20 µm-pitch complaint-bump-bonded chip-on-flex by pre-applied wafer level adhesives

A novel process which combined wafer level package technology with ultra-fine pitch chip-on-flex (COF) by sidewall-insulated compliant bumps was developed. We laminated two types of adhesives, single-layer non-conductive adhesive (NCA) and double-layer of non-conductive adhesive/anisotropic conductive adhesive (NCA/ACA), on wafers, respectively. After wafers with laminated adhesives were diced into chips, thermo-compression bonding process was executed by using high accuracy flip-chip bonder. Proper bonding parameters, such as bonding temperature, time, and pressure, were performed during bonding process. Both mechanical and electrical tests were carried out to evaluate bonding quality of adhesive-bonded COFs. 90-degree of peeling test was conducted as mechanical test to evaluate adhesion of bonding interface. Measurements of electrical insulating resistance and 606 I/Os daisy chain resistance were conducted. The reliability of pre-applied adhesive COFs with 20 μm-pitch sidewall-insulated compliant bumps was also examined. Samples that passed electrical tests were then performed to reliability test in terms of thermal humidity storage test (THST) with 85% related humidity (RH) at 85°C. From the results presented, 20 μm-pitch sidewall-insulated compliant-bump-bonded COF packages with pre-applied NCA and NCA/ACA chips were successfully demonstrated. It showed high reliability and potentiality for ultra-fine pitch COF interconnections.