Paul: This type of testing is commonly caled Mixed Flowing Gas or MFG.
This test simulates environmental exposure through controlled temperature,
humidity and the introduction of trace quantities of corrosive gases in an
enclosed chamber. It is designed to accelerate corrosive degradation
processes. Measured hours of chamber time can be correlated to years of
exposure in the field.

There are increasing degrees of severity for different environmental
exposures ie business office, light industrial, refinery, water treatment
plant etc. These are called out as method G,H and K, with increasing
corrosive effects. Gases used are H2S, SO2 and chlorine in ppb ranges. These
then contribute to varying degrees of oxidation and corrosion of the PCB.

We have used the Microelectronics Div of IBM, Endicott N.Y.(800-934-0104)for
our testing. This was a few years back, not sure if they are still around.
There are other that can do the same testing.



Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076

-----Original Message-----
From: Paul Bannister [mailto:[log in to unmask]]
Sent: Tuesday, May 15, 2001 11:36 AM
To: [log in to unmask]
Subject: [TN] ISA-S71.04 G3 "Environmental Conditions for Process
Measurements"


Does anyone have information about the effects of corrosive gases on printed
circuit board assemblies.  Specifically what I am interested in is what
happens to PCB's when exposed to corrosive levels as described in ISA-S71.04
G3 (Harsh) specification, what is the failure mode?  We are conformally
coating our printed circuit boards now to meet this specification but it is
not clear to me what would happen to the PCB if it were not coated.  Do
people meet this specification without conformal coating?
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