Werner,
Yes, definitely agreed.
We and our customer had been ignoring this part of the study for that reason.  But, we have picked up on some planarity issues between the heat spreader (it’s rather thick) and the board.  Also the clips are rather low force.
So, brainstorming.. I thought there might be a differential compression across the BGA, combined with all the differential CTEs…  These things got hot.
Just a thought.
Wondering if anyone had been there and got the t-shirt already.

Chris

From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Tuesday, September 14, 2010 9:17 AM
To: [log in to unmask]; Chris Mahanna
Subject: Re: [TN] Bergquist Gap Pad

Hi Chris,
These clips would put the SJs into compression—that means that even when fatigued to fracture, you will not see a functional failure.
Werner



-----Original Message-----
From: Chris Mahanna <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, Sep 13, 2010 10:25 pm
Subject: [TN] Bergquist Gap Pad

We are working on a memory module FA.  Sandwich looks like this:







top of clip







Ni plated Cu heat spreader (goes across all 8 BGAs)







Gap Pad







8 BGAs in a single row







board







Gap Pad







bottom of clip














Has anyone seen more than [expected] damage after natural field cycling (maybe)







caused by the gap pad?  The material appears to be patented for low-modulus,







high W/mk  but...














Chris





















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