There isn't much to my system. I use an Epson colour printer with Rapid
Electronics inkjet transparency. I found that green works best. Black
and red both seem to have a crazing effect which can cause broken
tracks. This is with the new Durabrite inks. The older inks seemed to
work better but my old Stylus Color 600 died. The layout has to be
printed so the ink side goes towards the board.
The light box is a simple wooden box with four UV tubes about 100mm
under sheet of glass. There is a sheet of aluminium foil under the tubes
to reflect the light upwards. There is a lid to clamp the board in place
while exposing it and I found that a couple of layers of bubble wrap
between the lid and board gives a good even pressure. When you first set
up you need to work out how long an exposure is needed. This is pretty
simple. Print a layout and stick the transparency to a piece of board
with sticky tape. On the back of the board make a series of marks,
roughly even spaced. About 7 or 8 will probably do. Place it in the
light box with a piece of aluminium foil between the board and the
glass, with one edge lined up with the first mark leaving a small strip
exposed. Expose the board for 1 minute, move the strip to line up with
the next mark, expose for 1 minute and so on. You now have a board that
at one end has been exposed for 8 or 9 minutes and the other end that
has only been exposed for 1 minute. When you develop the board it is
quite easy to see where it is under and over developed. Find the best
part of the board and you will know how long you need to expose the
board. This is a bit tedious but you only need to do it once. Some
boards are very sensitive so you may have to repeat the experiment using
different timing.
Exposure time varies as the tubes warm up so I usually turn them on
10-15 minutes in advance to give them time to warm up. I use precoated
board and I can recommend Microtrak board from Mega Electronics - I
think It is actually made by Bungard. It has a thin coating which
reduces undercutting and the resist coating is fairly tolerant to
under/over exposure. Developer is a level teaspoon of caustic soda
granules in a litre of water. A few drops of detergent added to the mix
helps the developer wet the surface. I drop the board in a tray, add
enough developer to cover the surface then rock the tray. As developing
progresses you see streaks of darker resist appearing in the developer.
Once they stop appearing the board is done. A quick dip in the etch tank
will hilight any areas that have been missed.
I normally use .012" track+gap (~0.3mm) because I know it is reliable.
0.25T&G shouldn't be a problem. The most important thing is to get a
good quality print out of your printer. I tried a Lexmark and that
produced a very fuzzy print.
Les
about 100mm awa
Jim Miller wrote:
>Hi Les
>
>Is your method written up somewhere?
>
>What sort of linewidths do you have success with? I'm looking at doing some
>work with AD9958 this winter and it has 0.25mm pads on 0.5mm pitch.
>
>tnx
>jim
>
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