Predictive reliability models through validated correlation between power cycling and thermal cycling accelerated life tests

Abstract

Aims to show that with careful modelling, the fatigue life of solder joints of identical geometry and microstructure can be predicted very accurately (through empirical correlations) under different environmental test or field use conditions. Here, on the TI 144 chip ‐scale package, the empirical correlation for fatigue life developed under thermal cycling conditions is used to predict the life under power cycling. This accurate model has served as the physical basis which in to demonstrate quantitatively the equivalence of thermal cycling and power cycling as valid accelerated life tests. Describes the great importance of spatial refinement, temporal refinement, and accurate boundary conditions, including the often ignored natural convection boundary conditions, and their effect on predicted life.

Powercycling Reliability, Failure Analysis and Acceleration Factors of Pb-Free Solder Joints

“…As observed in [7][8][9][10] predicting the thermal fatigue of a solder joint on a chip scale package is a unique problem since it contains failure attributes common to both high cycle and low cycle fatigue. The loading is in the low cycle regime since the solder joints experience stresses that induce large scale yielding.…”

“…It is not always sufficient to examine just the stresses or just the microstructural deformation mechanisms particularly when the two may vary considerably on the same package. An examination of the local deformation mechanisms in the solder joints coupled with finite element simulations to elucidate local fatigue/creep driving forces can provide a more comprehensive understanding of the cyclic degradation processes [7][8][9][10]. A thorough understanding of the relationship between the microstructural deformation mechanisms and the thermal stresses engenders failure models and standards that are in agreement with physical damage processes.…”

“…Thus, it is believed that power cycling accelerated test, in which the package is differentially heated (Fig. 2), is more representative of the field use conditions and that no one test is preferred from a failure mechanism point of view [7]. One advantage of power cycling test is that the typical cycle is nearly an order of magnitude shorter than the typical thermal cycling test.…”

Modeling of the Power Cycling Performance of a Si on Si Flip Chip Assembly

“…In service, the assembly is more likely to experience an anisothermal temperature distribution due to a combination of variations in the temperature of the operating environment and local changes due to heat dissipation within the components. In the latter case, for components generating significant heat, the internal temperature may be much greater than that of the substrate [4][5][6]. Furthermore, thermal cycling typically imposes temperature ramp rates that are quite slow compared to the rate at which an assembly heats up due to internal power generation.…”

“…Power cycling will therefore better capture the transient nature of a component heating up or cooling down, which may have significant reliability implications. When traditional organic substrates are used, monitoring of the transient behaviour of FC devices has revealed that the joints first endure shear stress in one direction as the die heats up rapidly, but then in the opposing direction due to the substrate heating up more slowly but with typically a significantly larger Coefficient of Thermal Expansion (CTE) [5,6]. In a Si on Si assembly the uniform temperatures within the device during thermal cycling may result in minimal stresses due to the matched CTEs, however, depending on its duty cycle, the chip is likely to endure a greater and more rapid temperature change than the substrate [4].…”