Hi Mike
Do you mean like me you get momentarily puzzled when people say good reply
Mike, or as Mike said, and you don't remember sending the mail in, but wish
you had.......
Regards
Mike
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Mike Anderson
Sent: 10 August 2004 22:23
To: [log in to unmask]
Subject: Re: [LF] backwards compatibility of Sn/Bi plated components with
Sn/Pb solder paste
Now I know why your name is so familiar........
Mike
-----Original Message-----
From: Leo Higgins [mailto:[log in to unmask]]
Sent: Monday, August 09, 2004 10:38 PM
To: [log in to unmask]
Subject: Re: [LF] backwards compatibility of Sn/Bi plated components
with Sn/Pb solder paste
I think this assessment is correct. At the moment ~ only Japanese suppliers
are endorsing the use of Sn-Bi lead finishes, and the most common Bi content
is 2%. (Apparently the Bi is effective in inhibiting Sn whiskers). When
you consider the large volume of solder from solder paste on a bond pad or
in a PTH from a wave, the dissolution of the Sn-2Bi should be rapid and
complete. The hypothesis is that with reasonably slow cooling, the Bi would
be swept from the crystallizing solder front towards the hottest remaining
point in a connection via a zone-refining type of process. The thought
being that the last liquid phase present upon cooling would be the ternary
eutectic, and the last interface to cool would be where this material would
be swept via zone refining. I suspect that this elegant scenario is likely
to be foiled by dilution in the 'large' volumes of solder in an SMT or PTH
connection, and cooling rates too fast to allow this zone refining process
to be effective. This issue is likely to be of much greater concern is one
were to use a Bi-containing paste and a Sn-Pb plated lead.
Regards,
Leo
------------------------------------
Leo M. Higgins III, Ph.D.
Director of Applications Engineering / ASAT Inc.
[log in to unmask]
3755 Capital of Texas Hwy-So
Suite 100
Austin, TX USA 78726
tel: 512-383-4593
fax: 512-383-1590
mobile: 512-423-2002
------------------------------------
-----Original Message-----
From: Mike Fenner [mailto:[log in to unmask]]
Sent: Thursday, August 05, 2004 8:19 AM
To: [log in to unmask]
Subject: Re: backwards compatibility of Sn/Bi plated components with
Sn/Pb solder paste
Can I just go a little forensic on this? (and I am happy to be further
nitpicked).
Certainly if Bi is present in the surface finish there is the theoretical
possibility of the ternary 46Bi/34Sn/20Pb eutectic MP 96C being formed in
the joint. Certainly there have been studies which demonstrate that under
ALT testing the strength of solder joints can be reduced.
But it is possible that with only 4% Bi in otherwise Sn on the component,
that there is not enough Bi present in the total joint for this to form.
I am just mindful that in real life most solders are not 100%% pure -
typically solders are in the 99.9X% to 99.99% range. So in practice quite a
few "known hazardous" items could at least be measurably present although so
diluted as to have no practical effect.
So possibly this level of Bi would be too diluted to do anything, that
presumably is the contention. In addition 2-3% Bi was - maybe still is -
customarily added to wave solder as a dulling agent for inspection purposes
for years with no reported failures. This was in consumer goods though so
maybe they never got stressed enough for it to matter. Depending on the
application this could still be the case even with Bi above 0.0X% levels.
Have the component manufacturers given out any data, or has anybody seen
data, which support their claims for compatibility?
Regards
Mike Fenner
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Pb-free: www.Pb-Free.com
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Danielle Casha
Sent: 05 August 2004 13:10
To: [log in to unmask]
Subject: Re: [LF] backwards compatibility of Sn/Bi plated components with
Sn/Pb solder paste
Its not so much a question of reliability, as it is melting temp.
When Bismuth is added to Lead, an alloy forms with a melting temp of less
than 100 deg C.
This can cause many issues, especially when trying to double side reflow!
Regards,
Danielle
Danielle L. Casha
Process Technician
EPM
905-479-6203 ext 272
-----Original Message-----
From: mech_eng [SMTP:[log in to unmask]]
Sent: Thursday, August 05, 2004 8:53 AM
To: [log in to unmask]
Subject: [LF] backwards compatibility of Sn/Bi plated components with
Sn/Pb
solder paste
Hi,
I have gotten conflicting information on the backwards compatibility of
using Sn/Bi plated components with Sn/Pb solder paste.
As I understood the situation, under no circumstances could Bismuth be
mixed with Pb.
However, chip suppliers are stating that if the bismuth is maintained to
below 4% of the plating, the reliability of the solder joint is not
compromised.
Can someone shine some light on this specific backwards compatibility
issue.
Thanks,
Haim Halpert
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Messages sent via this medium may be subject to delays, non-delivery and unauthorized alteration. This email has been prepared using information believed by the author to be reliable and accurate, but Indium Corporation makes no warranty as to accuracy or completeness. In particular, Indium Corporation does not accept responsibility for changes made to this email after it was sent. Any opinions or recommendations expressed herein are solely those of the author. They may be subject to change without notice.
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