Defect detection of flip chip solder bump with wavelet analysis of laser ultrasound signals

A novel laser ultrasound and interferometer inspection system has been successfully applied to detect interconnection defects including missing, misaligned, open, and cracked solder bumps in flip chips, chip scale packages and chip capacitors. In this paper, wavelet analysis of ultrasound vibration signals is presented and compared to previous methods, including error ratio and correlation coefficient. Wavelet analysis increases the sensitivity to defect detection of flip chip solder bumps. The versatility of the system for inspecting flip chips solder joints made from eutectic and lead-free materials is discussed. The results show that wavelet analysis is a strong tool for ultrasound vibration signal processing. Wavelet analysis has the capability for real-time processing and can improve the efficiency of on-line evaluation. The fully developed system can be used online and serve as a real-time inspection tool for solder bump interconnections in the manufacturing process of electronic packages. It can be concluded that the developed system is capable for quality inspection of solder bumps made from tin-lead and lead-free materials