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TechNet E-Mail Forum <[log in to unmask]>, "Thayer, Wayne" <[log in to unmask]>
Date:
Wed, 15 Apr 2009 16:26:34 -0400
Reply-To:
TechNet E-Mail Forum <[log in to unmask]>, Joyce Koo <[log in to unmask]>
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From:
Joyce Koo <[log in to unmask]>
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Here is a CFO in the making. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne
Sent: Wednesday, April 15, 2009 4:24 PM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

Can't you cash those bad boards in at the local exchange?

Actually, with that much gold, you may not have near the problem you
would if it was only 30-100 microinches:

It is doubtful you could get the solder hot enough to dissolve all of
the gold, so gold-tin intermetallics had a nice buffer of malleable pure
gold before you got down to the copper!

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Wednesday, April 15, 2009 1:42 PM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

Some seem to have plenty of gold, or poor process control. In the
example I mentioned, the gold thickness was 10 microns = 10 um = 10
micrometers = 0.4 mils.

Inge

----- Original Message -----
From: "Joyce Koo" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, April 15, 2009 6:36 PM
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?


My question would be why such a thick gold?  No body want to put more
gold
than it is necessary.  Either the part was mean to be contact only, e.g.
Connector chage from contact to solder on; or someone try to save money
to
use the wrong vendor, normally, the good flash or igen, and hard gold
electrolytic gold plater are not the same vendor.  The 3rd possibility,
you
got a newbie designer with tennis shoes, copy and paste the old drawing
notes without proper review and signing off process in place.  If it is
the
last case, may god be with you.
--------------------------
Sent using BlackBerry


----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Wed Apr 15 12:01:43 2009
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

Hi Guy! Ah, the whole "lost in conversion issues" discussion. As TechNet
pointed out yesterday, one system would be soo nice. Ok, back to gold
embrittlement. Your 3.8 microns is 152 microinches (thanks George
Wenger)
so yes, you had a very high probability that your solder joints were
gold
embrittled to some level. Now, let's split this discussion into
"classic"
and "new" gold embrittlement. The industry tribal knowledge has always
been that you needed to satisfy two conditions to avoid gold
embrittlement: a) do you have enough solder volume to allow for uniform
distribution (e.g. keep the gold percentage below 3 weight percent) for
the amount of gold present?; 2) Are you using a soldering process that
has
sufficient time/temperature parameters to allow (a) to occur? If we are
talking about gold plating situations with no nickel finishes involved,
then these rules hold true. If you get the gold evenly distributed
across
the solder joint and stay below 3 wt. %, you will not have a gold
embrittlement issue. However, the use of the ENIG surface finish has
changed the rules slightly. The presence of nickel plating causes a
diffusion reaction that we didn't see with a copper surface. The energy
of
formation for the gold/tin intermetallic is influenced by the presence
of
nickel (you get some interesting Sn/Ni/Au phases) such that the gold
does
not always stay evenly distributed across the solder joint. The majority
of the time, this redistribution and phase formation is so small/minimal
that there is no gold embrittlement issue. ENIG is considered a non-gold
embrittlement generator as a general industry rule. However, if you have
an ENIG finish and a heavily plated gold finished component, you could
have a gold embrittlement risk. As Richard pointed out, there are a
number
of good paper documenting this phenomena available for reading (Journal
of
Electronics has had some good papers on the topic).

Dave



Guy Ramsey <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
04/15/2009 10:11 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Guy Ramsey <[log in to unmask]>


To
[log in to unmask]
cc

Subject
Re: [TN] Gold/Tin Intermetallics, why are we afraid?






I think microns and micrometers are the same thing.

http://en.wikipedia.org/wiki/Micron

Our board house considers 3 to 10 micro-inches to be gold flash, 50-150
is
heavy plate.

3.8 micrometers is something like 150 micro-inches



From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, April 15, 2009 8:49 AM
To: TechNet E-Mail Forum; Guy Ramsey
Cc: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?




Hi Guy! I am metrically impaired - what is 3.8 micron in inches? Is your
3.8
micron referring to micrometers or nonSI units? (Given our recent SI
units
discussion, my question is way too ironic!).

Dave Hillman
Rockwell Collins
[log in to unmask]





Guy Ramsey <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>

04/15/2009 07:37 AM


Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Guy Ramsey <[log in to unmask]>


To

[log in to unmask]


cc



Subject

Re: [TN] Gold/Tin Intermetallics, why are we afraid?








We build a lot of boards with electroplated gold finish, primarily for
the
semiconductor test sector of our industry.

On one occasion we were populating little printed circuit wave guides
with
SMT SMA shrouds. We noticed very poor solder appearance and very weak
solder
connections. Some connections broke while attaching the cables.

We determined that the gold plate was 3.8 micron. And judged the
thickness
of the gold to be the cause of poor mechanical performance of the solder
connection.

We replaced the boards with versions having about 0.3 micron gold plate.
The
connections were much stronger. We were able to install all the cables,
no
connection failures. To satisfy my own curiosity, I attempted to break
one
of the connectors off the board. The solder connection did not fail. The
copper peeled off the board.

Thoughts?

Guy

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Wednesday, April 15, 2009 2:42 AM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

Thank you, George,
sometimes one needs kind of technical pragmatism.
Inge

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: tisdag 14 april 2009 23:41
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

I think both you and Vladimir are correct.  If the bond Ingemar,

I think both you and Vladimir are correct.  If the bond sits are room
temperature without any power cycling or mechanical stress it probably
won't
degrade.  I assume Vladimir has seen the same kinds of failures I've
seen
and there has always been a thermal and/or mechanical stress associated
with
the failures.

Regards,
George
George M. Wenger
Andrew Wireless Solutions
Senior Principal FMA / Reliability Engineer 40 Technology Drive, Warren,
NJ
07059
(908) 546-4531 [Office]  (732) 309-8964 [Cell] [log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Tuesday, April 14, 2009 5:15 PM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

You mean that such a bond degrades even if just being in constant room
temperature and no power switching?
Inge


----- Original Message -----
From: <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge"
<[log in to unmask]>
Sent: Tuesday, April 14, 2009 11:07 PM
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?


> Hi Inge,
>
> Yes, the intermetallics itself is strong, BUT it doesn't count, as all

> failures I've seen goes at the tin/intermetallics interface. The
larger
> were the platelets, the worse it looked.
>
> Regards,
>
> Vladimir
> ------Original Message------
> From: Inge
> Sender: TechNet
> To: [log in to unmask]
> ReplyTo: TechNet E-Mail Forum
> ReplyTo: Inge
> Sent: Apr 14, 2009 16:55
> Subject: [TN] Gold/Tin Intermetallics, why are we afraid?
>
> These infamous IMCs are like parias or ghosts in most people's mind in
our
> business. I shocked our production guys recently by giving the advice
to
> let
> the boards go on. Large crystals and bad looking. But I always  try to

> avoid
> exaggerations. If no serious temp changes are predicted, nor any
severe
> power switching, why rework and risk introducing failures?  The actual
> components were very hard to rework, the cost had been unacceptable. I
can
> see many of you get  the coffee wrong. I don't mean to spread quality
> distractions, I talk about very few boards and a unique situation. My
> statement was based on the fact that a gold tin intermetallic bond is
> extremly strong and can last long, if not exposed to what I pointed at
> earlier. I expect to be hammered down in the shop floor until only the

> nose
> is visible....
>
> Inge
>
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