Masashi Shimoyama

XeCl excimer laser ablation of a polyethersulfone film: Dependence of periodic microstructures on a polarized beam

Highly periodic stable microstructures appeared on the surface of polyethersulfone (PES) by XeCl excimer laser ablation with a single polarized beam in ambient air. Its formation mechanism was investigated using the time‐resolved light scattering technique with the pulsed light of an XeF excimer laser. In addition to the polarization of the ablating beam, thermal processes on the etched surface play a significant role in microstructure formation.

Processing, properties, and reliability of electroplated lead-free solder bumps

Eutectic tin-silver (Sn-Ag), tin-copper (Sn-Cu), and tin-silver-copper (Sn-Ag-Cu) solder alloys are potential lead-free materials for low-temperature processing of solder bumps on wafers. But, before they can be adopted to replace the existing lead-free materials, processes have to be developed to provide controls over composition, height and shape uniformity, and defect formation, such as micro-voids, which are detrimental to bump reliability. Over the last six years, we have developed an electroplating technology using a dip-plating machine for processing the three types of eutectic lead-free solder bumps on silicon wafer. Our process is suitable for mass production with well-controlled bump geometry and composition, and uniformity within 10% over the entire wafer. In this paper, we will describe our process and present our results on the bump properties, such as composition, melting point, and microstructure of the bumps.