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April 2003

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Subject:
From:
"Morse, Carrie" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 28 Apr 2003 11:20:37 -0400
Content-Type:
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text/plain (92 lines)
Dave,
Since we need to keep this forum technical, I won't get into
what happens when we "AssUme" a process is in control....

What are you masking with?  If you are masking with Kapton or something
similar you are likely imparting pressure on the top of the BGA.
When the BGA heats up and the sphere become liquid, the downward pressure
will cause bridging.  WHY are you masking?  Have you considered trying
the wave process without masking?

It may also be possible that solder is coming up through the vias.
How thick is the board and how large are the vias?  Are the vias
connected topside to the solder pads?

-Carrie

-----Original Message-----
From: Dave Chapman [mailto:[log in to unmask]]
Sent: Monday, April 28, 2003 10:03 AM
To: [log in to unmask]
Subject: Re: [TN] BGA


Happy Monday, I have a BGA 256 Tundra which has no shorts in SMT (we x-rayed
all 16 boards) When it goes over the wave we get a short or two. Please
assume the wave is in control.
We mask the topside of the BGA because there are a lot of vias which when
they test it would leak and not get pulled down good in the fixture. I need
the vias on the bottomside under the BGA to be filled with solder for
testing so I can't mask the bottom. What should I do?

Dave Chapman
Manufacturing Engineer
Circuit Service Inc.









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