layer after which the unused pads can be
removed manually.
Using the light-box frame
After both films have been printed they can
be cut to size using a sharp knife. Leave
enough of a margin round the actual board
dimensions. The corners of the film are stuck
to the glass using sticky tape. Something that
should be avoided is for a corner of the PCB
to lie on top of the sticky tape. In this case
there will be a gap between the film and the
light sensitive layer, causing the tracks to be
over-exposed in that area.
With both films stuck to the glass panes
the wing nuts are loosened such that the alu-
minium sliders can move freely. Put the
frames on top of each other with the V-
shaped holes of the sliders going over the
pins. Now it’s just the case of moving the top
frame until the films are aligned. Once the
correct position has been found the sliders
should be moved tightly against the pins. The
wing nuts are then tightened and the align-
ment is complete.
The protective films on the PCB should be
removed in a dark room. The top frame can
now be removed from the bottom frame, tak-
ing great care that the sliders don’t move! Put
the PCB onto the bottom film (avoid-
ing the sticky tape) and replace the
top frame again; this should auto-
matically stay aligned with the bot-
tom frame.
The films are pressed tightly to
the board by using two thick elastic
bands to force the frames together.
That is the purpose of the fork
shaped cutouts in the corners of the
frames.
And finally
After the exposing, developing, etch-
ing and drilling we end up with a
PCB that has its drilled holes neatly
in the centre of the pads on both
sides. Through-plated holes can be
made as usual, by soldering compo-
nents on both the top and bottom
side of the board at specific places.
(020132)
GENERAL
INTEREST
54
Elektor Electronics
11/2002
Figure 3. Close-up of the stay-peg/slider/wing nut.
Summary of Contents for EPROM
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