Soldering Problems due to Residues of a Surfactant

The success of a cleaning step is not only determined by the character of the contamination that needs to be removed. The choice of surfactant and the frequency for changing the rinsing solution or the cleaning tools also have a considerable influence on the effectiveness of the cleaning step. The quality of the final rinsing step is often neglected, resulting in the presence of surfactant residues on the surface, which can lead to adhesion problems.

Example: Despite a thorough degreasing step and a subsequent plasma cleaning treatment, adhesion problems occurred on a nickel surface. In order to identify the problem, the lateral distribution of detected components was investigated with the aid of ToF-SIMS. This analysis showed the presence of dodecylbenzenesulphonic acid (DBSA) on the surface of the cleaned metal. This chemical was identified as a component of the cleaning agent; however, as a result of insufficient rinsing, the chemical was not removed completely from the metal surface.  A subsequent plasma cleaning step did not lead to a complete removal of the DBSA layer either. The presence of residual DBSA led to adhesive failure in the next process step. Based on these analytical results, the final cleaning of the nickel plate could be improved and the failure rate due to adhesive failure could be reduced considerably.