An Analytical Approach to Determine the Influence of Different Parameters on the Thermo Mechanical Reliability of PTH Copper in PCBs
To determine the thermo mechanical reliability of plated through holes (PTH) in printed circuit boards (PCB) different test methods are applied (e.g. thermo cycle test (TCT), interconnect stress test (IST), highly accelerated thermal shock (HATS)).The general temperature extremes of above mentioned methods induce stresses and strains in the plated copper which are below the tensile strength and the fracture strain, respectively, which leads to a trength-dependent fatigue failure mechanism.By reason of time saving (1000 cycles TCT with 1h cycling last about 40 days) and material saving a knowledge of the functional relationship of the determining factors for the cycles to failure can be very helpful as it provides the possibility to compute the dependency of the PTH copper reliability on different variables.This paper introduces an extension to the analytical considerations to estimate the influence of various parameters (e.g. coefficient of thermal expansion, temperature range, through hole diameter, thickness of PCB, thickness of plated copper) on the fatigue life of PTH copper during thermal excursions published by Werner Engelmaier 1.Based on a simple model (linear stress strain relationship below and above yield strength, no inner lands, stiff outer lands, punctual glass transition of base material, athermal behavior of Young’s modulus, tensile strength and elongation at break) the effect of the glass transition temperature and the presence of copper finish (e.g. ENIG, HASL) is included. The thermo mechanical stress problem is approached by analogy using a spring system.A discussion of the contribution of different parameters to the reliability of PTH copper completes this paper.
Stefan Neumann
Atotech Deutschland GmbH Berlin,Germany
国际会议
上海
英文
2008-03-17（万方平台首次上网日期，不代表论文的发表时间）