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 over 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 in the behaviour or characteristics of the material must be identified as the process changes. The assembly process itself may sometimes be the cause for package failure, as it could have caused the material to change in behavior or even be destroyed. A recent study has looked at the flow characteristics and the matching of the underfill material and the substrate or die. This study of a cyanate ester based underfill material focuses specifically at the adhesion strength of the material as it proceeds through the flip chip packaging assembly process. The assembly process includes underfill cure, encapsulation material cure followed by preconditioning and IR reflow. An epoxy based underfill material is used as control to compare the performance of the cyanate ester based material. Additional information such as modulus, weight loss and warpage are also presented. From the results obtained, it is clear that the initial performance of the underfill material after cure is not a good indicator of its actual performance after flip chip assembly. Some key parameters such as outgassing and moisture absorption are also deduced from the results.