Residue-free and easy-to-erase electronic soldering flux and preparation method thereof

Abstract

The invention discloses a preparation method of a residue-free and easy-to-erase electronic soldering flux. The preparation method specifically comprises the following steps: step 1, modifying rosin by adopting cinnamic acid; step 2, modifying the nano cellulose by adopting ammonium salt; step 3, preparing cinnamic acid composite nano cellulose according to products obtained in the step 1 and the step 2; 4, synthesizing a rosin monomer; 5, synthesizing a cinnamic acid monomer; 6, synthesizing rosin macromolecules according to products obtained in the step 4 and the step 5; and 7, the scaling powder is prepared according to products obtained in the step 3 and the step 6. The electronic soldering flux prepared through the method has the advantages of being free of residues and easy to erase.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic soldering, and relates to an electronic soldering flux without residue and easy to erase. The present invention also relates to a preparation method of the electronic soldering flux without residue and easy to erase. Background Art

[0002] Rosin soldering flux is an efficient soldering flux composed of rosin or / and rosin derivatives, and is widely used in electronic soldering technology. Rosin is a kind of fatty acid, which contains carboxyl groups in its structure. It can remove metal oxides during high-temperature soldering. When rosin melts during high-temperature soldering, a stable film is formed. Therefore, it can protect the metal surface during soldering and automatically form an isolation layer to avoid re-oxidation after removing oxides. The organic film formed by rosin or / and rosin derivatives after soldering has good electrical insulation and moisture resistance, providing a protective layer for the soldered joints. In addition, in the molten state, the wettability of rosin or / and rosin derivatives with the soldering material will affect the spreading rate when using the soldering flux. It can be seen that the use of soldering flux has many advantages for soldering. However, in order to greatly improve the soldering strength, trace halogens are introduced into the soldering flux, but the halogen residues are not easy to erase after soldering, which will have an adverse impact on the soldering quality. At the same time, organic acids such as succinic acid, adipic acid, and dibromosuccinic acid play a role in removing oxides, reducing the surface tension of the soldered material surface, and removing oil stains in the soldering flux. However, after soldering, it is also difficult to erase after the small molecule acids act with the soldered material, and the acids will also corrode the electronic circuit board. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of an electronic soldering flux without residue and easy to erase, and the electronic soldering flux prepared by this method has the characteristics of no residue and easy to erase.

[0004] Another purpose of the present invention is to provide an electronic soldering flux without residue and easy to erase.

[0005] The first technical solution adopted by the present invention is a preparation method of an electronic soldering flux without residue and easy to erase, which specifically includes the following steps:

[0006] Step 1, modify rosin with cinnamic acid;

[0007] Step 2, modify nano-cellulose with ammonium salt;

[0008] Step 3, prepare cinnamic acid composite nano-cellulose according to the products obtained in Step 1 and Step 2;

[0009] Step 4, synthesize rosin monomer;

[0010] Step 5, synthesize cinnamic acid monomer;

[0011] Step 6, synthesize rosin polymer according to the products obtained in Step 4 and Step 5;

[0012] Step 7: Prepare a soldering flux according to the products obtained in Step 3 and Step 6.

[0013] The feature of the first technical solution of the present invention is further that:

[0014] The specific process of Step 1 is as follows:

[0015] Step 1.1: Take 3 - 6 g of rosin and dissolve it in 10 - 20 mL of dimethyl sulfoxide solution, heat it to 120 - 150 °C to obtain a rosin solution;

[0016] Step 1.2: Dissolve 1.5 - 3 g of cinnamic acid in 10 - 20 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution;

[0017] Step 1.3: Dropwise add the cinnamic acid solution obtained in Step 1.2 to the rosin solution prepared in Step 1.1, with the dropping time being 30 - 60 min. After the dropping is completed, heat it to 150 - 180 °C and continue to react for 3 - 6 h. After the reaction is completed, cool it to room temperature, pour the reaction solution into 100 - 200 mL of water at 0 °C, stir evenly to obtain a yellow precipitate. Filter the precipitate, and continue to wash the precipitate three times with a mixed solution of 100 - 200 mL of ethanol and water at 0 °C. Finally, dry it at 45 - 60 °C to obtain cinnamic acid - modified rosin.

[0018] The specific process of Step 2 is as follows:

[0019] Take 0.2 - 0.4 g of nanocellulose and add it to 100 - 200 mL of anhydrous tetrahydrofuran solution, ultrasonically disperse it for 1 - 2 h. Then, add 0.1 - 0.2 g of sodium ethoxide, stir at room temperature for 10 - 20 min, and then add 0.1 - 0.2 g of 3 - bromopropyltrimethylammonium bromide. Heat it to 60 - 80 °C and react for 4 - 8 h. After the reaction is completed, wait for the temperature to cool to room temperature, put the obtained reaction solution into a dialysis bag with a molecular weight cut - off of 7000 - 10000 Da, and dialyze it with 500 - 800 mL of ethanol. Repeat dialysis three times, and dry the obtained sample overnight at 45 - 60 °C to obtain ammonium - salt - modified nanocellulose.

[0020] The specific process of Step 3 is as follows:

[0021] Take 1.2 - 2.4 g of cinnamic acid - modified rosin and dissolve it in 8 - 16 mL of turpentine. Add 0.3 - 0.6 g of sodium ethoxide, stir at room temperature for 10 - 20 min, and then add 0.1 - 0.2 g of ammonium - salt - modified nanocellulose. Stir at room temperature for 30 - 60 min. Put the obtained mixture into a dialysis bag with a molecular weight cut - off of 7000 - 10000 Da, and then put the dialysis bag into 50 - 100 mL of deionized water. Ultrasonically agitate during dialysis, and then freeze - dry to obtain cinnamic acid - composite nanocellulose.

[0022] The specific process of Step 4 is as follows:

[0023] Take 3 - 6 g of rosin and dissolve it in 30 - 60 mL of N,N - dimethylformamide solution, then add 0.1 - 0.2 g of EDC - NHS catalyst, and subsequently add 4 - aminostyrene in three batches, stir at room temperature for 12 - 24 h. After the reaction is completed, pour the obtained reaction solution into 100 - 200 mL of ice water, and dry at 45 - 60 °C to obtain a yellow precipitate of rosin monomer.

[0024] The specific process of Step 5 is as follows:

[0025] Dissolve 1.5 - 3 g of cinnamic acid in 30 - 60 mL of N,N - dimethylformamide solution, then add 0.1 - 0.2 g of EDC - NHS catalyst, and subsequently add 4 - aminostyrene in three batches, stir at room temperature for 12 - 24 h. After the reaction is completed, pour the obtained reaction solution into 100 - 200 mL of ice water, and dry at 45 - 60 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0026] The specific process of Step 6 is as follows:

[0027] Take 0.9 - 1.8 g of rosin monomer, 0.2 - 0.4 g of acrylic acid, and 0.3 - 0.6 g of cinnamic acid monomer, dissolve them in 8 - 16 mL of turpentine, add 15 - 30 mg of azobisisobutyronitrile, stir evenly, and then heat to 60 - 80 °C for reaction for 2 - 4 h, and cool to room temperature to obtain rosin polymer.

[0028] In Step 6, the viscosity of the rosin polymer is controlled at 10000 - 20000 cps.

[0029] The specific process of Step 7 is as follows:

[0030] Take 1 - 2 g of cinnamic acid composite nanocellulose and 0.5 - 1 g of rosin polymer, heat to 45 - 60 °C, stir for 30 - 60 min, and put the obtained mixed product into a refrigerator at 5 - 10 °C for 12 - 24 h to obtain a soldering flux.

[0031] The second technical solution adopted by the present invention is an electronic soldering flux without residue and easy to erase, which is prepared by using the above - mentioned preparation method of an electronic soldering flux without residue and easy to erase.

[0032] The beneficial effects of the present invention are as follows. The present invention prepares a soldering flux by compounding cinnamic acid-modified rosin and rosin polymer. It can achieve UV tack reduction of the soldering flux, and realize the characteristics of no residue and easy erasure after the use of the soldering flux. Carboxyl groups are introduced into both the rosin polymer and the cinnamic acid-modified rosin, which can greatly improve the wettability and spreadability of the soldering flux. At the same time, cinnamic acid composite nanocellulose is introduced into the soldering flux. Under the combined action of the ammonium salt-modified nanocellulose and the cinnamic acid-modified rosin, after the solder is subjected to high-temperature soldering, an organic film can be formed at the soldering point to improve the surface insulation (increase the resistivity). The cinnamic acid-modified rosin contains two carboxyl groups, which also improves the spreadability and wettability of the solder. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a comparative diagram of the surface contact angles of the soldering fluxes prepared in Example 1 of the preparation method of the residue-free and easy-to-erase electronic soldering flux of the present invention and Comparative Examples 1 to 6 with tin metal. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0035] The preparation method of the residue-free and easy-to-erase electronic soldering flux of the present invention is specifically as follows:

[0036] Step 1: Use cinnamic acid to modify rosin, specifically:

[0037] Take 3 - 6 g of rosin and dissolve it in 10 - 20 mL of dimethyl sulfoxide solution, heat it to 120 - 150 °C to obtain a rosin solution; dissolve 1.5 - 3 g of cinnamic acid in 10 - 20 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; dropwise add the cinnamic acid solution to the rosin solution, and the dropping time is 30 - 60 min. After the dropping is completed, heat it to 150 - 180 °C and continue to react for 3 - 6 h. After the reaction is completed, wait until it cools to room temperature. Pour the reaction solution into 100 - 200 mL of an aqueous solution at 0 °C, stir evenly to obtain a yellow precipitate. Filter the precipitate, and continue to wash the precipitate three times with a mixed solution of ethanol and water (v:v = 1:2) at 0 °C and 100 - 200 mL. Finally, dry it at 45 - 60 °C to obtain cinnamic acid-modified rosin. The synthesis route is as follows:

[0038]

[0039] Step 2: Prepare ammonium salt-modified nanocellulose, specifically:

[0040] Take 0.2 - 0.4 g of nanocellulose (H 2 SO 4(Prepared by hydrolysis method, freeze-dried) was added to 100 - 200 mL of anhydrous tetrahydrofuran solution and ultrasonically dispersed for 1 - 2 h. Then, 0.1 - 0.2 g of sodium ethoxide was added and stirred at room temperature for 10 - 20 min. Subsequently, 0.1 - 0.2 g of 3-bromopropyltrimethylammonium bromide was added and the mixture was heated to 60 - 80 °C and reacted for 4 - 8 h. After the reaction, when the temperature cooled to room temperature, the reaction solution was placed in a dialysis bag with a molecular weight cut-off of 7000 - 10000 Da and dialyzed with 500 - 800 mL of ethanol. The dialysis was repeated three times, and the sample was dried overnight at 45 - 60 °C to obtain ammonium salt-modified nanocellulose.

[0041] Step 3: Preparation of cinnamic acid composite nanocellulose, specifically:

[0042] Take 1.2 - 2.4 g of (the product obtained in Step 1) cinnamic acid-modified rosin and dissolve it in 8 - 16 mL of turpentine. Add 0.3 - 0.6 g of sodium ethoxide and stir at room temperature for 10 - 20 min. Add 0.1 - 0.2 g of (the ammonium salt-modified nanocellulose prepared in Step 2) and stir at room temperature for 30 - 60 min. Place the mixture in a dialysis bag with a molecular weight cut-off of 7000 - 10000 Da, and then place the dialysis bag in 50 - 100 mL of deionized water. During dialysis, ultrasonicate for 12 - 24 h (ultrasonic power is 45 W) and freeze-dry at -70 °C to obtain cinnamic acid composite nanocellulose.

[0043] Step 4: Synthesis of rosin monomer, specifically:

[0044] Take 3 - 6 g of rosin and dissolve it in 30 - 60 mL of N,N-dimethylformamide solution. Then, add 0.1 - 0.2 g of EDC-NHS catalyst (EDC: 0.06 - 0.12 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 - 0.08 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (each time adding 0.4 - 1.2 g) and stir at room temperature for 12 - 24 h. After the reaction, pour the obtained reaction solution into 100 - 200 mL of ice water and dry at 45 - 60 °C to obtain a yellow precipitate, which is the rosin monomer. The synthesis route is as follows:

[0045]

[0046] Step 5: Synthesis of cinnamic acid monomer, specifically:

[0047] Dissolve 1.5 - 3 g of cinnamic acid in 30 - 60 mL of N,N - dimethylformamide solution, and then add 0.1 - 0.2 g of EDC - NHS catalyst (EDC: 0.06 - 0.12 g of 1 - ethyl - 3 - (3 - dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 - 0.08 g of N - hydroxysuccinimide). Then, add 4 - aminostyrene in three batches (0.4 - 1.2 g each time), and stir at room temperature for 12 - 24 h. After the reaction is completed, pour the obtained reaction solution into 100 - 200 mL of ice water, and dry at 45 - 60 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0048] Step 6, synthesis of rosin polymer, specifically:

[0049] Take 0.9 - 1.8 g of rosin monomer, 0.2 - 0.4 g of acrylic acid, and 0.3 - 0.6 g of cinnamic acid monomer respectively, dissolve them in 8 - 16 mL of turpentine, add 15 - 30 mg of azobisisobutyronitrile, stir evenly, and then heat to 60 - 80 °C for reaction for 2 - 4 h. Cool to room temperature to obtain rosin polymer, and the viscosity of the rosin polymer is controlled at 10000 - 20000 cps.

[0050] Step 7, preparation of soldering flux, specifically:

[0051] Take 1 - 2 g of cinnamic acid composite nanocellulose and 0.5 - 1 g of rosin polymer, heat to 45 - 60 °C, stir mechanically for 30 - 60 min, and put the obtained mixed product into a refrigerator at 5 - 10 °C for 12 - 24 h to obtain the soldering flux.

[0052] Performance testing and erasure, specifically:

[0053] The performance testing of the soldering agent is carried out according to the testing method specified in SJ / T11389 - 2009 "Flux for Lead - free Soldering". The erasure method of the used soldering agent is mainly to manually peel it off after irradiating with a 36 - 45 W ultraviolet lamp for 20 - 40 s.

[0054] Example 1

[0055] Step 1, modification of rosin with cinnamic acid, specifically:

[0056] Take 3 g of rosin and dissolve it in 10 mL of dimethyl sulfoxide solution. Heat it to 120 °C to obtain a rosin solution. Dissolve 1.5 g of cinnamic acid in 10 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution. Dropwise add the cinnamic acid solution to the rosin solution, and the dropping time is 30 min. After the dropping is completed, heat it to 150 °C and continue to react for 3 h. After the reaction is completed, wait until it cools to room temperature. Pour the reaction solution into 100 mL of an aqueous solution at 0 °C, stir evenly to obtain a yellow precipitate. Filter the precipitate, and continue to wash the precipitate three times with a mixed solution of ethanol and water (v:v = 1:2) at 0 °C and 100 mL. Finally, dry it at 45 °C to obtain cinnamic acid-modified rosin.

[0057] Step 2, prepare ammonium salt-modified nanocellulose, specifically:

[0058] Take 0.2 g of nanocellulose and add it to 100 mL of anhydrous tetrahydrofuran solution. Ultrasonically disperse it for 1 h. Then, add 0.1 g of sodium ethoxide and stir at room temperature for 10 min. Then add 0.1 g of 3-bromopropyltrimethylammonium bromide and heat to 60 °C to react for 4 h. After the reaction is completed, wait until the temperature cools to room temperature. Put the reaction solution into a dialysis bag with a molecular weight cut-off of 7000 Da and dialyze it with 500 mL of ethanol. Repeat dialysis three times. Dry the obtained sample overnight at 45 °C to obtain it.

[0059] Step 3, prepare cinnamic acid composite nanocellulose, specifically:

[0060] Take 1.2 g of cinnamic acid-modified rosin and dissolve it in 8 mL of turpentine. Add 0.3 g of sodium ethoxide and stir at room temperature for 10 min. Add 0.1 g of ammonium salt-modified nanocellulose and stir at room temperature for 30 min. React the mixed solution in a dialysis bag with a molecular weight cut-off of 7000 Da. Then put the dialysis bag into 50 mL of deionized water and ultrasonically agitate it for 12 h (ultrasonic power is 45 W) during dialysis. Freeze-dry it at -70 °C to obtain cinnamic acid composite nanocellulose.

[0061] Step 4, synthesis of rosin monomer, specifically:

[0062] Take 3 g of rosin and dissolve it in 30 mL of N,N-dimethylformamide solution. Then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time). After stirring evenly, stir at room temperature for 12 h. After the reaction is completed, pour the obtained reaction solution into 100 mL of ice water and dry it at 45 °C to obtain a yellow precipitate of rosin monomer.

[0063] Step 5, synthesis of cinnamic acid monomer, specifically:

[0064] Dissolve 1.5 g of cinnamic acid in 30 mL of N,N-dimethylformamide solution, and then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time), and stir at room temperature for 12 h. After the reaction is completed, pour the obtained reaction solution into 100 mL of ice water, and dry at 45 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0065] Step 6, synthesis of rosin polymer, specifically:

[0066] Take 0.9 g of rosin monomer, 0.2 g of acrylic acid, and 0.3 g of cinnamic acid monomer respectively, dissolve them in 8 mL of turpentine, add 15 mg of azobisisobutyronitrile, stir evenly, and then heat to 60 °C for reaction for 2 h. Cool to room temperature to obtain rosin polymer, and the viscosity of the rosin polymer is controlled at 10,000 - 20,000 cps.

[0067] Step 7, preparation of soldering flux, specifically:

[0068] Take 1 g of cinnamic acid composite nanocellulose and 0.5 g of rosin polymer, heat the temperature to 45 °C, and stir mechanically for 30 min. Put the obtained mixed product into a refrigerator at 5 °C for 12 h to obtain the soldering flux.

[0069] Performance testing and erasure, specifically:

[0070] The performance testing of the soldering agent is carried out according to the testing method specified in SJ / T11389-2009 "Flux for Lead-Free Soldering". The erasure method of the used soldering agent is mainly by irradiating with a 36 W ultraviolet lamp for 20 s and then manually peeling.

[0071] Comparative Example 1 (without dialysis during the preparation of cinnamic acid composite nanocellulose, with bromine present)

[0072] Step 1, modification of rosin with cinnamic acid, specifically:

[0073] Dissolve 3 g of rosin in 10 mL of dimethyl sulfoxide solution and heat to 120 °C to obtain a rosin solution; dissolve 1.5 g of cinnamic acid in 10 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; dropwise add the cinnamic acid solution to the rosin solution, and the dropping time is 30 min. After the dropping is completed, heat to 150 °C and continue to react for 3 h. After the reaction is completed, wait until it cools to room temperature. Pour the reaction solution into 100 mL of an aqueous solution at 0 °C, stir evenly to obtain a yellow precipitate, filter the precipitate, and continue to wash the precipitate three times with a mixed solution of ethanol and water (v:v = 1:2) at 0 °C and 100 mL. Finally, dry at 45 °C to obtain cinnamic acid-modified rosin.

[0074] Step 2, prepare ammonium salt-modified nanocellulose, specifically:

[0075] Add 0.2 g of nanocellulose to 100 mL of anhydrous tetrahydrofuran solution and ultrasonically disperse for 1 h. Then, add 0.1 g of sodium ethoxide and stir at room temperature for 10 min. Then add 0.1 g of 3-bromopropyltrimethylammonium bromide and heat to 60 °C to react for 4 h. After the reaction is completed, wait until the temperature cools to room temperature, put the reaction solution into a dialysis bag with a molecular weight cut-off of 7000 Da, and dialyze with 500 mL of ethanol three times. Dry the sample overnight at 45 °C to obtain it.

[0076] Step 3, prepare cinnamic acid composite nanocellulose, specifically:

[0077] Dissolve 1.2 g of cinnamic acid-modified rosin in 8 mL of turpentine, add 0.3 g of sodium ethoxide, and stir at room temperature for 10 min. Add 0.1 g of ammonium salt-modified nanocellulose and stir at room temperature for 30 min. Freeze-dry at -70 °C to obtain cinnamic acid composite nanocellulose.

[0078] Step 4, synthesis of rosin monomer, specifically:

[0079] Dissolve 3 g of rosin in 30 mL of N,N-dimethylformamide solution, and then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time), stir evenly, and stir at room temperature for 12 h. After the reaction is completed, pour the obtained reaction solution into 100 mL of ice water and dry at 45 °C to obtain a yellow precipitate of rosin monomer.

[0080] Step 5, synthesis of cinnamic acid monomer, specifically:

[0081] Dissolve 1.5 g of cinnamic acid in 30 mL of N,N-dimethylformamide solution, and then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time), stir well, and stir at room temperature for 12 h. After the reaction is completed, pour the obtained reaction solution into 100 mL of ice water, and dry at 45 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0082] Step 6, synthesis of rosin polymer, specifically:

[0083] Take 0.9 g of rosin monomer, 0.2 g of acrylic acid, and 0.3 g of cinnamic acid monomer, dissolve them in 8 mL of turpentine, add 15 mg of azobisisobutyronitrile, stir well, heat to 60 °C and react for 2 h, then cool to room temperature to obtain rosin polymer. The viscosity of the rosin polymer is controlled at 10,000 - 20,000 cps.

[0084] Step 7, preparation of soldering flux, specifically:

[0085] Take 1 g of cinnamic acid composite nanocellulose and 0.5 g of rosin polymer, heat to 45 °C, and stir mechanically for 30 min. Put the obtained mixed product into a refrigerator at 5 °C for 12 h to obtain the soldering flux.

[0086] Performance testing and erasure, specifically:

[0087] The performance testing of the soldering agent is carried out according to the testing method specified in SJ / T11389-2009 "Flux for Lead-Free Soldering". The erasure method of the used soldering agent is mainly to irradiate with a 36 W ultraviolet lamp for 20 s and then manually peel it off.

[0088] Comparative Example 2 (When synthesizing rosin polymer, cinnamic acid monomer was not added, and DA reaction could not be formed between polymer chains. It could not be manually peeled off, and there was polymer residue after ethanol erasure)

[0089] Step 1, modification of rosin with cinnamic acid, specifically:

[0090] Dissolve 3 g of rosin in 10 mL of dimethyl sulfoxide solution and heat it to 120 °C to obtain a rosin solution; dissolve 1.5 g of cinnamic acid in 10 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; dropwise add the cinnamic acid solution to the rosin solution, and the dropping time is 30 min. After the dropping is completed, heat it to 150 °C and continue to react for 3 h. After the reaction is completed, wait until it cools to room temperature. Pour the reaction solution into 100 mL of aqueous solution at 0 °C, stir evenly to obtain a yellow precipitate, filter the precipitate, and continue to wash the precipitate with a mixed solution of ethanol and water (v:v = 1:2) at 0 °C and 100 mL for three times, and finally dry it at 45 °C to obtain cinnamic acid-modified rosin.

[0091] Step 2, prepare ammonium salt-modified nanocellulose, specifically:

[0092] Take 0.2 g of nanocellulose and add it to 100 mL of anhydrous tetrahydrofuran solution, and ultrasonically disperse it for 1 h. Then, add 0.1 g of sodium ethoxide and stir at room temperature for 10 min. Then add 0.1 g of 3-bromopropyltrimethylammonium bromide and heat to 60 °C for reaction for 4 h. After the reaction is completed, wait until the temperature cools to room temperature, put the reaction solution into a dialysis bag with a molecular weight cut-off of 7000 Da, and dialyze it with 500 mL of ethanol for three times, and dry the obtained sample overnight at 45 °C to obtain it.

[0093] Step 3, prepare cinnamic acid composite nanocellulose, specifically:

[0094] Take 1.2 g of cinnamic acid-modified rosin and dissolve it in 8 mL of turpentine, add 0.3 g of sodium ethoxide, and stir at room temperature for 10 min. Add 0.1 g of ammonium salt-modified nanocellulose and stir at room temperature for 30 min, and freeze-dry at -70 °C to obtain cinnamic acid composite nanocellulose.

[0095] Step 4, synthesis of rosin monomer, specifically:

[0096] Take 3 g of rosin and dissolve it in 30 mL of N,N-dimethylformamide solution, and then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time), stir evenly, and stir at room temperature for 12 h. After the reaction is completed, pour the obtained reaction solution into 100 mL of ice water and dry it at 45 °C to obtain a yellow precipitate of rosin monomer.

[0097] Step 5, synthesis of rosin polymer, specifically:

[0098] Take 0.9 g of rosin monomer and 0.2 g of acrylic acid, dissolve them in 8 mL of turpentine, add 15 mg of azobisisobutyronitrile, stir evenly, heat to 60 °C and react for 2 h, then cool to room temperature to obtain rosin polymer, and control the viscosity of the rosin polymer at 10,000 - 20,000 cps.

[0099] Step 6, preparation of the soldering flux, specifically:

[0100] Take 1 g of cinnamic acid composite nanocellulose and 0.5 g of rosin polymer, heat to 45 °C, and mechanically stir for 30 min. Put the obtained mixed product into a refrigerator at 5 °C for 12 h to obtain the soldering flux.

[0101] Performance test, specifically:

[0102] The performance test of the soldering agent is carried out according to the test method specified in SJ / T11389 - 2009 "Flux for Lead - free Soldering".

[0103] Comparative Example 3 (Rosin monomer, acrylic acid, and cinnamic acid monomer do not polymerize, and the soldering agent is directly prepared in the form of monomers, which cannot be manually peeled off and there is residue when wiped with ethanol)

[0104] Step 1, modification of rosin with cinnamic acid, specifically:

[0105] Take 3 g of rosin and dissolve it in 10 mL of dimethyl sulfoxide solution, heat to 120 °C to obtain a rosin solution; dissolve 1.5 g of cinnamic acid in 10 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; drop the cinnamic acid solution into the rosin solution drop by drop, and the dropping time is 30 min. After the dropping is completed, heat to 150 °C and continue to react for 3 h. After the reaction is completed, wait until it cools to room temperature. Pour the reaction solution into 100 mL of aqueous solution at 0 °C, stir evenly to obtain a yellow precipitate. Filter the precipitate, and continue to wash the precipitate with a mixed solution of ethanol and water (v:v = 1:2) at 0 °C and 100 mL for three times. Finally, dry at 45 °C to obtain cinnamic acid - modified rosin.

[0106] Step 2, preparation of ammonium - salt - modified nanocellulose, specifically:

[0107] Take 0.2 g of nanocellulose and add it to 100 mL of anhydrous tetrahydrofuran solution, ultrasonically disperse for 1 h. Then, add 0.1 g of sodium ethoxide, stir at room temperature for 10 min. Then add 0.1 g of 3 - bromopropyltrimethylammonium bromide, heat to 60 °C and react for 4 h. After the reaction is completed, wait until the temperature cools to room temperature, put the reaction solution into a dialysis bag with a molecular weight cut - off of 7000 Da, and dialyze with 500 mL of ethanol for three times. Dry the obtained sample overnight at 45 °C to obtain it.

[0108] Step 3: Preparation of cinnamic acid composite nanocellulose, specifically as follows:

[0109] Dissolve 1.2 g of cinnamic acid-modified rosin in 8 mL of turpentine, add 0.3 g of sodium ethoxide, and stir at room temperature for 10 min. Add 0.1 g of ammonium salt-modified nanocellulose, stir at room temperature for 30 min, transfer the mixture to a dialysis bag with a molecular weight cut-off of 7000 Da, then place the dialysis bag in 50 mL of deionized water, and ultrasonicate for 12 h (ultrasonic power: 45 W) during dialysis. Freeze-dry at -70 °C to obtain cinnamic acid composite nanocellulose.

[0110] Step 4: Synthesis of rosin monomer, specifically as follows:

[0111] Dissolve 3 g of rosin in 30 mL of N,N-dimethylformamide solution, then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time), stir evenly, and stir at room temperature for 12 h. After the reaction is completed, pour the resulting reaction solution into 100 mL of ice water and dry at 45 °C to obtain a yellow precipitate of rosin monomer.

[0112] Step 5: Synthesis of cinnamic acid monomer, specifically as follows:

[0113] Dissolve 1.5 g of cinnamic acid in 30 mL of N,N-dimethylformamide solution, then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time), stir evenly, and stir at room temperature for 12 h. After the reaction is completed, pour the resulting reaction solution into 100 mL of ice water and dry at 45 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0114] Step 6: Preparation of flux, specifically as follows:

[0115] Take 1 g of cinnamic acid composite nanocellulose, 0.35 g of rosin monomer, 0.078 g of acrylic acid, and 0.117 g of cinnamic acid monomer, heat to 45 °C, and stir mechanically for 30 min. Place the resulting mixed product in a refrigerator at 5 °C for 12 h to obtain the flux.

[0116] Performance testing and erasure, specifically as follows:

[0117] The performance test of the soldering agent is based on the test method specified in SJ / T 11389-2009 "Flux for Lead-Free Soldering". The erasure method of the used soldering agent is mainly that after irradiating with a 36W ultraviolet lamp for 20s, it cannot be manually peeled off.

[0118] Comparative Example 4 (no ammonium salt-modified nanocellulose component is added to the flux, and the poor soldering performance is reflected in the poor surface insulation performance after soldering)

[0119] Step 1: Modify rosin with cinnamic acid, specifically:

[0120] Take 3g of rosin and dissolve it in 10mL of dimethyl sulfoxide solution, heat it to 120°C to obtain a rosin solution; dissolve 1.5g of cinnamic acid in 10mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; drop the cinnamic acid solution into the rosin solution drop by drop, and the dropping time is 30min. After the dropping is completed, heat it to 150°C and continue to react for 3h. After the reaction is completed, wait until it cools to room temperature. Pour the reaction solution into 100mL of aqueous solution at 0°C, stir evenly to obtain a yellow precipitate, filter the precipitate, and continue to wash the precipitate three times with a mixed solution of ethanol and water (v:v = 1:2) at 0°C and 100mL. Finally, dry it at 45°C to obtain cinnamic acid-modified rosin.

[0121] Step 2: Synthesis of rosin monomer, specifically:

[0122] Take 3g of rosin and dissolve it in 30mL of N,N-dimethylformamide solution, and then add 0.1g of EDC-NHS catalyst (EDC: 0.06g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4g each time), stir evenly, and stir at room temperature for 12h. After the reaction is completed, pour the obtained reaction solution into 100mL of ice water and dry it at 45°C to obtain a yellow precipitate of rosin monomer.

[0123] Step 3: Synthesis of cinnamic acid monomer, specifically:

[0124] Dissolve 1.5g of cinnamic acid in 30mL of N,N-dimethylformamide solution, and then add 0.1g of EDC-NHS catalyst (EDC: 0.06g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4g each time), stir evenly, and stir at room temperature for 12h. After the reaction is completed, pour the obtained reaction solution into 100mL of ice water and dry it at 45°C to obtain a colorless precipitate of cinnamic acid monomer.

[0125] Step 4: Synthesis of rosin polymer, specifically:

[0126] Take 0.9 g of rosin monomer, 0.2 g of acrylic acid, and 0.3 g of cinnamic acid monomer, dissolve them in 8 mL of turpentine, add 15 mg of azobisisobutyronitrile, stir evenly, heat to 60 °C and react for 2 h, then cool to room temperature to obtain rosin polymer. The viscosity of the rosin polymer is controlled at 10,000 - 20,000 cps.

[0127] Step 5, preparation of the soldering flux, specifically:

[0128] Take 1 g of cinnamic acid-modified rosin and disperse it in 8 mL of turpentine. Further add 0.5 g of rosin polymer, heat to 45 °C, and mechanically stir for 30 min. Place the obtained mixed product in a refrigerator at 5 °C for 12 h to obtain the soldering flux.

[0129] Performance testing and erasure, specifically:

[0130] The performance testing of the soldering agent is carried out according to the testing method specified in SJ / T11389 - 2009 "Flux for Lead-Free Soldering". The erasure method of the used soldering agent is mainly by irradiating with a 36 W ultraviolet lamp for 20 s and then manually peeling.

[0131] Comparative Example 5 (When synthesizing rosin polymer, acrylic acid monomer is not added, and the wettability of the soldering flux is poor, resulting in a low spreading rate during soldering)

[0132] Step 1, adopt cinnamic acid-modified rosin, specifically:

[0133] Take 3 g of rosin and dissolve it in 10 mL of dimethyl sulfoxide solution, heat to 120 °C to obtain a rosin solution; dissolve 1.5 g of cinnamic acid in 10 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; dropwise add the cinnamic acid solution to the rosin solution, and the dropping time is 30 min. After the dropping is completed, heat to 150 °C and continue to react for 3 h. After the reaction is completed, wait until it cools to room temperature. Pour the reaction solution into 100 mL of an aqueous solution at 0 °C, stir evenly to obtain a yellow precipitate. Filter the precipitate, and continue to wash the precipitate three times with a mixed solution of 0 °C, 100 mL of ethanol and water (v:v = 1:2). Finally, dry at 45 °C to obtain cinnamic acid-modified rosin.

[0134] Step 2, preparation of ammonium salt-modified nanocellulose, specifically:

[0135] Take 0.2 g of nanocellulose and add it to 100 mL of anhydrous tetrahydrofuran solution, and ultrasonically disperse for 1 h. Then, add 0.1 g of sodium ethoxide and stir at room temperature for 10 min. Then add 0.1 g of 3-bromopropyltrimethylammonium bromide and heat to 60 °C for reaction for 4 h. After the reaction is completed, wait for the temperature to cool to room temperature, put the reaction solution into a dialysis bag with a molecular weight cut-off of 7000 Da, and dialyze with 500 mL of ethanol. Repeat dialysis three times, and dry the sample overnight at 45 °C to obtain the product.

[0136] Step 3, prepare cinnamic acid composite nanocellulose, specifically:

[0137] Take 1.2 g of cinnamic acid-modified rosin and dissolve it in 8 mL of turpentine. Add 0.3 g of sodium ethoxide and stir at room temperature for 10 min. Add 0.1 g of ammonium salt-modified nanocellulose and stir at room temperature for 30 min. Transfer the mixture into a dialysis bag with a molecular weight cut-off of 7000 Da, and then put the dialysis bag into 50 mL of deionized water. During dialysis, ultrasonicate for 12 h (ultrasonic power is 45 W), and freeze-dry at -70 °C to obtain cinnamic acid composite nanocellulose.

[0138] Step 4, synthesize rosin monomer, specifically:

[0139] Take 3 g of rosin and dissolve it in 30 mL of N,N-dimethylformamide solution. Then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time). After stirring evenly, stir at room temperature for 12 h. After the reaction is completed, pour the obtained reaction solution into 100 mL of ice water and dry at 45 °C to obtain a yellow precipitate of rosin monomer.

[0140] Step 5, synthesize cinnamic acid monomer, specifically:

[0141] Dissolve 1.5 g of cinnamic acid in 30 mL of N,N-dimethylformamide solution. Then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time). After stirring evenly, stir at room temperature for 12 h. After the reaction is completed, pour the obtained reaction solution into 100 mL of ice water and dry at 45 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0142] Step 6, synthesize rosin polymer, specifically:

[0143] Take 0.9 g of rosin monomer and 0.3 g of cinnamic acid monomer, dissolve them in 8 mL of turpentine, add 15 mg of azobisisobutyronitrile, stir evenly, heat to 60 °C and react for 2 h, then cool to room temperature to obtain rosin polymer, and the viscosity of the rosin polymer is controlled at 10,000 - 20,000 cps.

[0144] Step 7, preparation of the soldering flux, specifically:

[0145] Take 1 g of cinnamic acid composite nanocellulose and 0.5 g of rosin polymer, heat to 45 °C, and mechanically stir for 30 min. Put the obtained mixed product into a refrigerator at 5 °C for 12 h to obtain the soldering flux.

[0146] Performance testing and erasure, specifically:

[0147] The performance testing of the soldering agent is carried out according to the testing method specified in SJ / T11389 - 2009 "Flux for Lead - Free Soldering". The erasure method of the used soldering agent is mainly to irradiate with a 36 W ultraviolet lamp for 20 s and then manually peel it off.

[0148] Comparative Example 6 (The soldering flux does not contain cinnamic acid - modified rosin and contains bromine, and a protective film cannot be formed on the soldering point after soldering, and the surface insulation performance is poor)

[0149] Step 1, preparation of ammonium - salt - modified nanocellulose, specifically:

[0150] Take 0.2 g of nanocellulose and add it to 100 mL of anhydrous tetrahydrofuran solution, ultrasonically disperse for 1 h. Then, add 0.1 g of sodium ethoxide, stir at room temperature for 10 min. Then add 0.1 g of 3 - bromopropyltrimethylammonium bromide, heat to 60 °C and react for 4 h. After the reaction ends, wait for the temperature to cool to room temperature, put the reaction solution into a dialysis bag with a molecular weight cut - off of 7000 Da, and dialyze with 500 mL of ethanol, repeat dialysis three times, and dry the obtained sample overnight at 45 °C to obtain it.

[0151] Step 2, synthesis of rosin monomer, specifically:

[0152] Take 3 g of rosin and dissolve it in 30 mL of N,N - dimethylformamide solution, then add 0.1 g of EDC - NHS catalyst (EDC: 0.06 g of 1 - ethyl - 3 - (3 - dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N - hydroxysuccinimide). Then, add 4 - aminostyrene in three batches (0.4 g each time), stir evenly, and stir at room temperature for 12 h. After the reaction ends, pour the obtained reaction solution into 100 mL of ice water, and dry at 45 °C to obtain a yellow precipitate of rosin monomer.

[0153] Step 3, synthesis of cinnamic acid monomer, specifically:

[0154] Dissolve 1.5 g of cinnamic acid in 30 mL of N,N-dimethylformamide solution, and then add 0.1 g of EDC-NHS catalyst (EDC: 0.06 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.04 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.4 g each time), stir well, and stir at room temperature for 12 h. After the reaction is completed, pour the obtained reaction solution into 100 mL of ice water and dry at 45 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0155] Step 4, synthesis of rosin polymer, specifically:

[0156] Take 0.9 g of rosin monomer, 0.2 g of acrylic acid, and 0.3 g of cinnamic acid monomer, dissolve them in 8 mL of turpentine, add 15 mg of azobisisobutyronitrile, stir well, heat to 60 °C and react for 2 h, then cool to room temperature to obtain rosin polymer. The viscosity of the rosin polymer is controlled at 10000 - 20000 cps.

[0157] Step 5, preparation of soldering flux, specifically:

[0158] Take 1 g of ammonium salt-modified nanocellulose and disperse it in 8 mL of turpentine, add 0.5 g of rosin polymer, heat to 45 °C, and stir mechanically for 30 min. Put the obtained mixed product into a refrigerator at 5 °C for 12 h to obtain the soldering flux.

[0159] Performance testing and erasure, specifically:

[0160] The performance testing of the soldering flux is carried out according to the testing method specified in SJ / T11389-2009 "Flux for Lead-Free Soldering". The erasure method of the used soldering flux is mainly to irradiate with a 36 W ultraviolet lamp for 20 s and then manually peel it off.

[0161] The following Table 1 shows the performance comparison results of the soldering fluxes obtained in Example 1 and Comparative Examples 1 - 6:

[0162] Table 1

[0163]

[0164] The erasability refers to whether there is any residue of the soldering flux when manually peeling after UV irradiation after the soldering flux is used.

[0165] In Example 1, there is a D-A cyclization reaction in the double bond of the cinnamic acid structural unit after UV irradiation, resulting in the formation of a cross-linked structure between polymer chains and volume shrinkage to achieve UV viscosity reduction. Due to the existence of the UV viscosity reduction function, the flux is easy to erase after use; and the generated sodium bromide is well removed by dialysis in the preparation of cinnamic acid composite nanocellulose; carboxyl groups are introduced into both rosin polymers and cinnamic acid-modified rosins, which can greatly improve the wettability and spreadability of the flux. Ammonium salt-modified nanocellulose in the flux improves the welding performance of cinnamic acid-modified rosin, thus effectively improving the insulation of the welding point.

[0166] In Comparative Example 1, during the preparation of cinnamic acid composite nanocellulose, dialysis was not carried out, and the formed sodium bromide inorganic salt could not be removed, resulting in the presence of bromine. The flux containing bromine will be corrosive to the electronic circuit.

[0167] In Comparative Example 2, cinnamic acid monomer was not added during the synthesis of the rosin polymer, and the D-A reaction could not occur between polymer chains during UV irradiation, so UV viscosity reduction could not be achieved, manual peeling was impossible, and there was polymer residue after ethanol wiping.

[0168] In Comparative Example 3, rosin monomer, acrylic acid, and cinnamic acid monomer did not polymerize, and the soldering agent was directly prepared in the form of monomers. Manual peeling was impossible (cinnamic acid composite nanocellulose was welded with rosin monomer, acrylic acid, and cinnamic acid, and no film could be formed after UV irradiation, so peeling was impossible), and there was residue after ethanol wiping; since rosin monomer, acrylic acid, and cinnamic acid monomer were directly used in the soldering agent, compared with rosin polymer, their lower melting point and smaller molecules led to easier diffusion of molecules, and their spreading rate was relatively higher than that of the rosin polymer-based flux.

[0169] In Comparative Example 4, the ammonium salt-modified nanocellulose component was not added to the flux, lacking the ammonium salt component, resulting in poor welding performance and finally poor surface insulation performance after welding.

[0170] In Comparative Example 5, acrylic acid monomer was not added during the synthesis of the rosin polymer, and the wettability of the flux was poor, resulting in the lowest spreading rate during welding, poor welding performance, and low film resistivity after welding.

[0171] In Comparative Example 6, cinnamic acid-modified rosin was not added to the flux, but a large amount of bromine was contained in the ammonium salt-modified nanocellulose, making the flux contain bromine; at the same time, lacking the cinnamic acid-modified rosin component, the welding performance was poor, a protective film could not be formed, and the surface insulation performance was the worst.

[0172] Wettability affects the spreading of the flux on the metal surface. The surface contact angle between the flux and tin metal can be measured; such as Figure 1As shown, among them, the contact angle of Comparative Example 3 is the smallest, while the contact angle of Comparative Example 5 is the largest. Since the smaller the contact angle, the more beneficial it is for the solder flux to spread on the metal surface. The larger the contact angle, the worse the wettability.

[0173] Example 2

[0174] Step 1: Modify rosin with cinnamic acid. Specifically:

[0175] Take 6 g of rosin and dissolve it in 20 mL of dimethyl sulfoxide solution, heat to 150 °C to obtain a rosin solution; dissolve 3 g of cinnamic acid in 20 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; dropwise add the cinnamic acid solution to the rosin solution, and the dropping time is 60 min. After the dropping is completed, heat to 180 °C and continue to react for 6 h. After the reaction is completed, wait until it cools to room temperature. Pour the reaction solution into 200 mL of an aqueous solution at 0 °C, stir evenly to obtain a yellow precipitate. Filter the precipitate, and continue to wash the precipitate three times with a mixed solution of ethanol and water (v:v = 1:2) at 0 °C and 200 mL. Finally, dry at 60 °C to obtain cinnamic acid-modified rosin.

[0176] Step 2: Prepare ammonium salt-modified nanocellulose. Specifically:

[0177] Take 0.4 g of nanocellulose and add it to 200 mL of anhydrous tetrahydrofuran solution, and ultrasonically disperse for 2 h. Then, add 0.2 g of sodium ethoxide and stir at room temperature for 20 min. Then add 0.2 g of 3-bromopropyltrimethylammonium bromide, heat to 80 °C and react for 8 h. After the reaction is completed, wait until the temperature cools to room temperature. Put the reaction solution into a dialysis bag with a molecular weight cut-off of 10000 Da, and dialyze with 800 mL of ethanol three times. The obtained sample is dried overnight at 60 °C.

[0178] Step 3: Prepare cinnamic acid composite nanocellulose. Specifically:

[0179] Take 2.4 g of cinnamic acid-modified rosin and dissolve it in 16 mL of turpentine, add 0.6 g of sodium ethoxide, and stir at room temperature for 20 min. Add 0.2 g of ammonium salt-modified nanocellulose and stir at room temperature for 60 min. Put the mixed solution into a dialysis bag with a molecular weight cut-off of 10000 Da, and then put the dialysis bag into 100 mL of deionized water. During dialysis, ultrasonically irradiate for 24 h (ultrasonic power is 45 W), and freeze-dry at -70 °C to obtain cinnamic acid composite nanocellulose.

[0180] Step 4: Synthesis of rosin monomer. Specifically:

[0181] Dissolve 6 g of rosin in 60 mL of N,N-dimethylformamide solution, and then add 0.2 g of EDC-NHS catalyst (EDC: 0.12 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.08 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (1.2 g each time), stir evenly, and stir at room temperature for 24 h. After the reaction is completed, pour the obtained reaction solution into 200 mL of ice water, and dry at 60 °C to obtain a yellow precipitate of rosin monomer.

[0182] Step 5, synthesis of cinnamic acid monomer, specifically:

[0183] Dissolve 3 g of cinnamic acid in 60 mL of N,N-dimethylformamide solution, and then add 0.2 g of EDC-NHS catalyst (EDC: 0.12 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.08 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (1.2 g each time), and stir at room temperature for 24 h. After the reaction is completed, pour the obtained reaction solution into 200 mL of ice water, and dry at 60 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0184] Step 6, synthesis of rosin polymer, specifically:

[0185] Take 1.8 g of rosin monomer, 0.4 g of acrylic acid, and 0.6 g of cinnamic acid monomer respectively, dissolve them in 16 mL of turpentine, add 30 mg of azobisisobutyronitrile, stir evenly, heat to 80 °C and react for 4 h, and cool to room temperature to obtain rosin polymer. The viscosity of the rosin polymer is controlled at 10000 - 20000 cps.

[0186] Step 7, preparation of soldering flux, specifically:

[0187] Take 2 g of cinnamic acid composite nanocellulose and 1 g of rosin polymer, heat to 60 °C, and stir mechanically for 60 min. Put the obtained mixed product into a refrigerator at 10 °C for 24 h to obtain the soldering flux.

[0188] Performance testing and erasure, specifically:

[0189] The performance testing of the soldering flux is carried out according to the testing method specified in SJ / T11389-2009 "Flux for Lead-Free Soldering". The erasure method of the used soldering flux is mainly by irradiating with a 45 W ultraviolet lamp for 40 s and then manually peeling.

[0190] Example 3

[0191] Step 1, modify rosin with cinnamic acid, specifically:

[0192] Dissolve 5 g of rosin in 15 mL of dimethyl sulfoxide solution and heat it to 130 °C to obtain a rosin solution; dissolve 2 g of cinnamic acid in 15 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; dropwise add the cinnamic acid solution to the rosin solution, and the dropping time is 45 min. After the dropping is completed, heat it to 170 °C and continue to react for 5 h. After the reaction is completed, wait for it to cool to room temperature. Pour the reaction solution into 150 mL of an aqueous solution at 0 °C, stir evenly to obtain a yellow precipitate, filter the precipitate, and continue to wash the precipitate three times with a mixed solution of 100 mL of ethanol and water (v:v = 1:2) at 0 °C, and finally dry it at 55 °C to obtain cinnamic acid-modified rosin.

[0193] Step 2, prepare ammonium salt-modified nanocellulose, specifically:

[0194] Take 0.3 g of nanocellulose and add it to 150 mL of anhydrous tetrahydrofuran solution, and ultrasonically disperse it for 1.5 h. Then, add 0.15 g of sodium ethoxide and stir at room temperature for 15 min. Then add 0.15 g of 3-bromopropyltrimethylammonium bromide and heat to 70 °C to react for 6 h. After the reaction is completed, wait for the temperature to cool to room temperature, put the reaction solution into a dialysis bag with a molecular weight cut-off of 8000 Da, and dialyze it with 700 mL of ethanol three times. The obtained sample is dried overnight at 55 °C.

[0195] Step 3, prepare cinnamic acid composite nanocellulose, specifically:

[0196] Take 1.8 g of cinnamic acid-modified rosin and dissolve it in 10 mL of turpentine, add 0.5 g of sodium ethoxide, and stir at room temperature for 15 min. Add 0.15 g of ammonium salt-modified nanocellulose and stir at room temperature for 50 min. Transfer the mixed solution to an 8000 Da dialysis bag, and then put the dialysis bag into 100 mL of deionized water. During dialysis, ultrasonicate for 20 h (ultrasonic power is 45 W), and freeze-dry at -70 °C to obtain cinnamic acid composite nanocellulose.

[0197] Step 4, synthesis of rosin monomer, specifically:

[0198] Take 5 g of rosin and dissolve it in 50 mL of N,N-dimethylformamide solution, and then add 0.15 g of EDC-NHS catalyst (EDC: 0.09 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.06 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.8 g each time), stir evenly, and stir at room temperature for 16 h. After the reaction is completed, pour the obtained reaction solution into 150 mL of ice water and dry it at 55 °C to obtain a yellow precipitate of rosin monomer.

[0199] Step 5, synthesis of cinnamic acid monomer, specifically:

[0200] Dissolve 2 g of cinnamic acid in 50 mL of N,N-dimethylformamide solution, and then add 0.15 g of EDC-NHS catalyst (EDC: 0.09 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, NHS: 0.06 g of N-hydroxysuccinimide). Then, add 4-aminostyrene in three batches (0.8 g each time), and stir at room temperature for 18 h. After the reaction is completed, pour the obtained reaction solution into 150 mL of ice water, and dry at 50 °C to obtain a colorless precipitate of cinnamic acid monomer.

[0201] Step 6, synthesis of rosin polymer, specifically:

[0202] Take 1.2 g of rosin monomer, 0.3 g of acrylic acid, and 0.5 g of cinnamic acid monomer respectively, dissolve them in 12 mL of turpentine, add 18 mg of azobisisobutyronitrile, stir evenly, and then heat to 70 °C for reaction for 3 h, and cool to room temperature to obtain rosin polymer. The viscosity of the rosin polymer is controlled at 10000 - 20000 cps.

[0203] Step 7, preparation of soldering flux, specifically:

[0204] Take 1.5 g of cinnamic acid composite nanocellulose and 0.8 g of rosin polymer, heat the temperature to 55 °C, and stir mechanically for 50 min. Put the obtained mixed product into a refrigerator at 8 °C for 18 h to obtain the soldering flux.

[0205] Performance testing and erasure, specifically:

[0206] The performance testing of the soldering agent is carried out according to the testing method specified in SJ / T11389-2009 "Flux for Lead-Free Soldering". The erasure method of the used soldering agent is mainly to manually peel it off after irradiating with a 40 W ultraviolet lamp for 30 s.

[0207] The present invention constructs a composite of cinnamic acid-modified rosin and rosin polymer to prepare a soldering flux, introduces organic acid into the polymer skeleton to improve the soldering performance (reduce the surface tension and improve the wettability), and at the same time utilizes the D-A cyclization of cinnamic acid under UV irradiation, with volume shrinkage, to achieve viscosity reduction, making it easy to directly peel off and achieving a residue-free effect; the composite of ammonium salt-modified nanocellulose and cinnamic acid-modified rosin finally constructs a bromine-free soldering flux. The organic metal salt in the ammonium salt-modified nanocellulose is used to replace bromine to improve the soldering performance.

Claims

1. A method for preparing a residue-free and easily erasable electronic soldering flux, characterized in that: The specific steps include: Step 1, modifying rosin with cinnamic acid; Step 2, modifying the nanocellulose with ammonium salt; Step 3, preparing cinnamic acid composite nanocellulose according to the products obtained in step 1 and step 2; Step 4, synthesizing rosin monomer; Step 5, synthesizing cinnamic acid monomer; Step 6, synthesizing rosin polymer according to the products obtained in step 4 and step 5; Step 7, preparing soldering flux according to the products obtained in step 3 and step 6.

2. The method for preparing the residue-free and easily erasable electronic soldering flux according to claim 1, characterized in that: The specific process of step 1 is as follows: Step 1.1: dissolve 3-6 g of rosin in 10-20 mL of dimethyl sulfoxide solution and heat at 120-150° C. to obtain a rosin solution; Step 1.2, dissolving 1.5-3 g of cinnamic acid in 10-20 mL of dimethyl sulfoxide solution to obtain a cinnamic acid solution; Step 1.3, adding the cinnamic acid solution obtained in step 1.2 dropwise to the rosin solution prepared in step 1.1, the dropping time is 30-60min, heating to 150-180°C after the dropping is completed, and continuing the reaction for 3-6h. After the reaction is completed, cooling to room temperature, pouring the reaction solution into 100-200mL, 0°C water, stirring evenly to obtain a yellow precipitate, filtering the precipitate, and continuing to use 0°C, 100-200mL ethanol and water mixed solution to wash the precipitate three times, and finally drying at 45-60°C to obtain cinnamic acid modified rosin.

3. The method for preparing the residue-free and easily erasable electronic soldering flux according to claim 2, characterized in that: The specific process of step 2 is: 0.2-0.4 g of nanocellulose is added to 100-200 mL of anhydrous tetrahydrofuran solution, ultrasonically dispersed for 1-2 h, then 0.1-0.2 g of sodium ethoxide is added, stirred at room temperature for 10-20 min, and then 0.1-0.2 g of 3-bromopropyltrimethylammonium bromide is added, heated to 60-80 ° C for reaction for 4-8 h, after the reaction is completed, the temperature is cooled to room temperature, the obtained reaction solution is placed in a 7000-10000 Da dialysis bag, and dialyzed with 500-800 mL of ethanol, the dialysis is repeated three times, and the sample is dried overnight at 45-60 ° C to obtain ammonium salt-modified nanocellulose.

4. The method for preparing the residue-free and easily erasable electronic soldering flux according to claim 3, characterized in that: The specific process of step 3 is as follows: 1.2-2.4 g of cinnamic acid-modified rosin is dissolved in 8-16 mL of turpentine oil, 0.3-0.6 g of sodium ethoxide is added, and the mixture is stirred at room temperature for 10-20 min. Then, 0.1-0.2 g of ammonium salt-modified nanocellulose is added, and the mixture is stirred at room temperature for 30-60 min. The obtained mixed solution is placed in a 7000-10000 Da dialysis bag, and then the dialysis bag is placed in 50-100 mL of deionized water. Ultrasound is performed during dialysis, and the mixture is freeze-dried to obtain cinnamic acid composite nanocellulose.

5. The method for preparing the residue-free and easily erasable electronic soldering flux according to claim 4, characterized in that: The specific process of step 4 is as follows: Take 3-6g of rosin and dissolve it in 30-60mL of N,N-dimethylformamide solution, then add 0.1-0.2g of EDC-NHS catalyst, then add 4-aminostyrene in three batches, stir at room temperature for 12-24h, after the reaction is completed, pour the obtained reaction solution into 100-200mL of ice water, dry at 45-60℃, and obtain yellow precipitate rosin monomer.

6. The method for preparing the residue-free and easily erasable electronic soldering flux according to claim 5, characterized in that: The specific process of step 5 is as follows: Dissolve 1.5-3g of cinnamic acid in 30-60mL of N,N-dimethylformamide solution, then add 0.1-0.2g of EDC-NHS catalyst, then add 4-aminostyrene in three batches, and stir at room temperature for 12-24h. After the reaction is completed, pour the obtained reaction solution into 100-200mL of ice water and dry at 45-60℃ to obtain colorless precipitate cinnamic acid monomer.

7. The method for preparing the residue-free and easily erasable electronic soldering flux according to claim 6, characterized in that: The specific process of step 6 is as follows: Take 0.9-1.8g of rosin monomer, 0.2-0.4g of acrylic acid, and 0.3-0.6g of cinnamic acid monomer respectively, dissolve them in 8-16mL of turpentine oil, add 15-30mg of azobisisobutyronitrile, stir evenly, heat to 60-80℃ for reaction for 2-4h, and cool to room temperature to obtain rosin polymer.

8. The method for preparing the residue-free and easily erasable electronic soldering flux according to claim 7, characterized in that: In step 6, the viscosity of the rosin polymer is controlled at 10,000-20,000 cps.

9. The method for preparing the residue-free and easily erasable electronic soldering flux according to claim 7, characterized in that: The specific process of step 7 is as follows: Take 1-2g of cinnamic acid composite nanocellulose and 0.5-1g of rosin polymer, heat to 45-60°C, stir for 30-60min, put the obtained mixed product in a refrigerator at 5-10°C for 12-24h to obtain the flux.

10. A residue-free, easily erasable electronic soldering flux, prepared by the method for preparing a residue-free, easily erasable electronic soldering flux as claimed in any one of claims 1 to 9.

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