To be more specific, the tests were originally designed to accelerate
corrosive degradation processes on contact surfaces. They were developed in
a hugh research programme led by the Battelle Institute in the eighties.
For corrosion of contact surfaces the test methods were proved to be
relavent and the acceleration factors are only valid for that case. For
other types of corrosion mechanisms, the relevance of the test has not been
evaluated to my knowledge. Since contact surfaces are not conformally
coated, conformally coated samples were included in the original work.
Electrochemical migration, which is on of the major failure mechanisms that
you want to prevent by conformally coating, would not be cover by the MFG
tests unless a bias is applied to the assemblies during the test.
Per-Erik Tegehall
IVF
SWEDEN
Phone: +46-31-706 6148
Fax: +46-31-27 61 30
Email: [log in to unmask]
Homepage: http://www.ivf.se
-----Ursprungligt meddelande-----
Från: Barmuta, Mike [mailto:[log in to unmask]]
Skickat: den 15 maj 2001 22:38
Till: [log in to unmask]
Ämne: Re: [TN] ISA-S71.04 G3 "Environmental Conditions for Process Meas
urements"
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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