Millimeter-wave frequencies were once considered the exotic realm of radio astronomers and military missile guidance systems. But recent frequency allocations by the United States Federal Communications Commission (FCC) and other global regulatory agencies have opened opportunities for communications systems at 60 GHz, 80 GHz, and other millimeter-wave bands. Still, the question has always been: Can devices, components, and circuits be made repeatably and affordably for these frequencies? At least one printed-circuit-board (PCB) fabricator, Filtran Microcircuits, Inc. (FMI), believes they can.
FMI (Ottawa, Ontario, Canada), a subsidiary of Merrimac Industries, has long been associated with the processes and skills needed to make practical millimeter-wave circuits. With increasing demands for high-data-rate and video communications links, millimeter-wave technology may get the commercial boost it needs from services at 60 and 80 GHz. And FMI is ready with the skills and equipment to fabricate fine-geometry circuits through 100 GHz.
FMI does not play favorites when it comes to circuit-board materials, since the company works with microstrip, bonded stripline, thick-metal-backed polytetrafluoroethylene (PTFE), and even multilayer circuits with homogeneous and mixed-dielectric layers. Working with design engineers at Merrimac Industries and with additional high-volume manufacturing capability at the firm's facility in San Jose, Costa Rica, Filtran can produce precision PCBs in small to large volumes for commercial, military, and space customers.
Using custom magnetron sputtering systems and advanced microlithographic techniques, FMI can realize printed-circuit line widths and spacing as fine as 1 mil (0.001 in. or 25 µm) with ±0.2-mil accuracy on both hard (ceramic) and soft (PTFE) circuit-board materials. FMI adds embedded resistors for soft substrates and sputtered nickel-chromium resistors for hard substrates at standard resistance values of 50 Ω/square, although other values are also available. The company features a proprietary liquid photoresist process for creating single-sided, double-sided, and multilayer circuits with plated through holes.
For thermal and ground interconnections, FMI can realize filled viaholes as small as 0.010 in. in diameter. FMI can metalize viaholes by several approaches, including its proprietary sputtered-blind-hole (SBH) process (see figure). The unique process involves using a thin-film copper "seed" metalization on a viahole, reinforced by electroplated copper. A surface finish, such as tin, tin-lead, nickel, or gold, is added on top of the copper layers.
FMI can process single-sided circuits on panels up to 24 X 24 in. and multilayer circuits on panels as large as 18 X 24 in. The company accepts many standard circuit layout files, including DXF, Gerber, and IGES formats, and can even help a customer optimize their layouts.