Bill,
I absolutelly agree with you about the hygroscopic nature of the polyimide. If boards are not baked prior to soldering we get quite ugly delaminations. That is very right, and that's why the phenomena described in my original message was so puzzling:

Two years ago the boards were received in the assembly shop with reflowed Pb/Sn finishing. There was NO sign of measling, delam, etc. The lot was 100% visually examined.

Last month some boards from the ORIGINAL LOT were taken out of storage and showed signs of measling/delam. This was WITHOUT subjecting the boards to any thermal or mechanical shock. As if the delam was developed during storage.


Even with the highly hygroscopic nature of polyimide this seems very inprobable to me (they were not stored in an aquarium !!). I haven't heard of such a failure till now and I can't find a mechanism that describes it.

Can you or any of the technetters offer an explanation ???

Yehuda

    ************************************* 
    *          Yehuda E. Weisz              
    *  e-mail: [log in to unmask]
    *  Tel: 972-3-5240362                    
    ************************************

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* 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]      *
***************************************************************************