Prediction of robustness of packages by cohesive zone finite element simulation and verification by non-destructive tests

Abstract

Thermo-mechanical stress caused by the mismatch of coefficients of thermal expansion (CTE) and temperature variations remain a major concern for the reliability of semiconductor components. Over the last decade a lot of effort was spent to find solutions to avoid delamination in packages by increasing adhesion. Cohesive zone element simulation allows predicting delamination behaviour and the location of critical areas which are prone to unstable crack propagation. During failure analyses, scanning acoustic microscopy (SAM) is often the method of choice for the detection of delaminated interfaces. Exposed pad packages demand a more sophisticated method to detect lead frame side wall cracks and delamination as well. To fulfil the requirements for future exposed pad packages for automotive applications, we introduce a simulation based approach for estimating how much adhesion is necessary to avoid delamination at critical locations. Partly released elastic energy stored at critical interfaces (limited delamination) can help to avoid unstable crack propagation and, thus, increase the robustness of these packages under cyclic loading. Helpful would be a method (preferable non-destructive) to verify the amount of delaminated side wall area (lead frame, die paddle, and moulding compound) to identify the critical delamination temperature for the exposed pad packages.