Nick, I can assure you that pretinning is not vasted. We have exactly the problem with a part now, like you just describe: gold/tin intermetallics. I'm frustrated and angry. The company that deliver should know better, they have own metallurgists, but made the following mistake: they solder mounted gold/nickel/kovar leads on goldplated copper pads, both parts with relatively thick gold. The solder has an extremly high content of Tin, which makes it worse. So, when the packages were tempcycled, microcracks developped under between lead and pad. If both parts had been pretinned or de-golded before the soldering operation, nothing like that would occur. Alternatively, one could use very thin gold in order to get less gold percentage in the solder joint. The parts I talk about are for military equipments, so we must have the whole batch of packages redone.

By the way, if you don't have Klein Wassink's Soldering Bible, you should buy it. Better than reading cryptic MIL specs.

Best wishes
Ingemar Hernefjord
Ericsson Microwave Systems



-----Original Message-----
From: Nick D'Onofrio [mailto:[log in to unmask]]
Sent: den 31 augusti 1999 15:26
To: [log in to unmask]
Subject: [TN] Pre-tinning gold leads
Importance: Low


  We are pre-tinning the gold leads prior to assembly on our military
products. I'm looking for some constructive data or argument to decide if we
should continue this practice.
  My concern would be gold embrittlement in the solder joint and any latent
failures attributed to this.
  Any comments or guidance in this matter would appreciated.

Regards,
Nick D.

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