Re: gEDA-user: wacky (or not?) solder stencil ideas

[DJ Delorie <dj@xxxxxxxxxxx>]

> Actually, TechShop is gearing up for franchising.  By next year this
> time, you, too might have a TechShop close by.  Warning: time sink
> ahead. :)

Are you kidding?  I don't even have a Starbucks nearby.  Not that I
wouldn't mind opening a TS franchise, but I don't think there's enough
market for it around here.

> No, I believe they are YIG laser.

Ah.

> Does the undercut really make the stencil unusable?

It makes the stencil more... unpredictable.  The shape of the sides
means that the masked side must be towards the board (else the angled
sides won't release the paste), so the "hole" size is always going to
be bigger than the actual resist opening.  Thus, you have to shrink
the resist by some fraction of the thickness of the foil, the fraction
depends on the etch technique (different techniques have different
amounts of undercut) and the precision of your plot.

http://www.delorie.com/pcb/brass/20070221-60-top.jpg

For my sized boards, I usually end up with one web etched through
somewhere and one hole elsewhere not etched through.

> What kind of photo resist? Got a pointer?

Any kind of dry-film resist should do.

> I've tried 65# card stock, mainly because it was handy.  Too thick
> for a stencil, 40# might be about right?

20lb is 4 mil, just right.

> I'm concerned about contamination from carrying ash residue 
> into the solder joint.

Flux should fix that?


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