Hi Randy,

I recommend that for you to ensure that you have a reliable design configuration
existing you proceed as follows:

First, I would start with performing a thermal elastic structural stress
analysis and then I would perform an engineering evaluation test that exposes
the CQFP device to an appropriate type of accelerated environmental testing with
the CQFP mounted to its PWB.

The weakest link I believe for the CQFP is relative to the CQFP's dimension
"A2", which states that it is 5-mils to 15-mils high.  Of course, this assumes
that the ASI data sheet (page 19) for the CQFP, that refers to the "A2"
dimension is truly relative to the vertical height of the lead wire from the
surface of the pad on the PWB to the bottom surface of the CQFP's body.  In my
opinion the "A2" value is an extremely short vertical height beam, and may not
provide the proper stress relief to ensure adequate fatigue life survival during
and after exposure to the appropriate temperature cycling, temperature shock or
vibration environmental conditions.

Hope this helps.  Good hunting!

best regards,

faz

____________________Reply Separator____________________
Subject:    [TN] CTE mismatch issue
Author: "Mummert; Randy" <[log in to unmask]>
Date:       12/18/2002 11:04 AM

Hi,
I've been analyzing a fractured solder issue and I just received data
concerning the CTE of my PWB and the device in question.
The CTE of the PWB measured 23 in the x-y plane and the CTE of the device
measured 5.8 in the same plane.
The device measures 25.4mm lead to lead. I calculate the difference due to
CTE mismatch at delta-T 100C to be:
PWB    23E-6 X 25.4mm X 100C =    .0584mm
DEV    5.8E-6 X 25.4mm X 100C =    .0147mm
delta distance is the difference =        .0437mm

My question is - what is a reliable ratio between CTE mismatch and point at
which the IC leads will move? My best estimate is that the IC leads will
move by 0.25mm. Is my situation a reliable one?
Thanks in advance,

Randy Mummert




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