Theoretical Study And Process Optimization On The Peeling Technology Of Ultrathin Silicon Dies

Chip peeling-off is one of the key technologies to accurately transfer a single die from the wafer to a target circuit. Especially as the integrated circuit chips tend to be thinner than in the past, the reliable peeling process is of significance to promise to lower the package costs, en-hance the end product yield rate, and improve the reliability of the electronic devices as well. This dissertation addresses some important problems of the nondestructive peeling technique for a silicon-based ultrathin die including mechanics modeling, physical mechanism, and re-lated experiments of the normal ejection process with one/multi-needle, and then a theoretical and practical peeling process window is established finally. The main research effort and con-tributions of the presented dissertation are introduced as follows:Firstly, a mechanical model is established to address the typical chip-adhesive-tape struc-ture. The chip and substrate layers are connected by a deformable interface considered a con-tinuous distribution of elastic-brittle springs, which is able to simulate the peel and shear be-havior of the adhesive layer. And also, we have shown the corresponding analytical solution strategy. Rupture of the springs is governed by a mixed-mode crack-growth criterion expressed in terms of the energy release rate, and could successfully reproduce the chip peeling process.Secondly, we focus on the theoretical analysis and consider the finite element analysis as a supplement to introduce the adhesive fracture mechanics theory into the analysis of chip peel-ing, where several important factors are investigated involving the geometrical dimensions, material properties of the adhesive structure as well as the ejecting needle force. The typical peeling processes are formulated such as the cohesive peeling-off of an array of IC chips bonded a stretched substrate, and the cohesive fracture of the chip-adhesive-tape structure with needle reactions. In particular, the mechanics principle and technics predominance of the multi-needle process is uncovered compared with the traditional single-needle technology.Thirdly, aiming at the nonlinear characteristic of ultrathin silicon die in the fracture strength testing, the large deformation theory is introduced to deal with the errors from the linear formula. Meanwhile, a correction factor is defined to conveniently apply the proposal nonlinear solution into the practical test in order to obtain the precise evaluation values for the chip strength by the experimental data.Fourthly, based on the adhesive peel mechanics we have obtained the evaluation formula of critical adhesive fracture energy considering the extensibility of the adhesive tape. Then, the strippable properties of the soft adhesive tape is experimentally studied by implementing peel test, which shows the angle-dependence of the peel force and rate-dependence of critical exper-imental adhesive fracture energy. And it is expected that this presented test method would be an available to experimentally obtain the initial peeling condition.Lastly, competing fracture between ultrathin chip peeling and chip cracking is discussed, where the peeling criterion without any damage is established for a single silicon die combining strength theory and Griffith fracture criterion. Based on the novel criterion we focus our atten-tions to investigate the effects of the geometries of the die such as the thickness and the length. At last, the theoretical process windows is applied to guide the peeling experiments with needles for the ultrathin die with different dimensions, and the satisfactory results could verify the fea-sibility of the presented process design theory and method.