Process and reliability characteristics of polymer flip chip assemblies utilizing stencil printed thermosets and thermoplastics

The implementation of low cost, highly reliable solutions for advanced packaging requirements is the culmination of successfully integrating different technology disciplines into the final product. These include advanced IC design, substrate design, and fabrication, as well as specially formulated materials and processes for production of the flip chip bump interconnect and underfill methodology. Advanced stencil printing of thermoset and thermoplastic pastes for bump formation is perhaps the most critical parameter in the fabrication of solderless flip chip assemblies with high reliability. This discussion in this paper focuses on the stencil print process when conductive thermoset and thermoplastic pastes are processed to produce the bump pattern on wafers and/or substrates. Investigation of the relationships between the stencil type, paste characteristics, and print parameters are made and correlated with resulting bump yield, uniformity and electrical resistance measurements. Long term reliability is discussed with respect to thermoset vs. thermoplastic pastes, uniformity and quality of stencil apertures, and the ability to produce repeatable, uniform bumps on wafers for flip chip assembly. Finally, suggestions are made as to the best methods for achieving high performance flip chip solutions without solder.