Freezing an IC will modify its physical dimension but also will change its
electrical property.
From what you said I would guess that one of the timing of your design is
very marginal and most probably too slow.
When cooling some of the components the electronics actually goes faster
and, the timing being then correct, your design start to behave correctly.

Your engineer should review the timing of the design and can actually check
on the board what happens to the signals when applying the freeze spray.
But be carefull that probing on some signal will also change their
timing...

It may also well be that the timing problem is inside the PLD, to solve
that one the engineer got to redo some simulation with min and max timing.

Now freeze spray can also induce other circuitry to work. For example, an
analog circuit could start working only when cooled down because it was too
hot under normal ambient condition. Too hot because the design or assembly
is incorrect and the component is actually used outside its maximum
temperature rating...

The best way to find which component is faulty, is to use a slim tube and
spray directly on each component, making sure not to freeze the adjacent
one.
The component that will show the most effect on the fonctionnality is
likely to be the one you should look at.

Hope this helps,
Jean-Luc Lehmann



We recently received a prototype batch of 4 boards and experienced 4 for 4
failing test.  Our techs sprayed down certain chips with Freeze Spray and
the board began working properly, at least for a short period of time.  I
have checked prior tech net postings and have found fantastic responses as
to why Freeze Spray can damage a the IC or board, but can anyone explain
why
they would begin functioning properly.  Being a rookie component engineer I
can fully understand the issues related to freeze spray, but out techs and
design engineers are just going to point the finger since their units work
when sprayed.  To further complicate the matter the chips that are being
sprayed are not all the same manufacturer and I can easily rule out a
component failure.  Our senior engineer thinks that it may be timing
related
since the main circuit being froze is the Altera PLD (20K400E) and related
circuitry.

Can anyone defend the use of Freeze Spray?

Can anyone present a logical failure mechanism?

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

The best Freeze Spray argument to date was Werner Engelmaier's:
http://jefry.ipc.org/scripts/wa.exe?A2=ind9907&L=TechNet&D=0&m=23823&P=55370


However this points to failure after spray not the opposite.

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