A low temperature solidified tin paste for microelectronic packaging and a method of making the same

Abstract

This invention belongs to the field of microelectronic packaging technology, specifically relating to a low-temperature curing solder paste for microelectronic packaging and its preparation method. The low-temperature curing solder paste for microelectronic packaging, by mass percentage, comprises 85-90% modified solder powder, 1-2% modified nano-silver particles, and 8-14% flux; the solder powder, by mass percentage, comprises 42% Sn and 58% Bi; the preparation method of the modified solder powder is as follows: a solder powder-containing alcohol solution, an alcohol solution containing a terminal amino silane coupling agent, and a natural macromolecular organic acid are mixed evenly, ultrasonically treated, filtered after treatment, washed with sodium humate solution, and dried to obtain the final product. This invention, by using specific modified solder powder and modified nano-silver particles, combined with flux, produces a solder paste that can be stored at room temperature and exhibits excellent spreadability.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic packaging technology, specifically relating to a low-temperature curing solder paste for microelectronic packaging and its preparation method. Background Technology

[0002] Solder paste, also known as soldering compound, is a core material in advanced electronic packaging technology. Its function is to enable electronic interconnection between electronic components and the substrate during the reflow soldering process. Solder paste is a paste-like mixture made by mixing solder alloy powder, flux, and other additives.

[0003] As electronic components become increasingly thinner and smaller, the high curing temperature of Sn-Ag-Cu solder paste cannot meet the packaging requirements of temperature-sensitive electronic components. Low-temperature solder paste products are a key focus of industry development.

[0004] In the prior art, Chinese Patent No. CN 107088716 B discloses an environmentally friendly low-temperature residue-free solder paste and its preparation method. The key points of its technical solution are: 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%, and 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%, and corrosion inhibitor 1.48%~3.5%. This technical solution uses a halogen-free formulation, resulting in solder paste with no volatile components and no odor during use. The residue after soldering is colorless and transparent, effectively replacing Pb-containing or halogen-containing solder pastes. Under low-temperature soldering conditions, the addition of nano-aluminum powder forms a high-temperature solid solution during soldering, acting as an auxiliary soldering aid and effectively improving soldering defects in Sn-Bi alloys. This meets the soldering requirements of aluminum components on the surface of electronic devices and simultaneously extends the shelf life of the solder paste, resulting in better spreadability. However, in reality, the spreadability of this technical solution can only reach a maximum of 85.5%, and it requires refrigerated storage at 0°C.

[0005] Chinese Patent Publication No. CN 115781106 A discloses a low-temperature halogen-free and lead-free solder paste and its preparation method. This technical solution uses a flux that does not use halogen-containing components, making it environmentally friendly. It employs a compound of an organic binary short-chain acid, a halogen-free salt, and an ester-based acidic surfactant in a specific ratio as the main active system, combined with an anhydride-based curing agent. This results in a paste with good stability and mechanical properties at room temperature, excellent antioxidant properties, and effectively reduces residue, preventing black spots from affecting product aesthetics. The halogen-free and lead-free low-temperature solder paste prepared using this flux solution can well meet the requirements of low-temperature production of Sn-Bi alloys; however, the solder paste obtained by this solution also needs to be stored at 4°C. Summary of the Invention

[0006] This invention addresses the problems of low spreadability and the need for low-temperature storage in existing low-temperature solder pastes by providing a low-temperature curing solder paste for microelectronic packaging and its preparation method. By using specific modified solder powder and modified nano-silver particles, combined with flux, the resulting solder paste can be stored at room temperature and has a high spreadability and a low solder joint void rate.

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

[0008] The first aspect of this invention provides a low-temperature curing solder paste for microelectronic packaging, comprising, by weight percentage, 85-90% modified solder powder, 1-2% modified nano-silver particles, and 8-14% flux;

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

[0010] The modified solder powder is prepared by mixing an alcohol solution containing solder powder, an alcohol solution containing a terminal amino silane coupling agent and a natural macromolecular organic acid evenly, ultrasonically treating the mixture, filtering it after the process, washing it with sodium humate solution, and drying it.

[0011] In some preferred embodiments, the mass ratio of the solder powder, the amino-terminated silane 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 terminal aminosilane coupling agent is selected from one or more combinations of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, and 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 terminal aminosilane coupling agent and the natural macromolecular organic acid is wherein the terminal aminosilane coupling agent and the natural macromolecular organic acid are dispersed in ethanol, wherein the mass concentration of the terminal aminosilane coupling agent is 5-10%, preferably 8%; and 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; and 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 washing is performed 1-3 times.

[0019] In some preferred embodiments, the modified silver nanoparticles are prepared by mixing silver nanoparticles, single-walled carbon nanotubes, carboxymethyl cellulose and water evenly, stirring and reacting, filtering after the reaction, washing with sodium humate solution and drying to obtain the modified silver nanoparticles.

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

[0021] In some preferred embodiments, the surface groups of the single-walled carbon nanotubes are hydroxyl groups, 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 stirring speed is 300-500 rpm, preferably 400 rpm; the stirring temperature is 70-90℃, preferably 80℃; and the stirring time 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 washing is performed 1-3 times.

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

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

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

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

[0030] The choice of activator in the flux affects post-soldering residue and solder paste spread rate, but also affects the stability of the solder paste.

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

[0032] The solvent in flux not only dissolves the components of the flux, but also affects the stability and spread of solder paste.

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

[0034] The role of thixotropic agents in flux is to impart a certain thixotropic property to 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 bis-stearamide, preferably hydrogenated castor oil.

[0036] The antioxidants in flux prevent the solder powder from forming oxides with the substrate, prevent the active substances in the flux from being oxidized, and also affect the stability and spread of the solder paste.

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

[0038] The role of corrosion inhibitors in flux is to prevent reaction between solder powder and flux, thereby improving the stability of solder paste.

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

[0040] The second aspect of the present invention provides a method for preparing a low-temperature curing solder paste for microelectronic packaging, comprising the following steps: mixing and stirring rosin, activator, thixotropic agent, antioxidant, corrosion inhibitor and solvent to obtain flux; mixing and stirring flux, modified solder powder and modified nano silver particles to obtain a low-temperature curing solder paste for microelectronic packaging.

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

[0042] 1. This invention uses an amino-terminated silane coupling agent and natural macromolecular organic acids to modify solder powder, forming a coating on the surface of the solder powder. It was unexpectedly discovered that when the natural macromolecular organic acid is at least one of lauric acid, cinnamic acid, and myristic acid, the resulting solder paste can be stored at room temperature for 10 months while still maintaining excellent spreadability and a low solder joint void rate. The effect is particularly good with cinnamic acid, presumably because the melting temperature of cinnamic acid is relatively higher than that of lauric acid and myristic acid, preventing excessive volatilization before the soldering process is complete. Simultaneously, the inventors unexpectedly discovered that using sodium humate for washing can improve the room temperature storage stability, spreadability, and reduce the solder joint void rate of the solder paste. This is presumably because sodium humate is alkaline, which can neutralize excess natural macromolecular organic acids to a certain extent while adsorbing them onto the surface of the solder powder, further increasing its stability and reducing the volatile gases generated during the soldering process.

[0043] 2. This invention uses silver nanoparticles with citric acid as the surface group and single-walled carbon nanotubes with hydroxyl as the surface group to react. Carboxymethyl cellulose is added during the preparation process to graft the silver nanoparticles and single-walled carbon nanotubes together. This allows the silver nanoparticles and single-walled carbon nanotubes to work together to enhance the mechanical strength of the solder joint, reduce the void rate of the solder joint, and improve the storage stability and spread rate of the solder paste. It is speculated that this is because the long molecular chains of carboxymethyl cellulose isolate the grafted silver nanoparticles and single-walled carbon nanotubes, preventing agglomeration and possibly coating their surfaces, thus enabling them to exist stably.

[0044] 3. The present invention uses specific modified solder powder and modified nano silver particles, combined with flux, to obtain solder paste that can be stored at room temperature and has excellent spreadability and low solder joint void rate. Detailed Implementation

[0045] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail. The invention is further described below with reference to embodiments, but it is not limited to these embodiments. The implementation conditions used in the embodiments can be further adjusted according to different specific application requirements; implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of this invention can be combined with each other as long as they do not conflict with each other.

[0046] Unless otherwise specified, all raw materials used in the following examples and comparative examples are 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, sonicate at 25°C for 30 minutes, filter after the treatment, wash three times with a 6% sodium humate solution, and dry to obtain the final product.

[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 alcoholic solution of γ-aminopropyltriethoxysilane and cinnamic acid is an amino-terminated silane coupling agent and cinnamic acid dispersed in ethanol, wherein the mass concentration of γ-aminopropyltriethoxysilane is 8% and 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 in Preparation Example 1, except that cinnamic acid is replaced with an equal mass of lauric acid.

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

[0056] The specific implementation method is the same as in Preparation Example 1, except that cinnamic acid is replaced with an equal mass of myristic acid.

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

[0058] The specific implementation method is the same as in Preparation Example 1, except that washing three times with a 6% sodium humate solution is replaced with washing three times with water.

[0059] Preparation Example 5: Preparation of Modified Silver Nanoparticles A:

[0060] Nano-silver particles, single-walled carbon nanotubes, carboxymethyl cellulose and water are mixed evenly and stirred at 400 rpm and 80°C for 40 min. After the reaction is completed, the mixture is filtered, washed three times with a 6% sodium humate solution, and dried to obtain the final product.

[0061] The surface group of the silver nanoparticles is citric acid, the particle size is 15nm, and they were purchased from Nanjing Dongna Biotechnology Co., Ltd., product number: AgP01.

[0062] The single-walled carbon nanotubes have hydroxyl groups on their surface and a diameter of 1-2 nm. They were purchased from Chengdu Organic Chemistry Co., Ltd., Chinese Academy of Sciences, under the product number TNSRH.

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

[0064] Preparation Example 6: Preparation of Modified Silver Nanoparticles B

[0065] The specific implementation method is the same as in Preparation Example 5, except that carboxymethyl cellulose is not present, 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 Silver Nanoparticles C:

[0067] The silver nanoparticles and single-walled carbon nanotubes are directly mixed; the mass ratio of the silver nanoparticles to the single-walled carbon nanotubes is 15:1.5.

[0068] Examples 1-9 provide low-temperature curing solder pastes for microelectronic packaging, with compositions shown in Table 1 by weight percentage.

[0069] Table 1

[0070]

[0071] In Examples 1-9, the flux, by mass ratio, consists of 30 parts hydrogenated rosin, 8 parts activator, 35 parts solvent, 3 parts hydrogenated castor oil, 2 parts tert-butylhydroquinone, and 2 parts lauryl hydroxyethyl imidazoline.

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

[0073] The activator is succinic acid and salicylic acid in a mass ratio of 2.5:1.

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

[0075] The preparation method of low-temperature curing solder paste for microelectronic packaging is as follows: rosin, activator, hydrogenated castor oil, tert-butylhydroquinone, lauryl hydroxyethyl imidazoline and solvent are mixed and stirred evenly to obtain flux. The flux, modified solder powder and modified nano silver particles are mixed and stirred evenly to obtain low-temperature curing solder paste for microelectronic packaging.

[0076] Performance tests were conducted on the low-temperature curing solder pastes of Examples 1-9:

[0077] 1. Expansion ratio: Refer to GB / T 9491-2002 standard;

[0078] 2. Solder joint void ratio: The solder joint void ratio is tested using X-ray equipment; 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 at 25°C and 60% humidity for 10 months: (1) Observe whether it agglomerates or clumps. If no agglomeration or clumping occurs, it is considered qualified; (2) Test the spread rate according to GB / T 9491-2002 standard; the results are shown in Table 2.

[0080] Table 2

[0081]

[0082] As shown in Table 2, when 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 rate. This indicates that the best effect is achieved when the natural macromolecular organic acid is cinnamic acid.

[0083] Modified solder powder D was not washed with sodium humate solution, resulting in significantly worse stability of the solder paste, decreased spread rate, and increased solder joint void rate.

[0084] The stability of the solder paste obtained from unmodified solder powder is significantly worse, the spread rate is significantly reduced, and the void rate of the solder joints is significantly increased.

[0085] In the preparation of modified silver nanoparticles B, carboxymethyl cellulose was not added, and in the preparation of modified silver nanoparticles C, silver nanoparticles and carbon nanotubes were directly mixed. The resulting solder paste had significantly worse stability, significantly lower spread rate, and significantly higher solder joint void rate.

[0086] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do 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, By weight percentage, it includes 85-90% modified solder powder, 1-2% modified nano silver particles, and 8-14% flux; The solder powder, by weight percentage, comprises 42% Sn and 58% Bi; The modified solder powder is prepared by mixing an alcohol solution containing solder powder, an alcohol solution containing a terminal amino silane coupling agent and a natural macromolecular organic acid evenly, ultrasonically treating the mixture, filtering it after the process, washing it with sodium humate solution, and drying it.

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 low-temperature curing solder paste for microelectronic packaging according to claim 3, characterized in that, The modified silver nanoparticles are prepared by mixing silver nanoparticles, single-walled carbon nanotubes, carboxymethyl cellulose and water evenly, stirring and reacting, filtering after the reaction, washing with sodium humate solution and drying.

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

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 1-6, characterized in that, The flux, by weight, comprises the following raw materials: 25-35 parts rosin, 5-10 parts activator, 30-40 parts solvent, 2-5 parts thixotropic agent, 1-3 parts antioxidant, and 1-3 parts 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 icy white rosin.

9. The low-temperature curing solder paste for microelectronic packaging according to claim 8, characterized in that, The activator 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 1-9, characterized in that, The process includes the following steps: mixing rosin, activator, thixotropic agent, antioxidant, corrosion inhibitor and solvent evenly to obtain flux; mixing flux, modified solder powder and modified nano silver particles evenly to obtain low-temperature curing solder paste for microelectronic packaging.

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