Analysis Of Anisotropic Conductive Adhesive Interconnection Under Multi-factors Influence And Optimization For Its Performance

Anisotropic conductive adhesive (ACA) interconnection is widely used in electronic products to supply electrical and mechanical connection as it is lead-free and offers the potential for low cost, and further pitch reduction. In application, many factors in packaging process and service environments have effects on the performance of ACA interconnection which could lead to electrical deterioration or even failure of interconnection. How to improve the electrical performance and mechanical reliability is one of the most concerned issues in ACA interconnection. This paper researches into the principles of coupled physics fields problems including the thermal, curing and mechanical phenomena. Various factors'effects are analyzed on the performance of ACA interconnection; relations among them are proposed, and parameters are optimized. The work is organized as follows:The mechanisms of electrical and mechanical interconnection are researched. Through the process analysis of interconnection and solidification of the adhesive, the effect of particles deformation on electrical performance and the effect of residual stress on mechanical properties of ACA interconnection are studied. The process parameters' effects are analyzed through experiments. The results show that enough curing time is necessary to make the conductive adhesive cure fully. Proper pressure should be applied in the assembling process for the conductive particles in the adhesive to make good contact with the bump and the pad without much residual stress left at interface of the interconnection. And proper temperature is important to make the conductive adhesive cure quickly and avoid its degradation. Low curing temperature and enough curing time should be used to keep low thermal stress at the interface. Thus, parameters should be chosen properly to improve the interconnection performance based on application and avoid the confliction of various factors.A numerical analysis method of the ACA interconnection is proposed under multi-physics effects. The effects and principles of various factors are investigated, and rules of choosing parameters are indicated under different environments. The curing reaction of ACA is studied using thermal analysis experiments and the curing kinetic model is obtained. The coupled effect of curing and thermal is simulated and as well verified by experiment. A method is developed to solve coupled physics fields problems including the thermal, curing and mechanical factors, which is verified by existed research. The sub-modeling technique for solving the transient thermal-curing-mechanical problem is proposed and the numerical model of conductive particles is derived in the interconnection process. Various factors and interaction are analyzed by the parametric Finite Element Model using the methodology of design of experiments (DOE). The key factors'effects on the quality are summarized. The conclusion is that higher pressure adds to the electrical performance; higher curing temperature and more rigid conductive adhesive and substrate help to achieve full contact among conductive particles, chips and the substrate, which however decrease the mechanical reliability in contrast; the height of chip bumps has little effect on both the electrical and mechanical performance. In the end, a quality index considering the mechanical reliability and electrical performance simultaneously is proposed, and rules of choosing parameters are indicated under various environments.The ACA interconnection process is optimized through a modified differential evolution (DE) method. Multi-objects optimization is performed, which chooses the electrical and mechanical performance of interconnection as sub-objects while the cure temperature, cure pressure, adhesive type, and substrate type as the optimization variables. During the optimization process, the surrogate model technology and DOE method are employed to cope with the high computational cost in the iterative calculations. The standard differential evolution (DE) method is modified to calculate the optimal results. The procedure for optimizing the parameters in ACA interconnection is proposed based on the agent model and modified DE method. Finally the conclusions are obtained that lower cure pressure, adhesive of low Young's Modulus, and low rigid substrates can improve the mechanical reliability; and enhancing the cure pressure properly can lead to better combined performance considering both electrical and mechanical requirements. The application in the industry validates the conclusion.An integrated software tool is developed to analyze the ACA interconnection, which can help to calculate the deformation of conductive particles and residual stress of the interface under different process parameters. Also, the process of ACA interconnection can be optimized. And an ACA interconnection example of RFID card packaging is simulated and optimized using the software tool, which boosts the quantity of production and yield rate.