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January 2001

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Sender:	DesignerCouncil <[log in to unmask]>
Subject:	Re: Controlled depth drilling
From:	David Cary <[log in to unmask]>
Date:	Thu, 4 Jan 2001 18:39:06 -0600
Content-type:	text/plain; charset=us-ascii
X-To:	"Brooks,Bill" <[log in to unmask]>
Reply-To:	"DesignerCouncil E-Mail Forum." <[log in to unmask]>, David Cary <[log in to unmask]>
Parts/Attachments:	text/plain (36 lines)

That's a good idea, Bill Brooks. My assembly house makes[*] a new stencil -- a
piece of sheet metal with a bunch of rectangular holes punched in it -- for
every new board we give them. They use it to squeege just the right amount of
solder paste in just the right locations on my board.

[*] Actually, I think they outsource it to someone else. Since every board
assembly house needs these stencils, I imagine that converting a "paste mask"
Gerber file to a thin piece of sheet metal with lots of holes in it should be
pretty cheap -- high volume, high automation, etc. Sorry I don't know who
exactly makes these or what they charge for it.

"Brooks,Bill" <[log in to unmask]> on 2001-01-04 11:09:45 AM

...
Here's another thought... and something I have seen, bonding or just
loosely placing an etched aluminum sheet under the board.. it doesn't need
to be very thick... just enough to clear the via pads on the back
side...like .032 sheet stock.
Also I have done a board where we left the pads off the back side, and had
them countersink the vias from the backside, to gain clearance from the
chassis and ground plane. I think we had them screen soldermask into the
countersinked holes just to make sure... anyway keep coming up with ideas...
it's a problem without an elegant solution. Good to see you're still out
there designing.
...

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