Reflectivity of Tin coating for PCB

Hi, pretty new here. I was wondering if I could use the glowforge to remove solder mask from a PCB. There are some tutorials on how to do it with a CO2 laser but researching a little more is seems like there would be a risk of damaging the glowforge because the copper beneath the solder mask would reflect the laser. Has anyone actually damaged their glowforge by doing this?

I was thinking a potential work around would be to tin the copper before applying the solder mask. That way after etching off the solder mask the laser would be hitting tin instead of copper. Only problem is that I cannot find any information on if tin is as reflective as copper. Also the tin layer would be very thin.

Any insights from this group?

Tinning doesn’t refer to “tin” as the actual metal. Tinning means applying a coating of solder to the surface. Tin may be included in the solder alloy, but doesn’t have to be.

Silver is one of the main ingredients in lead-free solder and is highly reflective in the CO2 wavelength. Not quite the same as copper, but close. I think the information I read was copper is 95% reflective and silver is 85-90%, but it may have been a little lower.

You can look up the reflectivity bandwidth of metals online and you can look up the wavelength of the laser and get data that will tell you the risk in just a few minutes, depending on the exact alloy of the solder you are using to tin the copper.


Thanks for the response! I actually was going to use liquid tin which as far as I tell is 100% tin.
I did find a site where you can calculate the reflectivity ( and it says the reflectance is 0.967 which seems high to me, copper is .99. But I am not sure if I am understanding these numbers correctly. When I look up aluminum, it is .988, but I know people engrave anodized aluminum all the time on the glowforge.

Anodized aluminum has a coating of aluminum oxide on top of it. The laser doesn’t break this layer and doesn’t touch the bare aluminum. It only ablates the dye out of the anodization. This means the aluminum oxide is the reflective layer. I won’t be the same as bare aluminum.

I wouldn’t laser most bare metals, honestly, as they have a high reflectivity of IR wavelengths. Just the steel of the grid reflects enough energy back to burn the back of your material.


Makes sense, thanks!

No. A 40/45W hobby laser is not suitable for this.

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Solder Mask keeps solder from flowing over the underlying copper. If you remove it, you are exposing copper. The laser doesn’t move off the moment the copper is exposed, there’s “dwell time”. So the copper is going to reflect most of the laser energy and since a PCB is generally fairly flat, most of that energy is going to go right back in to the “print head”. And while the laser spot moves and no one spot of the PCB is heated continually, the reflected beam is always going to be hitting about the same spot on the print head for the duration of the print run.

The Solder Mask isn’t even going to slow the laser down. You might as well ask “is it OK to put a sheet of clean unoxidized copper in my laser cutter?” and the answer to that is “no”. :slight_smile:

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