Issues in assembly process of next-generation fine-pitch chip-on-flex packages for LCD applications

Some of the current assembly issues of fine-pitch chip-on-flex (COF) packages for LCD applications are reviewed. Traditional underfill material, anisotropic conductive adhesive (ACA), and nonconductive adhesive (NCA) are considered in conjunction with two applicable bonding methods including thermal and laser bonding. Advantages and disadvantages of each material/process combination are identified. Their applicability is further investigated to identify a process most suitable to the next-generation fine-pitch packages (less than 35 mu m). Numerical results and subsequent testing results indicate that the NCA/laser bonding process is advantageous for preventing both lead crack and excessive misalignment compared to the conventional bonding process.