GENERAL
INTEREST
52
Elektor Electronics
11/2002
Making your own PCBs is fairly straightfor-
ward when you make use of the readily avail-
able products on the market. When the board
is single sided, its exposure is easy. But for
double-sided boards the artwork films have
to be aligned precisely on both sides of the
board in order to make sure that the holes
drilled will be neatly centred in the copper
pads on both sides.
Most light-boxes are provided with align-
ment crosses to aid lining up the films. In
practise they were not found to be accurate
enough.
The light-box frame
The accuracy can be improved with the help
of this easily built light-box frame, which
allows both films to be lined up precisely.
The complete frame consists of
two frames, each with a pane of
glass onto which the film can be
stuck (
Figure 1
). When both frames
are on top of each other, the position
of the top one can be adjusted in
order to align the films. The position
of the top frame is then fixed using
two bolts and both frames can then
be taken apart for the PCB to be put
between them.
After that the PCB can be
exposed, either both sides simulta-
neously or one side at a time, turn-
ing the frame over halfway through.
The dimensions of the frame have
been chosen to give a snug fit in the
UV exposure box from Conrad Elec-
tronics (order number 53 06 89-33)
that has its existing window
removed. You can of course change
the dimensions for use with a differ-
ent type of exposure box.
The parts
The frames are made from two
pieces of 8 mm thick MDF. This
material can be easily worked on
without splintering. Cut out both
frames using a jigsaw. The openings
for the glass should not be cut until
the grooves have been milled out.
The dark grey areas in
Figure 1
have
to be milled to a depth of 3 mm using
a router with a straight cutting bit.
The diameter isn’t critical; 6 mm
seems to do the job well. If you can’t
get hold of a router you could also
use a sharp chisel and knife.
After milling the grey areas the
openings can be cut which will later
hold the glass panes. The holes for
the various bolts can also be drilled
now. All corners and edges should be
filed at an angle to give a neat finish.
The next step is the mounting of
the glass panes. This can be ordi-
nary window glass, which can usu-
ally be cut to size free of charge at a
hardware store or DIY store. The
thickness of 4 mm is very important,
since the glass has to stick out a lit-
tle above the MDF frame. This way
the films will be touching during the
alignment process. If the glass were
below the surface of the MDF frame
there would be a gap between the
films, which makes accurate align-
Double-sided PCBs
etch your own — trouble-free
By J. van de Kamer
This light-box frame can be easily built by anybody and lets you accurately
align films on double-sided PCBs.
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