Homebrew PCBs

In a message dated 2/16/2004 9:31:08 PM Central Standard Time, 
joshdewinter@... writes:
Now I have another question...just as I was about to submit my 
circuits to a board house...I need a method to align my top and 
bottom sides.  Is there anything anyone does that works especially 
well?  I have looked through the messages from the group and have 
heard of people taping both top and bottom on, and running them 
through at the same time.  That sounds like it would work, but how do 
you align them accurately?
Drill the holes FIRST.

Or, if you MANUALLY drill all the holes (and break more $$ worth of bits than 
having the PC professionally-etched would cost!), and you MUST have the 
"copper pattern" present for drilling, then, using a light-box, place the negatives 
for top/bottom together, emulsion "inside", and tape them together along TWO 
sides, being careful to keep the "targets" aligned while taping.  THEN, just 
SLIP the sensitized blank between, clamp in a contact-printing-frame, and 
expose.  Remove, reverse, and repeat.  Now develop and etch.  

But, if redundant, if the holes are there FIRST, you could use the negatives 
"one at a time", and be CERTAIN of registration.   Yes, I realize drilling 
first would require either a home-brew CNC drilling rig, or the use of some kind 
of, say, self-adhesive pattern showing all the hole-centers.  And, sadly, most 
photo-copy machines will NOT sufficiently accurately copy a pattern for this 
purpose.  If you "draw" your pattern with an ink-jet printer, then print a 
copy on Avery 5265 (etc.) full-sheet adhesive-backed label-stock, and stick that 
to your blank, and drill.  The paper helps a tiny bit to "center" the bits as 
they enter the work.  A slow and kludgy method, but possible when the wallet 
is so severely challenged.          Jan Rowland


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