Homebrew PCBs

At 09:44 PM 3/21/2009, DJ Delorie wrote:
>  converted my UV exposure box to vacuum hold-down.. . . the glass bow in so
>much I feared it would break!

i've built several vac hold downs over the years and the trick is to 
have the substrate supported everywhere. one way i did this was to 
take a piece of good quality flat plywood and cut parallel groves 
with a table saw in both directions about 1/8 inch deep on one side 
across the entire face of the board. (say, 1/2" apart) spray it with 
acrylic or some other sealer to seal the wood, drill a 3/4" or 
whatever size hole you need to connect to the vacuum line in the 
center of the board and then glue a piece of Formica on the top of 
the grooved side carefully so's not to get glue in the grooves (i 
used contact cement on a 2 ft x 3 ft table that lasted over 20 years 
for screen printing). now you can see from the edges where the 
grooves are and draw pencil lines across the formica and use these 
guides to drill 1/16" holes across the entire surface over the 
grooves beneath. now tape up the edges to seal the ends of the 
grooves and attach the vac hose (maybe with a 90 degree connector). 
you will have to put wooden feet on the bottom so the hose can exit 
from beneath and keep the board sitting level. now whatever size 
board you place on the top, just tape around it's edge to seal off 
the uncovered vac holes and any size board can be accommodated. if 
you want to expose negs to photoresist, you can also place a piece of 
flexible clear plastic over the top of the board/litho neg sandwich 
that covers the entire hold-down surface and get perfect contact for 
exposures. i used to use sunlight to expose and place a toy dart 
stuck on the top edge of the board to orient to the sun. when you 
move the board so that the shadow of the darts shaft disappears, the 
board is exactly perpendicular to the sun's rays. i now have access 
to some free corian and will build one from that which has a 
perfectly flat and smooth surface.


William Alford

GI Motility Medical Research Page
http://alford.grimtrojan.com/ 

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