Organic solderability preservative and preparation method of organic solderability preservative for forming protective film on copper surface

Abstract

The invention provides an organic solderability preservative and a preparation method for forming a protective film on the surface of copper, the organic solderability preservative comprises the following components in parts by weight: 3.0-4.5 parts of 2-(3, 4-dichlorobenzyl) benzimidazole, 52.5 parts of acetic acid, 0.75 part of n-heptanoic acid, 0.25-0.5 part of zinc acetate, 0.25-0.5 part of copper sulfate, 0.2 part of citric acid modified nano cerium oxide, and the balance of deionized water and a pH regulator; the preparation method for forming the protective film on the copper surface comprises the following steps: oil removal treatment: treating a circuit board in a sodium hydroxide solution; pickling treatment: treating in a sulfuric acid solution; micro-etching treatment: treating in a solution of sodium persulfate and sulfuric acid; pickling treatment: treating in a sulfuric acid solution; film forming treatment: dipping in an organic solderability preservative at 45 DEG C;

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board surface treatment, in particular to an organic solder preservative and a preparation method thereof for forming a protective film on a copper surface. Background Art

[0002] As electronic devices evolve towards lighter weight and higher density, the requirements for printed circuit board (PCB) surface treatment technologies are becoming increasingly stringent. Common surface treatment technologies include lead-free hot air leveling, chemical immersion silver, chemical immersion tin, and organic solder preservative (OSP). Although lead-free hot air leveling processes have improved environmental performance, they can still suffer from poor surface flatness, hindering high-density assembly. Chemical immersion tin technology offers a strong affinity for molten solder, providing excellent wettability during soldering and reducing issues such as cold solder joints and voids. However, the tin layer can spontaneously grow micron-sized whiskers in humid, hot, or stressful environments, creating a risk of short circuits, which is particularly critical for high-density electronic devices. Chemical immersion silver technology, leveraging the excellent conductivity and signal transmission properties of the silver plating layer, significantly reduces contact resistance, making it suitable for high-frequency circuits. However, silver is a precious metal, and the raw material cost is significantly higher than other processes.

[0003] Organic solder preservative (OSP) has played an important role in the field of PCB surface treatment in recent years due to its advantages such as simple process, low cost and little environmental pollution.

[0004] OSP is a chemical process that grows an organic film on a clean, bare copper surface. This film is resistant to oxidation, heat shock, and moisture, protecting the copper surface from further rust (oxidation or sulfide) in normal environments. However, during subsequent high soldering temperatures, this protective film must be easily removed by flux, allowing the exposed, clean copper surface to bond with the molten solder in a very short time, forming a strong solder joint.

[0005] The heat resistance of the current OSP process has been significantly improved through multiple generations of technology iteration, but challenges still exist. The decomposition temperature of traditional OSP film is approximately 250°C, and it can only withstand one or two reflow soldering cycles. If used for multiple soldering cycles (such as double-sided soldering or rework), the protective film will decompose after the first high-temperature soldering, causing oxidation on the copper surface and affecting the reliability of subsequent soldering.

[0006] Since the implementation of the EU's Restriction of Hazardous Substances in Electrical and Electronic Equipment (RoHS) and Waste Electrical and Electronic Equipment (WEEE) directives on July 1, 2006, the global electronics manufacturing industry has fully entered the lead-free era. In lead-free soldering processes, to meet stringent environmental regulations for solder alloys, traditional lead-containing solders have been banned. The melting point of lead-free solders (such as SAC305) has been significantly increased, forcing peak reflow soldering temperatures to generally exceed 260°C and requiring multiple high-temperature soldering cycles. This transformation poses significant challenges to printed circuit board (PCB) surface treatment processes. Conventional organic solderability preservatives (OSP) are susceptible to decomposition and failure under repeated high-temperature thermal shock, leading to copper surface oxidation and reduced solderability. Therefore, the development of new OSP organic solderability preservatives that combine high-temperature resistance, long-lasting antioxidant properties, environmental friendliness, and cost-effectiveness has become a key technological breakthrough for achieving high-reliability electronics manufacturing. Summary of the Invention

[0007] The present invention provides an organic solder preservative and a preparation method thereof for forming a protective film on a copper surface, in order to solve the problems raised in the above background technology.

[0008] To solve the above technical problems, the present invention discloses an organic solder preservative, comprising the following components: 2-(3,4-dichlorobenzyl)benzimidazole, acetic acid, n-heptanoic acid, zinc acetate, copper sulfate, citric acid-modified nano-cerium oxide, and the balance being deionized water and a pH regulator.

[0009] Furthermore, the organic solder paste comprises the following components, calculated by weight: 3.0-4.5 parts of 2-(3,4-dichlorobenzyl)benzimidazole, 52.5 parts of acetic acid, 0.75 parts of n-heptanoic acid, 0.25-0.5 parts of zinc acetate, 0.25-0.5 parts of copper sulfate, 0.2 parts of citric acid-modified nano-cerium oxide, and the balance is deionized water and a pH regulator. The pH value of the organic solder paste is 3.0±0.2.

[0010] Furthermore, the pH regulator is aqueous ammonia, and the mass ratio of the 2-(3,4-dichlorobenzyl)benzimidazole to acetic acid is 1:8-1:12.

[0011] Furthermore, the preparation method includes the following steps: mixing 2-(3,4-dichlorobenzyl)benzimidazole and acetic acid and stirring for 30 minutes; adding n-heptanoic acid, citric acid-modified nanocerium oxide, zinc acetate and copper sulfate in sequence; adding deionized water to a total liquid volume of 250 mL; adding ammonia water to adjust the pH to 3.0±0.2; heating to a constant temperature of 45±2°C and storing.

[0012] A preparation method for forming a protective film on the copper surface is characterized by being processed with the above-mentioned organic solder preservative.

[0013] Furthermore, the preparation method of the copper surface protective film comprises the following steps:

[0014] a. Degreasing treatment: The circuit board is treated in a 3-10wt% sodium hydroxide solution at 30°C for 2-5 minutes;

[0015] b. Pickling treatment: in 3-10wt% sulfuric acid solution at 30°C for 2-5 minutes;

[0016] c. Microetching: in a solution containing 10-20wt% sodium persulfate and 3-10vol% sulfuric acid at 30°C for 1-5 minutes;

[0017] d. Pickling treatment: treatment in 1-5 vol% sulfuric acid solution for 1-5 minutes;

[0018] e. Film forming treatment: immersing in the organic solderability agent according to any one of claims 1 to 4 at 45°C for 1 to 5 minutes to obtain an organic copper coordination polymer film.

[0019] Furthermore, the concentration ratio of sodium persulfate to sulfuric acid in the micro-etching treatment is 3:1-5:1, and the micro-etching thickness is controlled at 1.0-1.5 μm; the immersion time in the film-forming treatment is 90±30 seconds, and the thickness of the formed film layer is 0.25-0.35 μm. The copper surface roughness Ra after the micro-etching treatment is ≤0.15 μm, and the contact angle is ≤80°.

[0020] Furthermore, the molar ratio of copper to zinc in the organic copper coordination polymer film layer is 3:1-5:1, and the sulfur content is ≤0.5wt%.

[0021] Furthermore, after the organic copper coordination polymer film is subjected to three thermal cycle treatments at 288° C., the copper surface oxidation discoloration level is ≤ level I, and the solder joint shear strength is ≥12 MPa.

[0022] Compared with the prior art, the present invention provides an organic solder preservative and a method for preparing the same to form a protective film on the copper surface, which has the following beneficial effects:

[0023] 1. The present invention selects imidazole compounds as the main film-forming substances of the organic solderability protective agent, which significantly improves the heat resistance of the organic solderability protective film layer of the printed circuit board formed subsequently. It can still remain stable after multiple reflow soldering processes, and can meet the high temperature conditions required for lead-free soldering, thereby reducing pollution to the environment and meeting the needs of the PCB surface treatment production process. In addition, the OSP solution used is very stable and can form an effective film layer on the PCB surface to prevent copper from being oxidized and maintain good solderability under lead-free reflow temperature soldering conditions. Among them, the organic acid can promote the solubility of the imidazole organic matter and the aqueous solution, promote the formation of the subsequent coordination protective film, and help maintain the long-term stability of the OSP treatment solution; while the long-chain acid promotes the formation of the OSP film.

[0024] 2. 2-(3,4-dichlorobenzyl)benzimidazole is used as an imidazole compound. The imidazole compound contains a chlorophenyl group, which greatly improves the heat resistance of the OSP treatment solution. A preparation method for forming a protective film on the bare copper surface to be soldered on a printed circuit board is provided. The method is characterized in that the film layer formed by the process has a thin and dense structural characteristic with uniform thickness, and has excellent multiple solderability, oxidation resistance and heat resistance. In addition, the present invention uses a sulfuric acid / sodium persulfate system micro-etching solution for micro-etching, and the micro-etching rate is stable and controllable, with a micro-etching thickness of 1.0-1.5 μm. This solves the problem that the use of a sulfuric acid / hydrogen peroxide system micro-etching solution is very sensitive to chloride ion concentration. When the chloride ion reaches 10 mg / L, the micro-etching rate of the micro-etching system will remain unchanged at a very low value, and the micro-etching rate and micro-etching thickness are difficult to control.

[0025] 3. The oxygen vacancies of nano CeO2 involved in this application capture the active oxygen free radicals generated by the copper surface, thereby inhibiting the high-temperature oxidation of the copper surface. The carboxyl group (-COOH) of citric acid forms a hydrogen bond with the nitrogen atom of benzimidazole, thereby enhancing the cross-linking density of the film layer. 4+ Oxidation of trace Cu + →Cu 2+ , maintain the stability of the copper ion valence and avoid the formation of sulfide (Cu2S). The uniformly dispersed nanoparticles fill the defects of the zinc-copper coordination network through physical filling, improving the uniformity of film thickness and film density, reducing the risk of high-temperature exposure and oxidation of the copper surface, and ensuring direct bonding between copper and solder during welding. 4+ Cu +The oxidation process is inhibited from the source, and the generation of sulfides is inhibited, avoiding the embrittlement of the solder joint; more importantly, the dense and uniform film layer effectively protects the underlying copper substrate, and the surface roughness and hydrophilicity formed by micro-etching are maintained stable during the storage or pre-welding stage, providing an ideal / controlled interface state for welding. The citric acid modified nanometer cerium oxide solves the oxidation failure problem of traditional OSP film in lead-free high-temperature welding through the triple mechanism of physical filling, chemical bonding and redox control, and significantly improves the heat resistance, oxidation resistance and solder joint reliability of the film layer. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A process flow chart of a preparation method of a protective film formed on a copper surface according to an embodiment of the present application;

[0027] Figure 2 A contact angle test result graph of a sample after an organic solderability preservative process and a sample before the process;

[0028] Figure 3 A discoloration of a plate surface after heat treatment, the left side is a film layer formed by Comparative Example 1, and the right side is a film layer formed by Embodiment 1 of the present application. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present application are described below, and it should be understood that the preferred embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0030] In addition, the description such as "first", "second" and the like in the present application is only for the purpose of description, and does not mean to specially indicate the order or sequence, nor to limit the present application, which is only to distinguish the components or operations described by the same technical terms, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions and technical features of various embodiments can be combined with each other, but it must be based on the realization of ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the protection scope required by the present application.

[0031] Unless otherwise specified, the examples and comparative examples are parallel tests with the same components, component contents, preparation steps and preparation parameters. The experimental methods in the following examples are conventional methods unless otherwise specified. The test materials used in the following examples are analytical reagents (A.R.) unless otherwise specified, and are purchased from commercial channels.

[0032] Example 1: The organic solderability preservative comprises, by weight, 4.5 parts of 2-(3,4-dichlorobenzyl)benzimidazole, 52.5 parts of acetic acid, 0.75 parts of n-heptanoic acid, 0.25 parts of zinc acetate, 0.5 parts of copper sulfate, deionized water and ammonia water. The pH value of the organic solderability preservative is 3.

[0033] Example 2: The organic solderability preservative comprises, by weight, 3.0 parts of 2-(3,4-dichlorobenzyl)benzimidazole, 52.5 parts of acetic acid, 0.75 parts of n-heptanoic acid, 0.25 parts of zinc acetate, 0.5 parts of copper sulfate, deionized water and ammonia water. The pH value of the organic solderability preservative is 3.

[0034] Example 3: The organic solderability preservative comprises, by weight, 4.5 parts of 2-(3,4-dichlorobenzyl)benzimidazole, 52.5 parts of acetic acid, 0.75 parts of n-heptanoic acid, 0.5 parts of zinc acetate, 0.25 parts of copper sulfate, deionized water and ammonia water, and the pH value of the organic solderability preservative is 3.

[0035] Example 4: The organic solderability preservative comprises, by weight, 3.0 parts of 2-(3,4-dichlorobenzyl)benzimidazole, 52.5 parts of acetic acid, 0.75 parts of n-heptanoic acid, 0.5 parts of zinc acetate, 0.25 parts of copper sulfate, deionized water and ammonia water, and the pH value of the organic solderability preservative is 3.

[0036] In the above embodiment, the organic solderability preservative further comprises 0.2 parts by weight of citric acid-modified nano-cerium oxide. The preparation method of the citric acid-modified nano-cerium oxide comprises the following steps: dissolving 1 part by weight of ceric ammonium nitrate in 80 parts of 80°C deionized water, adding 4.2 parts of 28% aqueous ammonia dropwise at a rate of 2 mL / min under nitrogen protection, and reacting at 80°C for 45 minutes to produce a cerium hydroxide precipitate. After centrifugal acid and alcohol washing, the precipitate is dispersed in 130 parts of water, 0.15 parts of citric acid is added, and the surface modification is completed by stirring at 500 rpm in an autoclave at 160°C and 0.6 MPa for 3 hours (pH = 4.8 ± 0.05). Subsequently, a nanosuspension is obtained by ultra-high-speed dispersion (10,000 rpm → 25,000 rpm). Finally, a powdered additive is obtained by spray drying at 190°C and vacuum activation at 60°C. The particle size D90 is 30 nm and the citric acid grafting efficiency is 95%.

[0037] In the above embodiment, the organic solderability preservative is prepared by weighing 2-(3,4-dichlorobenzyl)benzimidazole and placing it in a beaker. Then, acetic acid and benzimidazole are weighed, mixed, stirred, and dissolved for half an hour. Then, n-heptanoic acid and citric acid-modified nano-cerium oxide are added. Finally, zinc acetate and copper sulfate are added to the beaker in sequence. Deionized water is added to 250 mL, and the mixture is stirred and dissolved for another half an hour. Then, ammonia water is added to adjust the pH to 3, and the mixture is stirred and dissolved for another half an hour. The mixture is heated to 45° C. and kept constant for use.

[0038] Comparative Example 1: ENTEK 106A from ENTEK Corporation of the United States, comprising an alkylbenzimidazole compound, an organic acid, a metal compound, a long-chain acid, deionized water, and ammonia water. The pH value of the organic solderability preservative is 3.7.

[0039] Comparative Example 2

[0040] The difference from Example 1 is the lack of zinc acetate of equal mass, and the other contents are consistent with Example 1.

[0041] Comparative Example 3

[0042] The difference from Example 1 is the lack of copper sulfate of equal mass, and other contents are consistent with Example 1.

[0043] Performance tests were performed on Examples 1-4 and the comparative example.

[0044] 1. Film thickness test

[0045] The coated copper plate was placed in a 250 mL beaker, 50 mL of 5% hydrochloric acid was added and stirred for 3 min to dissolve the film layer completely to obtain the test solution. The 5% hydrochloric acid was used as the reference solution, and the absorbance value A of the test solution at a wavelength of 289.5 nm was tested using a UV-visible spectrophotometer. The film thickness was calculated as: h = C × A, where C is the film thickness coefficient. The thickness test results are shown in Table 1.

[0046] Table 1 Copper mask layer thickness

[0047] Example Film thickness / μm Example 1 0.334 Example 2 0.265 Example 3 0.287 Example 4 0.243 Comparative Example 1 0.351 Comparative Example 2 0.215 Comparative Example 3 0.198

[0048] 2. Heat resistance test

[0049] After baking the test pieces at different temperatures and for different times, visually observe the color changes of the test pieces. The test method is as follows:

[0050] The test plate was baked at a constant temperature of 150°C for 15 min, which was recorded as treatment A;

[0051] The test plate was baked at a constant temperature of 260°C for 5 min, which was recorded as treatment B;

[0052] The test plate was baked at a constant temperature of 288°C for 10 seconds, placed at room temperature for 10 seconds, and baked for 30 seconds three times in a row. This was recorded as treatment C. The test results are shown in Table 2. Table 3 describes the oxidation discoloration level of the copper plate.

[0053] Table 2 Oxidation discoloration of coated copper plate after heat treatment

[0054]

[0055]

[0056] Table 3 Copper plate oxidation discoloration grade description

[0057] grade Copper plate oxidation discoloration grade description Level I Almost no discoloration Level II Slight discoloration Level III The color becomes darker or uneven color appears Level IV The color becomes seriously darker and purple appears in some parts V-level The whole piece is purple and oxidized very seriously

[0058] As can be seen from the data in Table 2, after the copper surface of the coated copper plate treated by the organic solderability preservative example 1 of the present application is tested by different heat treatment, the copper surface is almost not discolored, while the copper surface of the coated copper plate of the comparative example 1 is partially oxidized after baking treatment.

[0059] Example 5

[0060] As Figure 1 shown, the preparation method of the protective film on the copper surface provided by the example of the present application comprises the following steps:

[0061] a. Oil removal: the circuit board is placed in the alkaline oil removal liquid for 2-5 min for soaking to remove the oil on the surface of the circuit board, and then water washing is performed.

[0062] b. Pickling: the circuit board after oil removal is placed in the pickling liquid for 2-5 min for soaking to perform pickling, and then water washing is performed.

[0063] c. Micro-etching: the circuit board after pickling is placed in the micro-etching liquid for 1-5 min for soaking to perform micro-etching to remove the oxides on the copper surface, and then water washing is performed.

[0064] d. Acid immersion: the circuit board after micro-etching is placed in the acid immersion liquid for 1-5 min for soaking to remove the residual substances of the micro-etching liquid, and then water washing is performed.

[0065] e. Film forming: the circuit board is placed in the organic solderability preservative prepared by example 1 for 1-5 min for soaking to perform film forming operation, and after film forming, the organic solderability preservative layer of the PCB board is obtained.

[0066] The preparation method of the protective film on the copper surface provided by the above example has the structural characteristics of thin and dense, uniform thickness, and also has excellent multiple solderability, oxidation resistance and heat resistance. In addition, the present application uses the sulfuric acid / sodium persulfate system micro-etching liquid for micro-etching treatment, and the micro-etching rate is stable and controllable, and the micro-etching thickness is 1.0-1.5 μm. The problem that the micro-etching rate of the sulfuric acid / hydrogen peroxide system micro-etching liquid is very sensitive to the concentration of chloride ions, and when the chloride ion reaches 10 mg / L, the micro-etching rate of the micro-etching system remains at a very low value, and the micro-etching rate and micro-etching thickness are not easy to control is solved.

[0067] In the above example, deionized water is preferably used for water washing.

[0068] Optionally, the thickness of the organic copper coordination polymer film is 0.25 μm-0.35 μm.

[0069] Optionally, the alkaline degreasing solution comprises sodium hydroxide and deionized water, wherein the mass percentage concentration of sodium hydroxide is 3%-10%.

[0070] For example, prepare 250 ml of an alkaline degreasing solution using 5% sodium hydroxide by mass. Heat the solution to 30°C and maintain the temperature until ready for use. The present invention does not limit the composition of the alkaline degreasing solution. In addition to the above-described embodiments, the composition of the alkaline degreasing solution used in the present invention is not limited thereto.

[0071] Optionally, the pickling solution includes sulfuric acid and deionized water, wherein the mass percentage concentration of the sulfuric acid is 3%-10%.

[0072] For example, prepare 250 ml of pickling solution using 5% sulfuric acid by mass. Heat to 30°C and keep constant for use. The present invention does not limit the composition of the pickling solution. In addition to the above-mentioned embodiment, the composition of the pickling solution used in the present invention is not limited thereto.

[0073] Optionally, the micro-etching solution comprises sodium persulfate, sulfuric acid and deionized water, wherein the mass percentage concentration of sodium persulfate is 10%-20%, and the volume percentage concentration of sulfuric acid is 3%-10%.

[0074] For example, sodium persulfate, sulfuric acid, and deionized water are weighed and mixed in a certain ratio, wherein the mass percentage concentration of sodium persulfate is 10%-15% and the volume percentage concentration of sulfuric acid is 2-5%. The mixture is heated to 30°C and kept constant for use. The present invention does not limit the composition of the micro-etching solution. In addition to the above-mentioned embodiment, the composition of the micro-etching solution used in the present invention is not limited thereto.

[0075] Optionally, the pickling solution includes sulfuric acid and deionized water, wherein the volume percentage concentration of the sulfuric acid is 1%-5%.

[0076] For example, 250 ml of pickling solution is prepared with 2% sulfuric acid by volume. The present invention does not limit the composition of the pickling solution. In addition to the above embodiment, the composition of the pickling solution used in the present invention is not limited thereto.

[0077] Optionally, the degreasing treatment is performed at a temperature of 20°C to 40°C and for a time of 1 to 5 minutes;

[0078] and / or the pickling treatment is performed at a temperature of 20°C to 40°C and for a time of 1 to 5 minutes;

[0079] and / or the micro-etching treatment has a treatment temperature of 20° C.-40° C. and a treatment time of 1-5 min;

[0080] and / or the pickling treatment temperature is 20°C-40°C, and the treatment time is 1-5 minutes;

[0081] And / or the treatment temperature of the OSP treatment is 30° C.-50° C., and the treatment time is 1-5 min.

[0082] In the above embodiment, the processing time of the alkaline degreasing treatment is preferably 5 minutes, the processing time of the pickling treatment is preferably 5 minutes, the processing time of the micro-etching treatment is preferably 1.5 minutes, the processing time of the pickling treatment is preferably 1 minute, and the processing time of the OSP treatment is preferably 1.5 minutes.

[0083] Comparative Example 5.1

[0084] The difference from Example 5 is that only step e (film formation) is performed, and the pre-treatment steps ad (direct film formation on the untreated copper / gold substrate) are skipped, and the rest are the same.

[0085] Comparative Example 5.2

[0086] The difference from Example 5 is that the method with application number CN202410131547.9 is used, and the circuit board is immersed in the organic solderability preservative prepared in Example 1 during film formation.

[0087] Comparative Example 5.3

[0088] The difference from Example 5 is that the circuit board is immersed in the high-temperature resistant organic solder preservative with application number CN202410131547.9, and the rest is the same.

[0089] A selectivity test was conducted using the preparation method of Example 5 to prepare a test board. The copper / gold film thickness ratio was measured. Referring to IPC J-STD-003, a copper coupon was immersed in molten SAC305 solder at 255°C and the zero-crossing time (T0) was recorded. The copper coupon was then reflow-soldered with a 0.3 mm diameter BGA solder ball in a nitrogen environment (O2 ≤ 500 ppm) (peak temperature 250 ± 5°C, TAL = 60 ± 5 s). A shear force test was performed at a rate of 200 μm / s according to IPC / JEDEC J-STD-002. The results are shown in Table 4.

[0090] Table 4

[0091]

[0092] Figure 2 The contact angle test results of the sample after being treated with organic solderability protective agent and the sample before treatment are shown in the figure. Figure 2It can be seen that the contact angle of the copper surface before OSP treatment is 69.0°, and the contact angle of the copper surface after OSP treatment is 103.2°, the contact angle of the copper surface has changed, and it is speculated that a layer of organic film is formed on the copper surface after OSP treatment. The film layer thickness of the organic copper coordination polymer film prepared in the embodiment of the present application is uniform, and the film forming effect is good.

[0093] Figure 3 After the test plate is baked at a constant temperature of 288℃ for 10s, placed at room temperature for 10s, and baked for 30s continuously for three times, the discoloration of the plate surface is observed, Figure 3 The left side is the film layer formed by Comparative Example 1, and the film layer after high temperature test appears oxidation discoloration; the right side is the film layer formed by the embodiment 1 of the present application, and there is almost no discoloration.

[0094] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. If these modifications and variations of the present application belong to the scope of the claims of the present application and their equivalents, the present application also intends to include these modifications and variations.

Claims

1. An organic solder paste, characterized in that The invention comprises the following components: 2-(3,4-dichlorobenzyl)benzimidazole, acetic acid, n-heptanoic acid, zinc acetate, copper sulfate, citric acid-modified nano-cerium oxide, and the balance is deionized water and a pH regulator.

2. The organic solder paste according to claim 1, characterized in that The organic solder preservative comprises the following components in parts by weight: 3.0-4.5 parts of 2-(3,4-dichlorobenzyl)benzimidazole, 52.5 parts of acetic acid, 0.75 parts of n-heptanoic acid, 0.25-0.5 parts of zinc acetate, 0.25-0.5 parts of copper sulfate, 0.2 parts of citric acid-modified nano-cerium oxide, and the balance is deionized water and a pH regulator. The pH value of the organic solder preservative is 3.0±0.

2.

3. The organic solderability preservative according to claim 1, characterized in that The pH regulator is aqueous ammonia, and the mass ratio of the 2-(3,4-dichlorobenzyl)benzimidazole to acetic acid is 1:8-1:

12.

4. The organic solderability preservative according to claim 1, wherein The preparation method comprises the following steps: mixing 2-(3,4-dichlorobenzyl)benzimidazole and acetic acid and stirring for 30 minutes; sequentially adding n-heptanoic acid, citric acid-modified nano-cerium oxide, zinc acetate and copper sulfate; adding deionized water to a total liquid volume of 250 mL; adding ammonia water to adjust the pH to 3.0±0.2; and heating to a constant temperature of 45±2°C for storage.

5. A method for preparing a protective film formed on a copper surface, characterized in that The solder paste is processed by using the organic solder preservative according to any one of claims 1 to 4.

6. The method for forming a protective film on a copper surface according to claim 5, wherein: The following steps are involved: a. Degreasing treatment: The circuit board is treated in a 3-10wt% sodium hydroxide solution at 30°C for 2-5 minutes; b. Pickling treatment: in 3-10wt% sulfuric acid solution at 30°C for 2-5 minutes; c. Microetching: in a solution containing 10-20wt% sodium persulfate and 3-10vol% sulfuric acid at 30°C for 1-5 minutes; d. Pickling treatment: treatment in 1-5 vol% sulfuric acid solution for 1-5 minutes; e. Film forming treatment: immersing in the organic solderability agent according to any one of claims 1 to 4 at 45°C for 1 to 5 minutes to obtain an organic copper coordination polymer film.

7. The preparation method according to claim 6, characterized in that The concentration ratio of sodium persulfate to sulfuric acid in the micro-etching treatment is 3:1-5:1, and the micro-etching thickness is controlled at 1.0-1.5 μm. The immersion time in the film-forming treatment is 90±30 seconds, and the thickness of the formed film layer is 0.25-0.35 μm. The copper surface roughness Ra after the micro-etching treatment is ≤0.15 μm, and the contact angle is ≤80°.

8. The preparation method according to claim 6, characterized in that The molar ratio of copper to zinc in the organic copper coordination polymer film layer is 3:1-5:1, and the sulfur content is ≤0.5 wt%.

9. The preparation method according to claim 6, characterized in that After the organic copper coordination polymer film is subjected to three thermal cycle treatments at 288° C., the copper surface oxidation discoloration level is ≤ level I, and the solder joint shear strength is ≥12 MPa.

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