Development of ultrasonic flip chip bonding for flexible printed circuit

Small form factor and high density printed circuit boards (PCB) have been already realized by flip chip (FC) bonding technology. However, the requirement for finer pitch PCB is still increasing with shrinkage of die and wiring. Therefore, conventional flip chip bonding technology will not provide sufficient capability or productivity to meet future demands. The authors have focused on flip chip bonding method utilizing ultrasonic vibration. Flip chip modules using flexible printed circuit (FPC) are strongly required for such as mobile phone applications. For that purpose, we have investigated to assemble semiconductor devices with FPCs applying this method, particularly for large size die with multiple pads. In this report, we have evaluated relationship between bonding parameters and reliability using several kinds of copper clad laminate (CCL) with different plating conditions. We show the correlation between formation of microscopic metallic bond and actual chip on flex (COF) module performance. As a result, we succeed to realize 35μm pad pitch COF module.