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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 7 Oct 2008 14:00:25 -0500
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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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TechNet E-Mail Forum <[log in to unmask]>; Please respond to
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Subject
[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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