Development of crack propagation models for solder joints under creep-fatigue conditions

In electronic assemblies, solder joints are the mechanical and electrical connections between the electronic components and the printed wiring board. In the design phase it is crucial to estimate the solder joint life of an electronic component subjected to certain load conditions. In order to predict the solder joint life specific damage models, based on the failure mechanism that caused the failure, are applied. In temperature cycling, the failure mechanism for the solder joint is creep-fatigue.; In this thesis, two different kinds of components are analyzed to predict their solder joint life: the leadless chip resistors/capacitors and the sluggers. A fracture mechanics crack propagation damage model is proposed for eutectic solder Sn63Pb37 under fatigue and steady state creep conditions, and other empirical crack propagation models are investigated. The fracture mechanics damage model developed is a relationship between C* and the crack growth rate, and it is based on experiment data. It turns out that a power law relationship relates C* and crack growth rate. C* can be used only in steady state creep conditions, and the energy rate definition given by Landes and Begley is used to calculate C*. Another way to calculate C* is also proposed by the author of this thesis. The fatigue contribution is indirectly accounted into C* because it is calculated during cyclic loads instead of monotonic loads, while J is not included in this model. This fracture mechanics damage model can be used to predict the solder joint life of electronic components in steady state creep conditions. The independent variable, C*, can be determined from FEA modeling and the dependent variable obtained is the crack growth rate.; Temperature cycling experiments are conducted on sets of leadless chip resistors, capacitors and sluggers to study the crack growth behavior and measure the crack extension. Some empirical crack propagation models are also investigated. One is Darveaux's crack propagation model, which is applied to the slugger to verify if the model can be used for components different from those for which it was developed. Two other empirical crack propagation models are proposed based on the crack propagation behaviour in the solder joints of the leadless chip resistors and the sluggers. Finally, an initiation damage model is investigated as a damage prediction model for leadless chip resistors and capacitors, and the simulation results are compared with the experiment results.