Probabilistic approaches and reliability design of power modules

¹ LGP-ENIT, 47 av. d'Azereix, BP 1629, 65016 Tarbes Cedex, France
² Power Electronics Associated Research Laboratory (PEARL), rue du Docteur Guiner, 65600 Semeac, France

Corresponding author: alexandre.micol@enit.fr

Received: 21 December 2007
Accepted: 25 March 2008

Abstract

The weak point for the standard power IGBT modules in terms of reliability is thermal fatigue in solder joints due to the thermal stress induced by constitutive materials with different coefficients of thermal expansion (CTE). So far, many researches are aimed at defining accurate finite element simulation with constitutive equations of materials behaviour and fatigue failure relation connecting the inelastic strain and the number of cycles before failure. Even if these relations can be clearly identified, we can see that the validation of the finite element model is difficult due to the scatter of input data. In fact, the fatigue life of solder joints strongly depends on geometric shape, solders behaviour (due to the process) and applied load. The aim of this paper is to estimate the probability of failure of power module with the structural reliability methods. Thus the geometric, materials and loading variables are considered as random variables and the failure mode is modelled with the called limit state function. The two methods, response surface method and neural network method, are used here to evaluate the reliability of the lead-free solder. The sensitivities of the mean and the standard deviation for each random variable have been evaluated.