INVESTIGATION OF ALLOTROPIC β→αSn TRANSITION IN HIGH TIN CONTENT SOLDER ALLOYS WITH DIFFERENT MICROSCOPY AND SPECTROSCOPY TECHNIQUES

Abstract

Abstract. In the microelectronics, ?-Sn (white tin) is the base material of the solder alloys and surface finishes. The so called “tin pest” phenomenon is the spontaneous allotropic transition of ß-Sn to the semiconductor ?-Sn (gray tin) below 13.2°C. In this work, different microscopy and spectroscopy techniques were applied in order to characterize the tin pest phenomenon in the case of different solder alloys and inoculator materials as well as to study the applicability of these techniques in tin pest research. Optical imaging technique were used to compare the surface marks of the allotropic transition in the case of different inoculator materials. The development of the transition towards the sample bodies was studied on metallurgical cross-sections. Electrical resistance measurements were applied in order to determine the different phases of the transition in the case of different alloys and inoculators. The grain sliding and ? -Sn expansion during the transition was observed by scanning electron microscopy and focused ion beam - scanning ionic microscopy. The ratio of the transitioned tin and the duration of the transition process was determined by Mössbauer spectroscopy. Our results have shown that the transition phases can considerably differ at the different alloys and inoculators, like different nucleation, growth and the saturation phase. The accurate characterization of the transition in the given material combinations is possible only with the combined application of the applied analytical methods.