A metal solder paste for power device packaging, its preparation method and application

Abstract

The present invention provides a metal solder paste for power device packaging, and a preparation method and application thereof. The preparation method of the metal solder paste for power device packaging of the present invention comprises the following steps: S1: coating metal particles with a binder to obtain coated metal particles; S2: uniformly mixing a dispersant, an antioxidant and an organic solvent to obtain an organic solvent system; S3: mixing and stirring the coated metal particles with the organic solvent system to obtain a mixture; S4: mixing and stirring the mixture with a thermosetting resin to obtain a metal solder paste for power device packaging. The metal solder paste prepared by the present invention has good chip mounting performance and can maintain a certain strength after mounting, thereby ensuring that the chip and the lower substrate do not shift relative to each other during the subsequent movement and sintering process, and effectively solves the problems such as mounting difficulties faced in the chip mounting link during actual production applications.

Description

Technical Field

[0001] The present invention relates to the technical field of third-generation semiconductor power device packaging, and in particular to a metal solder paste for power device packaging, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous development of fields such as aerospace and electric vehicles, the requirements for core power devices are gradually increasing. Third-generation wide-bandgap semiconductors have gradually received increasing research and attention. Third-generation wide-bandgap semiconductors have higher operating junction temperatures and can maintain good operating performance above 350°C.

[0003] The reliability of the package interconnects determines the performance and usability of the power module. The coating material used for the interconnect layer also determines the reliability of the package interconnect structure. Traditional tin-based solders operate below 175°C, so nano / micron metal solder pastes, which offer low-temperature sintering and high-temperature performance, are widely used.

[0004] Currently, extensive research has been conducted on solder pastes made from silver and copper. In actual production applications, die placement is performed after the pre-drying step. This involves performing die placement at a specific temperature and low pressure to ensure that the relative position of the chip and substrate remains unchanged during subsequent transfer and pressure sintering. However, the bonding strength between the chip and solder paste after die placement using existing solder paste is too low, leading to risks such as chip shifting in subsequent processes.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a metal solder paste for power device packaging, a preparation method and application thereof, wherein the metal solder paste has good chip mounting performance and can maintain a certain strength after chip mounting, thereby ensuring that no relative displacement of the chip and the lower substrate occurs during subsequent movement and sintering, and effectively solving the problems such as chip mounting difficulties faced in the chip mounting link during actual production and application.

[0007] The present invention provides a method for preparing a metal solder paste for power device packaging, comprising the following steps:

[0008] S1: coating the metal particles with a binder to obtain coated metal particles;

[0009] S2: uniformly mixing the dispersant, antioxidant and organic solvent to obtain an organic solvent system;

[0010] S3: mixing and stirring the coated metal particles with the organic solvent system to obtain a mixture;

[0011] S4: The mixture is mixed and stirred with a thermosetting resin to obtain a metal solder paste for power device packaging.

[0012] In the present invention, the mass ratio between the coated metal particles, the organic solvent system and the thermosetting resin can be (75-89): (10.5-22): (0.5-3), preferably (79.5-81.5): (17-19): 1.5; the mass ratio of the binder to the metal particles is (0.1-5): (95-99.9).

[0013] In the present invention, step S1 includes:

[0014] S11: pre-treating the metal particles to obtain pre-treated metal particles;

[0015] S12: mixing the pretreated metal particles with the binder solution and then performing ultrasonic treatment, and removing the supernatant by centrifugation to obtain binder-coated metal particles;

[0016] S13: mixing the binder-coated metal particles with the ethanol solution, performing ultrasonic treatment, and removing the supernatant by centrifugation to obtain coated metal particles.

[0017] Specifically, step S11 includes the following steps performed in sequence:

[0018] A) mixing metal particles with acid solution, performing ultrasonic treatment, and removing the supernatant by centrifugation;

[0019] B) adding alcohol for ultrasonic treatment, and removing the supernatant by centrifugation to obtain pretreated metal particles.

[0020] In the above step A), the acid solution may be at least one of a dilute sulfuric acid solution and a lactic acid solution, and the ultrasonic treatment conditions after mixing with the acid solution include: an ultrasonic time of 3-30 min.

[0021] In the above step B), the ultrasonic treatment conditions for adding alcohol include: ultrasonic time is 3-20 minutes.

[0022] In step S12, the binder solution may be an ethanol solution of the binder; the binder content in the binder solution may be 0.5-5% by mass; and the ultrasonic treatment conditions after the pretreated metal particles are mixed with the binder solution include: ultrasonic treatment time of 30-90 min.

[0023] In step S13, the ultrasonic treatment conditions for mixing the binder-coated metal particles with the ethanol solution include: ultrasonic treatment time of 10-40 minutes.

[0024] In step S1, the metal particles are silver particles or copper particles; the particle size range of the metal particles is 100-2200 nm, preferably 300-1200 nm, and the particle size of the metal particles can be 300 nm, 400 nm, 500 nm, 800 nm, 1000 nm, or 1200 nm.

[0025] The binder is selected from at least one of polyvinyl alcohol, polyacrylate, polyvinyl acetate, polymethyl methacrylate, methyl cellulose and ethyl cellulose, preferably methyl cellulose or polymethyl methacrylate.

[0026] In step S2, the mass ratio of the dispersant, antioxidant, and organic solvent in the organic solvent system is (0.5-3):(0-3):(94-99.5), preferably (1-1.5):(0-1):(98-98.5). There is no strict limitation on the mixing method of the dispersant, antioxidant, and organic solvent, as long as they are uniformly mixed, for example, magnetic stirring for 1-3 hours.

[0027] In an organic solvent system, a dispersant is used to prevent metal particles from agglomerating during the preparation and printing of the sintered solder paste. The organic solvent is used to adjust the viscosity of the sintered solder paste. An antioxidant can be added optionally. When the metal particles are silver, the mass ratio of the dispersant, antioxidant, and organic solvent in the organic solvent system is (0.5-3):0:(97-99.5), for example, 1.5:0:98.5. In this case, the antioxidant is not required. When the metal particles are copper, the mass ratio of the dispersant, antioxidant, and organic solvent in the organic solvent system is (0.5-3):(0.5-3):(94-99), for example, 1:1:98. In this case, the antioxidant is used to prevent oxidation of the copper powder surface and inhibit the formation of oxides in the copper paste during subsequent processes.

[0028] Specifically, the dispersant is at least one of fatty acids; the antioxidant is at least one of α-hydroxy acid compounds; the organic solvent is at least one of alcohol organic solvents; preferably, the dispersant is selected from at least one of saturated fatty acids having a carbon number greater than or equal to 10 and less than or equal to 18; further, the dispersant is selected from at least one of stearic acid, caprylic acid and capric acid, more preferably caprylic acid or capric acid; the antioxidant is selected from at least one of malic acid, citric acid and ascorbic acid, more preferably citric acid and ascorbic acid; the organic solvent is selected from at least one of ethanol, ethylene glycol, propylene glycol, glycerol, terpineol and diethylene glycol, more preferably ethylene glycol, propylene glycol and glycerol, or glycerol, ethylene glycol and diethylene glycol.

[0029] In step S3, the stirring includes: stirring for 10-30 minutes using a vacuum degassing machine.

[0030] In step S4, the thermosetting resin is selected from at least one of bisphenol A epoxy resin, polyol epoxy resin, acid anhydride resin, phenolic resin, unsaturated polyester resin and silicone ether resin; and the stirring comprises: stirring for 20-40 minutes using a vacuum degassing machine.

[0031] The present invention also provides a metal solder paste for power device packaging, which is prepared according to the above preparation method.

[0032] The present invention also provides the use of the metal solder paste for power device packaging in power device packaging. The metal solder paste for power device packaging can be well applied to the chip mounting step in actual production.

[0033] The packaging interconnection structure of the power device includes a chip, a substrate, and a connection layer for connecting the chip and the substrate. The connection layer is formed by printing, drying, chip mounting, sintering and other steps using the metal solder paste for power device packaging mentioned above. Among them, the substrate can be a substrate with three metallized coatings of copper, silver and gold; the chip can be a silicon or silicon carbide chip.

[0034] The present invention also provides a method for attaching a metal solder paste for power device packaging, comprising the following steps:

[0035] a) uniformly coating the metal solder paste for power device packaging on the connection surface of the substrate by steel screen printing to obtain a stacked structure of the solder paste and the substrate;

[0036] b) placing the stacked structure of the solder paste and the substrate in a drying oven, heating it to 100-140° C., keeping it warm for 10-30 minutes, and drying it without pressure to obtain a dried structure;

[0037] c) Place the drying structure on a heating platform at 90-130°C, maintain nitrogen 7 gas blowing, use a semi-automatic suction pen to take the crystal, apply 0.2-3MPa pressure, and attach the chip to the solder paste layer of the drying structure.

[0038] In step a), the substrate is pretreated before coating. The pretreatment includes: cleaning the substrate with a cleaning agent to remove contaminants on the substrate surface, ultrasonically washing the cleaned substrate in anhydrous ethanol to remove impurities on the substrate surface, and then drying the substrate in a vacuum drying oven to remove the anhydrous ethanol.

[0039] In step c), the temperature of the heating stage is preferably 95-125°C.

[0040] The implementation of the present invention has at least the following advantages:

[0041] The present invention uses a binder to coat metal particles and adds a thermosetting resin under a specific system to prepare a metal solder paste for power device packaging. The binder has a high volatilization temperature and is not completely removed after the drying step. The resin is not solidified at the drying temperature, which plays an auxiliary role in chip mounting. The metal solder paste has good chip mounting performance and can maintain a certain strength after mounting, thereby ensuring that no relative displacement of the chip and the lower substrate occurs during subsequent movement and sintering processes, and effectively solves the problems of chip mounting difficulties faced in the chip mounting link during actual production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 The process flow chart for preparing metal solder paste for power device packaging;

[0044] Figure 2 This is a schematic diagram of the chip mounting process;

[0045] Figure 3 The strength variation diagram of the chip mounting structure at different temperatures;

[0046] Figure 4 This is a graph showing the sintering strength of metal solder paste used for power device packaging at different temperatures. DETAILED DESCRIPTION

[0047] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0048] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular also includes the plural. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0049] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0050] Example 1

[0051] See also Figure 1 As shown, the method for preparing the metal solder paste for power device packaging in this embodiment comprises the following steps:

[0052] 1. Pretreatment of metal particles

[0053] Silver particles (particle size 1200 nm) were mixed with dilute sulfuric acid solution, ultrasonicated for 10 min, and centrifuged to remove the supernatant.

[0054] Subsequently, alcohol was added, ultrasonic treatment was performed for 8 minutes, and the supernatant was removed by centrifugation to obtain pretreated silver particles.

[0055] 2. Adhesive coating

[0056] The pretreated silver particles were mixed with a methylcellulose ethanol solution, wherein the mass ratio of methylcellulose to ethanol was 2:98, and ultrasonic treatment was performed for 30 minutes. The supernatant was removed by centrifugation to obtain binder-coated silver particles.

[0057] The binder-coated silver particles were mixed with the ethanol solution according to the dosage ratio, ultrasonically treated for 40 minutes, and centrifuged to remove the supernatant to obtain coated silver particles.

[0058] 3. Preparation of organic solvent system

[0059] Caprylic acid, ethylene glycol, propylene glycol, and glycerol were mixed in a mass ratio of 1.5:30:30:38.5 and magnetically stirred for 1 hour to obtain an organic solvent system.

[0060] 4. Mix

[0061] The coated metal particles of step 2 were mixed with the organic solvent system of step 3, and stirred in a vacuum degasser for 10 minutes to obtain a mixture.

[0062] 5. Preparation of silver paste for power device packaging

[0063] The mixture of step 4 was mixed with bisphenol A epoxy resin, and the mass ratio of the coated silver particles, the organic solvent system and the bisphenol A epoxy resin was controlled to be 81.5:17:1.5. The mixture was stirred in a vacuum degassing machine for 40 minutes to obtain a silver paste for power device packaging.

[0064] The silver paste for power device packaging prepared above is applied to the packaging interconnection structure of wide bandgap semiconductor devices. The schematic diagram of the chip mounting process of the silver paste for power device packaging is shown in FIG. Figure 2 As shown, the substrate of the package interconnect structure is a silver-plated substrate, and the chip is a silicon carbide chip with an area of 5×6mm. 2 , the silver-plated substrate area is 15×15mm 2 , the specific steps are as follows:

[0065] (1) using a cleaning agent to remove contaminants from the surface of the substrate, ultrasonically washing the treated substrate in anhydrous ethanol to remove impurities on the surface, and drying in a vacuum drying oven to remove the anhydrous ethanol;

[0066] (2) uniformly coating the silver paste for power device packaging prepared above on the connection surface of the substrate obtained in step (1) by screen printing to obtain a stacking structure of solder paste and substrate;

[0067] (3) placing the stacked structure of the solder paste and the substrate obtained in step (2) in a drying oven, heating it to 140° C., keeping it warm for 10 minutes, and drying it without pressure to obtain a dried structure;

[0068] (4) placing the dried structure obtained in step (3) on a heating table at 90-130° C. and maintaining nitrogen blowing;

[0069] (5) The silicon carbide chip is taken out of the crystal using a semi-automatic suction pen, a pressure of 0.2 MPa is applied, and the chip is attached to the solder paste layer of the drying structure to complete the chip mounting process.

[0070] After use test, the silver paste for power device packaging prepared in this embodiment can complete the chip mounting step well, and the stacked structure after mounting has a certain strength. The structural strength after chip mounting at different temperatures is as follows: Figure 3 As shown in the figure, the results show that the mounting structure can well meet the actual production needs and ensure good sintering quality.

[0071] After the chip is mounted, it is sintered. The sintering strength at different temperatures and 20MPa pressure is as follows: Figure 4 As shown in the figure, the results show that the metal solder paste has good chip mounting performance and can maintain a certain strength after mounting, thereby ensuring that there is no relative displacement between the chip and the lower substrate during the subsequent movement and sintering process, and effectively solving the problems of chip mounting difficulties faced in the actual production application process.

[0072] Example 2

[0073] The method for preparing the metal solder paste for power device packaging of this embodiment comprises the following steps:

[0074] 1. Pretreatment of metal particles

[0075] Copper particles (particle size 300 nm) were mixed with lactic acid solution, ultrasonicated for 10 min, and centrifuged to remove the supernatant.

[0076] Subsequently, alcohol was added, ultrasonic treatment was performed for 6 min, and the supernatant was removed by centrifugation to obtain pretreated copper particles.

[0077] 2. Adhesive coating

[0078] The pretreated copper particles were mixed with a polymethyl methacrylate ethanol solution, wherein the mass ratio of methyl methacrylate to ethanol was 1:99, and ultrasonically treated for 90 minutes. The supernatant was removed by centrifugation to obtain binder-coated copper particles.

[0079] The binder-coated copper particles were mixed with an ethanol solution, ultrasonically treated for 10 minutes, and centrifuged to remove the supernatant to obtain coated copper particles.

[0080] 3. Preparation of organic solvent system

[0081] Capric acid, citric acid, ascorbic acid, glycerol, ethylene glycol, and diethylene glycol were mixed in a mass ratio of 1:0.5:0.5:32:32:33 and magnetically stirred for 3 hours to obtain an organic solvent system.

[0082] 4. Mix

[0083] The coated metal particles of step 2 were mixed with the organic solvent system of step 3, and then stirred in a vacuum degasser for 30 minutes to obtain a mixture.

[0084] 5. Preparation of silver paste for power device packaging

[0085] The mixture of step 4 was mixed with phenolic resin, and the mass ratio of the coated copper particles, the organic solvent system and the phenolic resin was controlled to be 79.5:19:1.5. The mixture was stirred in a vacuum degassing machine for 20 minutes to obtain a silver paste for power device packaging.

[0086] The silver paste for power device packaging prepared above is applied to the packaging interconnection structure of wide bandgap semiconductor devices. The schematic diagram of the chip mounting process of the silver paste for power device packaging is shown in FIG. Figure 2 As shown, the substrate of the package interconnect structure is a bare copper substrate, the chip is a silicon carbide chip, and the chip area is 5×6mm 2 , copper-plated substrate area is 15×15mm 2 , the specific steps are as follows:

[0087] (1) using a cleaning agent to remove contaminants from the surface of the substrate, ultrasonically washing the treated substrate in anhydrous ethanol to remove impurities on the surface, and drying in a vacuum drying oven to remove the anhydrous ethanol;

[0088] (2) uniformly coating the silver paste for power device packaging prepared above on the connection surface of the substrate obtained in step (1) by screen printing to obtain a stacking structure of solder paste and substrate;

[0089] (3) placing the stacked structure of the solder paste and the substrate obtained in step (2) in a drying oven, heating it to 100° C., keeping it warm for 30 minutes, and drying it without pressure to obtain a dried structure;

[0090] (4) placing the dried structure obtained in step (3) on a heating table at 90-130° C. and maintaining nitrogen blowing;

[0091] (5) The silicon carbide chip is taken out using a semi-automatic suction pen, and a pressure of 3 MPa is applied to the chip and the chip is attached to the solder paste layer of the drying structure to complete the chip mounting process.

[0092] After use tests, the silver paste for power device packaging prepared in this embodiment can complete the chip mounting step well. The stacked structure after mounting has a certain strength. The thermal mounting strength at a thermal mounting temperature of 110°C reaches 1.5 MPa, and the shear strength under sintering conditions of 250°C / 20 MPa reaches 75 MPa. It can be well applied to the chip mounting process in actual production and effectively improves the final sintering quality.

[0093] Comparative Example 1

[0094] Except that the mass ratio of the coated silver particles, the organic solvent system and the bisphenol A epoxy resin is controlled to be 83:17:0 (i.e., no thermosetting resin is added) in step 5, the rest is basically the same as in Example 1.

[0095] After use testing, the silver paste for power device packaging prepared in this comparative example has a thermal bonding strength of only 0.2 MPa at a thermal bonding temperature of 110°C after the chip mounting step. It cannot guarantee that the chip and the lower substrate will not be relatively displaced during the subsequent movement and sintering process, and cannot be well applied in actual production.

[0096] Comparative Example 2

[0097] The process was substantially the same as in Example 1, except that the binder coating in step 2 was not performed (i.e., the pretreated silver particles in step 1 were directly used for subsequent steps 4 and 5), and the mass ratio of the pretreated silver particles, the organic solvent system, and the bisphenol A epoxy resin in step 5 was controlled to be 81.5:17:1.5.

[0098] After use testing, the silver paste for power device packaging prepared in this comparative example has a thermal bonding strength of only 0.4 MPa at a thermal bonding temperature of 110°C after the chip mounting step. It cannot guarantee that the chip and the lower substrate will not undergo relative displacement during the subsequent movement and sintering process, and cannot be well applied in actual production.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 metal solder paste for power device packaging, characterized in that: The steps include: S1: coating the metal particles with a binder to obtain coated metal particles; S2: uniformly mixing the dispersant, antioxidant and organic solvent to obtain an organic solvent system; S3: mixing and stirring the coated metal particles with the organic solvent system to obtain a mixture; S4: mixing and stirring the mixture with a thermosetting resin to obtain a metal solder paste for power device packaging; The mass ratio of the coated metal particles, the organic solvent system and the thermosetting resin is (75-89):(10.5-22):(0.5-3); Step S1 includes: S11: pre-treating the metal particles to obtain pre-treated metal particles; S12: mixing the pretreated metal particles with the binder solution and then performing ultrasonic treatment, and removing the supernatant by centrifugation to obtain binder-coated metal particles; S13: mixing the binder-coated metal particles with the ethanol solution, performing ultrasonic treatment, and removing the supernatant by centrifugation to obtain coated metal particles; Step S11 includes the following steps performed in sequence: A) mixing metal particles with acid solution, performing ultrasonic treatment, and removing the supernatant by centrifugation; B) adding alcohol for ultrasonic treatment, and removing the supernatant by centrifugation to obtain pretreated metal particles; The mass ratio of the binder to the metal particles is (1-10):(90-99).

2. The preparation method according to claim 1, characterized in that In step S1, the metal particles are silver particles or copper particles; the particle size of the metal particles ranges from 100 to 2200 nm; and the binder is selected from at least one of polyvinyl alcohol, polyacrylate, polyvinyl acetate, polymethyl methacrylate, methyl cellulose, and ethyl cellulose.

3. The preparation method according to claim 1, characterized in that In step S2, the mass ratio of the dispersant, the antioxidant and the organic solvent in the organic solvent system is (0.5-3): (0-3): (94-99.5).

4. The preparation method according to claim 3, characterized in that When the metal particles are silver particles, the mass ratio of the dispersant, the antioxidant and the organic solvent in the organic solvent system is (0.5-3):0:(97-99.5).

5. The preparation method according to claim 3, characterized in that When the metal particles are copper particles, the mass ratio of the dispersant, the antioxidant and the organic solvent in the organic solvent system is (0.5-3): (0.5-3): (94-99).

6. The preparation method according to claim 1, characterized in that In step S2, the dispersant is at least one of fatty acids; the antioxidant is at least one of α-hydroxy acid compounds; and the organic solvent is at least one of alcohol organic solvents.

7. The preparation method according to claim 6, characterized in that The dispersant is at least one selected from saturated fatty acids having 10 or more and 18 or less carbon atoms.

8. The preparation method according to claim 6, characterized in that The dispersant is selected from at least one of stearic acid, caprylic acid and capric acid; the antioxidant is selected from at least one of malic acid, citric acid and ascorbic acid; and the organic solvent is selected from at least one of ethanol, ethylene glycol, propylene glycol, glycerol, terpineol and diethylene glycol.

9. The preparation method according to claim 1, characterized in that In step S3, the stirring includes: stirring for 10-30 minutes using a vacuum degassing machine.

10. The preparation method according to claim 1, characterized in that In step S4, the thermosetting resin is selected from at least one of bisphenol A epoxy resin, polyol epoxy resin, acid anhydride resin, phenolic resin, unsaturated polyester resin and silicone ether resin.

11. The preparation method according to claim 1, characterized in that In step S4, stirring includes: stirring for 20-40 minutes using a vacuum degassing machine.

12. A metal solder paste for power device packaging, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 11.

13. Use of the metal solder paste for power device packaging according to claim 12 in power device packaging.

14. A chip mounting method for metal solder paste for power device packaging, characterized in that: The steps include: a) uniformly coating the metal solder paste for power device packaging according to claim 12 on the connection surface of the substrate by steel screen printing to obtain a stacked structure of the solder paste and the substrate; b) placing the stacked structure of the solder paste and the substrate in a drying oven, heating it to 100-140° C., keeping it warm for 10-30 minutes, and drying it without pressure to obtain a dried structure; c) Place the drying structure on a heating platform at 90-130°C, keep nitrogen blowing, use a semi-automatic suction pen to remove the crystal, apply 0.2-3MPa pressure, and attach the chip to the solder paste layer of the drying structure.

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