It sounds like a board warpage problem on the larger design.  Can you up
the thickness (0.093" or 0.125") on the design to add a little strength
and reduce the warping?  I've seen under extreme temp. cycling that the
extra thickness on the PCB helps warping thus reducing cracked
components.  This wouldn't be a problem on the smaller boards 2" x 2"
due to it doesn't fluctuate that much with warping.

Just an idea.
John

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Tuesday, January 31, 2006 8:32 AM
To: [log in to unmask]
Subject: [TN] Large SMT physical failure prevention


Good morning,
 
We have some designs that are calling for large, 1825 and 2225
components.  We have seen some mechanical failures where the parts have
cracked.  If we need to use these monster components, how do we ensure
we reduce or eliminate the mechanical failures.
 
Our failures were seen on a 16 inch by 17 inch 0.062 thick board.  On
these we have changed our handling methods.
 
On smaller 2 inch by 2 inch boards is this a don't care?  I know that
rapid temperature ramp up or down in the reflow process could be a
killer.  Something to work out with our CM.
 
Phil

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