Hi, Julie.
That rule of thumb may have worked well for you so far, but there are
many factors that affect the chances of having issues with gold
embrittlement. Many papers have been written of examples showing that as
little as 1% gold by volume within the solder joint has led to premature
failures due to gold nucleation, and the subsequent formation of
gold/tin intermetallics along the surface. I myself have seen 1.5% to 2%
gold embrittlement lead to premature fractures, usually after 8 months
or longer. One example of this is gold-plated solder cups that had 10-15
uinches of gold plating. Another that I have seen occur frequently is on
gold-finished castellations on QFNs. Small through-hole metal-can
crystals is another.
If tinning cannot be performed such that it does not damage the
component or leaves the terminations with lumps of solder on them,
something is certainly wrong with the tinning process. An article on
this subject will be published in the February or March issue of
Circuits Assembly. Watch for it.

The experts did not put the verbiage requiring removal of gold in
J-STD-001D and -DS lightly, there was a lot of study and work done that
fully supported those requirements.

If the part has 2-3 uinches of gold on its terminations, that is not
very likely to lead to issues, but that does not correlate to 2%-3% of
gold in the solder joint.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
Sent: Wednesday, December 23, 2009 12:18 PM
To: [log in to unmask]
Subject: Re: [TN] Gold removal of SMT component

If the part only has 2-3 uinch of gold, it has no more gold than an ENIG
pc 
board.  So why would you try to remove it?  Removal of gold adds process

steps that have the potential to damage or age the component.  The
result is 
likely leads with lumps of solder on them or shorts.  Allowable gold
content in 
lead-free joints is not yet understood, although since I suspect it has
more to 
do with the quantity of gold-tin intermetallics vs the amount of tin
left in the 
joint, the rule of thumb is about the same as for tin-lead.  The rule of
thumb 
has worked well for us.

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