Low-temperature curing solder paste for microelectronic packaging and preparation method of low-temperature curing solder paste

Abstract

The invention belongs to the technical field of microelectronic packaging, and particularly relates to low-temperature curing solder paste for microelectronic packaging and a preparation method of the low-temperature curing solder paste. The low-temperature curing solder paste for microelectronic packaging comprises the following components in percentage by mass: 85-90% of modified solder powder, 1-2% of modified nano-silver particles and 8-14% of soldering flux, the soldering powder comprises, by mass, 42% of Sn and 58% of Bi. The preparation method of the modified solder powder comprises the following steps: uniformly mixing an alcoholic solution containing solder powder, an amino-terminated silane coupling agent and an alcoholic solution of natural macromolecular organic acid, performing ultrasonic treatment, filtering after the ultrasonic treatment is finished, washing with a sodium humate solution, and drying, thereby obtaining the modified solder powder. By adopting the specific modified solder powder and the modified nano-silver particles and cooperating with the soldering flux, the obtained solder paste can be stored at normal temperature and has an excellent expansion rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of microelectronic packaging, and particularly relates to a low-temperature curing solder paste for microelectronic packaging and a preparation method thereof. Background Art

[0002] Solder paste, also known as "soldering paste", is the core material of advanced electronic packaging technology, and its function is to achieve electrical interconnection between electronic components and substrates in the reflow soldering process. Solder paste is a paste-like mixture formed by stirring and mixing solder alloy powder, flux, and other additives.

[0003] With the increasing thinning, lightening, and miniaturization of electronic components, the curing temperature of Sn-Ag-Cu series solder paste is high and cannot meet the packaging requirements of temperature-sensitive electronic components. Low-temperature solder paste products are the focus of the industry's development.

[0004] In the prior art, a Chinese patent with the authorized publication number of CN 107088716 B discloses an environmentally friendly low-temperature residue-free solder paste and a preparation method thereof. The key points of its technical solution are as follows: The solder paste contains the following weight components: Sn 41.0% - 60.0%, Bi 26.6% - 37.7%, third-element alloy 2.1 - 4.4%, flux 9.0 - 19.0%; the flux contains the following weight components: carrier 67.0 - 75.0%, activator 14.8 - 18.8%, thixotropic agent 4.6 - 8.72%, surfactant 0.32 - 3.2%, corrosion inhibitor 1.48 - 3.5%. The formula of this technical solution uses halogen-free components, the solder paste has no volatile components and has no odor during use, and the residue after welding is colorless and transparent, achieving the effect of replacing Pb-containing solder paste or halogen-containing solder paste. Under low-temperature welding conditions, adding nano-aluminum powder forms a high-temperature solid solution during welding, serving as an auxiliary supplement for welding, effectively improving the welding defects of Sn-Bi alloy, being able to meet the welding requirements of aluminum components on the surface of electronic components, and at the same time extending the storage period of the solder paste, bringing a better expansion rate. However, in fact, the expansion rate of this technical solution can only reach 85.5% at most, and it needs to be stored refrigerated at 0°C.

[0005] A Chinese patent with the publication number of CN 115781106 A discloses a low-temperature halogen-free and lead-free solder paste and a preparation method thereof. The flux of this technical solution does not use halogen-containing components, which is green and environmentally friendly; it uses a compound of organic binary short-chain acid, halogen-free salt, and an ester-based acidic surfactant in proportion as the main active system, combined with an acid anhydride-based curing agent, making the paste have good stability at room temperature, good mechanical properties, good oxidation resistance, and being able to effectively reduce residues and avoid the generation of black spots, which affect the appearance of the product. The halogen-free and lead-free low-temperature solder paste prepared with the flux of this technical solution can well meet the requirements of low-temperature production of Sn-Bi alloy. However, the solder paste obtained by this technical solution also needs to be stored at 4°C. Summary of the Invention

[0006] In view of the problems of low spreading rate and the need for low-temperature storage of existing low-temperature solder pastes in the prior art, the present invention provides a low-temperature curing solder paste for microelectronic packaging and a preparation method thereof. By using specific modified solder powder and modified nano silver particles, and cooperating with a flux, the obtained solder paste can be stored at room temperature, has a high spreading rate, and a low solder joint void rate.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] In the first aspect of the present invention, there is provided a low-temperature curing solder paste for microelectronic packaging, which, by mass percentage, comprises 85-90% of modified solder powder, 1-2% of modified nano silver particles, and 8-14% of flux;

[0009] The solder powder, by mass percentage, comprises 42% Sn and 58% Bi;

[0010] The preparation method of the modified solder powder is: mixing an alcohol solution containing solder powder, an alcohol solution containing an aminoalkyltrialkoxysilane coupling agent and a natural macromolecular organic acid evenly, performing ultrasonic treatment, filtering after completion, washing with a sodium humate solution, and drying to obtain.

[0011] In some preferred embodiments, the mass ratio of the solder powder, the aminoalkyltrialkoxysilane coupling agent and the natural macromolecular organic acid is 40-50:1-3:1, preferably 45:2:1.

[0012] In some preferred embodiments, the alcohol solution containing solder powder is solder powder dispersed in ethanol, and the mass concentration of the solder powder is 10-20%, preferably 15%.

[0013] In some preferred embodiments, the aminoalkyltrialkoxysilane coupling agent is selected from one or a combination of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropylmethyldimethoxysilane, preferably γ-aminopropyltriethoxysilane.

[0014] In some preferred embodiments, the natural macromolecular organic acid is selected from at least one of lauric acid, cinnamic acid, and myristic acid, preferably cinnamic acid.

[0015] In some preferred embodiments, the alcohol solution containing the aminoalkyltrialkoxysilane coupling agent and the natural macromolecular organic acid is the aminoalkyltrialkoxysilane coupling agent and the natural macromolecular organic acid dispersed in ethanol, the mass concentration of the aminoalkyltrialkoxysilane coupling agent is 5-10%, preferably 8%; the mass concentration of the natural macromolecular organic acid is 2-5%, preferably 3%.

[0016] In some preferred embodiments, the temperature of the ultrasonic treatment is 25 - 30 °C, preferably 25 °C; the time of the ultrasonic treatment is 20 - 40 min, preferably 30 min.

[0017] In some preferred embodiments, the mass concentration of the sodium humate solution is 4 - 8%, preferably 6%.

[0018] In some preferred embodiments, the number of washing times is 1 - 3 times.

[0019] In some preferred embodiments, the preparation method of the modified silver nanoparticles is as follows: mix silver nanoparticles, single-walled carbon nanotubes, carboxymethyl cellulose and water evenly, carry out stirring reaction, after completion, filter, wash with sodium humate solution, and dry to obtain.

[0020] In some preferred embodiments, the surface group of the silver nanoparticles is citric acid, the particle size is 10 - 20 nm, preferably 15 nm.

[0021] In some preferred embodiments, the surface group of the single-walled carbon nanotubes is hydroxyl, and the tube diameter is 1 - 2 nm.

[0022] In some preferred embodiments, the mass ratio of the silver nanoparticles, single-walled carbon nanotubes, carboxymethyl cellulose and water is 10 - 20:1 - 2:1 - 2:15 - 30, preferably 15:1.5:1:25.

[0023] In some preferred embodiments, the rotation speed of the stirring reaction is 300 - 500 rpm, preferably 400 rpm; the temperature of the stirring reaction is 70 - 90 °C, preferably 80 °C; the time of the stirring reaction is 30 - 60 min, preferably 40 min.

[0024] In some preferred embodiments, the mass concentration of the sodium humate solution is 4 - 8%, preferably 6%.

[0025] In some preferred embodiments, the number of washing times is 1 - 3 times.

[0026] In some preferred embodiments, the solder flux, by mass parts, comprises the following raw materials: 25 - 35 parts of rosin, 5 - 10 parts of activator, 30 - 40 parts of solvent, 2 - 5 parts of thixotropic agent, 1 - 3 parts of antioxidant, and 1 - 3 parts of corrosion inhibitor.

[0027] The main function of rosin in the solder flux is to remove metal oxides during the welding process and form an organic film to prevent the secondary oxidation of the solder powder. However, the selection of rosin will also affect the spreading rate of the solder paste.

[0028] In some preferred embodiments, the rosin is selected from at least one of hydrogenated rosin, polymerized rosin, and ice white rosin, preferably hydrogenated rosin.

[0029] In some preferred embodiments, the hydrogenated rosin comprises KE-604 rosin and KR-610 rosin with a mass ratio of 3-5:2-3, preferably KE-604 rosin and KR-610 rosin with a mass ratio of 4:3.

[0030] The selection of the active agent in the flux affects the post-welding residue and the spreading rate of the solder paste, but also affects the stability of the solder paste.

[0031] In some preferred embodiments, the active agent is selected from at least one of succinic acid, glutaric acid, and salicylic acid, preferably succinic acid and salicylic acid with a mass ratio of 2-3:1, and further preferably succinic acid and salicylic acid with a mass ratio of 2.5:1.

[0032] The function of the solvent in the flux is not only to dissolve the components in the flux, but also to affect the stability and spreading rate of the solder paste.

[0033] In some preferred embodiments, the solvent is selected from at least one of n-butanol, tetrahydrofurfuryl alcohol, propylene glycol monobutyl ether, diethylene glycol monoethyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether, preferably tetrahydrofurfuryl alcohol and diethylene glycol monoethyl ether with a mass ratio of 2-3:1-2, and further preferably tetrahydrofurfuryl alcohol and diethylene glycol monoethyl ether with a mass ratio of 3:2.

[0034] The function of the thixotropic agent in the flux is to impart a certain thixotropy to the solder paste.

[0035] In some preferred embodiments, the thixotropic agent is selected from at least one of hydrogenated castor oil, fatty acid amide, modified hydrogenated castor oil, and ethylene bisstearamide, preferably hydrogenated castor oil.

[0036] The function of the antioxidant in the flux is to prevent the formation of oxides between the solder powder and the substrate, prevent the active substances in the flux from being oxidized, and also affect the stability and spreading rate of the solder paste.

[0037] In some preferred embodiments, the antioxidant is selected from at least one of hydroquinone, resorcinol, tert-butylhydroquinone, dibutylhydroxytoluene, and 4-hexylresorcinol, preferably tert-butylhydroquinone.

[0038] The function of the corrosion inhibitor in the flux is to prevent the reaction between the solder powder and the flux and improve the stability of the solder paste.

[0039] In some preferred embodiments, the corrosion inhibitor is selected from at least one of benzotriazole and lauryldiethanolamine, preferably lauryldiethanolamine.

[0040] The second aspect of the present invention provides a preparation method of a low-temperature curing solder paste for microelectronic packaging, comprising the following steps: rosin, an active agent, a thixotropic agent, an antioxidant, a corrosion inhibitor and a solvent are mixed and stirred evenly to obtain a soldering flux, and then the soldering flux, modified solder powder and modified nano silver particles are mixed and stirred evenly to obtain the low-temperature curing solder paste for microelectronic packaging.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The present invention uses an amino-terminated silane coupling agent and a natural macromolecular organic acid to modify the solder powder to form a coating on the surface of the solder powder. It is unexpectedly found that when the natural macromolecular organic acid is at least one of lauric acid, cinnamic acid and myristic acid, the obtained solder paste can be stored at room temperature for 10 months while still having excellent spread rate, and the solder joint void ratio is small. Especially when it is cinnamic acid, the effect is the best. It is speculated that because the melting temperature of cinnamic acid is relatively higher than that of lauric acid and myristic acid, it avoids a large amount of volatilization before the end of soldering. At the same time, the inventor unexpectedly finds that when sodium humate is used for washing during washing, the room temperature storage stability, spread rate of the solder paste can be improved and the solder joint void ratio can be reduced. It is speculated that because sodium humate is alkaline, it can neutralize the excess natural macromolecular organic acid to a certain extent and adsorb on the surface of the solder powder, further increasing its stability and reducing the volatilized gas generated during the soldering process.

[0043] 2. The present invention uses nano silver particles with citric acid surface groups and single-walled carbon nanotubes with hydroxyl surface groups to react, and carboxymethyl cellulose is added during the preparation process to graft the nano silver and the single-walled carbon nanotubes together, so that the nano silver and the single-walled carbon nanotubes act together to enhance the mechanical strength of the solder joint, reduce the solder joint void ratio, and improve the storage stability and spread rate of the solder paste. It is speculated that because the long molecular chain of carboxymethyl cellulose isolates the grafted nano silver particles and single-walled carbon nanotubes, avoiding agglomeration and possibly coating their surfaces, enabling them to exist stably.

[0044] 3. By using specific modified solder powder and modified nano silver particles and cooperating with a soldering flux, the solder paste obtained by the present invention can be stored at room temperature, and has excellent spread rate and low solder joint void ratio. Detailed implementation manners

[0045] For a clearer understanding of the technical features, objectives, and effects of the present invention, specific implementation embodiments are now described in detail. The present invention will be further described below in conjunction with embodiments, but the present invention is not limited to the following embodiments. The implementation conditions adopted in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are the conventional conditions in the industry. The technical features involved in various implementation manners of the present invention can be combined with each other as long as they do not conflict with each other.

[0046] In the following examples and comparative examples, unless otherwise specified, the raw materials used are all commercially available or prepared by conventional methods in the art.

[0047] Preparation Example 1 Preparation of Modified Solder Powder A:

[0048] Mix the alcohol solution containing solder powder and the alcohol solution containing γ-aminopropyltriethoxysilane and cinnamic acid evenly, perform ultrasonic treatment at 25 °C for 30 min, filter after completion, wash 3 times with a sodium humate solution with a mass concentration of 6%, and dry to obtain.

[0049] The solder powder, by mass percentage, consists of 42% Sn and 58% Bi;

[0050] The mass ratio of the solder powder, γ-aminopropyltriethoxysilane, and cinnamic acid is 45:2:1.

[0051] The alcohol solution containing solder powder is solder powder dispersed in ethanol, and the mass concentration of the solder powder is 15%.

[0052] The alcohol solution of γ-aminopropyltriethoxysilane and cinnamic acid is an amino-terminated silane coupling agent and cinnamic acid dispersed in ethanol, the mass concentration of γ-aminopropyltriethoxysilane is 8%; the mass concentration of cinnamic acid is 3%.

[0053] Preparation Example 2 Preparation of Modified Solder Powder B:

[0054] The specific implementation method is the same as that of Preparation Example 1, the only difference being that cinnamic acid is replaced with lauric acid of the same mass.

[0055] Preparation Example 3 Preparation of Modified Solder Powder C:

[0056] The specific implementation method is the same as that of Preparation Example 1, the only difference being that cinnamic acid is replaced with myristic acid of the same mass.

[0057] Preparation Example 4 Preparation of Modified Solder Powder D:

[0058] The specific implementation method is the same as that of Preparation Example 1, the only difference being that washing 3 times with a sodium humate solution with a mass concentration of 6% is replaced with washing 3 times with water.

[0059] Preparation Example 5 Preparation of Modified Nano-Silver Particles A:

[0060] Mix the nano-silver particles, single-walled carbon nanotubes, carboxymethyl cellulose and water evenly, carry out a stirring reaction at 400 rpm and 80 °C for 40 min, filter after completion, wash 3 times with a 6% sodium humate solution by mass concentration, and dry to obtain.

[0061] The surface groups of the nano-silver particles are citric acid, the particle size is 15 nm, purchased from Nanjing Dongna Biotechnology Co., Ltd., product number: AgP01.

[0062] The surface groups of the single-walled carbon nanotubes are hydroxyl groups, the tube diameter is 1-2 nm, purchased from Chengdu Organic Chemistry Co., Ltd., Chinese Academy of Sciences, product number: TNSRH.

[0063] The mass ratio of the nano-silver particles, single-walled carbon nanotubes, carboxymethyl cellulose and water is 15:15:1:25.

[0064] Preparation Example 6 Preparation of Modified Nano-Silver Particles B:

[0065] The specific implementation method is the same as that of Preparation Example 5, the only difference is that there is no carboxymethyl cellulose, and the mass ratio of the nano-silver particles, single-walled carbon nanotubes and water is 15:1.5:25.

[0066] Preparation Example 7 Preparation of Modified Nano-Silver Particles C:

[0067] Mix the nano-silver particles and single-walled carbon nanotubes directly; the mass ratio of the nano-silver particles to the single-walled carbon nanotubes is 15:1.5.

[0068] Examples 1-9 provide a low-temperature curing solder paste for microelectronic packaging, and the composition is shown in Table 1 by mass percentage.

[0069] Table 1

[0070]

[0071] Among them, in Examples 1-9, for the flux, by mass ratio, the raw materials are composed of 30 parts of hydrogenated rosin, 8 parts of active agent, 35 parts of solvent, 3 parts of hydrogenated castor oil, 2 parts of tert-butylhydroquinone, and 2 parts of lauryl hydroxyethyl imidazoline;

[0072] The hydrogenated rosin is a 4:3 mixture of KE-604 rosin and KR-610 rosin, purchased from Arakawa Chemical.

[0073] The active agent is succinic acid and salicylic acid with a mass ratio of 2.5:1.

[0074] The solvent is a 3:2 mixture of tetrahydrofurfuryl alcohol and diethylene glycol monoethyl ether.

[0075] The preparation method of the low-temperature curing solder paste for microelectronic packaging is as follows: mix rosin, surfactant, hydrogenated castor oil, tert-butylhydroquinone, lauryl hydroxyethyl imidazoline and solvent, and stir evenly to obtain a soldering flux. Then, mix the soldering flux, modified solder powder and modified nano-silver particles evenly to obtain the low-temperature curing solder paste for microelectronic packaging.

[0076] Perform performance tests on the low-temperature curing solder pastes of Examples 1-9:

[0077] 1. Spread rate: Refer to the standard of GB / T 9491-2002;

[0078] 2. Solder joint void ratio: Use an X-ray device to test the solder joint void ratio; Solder joint void ratio = void volume / solder joint volume;

[0079] 3. Storage stability: Place the low-temperature curing solder paste in a sealed container, and then place it for 10 months under the conditions of 25°C and 60% humidity: (1) Observe whether there is agglomeration and caking. If not, it is recorded as qualified; (2) Refer to the standard of GB / T 9491-2002 to test the spread rate; The results are shown in Table 2.

[0080] Table 2

[0081]

[0082] It can be seen from Table 2 that by comparing Modified Solder Powder A, Modified Solder Powder B and Modified Solder Powder C, the solder paste using Modified Solder Powder A has the highest spread rate, the best storage stability and the lowest solder joint void ratio. That is, when the natural macromolecular organic acid is cinnamic acid, the effect is the best.

[0083] Modified Solder Powder D was not washed with a sodium humate solution, and the stability of the obtained solder paste deteriorated significantly, the spread rate decreased, and the solder joint void ratio increased.

[0084] The stability of the solder paste obtained with unmodified solder powder deteriorated significantly, the spread rate decreased significantly, and the solder joint void ratio increased significantly.

[0085] During the preparation of Modified Nano-Silver Particle B, carboxymethyl cellulose was not added, and Modified Nano-Silver Particle C directly mixed nano-silver particles and carbon nanotubes. The stability of the obtained solder paste deteriorated significantly, the spread rate decreased significantly, and the solder joint void ratio increased significantly.

[0086] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than a limitation on the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art does not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A low temperature curing solder paste for microelectronic packaging, characterized in that: Calculated by mass percentage, it includes 85-90% of modified solder powder, 1-2% of modified nano silver particles, and 8-14% of flux; The solder powder comprises 42% Sn and 58% Bi by mass percentage; The preparation method of the modified solder powder comprises the following steps: uniformly mixing an alcohol solution containing solder powder, an alcohol solution containing an amino-terminated silane coupling agent and a natural macromolecular organic acid, subjecting the mixture to ultrasonic treatment, filtering the mixture after the treatment, washing the mixture with a sodium humate solution, and drying the mixture to obtain the modified solder powder.

2. The low temperature curing solder paste for microelectronic packaging according to claim 1, characterized in that: The natural macromolecular organic acid is selected from at least one of lauric acid, cinnamic acid and myristic acid.

3. The low temperature curing solder paste for microelectronic packaging according to claim 2, characterized in that: The natural macromolecular organic acid is cinnamic acid.

4. The method according to claim 3 is characterized in that the preparation method of the modified nano-silver particles is: nano-silver particles, single-walled carbon nanotubes, carboxymethyl cellulose and water are uniformly mixed, stirred for reaction, filtered, washed with sodium humate solution, and dried to obtain the modified nano-silver particles.

5. The low temperature curing solder paste for microelectronic packaging according to claim 4, characterized in that: The surface group of the nano silver particles is citric acid, and the particle size is 10-20nm.

6. The low temperature curing solder paste for microelectronic packaging according to claim 5, characterized in that: The surface groups of the single-walled carbon nanotubes are hydroxyl groups, and the tube diameter is 1-2 nm.

7. The low temperature curing solder paste for microelectronic packaging according to any one of claims 1 to 6, characterized in that: The soldering flux comprises, by weight, 25-35 parts of rosin, 5-10 parts of activator, 30-40 parts of solvent, 2-5 parts of thixotropic agent, 1-3 parts of antioxidant and 1-3 parts of corrosion inhibitor.

8. The low temperature curing solder paste for microelectronic packaging according to claim 7, characterized in that: The rosin is selected from at least one of hydrogenated rosin, polymerized rosin and ice white rosin.

9. The low temperature curing solder paste for microelectronic packaging according to claim 8, characterized in that: The active agent is selected from at least one of succinic acid, glutaric acid and salicylic acid.

10. The method for preparing the low temperature curing solder paste for microelectronic packaging according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: mixing rosin, an activator, a thixotropic agent, an antioxidant, a corrosion inhibitor and a solvent, and stirring them uniformly to obtain a solder flux; and mixing the solder flux, modified solder powder and modified nano silver particles, and stirring them uniformly to obtain a low-temperature curing solder paste for microelectronic packaging.

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