On The Modeling And Control For The Pick-up Process Of Thin IC Chips

Accurate and uninjurioushandling and transferringof IC chips plays a critical role in advanced electronic packaging technology. It affects directly the performance, cost, miniaturization, reliability, and the lifecycle of the ultimate electronic devices on assembly lines, especially for thin IC chips. This dissertation addresses some important issues of the chip pick-up process, including the physical mechanism of chip peeling, evaluation of failure, process parameter control, new mechanical devices for picking up chips, etc.; and some theoretical and practical achievements are obtained. The main research work and contributions of the dissertation are introduced as follows:Physical mechanism of the chip peeling is investigated.The dissertation investigates analytically the interfacial peeling mechanism of a chip-on-substrate structure subjected to a transverse concentrated load resulting from the ejecting needle,from the point of view of interfacialfracture mechanics of layered structures.Effects of keyfactorson the chip pick-up process,including chip size, initial crack length and substrate material,are analyzed, especially for thin chips. Practical advices are given as well.Competing fracture in the pick-up process is disclosed.A competing relationship between chip peeling-off and chip cracking is discovered based on experimental observations of electronic packaging. A competing index is proposed to characterize the competing fracture behavior, and the competing fracture mechanism is then uncovered fundamentally. Based on the index, the effects of chip geometry on the competing behavior, and further on successful chip pick-up process,are investigated. A method for evaluating critical chip sizes including the critical length and the critical thickness are presented, which describes the extremity of the single-needled chip pick-up process. Process margin is proposed, based on which, advices for the pick-up process are discussed detailedly, especially for thin chips.The local damage to the chip during the pick-up process is addressed.The contactimpact effect of the ejecting needle is analyzed, considering three key factors involving impact speed, distance from the contact center and whether to penetrate the substrate or not. Critical impact speed is calculated to optimize process parameters, for the purpose of ununjurious chip picking up.A new device for secure chip peeling is explored.The design method and procedures are given as well as the design inequation, which is mainly based on the theory of buckling of compressed bars. The device has the characteristic of constant upper limitof ejecting force, and can be used for secure chip peeling.Two process control issues are dealt with. The two issues are the high-speed high-accuracy point-to-point positional control problem and the soft-landing control problem, which adapt to two chip pick-up styles with and without contacting, respectively. And, a modified trajectory planning with smooth speed switching is proposed, which improves greatly the efficiency of chip pick-up on the premise that the force control is not hampered.