Hi Vlad! I thought we had answered the solderability questions.
Intermetallic phases are typically as solderable as the parent metals
until they become oxidized (then they are impossible to solder!). So as
long as the Au/Sn IMC phases are not oxidized as a function of Bev's
soldering process, there should be not issue. Both Inge's and my photos
that Steve posted show that a non-oxidized Au/Sn IMC is fully integrated
into the solder joint structure and I don't believe Bev's situation is any
different. The gold embrittlement discussion that has streamed along is
just the TechNet metallurgists having way too much fun.
Dave
"Igoshev, Vladimir" <[log in to unmask]>
01/17/2008 08:56 AM
To
"TechNet E-Mail Forum" <[log in to unmask]>, [log in to unmask]
cc
Subject
RE: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Dave and almost everyone else,
I believe we are missing the point. Bev has NEVER asked whether "his"
joints can experience gold embrittlement, but whether the presence of
gold/tin intermetallics can/will affect the solderability.
I think he is not the only one who would want to know the answer and so
far the answer is almost unknown.
As far as I remember, Werner said that the solderability to AuSn4 is poor.
Are their any papers with data?
I think it would be great to have data on solderability of of common
solders (Pb-free and PB-Sn) to Sn-Au alloys (with Au content from 30% down
to 0).
Regards,
Vladimir
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, January 17, 2008 8:21 AM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
Hi Bev - Arguably, the "magic" industry number is "3%" for gold content.
The AuSn4 phase formation kicks into gear around that percentage. The
amount of gold you have is low and provided it is well distributed through
out the solder joint (e.g. not segregated in one area) then you should not
have any solder joint integrity issues. Some of the work done by Bester (
M. Bester, ?Metallurgical Aspects of Soldering Gold and Gold Plating?,
InterNEPCON Proceedings, 1968) shows that 1-2% gold actually strengthens
the solder joint a bit. I believe you have a low-to-no risk situation.
Dave
"Bev Christian" <[log in to unmask]>
01/16/2008 04:24 PM
To
"TechNet E-Mail Forum" <[log in to unmask]>, <[log in to unmask]>
cc
Subject
RE: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Dave,
I only have 0.8 to 1.2% gold in the solder balls - as determined by XRF.
Bev
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, January 16, 2008 5:06 PM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
Hi gang! Steve - I just sent you another set of photos showing a solder
joint that has gold embrittlement. Bev - if you have a solder joint that
contains the AuSn4 microstructure phase then you have an indication that
your overall composition has exceeded the "magical" 4% limit. The
presence of the AuSn4 platelets cause the solder joint to behave in a
brittle manner when subjected to some use environments. The formation of
the AuSn4 phase isn't going to interfere with the formation of your solder
joint but they do result in solder joint integrity degradation. The
pretinning of gold plated component leads is an attempt to replace the
gold with a solder coating and lower the overall total percentage of gold
that would exist in the solder joint - the lower the overall solder joint
gold content, the lower the likelihood for the AuSn4 phase to form.
Dave Hillman
Rockwell Collins
[log in to unmask]
Steve Gregory <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
01/16/2008 03:35 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steve Gregory <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Hi Inge ol' pal!
I went back and looked on my pages, and am not sure if they're still
there. But one of these might be:
http://stevezeva.homestead.com/files/fracture_bad.jpg
http://stevezeva.homestead.com/files/fracture_bad_2.jpg
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
Sent: Wednesday, January 16, 2008 3:09 PM
To: [log in to unmask]
Subject: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Not really true, the Scottish blood in my veines tells me to be careful
with money, the kyrgise blood makes me crush the table, therefore, noone
can actually be under it.
I think there are pictures from my large AuSn platelets somewhere on
Gregory's wall. If not, I can probably dig them up again from some old
report. If such crystals are abundant in a solder joint, the components
may just jump off the board when giving a mechanical shock.
/Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Werner Engelmaier /*
Skickat: den 16 januari 2008 20:30
Till: [log in to unmask]
Ämne: Re: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Hi Inge,
As usual people are well advised not to argue with a (this) Swede; 1) he
usually knows what he is talking about, and 2) if not, he will drink you
under the table.
The IMCs formed by Sn/Pb, and Sn/Ag as well, are platellet-shaped crystals
(in cross-section they may look like needles but are always plateletts),
and I have seen no evidence that they are solderable. Solderability simply
depends on how much Sn, or SnPb, to which you wet, is present. So the
amount of these IMCs affect both solderability as well as
Au/Ag-embrittlement.
Inge, how is Gerd? I sure have not heard anything about him for some time.
Werner
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