Ingemar, I always believed the Ag layer to be essentially a "flash" to cheaply (rather than gold) passivate the solderable Nickel layer, with the Cr/Ni-Cr layer being the adhesion layer to the silicon. Like a gold passivation, the silver should immediately go into solution and allow the solder to wet to the underlying nickel layer. Once alloyed, it should create no more of a migration problem than silver bearing solders like Sn62/Pb36/2Ag - should it??? Guess, I will have to re-check my assumption that it is a 'flash' of silver. Regarding use of conductive adhesives - while it does seem rather silly to attach (a generally high-power device) with poor thermal and electrical conductivity polymers, we have done it (rarely) for those occasions that did not require sustained current handling capability. I believe they were more of a Commercial application than Military, however. Definitely not Space or Implantable applications. At least the silver presents a more chemically bondable surface than does pure gold, for example. We even used some of the silver-glass materials for a Mil application, but the die were only ~3mm square. Die were mounted on moly-tabs (spreaders) to facilitate re-work, if required. The tabs were adhesively bonded with traditional Ablebond 84-1 series adhesive - now that the thermal capacity and 'contact' area was increased by the tab. Steve Creswick At 03:49 PM 6/7/00 +0200, you wrote: >Short q: Ag/Ni/Cr, what do you like that chip backsides for attaching power FETs? Ag is 90%. Unusual? IRC make such backside metalizing. Wonder why...I'm somewhat concerned, Ag migration and strange intermetallics may occur, depending on what solder or glue you use. Anyone mounting these creeps? Steve? >Ingemar Hernefjord >Ericsson Microwave Systems > >############################################################## >TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c >############################################################## >To subscribe/unsubscribe, send a message to [log in to unmask] with following text in >the body: >To subscribe: SUBSCRIBE TECHNET <your full name> >To unsubscribe: SIGNOFF TECHNET >############################################################## >Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional >information. >If you need assistance - contact Keach Sasamori at [log in to unmask] or >847-509-9700 ext.5315 >############################################################## > > ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################