Thermomechanical fatigue testing and analysis of solder alloys

Thermomechanical fatigue (TMF) is one of the most common causes of failure in solder joints. TMF occurs due to the introduction of stresses arising fr om thermal expansion mismatch during thermal cycling caused by either inter nal heating from power dissipation, the external environment, or both. Due to its complicated nature including partial compliance of joints, evolution of microstructure, and multiple deformation mechanisms, testing a material 's resistance to TMF is not straightforward. A method developed at Renssela er, based on an apparatus designed at North Carolina State University, allo ws the direct measurement of each stress-strain cycle during thermal cyclin g. Through further analysis, using spreadsheet macros, it is possible to co nsider the energy absorbed by the joint on a per cycle basis. The interpret ation of such data as well as the cumulative energy absorption can provide insight into the failure process. The behavior of three alloys, eutectic Sn -Bi, Sn-Pb, and Sn-Ag, will be presented. These data will be compared with that generated by other methods. A comparison of the behavior of these allo ys, as well as the apparatus design, test method, interpretation, and possi ble enhancements is discussed. [S1043-7398(00)01201-9].