Thermal Fatigue Life and Quantitative Reliability Analysis of Wafer-Level Chip Scale Packages
Date Issued
2008
Date
2008
Author(s)
Hsu, Teng-Kai
Abstract
In study the reliability of electronic packages from mechanics point of view, the results of stress and strain obtained from finite element analysis are deterministic values. The fatigue life of the package predicted based on a modified Coffin-Manson equation or its equivalent is also a deterministic value. However, the real test outcomes reflect the package life is, in fact, a random variable following a certain probability distribution. Consequently, the tested lives of a certain type of package are frequently plotted in a Weibull probability paper but not a unique and deterministic value. In order to find out possible causes of the contradiction, some parameters involved in the finite element and life prediction analyses are considered random variables in the present paper. A certain type of wafer-level chip-scale package is used as an example. With regard to the finite element analysis, it is found, through parametric sensitivity study, the size of the solder bump affects the fatigue life of the package the most. Therefore, in the first stage of the nondeterministic analysis, the solder-bump size of the package is modeled a random variable in consideration of real manufacturing tolerance. Its effect on the random fatigue life prediction and quantitative reliability assessment of the package is investigated and discussed through statistical analysis of the simulation result. In the second stage of the nondeterministic analysis, parameters appearing in the modified Coffin-Manson equation are modeled as random variables in consideration of data scatter of the fatigue test result. Their effects on random fatigue life prediction of the package are investigated and discussed through either analytical derivation or simulations. The degrees of influence of all studied parameters on the fatigue life and reliability prediction of the package are discussed in detail in the present paper.
Subjects
WLCSP
fatigue life
reliability
Type
thesis
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