Contact resistance measurement for Au bumped IC to ITO on glass for LCD´s

A 4-wire resistance measurement method is used to evaluate the contact resistance of Chip On Glass (COG) bonding using Anisotropic Conductive Film (ACF) to prevent the need of compensation for series resistance of the ITO tracks. A comparison is made between the 4-wire measuring method and a Daisy chain measuring method. In the Daisy chain design the ITO tracks are metalized except for the contact area. The results show a very large difference between these measuring methods. To understand this difference, simulations are done, showing a systematic error in the 4-wire measuring method. Extending the measurements and simulations from ITO to metal tracks covered with ITO, using the same contact resistance for a single ACF particle show for the 4-wire measuring method as for the Daisy chain measuring method a perfect fit. The simulations also resulted in a reliable value for the contact resistance for a single ACF particle.