Encapsulant materials for flip-chip attach

The properties of the underfill and its characteristics, before and after curing, have a significant impact on the assembly process and the reliability of the product. Some of these are flow characteristics, filler settling, filler particle size, voiding, glass transition, coefficient of thermal expansion, adhesion strength, modulus, fracture toughness, etc. The time associated with 'underfilling' a flip chip assembly has to be 'optimized' in order to improve throughput without sacrificing assembly reliability. It depends on a variety of parameters such as the die size, the encapsulant material type, standoff height, etc. Therefore, it is critical to develop an understanding of these parameters and their effect on dispensing time. This paper provides a review of the critical factors that influence the development and implementation of an effective and efficient underfill process for flip chip assemblies. The flow properties (flow front, filler settling, and voiding) of an encapsulant not only have an impact on the dispensing time, but also significantly influence the reliability of the flip-chip assembly. This research studied the effect of encapsulant material type and standoff height on the time taken to flow to specified distances. These factors and the interactions between them were analyzed using statistically designed flow experiments. The effect of these input factors on the flow front, filler settling, and voiding have been considered. A detailed understanding of the material's flow properties and an effective estimate of the encapsulant's flow time can help to develop a robust process.