PCB two-phase tin stripping method

Abstract

The invention discloses a PCB two-phase tin stripping method. In the first phase of tin stripping, a SnCl4-HCl system is adopted; and in the second phase, a HNO3-Fe(NO3)3 system is adopted. A specificquantity of tin on the surface of a tin plated board is stripped by first-phase tin stripping treatment; and then, through second-phase tin stripping, the remained tin on the surface of the PCB is stripped to obtain a bright copper plate. After first-phase tin stripping, liquid is pumped in a diaphragm electrolysis system for diaphragm electrodeposition to extract tin and to regenerate a tin stripping agent. Through two-phase tin stripping, the tin stripping speed of the PCB can be guaranteed, tin in the liquid after first-phase tin stripping can be recovered online, and meanwhile, the SnCl4-HCl tin stripping agent can be regenerated. Through second-phase tin stripping by the HNO3-Fe(NO3)3 system, the remained tin on the surface of the PCB can be totally stripped, and the smoothness of the copper substrate can be maintained. The method can effectively solve the problems of high tin stripping waste water quantity and difficult resourceful recycling in a traditional nitric acid system.

Description

technical field [0001] The invention belongs to the field of hydrometallurgy, and in particular relates to a two-stage method for stripping tin from a PCB board and a method for on-line tin recovery. Background technique [0002] In the manufacturing process of general printed circuit boards and electronic components, it is often necessary to electroplate tin on the surface of the copper layer as a protective layer for alkaline etching. After the copper layer of the non-circuit part is etched and removed, the electrolytic tin layer must be removed with tin stripping water to make the copper circuit appear. [0003] At present, most domestic PCB manufacturers use nitric acid or nitric acid-alkylsulfonic acid type tin stripping water for tin stripping. After the tin stripping water has been stripped for many times, the properties of the tin stripping water have changed greatly. The tin content reaches 100-150g / L, the copper and iron content reaches 20-30g / L, and the residual ...

AI Technical Summary

Problems solved by technology

[0004] Generally speaking, there are still two major problems in the tin stripping process and the treatment of tin stripping waste liquid in the current tin stripping water with nitric acid or nitric acid-alkylsulfonic acid system: (1) The tin stripping process mainly dissolves tin and copper with nitric acid Mainly, there is NO x The problems of heavy gas pollution, large amount of sludge, high amount of residual acid, and high cost; (2) The process of treating waste tin stripping water by precipitation, electrolysis, and distillation has large consumption of reagents, low metal recovery rate, Serious problems such as large amount of waste water

However, when this method was later applied to the industrial practice of removing tin from printed circuit boards (PCB boards) and recovering tin, it encountered "slow tin removal speed (more than 10 minutes), severe corrosion of PCB copper substrates, and electrowinning of diaphragms to extract tin." Serious problems such as "tin whisker" phenomenon and low electrodeposition efficiency

The reason is that, compared with the current nitric acid or nitric acid-alkyl sulfonic acid system tin stripping water, the oxidation performance of the tin stripping water of the hydrochloric acid-tin salt system is relatively weaker, and its solubility to PCB board tin is weaker, and the tin stripping water of the hydrochloric acid-tin salt system is relatively weaker. Tin is also slower

And if you want to use this tin stripping water to remove more tin on the PCB, you must prolong the tin stripping time. However, due to the hydrochloric acid-tin salt system Cl in the tin stripping water - Corrosion to the PCB board belongs to "pitting corrosion", which tends to form many small holes distributed in dots on the PCB board, resulting in very uneven surface of the copper substrate after tin stripping, thus affecting the subsequent electronic processing performance of the PCB

In addition, due to the addition of a variety of organic substances, the composition of the tin stripping solution is more complex, resulting in serious problems such as "tin whiskers" and low electrowinning efficiency when the tin stripping solution extracts tin by diaphragm electrowinning.

[0006] For printed circuit board (PCB) stripping companies, due to the limitation of the length of the stripping machine and the requirements of the stripping speed, the stripping time of the PCB board in the stripping machine is usually required to be less than 120 seconds, and the PCB after stripping is required to be less than 120 seconds. The surface of copper substrate must be smooth and bright, otherwise it cannot meet the high requirements of electronic processing for copper substrate

That is to say, the technology of "a tin stripping water based on a hydrochloric acid-tin salt system and a method for recovering tin from waste stripping water (application number 201410011267.0)" developed by the applicant is difficult to apply to printed circuit board (PCB board) tin stripping And efficiently recycle the tin online