the long-term stable operation of these third-generation wide-bandgap semiconductor devices.

[0003] To improve the reliability of top-side interconnects on chips, the industry has proposed and promoted a copper wire bonding process that features high electrical and thermal conductivity, a low coefficient of thermal expansion, and cost-effectiveness. However, due to the high hardness of copper wires, the bonding process typically requires strict process specifications and a long soldering time, which may damage the top surface of the chip, leading to reliability issues.

[0004] To address the aforementioned issues, existing technologies suggest using sintered silver as a bonding layer on the top surface of the chip, with a copper sheet attached, followed by bonding of copper leads to the copper sheet. In this process, the copper sheet acts as a buffer layer, protecting the chip during bonding. Specifically, the sintered silver is typically pre-printed on the copper sheet, dried, and then transferred and assembled to the sintering location for bonding with the top surface of the chip. However, during the actual transfer and sintering process, there is a risk of the copper sheet attached to the chip detaching or shifting.

[0005] Currently, the industry has proposed using fixatives to ensure a stable connection between the copper sheet and the chip. However, the use of fixatives brings the risk of organic pollution, and the flexibility of top wiring is affected because the top wiring needs to avoid the fixative adhesion points.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a coated copper sheet for interconnecting copper electrodes on the front side of a chip, its preparation method, and its application. During the transfer and sintering process, it provides a temporary and sufficient adhesive force between the coated copper sheet and the chip. During the sintering process, the temporary adhesive and the metal solder paste achieve organic miscibility, which solves the problems of organic contamination and reduced bonding area.

[0008] This invention provides a method for preparing a coated copper sheet for interconnecting copper electrodes on the front side of a chip, comprising the following steps:

[0009] S1: Pre-process and single-sided metallization of bare copper sheets to obtain copper sheets with single-sided metallization layers;

[0010] S2: Apply metal solder paste to a single-sided metallization layer of a copper sheet, and then dry it in an inert or reducing atmosphere to obtain a copper sheet with a metal solder film.

[0011] S3: Apply temporary adhesive to certain points of the metal solder film on the copper sheet to obtain a coated copper sheet for interconnecting copper electrodes on the front side of the chip.

[0012] In step S1, the bare copper sheet can be made of oxygen-free copper, pure copper, etc., and the thickness of the bare copper sheet can be 20-200μm; the hardness can be 70-120HV.

[0013] The pretreatment includes: soaking the bare copper sheet in dilute sulfuric acid solution, anhydrous ethanol, and deionized water sequentially, repeating 2-3 times, and then drying it under an inert atmosphere; wherein, the concentration of dilute sulfuric acid solution is 2-5 wt%, the soaking time of dilute sulfuric acid solution is 10-15 min, the soaking time of anhydrous ethanol is 3-5 min, the soaking time of deionized water is 3-5 min; the inert atmosphere is nitrogen atmosphere, the drying temperature is 40-60℃, and the drying time is 20-40 min.

[0014] The single-sided metallization process includes: forming a single-sided metallization layer on the surface of a pre-treated bare copper sheet. The single-sided metallization layer can be an Ag plating layer, a Ni / Ag plating layer, or a Ni / Pd / Au plating layer, with a thickness of 1-3 μm. The Ni / Ag plating layer comprises a Ni plating layer and an Ag plating layer sequentially disposed on the surface of the bare copper sheet, with a thickness ratio of (1.5-2.5):1, for example, 2:1. The Ni / Pd / Au plating layer comprises a Ni plating layer, a Pd plating layer, and an Au plating layer sequentially disposed on the surface of the bare copper sheet, with a thickness ratio of (1.5-2):(0.1-0.5):1, for example, 1.8:0.2:1. The presence of this single-sided metallization layer on the surface of the bare copper sheet improves the adhesion between the metal film and the copper sheet.

[0015] In step S2, metal solder paste can be applied to the single-sided metallization layer of the copper sheet by means of coating or printing. During the coating process, the thickness of the metal solder paste should be controlled to be uniform, and the coating thickness should be 50-200μm.

[0016] The metal solder paste comprises the following components in parts by weight: 80-90 parts of corrosion inhibitor coating metal particles and 10-20 parts of organic solvent system; wherein, the mass ratio of metal particles to corrosion inhibitor in the corrosion inhibitor coating metal particles can be 80:(3-5); the corrosion inhibitor is selected from at least one of malic acid and tartaric acid; the organic solvent system comprises the following components in parts by weight: 2-5 parts of antioxidant and 95-98 parts of organic solvent; the antioxidant is selected from at least one of citric acid, succinic acid, lactic acid, oxalic acid and ascorbic acid; the organic solvent is selected from at least one of ethylene glycol, diethylene glycol, terpineol, glycerin and n-decaol.

[0017] Specifically, the preparation method of metal solder paste includes the following steps:

[0018] a) Deoxidize the metal particles to obtain deoxidized metal particles;

[0019] b) After mixing the deoxidized metal particles, corrosion inhibitor and organic solvent, ultrasonication, centrifugation and washing are performed to obtain corrosion inhibitor-coated metal particles.

[0020] c) Mix the antioxidant with the organic solvent and stir to obtain the organic solvent system;

[0021] d) After mixing the corrosion inhibitor-coated metal particles with the organic solvent system, stir to obtain metal solder paste.

[0022] In step a), the metal particles are selected from silver particles or copper particles, preferably silver particles. The morphology of the metal particles is plate-like or spherical; when the metal particles are spherical, the particle size is 100-1000 nm, preferably 500-1000 nm, for example 1000 nm; when the metal particles are plate-like, the particle size is 1000-2000 nm, preferably 1000-1500 nm, for example 1200 nm.

[0023] The deoxidation treatment includes: first, placing the metal particles in hypophosphite solution, hypochlorous acid solution, or dilute hydrochloric acid solution, ultrasonically washing them, and then centrifuging them; then, placing the metal particles in anhydrous ethanol, ultrasonically washing them, and then centrifuging them. More specifically, first, placing the metal particles in 2-3 mol / L hypophosphite solution, 1-3 mol / L hypochlorous acid solution, or 3-5 mol / L dilute hydrochloric acid solution, ultrasonically washing them for 10-30 min, and then centrifuging them at 2000-5000 r / min; then, placing the metal particles in anhydrous ethanol, ultrasonically washing them for 10-15 min, and then centrifuging them at 2000-3000 r / min.

[0024] In step b), the corrosion inhibitor preferably includes tartaric acid and malic acid, with a mass ratio of tartaric acid to malic acid of (1-5):1; the organic solvent is anhydrous ethanol, and the mass ratio between the deoxidized metal particles, the corrosion inhibitor and the organic solvent is (75-80):(2-5):(15-23), preferably 80:(3-5):(15-17); the ultrasonic time is 35-40 min, after ultrasonic treatment, centrifuge at 5000-5500 r / min, then place in anhydrous ethanol, ultrasonically clean for 10-15 min and centrifuge at 2000-3500 r / min.

[0025] In step c), the antioxidant is preferably citric acid or succinic acid; the organic solvent preferably includes ethylene glycol, terpineol and n-decayl alcohol, and the mass ratio between ethylene glycol, terpineol and n-decayl alcohol is 1:(1-2):1; the mass ratio of antioxidant to organic solvent in the organic solvent system is preferably (2-5):(95-98), and the stirring is magnetic stirring for 30-50 min.

[0026] In step d), the mass ratio of the corrosion inhibitor-coated metal particles to the organic solvent system is (80-90):(10-20); the stirring is done by magnetic stirring for 15-30 minutes.

[0027] After applying the metal solder paste, the material is dried under an inert or reducing atmosphere. The inert atmosphere may be nitrogen or argon, while the reducing atmosphere may be formic acid, platinum-catalyzed formic acid, or a mixture of nitrogen and hydrogen. The heating rate during drying is 2-50℃ / min, preferably 10-40℃ / min, the drying temperature is 100-200℃, preferably 120-160℃, and the drying time is 2-60 min, preferably 10-20 min. After drying, a metal solder film with a thickness of 25-150 μm is formed on the copper sheet surface, preferably 25-50 μm.

[0028] Further, after drying, an activation treatment is performed. The activation treatment includes: a first immersion in a phosphoric acid solution or citric acid solution, followed by washing and drying; wherein the phosphoric acid solution contains 10-20% by mass, and the citric acid solution contains 5-10% by mass; the first immersion time is 5-10 minutes. The activation treatment also includes a second immersion in a sodium sulfate solution, followed by washing and drying; wherein the sodium sulfate solution contains 5-10% by mass; the second immersion time is 5-10 minutes. These activation treatments are beneficial for further improving the sintering strength.

[0029] Further, after activation treatment, a coating solution is used for coating treatment; the coating solution includes a first organic compound and a second organic compound, the first organic compound being selected from at least one of diethyl phthalate, dibutyl phthalate, butyl acetate, dimethyl terephthalate, dioctyl phthalate, ethyl propionate, phenyl acetate, isoamyl acetate, and dipropyl phthalate, and the second organic compound being selected from at least one of ethanol, acetone, and ethyl acetate; the mass ratio of the first organic compound to the second organic compound in the coating solution is (10-20):(80-90).

[0030] In step S3, the temporary adhesive comprises the following components in parts by weight: 77-80 parts resin component, 20-25 parts diluent, and 1-3 parts dispersant; further, the temporary adhesive comprises the following components in parts by weight: 77-78 parts resin component, 20 parts diluent, and 2-3 parts dispersant; wherein, the resin component is selected from at least one of tetramethylbiphenyl epoxy resin, polyethylene terephthalate, and polyethylene glycol; the diluent is selected from at least one of ethylene glycol, propylene glycol, glycerol, n-butanol, diethylene glycol, acetone alcohol, and polyethylene glycol, for example, ethylene glycol, propylene glycol, and n-butanol; the dispersant is selected from at least one of n-decanol, methanol, cyclohexanol, and ethanol, for example, cyclohexanol, ethanol, and methanol.

[0031] Temporary adhesive is applied to specific points on the metal solder film of a copper sheet using a dispensing process. The dispensing parameters include: a dot diameter of 150-450 μm and a dot height of 10-40 μm. There are no strict restrictions on the locations where the temporary adhesive is applied; they can be determined reasonably based on the actual situation. The number of dots can be 1-2, and they can be located around the perimeter of the copper sheet, such as two diagonal dots, one center dot, or two dots on either side. Applying temporary adhesive to specific points on the metal solder film of the copper sheet helps reduce the amount of adhesive used, which in turn helps reduce the porosity of the sintered solder paste, resulting in a denser, stronger, and more reliable sintered structure.

[0032] The present invention also provides a coated copper sheet for interconnecting copper electrodes on the front side of a chip, which is prepared according to the above preparation method.

[0033] The present invention also provides a method for interconnecting copper electrodes on the front side of a chip, comprising the following steps:

[0034] A) Place the chip on a heating platform and heat it to the heat-attach process temperature;

[0035] B) Heat the suction head to the hot-mount process temperature, and use the heated suction head to pressurize and bond the coated copper sheet for interconnecting the copper electrodes on the front side of the chip to the front side of the chip, and then place it in a sintering furnace for sintering.

[0036] In step A), the heat-applied process temperature is 40-120℃, for example, 60-80℃.

[0037] In step B), the bonding pressure is 1-8 kg, for example 1-3 kg, and the bonding time is 0.1-2 s, for example 0.3-0.5 s. Applying pressure to bond the coated copper sheet to the front side of the chip initially achieves interfacial bonding, fixing the coated copper sheet to the front side of the chip. The sintering temperature is 200-300℃, for example 250-260℃, the sintering pressure is 1-25 MPa, for example 10-20 MPa, and the sintering time is 1-30 min, for example 3-10 min. Sintering under the above temperature and pressure achieves interfacial metallurgical bonding between the coated copper sheet and the chip.

[0038] This invention performs single-sided metallization on bare copper sheets, improving the adhesion between the metal film and the copper sheet. Further activation and coating of the copper sheet improves the quality of the coated copper sheet, thereby reducing the risk of heat-bonded detachment. In particular, by using a specific combination of metal solder paste and temporary adhesive, sufficient temporary adhesion can be provided between the coated copper sheet and the chip during the transfer and sintering process. During sintering, the temporary adhesive can achieve organic miscibility with the metal solder paste, solving problems such as organic contamination and reduced bonding area. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 Ultrasonic non-destructive scanning image of the power device packaging structure prepared in Example 1;

[0041] Figure 2 A cross-sectional view of the sintered microstructure of the power device packaging structure prepared in Example 1;

[0042] Figure 3 CCD scan image of the power device package structure prepared for Comparative Example 2. Detailed Implementation

[0043] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0044] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0045] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Example 1

[0047] I. Preparation of silver solder paste

[0048] 1) Deoxidation treatment

[0049] Silver particles with a flake-like morphology and a size of 1200 nm were placed in a 3 mol / L hypophosphite solution, ultrasonically washed for 10 min, and then centrifuged at 2000 r / min. The silver particles were then placed in anhydrous ethanol, ultrasonically washed for 12 min, and centrifuged at 2000 r / min to obtain deoxidized silver particles.

[0050] 2) Corrosion inhibitor coating

[0051] The corrosion inhibitor is obtained by mixing 5 parts tartaric acid and 1 part malic acid by weight.

[0052] Mix 80 parts of the deoxidized silver particles prepared in step 1), 5 parts of the corrosion inhibitor prepared above, and 15 parts of anhydrous ethanol according to the mass ratio. After ultrasonic treatment for 40 min, centrifuge at 5000 r / min, then place in anhydrous ethanol, ultrasonically clean for 10 min, and centrifuge at 2000 r / min to obtain corrosion inhibitor-coated silver particles.

[0053] 3) Preparation of organic solvent system

[0054] Mix 1 part ethylene glycol, 1 part terpineol and 1 part n-decaol by mass to obtain a mixed organic solvent.

[0055] Five parts by weight of antioxidant citric acid and 95 parts by weight of the above-prepared mixed organic solvent were mixed and magnetically stirred for 30 minutes at room temperature to obtain the organic solvent system.

[0056] 4) Preparation of silver solder paste

[0057] Mix 90 parts by weight of the corrosion inhibitor-coated silver particles prepared in step 2) with 10 parts by weight of the organic solvent system prepared in step 3), and stir magnetically for 15 minutes at room temperature to obtain silver solder paste.

[0058] II. Preparation of Coated Copper Sheets

[0059] 1) Preprocessing

[0060] A bare copper sheet with a thickness of 50 μm, a hardness of 80 HV, and made of red copper was immersed in a 5% dilute sulfuric acid solution for 10 minutes and then removed. The bare copper sheet was then immersed in anhydrous ethanol for 5 minutes and then removed. The bare copper sheet was then immersed in deionized water for 5 minutes and then removed. After repeating this process 3 times, the sheet was dried in a nitrogen atmosphere at 50°C for 40 minutes to obtain a surface-treated bare copper sheet.

[0061] 2) Single-sided metallization treatment

[0062] The bare copper sheet prepared in step 1) is subjected to single-sided metallization to obtain a copper sheet with an Ag plating layer, the thickness of which is 1 μm.

[0063] 3) Apply silver solder paste

[0064] The silver solder paste prepared in step one is coated onto the Ag plating layer of the copper sheet prepared in step 2) by printing. The coating thickness of the silver solder paste is controlled to be about 100 μm and the thickness is uniform. After coating, it is placed in a drying oven.

[0065] 4) Drying

[0066] The copper sheet coated with silver solder paste in step 3) was dried under a nitrogen atmosphere. The heating rate during drying was 10℃ / min, the drying temperature was 160℃, and the drying time was 20min. After drying, a copper sheet with a metal solder film on the surface was obtained, and the thickness of the metal solder film was 50μm.

[0067] 5) Apply temporary adhesive

[0068] The temporary adhesive comprises the following components by weight: 77 parts resin, 20 parts diluent, and 3 parts dispersant; wherein the resin is tetramethylbiphenyl epoxy resin, the diluent is ethylene glycol, and the dispersant is cyclohexanol. The dispensing process parameters include: a dot diameter of 300 μm, a dot height of 20 μm, and two dots; the dots are located diagonally opposite the copper sheet, with the center of each dot 300 μm from both sides of the copper sheet.

[0069] The copper sheet processed in step 4) is cut into the specified shape using laser cutting, then placed in a material box, and temporary adhesive is applied to the parts of the copper sheet with the metal solder film using a dispensing process to obtain a coated copper sheet.

[0070] III. Interconnection between Coated Copper Sheets and Chips

[0071] The chip is placed on a heating platform and heated to the heat-attach process temperature of 60°C.

[0072] Heat the suction head to the thermal bonding process temperature of 60°C. Use the heated suction head to remove the coated copper sheet prepared in step two from the material box. Then apply pressure and thermally bond it to the front of the chip. The thermal bonding pressure is 1 kg and the thermal bonding time is 0.3 s.

[0073] The chip with the copper film coating was placed in a sintering furnace and sintered for 3 minutes at a sintering temperature of 250°C and a sintering pressure of 15MPa to obtain the power device packaging structure.

[0074] The ultrasonic non-destructive scanning image and sintered microstructure cross-sectional view of the power device packaging structure in this embodiment are shown below. Figure 1 , Figure 2 The results show that the temporary adhesive in this embodiment can achieve organic miscibility with the metal solder paste during the sintering process and almost completely evaporates in the subsequent process, without causing bulging, and there are no problems such as organic pollution and reduced bonding area.

[0075] Example 2

[0076] I. Preparation of copper solder paste

[0077] 1) Deoxidation treatment

[0078] Copper particles with a spherical morphology and a particle size of 1000 nm were placed in a 2 mol / L hypophosphite solution, ultrasonically washed for 30 min, and then centrifuged at 5000 r / min. The copper particles were then placed in anhydrous ethanol, ultrasonically washed for 10 min, and centrifuged at 3000 r / min to obtain deoxidized copper particles.

[0079] 2) Corrosion inhibitor coating

[0080] Mix 1 part tartaric acid and 1 part malic acid by weight to obtain a corrosion inhibitor.

[0081] Mix 80 parts of the deoxidized copper particles prepared in step 1), 3 parts of the corrosion inhibitor prepared above, and 17 parts of anhydrous ethanol according to the mass ratio. After ultrasonic treatment for 35 min, centrifuge at 5500 r / min, then place in anhydrous ethanol, ultrasonically clean for 15 min, and centrifuge at 3500 r / min to obtain corrosion inhibitor-coated copper particles.

[0082] 3) Preparation of organic solvent system

[0083] Mix 1 part ethylene glycol, 1 part terpineol and 1 part n-decaol by mass to obtain a mixed organic solvent.

[0084] Two parts by weight of antioxidant citric acid and 98 parts by weight of the above-prepared mixed organic solvent were mixed and magnetically stirred for 50 minutes at room temperature to obtain the organic solvent system.

[0085] 4) Preparation of copper solder paste

[0086] Mix 80 parts by weight of the copper particles coated with the corrosion inhibitor prepared in step 2) with 20 parts by weight of the organic solvent system prepared in step 3), and stir magnetically for 30 minutes at room temperature to obtain copper solder paste.

[0087] II. Preparation of Coated Copper Sheets

[0088] 1) Surface treatment

[0089] A bare copper sheet with a thickness of 50 μm, a hardness of 80 HV, and made of red copper was immersed in a 5% dilute sulfuric acid solution for 10 minutes and then removed. The bare copper sheet was then immersed in anhydrous ethanol for 5 minutes and then removed. The bare copper sheet was then immersed in deionized water for 5 minutes and then removed. After repeating this process 3 times, the sheet was dried in a nitrogen atmosphere at 60°C for 20 minutes to obtain a surface-treated bare copper sheet.

[0090] 2) Single-sided metallization treatment

[0091] The surface-treated bare copper sheet prepared in step 1) is subjected to single-sided metallization treatment, and a Ni plating layer, a Pd plating layer and an Au plating layer (collectively referred to as the Ni / Pd / Au plating layer) are formed on the surface of the bare copper sheet in sequence; wherein, the thickness of the Ni plating layer is 1.8 μm, the thickness of the Pd plating layer is 0.2 μm, the thickness of the Au plating layer is 1 μm, and the total thickness of the Ni / Pd / Au plating layer is 3 μm.

[0092] 3) Apply copper solder paste

[0093] The copper solder paste prepared in step one is coated onto the Ag plating layer of the copper sheet prepared in step 2) by printing. The coating thickness of the copper solder paste is controlled to be about 100 μm and the thickness is uniform. After coating, it is placed in a drying oven.

[0094] 4) Drying

[0095] The copper sheet coated with copper solder paste in step 3) was dried under a nitrogen atmosphere. The heating rate during drying was 40℃ / min, the drying temperature was 120℃, and the drying time was 10min. After drying, a copper sheet with a metal solder film on the surface was obtained, and the thickness of the metal solder film was 50μm.

[0096] 5) Apply temporary adhesive

[0097] The temporary adhesive comprises the following components by weight: 77 parts resin, 20 parts diluent, and 3 parts dispersant; wherein the resin is tetramethylbiphenyl epoxy resin, the diluent is ethylene glycol, and the dispersant is cyclohexanol. The dispensing process parameters include: a dot diameter of 300 μm, a dot height of 20 μm, and two dots; the dots are located diagonally opposite the copper sheet, with the center of each dot 300 μm from both sides of the copper sheet.

[0098] The copper sheet processed in step 4) is cut into the specified shape using laser cutting, then placed in a material box, and temporary adhesive is applied to the parts of the copper sheet with the metal solder film using a dispensing process to obtain a coated copper sheet.

[0099] III. Interconnection between Coated Copper Sheets and Chips

[0100] The chip is placed on a heating platform and heated to the heat-attach process temperature of 60°C.

[0101] Heat the suction head to the thermal bonding process temperature of 60°C. Use the heated suction head to remove the coated copper sheet prepared in step two from the material box. Then apply pressure and thermally bond it to the front of the chip. The thermal bonding pressure is 1 kg and the thermal bonding time is 0.5 s.

[0102] The chip with the copper film coating was placed in a sintering furnace and sintered for 10 minutes at a sintering temperature of 260°C and a sintering pressure of 15MPa to obtain the power device packaging structure.

[0103] Example 3

[0104] Except for step two, when preparing the coated copper sheet, after drying, an activation treatment is performed and then a temporary adhesive is applied, the rest is the same as in Example 1.

[0105] The activation process in this embodiment is as follows: The copper sheet treated in step 4) is immersed in a 15% phosphoric acid solution for 8 minutes. After immersion, it is taken out, rinsed with clean water, and air-dried. The air-dried copper sheet is then immersed in a 6% sodium sulfate solution for 6 minutes. After immersion, it is taken out, rinsed with deionized water, and air-dried. Then, the subsequent application of temporary adhesive is carried out.

[0106] Example 4

[0107] Except for step two, when preparing the coated copper sheet, after activation treatment, a coating treatment is performed and a temporary adhesive is applied, the rest is the same as in Example 3.

[0108] The coating process steps in this embodiment are as follows:

[0109] The coating solution comprises the following components by mass: 8 parts diethyl phthalate, 3 parts dibutyl phthalate, 4 parts butyl acetate, and 85 parts ethanol.

[0110] Weigh each component according to the mass fraction. First, add diethyl phthalate to the mixing container, then add dibutyl phthalate. After stirring magnetically for 8 minutes, add butyl acetate and continue stirring magnetically for 8 minutes. Then gradually add ethanol while stirring continuously until all components are completely dissolved to obtain a uniform coating solution.

[0111] The activated copper sheet is slowly immersed in the coating solution using an immersion method, ensuring that the surface of the copper sheet is in complete contact with the coating solution. After 5 minutes, it is slowly removed and dried in clean hot air at 70°C for 30 minutes to allow the film to solidify evenly. Then, the subsequent step of applying temporary adhesive is carried out.

[0112] Example 5

[0113] Except for the different composition of the temporary adhesive used in step two when preparing the coated copper sheet, the rest is the same as in Example 4.

[0114] The temporary adhesive of this embodiment comprises the following components in parts by weight: 78 parts resin component, 20 parts diluent and 2 parts dispersant; wherein the resin component is polyethylene glycol ester, the diluent is propylene glycol and the dispersant is ethanol.

[0115] Example 6

[0116] Except for the different composition of the temporary adhesive used in step two when preparing the coated copper sheet, the rest is the same as in Example 4.

[0117] The temporary adhesive of this embodiment comprises the following components in parts by weight: 78 parts resin component, 20 parts diluent and 2 parts dispersant; wherein the resin component is polyethylene terephthalate, the diluent is n-butanol and the dispersant is methanol.

[0118] Compare with Example 1

[0119] Except for step 5) of applying temporary adhesive in step 2 of preparing the coated copper sheet, i.e., not applying temporary adhesive to the parts of the copper sheet with the metal solder film, the rest is the same as in Example 1.

[0120] Compare with Example 2

[0121] Except for the use of (meth)acrylic acid copolymer in the temporary adhesive instead of tetramethylbiphenyl epoxy resin in Example 1, the rest is the same as in Example 1.

[0122] The ultrasonic non-destructive scanning image of the power device package structure in this comparative example is shown below. Figure 3The results showed that the (meth)acrylic acid copolymer could not completely volatilize or dissolve into the solder paste during the sintering process. Instead, it would generate a cross-linked material with a certain hardness. After sintering, it would lift up the substrate at that point, causing permanent deformation and bulging, which would significantly reduce the bonding area of ​​the chip.

[0123] Compare with Example 3

[0124] Except for the use of ethylene-vinyl acetate copolymer in the temporary adhesive instead of tetramethylbiphenyl epoxy resin in Example 1, the rest is the same as in Example 1.

[0125] Experimental Example 1

[0126] The following methods were used to test the thermally bonded and sintered coated copper sheets:

[0127] Heat-applied peeling rate: The probability of 100 heat-applied coated copper sheets falling off naturally.

[0128] Average heat-applied thrust: The average thrust when 30 heat-applied coated copper sheets are pushed horizontally until they detach;

[0129] Sintered average shear strength: The ratio of the average thrust to the area of ​​force applied when 30 sintered coated copper sheets are pushed horizontally until they fall off.

[0130] The results are shown in Table 1.

[0131] Table 1

[0132]

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a coated copper sheet for interconnecting copper electrodes on the front side of a chip, characterized in that, Includes the following steps: S1: Pre-process and single-sided metallization of bare copper sheets to obtain copper sheets with single-sided metallization layers; S2: Apply metal solder paste to a single-sided metallization layer of a copper sheet, and then dry it in an inert or reducing atmosphere to obtain a copper sheet with a metal solder film. S3: Apply temporary adhesive to certain points of the metal solder film on the copper sheet to obtain a coated copper sheet for interconnecting copper electrodes on the front side of the chip. The metal solder paste comprises the following components in parts by weight: 80-85 parts of corrosion inhibitor coating metal particles and 15-20 parts of organic solvent system. The mass ratio of metal particles to corrosion inhibitor in the corrosion inhibitor coating metal particles is (75-80):(2-5). The corrosion inhibitor is selected from at least one of malic acid and tartaric acid. The organic solvent system is composed of the following components in parts by weight: 1-3 parts of antioxidant and 97-99 parts of organic solvent. After drying, the copper sheet undergoes activation treatment. The activation treatment includes: a first immersion in a phosphoric acid solution or citric acid solution, followed by rinsing and drying; and a second immersion in a sodium sulfate solution, followed by rinsing and drying. The phosphoric acid solution contains 10-20% by mass, the citric acid solution contains 5-10% by mass, and the first immersion time is 5-10 minutes; the sodium sulfate solution contains 5-10% by mass, and the second immersion time is 5-10 minutes. The temporary adhesive comprises the following components in parts by weight: 77-80 parts resin component, 20-25 parts diluent and 1-3 parts dispersant, wherein the resin component is selected from at least one of tetramethylbiphenyl epoxy resin, polyethylene terephthalate and polyethylene glycol ester.

2. The preparation method according to claim 1, characterized in that, The single-sided metallization layer is an Ag plating layer, a Ni / Ag plating layer, or a Ni / Pd / Au plating layer, and the thickness of the single-sided metallization layer is 1-3 μm.

3. The preparation method according to claim 1, characterized in that, The antioxidant is selected from at least one of citric acid, succinic acid, lactic acid, oxalic acid and ascorbic acid; the organic solvent is selected from at least one of ethylene glycol, diethylene glycol, terpineol, glycerol and n-decaol.

4. The preparation method according to claim 1, characterized in that, The diluent is selected from at least one of ethylene glycol, propylene glycol, glycerol, n-butanol, diethylene glycol, acetone alcohol, and polyethylene glycol.

5. The preparation method according to claim 1, characterized in that, The dispersant is selected from at least one of n-decaol, methanol, cyclohexanol and ethanol.

6. The preparation method according to claim 1, characterized in that, After activation, a coating solution is used for coating treatment; wherein, the coating solution includes a first organic compound and a second organic compound, the first organic compound being selected from at least one of diethyl phthalate, dibutyl phthalate, butyl acetate, dimethyl terephthalate, dioctyl phthalate, ethyl propionate, phenyl acetate, isoamyl acetate, and dipropyl phthalate, and the second organic compound being selected from at least one of ethanol, acetone, and ethyl acetate; the mass ratio of the first organic compound to the second organic compound in the coating solution is (3-20):(80-95).

7. A coated copper sheet for interconnecting copper electrodes on the front side of a chip, characterized in that, Prepared according to the preparation method according to any one of claims 1-6.

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