PCB Solder Mask Removal Method

The PCB solder mask is a heat resistant coating material that can be applied to selected areas to prevent solder from depositing during subsequent soldering. The solder mask material can be liquid or dry film; it is also very effective in preventing surface damage of the PCB during PCB assembly operations.

If the test point, ground pad or even the component pins are accidentally stained with a solder mask, these are commonplace. However, it does not mean that these PCBs are definitely scrapped. There are several safe and reliable methods for removing the solder mask on the PCB surface: scraping, milling, micro-grinding and chemical stripping; each method has its own advantages and disadvantages.

Scraping

This method is not peculiar and has large noise. A skilled technician typically removes the solder mask from unwanted areas with a knife, scraper or chisel. This technology is easy to control and requires no special settings. However, if the removal area is large, the operator will feel tired after a long operation. And it needs to be methodical and is often used to remove thin solder mask.

Milling

Carbide vertical milling cutters are the most common type of tool. Because they are very sharp and must control depth accuracy, so they can easily to enter the coating and reach the surface of the PCB. Rotating the milling cutter back and forth in the opposite direction is an effective way to control depth, thus the skill and experience of the operator is particularly important. This method looks extreme, but it is a very effective and accurate way to remove the solder mask.

Chemical stripping

This method is the most effective way to remove the solder mask on the copper or post-weld surface. Protective gear or other protective material should be placed on the surface of the PCB to isolate the area to be stripped. The chemical release agent is then applied to the surface of the PCB with a brush or cotton swab. Since the release agent is a liquid, it is often difficult to control. This method is costly but fast.

Micro-grinding

This is the best technique for removing a large area of solder mask on the surface of a PCB. The abrasive material is only used for the friction coating, the main step of the process is friction, thus creating an electrostatic charge. If the grinding PCB is equipped with electrostatic sensitive devices, the micro-grinding system must eliminate potential electrostatic damage. Therefore, in order to control the removal area, a large amount of preparation time and protection measures are usually essential. And the abrasive material on the PCB must be thoroughly cleaned.

Each type of PCB solder mask removal methods has its own advantages. When you need to remove PCB solder mask, you should choose the applicable method based on your own conditions, which will not only save costs, but also greatly improve work efficiency.