Failure Modes and Fatigue Testing Characteristics of SMT Solder Joints

The work is connected with implementation of lead-free technology by small producers of electronic equipment, according to RONS Directive of European Community. Results of accelerated mechanical and thermal cycling fatigue tests of PbSn and lead-free solder joints, realized in GreenRoSE EC Project, for accelerated reliability assessment, are described. The aim of the work is development of cheap test methods, applicable by small producers of electronic equipment. Thermal shock cycling method and mechanical method of cycling bending of PCB samples with soldered SMT components are discussed. Charge factors applied by mechanical and thermal tests are compared. FEM models are applied. Thermal shock cycling is realized in two-zone climatic chamber. Developed in TU Warsaw PC controlled mechanical test stand is presented. For obtaining of relative deformation between soldered component and PCB, was applied the bending system exerting moment, flexion radius and other charge conditions, uniform for all components soldered on whole surface of the PCB sample. The failures are detected by measuring the joints resistance. Design and data of special test samples for simple resistance measurements and failures detection are shown. Relation between bending curvature of PCB sample and joint resistance, before and after the test, is shown. The failure modes are classified. Influence of test parameters on failure distribution data and characteristic of joint parameters are discussed. The failure distribution on Weibull plots for mechanical and thermal cycling are compared. The investigations showed the possibility of simplified reliability assessment of lead-free electronic products by mechanical fatigue testing. Advantage of this method is lower cost and shorter test time in comparing with thermal cycling