Study of flip ultrasonic bonding process with Non-conductive paste

In the process of interconnecting flip chip packages, the reliability of chip interconnection is enhanced by employing underfill technology after the bonding is completed. However, with the continuous reduction in chip pitch and fill gap, the conventional underfill technique utilizing capillary action fails to meet the requirements. This paper investigates a novel filling technique that combines inverted ultrasonic bonding with non-conductive paste. The aim is to achieve high-quality solder joint interconnection interfaces through low-temperature ultrasonic bonding without utilizing the conventional underfill that depend on capillary action. Experimental results demonstrate that a reliable solder joint interconnection with a high-quality interface morphology is formed between the chip and the substrate when employing the bonding process with a bonding head temperature of 100° C, bonding force of 24N, ultrasonic power of 10w, and a duration of 3s, while the substrate remains at room temperature. Furthermore, the study examines the impact of bonding force and ultrasonic time on the formation of a desirable interfacial morphology and discusses the mechanism of non-conductive paste (NCP) in the ultrasonic bonding process.