14 Sep
2005
14 Sep
'05
10:48 p.m.
Developer and stripper are not etchant. After
applying and exposing
photoresist, one uses developer to remove the unexposed (or exposed
for positive) photoresist without affecting the exposed (or
unexposed) photoresist. After etching the excess copper away with an
etchant, the polymerized photoresist is still present on the
protected copper traces and must be removed using a stripper.
Most photoresists can be 'soldered through' so it's not necessary to
strip them. On the other hand, boards look a lot better if you do strip...
The method I've always used is to etch the board as usual, wash it, then
give it another (longer-than-normal) UV exposure with no artwork -- thus
'fogging' the remaining resist. Then pop it back in the developer and it
will all strip off nicely. Remember on most photoresist boards, the bits
that are exposed to UV are the bits you want to etch away (the artwork is
black for the traces, etc), so the resist that's been exposed is the
stuff that comes off.
So, when using a photoresist system, one needs developer, etchant and
stripper. However, I suspect that the stripper, at least, may be
some commonly available chemical such as acetone. And I believe that
Tony mentioned that developer is usually just a strong alkalai.
It's actally not _that_ strong. Strong enough to feel 'soapy' (it
hydrolyses the fats in your fingers), but not strong enough to cause an
alkali burn in my experience.
-tony