Analysis of Thermo-mechanical Strains Induced in the Plated Through Holes in Thick Advanced Printed Wiring Boards

摘要

Analysis of thermo-mechanical stresses and strains induced in plated through holes (PTHs) in thick advanced printed wiring boards (PWBs) has been carried out for the conditions of their assembly processes ans stress tests. Thermo-mechanical strains and the interfacial stresses induced in signal and power plane connected pTHs have been computer using a two-dimensional axisymmetric unit cell model of the PTH and the POWB lay-up. An elasto-plastic finite element (FE) analysis of a single PTH in a unit cell has been carried out using temperature dependent stress-strain curves for plated copper and temperature dependent elastic properties for the dielectric material. Dielectric material set in the study is traditional FR4, which has a glass transition temperature, T_g, of 135degC. One half the PWB lay-up has been modeled due to symmetry in the axial direction. Two different PWB lay-ups, containing copper planes with 0.071 mm and 0.142 mm thickness and with total thickness of 6.142 mm and 7.95 mm, have been analyzed for temperatures up to 200degC.