The creep behaviour and microstructure of ultra small solder joints

The creep behavior of Sn-based solders undergoes a significant scaling effect. Therefore this paper compares creep data that was gained on bulky samples and on small solder joints. Optical microscopy techniques and SEM-microprobe analysis were used to examine the microstructural properties of the bulk specimens and real solder joints were after metallographic sectioning. The results of these microstructural analysis were related to the investigated mechanical properties of the solders. The solidification behaviour of SnAg- and SnAgCu was investigated experimentally. Microstructural analysis point out that bulk solder has typically a dendritic microstructure. At ultra small solder joints complex forms of solidification behaviour were detected. The different nucleation behaviour is supposed to be the reason for the differences in solidification. Creep experiments on SnAgCu-based solders have been conducted on several types of specimens: flip chip and bulk specimens. The results of these experiments show that the influence of size and composition of SnAgCu-based solders is very complex. Size and composition are no independent factors.