Abstract
ABSTRACT The morphology and the development of the intermetallic phases at the Sn-Pb/Alloy 42 interface with different Pb content were studied in this work. By a new technique of pulling by epoxy resin after taper grinding, the interface intermetallic compound could be observed. The influences of the soldering time and Pb content on the development of the intermetallic compounds were investigated in this study. An interface layer in a thickness of 3μm was observed at the interface between the solder and the Alloy 42. There are four kinds of intermetallic phases in the interface plane. The first is a continuous layer which has been identified by X-ray analysis and was found to be FeSn2. The second is the sweet-flag-leaf (SFL) phase which was identified by X-ray diffractometer as the Ni3Sn4. The SFL phases are very long, narrow and thin and are scattered densely on the interface plane. They lie on the interface in just one single layer. Since the thickness of them is smaller than one micrometer, they are generally not visible from the cross section (side view). There are also some cubic and hexagonal column shaped particles on the interface. Both of them are in very small quantity. The sizes of the column particles are relatively large and the Sn to Ni atomic ratio of it is about 70:30. There is no previous report about this phase. The cubic particles are just in the size of several micrometers and are found to lie among the SFL particles. A mechanism is proposed to explain the formation and growth of the SFL phases. It explains the shape of the SFL phases and why they form only in a single layer. The mechanical properties of the soldered specimen were investigated in this study. For the tensile-shear strength test, failures of the joint all occur in the solder, away from the interface. When the pure Sn or 90 Sn-10 Pb solders are used, the shear strength of the solder increase obviously with the decrease of thickness of solders. However, the shear strength is almost unchanged for solders of higher Pb content.