Homebrew PCBs

In a message dated 3/24/2004 9:03:44 AM Central Standard Time, 
geovar13@hotmail.com writes:
The board an't een etch yet but I wondering if I should drill the holes fist 
that way I can add more resist in case I screw up.

   My second question is about sharpie pen. When I was transfering my desing 
a few pads and trces did not transfer properly. I took a sharpie pen and fille 
in the missing gap. Will the sharpie resist ferric cloride or will it fail?

Geo:

There are surely OTHERS "in here" with more experience on these details than 
I have, but perhaps I CAN help a bit, anyway:  I have drilled AFTER etch, AND 
before, using the holes as "center" for resist-laydown.  There are small 
advantages and DISadvantages to both approaches for us hobbiests.  HOWEVER, as you 
may know, when professionals do even single-sided NON-PTH boards, they DRILL 
first, and then etch.  The holes serve as "targets" for laying on the film for 
photo-resist exposure.  This is probably the better method, IF you can drill 
accurately.  I use a home-brew CNC drill, myself, so all the holes are within 5 
tenths repeatability.  But I often do very small single boards where I don't 
even use film, but put the resist right on the copper with a pen, such as the 
R.S. resist pen, or the Städtler red pen kinda thing (I'm gonna go buy one 
today, if Office Despot stocks those!).  I have used "Sharpie" pens in the past, 
but they must be BRAND NEW and "fresh" (don't leave the cap off long, each 
time!), and you have to "press LIGHTLY" so as much ink is laid down for each mark 
on the copper!  Also, the copper should be scrubbed clean with some 
mildly-abrasive cleaner like Comet, etc., and RINSED very, very well!  Keep your 
pinkies OFF the copper!  Dry with CLEAN paper- or "let dry" in air before applying 
resist.  And, yes, the Sharpie is NOT very durable for this application, but it 
WILL work "kinda OK" for FeCl³ if you are VERY careful.  The marks should be 
so black (or whatever color) that NO copper shows through at all.  This 
becomes difficult after a sharpie has been OPEN a total of an hour or so (and 
probably no good at all if left open the WHOLE hour at ONE time!

Lotsa luck!  By the way:  If you want to make only ONE board, never to be 
copied, the DATAK or Radio Shack pressure-applied resist-patterns ("rub-off 
letters" kinda stuff they make) is EXCELLENT, if you use CLEAN copper, and rub-down 
"again" using the waxy "backing paper" between the applied pattern and your 
burnishing-tool (thumbnail?).  

Jan Rowland
Old Troll


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