CN102363885A - Pretreatment solution for selective stripping of silver coating and quantitative analysis of elements in silver coating - Google Patents

Abstract

The invention relates to a solution for selective stripping of a silver coating. The solution consists of the following components in percentage by mass: 0.01 to 10 percent of chloroacetic acid, 0.01 to 10 percent of carboxylic acid, 1 to 20 percent of hydrogen peroxide, and the balance of deionized water. The solution has the advantages that: the solution does not contain nitric acid, hydrochloric acid, sulfuric acid and other strong acid, so when the silver coating is stripped, the solution can greatly improve the environment of field production operation; and the solution has the property of selectively corroding silver, so that the solution slightly influences the surface of a base material and can be used as the pretreatment solution for the quantitative analysis of elements in the silver coating.

Description

Pretreatment solution for selective stripping of silver coating and quantitative analysis of elements in silver coating

technical field

The invention relates to a pretreatment solution for selective stripping of silver coating and quantitative analysis of elements in the silver coating.

Background technique

In the manufacturing process of printed circuit boards or electronic connectors, in order to protect the substrate and increase solderability, silver plating is often performed on the surface of the substrate. In the process of manufacturing printed circuit boards, part of the silver coating may be stripped according to the needs of the process, or the silver coating may be stripped when dealing with unqualified silver coatings, and it is also possible to analyze the metal elements in the silver coating The content of silver plating will be stripped.

Solutions for silver plating stripping usually use cyanide, chromate and strong acid solutions. It is well known that cyanide is a highly toxic substance that pollutes the environment greatly; and chromate is gradually not used due to its pollution to the environment; because strong acid is easy to produce acid mist, it will cause adverse effects on the production site. At the same time, commonly used silver plating stripping solutions will directly corrode the substrate and have no selectivity for the silver plating.

Contents of the invention

The technical problem to be solved by the present invention is: in order to solve the technical problem that the current solution for stripping the silver coating is extremely polluting to the environment; it will directly corrode the substrate and has no selectivity to the silver coating. The present invention provides a selective stripping silver coating And the pretreatment solution for quantitative analysis of elements in the silver coating, the selective stripping silver coating and the pretreatment solution for quantitative analysis of elements in the silver coating do not corrode the base material, and the silver removal speed is fast. Since the pretreatment solution for selective stripping of the silver coating and quantitative analysis of elements in the silver coating does not contain cyanide and strong acid, the pretreatment solution for selective stripping of the silver coating and quantitative analysis of elements in the silver coating is environmentally friendly.

The technical solution adopted by the present invention to solve the technical problem is: a pretreatment solution for selective stripping of the silver coating and quantitative analysis of elements in the silver coating consists of chloroacetic acid, carboxylic acid, hydrogen peroxide and deionized water.

The mass percentage concentration of chloroacetic acid is 0.01-10%, the mass percentage concentration of carboxylic acid is 0.01-10%, the mass percentage concentration of hydrogen peroxide is 1-20%, and the rest is deionized water.

Chloroacetic acid is selected from one or more mixtures of monochloroacetic acid, dichloroacetic acid and trichloroacetic acid. When the mass percentage concentration of chloroacetic acid is greater than 10%, it is easy to corrode the base material, and the selectivity decreases; when the mass percentage concentration of chloroacetic acid is lower than 0.01%, the stripping effect of silver plating is not good, and the stripping time is too long. The mass percentage concentration range of chloroacetic acid is 0.01-10%, and the optimum mass percentage concentration range is 0.1-5%.

The addition of carboxylic acid helps to increase the stripping speed of the silver coating. The carboxylic acid is a monobasic acid or a dibasic acid with a carbon number of not more than 5, such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, ethyl Diacid, malonic acid, succinic acid, glutaric acid etc., when the mass percentage concentration of carboxylic acid is greater than 10%, simply for stripping silver coating, without any influence, but when stripping solution is used as stripping silver coating When carrying out quantitative analysis on other elements in the silver coating, too much carboxylic acid will lead to low measurement results. When the mass percent concentration of carboxylic acid is lower than 0.01%, the effect on accelerating the stripping of silver plating is difficult to appear. The mass percent concentration of carboxylic acid is 0.01-10%, and the optimum mass percent concentration range is 1-5%.

In the pretreatment solution for selective stripping of the silver coating and the quantitative analysis of elements in the silver coating of the present invention, the addition of hydrogen peroxide is 1 to 20% in mass percent concentration, and when the mass percent concentration of hydrogen peroxide is greater than 20%, the solution The stripping speed of the silver plating is very fast, but at the same time, the solution will also corrode the substrate, resulting in a decrease in selectivity. When the mass percentage concentration of hydrogen peroxide is less than 1%, the stripping speed of the silver coating is too low for the pretreatment solution of the selective stripping silver coating and the quantitative analysis of elements in the silver coating, and the optimal range of the hydrogen peroxide mass percentage concentration is 5～10 %.

Use the pretreatment solution method of the selective stripping silver coating of the present invention and the quantitative analysis of elements in the silver coating to be: the sample piece that wants to remove the silver coating is placed in the degreasing cleaning solution of 45 ℃ (NaOH 10g/L, Na ₂ CO _20g /L, Na ₃ PO ₄ 12H ₂ O 5g/L, OP-10 emulsifier 1g/L) 5min, after washing, the sample is placed in the pretreatment of selective stripping of the silver coating and quantitative analysis of elements in the silver coating of the present invention Solution, until the color of the substrate layer is completely exposed, take it out, wash it with water and dry it with hot air.

The technical effect of the present invention is: do not contain strong acids such as nitric acid, hydrochloric acid and sulfuric acid, when stripping the silver-plated layer, the use of this solution can greatly improve the environment of on-site production operations; characteristics, so the solution has little effect on the surface of the substrate, and can be directly used as a pretreatment solution for quantitative analysis of elements in the silver coating.

specific embodiment

The effects of the present invention are described below through specific examples.

Embodiment 1 The preparation of the pretreatment solution for selective stripping of silver coating and element quantitative analysis in silver coating of 1000g

Chloroacetic acid takes monochloroacetic acid as an example, and carboxylic acid takes acetic acid as an example. The preparation method of the silver plating stripping solution is explained. Get 0.1g of monochloroacetic acid and add it to 600g of deionized water. After fully mixing, add 100g of acetic acid. After fully mixing, add 200g of hydrogen peroxide, then add 99.9g of deionized water and stir to mix.

Embodiment 2 Preparation of pretreatment solution for selective stripping of silver coating and quantitative analysis of elements in silver coating of 1000g

Take dichloroacetic acid as an example for chloroacetic acid, and formic acid as an example for carboxylic acid. The preparation method of the silver plating stripping solution is explained. Get 1g of dichloroacetic acid and join it in 600g of deionized water. After fully mixing, add 50g of formic acid. After fully mixing, add 100 g of hydrogen peroxide, then add 240 g of deionized water and stir to mix.

Embodiment 3 Preparation of pretreatment solution for selective stripping of silver coating and quantitative analysis of elements in silver coating of 1000g

Take trichloroacetic acid as an example for chloroacetic acid, and acetic acid as an example for carboxylic acid. The preparation method of the silver plating stripping solution is explained. Take 50g of monochloroacetic acid and add it to 600g of deionized water. After mixing well, add 1g of glutaric acid After fully mixing, add 50g of hydrogen peroxide, then add 290g of deionized water and stir to mix.

Embodiment 4 Preparation of pretreatment solution for selective stripping of silver coating and element quantitative analysis in silver coating of 1000g

Chloroacetic acid is example with monochloroacetic acid and trichloroacetic acid, and carboxylic acid is example with malonic acid, and the preparation method of silver plating stripping solution is explained, and the monochloroacetic acid of 50g and the trichloroacetic acid of 50g are added to 600g of In deionized water, after fully mixing, add 0.1 g of malonic acid, after fully mixing, add 10 g of hydrogen peroxide, then add 289.9 g of deionized water and stir and mix.

The preparation of comparative example 1 1L silver coating stripping solution

Taking the sodium thiosulfate stripping solution as an example, the preparation method of the stripping solution is described. Take 300g of sodium thiosulfate and dissolve it in 1000ml of deionized water, and stir to fully dissolve the solid. (Because the strong acid type stripping solution is too corrosive to the base material, so it is not selected as a comparative example here. The mild sodium thiosulfate silver plating stripping solution is selected here as a comparison.)

Embodiment 5 Selective stripping of the silver coating and the influence of the pretreatment solution for the quantitative analysis of elements in the silver coating on the surface of the substrate when the silver coating is removed

After removing the silver coating, rework the silver-plated sample again, it is very important to keep the flatness of the substrate surface, so the use of the pretreatment solution for selective stripping of the silver coating and the quantitative analysis of elements in the silver coating of the present invention is evaluated in removing the silver coating. effect on the substrate surface. The specific method is as follows: First, use a microscope to measure the roughness of the copper foil on the surface of the copper clad laminate, and after the surface of the sample is plated with silver, use the pretreatment of selective stripping of the silver coating and quantitative analysis of elements in the silver coating according to Examples 1-4 of the present invention solution and the silver plating stripping solution of Comparative Example 1 to strip the silver layer, then measure the roughness of the copper foil surface, the roughness change is not greater than 10%, marked as ◎, and the roughness change is greater than 10% and not greater than 20% %, marked as ○, roughness change greater than 20%, marked as X. The results are shown in Table 1.

Table 1 Pretreatment solution for selective stripping of silver coating and quantitative analysis of elements in silver coating and change of surface roughness of copper foil after treatment with silver coating stripping solution

example Change rate of copper foil surface roughness after treatment Example 1 ◎ Example 2 ◎ Example 3 ◎ Example 4 ○ Comparative example 1 ○

The content analysis of other elements in the silver coating of embodiment 6

For the analysis of the content of other elements in the silver coating, such as Cd ²⁺ , Hg ²⁺ , Pb ²⁺ and Cr ⁶⁺ in the RoHS directive, the selective stripping of the silver coating is particularly important. Because if the silver plating stripping solution corrodes the base material excessively, the trace impurity elements in the base material will be brought into the stripping silver solution to be tested. Therefore, the selectivity of the pretreatment solution for selective stripping of the silver coating and the quantitative analysis of elements in the silver coating using the present invention was evaluated. The method was to place a 2×2 cm silver-plated copper-clad board in 50 mL of the selected solution of Examples 1-4 of the present invention. In the pretreatment solution (room temperature) for the permanent stripping of the silver coating and the quantitative analysis of elements in the silver coating (at room temperature) and the silver coating stripping solution (70° C.) of Comparative Example 1, after the surface of the copper substrate is completely exposed, the copper-clad board is taken out. The pretreatment solution and the silver stripping solution for the selective stripping of the silver coating and the quantitative analysis of elements in the silver coating that have been dissolved in silver are transferred to a 100ml volumetric flask respectively, diluted to the scale, and the copper ion in the stripping solution is measured by atomic absorption spectrophotometry To determine the selectivity of the pretreatment solution for the selective stripping of the silver coating and the quantitative analysis of elements in the silver coating of the present invention. The results are shown in Table 2.

Table 2 The concentration of copper ions dissolved in the selective stripping silver coating and the pretreatment solution for quantitative analysis of elements in the silver coating and the silver coating stripping solution

example Concentration of copper ion in stripping solution (μg/ml) Example 1 98 Example 2 79 Example 3 158 Example 4 220 Comparative example 1 178

(The glass time of Examples 1-4 at room temperature is about 6min, 4min, 5min, 8min respectively, and the peeling time of Comparative Example 1 at 70°C is 9min)

Inspired by the above-mentioned ideal embodiment according to the present invention, through the above-mentioned description content, relevant workers can make various changes and modifications within the scope of not departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, but must be determined according to the scope of the claims.

Claims (6)

1. a kind of pretreatment solution that is applicable to stripping silver coating and element quantitative analysis in silver coating, it is characterized in that: the composition of this solution is chloroacetic acid, carboxylic acid, hydrogen peroxide and deionized water. 2. the described pretreatment solution of claim 1 is characterized in that the mass percent concentration of chloroacetic acid is 0.01～10%, the mass percent concentration of carboxylic acid is 0.01～10%, and the mass percent concentration of hydrogen peroxide is 1～10%. 20%, and the rest is deionized water. 3. the described pretreatment solution of claim 1 is characterized in that the mass percent concentration of chloroacetic acid is 0.1～5%, the mass percent concentration of carboxylic acid is 0.1～10%, and the mass percent concentration of hydrogen peroxide is 5～5%. 10%, and the rest is deionized water. 4. The pretreatment solution according to claim 1, characterized in that chloroacetic acid is selected from one or more mixtures of monochloroacetic acid, dichloroacetic acid and trichloroacetic acid. 5. The pretreatment solution according to claim 1, characterized in that the carboxylic acid is a monobasic acid or a dibasic acid, wherein the carbon number is less than 5. 6. The pretreatment solution according to claim 1, characterized in that the silver coating is plated on copper, steel or iron-nickel alloy substrate.