Solder joint reliability of Sn and SnBi finished and refinished Sn (SAC/SnPb) SMT packages under temperature cycling test
by Wang, Weiqiang, M.S., UNIVERSITY OF MARYLAND, COLLEGE PARK, 2009, 84 pages; 1465447

Abstract:

Solder dip may be used as a peripheral leaded terminal refinishing process to replace the original pure tin finish with eutectic tin-lead finish to mitigate tin-whisker risk. Tin-silver-copper is an option of lead-free terminal finish. Solder dip is the way to obtain tin-silver-copper finish. However, the reliability of solder joints formed with these refinished terminals may be affected by the refinishing process. The solder joint reliability of refinished components under temperature cycling conditions need to be determined to study the effects of refinishing on the solder joint reliability. Tin-bismuth terminal finish is another tin-whisker mitigation strategy. The reliability of solder joints under temperature cycling conditions formed with tin-bismuth finished terminals also needs to be determined before the implementation.

The microstructure and strength of solder joints formed with refinished terminals were evaluated by comparing with those of solder joints formed with original pure tin finished terminals. The reliability of solder joints formed with original pure tin finished terminals, refinished terminals and original tin-bismuth finished terminals were tested under temperature cycling.

Under temperature cycling test, solder joints formed with Sn3.0Ag0.5Cu solder dipped terminals have shorter characteristic life for thin-small-outline-packages but longer characteristic life for 2512 resistors than those formed with the original pure tin finished terminals in both eutectic SnPb and Sn3.0Ag0.5Cu solder assembly. Solder joints formed with eutectic SnPb dipped terminals have equal characteristic life for thin-small-outline-packages, but longer characteristic life for 2512 resistors than those formed with the original pure tin finished terminals when reflowed with eutectic SnPb solder. Solder joints formed with tin-bismuth finished terminals have shorter characteristic life than original pure tin finished terminals for thin-small-outline-packages for both eutectic SnPb and Sn3.0Ag0.5Cu solder assembly.

If a 20% decrease in characteristic life of solder joints under temperature cycling conditions is acceptable, then the SAC solder dip process can be a potential choice for refinishing purpose. SnPb solder dip process is a good choice of refinish process without causing degradation to characteristic life under temperature cycling conditions. If a 25% decrease in characteristic life of solder joints under temperature cycling conditions can be accepted, then SnBi finish can be an alternative finish to tin finish.
 
AdviserMichael Pecht
SchoolUNIVERSITY OF MARYLAND, COLLEGE PARK
SourceMAI/ 47-06, p. , Aug 2009
Source TypeThesis
SubjectsMechanical engineering
Publication Number1465447
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