As an engineer in the electronics manufacturing industry, have you ever encountered the need to rework a printed circuit board (PCB) to remove the solder mask? If so, how did you approach this problem?

Traditionally, the solder mask is manually removed using a knife or hand grinding tool. However, this method often results in damage to the traces on the PCB, leading to a high scrap rate for both the PCB and PCB assembly.

WorkingBear would like to introduce a new method of removing the solder mask using a laser machine, which is highly efficient and reliable. By selecting the appropriate laser power, the solder mask can be removed without damaging the copper underneath.

In my company, we have not done this type of PCB rework for quite some time. Unfortunately, a new top manager has requested that we reduce the design phase and accelerate the product’s mass production timeline from 9 months to 6 months. Rapid design will require some sacrifices. We now need to rework approximately 10,000 pieces of the PCB to remove the solder mask and improve the ESD issue.

Initially, our research and development team could only offer the traditional solution of using a knife to remove the solder mask. However, this method requires highly skilled and knowledgeable technicians, and there is a high risk of damaging the PCB. Additionally, it is a time-consuming and inefficient process.

To salvage the 10,000 PCBs, we researched several alternative methods to remove the solder mask, including:

• Solder Mask Removal Chemical Solvent:

A company claims to have developed a chemical solvent that can remove the solder mask without damaging the copper and resin. However, there are concerns about the potential damage to the FR4 material. To use this chemical solvent, a mask jig would need to be created to prevent the solvent from flowing into areas that still require the solder mask.

• Hand Grinding Electric Tool:

WorkingBear has tried this method before and found that it is not effective in removing the solder mask without damaging the copper. Although it is useful for removing some of the plastic material, it is difficult to control the force for small areas.

An article on the website describes how to use a knife and grinding tool to remove the coating from the PCB. (Coating Removal, Grinding/Scraping Method)

• CNC Machine with Milling Head Replacement:

While this may be a good idea, we would need to find an outsourcing supplier to implement it. Therefore, we decided against it.

• Screw with Tooth Washer:

One suggestion was to use a semi-automatic screwdriver and a screw with a tooth washer to wear off the solder mask. WorkingBear tried this method but found that the washer would snap on the PCB, and the screw was easily stripped. While it sometimes worked, it resulted in scratches on the copper with varying depths.

• Laser cutting

Finally, WorkingBear discovered that a laser machine was efficient and effective in removing the solder mask without damaging the copper. We needed to find a laser machine with the appropriate properties to remove the solder mask. We finally found that the Altec Allprint DN series laser machine(Nd:YAG laser stroke marker) was suitable for our needs, and the rework result looked good.

▲The picture show the solder mask was removed by knife result. The solder mask removed area are not uniform.	▲Picture here to show the solder mask was removed by laser machine. The removed area are very uniform and consistence.

The two pictures above demonstrate the results of using a knife and a laser to remove the solder mask. It can be observed that the laser machine provides a better outcome with high quality, and also saves labor hours. If a laser machine is available, only a horizontal fixture to hold the PCB is needed.

The video show Altec Allprint DN series laser machine (Nd:YAG laser stroke marker) removing the solder mask.

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