Effects of bonding parameters and ACF material properties on the ACF joint morphology in ultrasonic bonding

In this study, effects of bonding parameters and ACF material properties on the ACF joint morphology were investigated to understand influencing factors for a stable ACF joint in US bonding. According to the experimental results, the morphology of acrylic-based ACFs with 8 um diameter particles significantly changed as the bonding parameters changed due to high viscosity and fast curing rate. However, epoxy-based ACFs showed similar joint morphologies regardless of bonding parameters due to low viscosity and slow curing rate. As the bonding temperature increased from 150°C to 250°C, ACF joint gaps of the acrylic-based ACFs increased up to 12 um due to a smaller resin flow by a faster curing rate at higher temperatures. At 200°C constant bonding temperature, the ACF joint gaps decreased from 7 um to 2 um with increasing bonding pressure in the range of 2MPa to 4MPa due to a larger resin flow at higher bonding pressures. This result indicates that higher bonding pressure is desirable for high-speed bonding at high temperatures using acrylic-based ACFs. However, Acrylic-based ACFs with 20 um diameter particles can be a simple solution for high-speed bonding because they showed stable particle contacts due to a large particle size than ACF joint gaps regardless of bonding parameters.