Experimental Determination Of Anand Constitutive Model Parameters For Micro-Electronics Lead-Free Material SnAgCu And Solder Joint Life Prediction

In recent year, developing lead-free solders for electronic devicesbecomes necessary because of the serious threat to human beings and theenvironment of Pb compound. Although there are more and more peoplestart to focus on studying the behavior of lead-free materials, the actual andreliable test data published are very limited. This provides us a chance tofurther study the mechanical property of lead-free material by experiment.In this paper, the standard test specimen are prepared, and theirmechanics properties and Anand constitutive model for lead-free materialare investigated based on the ASTM standards at normal temperature andhigh temperature tensile tests. A larger number of tensile tests for two lead-free materials (95.7Sn3.8Ag0.5Cu and 95.5Sn4.0Ag0.5Cu) under a widerange of temperatures and constant strain rates are conducted. A non-linearprocedure for the determination of Anand model parameters through datafitting is proposed to obtain Anand's nine parameters. To captureexperimental curves more accurately, three parameters, so (initial value ofdeformation resistance), (?) (coefficient for deformation resistance saturationvalue) andξ(stress multiplier), are modified as quadratic function oftemperature and strain rate. The modified model can indeed improve thedata fitting quality. An ANSYS model is used to predict the stress-inelasticstrain curve under constant displacement rate conditions which is used tocompare both the result of experimental measurements and the result of fitted Anand model. It is found that good agreements have been obtained incomparison.To compare with the results of bulk solder casting specimen, a seriesof tensile tests using solder wire directly at different temperatures andstrain rates are conducted. True stress-true strain curves from solder wiretests are used to compare with those from bulk solder tests.Finally, based on the Anand model parameters determined by aboveexperimental work and data fitting, a three-dimensional finite elementsimulation is applied to study the fatigue life prediction and reliability for atypical BGA solder joint under accelerated temperature cycling conditions.The life prediction based on Anand model with lead-free materials95.7Sn3.8Ag0.5Cu is investigated. The comparison with a Pb soldermaterial 62Sn36Pb2Ag has shown that the SnAgCu lead-free materialsseems to have better fatigue and creep properties. The thermal cyclingfatigue life of lead-free solder is longer than Pb solder material.