Acceleration of lifetime modeling by isothermal bending fatigue tests

Abstract

The generation of meaningful lifetime-models is a serious and time-consuming challenge throughout the field of packaging. Wherever different materials are joined, the CTE mismatch will usually lead to thermo-mechanical fatigue due to the temperature cycles during the usage of the system. As a result, the fatigue of interconnections is the limiting factor for reliability of electronic systems. Usually lifetime investigations are executed as active or passive thermal cycles using the final systems with fixed amplitudes. The main objective is rather the validation that the system will exceed a minimum threshold than the developing of a full lifetime-model. Detailed investigations are often bypassed due to time and financial limitations not realizing the future benefits of a lifetime-model, i.e. by gaining understanding of failure mechanisms and the possibility to predict them by modelling. Especially for interfaces based on new developed and mostly insufficiently examined materials like sintered (porous) or composite with their predicted time-depending or highly anisotropic behavior, more detailed experiments are necessary to understand the physics of failure. Such results are required for the technology developing and optimization of fatigue behavior. Therefor more experiments with samples of different technology-parameters as well as different amplitudes or load-regimes are necessary to examine the stability of failure mechanisms and the damage accumulation. New concepts to conduct such lifetime investigations faster are urgently needed. The idea presented in this paper is to show a suitable method to substitute lengthy thermal cycling tests by results obtained by rapid isothermal fatigue tests at different temperatures and how to establish a correlation between both of them. For now, samples based on galvanically deposited copper are used as common reference-material. Based on physics of failure principles, the applicability and viability of such a concept then is evaluated and discussed. In conclusion, this work shows a approach for a significant acceleration of the design for reliability procedure in system integration. It is based on the now possible rapid generation of a lifetime model by thin metal layer samples which are easily manufacturable with the same technology as the thermal cycling test (TCT) samples and should show the same failure mechanism. Detailed investigations are still needed to confirm an applicability of the method also to other metal layers used in the electronic packaging industry.