An In-Situ Technique for Measuring the Individual Contact Resistance between the Pins of an IC Package and the Board of a Flexible Hybrid Electronic System

An in-situ technique is presented for measuring the individual contact resistance between the pins of an IC package and a flexible substrate used in hybrid electronic systems. As the substrate flexes, the forces that adhere the IC to the substrate change and cause increase to the series contact resistance; sometimes catastrophically. Tracking this resistance is seen to be fundamental to the success of electronic systems mounted on a flexible substrate subjected to various levels of bending throughout its life cycle. The measurement technique exploits the electrostatic discharge protection circuitry in an IC chip to create a circuit loop involving the contact resistance and the series incremental resistance of the ESD circuit via two IC pins, one being the GND or VDD pin. While the series contact resistance between the pins of the IC package and the board can be measured with a four-point Kelvin measurement, it is extremely difficult to perform with small surface-mount IC package devices. The experimental results pertaining to Kapton polyimide substrate subjected to a controlled bending process will be described. The method proposed here will determine the contact resistance with a relative accuracy error of less than 1%.