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October 2001

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Subject:
From:
David Douthit <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 8 Oct 2001 08:48:29 -0700
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Bill,

If you are trying to duplicate a "temperature sensitive problem" then cold spray and heat
guns will only work because they amplify stress until the failure becomes easy to detect.
Unfortunately  this can be a lengthy and harmful process. The best way to troubleshoot these
issues is to recreate the thermal profile at the time of failure and gently "bump" or move
the temperature around this point. I have found this process able to capture 90% of the
thermal related failures on the first attempt.

There is a device (that was called an X-Air) which is a hand held vortex generator. It
connects to 100psi clean (no oil and dust free) shop air and puts -40 degrees C out of
one end and hot air out the other. The temperature could be controlled by how far the nozzle
was from the target. The other advantage was there was an endless supply  (at
virtually no cost) of cold and hot air for testing.

This process requires a little patience because the rate of temperature change is very slow
in polymers. The failures will occur within 20 degrees C of the original temperature.

David A. Douthit
Manager
LoCan LLC



William Raymond wrote:

> Hello all...
>
> I’m in need of some opinions. Our test and repair department (functional
> test) uses a cold spray (from a can) and hot air guns (heat-shrink heat
> guns) to heat and cool BGA devices (plus other IC devices like QFP’s, etc)
> to help diagnose boards that fail functional test.  I’m trying to make the
> point that this practice is very risky, especially to BGA type devices
> because of the severe stress applied to the solder ball connections.  The
> application of cold spray and/or hot air from a hand held heat gun are both
> VERY uncontrolled processes and should be eliminated from our procedures.
> Would anyone out there be willing to share their views and/or experiences
> with this?
>
> Thanks in advance,  Bill
>
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