Xref: utzoo rec.ham-radio:8369 sci.electronics:4976
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!rochester!kodak!ornitz
From: ornitz@kodak.UUCP (barry ornitz)
Newsgroups: rec.ham-radio,sci.electronics
Subject: Re: Repairing Intermittent Circuit Boards
Summary: Try a vortex cooler
Message-ID: <1677@kodak.UUCP>
Date: 1 Feb 89 20:38:24 GMT
References: <2910@hound.UUCP>
Reply-To: ornitz@kodak.UUCP (barry ornitz)
Followup-To: sci.electronics
Organization: Eastman Kodak Co, Rochester, NY
Lines: 41

In article <2910@hound.UUCP> wa2sff@hound.UUCP (J.WILKES) writes:
>The standard method to repair intermittents is to alternately heat up and cool
>down the circuit.   Heating is easy using a soldering iron or heat gun.
>However, the can of "freeze" stuff I had contained freon.  Since it is now
>positively known that freon destroys the ozone layer what chemical or process
>can I use to cool a PC board down.
>Does anyone have any ideas or know of non-freon based "freeze"?

The component "freeze" sprays are generally dichlorodifluoromethane, often
called Freon-12 or Refrigerant-12; they are one member of a family of fluoro-
carbons usually known as Freon.  Unfortunately the same chemical inertness
that makes it safe for electronic applications (non-flammable, low toxicity)
also makes it linger in the atmosphere for years before reacting to harmless
products.  During this time, it can interact with the UV-ozone reactions in
the upper atmosphere.

There are other chemicals with similar boiling points to CCl2F2 that might be
used as refrigerants in closed systems such as ammonia, sulfur dioxide, 
propane, and butane.  All of these, however, have severe problems with
toxicity, reactivity, or flammability.  Liquid carbon dioxide, as in the CO2
fire extinguishers, might be a good choice but high pressures and extremely
low temperatures are involved.  None of these materials are suitable as direct
replacements for Freon-12 in freeze sprays.

The best solution I can suggest is to use a voxtex cooler.  These units run
on compressed air, needing several cubic feet a minute at 50 to 100 psi.
They produce a stream of cold air at one end and a larger stream of hot air
at the other.  Several companies make these units specifically for the purpose
you describe.  One comapny that comes to mind is Vortec corporation; they make
several units capable of reaching -40 degrees (C or F - same thing!).  If you
look up vortex coolers, you may find them listed as Hilsch tubes coolers.
                                           Barry  WA4VZQ
 -----------------
|  ___  ________  |
| |  / /        | |  Dr. Barry L. Ornitz  UUCP:..rutgers!rochester!kodak!ornitz
| | / /         | |  Eastman Kodak Company
| |< < K O D A K| |  Eastman Chemicals Division Research Laboratories
| | \ \         | |  P. O. Box 1972
| |__\ \________| |  Kingsport, TN  37662       615/229-4904
|                 |
 -----------------