Miniaturization of devices leads to the appearance of high current densities inside
solder joints. These current densities may induce electromigration, which can lead
to the formation of thicker IMC layers, voids and Cu dissolution. In the case of Sn-Bi
solders it may lead to phase segregation as well. Test vehicles for the study of solder
joints of 0402 and 0201 chip resistors have been designed and realised on RO4350B
high performance PCB dielectric material. The PCBs have been populated with zero ohm
(jumper) 0402 and 0201 surface mounted chip-size resistors, using Sn-Bi and SAC solder,
allowing for a direct comparison of the electromigration behaviour of the two solder
types in the case of common component types. A test environment for high-current stressing
was prepared. The samples were examined after reflowing and after 500 h of current
stress, by shear testing and SEM crosssectional images. The microstructure of the
samples was analysed to inspect void growth, IMC growth and Bi-layer aggregation behaviour.
Besides the test samples taken out at 500 h aging, the test will continue until 4000
h total stress time, with additional analysis at the 1000h and 2000 h mark.
