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February 2001

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Subject:
From:
Trevor Goddard <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 6 Feb 2001 08:03:20 -0500
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Nicolas
 I have a couple of questions for you.
 Is this a new board or a new Rev of an existing product?
 Did you review the stencil design or did you actually have the stencil
measured?
 I got caught one time when I was given a new Rev of an existing product. We
had a couple of QFPs .20mm and a .50mm pitch  that were shorting out like
crazy, which was never a problem on the previous Rev. I questioned the guys
that ordered the stencil and the layout guys about what specs the stencil
was ordered to and if there had been a footprint changed. The answers to my
questions was that nothing had changed, but I could still not fix the
problem with process changes. Finally we were able to get the stencil
measured and the pad sizes measured and found out that the apertures on some
components were 100% of the pad size and another was a tiny bit bigger than
pad size.
 My guess is, if nothing has changed in your manufacturing process i.e..
screen printing parameters, reflow profile and your placement is good than
something may have changed in the design side.

Trevor
-----Original Message-----
From: Nicolas Ortiz [mailto:[log in to unmask]]
Sent: Monday, February 05, 2001 3:45 PM
To: [log in to unmask]
Subject: [TN] QFP144 solder bridging


Currently we are experiencing solder bridging on a 0.5mm pitch,  LQFP,  144
leads. I already reviewed the stencil design, screen printer parameters and
reflow profile. Everything is OK. We have HASL boards. Our current process
outputs 38 dpmo's. My concern is if I reduce more the apertures, I have the
risk to have solder open or insufficient solder, instead of bridging. Does
anybody has some input? What dpmo's do you have?

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