Anisotropic Conductive Film The Ultrasound Interconnection Cog Devices Process

The environmentally friendly manufacturing is most important goal for the electronic packaging industry. In particular, the use of anisotropic conductive film (ACF) instead of soldering and underfill encapsulation helps to achieve such goals. Nowadays, ACF is widely used in COG (Chip-on-Glass) assembles in flip chip. Generally, the ACF joints of COG assemblies are mainly completed by the thermo-compression processing. However, there are some shortcomings for the thermo-compression processing, for example, too high bonding temperature and too long will damage the chip, and cause larger interfacial residual stress, which will lower reliability of COG assembles. In this paper, a novel anisotropic conductive film bonding method using lateral ultrasonic vibration was put forwarded for COG assemblies. Through experiments and numerical modeling, the optimized ultrasonic bonding process parameters were gotten. This paper mainly includes:(1) Bonding monitor system was constructed, which could be used for acquisition and analysis of ultrasonic power and vibration of the chip.(2) By a large number of ultrasonic bonding and shear tests, the effects of the ultrasonic bonding process parameters on the bonding strength of COG assemblies were investigated. The results show that the bonding time and bonding power greatly affect the ACF joints strength of COG assembles, while the bonding force and temperature of the substrate slightly affect the ACF joints strength. The optimized ultrasonic bonding process parameters are:the bonding time is 3000ms, the substrate temperature ranges from 50 to 90℃, the ultrasonic power is 3.52W and bonding forces can be selected from 9N to 28N. Under the opotimized bonding process, the maximum bonding strength of the ACF joints in COG assemblies can be obtained as 34.5N.(3) By means of Fourier Transform Infrared Spectroscopy, the effects of the ultrasonic bonding process parameters on the curing degree of ACF material were studied. The results show that bonding time and bonding power greatly affect the curing degree of ACF, while the effects of the bonding force and substrate temperature are slight. The curing degree of ACF can reach 94% under the opotimized bonding process.(4) A mathematical model describing the relathionship between the ultrasonic bonding process parameters and the curing degree of ACF was established. The results showed that the model predictions well agreed with the experimental values.(5) One reasonable mechanics model was eatablished by introducing interfacial fracture energy, which was used to synthetically consider the effects of ultrasonic bonding parameters on the ACF joints strength of the COG assembles. The results showed that the maximum relative error between the predicted values from the established mechanics model and the experimental resuts was less than 6%. This validates the established mechanics model can be effectively used to predict the ACF joints strength of COG assemblies with the ultrasonic bonding process.