Hi Werner and other fellow Technetters,
The gold plating in question is not on the pads on the board, but on the leads of a TH component.The J-STD-001 says that gold should be removed from the component only when it is greater than 2.5 micrometers (approx. 0.09 mils) thick, while the part in question has 10 microinches of gold on it (0.01 mils). As Joyce pointed out, 2.5 micrometers comes to 100 microinches (0.1 mils).
I do not know what process was used by the vendor to coat the leads ( I can find out), but the core question still remains, what is the max thickness that is critical for Au embrittlement. As per J-STD-001, it is 100 microinches! (unless the J-STD-001 is talking about removing the gold for a different reason)
Makes sense?
Amol
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Friday, November 03, 2006 8:49 AM
To: [log in to unmask]
Subject: Re: [TN] Gold Embrittlement
Werner,
Excellent points, especially about uniform distribution. I argue quite
often with people on that issue. I think the last word was a Freudian
slip. With the information given you were "tipping your Hand", but I
think you meant to say dipping. Unless, of course, you meant by tipping
that the parts would come in with the correct final finish and thus
negate the need to dip.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, November 02, 2006 3:06 PM
To: [log in to unmask]
Subject: Re: [TN] Gold Embrittlement
Hi Amol,
I you have imersion Au, Au-embrittlement is not a problem because there
is
not enough Au. Be careful, however, if your PCBs come from China; I have
seen
much thicker Au-layers than are possible with iAu.
Calculating the wt% of Au in a soldert joint is an exercise in futility,
because you have to make the assumption--frequently not warranted--that
the
SnAu-IMCs are uniformally distributed.
In cases where you suspect thicker Au [and for the matter Ag; which is
equally as bad as Au in causing SJ-embrittlement] deposits, the safest
course of
action is to wash the Au (Ag) off by tipping.
Werner
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