A source for research in the matter is 'ASM Corrosion Handbook Nr 13',
1,000 pages or more. Also 'Electronic Packaging and Corrosion' by Morris
E. Nicholson (ISBN 0-87170-291-6). You will find something there, I'm
sure. / Ingemar Hernefjord
        Ericsson Microwave Systems


--------------------------------------------------------------------
> I need help tracing the possible root causes for a circuit failure
from
> the field. Does anyone have any experience with open circuit traces
due
> to a silver sulfide corrosion concentrated at the juncture tin-lead
> solder joints and silver thick films? We are seeing this only on
joints
> that are low voltage potential. There is silver sulfide corrosion at
> other randomn areas, but the heavy corrosion is primarily at just a
few
> points where the solder and silver meet. Under the microscope, it
looks
> like a black worm crawling along the interface between the solder
joint
> & the silver thick film. We pot the circuit board in silicone gel to
> protect the circuit from moisture. So far, we haven't traced the
source
> of sulfur to any material that we use to make or to package the
circuit
> board.
> The packaging does not contain cardboard, so sulfur from the packaging
> is out. We meticulously clean the board after reflow soldering the
> printed solder paste, so flux is out. Is it possible that we are
getting
> sulfur gas from the enviroment? The environment is automotive,
> underhood. Is it possible that there is a galvanic action that is
> concentrating the corrosion to just a few solder joints?
> Thank you all for your time.
>
> ################################################################
> TechNet E-Mail Forum provided as a free service by IPC using LISTSERV
1.8c
> ################################################################
> To subscribe/unsubscribe, send a message to <a href="/scripts/wa.exe?LOGON=A3%3Dind9809%26L%3DTECHNET%26E%3D7bit%26P%3D1575917%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522%5BTN%5D%2522%26N%3D%5BTN%5D" target="_parent" >[log in to unmask]</a> with
following text
>  in the body:
> To subscribe:   SUBSCRIBE TechNet <your full name>
> To unsubscribe:   SIGNOFF TechNet
> ################################################################
> Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
section for
> additional information.
> For technical support contact Hugo Scaramuzza at <a href="/scripts/wa.exe?LOGON=A3%3Dind9809%26L%3DTECHNET%26E%3D7bit%26P%3D1575917%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522%5BTN%5D%2522%26N%3D%5BTN%5D" target="_parent" >[log in to unmask]</a> or
847-509-9700
> ext.312
> ################################################################
>

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to <a href="/scripts/wa.exe?LOGON=A3%3Dind9809%26L%3DTECHNET%26E%3D7bit%26P%3D1575917%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522%5BTN%5D%2522%26N%3D%5BTN%5D" target="_parent" >[log in to unmask]</a> with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at <a href="/scripts/wa.exe?LOGON=A3%3Dind9809%26L%3DTECHNET%26E%3D7bit%26P%3D1575917%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522%5BTN%5D%2522%26N%3D%5BTN%5D" target="_parent" >[log in to unmask]</a> or 847-509-9700 ext.312
################################################################