MCM-D/L using copper/photosensitive-BCB multilayer for upper microwave band systems

This paper describes an MCM-D/L technology for upper microwave band systems. The substrate of this MCM is constructed of copper/photosensitive-benzocyclobutene (P-BCB) multilayer formatted onto a print wiring board (PWB). Features of the developed MCM are (1) a novel microstrip structure for improvement of high-frequency characteristics and (2) a low-cost simple copper/P-BCB process using polishing technology. As BCB has good thermal and electric characteristics compared with polyimide or epoxy, BCB is expected to be applied to high frequency systems. We have developed a low-cost copper/P-BCB multilayer process with a new microstrip structure, and measured the high-frequency characteristics (10 GHz~40 GHz). In the process technology, we took note of the adhesion of the metal film/BCB interface. As a result of a study of the adhesive metal and chemical/thermal treatment before and after fabrication of the film, we found that the necessary adhesion force was obtained by N₂ plasma treatment of the BCB surface before metal evaporation and annealing (250°C:BCB cure temperature) after evaporation. Also, Cr was found to be the best material for adhesion. The high-frequency characteristics (10 GHz~40 GHz) were estimated by a ring resonator and microstrip transmission line of copper/P-BCB multilayer fabricated on a PWB. Also, the S-parameters showed good characteristics. The developed MCM-D/L substrate has been proved to be suitable for high-frequency systems