Reply to:   RE>goldfinish on PC boards

Wolfgang:

A general rule to follow is, "If the gold content of the solder joint  is less
than 2% by volume, the solder joint will have long-term reliability".  With
gold greater than 2%, the solder joint will become brittle and subject to
cracking under thermal and/or mechanical stresses over the life of the
product.  This is based on an extensive test report published by Hewlett
Packard at least 5-7 years ago.  I do NOT have the report number.  Maybe
someone has a more recent report on the subject.

Solder paste is ~50% by volume metal (90% by weight).  Based on that rule, a
board with 30uinch of gold must have at least 0.003" of solder paste to have
good, reliable solder joints.

Good Luck!

Bill Fabry
Truevision, inc.
[log in to unmask]

--------------------------------------
Date: 11/4/96 12:46 PM
To: Bill Fabry
From: Wolfgang ERAT
Would appreciate any source for info on effects on solderjoint
reliability when assembling (solderpaste / IR Reflow ) a full gold
(approx 30 microinches thick) finished board. What are the effects of
the gold alloying with the tinlead in the joint ? / Thank you.

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