Low temperature chip on film bonding technology for 20 µm pitch applications

Abstract

We developed a low temperature and low cost chip on film (COF) bonding technology using Sn/Cu bumps and nonconductive adhesives (NCAs) for 20 µm pitch applications. 20 µm pitch Sn/Cu bumps were formed by electroplating and reflowing. COF bonding was performed at 150 °C for 10 s using a thermo-compression bonder after dispensing the NCA. Three different commercial NCAs were applied during bonding. The electrical properties of the COF joints were evaluated by measuring the contact resistance of each joint by using the four-point probe method. All COF joints were successfully bonded and the average contact resistance of each joint was approximately 7 mΩ, regardless of the type of NCA. To evaluate the reliability of the COF joints, a thermal cycling test (−55/125 °C, 1000 cycles) and a temperature and humidity test (70 °C/95 % RH, 1000 h) were performed. The contact resistance measurement showed that there were no failed bumps in any of the specimens and all of the joints passed the criterion after reliability testing. In the COF joints, metallurgical bonding was formed between the Sn/Cu bumps and Cu pads. This metallurgical bond provided strong and stable contact between the Sn/Cu bumps and Cu pads in the reliability tests.