Encapsulation process development for flexible-circuit based chip scale packages

The ultimate driving forces for the development of small form-factor chip scale packages (CSPs) are the market demands for small, light and high performance products. There are tremendous numbers of chip scale packages available in the market, some are simply evolved from conventional package formats with smaller package dimensions, such as area array molded ball grid arrays (BGAs) and lead frame based CSPs, others involve innovative developments such as the flex-based μBGA technology and wafer-level CSPs. The flex-based μBGA technology has been a very successful package format, and tremendous efforts have been implemented in the process development for the technology. In this article, three flex-based chip scale packages (based on patented μBGA technology) will be discussed. The focus will be on the encapsulation process development. Because of the unique package structures and material sets used in the flex-based CSPs, various encapsulation challenges were raised. The encapsulation solutions will be compared and discussed for each type of flex-based μBGA technologies, including the dispensing pump technologies, material characterization, process characterization and optimization. Based on the evaluation results, type C μBGA technology is recommended for its simple assemble process flow, balanced protection on beam leads and solder ball joints and shorter manufacturing cycle time as well.