Jun10
PCB rework: Selective solder mask removal by laser

PCB rework: Selective solder mask removal by laserDid you ever met a trouble need to rework to remove the solder mask from the PCB?  If yes then how you did?

We usually remove the solder mask manually  by knife or hand grinding tool. But these kinds of rework always damaged and broke the traces on the PCB and result in high scrap rate for PCB or PCB Assembly.

Today WorkingBear will introduce you a new method to remove the solder mask by laser machine. It is high efficiency and high reliability. If the laser power select property  then it will only remove the solder mask and without damage cooper under the solder mask.

Actually my company had never did this kind of PCB rework quite a long time. Unfortunately, new top manager ask to reduce the design phase and roll in the product to mass production from 9 months to 6 moths. Make design quickly will need to pay something. There are about 10K pcs of the PCB need to be reworked to remove the solder mask to improve the ESD issue.

The picture show the solder mask was removed by knife result. The solder mask removed area are not uniform.

At beginning that RD only can provide the tradition solution to remove the solder mask by knife. But using knife to remove the solder mask will need full skill and smart technician. Beside, it really take time and high risk to damage the PCB.

In order to save these 10K pcs of PCB. We research many methods to remove the solder mask as below list:

  • Solder Mask removal chemical solvent
    This company said they design a chemical solvent that can remove the solder mask and without damage the cooper and resin. But some people had concern it maybe damage the FR4 material. If apply this chemical solvent then need to make some mask jig to prevent solve flow to another location that still need to keep solder mask there.
  • Hand grinding electric tool
    WorkingBear had tried this hand grinding tool before and think it is not good enough to remove solder mask without damage the cooper. It is good to remove some of the plastic material but it is not easily to control the force for tiny stuff.
    Here  you can find a article on the website that teach people how to use knife and grinding tool remove the coating from PCB. (Coating Removal, Grinding/Scraping Method)
  • CNC machine and exchange the milling head to grinding head
    This maybe a good idea but we need to find outsource  supplier to do this. So we gave up.
  • Screw with tooth washer
    Someone proposal to apply semi-auto screw driver and use the screw with tooth washer to wear off the solder mask. WorkingBear had tried it but found the washer will be snapped on PCB and screw is easily stripped. Sometimes it works but it will scratch  the cooper  with different depth mark.
  • Laser
    WorkingBear finally found laser machine is good and high efficiency to remove the solder mask and without damage the cooper. You will need to find a property laser type machine to remove the solder mask. WorkdingBear found the Altec Allprint DN series laser machine (Nd:YAG laser stroke marker). The rework result looks pretty 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 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.

Above two pictures show the result to use knife and laser to remove the solder mask. You will find the laser machine did good result, high quality and also save the labor hours. If laser machine is available then only need to make a horizontal fixture to hold the PCB will be ok.


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



Leave a Reply