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
|---------+---------------------------->
| | Bev Christian |
| | <[log in to unmask]
| | om> |
| | |
| | 11/10/2005 09:45 |
| | AM |
| | |
|---------+---------------------------->
>--------------------------------------------------------------------------------------------------------------|
| |
| To: TechNet E-Mail Forum <[log in to unmask]>@SMTP@Exchange, Stephen R Gregory/LABARGE@LABARGE |
| cc: |
| Subject: RE: [TN] Gold plated components, what a pain!! |
>--------------------------------------------------------------------------------------------------------------|
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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