Local strength measurement technique for miniaturised silicon-based components

The ongoing trend to further miniaturise electronic devices in Printed Circuit Board (PCB) technologies has pointed out the embedding of components as a principal design strategy. The reliability of the PCB relies on the functionality of the embedded components as well as on their structural integrity in order to survive the embedding process. In the present work, the biaxial strength of metallised silicon chips used in PCB technologies has been tested on both the substrate and the metallised side, evidencing a significant influence of the metallic contacts on the strength and the mechanical reliability of the component. Specimens tested with the metallised side under tension underwent an early failure (lower fracture load), whereby a statistical analysis of the strength distribution evidenced the presence of a narrower critical defect size distribution (i.e. higher mechanical reliability). This phenomenon was explained by means of (i) finite elements (FE) simulations of the loading conditions, and (ii) Focussed Ion Beam (FIB) analyses of the metal-silicon interface. It was concluded that the presence of a stress concentration in the interfacial area during loading induces pre-cracks which can act as critical defects upon load enhancement, thus causing failure for a very well defined range of loads.