Rheology design considerations for one step chip attach materials (OSCA) used for conventional mass reflow processing

One step chip attach (OSCA) materials are dispensable polymeric materials for flip chip assembly, which are designed to flux metallic interconnections and subsequently cure into an underfill providing mechanical reinforcement and environmental resistance following reflow. OSCA-R materials are designed specifically for conventional mass reflow processing and thus enable a drastic simplification of the assembly process by combining the fluxing, soldering, defluxing and capillary underfilling steps into a single step: the integration of this technology is transparent for the customer (e.g no capital investment needed) provided the product design integrates the customer´s production line specificities. As an example, OSCA-R materials must have a process-friendly rheological design that accommodates the various steps during device assembly. Simply stated, if OSCA-R materials cannot be dispensed properly or the die placed correctly the OSCA process will not work. This paper presents the rheological design of OSCA-R materials with a focus on the flow requirements during the dispensing and die placement process steps.