Mechanics analysis of ultra-thin chip peeling from substrate under multi-needle-ejecting and vacuum-absorbing

Chip peeling-off, mainly accomplished through the cooperation of needle-ejecting and vacuum-absorbing, plays a critical role in chip transferring process. However, there are few studies involving the quantification of process parameters, such as optimal needle position, needle force or displacement, to access to a reliable chip peeling. In this paper, optimization criteria for a high success rate of thin chip peeling-off are presented. With the cooperation of multi-needle-ejecting and vacuum-absorbing, the chip-adhesive-substrate structure is modeled within the framework of Timoshenko’s beam theory, and the competing fracture behavior between chip cracking and peeling-off in the peeling process is analyzed. A dimensionless peeling health index Γis proposed to evaluate the health status of the chip in the peeling process, and the effects of the needle position, the chip-adhesive-substrate structure geometry and material on the peeling health index are examined. On a basis of the numerical results, the optimal conditions for high-productivity peeling are achieved, which are the optimal needle position roughly at the edges of the chip, and the optimal shift point of changing the condition from needle-ejecting to vacuum-absorbing where the crack length in the adhesive layer expands to nearly the half value of the chip length. In addition, the expressions of the optimal ejecting needle force/displacement corresponding to the optimal shift point are obtained by the dimensionless analysis and fitting method. Furthermore, the optimization criteria including the optimal needle position and the optimal shift point of changing the condition from needle-ejecting to vacuum-absorbing are verified by experiments.