Fatigue and thermal fatigue testing of Pb-Sn solder joints

Abstract

In an electronic package, materials of different thermal expansion coefficients are usually joined with Pb-Sn solder.The combination of temperature fluctuations and different thermal expansion coefficients creates a condition of thermal fatigue in the solder joints.This paper presents a discussion of experimental techniques developed to study fatigue in solder joints.Specimens have been developed to reproducibly test solder joints in shear using a modified double lap shear configuration.Tests were performed using a digitalloadframe especially designed to isothermally fatigue solder joints in shear.Joints tested had a nominal solder composition of 60Sn-40Pb soldered to Cu. Failures were found to occur in the solder joint after fewer cycles at 125C than at lower temperatures.Solder joints were also tested in shear thermal fatigue.A specimen design consisting of two materials with different thermal expansion coefficients constraining a solder joint was cycled between -55C and 125C.Results of these tests indicate that there is a coarsening of the solder near the joint interface and fatigue cracks initiate in these coarsened regions .