Don't think surface with silver sulphide will cause short circuit,
should be other cause.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Wednesday, 25 May 2011 9:38 PM
To: [log in to unmask]
Subject: Re: [TN] Silver Sulfide contamination
Leif Erik,
When you indicate that you confirmed the failure due to silver sulfide
do you mean that you can see silver migration or silver sulfide
corrosion products shorting features or corrosion causing an open
circuit? I couldn't tell from your email if the exposed silver on the
resistor network was corroding and causing an open circuit or if silver
had migrated causing a short circuit. It is not uncommon to see tarnish
and or silver sulfide corrosion on products with exposed silver.
However, the only failures we've seen were primarily due to ionic
residues left behind from assembly processes causing creep corrosion.
When residues aren't present we still see various degrees of silver
sulfide on silver surfaces from a light tarnish to a heavy Brown/Black
appearance depending on the amount of air pollution and exposure time
but no migration or detrimental corrosion.
Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum
Sent: Wednesday, May 25, 2011 9:12 AM
To: [log in to unmask]
Subject: [TN] Silver Sulfide contamination
Technetters,
We have confirmed that a returned product from the field has failed die
to silver sulfide contamination.
The conclusion from the analysis is:
Based on the analysis performed, the "black" contaminant material is
silver sulfide, a common silver corrosion product. This corrosion often
occurs when silver plating is exposed to atmospheric pollution that
contains high levels of sulfur compounds (exhaust from fossil fuels).
We have confirmed that in particular resistor networks are susceptible
due to the silver content that apparently is exposed on the top of the
component. We have not observed issues with any other component types.
The obvious answer to how to protect a product in this environment is to
use conformal coating. However, from what I have read there are only
very few coating materials that can actually protect from silver sulfide
corrosion. Epoxy based conformal coatings is the only ones that will
successfully pass ASTM N 809 test. My question to the experts is if
there are other solutions or coatings you have been successful with or
if someone has actually solved this issue in different ways. It seems
this should be an important issue for the automotive electronics
industry.
Some one suggested using solder to cover the component, but I can not
understand how that could work.
As always, thank you for your insight.
--
Leif Erik Laerum
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