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Development of Film Based Thin Multilayer PCB by Roll-to-Roll Process
Keywords: thinner and higher wiring density, multilayer process, roll-to-roll process
Thinner, lighter, higher wiring density and lower cost are the primary demands for resent consumer electronics such as mobile phones. To meet these demands, flexible printed circuit (FPC) has been getting more popular; however the wiring density is limited because of the difficulty of interconnection between the flexible film layers. On the other hand, conventional high density multilayer Printed Circuit Board (PCB) production process requires many steps and huge equipments resulting in higher cost. In this paper, a new thin multilayer PCB has been discussed that enables us to obtain a high density, thin and low cost multilayer substrate using simple roll-to-roll process. Poly p-Phenylene Terephthal Amide (PPTA) film with 4 micrometers thickness has been chosen as a core material. Epoxy resin ~10 micrometers was coated onto the both side of PPTA film as B-staged core film for multilayer lamination. Inner Via Hole (IVH) has been formed through the film using YAG laser and filled with newly developed conductive paste. This allows us to make IVH interconnection arbitrary in any layer of PCB. The resistance of a via was around 5m. The Cu wiring pattern down to 20/20 micrometers line/space was defined using etched Cu foil on a carrier foil. This Cu pattern was transcribed onto the B-staged core film which completes circuit wiring in plane. To combine the techniques above, 4-layer PCB with the thickness of 52 micrometers including Cu wiring has been obtained. Roll-to-roll process has been employed because handling of flexible thin film is the key factor to achieve lower cost operation. Reliability test results and high frequency characteristics comparing with electromagnetic simulation results will be also presented in the paper.
Takashi Ichiryu,
Matsushita Electric Industrial Co., Ltd.
Kadoma City, Osaka 571-8501,
Japan


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