Reliability and structure optimization of BGA packages

摘要

The fatigue strength of BGA solder joints was studied by an isothermal mechanical fatigue test method. It was found that the fatigue life of BGA solder joints could be estimated by Manson-Coffin's law as N{sub}f = AΔε{sub}in{sup}n, where theequivalent inelastic strain range Δε{sub}in was used as the associated fracture parameter. In order to conduct the fatigue life design easily, a statistical optimization method (SOM), which was based upon the concept of orthogonal table used in normaldesign of experiments, was applied for developing the estimation expression between the inelastic strain range Δε{sub}in and the design factors and thermal cyclic conditions. By substituting the expression of the Δε{sub}in in Manson-Coffin's law, adirect expression between the fatigue life N{sub}f and design factors was obtained, and the dispersion or the reliability of fatigue life could be easily evaluated by the expression. Further more, A mathematical programming (successive quadraticprograming) was employed to solve the optimization problem of the weight of solder joints, where the expression of fatigue life was used as the constraints of the problem. It was found that the SOM could be used as a very practical tool to estimate theproblem of fatigue life design of BGA solder joints.