A FINITE-ELEMENT PROCEDURE OF A CYCLIC THERMOVISCOPLASTICITY MODEL FOR SOLDER AND COPPER INTERCONNECTS

A finite element procedure using a semi-implicit time-integration sche me has been developed for a cyclic thermoviscoplastic constitutive mod el for Pb-Sn solder and OFHC copper, two common metallic constituents in electronic packaging applications. The scheme has been implemented in the commercial finite element (FE) code ABAQUS (1995) via the user- defined material subroutine, UMAT. Several single-element simulations are conducted to compare with previous test results, which include mon otonic tensile tests, creep tests, and a two-step ratchetting test for 62Sn36Pb2Ag solder; a nonproportional axial-torsional test and a ther momechanical fatigue (TMF) test for OFHC copper. At the constitutive l evel, we also provide an adaptive time stepping algorithm, which can b e used to improve the overall computation efficiency and accuracy espe cially in large-scale FE analyses. We also compare the computational e fforts of fully backward Euler and the proposed methods. The implement ation of the FE procedure provides a guideline to apply user-defined m aterial constitutive relations in FE analyses and to perform more soph isticated thermomechanical simulations. Such work can facilitate enhan ced understanding thermomechanical reliability issue of solder and cop per interconnects in electronic packaging applications.