An analytical study of thermo-mechanical failure mechanisms of a leadless chip resistor solder joint

Abstract

This paper describes results of an analytical study of thermo-mechanical failure mechanisms in a leadless chip resistor solder joint typically encountered in electronic assemblies. Electronic assemblies for the commercial and military aircraft industry are exposed to various environments that will affect their reliability. Fracturing of solder joints is a common failure mode in these electronic assemblies. The solder used in electronic assemblies is a tin-lead eutectic solder. The melting temperature of this type of solder is 183°C (361°F). Under typical operating conditions temperatures as high as 120°C (248°F) are encountered (Tₕ = 120/183 = 0.65). At this high temperature creep deformation mechanisms become important. A review of literature on solder joint failure is presented and it is apparent that a main cause of solder joint cracking is creep. A nonlinear Finite Element Model was created to determine the stresses and strain imposed on a chip resistor solder joint as a result of thermal cycling. The FEM was also used to show the effect of solder joint shape and size on the resulting stresses. The effect of creep and other mechanisms that contribute to solder joint cracking were identified.