Stress impact of moisture diffusion measured with the stress chip

•Measuring the stress during soldering, temperature cyclings, and moisture diffusion.•Verifying a high stress accuracy of the stress chip.•Simulating results of all loads for model characterizations and failure conclusions.•Detecting of stress development during temperature cycling test.•Parameter identification with a DoE of the coefficient of diffusion expansion.

The experimental observation of the actual thermo mechanical weak points in microelectronics packages remains a big challenge. Recently, a stress sensing system has been developed by the publicly funded project that allows measuring the magnitudes and the distribution of the stresses induced in the silicon dies by thermo-mechanical loads.Moisture can saturate a package very fast at high temperatures and high humidity within hours but also at low temperatures and low humidity within weeks or months. Every normal stored or used package will be swelled due to this moisture. A high temperature over a short time or within the first cycle of a temperature cycling test will dry the package and the internal stress of the package decrease. This moisture swelling will be investigated in this paper.All measurements are supplemented by finite element simulations based on calibrated models for in depth analysis and for extrapolating the stress results to sites of the package that are not measured directly. The methodology of closely combining stress measurements and FE simulation presented in this paper has been able to validate the stress sensing system for tasks of comprehensive design and process characterization as well as for health monitoring. It allows achieving both, a substantial reduction in time to-market and a high level of reliability under service conditions, as needed for future electronics and smart systems packages.

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