The study of cyanate ester underfill adhesives under typical flip chip assembly process conditions

The characteristics of underfills and flip chip packaging have been studied at length for the past few years. The correlation of the underfill and the assembly process, however, is key in ensuring a high performance flip chip package. Thus, the changes of the behaviour or characteristics of the mate rial need to be identified as the process changes. The assembly process its elf may sometimes be the cause for failure of the packages as it could have caused the material to change in behavior or even be destroyed. A recent s tudy has looked at the flow characteristics and the matching of the underfi ll material and the substrate or die. This study of a cyanate ester based u nderfill material focuses specifically at the adhesion strength of the mate rial as it proceeds through the flip chip packaging assembly process. The a ssembly process includes underfill cure, encapsulation material cure follow ed by preconditioning and IR reflow. An epoxy based underfill material is u sed as control to compare the performance of the cyanate ester based materi al. Additional information such as modulus, weight loss and warpage are als o presented. From the results obtained, it is clear that the initial perfor mance of the underfill material after cure is not a good indicator of its a ctual performance after flip chip assembly. Some key parameters such as out gassing and moisture absorption are also deduced from the results.