Development of a Time Efficient Method to Enhance the Process of Parallel Lapping

Abstract

Cracks, voids and delamination are the commonly observed defects inside a packaged chip. In order to determine the root cause of these defect, the selection of appropriate preparation or characterisation methods are vital to prevent from the formation of artefacts, therefore leading to the misinterpreting of the results. When one investigating the interface related defect such as delamination, scanning acoustic microscopy is usually used. However, this non-destructive investigation is often not suffice to make a conclusive result as the verification by destructive techniques are generally required in order to gain a better understanding regarding the actual root cause. Mechanical cross-section is no-doubt one of such destructive techniques which chosen by analyst to verify this type of defect. However, artefacts such as crack and contamination are generally formed during the process of cross-sectioning. Parallel lapping from front side follow by focus-ion-beam is a well-known alternative method to overcome the shortcomings of cross-section, but one of the main hurdles that is usually encountered by an analyst is the challenge to precisely measure and control the remaining thickness of the mould compound from overgrinding. In this paper, we propose a new time efficient work flow with high precision and accuracy which able to measure the mould compound thickness during front-side parallel lapping in order to prevent from overgrinding. This new work flow has demonstrated to shorten the preparation time drastically, and the remaining mould compound can be precisely measured to an accuracy of ∼0.2 um.