12 Sep
2005
12 Sep
'05
7:15 p.m.
Date: Wed, 07 Sep 2005 12:58:30 -0400
From: Roger Merchberger <zmerch at 30below.com>
Subject: Re: Homebrew Circuit Boards: Methods? Supplies?
In fact, I have
not been able to find precoated board (photoresist coated)
in the .050" thickness. So I will either need to use a liquid photoresist
or try a toner transfer system.
I dunno about 0.050", but would the 1/32" thickness be close enough?
(That's 0.03125" thickness, if you can believe the Winders calcaputer
applet ;-) Do the
developer and/or stripper usually turn out to be some commonly
(cheaply) available chemical? I would prefer to avoid paying $6+ for a
small bottle if I can avoid it.
One kg of ammonium persulfate will make 4 liters of etchant, 
14 Sep
14 Sep
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
15 Sep
15 Sep
8:30 a.m.
Tony Duell wrote:
Infact, sodium hydroxide is not strong in the concentrations used for
developping. The recipe I remember is
7 grams NaOH in 1 litre of water. One can use normal rubber gloves (as
used for cleaning puroses) if one is
afraid to touch the developer. I tried higher concentrations than 7g of
NaOH but this will likely attack also
the unexposed traces - you'll unfortunately encounter this during
etching :-(
Regards
Holger
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...
Besides better look, you'd better strip it in case you want to solder SMDs.
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.
I am wondering what you have against a stripper like acetone. I have
even used nail varnish remover in the
past which contains acetone, but unfortunately also some soap (which is
not bad) but also some hand-friendly oils
and perfumes, which then require another cleaning with water.
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.
7:31 p.m.
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.
I am wondering what you have against a stripper like acetone. I have 
12:49 p.m.
>>>> "Tony" == Tony Duell <ard
at p850ug1.demon.co.uk> writes:
> I believe that Tony mentioned that developer is
usually just a
> strong alkalai.
Tony> It's actally not _that_ strong. Strong enough to feel 'soapy'
Tony> (it hydrolyses the fats in your fingers), but not strong enough
Tony> to cause an alkali burn in my experience.
That sounds rather strong. Not strong enough to burn fingers, perhaps
-- then again, I don't think alkali usually does. But strong enough
that it's important to protect your eyes from splashes.
paul
12:57 p.m.
Paul Koning wrote:
Many alkaline solutions will burn skin at lower concentrations than
acids. Even tiny quantities of alkali can cause serious eye damage.
Peace... Sridhar
>>>>"Tony" == Tony Duell <ard at p850ug1.demon.co.uk> writes:
> I believe that Tony mentioned that developer
is usually just a
> strong alkalai.
Tony> It's actally not _that_ strong. Strong enough to feel 'soapy'
Tony> (it hydrolyses the fats in your fingers), but not strong enough
Tony> to cause an alkali burn in my experience.
That sounds rather strong. Not strong enough to burn fingers, perhaps
-- then again, I don't think alkali usually does. But strong enough
that it's important to protect your eyes from splashes.
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5 comments
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ard＠p850ug1.demon.co.uk -
holger.veit＠ais.fraunhofer.de -
pkoning＠equallogic.com -
ploopster＠gmail.com -
trag＠io.com