Time-dependent rheological behavior of fluids for electronics packaging

In electronics packaging, one of the key processes is dispensing fluid materials, such as adhesive, epoxy, encapsulant, onto substrates or printed circuit boards for the purpose of surface mounting or encapsulation. In order to precisely control the dispensing process, the understanding and characterization of the flow behavior of the fluid being dispensed is very important, as the behavior can have a significant influence on the dispensing process. However this task has proven to be very challenging due to the fact that the fluids for electronics packaging usually exhibit the time-dependent rheological behavior which has not been well defined in literature. In the paper a study on the characterization of the time-dependent rheological behavior of the fluids for electronics packaging is presented-In particular a model is developed based on structural theory and then applied to the characterization of the decay and recovery of fluid behavior which happen in the dispensing process due to the interruption of process. Experiments are carried out to verify the effectiveness of the model developed.