Physics of failure as a basis for solder elements reliability assessment in wind turbines

Traditionally assessment of reliability of electrical components is done by classical reliability techniques using failure rates as the basic measure of reliability. In this paper a structural reliability approach is applied in order to include all relevant uncertainties and to give a more detailed description of the reliability. A physics of failure approach is applied. A SnAg solder component used in power electronics is used as an example. Crack propagation in the SnAg solder is modeled and a model to assess the accumulated plastic strain is proposed based on a physics of failure approach. Based on the proposed model it is described how to find the accumulated linear damage and reliability levels for a given temperature loading profile. Using structural reliability methods the reliability levels of the electrical components are assessed by introducing scale factors for stresses.