How to Deal with the Discoloration of the Gold Surface of the PCB Circuit Board?

PCB Industries Company analyzes how the gold surface discoloration is generally related to the gold plating solution in this process and the solder mask in the previous process. As a solder resist engineer, I think that it may be that the plate is not cleaned during the development of this process. This should be solved by looking for a professional solder resist engineer to follow up; otherwise it will be caused by external pollution during the production process. It is more troublesome and requires the cooperation of influential people from different departments to effectively control the source of pollution.

The discoloration of the gold surface is one of the most common problems, mainly solved from the following aspects:

1. Copper pollution of nickel bath

2. Conductivity of deionized water washing before gold plating

3. Metal contamination of the gold tank

4. Pure gold concentration

It is not a problem of solder mask itself, but a problem of process. The fundamental reason for the discoloration of the gold face here is that the potion enters the hole and cannot be cleaned, causing contamination of the gold face. Improving the wet film process and strengthening cleaning will help.

Prototype PCB plate-making methods are divided into: direct plate-making method, indirect plate-making method, and indirect plate-making method. The materials used are: photosensitive paste photosensitive film, photosensitive film, indirect film

1. Direct plate-making method

Method: Apply a certain thickness of photosensitive paste on the stretched screen, dry it after coating, and then use the plate-making negative film to fit into the exposure machine for exposure. After developing, rinsing and drying, it becomes a screen printing screen. Version.

Technical process: photosensitive paste preparation has stretched net-degreasing-drying-coating-drying-exposure-development-drying-revision-final exposure-sealing

Methods and functions of each section

Degreasing: Use a degreasing agent to remove the grease on the silk screen so that the photosensitive paste and the silk screen are completely glued together so that it is not easy to peel off the film.

Drying: Dry the moisture to avoid the tension change of the mesh due to the high temperature. The temperature should be controlled at 40 ～ 45 ℃

Preparation of photosensitive paste: mix the photosensitizer with purified water, add it to the photosensitive paste and stir evenly. Leave it for 8 hours before use.

Coating film: The photosensitive paste is evenly coated on the silk screen by using a groove, and it is divided into automatic coating machine coating and manual coating according to the coating method.

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