Transcript Preparing Printed Circuit Boards (PCB's) for Flight Computers

Preparing Printed Circuit Boards
(PCB’s) for Flight Computers
AEM 1905, Fall 2008
Begin with copper-covered plastic
sheet called PCB Laminate
Cut the PCB Laminate to size
(I used a radial-arm saw).
Deburr the edges (I used a Dremel
tool with a grinding stone on it).
Print the circuit pattern in ink with a
laser printer onto glossy photo paper.
Scour the boards with a Scotch-brite pad then
rinse with acetone. Notice the fingerprints on
the board which has not been scoured yet.
Prepare a pattern to be ironed onto a board.
Use an iron (no steam!) on the hottest
setting to iron the pattern onto the copper
surface. Press down hard for about 3 min.
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.
Soak the board in hot water for about 10
minutes to soften the paper for removal.
After soaking, remove as much backing
paper as possible with the fingers. The ink
pattern will stick to the copper below.
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.
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.
Copper etching is done in a fume hood
while taking proper safety precautions.
Etching is done with a solution that is two
parts hydrogen peroxide to one part muriatic
acid. Acetone is used for clean-up.
Used etchant (and used acetone) are
disposed of as hazardous waste.
When immersed in etchant for a few minutes
the exposed copper is dissolved. This board is
not quite done near the bottom edge.
Continuously agitate the solution while
etching, always wearing gloves. The etch
solution turns greens from the copper.
Here is a demonstration board that was intentionally only dipped half-way into the etchant.
Here is a fully-etched board, ready for
clean up. The plastic under where there
used to be copper is actually white.
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.
Drill holes in the PCB (I
use a Dremel tool drill
press and a #64 bit for
use with PCB’s).
Drill gently – it is easy
to break off a drill bit
that small.