Carl,

I quit using "freeze cans" for troubleshooting because they did not work very well particularly on
conformally coating products.

When a "thermal failure" occurs it happens at a particular temperature or during a specific temperature
change. Because polymers
require much more time to change temperatures I discovered that freeze mist would "shoot by" or run
past the thermal failure point.
It would then require a long time to stabilize the circuit and try again. I used the EXair because I
could control
the temperature change by varying the distance from the nozzle to the circuit, had an endless supply of
"cold", air and very little if any
frost/moisture on the circuit. I discovered that 90% of the thermal failures could be "found" by
recreating the thermal conditions at time of failure and gradually "bumping" the temperature around
this point. I seldom had to go more than + 20 degrees C from the estimated thermal fail point to
recreate the failure.

Conformal coatings will "hold" joints in place until a certain thermal point is reached. Usually this
is a "window" because as the coating dimensions change
the joint will "make and break" contact.

Hope this helps!

David A. Douthit
Manager
LoCan LLC


Carl VanWormer wrote:

> According to the site:
> http://www.emsdiasum.com/ems/clean/duster.html
> The stuff I'm using claims "100% ozone-safe pressurized duster products".
>
> Since I turn the cans upside down (or refill my quick-freeze cans for a more
> convenient spraying position), am I being more gentle to the environment?
> If so, we can get down to the real question of "am I wrecking my electronics
> systems by using quick-freeze for troubleshooting?"
>
> Carl Van Wormer
> Cipher Systems
> 1815 NW 169th Place, Suite 5010
> Beaverton, OR  97006
> Phone (503)-617-7447    Fax (503)-617-6550
>
> -----Original Message-----
> From: Brian Ellis [mailto:[log in to unmask]]
> Sent: Friday, April 26, 2002 2:52 AM
> To: [log in to unmask]
> Subject: Re: [TN] Freeze Spray Trouble Shooting
>
> Bev
>
> I agree PFCs are the worst climate changers (with SF6) that exist. Some
> of them are over 10,000 times worse than CO2. As a rule of thumb, 6
> freezing cans which contain a PFC gas would have as much effect on
> climate change as a medium car over its whole lifetime (horrific
> thought). Furthermore, there will still be the contents of two of those
> cans in the atmosphere 40-odd generations from now (assuming man lives
> for another 40 generations!). However, I think most freezing cans
> contain HFC-134a, which is bad enough but not as bad as PFCs. Some may
> still contain HCFC-22 which is just as bad AND an ozone depleter, to
> boot, but is not phased out under the Montreal Protocol until 2010 (some
> countries may phase it out sooner).
>
> Brian
>
> ---------------------------------------------------------------------------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> ---------------------------------------------------------------------------------