Dispensing flip chip underfill process problems and solutions

Although flip chip is not a new technology, over the last few years we have seen this low cost interconnect solution applied to substrates other than ceramic. It is now more common that bare die and flip chip are mounted on FR4 and even flex substrates for low cost manufacturing of advanced electronics such as PDAs, pagers and mobile phones. Along with the use of these new substrates has arisen the need to "underfill" the die after reflow. This paper details the different hardware requirements and the process parameters involved and their effect on the final results obtained. Understanding each parameter and the controls that are required in a production environment is key to correct process implementation.