Low cost flex substrates for miniaturized electronic assemblies

Electronic power converters have been designed, produced, and disseminated to the market in mass quantities utilizing a number of fabrication techniques; ranging from standard printed circuit board (PCB) technologies for low cost applications, to conventional thick film on ceramic, to direct bond copper (DBC) approaches for high power, higher cost applications. Each of these approaches holds a share of the power packaging market, but they all demonstrate a limitation to conventional two dimensional "flat board" strategy. PCBs, thick films, and DBCs are all technologies which restrict, for the most part, circuit and package designs to two dimensional boards. The one potential pathway into the third dimension is through the use of multilayers; an approach, which becomes increasingly difficult with each additional layer added beyond the first, and with the exception of high performance solutions is typically cost prohibitive for the majority of applications. This paper will demonstrate the feasibility and viability of flexible polymer substrates. Flex technology employs industry standard PCB and/or thick film processes, offers the lower cost, higher performance solutions inherent with the majority of polymer plastics, and as a final bonus, essentially frees the designer to more efficiently utilize all three dimensions of space. The researchers have demonstrated the feasibility of this low cost alternative solution through the fabrication and testing of integrated power modules, which utilize flexible polymer substrates in conjunction with both surface mount and bare dice. These DC/DC power converters transform 120 V/240 V inputs to 9 V, 7-W outputs, and illustrate through their unique geometrical design the miniaturization advantages of fully utilizing the three dimensional space offered by flex circuitry. (C) 2002 Elsevier Science Ltd. All rights reserved.