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June 2008

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Subject:
From:
"Gumpert, Ben" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Gumpert, Ben
Date:
Thu, 5 Jun 2008 16:27:09 -0400
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text/plain
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text/plain (73 lines)
Werner,

What about my question makes you conclude that underfill is not needed?
Because I implied that the part is small by description of the solder
bump?

Why do you discount the need for underfill on small parts so easily?
There will be some stress induced in the solder joints due to CTE
mismatch, and although the strain in a small part will be exponentially
less than in a larger part, if the size and quantity of the solder bumps
are not enough to withstand the stress, then they will fail.

I am no expert on flip chip - are there industry standard designs that
ensure smaller chips will not need underfill?

Ben

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Thursday, June 05, 2008 3:36 PM
To: [log in to unmask]
Subject: Re: [TN] Chip on Board and Solder Mask

Hi Ben,
For the components for which the question was posed, you do not need
underfill.
Underfill have the function to put the solder joints of larger
components under compression, thereby imcresing fatigue life as well as
not showing functional failures even if SJs are fractured.



Werner
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, June 17, London
Interconnect Failures and Design for Reliability for PCB PTHs, June 17,
London Solder Joint Reliability: Parts 1 through 4, July 17/18, Thal,
Switzerland Pb-Free Soldering Processes-Survival, Quality, Reliability,
August 18, Orlando Reliability Issues with Lead-Free Soldering
Processes, September 22, Schaumburg Failure Mode and Root Cause Analyses
Reliability (Fatigue, Brittle Fracture, ENIG), September 22, Schaumburg



**************
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