Joyce,
That's what the J-STD says in section 3.9.3:
"Gold shall be removed from at least 95% of the surface to be soldered
of the through-hole component leads will 2.5um (.0984 mil) or more of
gold."
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Thursday, November 02, 2006 2:21 PM
To: [log in to unmask]
Subject: Re: [TN] [LF] Gold Embrittlement
Are you sure about 2.5 micron thick is OK? that is 100 u-inches!
Scary...
jk
abcd
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kane, Amol (349)
Sent: Thursday, November 02, 2006 3:12 PM
To: [log in to unmask]
Subject: Re: [TN] [LF] Gold Embrittlement
Thank you very much to all who answered promptly!...... I think we are
okay based on the thickness spec and the acceptable % vol of Au in the
joint.
Regards,
Amol
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Kane, Joseph E
(US
SSA)
Sent: Thursday, November 02, 2006 1:31 PM
To: [log in to unmask]
Subject: Re: [LF] Gold Embrittlement
You might not need to do a volumetric calculation, because J-STD-001 has
done some of the homework for you. You're not required to remove gold
from through-hole leads if it's less than 2.5 microns thick (in Rev.
D, Para. 3.9.3). If you can't get information from the supplier, XRF
can tell you the thickness.
-Joe
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Lester Subrattee
Sent: Thursday, November 02, 2006 1:18 PM
To: [log in to unmask]
Subject: Re: [LF] Gold Embrittlement
The typical number going around industry, as far as percentage of
acceptable gold in a joint, is about 3 percent.
>From your data you can approximate how much gold is in the joint and
thus
determine your safety margin.
However, there are two mechanisms at work regarding the "amount" of gold
in the joint.
If a good nickel/tin intermetallic joint is formed and you have too much
gold in the joint (let's say beyond the 3 percent) there could be
gold/tin planar intermetallics within the bulk joint which could result
in shearing along the intermetallic during impact.
So you keep the gold percentage below 3 to be safe.
Your work is not done.
The other mechanism at work is at the interface where the gold dissolves
into the liquid solder. If the soldering process does not allow for
sufficient dissolution of gold into the bulk solder you could end up
with a gold rich layer in at the interface. This could result in the
brittle interfacial fractures.
If you address these two, I think you're OK.
Hope it helps,
LS
-----Original Message-----
From: Kane, Amol (349) [mailto:[log in to unmask]]
Sent: Thursday, November 02, 2006 12:42 PM
To: [log in to unmask]
Subject: Gold Embrittlement
Dear Technetters,
One of the connectors that we use in an exempt application just went
lead f= ree. The surface finish on the connector is gold over nickel.
One end of th= e connector is soldered to the board by tin lead solder,
while the other en= d goes into a PTH and is hand soldered, again using
tin-lead solder. How ca= n I be sure that gold embrittlement will not be
an issue for this joint?
Is=
there a minimum % of gold that needs to be present in the solder joint
for= this to become an issue?
If I know the gold plating thickness, pin dimensions, and the PTH
dimension= s, can I figure out how much gold % would be in the joint,
and hence object= ively conclude one way or the other? What other
information do I need?
Regards,
Amol
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