Effect of fine dispersoids and anisotropic nature of β -Sn on thermal fatigue properties of flip chips connected by Sn– x Ag–0·5Cu ( x : 1,3 and 4 mass-%) lead free solders

Abstract

A significance of two factors, fine dispersoids in a solder and the anisotropic nature of β-Sn, on thermal fatigue endurance is discussed using flip chips connected by Sn–xAg–0·5Cu (x: 1, 3 and 4 mass-%) lead free solders, together with Sn and Sn–1·2Ag–0·5Cu–0·05Ni, for comparison. Both 3Ag and 4Ag showed better thermal fatigue properties than Sn and 1Ag, and a thermal fatigue life of 1·2Ag with Ni was close to that of 3Ag despite of its low silver content. Microstructures of the solders before thermal fatigue tests can be classified into a single crystal-like and a fine grain type. However, this classification, which affects the amount of thermal strain by the anisotropic nature of β-Sn, cannot accurately describe thermal fatigue lives observed. On the other hand, Vickers microhardness of the solders, which was resulted from fine dispersoids, showed good relationship with observed thermal fatigue endurance.