The reliability of COF Joints with Tin Bumps and Non-Conductive Adhesives for Image Sensor Module Application

Abstract

We developed a low cost and low temperature chip-on flex(COF) bonding technology by using Sn bumps and non-conductive adhesive(NCA) for image sensor device. Two types of Sn bumps, square and hemispherical bumps, were fabricated. Sn bumps were formed sequentially by electroplating and then were reflowed to form the hemispherical bumps. Device with Sn bumps was bonded with flexible-printed circuit board(F-PCB) using NCA at 180°C after the NCA was dispensed. To evaluate the reliability of the COF joints, a thermal cycling (TC) test, high temperature storage (HTS) test, and temperature and humidity (T&H) test have been performed. The bondability and reliability of joints were evaluated by measuring the contact resistance of each bump. The electrical test showed that COF bonding was successful with no failed bumps, and the contact resistance of COF joints was very low about 10mΩ per bump. After aging treatment at 150°C slightly increased the contact resistance. But failed COF joints were not observed before and after aging treatment. The reliability of COF joints fabricated using hemispherical bumps was good more than that of joint with square Sn bump. NCA trapping in the interface between bump and pad had an influence on the reliability of COF joints. The results of our experiments were successfully performed in application for the temperature sensitive devices such as image sensor module.