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September 2003

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Subject:
Re: stencil
From:
Dave Chapman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 5 Sep 2003 07:15:36 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (127 lines) 
The QFP butts right up to a resistor network on the bottom and a connector
on the top. On either side are resistors so not much room for a step down
but will look at it further, thanks Mike.
DC

-----Original Message-----
From: Mike McMonagle [mailto:[log in to unmask]]
Sent: Friday, September 05, 2003 7:09 AM
To: [log in to unmask]
Subject: Re: [TN] stencil


Dave,
        Have you considered using a 6 mil stencil, with the QFP area
stepped down to the .0040 - .0045 range? Use it with a moderately high
(~90+) durometer bonded (not clamped) poly blade, and provide as much
clearance for the step down area as possible. Taking the thickness down
for the QFP will also give you room to shave a little off the aperture
width and still get acceptable release. Have fun....

Mike McMonagle

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Chapman
Sent: Friday, September 05, 2003 6:41 AM
To: [log in to unmask]
Subject: Re: [TN] stencil


Well, we have our first 16 mil fine pitch device, 128 pin QFP. I am
worried about printing shorts on a 6 mil stencil. Everything else on the
board is 20 mil or better so 5 mil is not good idea. we normally do a
10% reduction and round the rectangles for better release. The pad width
is .7 mil, I would be pushing 6 mil with the reductions, when our normal
rule is on 20 mil pitch do not reduce overall width to less than 9. If I
don't reduce the width I'm sure we will get shorts. Am I going to have
problems if we leave the width alone and only take the reduction in
volume garnered by rounding the  rectangles? Dave C.

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