I haven't worked with the <6 wt % Bismuth alloy (the "Bi-starved"
region), but I have worked with the "Pb-starved" region and have had
trouble there: I used SnBi alloy to solder attach Sn-Pb plated leads.
Very bad results.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls
Sent: Tuesday, October 07, 2008 3:55 PM
To: [log in to unmask]
Subject: Re: [TN] Sn-Bi Alloy for soldering
I just love it when Dave uses himself as a reference..................
Doug Pauls
Rockwell Collins
"David D. Hillman" <[log in to unmask]> Sent by: TechNet
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10/07/2008 02:00 PM
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Subject
Re: [TN] Sn-Bi Alloy for soldering
Hi Amol! There is a couple of public domain investigations that would be
useful for component finishes. Celestica (Dr. P. Snugovsky et al), NIST
(Dr. C. Handwerker et al), and Rockwell Collins (D. Hillman et al) have
all published results of investigations demonstrating that if the
bismuth
content of a solder joint does not exceed 6 wt % then the impact on
solder
joint integrity is negligible. There is a common industry myth that the
tin/lead/bismuth eutectic ternary phase will form causing the solder
joint
to melt during service thus impacting solder joint integrity. The
published investigation results demonstrate the ternary phase does not
form. Here are some useful references:
[1] D. Hillman, ?Surface Mount Solder Joint Integrity Issues for
Lead-free Soldering Concerning Lead and Bismuth Interactions?, National
Physical Laboratory Lead-free Conference, June 22, 2006.
[2] P. Snugovsky, et al, ?Solder Joint Formation with Sn/Ag/Cu and
Sn/Pb Solderballs and Pastes?, SMTAI Conference Proceedings, 2002.
[3] iNEMI consortia, iNEMI Recommendations on Lead-free Finishes for
Components Used in High Reliability Products Report, Version 4
(12-1-06).
[4] J. Lau and Y. Pao, Solder Joint Reliability of BGA, CSP, Flip
Chip, and Fine Pitch SMT Assemblies, McGraw Hill, ISBN 0-07-036648-9.
[5] P. Viswanadham and P. Singh, Failure Modes and Mechanisms in
Electronic Packages, Chapman & Hall, ISBN 0-412-10591-8.
[6] C. Coombs, Coomb?s Printed Circuits Handbook, Fifth Edition,
McGraw Hill, ISBN 0-07-135016-0.
[7] P. Snugovsky, et al, ?Microstructure and Properties of Sn-Pb
Solder Joints with Sn-Bi Finished Components?, APEX Conference
Proceedings, 2006.
[8] K. Moon, et al, ?The Effect of Bi Contamination on the
Solidification Behavior of Sn-Pb Solders?, Journal of Electronic
Materials, Vol. 36, No. 6, pp. 676-681, June 2007.
[9] C. Hunt and M. Wickham, ?Impact of Lead Contamination on
Reliability of Lead-free Alloys?, APEX Conference proceedings, February
2006, Paper S39-01.
[10] NEC Electronics, Lead-Free Semiconductor Products, NEC Pamphlet
C14485EJ6V0PF00, March 2006.
[11] M. Meilunas, et al, ?Alternative Lead Finish QFP Assembly and
Lead
Pull Study?, UIC Area Array Consortium Report, December 2004.
[12] A. Syed, et al, Amkor TSOP-48 Internal Test Report, February
2002.
[13] xxx
[14] J. Clech, et al, ?A Comprehensive Surface Mount Reliability
Model
Covering Several Generations of Packaging and Assembly Technology?, IEEE
Transactions On components, Hybrids and Manufacturing Technology, Vol.
16,
No. 8, December 1993, pages 949-960.
[15] G. Gaylon, ?Annotated Tin Whisker Bibliography and Anthology?,
iNEMI consortia monograph, Version 1.2, 2003.
[16] GEIA-HB-0005-2, Technical Guidelines for Aerospace and High
Performance Electronic Systems Containing Lead-free Solder.
The SMTAI 2007 Proceedings contains the Rockwell Collins paper with this
reference list. As far as the use of a SnBi solder alloy, you are going
to
exceed the 6wt% maximum value and if there is lead present in the
process
(pwb pads, lead finishes, etc.) then you are going to have an issue with
the ternary alloy. One published case is this reference were a SnBi
solder
alloy and component with a tin/lead finish resulted in significant
solder
joint issues.
D. Hillman et al, ?JCAA/JGPP No-Lead Solder Project: -55C to +125C
Thermal
Cycle Testing Final Report?, SMTAI Conference Proceedings 2006
Good Luck.
Dave Hillman
Rockwell Collins
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"Kane, Amol (349)" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
10/07/2008 10:56 AM
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[TN] Sn-Bi Alloy for soldering
Does anybody have any experience with Sn-Bi alloy used for soldering
lead-free boards? I am looking at literature available out there and see
Sn-Bi used as a surface finish for components, but I have not yet found
a
reference where it is used for soldering.
Looking for pros/cons, good/bad experiences and things to look out for
during soldering.
The application is all SMT, with a temp sensitive part. The manufacturer
therefore wants to use Sn-Bi alloy as this is a lower melting point
alloy
Regards,
Amol
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