MCM-LD: large area processing using photosensitive-BCB

This paper demonstrates how laminate based printed-wiring-board technology (PWB) and thin film deposited dielectric technology (MCM-D) can be combined to form a low-cost solution for microelectronic interconnect schemes which require high density circuitry. A multilayer telecommunications module was fabricated to demonstrate the feasibility of this MCM-LD concept. Standard copper-clad laminates were processed using conventional PWB techniques to form the first level of metal interconnects (75 μm lines and spaces). A photosensitive benzocyclobutene layer was coated onto the boards and patterned to form 50 μm×200 μm nested vias down to the metal lines. A second metal interconnect layer was formed from a sputtered seed layer and plated up copper. Chip interconnection was carried out using gold wirebonding. Several large-area-processing (LAP) techniques were evaluated to determine the compatibility of the two interconnect technologies and to demonstrate the cost advantages of manufacturing large panels at high throughput levels. Spin coating, spray coating, meniscus coating, and extrusion coating were compared as dielectric deposition options and an in-line belt furnace was used to cure the dielectric layers on the laminate boards (rapid thermal curing). Laminate materials which were evaluated include: FR-4 (epoxy), BT (bismaleimide-triazine), PI (polyimide), and CE (cyanate ester)