Preparing Printed Circuit Boards (PCB

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Preparing Printed Circuit Boards (PCBs) for
Flight Computers

• AEM 1905, Fall 2008

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Begin with copper-covered plasticsheet called
PCB Laminate
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Cut the PCB Laminate to size(I used a radial-arm
saw).
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Deburr the edges (I used a Dremeltool with a
grinding stone on it).
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Print the circuit pattern in ink with a laser
printer onto glossy photo paper.
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Scour the boards with a Scotch-brite pad then
rinse with acetone. Notice the fingerprints on
the board which has not been scoured yet.
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Prepare a pattern to be ironed onto a board.
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Use an iron (no steam!) on the hottest setting to
iron the pattern onto the copper surface. Press
down hard for about 3 min.
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Another option is to iron the pattern onto the
board rolling on a dowel easier to apply more
pressure to every point on the board.
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Soak the board in hot water for about 10 minutes
to soften the paper for removal.
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After soaking, remove as much backing paper as
possible with the fingers. The ink pattern will
stick to the copper below.
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After cleaning off as much paper as possible by
hand, use a toothbrush to scrub the surface some
more. The ink should not come off the copper at
all during this process.
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Here is a set of boards, ready for etching. The
ink serves as a etch mask to protect the copper
when it is submerged in etchant.
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Copper etching is done in a fume hood while
taking proper safety precautions.
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Etching is done with a solution that is two parts
hydrogen peroxide to one part muriatic acid.
Acetone is used for clean-up.
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Used etchant (and used acetone) are disposed of
as hazardous waste.
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When immersed in etchant for a few minutes the
exposed copper is dissolved. This board is not
quite done near the bottom edge.
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Continuously agitate the solution while etching,
always wearing gloves. The etch solution turns
greens from the copper.
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Here is a demonstration board that was
inten-tionally only dipped half-way into the
etchant.
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Here is a fully-etched board, ready for clean up.
The plastic under where there used to be copper
is actually white.
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Use acetone to wash off the ink etch mask. At
right is a set of finished boards, all of which
have been etched (because the plastic looks
white) but only 3 of which have been cleaned.
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Drill holes in the PCB (I use a Dremel tool drill
press and a 64 bit for use with PCBs).
Drill gently it is easy to break off a drill
bit that small.