The underfill processing technologies for flip chip packaging

Flip chip technology has been developed for more than 30 years and is widely used in the assembly of high-performance devices that require good functionality on substrate space. Compared to traditional wire bonding interconnection, flip chip technology offers tremendous advantages such as eliminating wire bond connections, increasing input/output (I/O) density, and using less space on substrates. With the rapid growth in flip chip technology, the need for assembly services has been developed. The key challenge in flip chip technology development is to improve the reliability of flip chip assembly. To enhance reliability, underfill materials are applied to the gap between die and substrate to provide mechanical support as well as environmental protection to the assembly. Capillary flow underfill material is used to fill the gap and protect the flip chip bumps for better reliability performance for years, but it has the limitations of lower throughput, higher cost and storage. Transfer molded underfill was developed to replace liquid type underfill materials to provide a high productivity process, less expensive materials and reliable performance. This study compares capillary underfill and molded underfill processes. Suggestions for various flip chip package types and performance concerns are then provided.