Polymer flip-chip bonding of pressure sensors on a flexible Kapton film for neonatal catheters

In this paper, we describe the development of a new approach to mounting silicon pressure microsensors inside a 5 French (1.67 mm outer diameter) neonatal catheter tube for intravascular blood pressure measurements. Kapton film was used as a low-cost, flexible interface between the flip-chip bonded sensors at one end and wires to external electronics at the other end. Conductive polymer paste was used to flip-chip bond sensors to the flexible Kapton substrate at low temperature, while gold traces were used to form electrical interconnects on the film surface. Conductivity and bonding strength of the resulting polymer bumps were on the order of 100 mΩ and 4.43 mN mm−2, respectively. Piezoresistive pressure microsensors were successfully mounted on Kapton carriers, packaged inside catheter tubes, and characterized in both gas and liquid environments. The sensors exhibited sensitivity of approximately 60 µV mmHg−1 over the target pressure range of 0–350 mmHg. Two-week tests in water at 27 °C and 36 °C showed only slight variations in contact resistances, indicating that the developed approach to packaging microsensors was sufficiently robust for the target application.