Solder damage models

V. Stolkarts, B. Moran, and L. Keer, Constitutive and Damage Models for Solders, 48th Electronic Components and Technology Conf Proc., 1998, p 379-385... 

The aforementioned constitutive equations predict the continuum deformation in the solder. However, the total functional lifetime of a solder interconnection also includes the initiation and propagation of fatigue cracks. Crack development is addressed by so-called damage models. The... 

Stolkarts, M. Moran, B. Keer, L. Constitutive and damage model for solders. Proceedings of the Electronic Components and Technology Conference, New York, NY, IEEE NY, 1998 379-385 pp. 

A local model of a solder joint can be found in Hg. 59.17. The local model is subjected to multiple thermal cycles and a final damage parameter is extracted. A typical thermal cycling loading profile to which the model is subjected is similar to that shown in Fig. 59.3. About two to four cycles are run to achieve stability of the hysteresis loop. 

In a properly made solder joint, the solder should always be the weakest link, deforming to relieve stresses so they are not transmitted beyond the terminal pads on either side of the joint. Additionally, this is the preferred failure mode because solder fails due to the accumulation of plastic strain damage and the failure behavior can be modeled and predicted. That is, the interfaces in a proper solder joint fail when the interfacial strength is degraded due to any number of mechanisms such as a phase change, impurities, void accumulation, etc. If the interfacial strength is reduced below the applied stress, the interface fails. This type of failure mode is more difficult to model and predict compared to the accumulation of plastic strain damage in the bulk solder. 

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