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The twinning phenomenon in SnAgCu solder balls

 
: Mueller, M.; Wiese, S.; Wolter, K.-J.

:

Institute of Electrical and Electronics Engineers -IEEE-:
IEEE 59th Electronic Components and Technology Conference, ECTC 2009. Vol.2 : San Diego, CA, USA, 26 - 29 May 2009
New York, NY: IEEE, 2009
ISBN: 978-1-4244-4475-5
ISBN: 978-1-4244-4476-2
pp.1027-1036
Electronic Components and Technology Conference (ECTC) <59, 2009, San Diego/Calif.>
English
Conference Paper
Fraunhofer ISE ()

Abstract
The study focuses on a particular solidification phenomenon found in SnAg3.0Cu0.5 solder balls. Investigations on the microstructure of as cast solder spheres showed, that there is an abrupt change in grain structure during solidification. The microstructure of these specimen consists of areas with small grains that are surrounded by large areas with major grain orientations. In order to characterize this phenomenon Orientation Imaging Microscopy (OIM) done by Electron Backscatter Diffraction (EBSD) has been carried out. It will be shown that the fine grains as well as the large grains show three major, distinct orientations. These measurements indicate the existence of a phenomenon, which is supposed to be caused by a twinning mechanism that creates a misorientation angle of approx. 60° between adjoining grains. In further investigations multilayer cross-sections have been carried out, in order to get a 3- dimensional overview of this phenomenon. In a third row of expe riments the influence of solder volume and composition on the twinning phenomenon has been investigated. Therefore solder spheres of different diameter (130m - 1100m) and different solder alloys (SnAg3.5; SnCu0.7; SnAg3.8Cu0.7; SnAg2.7Cu0.4Ni0.005) were analyzed. It turned out that very little change in composition cause significant changes for this phenomenon. Moreover it was discovered, that the grain structure becomes finer with decreasing volume. In a final row of experiments the influence of the metallization system on the twinning phenomenon has been investigated and the differences between the chosen metallization systems Cu/Sn and Ni/Au will be shown. The effect of individual factors like composition, cooling rate, substrate metallization and solder volume on the phenomenon will be explained and discussed in comparison to real solder joints.

: http://publica.fraunhofer.de/documents/N-188323.html