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March 2005

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Subject:
From:
Sri Maganti <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Sri Maganti <[log in to unmask]>
Date:
Thu, 24 Mar 2005 13:37:48 -0800
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We had a similar issue, but in our case we had BGAs bumps instead of the
leads.
our symptom was overheating as the thermal slug did not get soldered
properly, as the the stencil specifications
was not correct ( thickness and aperture ). So we had insufficient
solder.  We opened up the aperture and added
a test pad to check( at ICT)  for continuity and hence positive contact
of the solder and problem went away.

However in the process of trouble shooting the issue, we also visited
the coplanarity spec. The general rule
of thumb is when you print 6 mil paste and reflow, one could approximate
50% reduction in height and in our case
4 mil gap made a positive contact of the solder bumps and the slug.

This is my 2 cents worth.

thanks

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