Use of BCB in high frequency MCM interconnects

Multichip modules (MCMs) are increasingly used for high frequency, microwave, and millimeter wave applications. This has prompted the need for low loss dielectrics to meet the performance requirements of multilayer interconnects used in MCMs. In the GE high density interconnect (HDI) process, adhesives are used to bond dielectric film layers over bare chips and components. After vias are formed in the dielectric and adhesive, patterned metal is fabricated, and additional layers of dielectric are bonded and additional patterned metal is fabricated to complete the interconnect structure. In this study, we evaluated the electrical performance of selected adhesives used to bond one dielectric film layer to another. The use of a low loss thermoset polymer such as benzocyclobutene (BCB) as the adhesive resulted in lower dielectric losses compared to an epoxy-based adhesive evaluated over the 10-20 GHz regime tested. Based on the experimental data derived in this study, the electrical performance improvement should be even more significant at higher frequencies