Chemical silver plating method for printed circuit board

文档序号：1942269 发布日期：2021-12-07 浏览：23次中文

阅读说明：本技术 印刷电路板化学镀银方法 (Chemical silver plating method for printed circuit board ) 是由邱美琴吴旭明蔡良胜曾剑珍田雪峰于 2021-09-29 设计创作，主要内容包括：本发明公开一种印刷电路板化学镀银方法,包括以下步骤：S10,对印刷电路板的铜层表面进行除油处理,清水洗净；S20,对经步骤S10处理后的铜层表面进行微蚀,清水洗净；S30,将经步骤S20处理后的印刷电路板先在25-35℃下于预浸液中进行预浸后,再浸入化学镀银液中,于45-55℃下进行沉银处理,清水洗净；其中,所述化学镀银液包括以下浓度的组分：0.2～5.0g/L银离子、1.0～100g/L络合剂、0.1～10g/L铜离子、0.01～100g/L表面活性剂以及0.01～10g/L铜防氧化剂。本发明通过添加表面活性剂,有效促进了溶液的交换,缓解了银下铜层空洞现象,能够控制银沉积效率；使用特定配方的化学镀银液在45～55℃下进行沉银处理,使得沉积速率控制在0.10～0.15μm/min,避免了因置换反应速率过快而形成过多的银下铜层空洞。(The invention discloses a chemical silver plating method for a printed circuit board, which comprises the following steps: s10, degreasing the copper layer surface of the printed circuit board, and cleaning with clean water; s20, microetching the surface of the copper layer processed in the step S10, and cleaning the copper layer with clear water; s30, pre-dipping the printed circuit board processed in the step S20 in a pre-dipping solution at 25-35 ℃, then dipping the printed circuit board in a chemical silver plating solution, performing silver precipitation treatment at 45-55 ℃, and cleaning with clear water; wherein the chemical silver plating solution comprises the following components in concentration: 0.2 to 5.0g/L silver ion, 1.0 to 100g/L complexing agent, 0.1 to 10g/L copper ion, 0.01 to 100g/L surfactant and 0.01 to 10g/L copper antioxidant. According to the invention, by adding the surfactant, the exchange of the solution is effectively promoted, the void phenomenon of the copper layer under the silver is relieved, and the silver deposition efficiency can be controlled; the chemical silver plating solution with a specific formula is used for carrying out silver deposition treatment at the temperature of 45-55 ℃, so that the deposition rate is controlled to be 0.10-0.15 mu m/min, and excessive copper layer cavities under silver caused by too high displacement reaction rate are avoided.)

1. A printed circuit board chemical silver plating method is characterized by comprising the following steps:

s10, degreasing the copper layer surface of the printed circuit board, and cleaning with clean water;

s20, microetching the surface of the copper layer processed in the step S10, and cleaning the copper layer with clear water;

s30, pre-dipping the printed circuit board processed in the step S20 in a pre-dipping solution at 25-35 ℃, then dipping the printed circuit board in a chemical silver plating solution, performing silver precipitation at 45-55 ℃, and cleaning with clear water;

wherein the chemical silver plating solution comprises the following components in concentration: 0.2-5.0 g/L silver ion, 1.0-100 g/L complexing agent, 0.1-10 g/L copper ion, 0.01-100 g/L surfactant and 0.01-10 g/L copper antioxidant.

2. The electroless silver plating method for printed circuit boards according to claim 1, wherein the silver ions are provided by silver ion sources, and the silver ion sources comprise one or more of elemental silver, silver nitrate, silver methylsulfonate and silver acetate; and/or the presence of a gas in the gas,

the copper ions are provided by a copper ion source, and the copper ion source comprises one or more of copper simple substance, copper nitrate, copper methylsulfonate and copper acetate; and/or the presence of a gas in the gas,

the complexing agent comprises one or more of complexing agent containing EDTA functional group, nitrilotriacetic acid salt and triethanolamine; and/or the presence of a gas in the gas,

the surfactant comprises a low-foaming nonionic surfactant free of sulfur, phosphorus and halogen elements; and/or the presence of a gas in the gas,

the copper antioxidant comprises one or more of benzimidazole, methylbenzimidazole, sodium mercaptobenzothiazole and hydrogen bond substituted imidazole.

3. The electroless silver plating process for printed circuit boards according to claim 2, wherein the surfactant comprises at least one of polyoxyethylene ether of isomeric deca-alcohols, fatty acid methyl esters and block polyethers.

4. The electroless silver plating method for printed circuit boards according to claim 1, wherein in step S10, the degreasing treatment is performed using an alkaline degreasing agent, wherein the alkaline degreasing agent has a pH of 11 to 13.

5. The electroless silver plating method for printed circuit board according to claim 4, wherein said alkaline degreasing agent comprises an organic base and/or an inorganic base; and/or the presence of a gas in the gas,

the temperature of the oil removing treatment is 0-50 ℃, and the treatment time is 0.1-10 min.

6. The chemical silver plating method for printed circuit board according to claim 5, wherein the alkaline degreaser comprises an organic base, the organic base comprises one or more of monoethanolamine, diethanolamine, triethanolamine and organic amine hydroxide, and the concentration of the organic base in the alkaline degreaser is 0.01-10 mol/L; and/or the presence of a gas in the gas,

the alkaline degreasing agent comprises inorganic base, the inorganic base comprises one or more of ammonia water, sodium hydroxide, potassium hydroxide and sodium carbonate, and the concentration of the inorganic base in the alkaline degreasing agent is 0.01-10 mol/L; and/or the presence of a gas in the gas,

the alkaline oil removing agent also comprises an imidazole derivative, and the concentration of the imidazole derivative in the alkaline oil removing agent is 0.01-100 g/L; and/or the presence of a gas in the gas,

the alkaline oil removing agent also comprises a surfactant, and the concentration of the surfactant in the alkaline oil removing agent is 0.01-100 g/L.

7. The electroless silver plating process for printed circuit boards according to claim 5, wherein said surfactant comprises one or more of sodium alkyl sulfonate type surfactant, NP type surfactant and OP type surfactant.

8. The electroless silver plating method for printed circuit boards according to claim 1, wherein in step S20, microetching is performed using a microetching agent so that the roughness of the surface of the copper layer is less than 0.2 μm.

9. The chemical silver plating method for the printed circuit board according to claim 8, wherein the microetching agent comprises a main component, a corrosion inhibitor and a leveling agent, the main component comprises at least one of hydrogen peroxide, inorganic acid and organic acid, the concentration of the leveling agent is 0.01-100 g/L, and the concentration of the corrosion inhibitor is 0.01-100 g/L; and/or the presence of a gas in the gas,

the microetching temperature is 0-40 ℃, and the processing time is 0.1-10 min.

10. The chemical silver plating method for the printed circuit board according to claim 9, wherein the main component comprises hydrogen peroxide, and the concentration of the hydrogen peroxide in the microetching agent is 0.2-2 mol/L; and/or the presence of a gas in the gas,

the main component comprises the inorganic acid, the concentration of the inorganic acid in the microetching agent is not more than 10mol/L, and the inorganic acid comprises one or more of sulfuric acid, phosphoric acid, sulfamic acid, nitric acid and hydrochloric acid; and/or the presence of a gas in the gas,

the main component comprises the organic acid, the concentration of the organic acid in the microetching agent is not more than 10mol/L, and the organic acid comprises one or more of methanesulfonic acid, formic acid and acetic acid; and/or the presence of a gas in the gas,

the corrosion inhibitor comprises one or more of urotropin, sodium glutamate and sodium glycinate; and/or the presence of a gas in the gas,

the leveler includes alkyl glycols.

Technical Field

The invention relates to the technical field of printed circuit board preparation, in particular to a chemical silver plating method for a printed circuit board.

Background

In a Printed Circuit Board (PCB) manufacturing process, silver is plated on a copper surface to improve the conductivity and solderability of the copper surface. The silver plating layer is formed by depositing chemical silver plating solution on the surface of copper. The acid chemical silver process is widely used for surface coating of PCBs (printed circuit boards), particularly in manufacturing of communication PCBs (printed circuit boards), due to the advantages of high plating speed, stable bath solution, high purity of the obtained silver layer, uniform thickness, excellent conductivity and signal conductivity and the like.

In the using process, the industry finds that some chemical silver PCB boards produced in a normal process are easy to have a soldering tin failure phenomenon during assembly, and the soldering tin failure phenomenon is caused by tiny holes of a lower silver copper layer during chemical silver plating through analysis and inspection. The copper layer under silver has too many holes, which can cause the micro-holes in the subsequent welding spots to be too dense, and finally causes the reliability problems of vibration failure, temperature change fatigue failure and the like of the welding spots.

Disclosure of Invention

The invention mainly aims to provide a chemical silver plating method for a printed circuit board, which aims to solve the problem that the number of holes of a lower copper layer of silver is large in the traditional acid chemical silver process.

In order to achieve the above object, the present invention provides a chemical silver plating method for a printed circuit board, comprising the steps of:

s10, degreasing the copper layer surface of the printed circuit board, and cleaning with clean water;

s20, microetching the surface of the copper layer processed in the step S10, and cleaning the copper layer with clear water;

Optionally, the silver ions are provided by a silver ion source comprising one or more of elemental silver, silver nitrate, silver methylsulfonate, and silver acetate; and/or the presence of a gas in the gas,

the complexing agent comprises one or more of complexing agent containing EDTA functional group, nitrilotriacetic acid salt and triethanolamine; and/or the presence of a gas in the gas,

the surfactant comprises a low-foaming nonionic surfactant free of sulfur, phosphorus and halogen elements; and/or the presence of a gas in the gas,

the copper antioxidant comprises one or more of benzimidazole, methylbenzimidazole, sodium mercaptobenzothiazole and hydrogen bond substituted imidazole.

Optionally, the surfactant comprises at least one of polyoxyethylene ether of isomeric deca-alcohol, fatty acid methyl ester and block polyether.

Optionally, in step S10, an alkaline degreasing agent is used for degreasing, wherein the pH of the alkaline degreasing agent is 11-13.

Optionally, the alkaline degreasing agent comprises an organic base and/or an inorganic base; and/or the presence of a gas in the gas,

the temperature of the oil removing treatment is 0-50 ℃, and the treatment time is 0.1-10 min.

Optionally, the alkaline degreasing agent comprises an organic base, the organic base comprises one or more of monoethanolamine, diethanolamine, triethanolamine and organic amine hydroxide, and the concentration of the organic base in the alkaline degreasing agent is 0.01-10 mol/L; and/or the presence of a gas in the gas,

the alkaline oil removing agent also comprises a surfactant, and the concentration of the surfactant in the alkaline oil removing agent is 0.01-100 g/L.

Optionally, the surfactant comprises one or more of a sodium alkyl sulfonate surfactant, an NP surfactant, and an OP surfactant.

Optionally, in step S20, microetching is performed using a microetching agent so that the roughness of the copper layer surface is less than 0.2 μm.

Optionally, the microetching agent comprises a main component, a corrosion inhibitor and a leveling agent, wherein the main component comprises at least one of hydrogen peroxide, inorganic acid and organic acid, the concentration of the leveling agent is 0.01-100 g/L, and the concentration of the corrosion inhibitor is 0.01-100 g/L.

Optionally, the main component comprises hydrogen peroxide, and the concentration of the hydrogen peroxide in the microetching agent is 0.2-2 mol/L; and/or the presence of a gas in the gas,

the corrosion inhibitor comprises one or more of urotropin, sodium glutamate and sodium glycinate; and/or the presence of a gas in the gas,

the leveler includes alkyl glycols.

According to the technical scheme provided by the invention, the surfactant is added into the chemical silver plating solution, so that the exchange of the solution is effectively promoted, the void phenomenon of a copper layer under silver is relieved, and the deposition efficiency of silver can be controlled; meanwhile, the chemical silver plating solution with a specific formula is used for carrying out silver deposition treatment at the temperature of 45-55 ℃, so that the deposition rate can be controlled to be 0.10-0.15 mu m/min, and excessive copper layer cavities under silver caused by too high displacement reaction rate are avoided.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other related drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is an electron micrograph of the surface of a copper layer after treatment according to example 1;

FIG. 2 is a photograph of the silver-plated side of the printed circuit board after treatment in example 1;

FIG. 3 is an electron micrograph of the surface of a copper layer after treatment according to example 2;

FIG. 4 is an electron micrograph of the surface of a copper layer after treatment according to example 3;

FIG. 5 is an electron micrograph of the surface of a copper layer after treatment according to example 4;

FIG. 6 is an electron micrograph of the surface of a copper layer after treatment according to example 5;

FIG. 7 is an electron micrograph of the surface of a copper layer after treatment according to example 6;

FIG. 8 is an electron micrograph of the surface of a copper layer after treatment according to example 7;

FIG. 9 is an electron micrograph of the surface of a copper layer after treatment according to example 8;

FIG. 10 is an electron micrograph of the surface of a copper layer after treatment according to example 9;

FIG. 11 is an electron micrograph of the surface of a copper layer after treatment according to example 10;

FIG. 12 is an electron micrograph of the surface of a copper layer after the comparative example treatment.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially. In addition, the meaning of "and/or" appearing throughout includes three juxtapositions, exemplified by "A and/or B" including either A or B or both A and B. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the silver deposition reaction process, the liquid medicine exchange of certain areas (such as solder resist residues, the junction of pollutants and the copper surface or the position with higher roughness) of the copper surface is slow, the silver ion supply is insufficient, the copper surface becomes a sacrificial anode, the copper layer at the position continuously loses electrons to form copper ions, and the copper ions are corroded to form a cavity finally; or the replacement reaction rate of the partial position of the copper surface is too fast, silver ions in the solution are too fast to be replenished, the copper corrosion rate is larger than the silver deposition rate, the deposited silver layer can not completely cover the copper surface, the copper surface at the uncovered position becomes an anode, and along with the continuation of the reaction, the copper is dissolved, so that a cavity is formed.

When an intensive cavity exists at the lower interface of silver, a copper layer at the edge of the cavity is easily oxidized into copper-containing oxide, a silver layer is dissolved and diffused into solder in the welding process, soldering flux is spread on the surface of a pad and enters the copper cavity, on one hand, the soldering flux extrudes gas in the cavity out of the cavity and is wrapped by tin material, on the other hand, the soldering flux can perform chemical reaction with copper wall oxide to reduce the copper-containing oxide and generate a small amount of micromolecule gas, the original gas and the gas generated by reaction in the cavity continuously move upwards in the molten tin material due to buoyancy and finally are concentrated in regions such as an IMC surface layer, after a point to be welded is cooled, even a layer of orderly micro-cavity can be formed in the IMC layer, so that the bonding force of the welding point is weakened, and the welding point is broken and fails in stress screening processes such as subsequent temperature impact, vibration test and the like.

In view of the above, the present invention provides a method for electroless silver plating of a printed circuit board.

The chemical silver plating method for the printed circuit board comprises the following steps:

step S10, degreasing the surface of the copper layer of the printed circuit board, and cleaning with clean water;

step S20, microetching the surface of the copper layer processed in the step S10, and cleaning the copper layer with clear water;

step S30, the printed circuit board processed in the step S20 is firstly presoaked in a presoaking solution at the temperature of 25-35 ℃, then is immersed in a chemical silver plating solution, is subjected to silver precipitation treatment at the temperature of 45-55 ℃, and is cleaned by clear water;

wherein the chemical silver plating solution comprises the following components in concentration: 0.2-5.0 g/L of silver ions, 1.0-100 g/L of complexing agent, 0.1-10 g/L of copper ions, 0.01-100 g/L of surfactant and 0.01-10 g/L of copper antioxidant, wherein the weight ratio of the complexing agent to the copper ions is more than 30.

Specifically, in step S10, the surface of the copper layer is degreased to improve the cleanliness of the copper surface. Studies have shown that the higher the cleanliness, the more slight the copper voiding under the silver after silver plating. There are various methods of degreasing, for example, acidic degreasing and alkaline degreasing. In view of the above, the invention adopts the alkaline degreasing agent to carry out degreasing treatment, the pH value of the alkaline degreasing agent is 11-13, and when the alkaline degreasing agent is adopted to carry out degreasing, the oxide, the residual dry film, the ink residue and the like attached to the surface of the copper layer can be well removed, so that the surface cleanliness is greatly improved. In the embodiment, the temperature for alkaline degreasing is 0-50 ℃, the treatment time is 0.1-10 min, and preferably 30-60 s.

The alkaline degreasing agent comprises organic alkali and/or inorganic alkali. Specifically, when the alkaline degreasing agent comprises an organic base, the total concentration of the organic base in the alkaline degreasing agent is 0.01-10 mol/L, wherein the organic base comprises one or more of monoethanolamine, diethanolamine, triethanolamine and organic amine hydroxide; when the alkaline degreasing agent comprises inorganic alkali, the concentration of the inorganic alkali in the alkaline degreasing agent is 0.01-10 mol/L, wherein the inorganic alkali comprises one or more of ammonia water, sodium hydroxide, potassium hydroxide and sodium carbonate.

In an embodiment, the alkaline oil remover further comprises an imidazole derivative, and after stains on the surface of the copper layer are cleaned, the imidazole derivative can play a role in protecting the surface of the copper layer, specifically, the concentration of the imidazole derivative in the alkaline oil remover is 0.01-100 g/L, wherein the imidazole derivative comprises one or more of benzimidazole, alkyl benzimidazole, benzotriazole and alkyl benzotriazole.

In another embodiment, the alkaline oil remover further comprises a surfactant, and the surfactant can improve the oil removing capability of the alkaline oil remover and improve the oil removing efficiency. The concentration of the surfactant in the alkaline oil removing agent is 0.01-100 g/L. Specifically, the surfactant includes one or more of sodium alkylsulfonate-based surfactants, NP-based surfactants, and OP-based surfactants.

Preferably, the basic oil removing agent contains both imidazole derivatives and surfactants.

In specific implementation, after the degreasing treatment is completed, the printed circuit board is cleaned by using deionized water with the conductivity of less than 20uS/cm, so as to carry out the following step S20.

In step S20, the surface of the copper layer is microetched to be surface-treated. As a preferred example, in this example, microetching is performed using a microetching agent so that the roughness of the surface of the copper layer is less than 0.2 μm. When the roughness of the surface of the copper layer is less than 0.2 mu m, the surface of the copper layer is uniform and smooth, and the void phenomenon of the copper layer under silver after silver plating is further improved.

Specifically, the microetching agent adopted in the embodiment comprises a main component, a corrosion inhibitor and a leveling agent, wherein the main component comprises at least one of hydrogen peroxide, inorganic acid and organic acid, the total concentration of the leveling agent is 0.01-100 g/L, and the total concentration of the corrosion inhibitor is 0.01-100 g/L. By adding a certain amount of corrosion inhibitor and leveling agent, the micro-etching process can effectively remove the oxide on the copper surface and ensure that the copper surface with ideal roughness (Ra value less than 0.2 mu m) can be obtained.

Specifically, the corrosion inhibitor comprises one or more of urotropin, sodium glutamate and sodium glycinate; the levelers include alkyl glycols, for example, the levelers include one or more of 1, 4-butynediol, 1, 4-butanediol, 1, 3-propanediol, and 1, 4-butenediol.

In one embodiment, the main component comprises hydrogen peroxide, and the concentration of the hydrogen peroxide in the microetching agent is 0.2-2 mol/L; in another embodiment, the main component includes the inorganic acid, the total concentration of the inorganic acid in the microetching agent is not more than 10mol/L, and the inorganic acid includes one or more of sulfuric acid, phosphoric acid, sulfamic acid, nitric acid, and hydrochloric acid; in yet another embodiment, the main component includes the organic acid, the total concentration of the organic acid in the microetching agent is not more than 10mol/L, and the organic acid includes one or more of methanesulfonic acid, formic acid, and acetic acid.

In addition, the temperature of the micro-etching is 0-40 ℃, and the processing time is 0.1-10 min.

In specific implementation, after the microetching treatment is completed, the printed circuit board is cleaned by using deionized water with the conductivity of less than 20uS/cm, so as to carry out the following step S30.

In step S30, the pre-immersion liquid is an electroless silver plating liquid for reducing the components of silver ions, and specifically, the pre-immersion liquid comprises the following components in concentration: 1.0-100 g/L of complexing agent, 0.1-10 g/L of copper ions, 0.01-100 g/L of surfactant and 0.01-10 g/L of copper antioxidant. In the chemical silver plating solution, the silver ions are provided by silver ion sources, and the silver ion sources comprise one or more of simple silver, silver nitrate, silver methylsulfonate and silver acetate; the copper ions are provided by a copper ion source, and the copper ion source comprises one or more of copper simple substance, copper nitrate, copper methylsulfonate and copper acetate; the complexing agent comprises one or more of complexing agent containing EDTA functional group, nitrilotriacetic acid salt and triethanolamine, wherein the complexing agent containing EDTA functional group refers to any agent with EDTA group, including but not limited to EDTA, EDTA salt and the like; the surfactant comprises a low-foam nonionic surfactant containing no sulfur, phosphorus and halogen elements, and is preferably at least one of polyoxyethylene ether, fatty acid methyl ester and block polyether of isomeric decacarbon alcohol; the copper antioxidant comprises one or more of benzimidazole, methylbenzimidazole, sodium mercaptobenzothiazole and hydrogen bond substituted imidazole.

In the specific implementation, after the silver deposition treatment is finished, the printed circuit board is cleaned by using deionized water with the electric conductivity of less than 20uS/cm, then post-protection is carried out, then the printed circuit board is cleaned by using deionized water with the electric conductivity of less than 20uS/cm, and finally drying treatment is carried out.

The technical solutions of the present invention are further described in detail below with reference to specific examples and drawings, it should be understood that the following examples are merely illustrative of the present invention and are not intended to limit the present invention.

Example 1

The formulation of each auxiliary agent involved in the process of the embodiment is as follows:

the printed circuit board was immersed for 45 seconds using the above-mentioned alkaline degreasing agent at 25 ℃ to degrease the copper layer surface thereof. The printed circuit board is then cleaned with deionized water having a conductivity of < 20 uS/cm.

And carrying out microetching treatment on the surface of the cleaned copper layer by using the microetching agent, wherein the microetching temperature is 25 ℃, the treatment time is 1min, the copper etching amount is 2.0um, and the Ra value of the etched copper surface is not higher than 0.2 um. The printed circuit board is then cleaned with deionized water having a conductivity of < 20 uS/cm.

And (3) pre-soaking the printed circuit board subjected to the microetching for 45s at 30 ℃, then placing the printed circuit board in the chemical silver plating solution, and depositing silver for 100s at 48 ℃, wherein the deposition rate is 0.10-0.15 mu m/min, so that a silver layer with the silver thickness of 0.25 mu m is obtained. The printed circuit board is cleaned by deionized water with the electric conductivity less than 20uS/cm, post-protection is carried out, then the deionized water with the electric conductivity less than 20uS/cm is used for cleaning, and finally drying treatment is carried out, so that the printed circuit board is obtained as shown in figure 2. The surface of the copper layer was observed, and as shown in FIG. 1, the voids exhibited the following: when the size of the copper surface is 20mm by 20mm pad, 5 cavities exist on the copper surface after silver stripping, and the requirement of sublimation is met; when the size is 10mm by 10mm pad, 1 hollow hole exists on the copper surface after silver stripping, and the standard of sublimation is met; when the size of the copper surface is 5mm by 5mm pad, 0 hollow holes exist on the copper surface after silver stripping, and the requirement of sublimation is met; when the size of 2mm by 2mm pad is large, 0 holes exist on the copper surface after silver stripping, and the standard of Hua is met.

Example 2

The formulation of each adjuvant involved in the process of this example was the same as in example 1.

Soaking the printed circuit board with the alkaline degreasing agent at 0 ℃ for 10min to degrease the copper layer surface of the printed circuit board. The printed circuit board is then cleaned with deionized water having a conductivity of < 20 uS/cm.

And carrying out microetching treatment on the surface of the cleaned copper layer by using the microetching agent, wherein the microetching temperature is 0 ℃, the treatment time is 10min, the copper etching amount is 1.0um, and the Ra value of the etched copper surface is not higher than 0.2 um. The printed circuit board is then cleaned with deionized water having a conductivity of < 20 uS/cm.

And (3) pre-soaking the printed circuit board subjected to the microetching for 35s at 25 ℃, then placing the printed circuit board in the chemical silver plating solution, and sinking silver for 60s at 45 ℃, wherein the deposition rate is 0.10-0.15 mu m/min, so that a silver layer with the silver thickness of 0.25 mu m is obtained. And (2) cleaning the printed circuit board by using deionized water with the electric conductivity of less than 20uS/cm, performing post-protection, cleaning by using deionized water with the electric conductivity of less than 20uS/cm, and finally drying to obtain the printed circuit board with uniform appearance, flat and uniform Imm Ag plating layers in the bonding pad and the hole, white silver surface, no pollution, yellowing and blackening. The surface of the copper layer was observed, and as shown in FIG. 3, the voids exhibited the following: when the size is 20mm by 20mm pad, 2 cavities exist on the copper surface after silver stripping, and the standard of sublimation is met; when the size is 10mm by 10mm pad, 3 cavities exist on the copper surface after silver stripping, and the standard of sublimation is met; when the size of the copper surface is 5mm by 5mm pad, 1 hollow hole exists on the copper surface after silver stripping, and the requirement of sublimation is met; when the size of 2mm by 2mm pad is large, 0 holes exist on the copper surface after silver stripping, and the standard of Hua is met.

Example 3

The formulation of each adjuvant involved in the process of this example was the same as in example 1.

Soaking the printed circuit board with the alkaline degreasing agent at 50 ℃ for 0.1min to degrease the copper layer surface. The printed circuit board is then cleaned with deionized water having a conductivity of < 20 uS/cm.

And carrying out microetching treatment on the surface of the cleaned copper layer by using the microetching agent, wherein the microetching temperature is 40 ℃, the treatment time is 0.1min, the copper etching amount is 3.0um, and the Ra value of the etched copper surface is not higher than 0.2 um. The printed circuit board is then cleaned with deionized water having a conductivity of < 20 uS/cm.

And (3) pre-soaking the printed circuit board subjected to the microetching for 60s at 35 ℃, then placing the printed circuit board in the chemical silver plating solution, and sinking silver for 120s at 55 ℃, wherein the deposition rate is 0.10-0.15 mu m/min, so that a silver layer with the silver thickness of 0.30 mu m is obtained. And (2) cleaning the printed circuit board by using deionized water with the electric conductivity of less than 20uS/cm, performing post-protection, cleaning by using deionized water with the electric conductivity of less than 20uS/cm, and finally drying to obtain the printed circuit board with uniform appearance, flat and uniform Imm Ag plating layers in the bonding pad and the hole, white silver surface, no pollution, yellowing and blackening. The surface of the copper layer was observed, and as shown in FIG. 4, the voids exhibited the following: when the size of the copper surface is 20mm by 20mm pad, 5 cavities exist on the copper surface after silver stripping, and the requirement of sublimation is met; when the size is 10mm by 10mm pad, 0 hollow holes exist on the copper surface after silver stripping, and the standard of sublimation is met; when the size is 5mm by 5mm pad, 3 cavities exist on the copper surface after silver stripping, and the standard of sublimation is met; when the size of 2mm by 2mm pad is large, 0 holes exist on the copper surface after silver stripping, and the standard of Hua is met.

Example 4