Hello, out there. 
How do we solder 80/20 Au/Sn without getting voids in the joint? The
three parts are:  #1 a Kovar Seal Frame with Gold over Nickel  #2 a
Gold/Tin Paste or a Gold/Tin 50um foil  #3 a gold metallised Alumina
substrate. 
        The results until now are not satisfying, even if they pass the
Helium Leakage Test (5 x 10 exp-8). The joint has voids and bubbles en
masse, and there seem to be no norm that tells what is accepted and not
in terms of void size and percentage etc...
         What is your experience of IR-belt, IR-batch and
vacuum-soldering in this case? Will plasmaetch or other cleaning be
necessary? Maybe the used solder type is not the best for this
application, which you can see is a MCM. I hope even this and such
questions are welcome among the dominating PWB issues. 

***************************************************************************
* 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]      *
***************************************************************************