Characterization and Modelling of Epoxy Mold Compounds for High-Voltage Integrated-Circuit Packages

(22:10 + Q&A) Prof. Luigi Balestra, University of Bologna
From the 2024 IEEE Symposium on Reliability for Electronics and Photonics Packaging
Summary: The rapid advancement in the high voltage integrated circuit (HV-IC) technology requires the development of packaging materials that exhibit high performance in terms of electrical and thermal stability. To this purpose, epoxy mold compounds (EMCs) with a large fraction of silica fillers have been recently adopted as encapsulating material for their ability to provide protection against mechanical and environmental stresses, such as heat and ultraviolet rays. The SiO₂ fillers contribute to reduce the thermal expansion coefficient and to increase the thermal conductivity, which are crucial for maintaining the integrity and performance of HV-ICs under high operational loads. Moreover, they contribute to reduce the current leakage through the package and increase the breakdown strength of the compound. However, the presence of moisture can severely compromise the electrical properties of the compound affecting both the leakage current and the maximum value of the electric field that can be sustained by the EMC. Conductivity measurements of samples with a significant amount of absorbed water reveal a strong increase of the current with time. This behaviour can be attributed to the reduction of the charge trapping phenomena and to the formation of hetero-charge due to water dissociation in to H₃O+ and OH- ions. Moreover, the presence of humidity leads to a slightly increase of the breakdown voltage (BV) and, at the same time, to a reduction of its frequency dependence due to the larger EMC conductivity which prevents the formation of space charge inside the sample.
In order to give a theoretical explanation to the observed phenomena and clarify the effects of water on the space charge accumulation in EMC, numerical simulations based on the bipolar charge transport model have been performed. The contour plot of the simulated space charge inside a wet sample subjected to a DC stress is reported. It clearly shows the formation of homocharge and its slow redistribution which leads to the increase of the electric field and consequent reduction of the Schottky barrier, giving rise to the current instability at larger stress times. The main goal of this abstract is thus to clarify the charge transport mechanisms in EMC by means of measurements and numerical simulations shading light on the role played by water absorption on the reliability of HV-ICs.
Bio: Luigi Balestra received the M.S and the PhD degrees in Electrical Engineering from the University of Bologna in 2018 and 2022, respectively. Currently, he serves as a Junior Assistant Professor at the same institution. His research interests include TCAD simulation of Si and GaN power semiconductor devices, as well as numerical modeling of advanced materials for the passivation and packaging of electronic devices.

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