The effect of different bonding temperatures on the mechanical and electrical performance of NCF-bonded flip-chip-on-flex packages

Liquid crystal displays (LCDs) and organic light emitting diodes (OLEDs) are the technology involved in electronic displays in order to get a better viewing angle and high-density resolution products. Fine-pitch, flip-chip interconnection is one method which is able to enhance the display performance with high color resolution. Nonconducting film (NCF) is a novel material developed for fine-pitch applications. This study investigates the temperature effect on the electrical contact performance of an NCF-bonded chip-on-flexible (COF) substrate package. The changes in contact resistance after reflow at a peak temperature of 260degC for three times were measured with a four-point probe method. The bonding temperature has a significant effect on the peel strength of the NCF-bonded COF. A high peel strength for the NCF COF bonded at a high temperature indicated that the NCF obtained sufficient mechanical strength to hold the interconnection joints. A low bonding temperature is preferable to obtain good electrical contact, but sufficient high temperature is needed to ensure a good mechanical and reliable joint. An excessively high bonding temperature is to be avoided because it gives instant curing at the contact point which restricts good electrical conduction. An NCF with a curing degree of ~86% was needed to ensure sufficient and reliable electrical joints in the COF