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February 2010

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Fri, 12 Feb 2010 12:47:47 -0600
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TechNet E-Mail Forum <[log in to unmask]>, "Stadem, Richard D." <[log in to unmask]>
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"Stadem, Richard D." <[log in to unmask]>
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Not delamination of diebond.
Not overstress from CTE.
Not flexure stress from underfill void.

Possible flexure stress crack from ICT (but not functional test or HASS
testing)
Possible flexure stress crack from handling issues prior to underfill.

Probable flexure stress crack from too rapid cooldown during reflow, or
insufficient PWB support. The solder solidifies, but the board is still
sagging from heat, and as it continues to cool down after the solder has
solidified it straightens out and this puts enormous stress on
components. Note that the fracture is through the length of the die in
the horizontal axis. This indicates a horizontal stress movement.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Friday, February 12, 2010 10:45 AM
To: [log in to unmask]
Subject: [TN] Die cracks

Hi TN

We are in desperate need of QUICK expertise and/or opinions wrt the die
cracks that can be seen from the links below.  Sorry Steve, didn't want
to circumvent you but I've got to come up with an opinion by EOD.
BGA/CSPs were encapsulated in slow cure epoxy prior to excision.  We
section BGAs everyday and rarely see die cracks.
I've got to decide whether we should recommend that the CM build up a
few more for NDT (acoustics, CT..)

I know: max cool-down was probably 2.2-2.8C/ second; ICT was not strain
engineered or tested;  SAC305 balls, paste; parts passed ICT, ..but
cracks don't look to reach active circuitry
Don't know: laminate, peak reflow
Can't say: pretty much anything else

Thanks!
Chris

https://robisan.sharefile.com/d-s7b37c04078d4889b
https://robisan.sharefile.com/d-sc19f7716a0645489
https://robisan.sharefile.com/d-sb215d22cbf54972b
https://robisan.sharefile.com/d-s22d269ff34d4018a






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