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Reply To: | TechNet E-Mail Forum. |
Date: | Tue, 10 Sep 2002 07:56:00 -0500 |
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Peter,
In our experience bridging occurs because the BGA warps ("pancakes") during
reflow. Wrap is induced by CTE mis-matches between the materials in the
package. We investigated this problem in depth by conducting a series of
designed experiments. Here is what we found:
1. Use a baffled nozzle
2. Minimize air flow rates
3. Maintain temperature on top of BGA package at < 220C
4. Minimize time above reflow beyond supplier recommendation
We pay very close attention to the above when generating profiles to rework
plastic BGAs that are > 35mm. The bigger the BGA and the finer the pitch,
the more prone they become to bridging at the corners. Some parts have such
a narrow process window that we down-graded them to non-preferred status.
I'll be glad to discuss in more detail. Contact me offline.
Tom Buschor, Harris Corp.
Melbourne, Florida
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