>Has any one seen failures of chip resistors after 1-2 years where the
>junction between the silver termination and the restive
>element on the top of the ceramic has corroded through. This results in a
>high resistance failure after this period of time.
>
>I understand that some people in the automotive industry have seen this
>even on conformally coated boards, the example I have been
>examining is not in the same type of environment.
>
>Look forward to hearing from a few people, many thanks.
>
>

Bob,
I finished working with a client with a similar problem. Sectioning parts
parallel and perpendicular to the resistive element it looked like
inadequate polymer coverage of the PdAg metallization. The vendor stated
that the customers  solder profile was over 300 degree C peak and that was
the problem. Actually the assembly was reflowed in a forced convection
system with peak temps less than 230 degree C. Look closely at the
protective polymer coating.

Regards,


John Maxwell

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