High volume capable direct chip attachment methods

In this communication potential high volume flip chip processes are compared. Special emphasis has been placed on new no-flow underfillers that combine fluxing and underfilling actions. These materials enable one to minimize process steps required for the flip chip assembly, since the dispensing of the underfiller after reflow is no longer required. It is also possible to avoid post-curing, because the curing action takes place during the reflow. The results showed that despite the benefits of the no-flow materials, conventional underfills have advantages especially in terms of reliability and process yield. However, the properties of fluxing adhesives are improving continuously, and so they are expected to become more viable for high volume direct chip attachment process. Furthermore, a new direct chip attachment option, called “transfusion bonding” (TFB) technique, is briefly explained. The TFB technique differs from the conventional soldering because it is not based on the intermetallic formation but on the generation of ductile, dilute Sn-based solid solution joints without using fluxing or lead-containing solders. The results pointed out that despite the novel nature of the technique reliable interconnections have been manufactured by using ICs down to 100 micron bump pitch and still with a good process yield