To do this you need to understand how materials react to laser- absorb
(material get removed), reflect (nothing happen), pass through (material is
transparent to laser).

Copper is a good reflector to IR (e.g. CO2) laser, so CO2 lasers won't do
what you want.

UV laser will be absorbed by both resin and copper with resin having a
lower threshold energy.  This means if the beam energy density is high
enough to remove copper it will remove resin as well.  So, with UV laser
you need to hit JUST the copper and STOP the laser immediately after all
the copper is removed - very, very difficult, if not impossible.

I have seen green laser (532 nm) being used to remove copper and stop right
at the resin interface, because resin is transparent to the green laser.
However, the problem with transparency is the copper in the next layer down
may get damaged.

Maybe there are things that I have not think of, but hopefully this will
spark some bright ideas in developing a good laser repair station.

Mason Hu

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