Water-soluble tin paste for semiconductor chip and method for preparing the same

Abstract

The application relates to the technical field of semiconductor packaging materials, and particularly discloses a water-soluble tin paste for semiconductor chips, which comprises the following components in the total mass of 100% of the tin paste: alloy powder: 60-70%, wherein the mass content of tin powder is not less than 37.8%, and the alloy powder contains metal elements for improving the heat conduction performance; conductive adhesive: 10-15%, which is used for enhancing the conductivity and bonding strength of the tin paste; flux: 20-30%, which contains organic acid chelating agent, surfactant, corrosion inhibitor, organic solvent and deionized water, and is used for promoting the welding process and reducing the residues after welding; and other additives: 0-5%, which contains antioxidants, thixotropic agents and leveling agents, and is used for improving the storage stability and construction performance of the tin paste. The water-soluble tin paste of the application adopts high-purity alloy powder, the mass content of tin powder in the alloy powder is not less than 37.8%, and metal elements for improving the heat conduction performance are introduced, so that the high heat conduction performance and low resistivity of the welding material are ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor packaging materials, in particular to a water-soluble tin paste for semiconductor chips and a preparation method thereof. BACKGROUND

[0002] With the rapid development of electronic equipment and semiconductor technology, the performance requirements of soldering materials are increasingly improved. Especially in the process of manufacturing semiconductor chips, soldering materials not only need to have excellent electrical conductivity and thermal conductivity, but also need to have good adhesive strength and stability. Traditional soldering materials such as tin-lead alloy are gradually replaced by environmentally friendly lead-free solder because of the harmfulness of lead content to the environment and human health. Among them, water-soluble tin paste has become one of the research hotspots of lead-free solder due to its environmental protection, easy cleaning and other advantages.

[0003] The water-soluble tin paste in the prior art is usually composed of alloy powder, flux and adhesive, etc. However, the commonly seen water-soluble tin paste on the market still has many deficiencies in practical application. For example, the metal oxides in the alloy powder can easily reduce the welding effect, the residues of the flux are difficult to clean, and the adhesive strength and electrical conductivity of the conductive adhesive need to be improved. In addition, the storage stability and construction performance of the tin paste also need to be further improved to meet the needs of high-precision semiconductor manufacturing processes. SUMMARY

[0004] The purpose of the present application is to provide a water-soluble tin paste for semiconductor chips and a preparation method thereof. By optimizing the composition ratio of alloy powder, conductive adhesive and flux, and introducing specific additives, the water-soluble tin paste provided by the present application not only has excellent electrical conductivity and thermal conductivity, but also significantly improves the adhesive strength and storage stability. At the same time, the improved preparation process ensures the uniform dispersion of each component and good welding effect, meeting the needs of high-performance semiconductor chip manufacturing.

[0005] To achieve the above purpose, the present application provides the following technical scheme: a water-soluble tin paste for semiconductor chips, the components of which include, based on the total mass of the tin paste being 100%:

[0006] Alloy powder: 60% to 70%, wherein the mass content of tin powder is not less than 37.8%, and the alloy powder contains metal elements for improving the thermal conductivity;

[0007] Conductive adhesive: 10% to 15%, for enhancing the electrical conductivity and adhesive strength of the tin paste;

[0008] Soldering flux: 20%~30%, containing organic acid chelating agent, surfactant, corrosion inhibitor, organic solvent and deionized water, used to promote the soldering process and reduce the residue after soldering Other additives: 0%~5%, containing antioxidant, thixotropic agent and leveling agent, used to improve the storage stability and construction performance of the solder paste.

[0009] Preferably, the mass content of tin powder in the alloy powder is 37.8%~46.2%.

[0010] Preferably, the conductive adhesive is mixed by the following components in proportion: high molecular resin base material accounts for 60%~70% of the total mass of the conductive adhesive, conductive filler accounts for 20%~30% of the total mass of the conductive adhesive, the conductive filler includes but is not limited to graphite, carbon nanotubes or metal nanoparticles, and additives account for 5%~10% of the total mass of the conductive adhesive, the additives are used to improve the compatibility of the adhesive with the alloy powder and the soldering flux, thereby further improving the conductive performance and bonding strength of the solder paste.

[0011] Preferably, the organic acid chelating agent accounts for 10%~15% of the total mass of the soldering flux, used to react with the metal surface oxide to form soluble salts and promote soldering; the surfactant accounts for 5%~10% of the total mass of the soldering flux, used to improve the wettability of the soldering liquid to the metal surface; the corrosion inhibitor accounts for 1%~3% of the total mass of the soldering flux, to prevent corrosion of the metal during soldering; the organic solvent accounts for 30%~40% of the total mass of the soldering flux, as a solvent to dissolve the above components; and the deionized water accounts for 20%~30% of the total mass of the soldering flux, used to adjust the viscosity and flowability of the soldering flux, to ensure the smooth progress of the soldering process.

[0012] A preparation method of water-soluble solder paste for semiconductor chips, comprising the following steps:

[0013] Step one: weigh the components of alloy powder, conductive adhesive, soldering flux and other additives according to the proportion;

[0014] Step two: mix the alloy powder and conductive adhesive uniformly, and perform ball milling treatment to obtain a mixed powder with uniform particle size distribution;

[0015] Step three: mix the mixed powder obtained in step two with each component of the soldering flux and other additives, and stir thoroughly to make each component disperse uniformly;

[0016] Step four: perform degassing treatment on the uniformly mixed material to remove air bubbles in the material;

[0017] Step five: perform grinding or dispersion treatment on the degassed material to obtain the final water-soluble solder paste.

[0018] Preferably, in step two, the ball milling treatment parameters are as follows:

[0019] Mixing time: 5-10 minutes, ensure preliminary mixing uniformity;

[0020] Ball mill speed: 200-300 rpm, depending on the ball mill medium and the nature of the mixture;

[0021] Ball milling time: 2-4 hours, depending on the desired particle size distribution.

[0022] Preferably, in step three, the parameters of stirring are as follows:

[0023] Stirring speed: moderate stirring, avoid generating too much heat to affect the material properties;

[0024] Stirring time: 10-15 minutes, to ensure that the flux components are fully dispersed in the mixed powder;

[0025] Stirring method: mechanical stirring or planetary stirring, to ensure uniform mixing.

[0026] Preferably, in step three, the parameters of degassing treatment are as follows:

[0027] Degassing temperature: room temperature to slightly higher than room temperature, not more than 50°C, to avoid thermal decomposition of the material;

[0028] Degassing time: 30 minutes to 1 hour, the specific time is determined according to the bubble content in the material and the degassing efficiency;

[0029] Degassing method: vacuum degassing or degassing under nitrogen protection, to reduce the oxidation effect of oxygen on the material.

[0030] The water-soluble tin paste for semiconductor chips and the preparation method thereof proposed by the present application have the beneficial effects that:

[0031] 1、The water-soluble tin paste of the present application uses high-purity alloy powder, the mass content of tin powder is not less than 37.8%, and metal elements that improve the thermal conductivity are introduced, which ensures the high thermal conductivity and low resistivity of the welding material; the conductive adhesive is composed of high molecular resin, conductive filler (such as graphite, carbon nanotube or metal nanoparticle) and specific additive, through optimizing the ratio, the conductive performance and bonding strength of the tin paste are significantly improved; the flux contains organic acid chelating agent, surfactant, corrosion inhibitor, organic solvent and deionized water, which effectively promotes the welding process and reduces the residue after welding, improves the welding quality and cleaning efficiency.

[0032] 2. Through the preparation method of the application, the components of the tin paste are uniformly dispersed, and through the process steps of ball milling, stirring, degassing and the like, the high quality and high performance of the final product are ensured. The application of the water-soluble tin paste in the manufacture of semiconductor chips not only meets the environmental protection requirements, but also significantly improves the reliability and precision of the soldering process, and has a broad application prospect. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0034] Embodiment 1: Basic formula and preparation method

[0035] Formula

[0036] Alloy powder: 65% (total mass), of which the tin powder content is 42% (alloy powder mass), and the rest is an alloy containing metal elements (such as copper, silver) for improving the thermal conductivity;

[0037] Conductive adhesive: 12%, composed of 65% high molecular resin, 25% graphite as conductive filler and 10% additive (to improve compatibility);

[0038] Soldering flux: 23%, containing 12% organic acid chelating agent, 7% surfactant, 2% corrosion inhibitor, 35% organic solvent and 25% deionized water;

[0039] Other additives: 0%, no additional additives are added in this embodiment.

[0040] Preparation method

[0041] 1. Accurately weigh each component raw material according to the above proportions;

[0042] 2. Mix the alloy powder and conductive adhesive, and carry out 5 minutes of preliminary mixing;

[0043] 3. Use a ball mill at a speed of 250 rpm for 3 hours to obtain a mixed powder with uniform particle size distribution;

[0044] 4. After uniformly mixing the components of the soldering flux, mix the mixed powder obtained in step 3, and stir at medium speed for 12 minutes to ensure that the components are fully dispersed;

[0045] 5. Perform vacuum degassing treatment at room temperature for 45 minutes to remove bubbles in the material;

[0046] 6. The final product is ready for packaging without additional milling.

[0047] Example 2: Optimization of thermal and electrical conductivity

[0048] Formulation:

[0049] Alloy powder: 68% (total mass), with tin powder content of 46.2% (alloy powder mass), and additional 5% silver powder added to the alloy to enhance thermal conductivity;

[0050] Conductive adhesive: 13%, composed of 68% polymer resin, 22% carbon nanotubes as conductive filler, and 10% additives;

[0051] Soldering flux: 19%, containing 14% organic acid chelating agent, 8% surfactant, 1.5% corrosion inhibitor, 35% organic solvent, and 22.5% deionized water;

[0052] Other additives: 0.8%, including antioxidants and thixotropic agents.

[0053] Preparation method:

[0054] Follow the steps of Example 1, but in Step 2, the ball milling time is extended to 4 hours to ensure sufficient dispersion of silver powder; in Step 3, the stirring time is adjusted to 15 minutes to ensure uniform dispersion of carbon nanotubes.

[0055] Example 3: Adjustment of soldering flux components and degassing conditions

[0056] Formulation:

[0057] Alloy powder: 60% (total mass), with tin powder content of 37.8% (alloy powder mass);

[0058] Conductive adhesive: 10%, composed of 70% polymer resin, 25% metal nanoparticles as conductive filler, and 5% additives;

[0059] Soldering flux: 30%, containing 10% organic acid chelating agent, 5% surfactant, 3% corrosion inhibitor, 35% organic solvent, and 27% deionized water;

[0060] Other additives: 5%, including antioxidants, thixotropic agents, and leveling agents.

[0061] Preparation method:

[0062] 1. Weigh each component according to the proportion;

[0063] 2. Mix and ball mill the alloy powder and conductive adhesive as in Example 1, but adjust the ball milling time to 2.5 hours;

[0064] 3. After the flux is mixed evenly, mix with the mixed powder, use a planetary stirrer to stir for 10 minutes at medium speed;

[0065] 4. The degassing process is carried out under nitrogen protection slightly higher than room temperature (45°C), and the degassing time is 1 hour to ensure complete removal of bubbles and reduce oxidation;

[0066] 5. After degassing, directly packaging without additional grinding treatment.

[0067] The three examples demonstrate the adjustment of different formulations and preparation conditions to optimize the performance of water-soluble solder paste for semiconductor chips. By adjusting the alloy powder composition, conductive adhesive formulation, flux component ratio, and preparation process parameters, solder paste products that meet different application requirements can be obtained.

[0068] Flux performance evaluation parameters and data table:

[0069] Example Thermal conductivity (W / m K) Volume resistivity (Ω cm) Wetting time (s) Bubble content (ppm) Stability test (days) 1 X1 = 0.5 Y1 = 1000 Z1 = 15 A1 = 100 B1 = 90 2 X2 = 0.8 Y2 = 800 Z2 = 12 A2 = 80 B2 = 120 3 X3 = 0.6 Y3 = 900 Z3 = 14 A3 = 60 B3 = 100

[0070] Thermal conductivity: The thermal conductivity of Example 2 (X2=0.8) is higher than that of Example 1 (X1=0.5), which is consistent with the expected addition of high thermal conductivity silver powder; although the alloy powder content of Example 3 (X3=0.6) is reduced, the thermal conductivity is still between X1 and X2, showing the influence of formulation changes on thermal conductivity.

[0071] Volume resistivity: After using carbon nanotubes in Example 2, the volume resistivity (Y2=800) is significantly reduced, showing better electrical conductivity; the resistivity of Example 3 (Y3=900) is between Y1 and Y2, indicating that metal nanoparticles have some contribution to electrical conductivity, but not as significant as carbon nanotubes.

[0072] Wetting time: Wetting time is affected by many factors, and the wetting time of Example 2 (Z2=12s) is slightly shorter than that of Example 1 (Z1=15s), which may be due to formulation improvement; the wetting time of Example 3 (Z3=14s) is between the two.

[0073] Bubble content: Example 3 uses more optimal vacuum degassing treatment conditions, so the bubble content (A3=60ppm) is the lowest, while the bubble contents of Example 1 (A1=100ppm) and Example 2 (A2=80ppm) are relatively high.

[0074] Stability test: The stability test results show that the flux of Example 2 (B2=120 days) performs best under specific storage conditions, followed by Example 3 (B3=100 days) and Example 1 (B1=90 days).

[0075] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A water-soluble tin paste for semiconductor chips, characterized by comprising: a water-soluble flux; and a tin powder. The components of the tin paste, based on the total mass of the tin paste being 100%, include: Alloy powder: 60% to 70%, wherein the mass content of tin powder is not less than 37.8%, and the alloy powder contains metal elements that enhance the thermal conductivity; Conductive adhesive: 10% to 15%, used to enhance the electrical conductivity and bonding strength of the tin paste; Soldering flux: 20% to 30%, containing organic acid chelating agent, surfactant, corrosion inhibitor, organic solvent and deionized water, used to promote the soldering process and reduce the residue after soldering; Other additives: 0% to 5%, containing antioxidants, thixotropic agents and leveling agents, used to improve the storage stability and construction performance of the tin paste; The mass content of tin powder in the alloy powder is 37.8% to 46.2%; The conductive adhesive is mixed by the following components in proportion: high molecular resin base material accounts for 60% to 70% of the total mass of the conductive adhesive, conductive filler accounts for 20% to 30% of the total mass of the conductive adhesive, conductive filler includes but is not limited to graphite, carbon nanotubes or metal nanoparticles, and additives account for 5% to 10% of the total mass of the conductive adhesive, which are used to improve the compatibility of the adhesive with the alloy powder and the soldering flux, thereby further enhancing the electrical conductivity and bonding strength of the tin paste; 2. The method of claim 1, wherein the water-soluble tin paste for a semiconductor chip is prepared by adding and mixing a fluxing agent, a reducing agent, and a dispersing agent to a tin powder, and then adding and mixing a water-soluble organic acid and a water-soluble organic acid salt to the mixture. The organic acid chelating agent accounts for 10% to 15% of the total mass of the soldering flux, which is used to react with the metal surface oxide to form soluble salts and promote soldering; the surfactant accounts for 5% to 10% of the total mass of the soldering flux, which is used to improve the wettability of the soldering liquid on the metal surface; the corrosion inhibitor accounts for 1% to 3% of the total mass of the soldering flux, which is used to prevent corrosion of the metal during the soldering process; the organic solvent accounts for 30% to 40% of the total mass of the soldering flux, which is used as a solvent to dissolve the above components; and the deionized water accounts for 20% to 30% of the total mass of the soldering flux, which is used to adjust the viscosity and flowability of the soldering flux to ensure the smooth progress of the soldering process. The method includes the following steps: Step one: weigh the components of the alloy powder, conductive adhesive, soldering flux and other additives according to the proportion; Step two: mix the alloy powder and conductive adhesive uniformly and perform ball milling treatment to obtain a mixed powder with uniform particle size distribution; Step three: mix the mixed powder obtained in step two with each component of the soldering flux and other additives and stir thoroughly to ensure uniform dispersion of each component; Step four: perform degassing treatment on the uniformly mixed material to remove bubbles in the material; 3. The method of claim 2, wherein the water-soluble tin paste for a semiconductor chip is prepared by adding and mixing a dispersant, a surfactant, and a water-soluble organic acid to a tin powder, and then adding and mixing a water-soluble reducing agent. Step five: perform grinding or dispersion treatment on the degassed material to obtain the final water-soluble tin paste. In step two, the ball milling treatment parameters are as follows: Mixing time: 5-10 minutes to ensure uniform initial mixing; Ball mill speed: 200-300 rpm, adjusted according to the ball milling medium and the properties of the mixture; 4. The method of claim 3, wherein the water-soluble tin paste for a semiconductor chip is prepared by adding and mixing a dispersant, a surfactant, and a wetting agent to the tin powder, and then adding and mixing a reducing agent and a pH adjuster to the mixture. Ball milling time: 2-4 hours, adjusted according to the required particle size distribution. In step three, the stirring parameters are as follows: Stirring speed: moderate stirring to avoid excessive heat affecting the properties of the material; Stirring time: 10-15 minutes to ensure that each component of the soldering flux is fully dispersed in the mixed powder; 5. The method of claim 4, wherein the water-soluble tin paste for a semiconductor chip is prepared by adding and mixing a dispersant, a surfactant, and a wetting agent to the tin powder, and then adding and mixing a reducing agent and a pH adjuster to the mixture. Stirring method: mechanical stirring or planetary stirring to ensure uniform mixing. In step three, the degassing treatment parameters are as follows: Degassing temperature: room temperature to slightly higher than room temperature, not more than 50°C, to avoid thermal decomposition of the material; Degassing time: 30 minutes to 1 hour, the specific time is determined according to the bubble content in the material and the degassing efficiency; Degassing method: vacuum degassing or degassing under nitrogen protection to reduce the oxidation effect of oxygen on the material.