MICROSTRUCTURAL CHARACTERIZATION OF AU SN SOLDER FOR PACKAGING IN OPTOELECTRONIC APPLICATIONS/

Preliminary results on the feasibility of using co-evaporation of eute ctic Au/Sn solder for semiconductor packaging are presented. Gold is e lectron beam evaporated, while Sn is thermally evaporated, onto Ti/Pt/ Au metallized InP substrates. Electron microscopy is utilized to deter mine the composition and uniformity of the solder and to characterize interfacial reactions between the solder and the semiconductor metalli zation. Eutectic Au/Sn solder, several microns thick, can be deposited with intermittent substrate cooling. Heating of the solder during sim ulated reflow experiments results in dissolution of Au and Pr into the solder, with Pt going into substitutional solid solution in AuSn. Par t of the Ti layer is consumed as well, forming Au,Ti containing Sn. Bo nding tests, reveal solder joints with a uniform distribution of small pores, significantly less than 1 mu m in size. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.