Mary:
What kind of resistors are these (e.g., polysilicon, cermet, etc.)? Next, to
chloride. Other than some historical belief that chlorine is electrically
bad (which I agree with), what evidence do you have that it's chlorine?
I would suspect the silicone first and foremeost. Silicone (organic,
carbon-bearing silicon) is highly mobile and attracts a wide variety of
contaminants due to its oxygen content. These two factors allow for all
sorts of materials to attach themselves at the molecular level to the
silicone and migrate within the matrix. Chlorine is certainly one example;
however, do not dismiss the other halides, especially bromine (usually found
in fire retardants as well as most synthetic fluxes). Inaddition, depending
on the specific type of reistor material in use, you may have some regrowth
as well, either empirical gfrowth such as happens on semiconductors, or a a
function of flux winds (such as electromigratory metals or dendritic
formations).
I know this merely muddies the waters, but you didn't give us a lot to go
on...
Bill Davis, Ph.D.
Principal & Vice President,
IP Managers, LLP
(408) 325-7868/321-4681
-----Original Message-----
From: Davis, Mary M. [mailto:[log in to unmask]]
Sent: Friday, August 06, 1999 1:12 PM
To: [log in to unmask]
Subject: [TN] Leakage in resistor networks
Lately, we are experiencing leakage (low resistance values and noise) at
temperature in laser trimmed resistor networks which have been potted in
silicone. As received, parts test out O.K. The parts are hand soldered
into an assembly using RMA flux, cleaned in a vapor degreaser in AK225AES,
coated with silicone primer and then potted in silicone. I know resistor
networks are very sensitive to chloride contamination. I suspect a sensitive
enough test will find a number of sources for something as common as
chloride but how much is too much? Any suggestions on how or where to look.
We are going to try testing parts at various stages of our process to try to
isolate the problem but I suspect we are looking for something that is very
subtle.
Your suggestions will be greatly appreciated.
Mary M. Davis
Materials & Process Engineer
ELDEC
[log in to unmask] <mailto:[log in to unmask]>
425-743-8327
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