I thought pd also form intermetallics with solder...jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kane, Joseph E (US
SSA)
Sent: Thursday, November 10, 2005 12:16 PM
To: [log in to unmask]
Subject: Re: [TN] Gold plated components, what a pain!!
The Cotts thing is interesting, but J-STD-001 does give
a pass for ENIG finish on boards, presumably based on
the industry's considerable history of semi-successful use.
Now the gold flash on nickel/palladium/gold is only 30 to
150 angstroms thick, which is way below the level where
you'd have to worry about gold embrittlement in the bulk
solder (like by a factor of 50). TI has a paper on this,
and it probably fits the definition of "objective evidence"
required by J-STD-001 for SMT parts:
http://focus.ti.com/lit/an/szza031/szza031.pdf
Now if you can identify particular component manufacturers
(like TI, maybe Phillips) that offer only NiPdAu rather than
gold over nickel, maybe you can flag those to bypass the
tinning pot. Not a complete solution, but may help some.
Joe Kane
BAE Systems
Johnson City, NY
-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Thursday, November 10, 2005 11:38 AM
To: [log in to unmask]
Subject: Re: [TN] Gold plated components, what a pain!!
Steve,
Hmmm.
Well if you know that the thickness of the gold is X, you know the
dimensions of the lead/pad/termination/castellation and you know the amount
of solder paste you are putting down/amount of solder in the PTH; you can
calculate the amount of gold that will be in the solder joint. Generally
people have for years been taking < 4% as OK. Is this "objective" enough?
Of course to throw a bug in the pudding - Dr. E. Cotts of SUNY Binghamton
has been finding that the gold of even an ENIG coating (pretty darn thin)
re-migrates back to the nickel/solder interface and forms a tin/gold/nickel
intermetallic that he says has some nasty properties.
http://www.binghamton.edu/physics/pub/cottsinterpack1999.pdf
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: November 10, 2005 10:57 AM
To: [log in to unmask]
Subject: Re: [TN] Gold plated components, what a pain!!
Hi Bev!
Removing gold on ALL gold plated SMT parts, because that's what J-STD-001
says to do, unless we have objective evidence available for review that
there are no gold related solder embrittlement issues...
We're a contract manufacturer, we're build-to-print for most everything
here, and we don't have the luxury of being able to take actual product and
do laboratory analysis on solder joints to prove there are no gold
embrittlement problems with certain gold plated parts...
Kind regards,
-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX
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| To: TechNet E-Mail Forum <[log in to unmask]>@SMTP@Exchange,
Stephen R Gregory/LABARGE@LABARGE |
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| Subject: RE: [TN] Gold plated components, what a pain!!
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Steve,
Let me get this right - you are removing all gold from all leads before you
solder? Or are you using XRF or x-sectioning to see which ones has THICK
gold that requires pre-removal? Bev RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: November 10, 2005 9:37 AM
To: [log in to unmask]
Subject: [TN] Gold plated components, what a pain!!
Good Mornin' Everyone!
We've got a little problem here that I think everyone goes through, and
maybe I can get some pointers on how to deal with it.
J-STD-001 states that:
3.9.3 Gold Removal
Gold shall be removed:
From at least 95% of the surface to be soldered of the through-hole
component leads with 2.5 ìm [0.0984 mil] or more of gold.
From 95% of all surfaces of surface mount components to be soldered
regardless of gold thickness.
From the surface of solder terminals plated with 2.5 ìm [0.0984 mil] or
more of gold.
A double tinning process or dynamic solder wave may be used for gold
removal.
Electroless nickel immersion gold (ENIG) finishes on PCBs are exempt from
this requirement.
These requirements may be eliminated if there is documented objective
evidence available for review that there are no gold related solder
embrittlement problems associated with the soldering process being used.
I have no problem with the requirement, and I understand why the requirement
is there, but the problem that we're having is that these gold plated parts
sometimes are discovered only when they've been pulled for a work order to
be released for production, or even worse, when they are being loaded on a
feeder during machine set-up.
"Hey Steve, we got a gold plated part here!" So the set-up will be delayed,
or the assembly will be built short and then the gold plated part
hand-soldered later after the gold has been removed depending on how urgent
the schedule is.
We try to catch these gold plated parts in parts in receiving, if they can
be identified there. But there are many parts are coming in sealed, and
we've discouraged sealed packaging from being opened until it is used.
Our manufacturing engineers say that they can't identify every single part
that is gold plated without going through the datasheet of every single
part, or calling the component manufacturer, which there isn't enough hours
in the day for them to do.
On top of the problem trying to identify the parts before they hit the SMT
line, there is the difficulty of actually removing the gold from some of
these little beasts because of the size and geometry. For example, look at:
http://www.stevezeva.homestead.com/LEDFootPrint.jpg
How do you go about removing the gold on something like that? JANTX
transistors are another one...
We've got a few customers that are giving indications that they might start
banning 100% tin plated components unless they've been tinned with standard
tin/lead solder which will only intensify the problems that we're seeing
now.
I'm just wondering how everyone else deals with this? I'm open for
anything...any suggestions at all.
Kind regards,
-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX
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