Accurate material models are necessary to obtain meaningful results in computational simulation. The results of materials testing and the process of developing a material model for solder under impact loading are presented in this paper. The material model will be used in the simulation of electronic packages under drop impacts. As such, it is necessary to incorporate the effects of strain rate sensitivity in the model. Dynamic materials properties of Sn63Pb37 solder were obtained by testing the solder using the Split Hopkinson Prt:ssure Bars. The accuracy of the material models was evduated by subjecting single solder balls to impulsive loads on the SHPB and comparing the test results with finite element simulation.During Split Hopkinson Pressure Bar tests on cylindrical solder (eutectic) specimens, it was found that the stress to achieve 2% strain increases from 79 to 112 MPa when the strain rate increased from 450 to 2720 s-'. Examination of the fractured surfaces showed that there is a transition from ductile to brittle fracture as strain rate is increased. SHPB tests on single solder balls also showed that the stiffhess of the solder balls is strongly dependent on rates of deformation. For example, when solder balls (eutectic) of diameter 0.76 mm were compressed at a rate of 2.35 d s , a force of 36 N was required to achieve 0.2 mm compression. For a deformation rat(: of 8.83 d s , the force increased to 50 N to achieve the same compression. 0*7803-836!L6/04/$20.00 02004 IEEE I * COLOR I ~~ Your accompanying CD-ROM contains a version of this paper with color images.httpYhwv.cpmt.org/proceedings/
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