Mechanics analysis and experimental study of ultra-thin chip peeling from pre-stretching substrates

Successful chip peeling from a substrate facilitates the transfer process for obtaining the final functional chips, but remains a challenge in the practical production of ultra-thin chips. Flexible ultra-thin chips are prone to fragmentation during the peeling process, due to their fragility. In this study, a substrate pre-stretching process is introduced to the picking process to achieve a high yield of chip peeling, and this process is explored via modelling and experiments. The chip-adhesive pre-stretched substrate structure is modelled, involving both multi-needle ejection and vacuum suctioning, within the framework of Timoshenko's beam theory. The theoretical analysis is validated using finite element analysis to compare the surface stress distribution on the chip and tip stress within the adhesive layer. During the peeling process, the competitive fracture behaviour of the chip between cracking and peeling is analysed using a dimensionless peeling health index as a metric to assess the health status of the chip. The effects of substrate pre-stretching on the adhesive layer stress, chip layer stress, and peeling health index are analysed. As substrate pre-stretching is found to improve the peeling health index only in the case of needle ejection, but impairs the peeling health index in the case of vacuum suctioning, needle ejection is considered the sole effective peeling method when a substrate pre-stretching process is introduced. Furthermore, through meticulous experimental verification, it is confirmed that pre-stretching of the substrate can significantly improve the success rate of chip peeling.