Effect of Time and Pressure on Ultrasonic Bonding Strength of Flexible Printed Circuit Board to Glass with Nonconductive Film

This study investigates the feasibility of ultrasonic bonding of flexible printed circuit board (FPCB) on glass with nonconductive film (NCF). The glass substrate is sputtered with Cr as a diffusion barrier and Cu to form the electrodes, whereas two different surface finishes are employed for the FPCB: immersion Sn and electroless Ni/immersion Au (ENIG). The peel strengths of the joints are investigated with various parameters, such as bonding time and pressure. The study showed that bonding time of the joints was not related to the degree of curing of NCF, because almost the same curing degree resulted when bonded for 1 or 3 s. Furthermore, the bonding pressure on the joints is strongly related to the amplitude of vibration at the horn.