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Investigation of the undercooling of SnCu solder spheres

: Schindler, S.; Mueller, M.; Wiese, S.


Institute of Electrical and Electronics Engineers -IEEE-; IEEE Components, Packaging, and Manufacturing Technology Society:
ESTC 2014, Electronics System Integration Technology Conference : Helsinki, Finland; 16.09. - 18.09.2014
Piscataway, NJ: IEEE, 2014
ISBN: 978-1-4799-4026-4
ISBN: 978-1-4799-4027-1
ISBN: 978-1-4799-4025-7
Electronics System Integration Technology Conference (ESTC) <5, 2014, Helsinki>
Conference Paper
Fraunhofer CSP ()

This study focuses on the influences on undercooling of SnCu solder alloys. Therefore Differential Scanning Calorimetry (DSC) measurements were carried out on commercially available solders with varying Cu content (from 0 wt.% to 3.0 wt.%). Furthermore the diameter of the investigated solder spheres was varied from 131 m to 1120 m in order to represent typical interconnect sizes of electronic packages. The results showed only little influence by composition and volume, which was unexpected. Further experiments showed that the undercooling of the investigated solder alloys is probably suppressed by an impurity which triggered heterogeneous nucleation at higher solidification temperatures. By now we were not able to detect the responsible impurity in our samples, but it was possible to reproducibly and permanently decrease the solidification temperature of our samples (e.g. SnCu0.7 from 210 °C to 150°C) by thermal preconditioning above 370 °C. These findings open the opportunity to directly modify undercooling in SnAgCu solders.