Micro-nano silver paste organic carrier, micro-nano silver paste and preparation method thereof

Abstract

The application belongs to the technical field of electronic paste for integrated circuit manufacturing industry, and relates to an organic carrier for micro-nano silver paste, a micro-nano silver paste and a preparation method thereof. The method selects specific organic solvents with different hydrophilic indexes as the organic carrier, matches the organic carrier with nano silver powder and micro silver powder with specific water contact angles, and combines the specific mixing sequence of the organic carrier and the silver powder with different sizes, so that the surface of the nano silver powder with a large specific surface area is coated with an organic solvent with a high hydrophilic index, the surface of the micro silver powder is coated with an organic solvent with a low hydrophilic index, and then the volatilization speed of the organic solvents on the surface of the nano silver powder and the surface of the micro silver powder is close, thereby solving the problem that the volatilization of the organic solvent on the surface of the nano silver powder is too fast, local agglomeration occurs, the viscosity rapidly increases, and the use performance of the micro-nano silver paste is affected.

Description

Technical Field

[0001] This application belongs to the field of electronic paste technology for integrated circuit manufacturing, and particularly relates to an organic carrier for micro / nano silver paste, micro / nano silver paste and its preparation method. Background Technology

[0002] Electronic paste is a fundamental material for manufacturing thick-film devices. It is a paste-like substance formed by uniformly mixing solid powder and organic solvent through three-roll milling. The solid powder, as the functional phase in the electronic paste, forms a dense film layer after sintering. With the development of industry technology and the limitations of supporting technologies, certain applications of electronic paste have raised requirements regarding sintering temperature and other aspects.

[0003] Sintered silver paste is a thermal interface material that exhibits high thermal conductivity and shear strength after sintering under certain conditions. Sintered silver paste composed of micron-sized silver requires sintering under pressure and at relatively high temperatures. For example, Heraeus Electronics' PE338 grade printed sintered silver requires sintering at ≥230℃ and ≥10MPa pressure to achieve optimal performance. However, such high-temperature sintering conditions can easily damage the chip and are difficult to integrate with other packaging processes. Nanomaterials have significantly lower melting points than bulk metals. Based on this principle, researchers have introduced nano-silver powder into micron-sized sintered silver paste, obtaining micro / nano-sized sintered silver paste. Thanks to the high sintering activity of nano-silver powder, micro / nano-sized silver paste can be sintered under low-temperature, pressureless conditions. However, the introduction of nano-silver powder presents new requirements for organic carriers.

[0004] In the traditional preparation process of slurries, the organic carrier is mixed with the solid powder. For example, patent CN116159997 A discloses a method for preparing sintered silver paste and its application. The sintered silver paste includes silver powder filler, sintering aid, and organic carrier; wherein the silver powder filler includes single-component or multi-component silver powder, and the silver powder filler is a pure micron-sized silver powder system or a micro-nano composite silver powder system. During the preparation process, all components are mixed evenly. As another example, patent CN 115846650 A discloses a low-modulus sintered silver paste and its preparation method. In this method, modified polymer microspheres are added to the silver paste to improve its mechanical properties. The silver particles are near-spherical particles with particle sizes of 50-300 nm and 3-5 μm. The silver particles of different sizes are also prepared by simultaneously adding organic solvents and aids.

[0005] To ensure gradient evaporation and a suitable service window during sintering, the solvent in the organic carrier is typically a combination of several high- and low-boiling-point solvents. Literature [①Increased Evaporation Kinetics of Sessile Droplets by Using Nanoparticles, Langmuir 2012, 28, 16725-16728; ②Effects of nanoparticles on nanofluid droplet evaporation, International Journal of Heat and Mass Transfer 53(2010)3677–3682] indicates that the presence of nanoparticles promotes solvent evaporation kinetics. The specific surface area and surface energy of nano-silver powder are much larger than those of micron-sized silver powder. In a homogeneous solution, the evaporation rate of the solvent surrounding nano-silver powder will be greater than that of micron-sized silver powder. The inventors discovered that when micro- and nano-silver powder is mixed with all organic carriers, the solvent evaporation rate on the surface of nano-silver in the micro- and nano-silver paste is greater than that of micro-silver powder, which causes local micro-agglomeration and a rapid increase in viscosity, thus affecting the performance of the micro- and nano-silver paste.

[0006] Therefore, it is necessary to design a micro / nano silver paste with stable and good adhesion and thermal conductivity, as well as an organic carrier for the micro / nano silver paste. Summary of the Invention

[0007] To address the aforementioned issues, the inventors discovered that when nano-silver powder and micron-silver powder possess different hydrophilic and hydrophobic properties, they exhibit a certain selective affinity for solvents with varying hydrophilic indices. Specifically, hydrophobic silver powder preferentially wets hydrophobic organic solvents, while hydrophilic silver powder preferentially wets hydrophilic organic solvents.

[0008] The inventors also discovered that, when solvents have the same or similar boiling points, solvents with a low hydrophilicity index evaporate at a faster rate than solvents with a high hydrophilicity index.

[0009] Inspired by this, this application adjusts the mixing order of micro-nano silver powder and organic carrier in micro-nano silver paste: first, hydrophilic nano-silver powder is mixed with an organic carrier containing a moderately hydrophilic and hydrophobic organic solvent; then, hydrophobic micron-sized silver powder is impregnated with an organic carrier containing a hydrophobic organic solvent; finally, the mixture of nano-silver powder and micron-sized silver powder is mixed evenly to obtain micro-nano silver paste. The moderately hydrophilic and hydrophobic organic solvents allow the hydrophilic and hydrophobic solvents to be miscible. This mixing order ensures that the surface of the large specific surface area nano-silver powder is coated with an organic solvent with a high hydrophilicity index, while the surface of the micron-sized silver powder is coated with an organic solvent with a low hydrophilicity index. This results in the evaporation rates of the organic solvents on the surfaces of the nano-silver powder and micron-sized silver powder being similar, thus solving the problem of excessively rapid evaporation of organic solvents on the surface of nano-silver powder, which causes localized agglomeration, rapid viscosity increase, and affects the performance of the micro-nano silver paste.

[0010] This application provides a method for preparing micro / nano silver paste, characterized by comprising the following steps:

[0011] 1) Prepare organic carrier A and organic carrier B separately;

[0012] The organic carrier A comprises: 40-80 wt% solvent A1, 20-60 wt% solvent A2, 0.5-10 wt% resin, 0.01-0.2 wt% dispersant and 0.01-0.05 wt% thixotropic agent;

[0013] The organic carrier B comprises: 90-100 wt% solvent B1, 0.5-10 wt% resin, 0.01-0.2 wt% dispersant and 0.01-0.05 wt% thixotropic agent;

[0014] 2) Disperse the nano-silver powder and the micro-silver powder in organic carrier A and organic carrier B respectively to obtain a mixture of nano-silver powder and a mixture of micro-silver powder;

[0015] 3) Mix the nano silver powder mixture and the micro silver powder mixture evenly to obtain micro-nano silver paste.

[0016] In some preferred embodiments, the hydrophilicity index of solvent A1 is greater than or equal to 0.4;

[0017] And / or the hydrophilicity index of solvent A2 is between -0.4 and 0.4;

[0018] And / or the hydrophilicity index of solvent B1 is less than or equal to -0.4.

[0019] In some preferred embodiments, the water contact angle of the nano-silver powder is 30° to 60°; and / or the water contact angle of the micron-sized silver powder is 80° to 150°.

[0020] In some preferred embodiments, the particle size of the nano-silver powder is 10–1000 nm; and / or the particle size of the micron-silver powder is 0.5–25 μm.

[0021] In some preferred embodiments, the solvent A1 is selected from one or more of diethylene glycol, diethanolamine, triethanolamine, and N-methyldiethanolamine;

[0022] And / or the solvent A2 is selected from one or more of butyl carbitol, tributyl citrate, and cyclohexanol;

[0023] And / or the solvent B1 is selected from one or more of butyl carbitol acetate, turpentine, dibutyl phthalate, dodecyl alcohol ester, and linalyl acetate.

[0024] In some preferred embodiments, the micro / nano silver paste comprises 30-70 wt% of a nano silver powder composition and 70-30 wt% of a micron silver powder mixture.

[0025] In some preferred embodiments, the nano-silver powder mixture consists of 80-90 wt% nano-silver powder and 20-10 wt% organic carrier A.

[0026] In some preferred embodiments, the micron-sized silver powder mixture consists of 85-95 wt% micron-sized silver powder and 15-5 wt% organic carrier B.

[0027] In some preferred embodiments, the dispersant comprises nonylphenol polyoxyethylene ether and / or BYK110.

[0028] In some preferred embodiments, the thixotropic agent comprises fumed silica and / or polyamide wax.

[0029] In some preferred embodiments, the resin comprises polyvinyl butyral and / or ethyl cellulose.

[0030] This application also provides a micro / nano silver paste obtained by the preparation method described above.

[0031] In addition, this application also provides an organic carrier for micro / nano silver paste, including the aforementioned organic carrier A and organic carrier B, wherein the organic carrier is used to prepare micro / nano silver paste containing micron and nano composite silver powder.

[0032] Beneficial effects:

[0033] 1. This application selects specific organic solvents with different hydrophilicity indices as organic carriers to combine with nano-silver powder and micron-silver powder with specific water contact angles, and combines the specific mixing order of organic carrier and silver powder, so that the surface of nano-silver powder with large specific surface area is coated with organic solvent with high hydrophilicity index, and the surface of micron-silver powder is coated with organic solvent with low hydrophilicity index. This makes the evaporation rate of organic solvent on the surface of nano-silver powder and micron-silver powder similar, thereby solving the problem of local agglomeration, rapid increase in viscosity, and impact on the performance of micro-nano silver paste caused by excessively rapid evaporation of organic solvent on the surface of nano-silver powder.

[0034] 2. The micro-nano silver paste described in this application exhibits viscosity changes of less than 10% to 20% within a 12-hour continuous dispensing or printing time range. After sintering, its adhesion performance to the gold-silver interface remains stable between 18 and 45 MPa, and its thermal conductivity remains stable between 90 and 220 W / mk, demonstrating significant performance. Detailed Implementation

[0035] The following detailed description of this application is provided in conjunction with specific embodiments: the following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0036] To achieve the above objectives, the technical solution proposed in this application involves first preparing organic carrier A and organic carrier B separately. Then, nano-silver powder is mixed uniformly with organic carrier A to obtain a nano-silver powder mixture, and micron-sized silver powder is mixed uniformly with organic carrier B to obtain a micron-sized silver powder mixture. Finally, the two are mixed uniformly to obtain a micro / nano silver paste.

[0037] The following specific embodiments illustrate the content of this application, but this application is not limited thereto. All materials used in the embodiments of this application are commercially available analytical grade products.

[0038] Example 1:

[0039] Table 1 Organic Carrier Formulation of Example 1

[0040]

[0041] 1) Weigh each component according to the formula of organic carrier A in Table 1, dissolve the resin completely at 80°C, and let it stand at room temperature for 24 hours before use.

[0042] According to the formula of organic carrier B in Table 1, weigh each component, dissolve the resin completely at 80°C, and let it stand at room temperature for 24 hours before use.

[0043] 2) Weigh 40g of surface-treated nano silver powder (80nm, with a tested water contact angle of 55°) and 12g of organic carrier A, grind them in an agate mortar for 10 minutes, and finally mix them with a vacuum degassing gravity mixer (2500rpm, 5min) to obtain a nano silver powder mixture.

[0044] Weigh 40g of surface-treated micron silver powder (2 microns, with a tested water contact angle of 109°) and 8g of organic carrier B, grind them in an agate mortar for 10 minutes, and finally mix them with a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain a micron silver powder mixture.

[0045] 3) Transfer the above-obtained nano silver powder mixture and micro silver powder mixture to a new stirring cup and mix evenly using a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain micro-nano silver paste.

[0046] Performance testing:

[0047] The obtained micro-nano silver paste exhibits a viscosity change rate of less than 20% within a 12-hour continuous dispensing or printing time range. After sintering, its adhesion performance to the gold-silver interface remains stable between 18 and 23 MPa, and its thermal conductivity remains stable between 90 and 110 W / mk, demonstrating excellent working performance.

[0048] Example 2:

[0049] Table 2 Organic Carrier Formulation in Example 2

[0050]

[0051] 1) Weigh each component according to the formula of organic carrier A in Table 2, dissolve the resin completely at 80°C, and let it stand at room temperature for 24 hours before use.

[0052] According to the formula of organic carrier B in Table 2, weigh each component, dissolve the resin completely at 80°C, and let it stand at room temperature for 24 hours before use.

[0053] 2) Weigh 40g of surface-treated nano silver powder (150nm, with a tested water contact angle of 43°) and 6g of organic carrier A, grind them in an agate mortar for 10 minutes, and finally mix them with a vacuum degassing gravity mixer (2500rpm, 5min) to obtain a nano silver powder mixture.

[0054] Weigh 50g of surface-treated micron silver powder (5 microns, with a tested water contact angle of 128°) and 4g of organic carrier B, grind them in an agate mortar for 10 minutes, and finally mix them with a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain a micron silver powder mixture.

[0055] 3) Transfer the above-obtained nano silver powder mixture and micro silver powder mixture to a new stirring cup and mix evenly using a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain micro-nano silver paste.

[0056] The obtained micro-nano silver paste exhibits a viscosity change rate of less than 15% within a 12-hour continuous dispensing or printing time range. After sintering, its adhesion performance to the gold-silver interface remains stable between 38 and 45 MPa, and its thermal conductivity remains stable between 200 and 220 W / mk, demonstrating excellent and significant working performance.

[0057] Example 3:

[0058] Table 3 Organic Carrier Formulation of Example 2

[0059]

[0060] 1) Weigh each component according to the formula of organic carrier A in Table 3, dissolve the resin completely at 80°C, and let it stand at room temperature for 24 hours before use.

[0061] According to the formula of organic carrier B in Table 3, weigh each component, dissolve the resin completely at 80°C, and let it stand at room temperature for 24 hours before use.

[0062] 2) Weigh 30g of surface-treated nano-silver powder (10nm, with a tested water contact angle of 60°) and 6g of organic carrier A, grind them in an agate mortar for 10 minutes, and finally mix them with a vacuum degassing gravity mixer (2500rpm, 5min) to obtain a nano-silver powder mixture.

[0063] Weigh 60g of surface-treated micron silver powder (1 micron, with a tested water contact angle of 151°) and 4g of organic carrier B, grind them in an agate mortar for 10 minutes, and finally mix them with a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain a micron silver powder mixture.

[0064] 3) Transfer the above-obtained nano silver powder mixture and micro silver powder mixture to a new stirring cup and mix evenly using a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain micro-nano silver paste.

[0065] The obtained micro-nano silver paste exhibits a viscosity change rate of less than 10% within a 12-hour continuous dispensing or printing time range. After sintering, its adhesion performance to the gold-silver interface remains stable between 35 and 40 MPa, and its thermal conductivity remains stable between 200 and 210 W / mk, demonstrating excellent and significant working performance.

[0066] Comparative Example 1:

[0067] 1) Organic carrier A and organic carrier B from Example 1 were used.

[0068] 2) The amounts of nano silver powder, micron silver powder, organic carrier A, and organic carrier B are the same as in Example 1;

[0069] 3) Mix all raw materials together and grind them in an agate mortar for 20 minutes. Finally, mix them evenly with a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain micro-nano silver paste.

[0070] Performance testing:

[0071] The obtained micro-nano silver paste exhibits a viscosity change rate of approximately 100% over a continuous dispensing or printing period of 12 hours, which is more than five times that of the example. Due to its gradually increasing viscosity, it shows a significant change and gradually becomes difficult to meet the requirements of the operational process.

[0072] As the working time of the silver paste increased, its adhesion to the gold-silver metal interface after sintering gradually decreased from 20 MPa to 5 MPa, and the adhesion decreased to about 25% of that in Example 1, which was a significant decrease.

[0073] As the working time of the silver paste increased, the thermal conductivity decreased from a maximum of 100W / mk to 20W / mk, showing a significant decrease. It was only about 20% of that in Example 1, indicating poor thermal conductivity that could not meet the requirements of subsequent applications.

[0074] Comparative Example 2:

[0075] 1) Organic carrier A and organic carrier B from Example 2 were used.

[0076] 2) The amounts of nano silver powder, micron silver powder, organic carrier A, and organic carrier B are the same as in Example 2;

[0077] 3) Mix all raw materials together and grind them in an agate mortar for 20 minutes. Finally, mix them evenly with a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain micro-nano silver paste.

[0078] Performance testing:

[0079] The viscosity of the obtained micro-nano silver paste changed by approximately 80% within a 12-hour period of continuous dispensing or printing. After sintering, its adhesion to the gold-silver interface decreased from the initial 40 MPa to 22 MPa, and its thermal conductivity decreased from 195 W / mk to 75 W / mk, showing a significant decline in both adhesion and thermal conductivity.

[0080] Comparative Example 3:

[0081] 1) Organic carrier A and organic carrier B from Example 3 were used.

[0082] 2) The amounts of nano silver powder, micron silver powder, organic carrier A, and organic carrier B are the same as in Example 3;

[0083] 3) Mix all raw materials together and grind them in an agate mortar for 20 minutes. Finally, mix them evenly with a vacuum degassing gravity mixer (2500 rpm, 5 min) to obtain micro-nano silver paste.

[0084] Performance testing:

[0085] The viscosity of the obtained micro-nano silver paste changed by approximately 40% within a 12-hour period of continuous dispensing or printing. After sintering, its adhesion to the gold-silver interface decreased from the initial 38 MPa to 25 MPa, and its thermal conductivity decreased from the initial 205 W / mk to 130 W / mk.

[0086] Based on the embodiments and comparative examples, it can be demonstrated that the technical route of this application is beneficial for preparing micro-nano silver paste with small viscosity change rate, stable adhesion and thermal conductivity.

[0087] Comparative Example 4:

[0088] Based on Example 1, nano silver powder was added to organic carrier B, and micro silver powder was added to organic carrier A. Other steps and dosages were the same as in Example 1 to obtain micro-nano silver paste.

[0089] Micron-sized silver powder cannot wet the organic carrier phase A, resulting in a mixture containing a large number of air bubbles, making it unusable.

[0090] This demonstrates a significant correlation between the water contact angle of silver powder and the hydrophilicity index of the organic carrier.

[0091] Comparative Example 5:

[0092] Based on Example 1, the A1 solvent in the organic carrier A was replaced with ethyl laurate (hydrophilic index: -0.856), and the other steps and amounts were the same as in Example 1.

[0093] Performance testing:

[0094] The obtained micro-nano silver paste exhibited a viscosity change rate of approximately 60% over a continuous dispensing or printing period of 12 hours, which is more than three times that of Example 1. Due to its gradually increasing viscosity, it showed a significant change and gradually became difficult to meet the operational process requirements.

[0095] As the working time of the silver paste increases, its adhesion to the gold-silver metal interface after sintering gradually decreases from 20 MPa to 3 MPa, a significant decrease.

[0096] As the working time of the silver paste increased, the thermal conductivity decreased from a maximum of 100W / mk to 15W / mk, showing a significant decrease. It was only about 16% of that in Example 1, indicating poor thermal conductivity that could not meet the requirements of subsequent applications.

[0097] Comparative Example 6:

[0098] Based on Example 1, the B1 solvent in the organic carrier B was replaced with diethylene glycol monohexyl ether (hydrophilic index: -0.202), and the other steps and amounts were the same as in Example 1.

[0099] The results showed that organic carrier B could not wet the micron-sized silver powder, making subsequent preparation and testing impossible.

[0100] Comparative Example 7:

[0101] Based on Example 1, the A2 solvent in the organic carrier A was replaced with diethylene glycol (hydrophilicity index: 1.118), and the other steps and amounts were the same as in Example 1.

[0102] The results showed that the mixture of nano silver powder and micron silver powder could not be mixed evenly, and there were a large number of air bubbles, making them unusable.

Claims

1. A method for preparing micro / nano silver paste, characterized in that, Includes the following steps: 1) Prepare organic carrier A and organic carrier B separately; The organic carrier A comprises: 40-80 wt% solvent A1, 20-60 wt% solvent A2, 0.5-10 wt% resin, 0.01-0.2 wt% dispersant, and 0.01-0.05 wt% thixotropic agent; wherein the sum of the amounts of all components in the organic carrier A is 100%. The organic carrier B comprises: 90-100 wt% solvent B1, 0.5-10 wt% resin, 0.01-0.2 wt% dispersant, and 0.01-0.05 wt% thixotropic agent; wherein the sum of the amounts of all components in the organic carrier B is 100%. 2) Disperse the nano-silver powder and the micro-silver powder in organic carrier A and organic carrier B respectively to obtain a mixture of nano-silver powder and a mixture of micro-silver powder; 3) Mix the nano-silver powder mixture and the micro-silver powder mixture evenly to obtain micro-nano silver paste; The hydrophilicity index of solvent A1 is greater than or equal to 0.4; The hydrophilicity index of solvent A2 is between -0.4 and 0.4; The hydrophilicity index of solvent B1 is less than or equal to -0.

4.

2. The method for preparing a micro / nano silver paste according to claim 1, characterized in that, The water contact angle of the nano silver powder is 43°~60°; and / or the water contact angle of the micron silver powder is 80°~150°.

3. The method for preparing a micro / nano silver paste according to claim 1 or 2, characterized in that, The nano-silver powder has a particle size of 10~150nm; and / or the micron-sized silver powder has a particle size of 2~25μm.

4. The method for preparing a micro / nano silver paste according to claim 1, characterized in that, The solvent A1 is selected from one or more of diethylene glycol, diethanolamine, triethanolamine, and N-methyldiethanolamine; And / or the solvent A2 is selected from one or more of butyl carbitol, tributyl citrate, and cyclohexanol; And / or the solvent B1 is selected from one or more of butyl carbitol acetate, turpentine, dibutyl phthalate, dodecyl alcohol ester, and linalyl acetate.

5. The method for preparing a micro / nano silver paste according to claim 1, characterized in that, The micro-nano silver paste comprises 30-70 wt% of a nano silver powder composition and 70-30 wt% of a micron silver powder mixture.

6. The method for preparing a micro / nano silver paste according to claim 1, characterized in that, The nano-silver powder mixture consists of 80-90 wt% nano-silver powder and 20-10 wt% organic carrier A.

7. The method for preparing a micro / nano silver paste according to claim 1, characterized in that, The micron-sized silver powder mixture consists of 85-95 wt% micron-sized silver powder and 15-5 wt% organic carrier B.

8. A micro-nano silver paste obtained by any one of the preparation methods of claims 1 to 7.

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