Reliability and failure analysis of electronic components induced by the reflection of laser beam in the laser jet solder ball bonding process

Abstract

With advantages of non-contact, high energy density and local heating, the laser jet solder ball bonding (SBB) technique provides a flexible packaging method for three dimensional (3D) package structure and temperature sensitive components. In previous works, the microstructure and reliability of solder joints fabricated by laser jet SBB were studied. In recent studies, the essential factors influencing the wettability of the molten solder on the bonding pad in flux-free laser jet SBB process were investigated deeply, and the results revealed that the thick oxidation layer of solder balls and the severe contamination of surface of Au bonding pads can lead to the poor wetting. Meanwhile, the corresponding mechanism of the poor wetting was also discussed and analyzed. However, some other important factors causing the reliability degradation even failure of solder joints are still unclear in the laser jet SBB process, for example, the burning failure of electronic components induced by the laser beam. Thus, how to prevent this type failure becomes a tough task for mass production. In this study, from the point of view of the laser characteristics, the essential factors leading to the burning failure have been clarified through microanalysis by using scanning electron microscopy (SEM) and optical microscope (OM). Firstly, the homogeneity of the laser beam was characterized by a laser profiler. Then, in order to determine the correlation between the burning failure and the transporting characteristics of the laser beam, the different displacements of the nozzle along horizontal (x) and vertical (z) directions were preset, and the burning points in the electronic components were confirmed by using OM and SEM. In addition, the reflection of the laser beam caused by the near spherical solder ball was also studied. The results show that the energy distribution of the laser beam is inhomogeneous and some laser micro-beam has higher energy. Meanwhile, the reflection of the laser beam occurs very commonly in laser jet SBB process, not only the Au bonding pad, but also the solder ball can reflect the laser beam. When a reflecting laser micro-beam contacts to the weak interface of the electronic components with sufficient energy density, the burning failure of the component may appear easily.