Investigation of IMC thickness effect on the lead-free solder ball attachment strength: comparison between ball shear test and cold bump pull test results

Ball pull test has emerged to be an attractive alternative to the traditional ball shear method for characterizing the attachment strength of solder interconnection. Since it is a relatively new development, so far there is not industrial standard to regulate this testing method. This paper discusses the effect of IMC growth after soldering and thermal aging at 150 degC. The attachment strength of solder balls with thermal aging is investigated by ball shear and cold bump pull (CBP) tests. The test configuration and the experimental data are reported in detail. The test results indicate that the CBP test method can reveal the brittle failure of solder joints with a higher sensitivity, especially under the fast pulling speed. As a result, the effect of IMC growth can be identified more easily. In addition to the correlation between the IMC thickness and the solder ball attachment strength, the micro-structure of IMC and the failure modes were discussed as well