At 04:00 PM 1/8/97 +0800, you wrote:
>Hi, 
>Recently we encountered some assembled PCB returned from the field where 
>humidity is high and temp is low. Some vias and pads were found to be corroded 
>with copper chloride after SEM analysis and when corrosion production were 
>removed from the board, the affected part of the vias was degraded.  This has 
>greatly affected the performance of the circuit.
>The fabrication house claimed that they are not liable as there was not
chloride 
>chemical used in their processes.  
>Does anyone has any insights to share?  Could the assembly process
contribute to 
>this corrosion?
>
>Thanks in advance for any information shared.
>
>
>stella yap


Stella,
   Lets visit the obvious first.  If your assembler uses humans, he has a
source of chlorides with every finger print.  If the area is small and in a
likely spot for such an event, that may be the answer.  Somehumans are more
acidic/corrosive than others, ask Dilbert.
   Second, lets visit his flux.  Although many flux suppliers claim their
flux does not contain chlorine, what they actually mean is that their flux
does not contain amounts of chlorine compounds that will cause it to fail
the silver chromate test from the milspecs.
   Third, your vendor may be right, but don't let them know that.  If the
PWB was HASL finished, it may be chock full of nasty stuff.  If you need a
difinitive answer as to the root cause of the problem, there are outfits who
find the needle in the hatstack for you.  I have used some and would gladly
state my opinion privately.

Steve Mikell
SCI Systems
Government Division, Plant 13
[log in to unmask]








***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************