William Alford <
walford@...> writes:
> I've built several vac hold downs over the years and the trick is to
> have the substrate supported everywhere.
Maybe I missed a bit of info... the first time I tested it, I had
nothing in it - just the glass panel with the gasket around the edges.
I guessed that the panel would be pulled down evenly, and I could
measure how far. What happened, obvious in retrospect, is that the
glass bowed down further in the middle. My solution, obviously, is to
use the pcb to support the middle of the glass. The trick will be to
support it enough but not too much - I want the glass flat on the
board at full pressure, not bowed down due to insufficient support or
arched over due to too much.
The gasket is 125 mil, the boards range from 8 to 65 mil, each sheet
of card stock is 8 mil, the film is a few mil, etc. So I can stack it
all up so that the glass is pulled down evenly over everything.