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108 DESIGN007 MAGAZINE I SEPTEMBER 2019 Editor's Note: Dominique Numakura first covered monocoque printed circuits in a column from May 2019. What would you think if electronic circuits could be built directly on a polyethylene tere- phthalate (PET) package of strawberries and birthday cakes? It was a dream for electron- ics engineers to draw 3D circuits directly on the surface of the housing or packages of prod- ucts. The idea behind molded interconnect de- vice (MIDs) was created about 30 years ago to satisfy this dream. Several new processes, such as laser engraving and inkjet printing, have been proposed to build electronic circuits on 3D-structured ob- jects. Unfortunately, no one was very successful with it as a popular cir- cuit technology because of the technical and eco- nomic difficulties. Wiring with flexible circuits could be a prac- tical solution. Nowa- days, most mobile device manufacturers are con- suming huge amounts of thin, flexible circuits to attach on the surface of the housing in limit- ed spaces. However, the cost of flexible circuits and assembling them is another headache for de- vice manufacturers be- cause they are not negligible in the whole cost of the devices. Now, a new idea has been created in Tai- wan to build 3D-printed circuits. It looks like an egg of Columbus, and the manufacturing process is very simple. Firstly, a silver-based thick-film circuit is printed on a thermoplas- tic sheet, such as PET. The baking temperature of the circuit must be lower than the melting temperature. It depends on the capability of the circuit manufacturer, but double-layer cir- cuits with via holes are available (Figure 1). The second step is to warm the whole circuit and put it in the forming die set. Under an ap- propriate temperature and pressure, the plastic Monocoque Printed Circuits: An Update EPTE Newsletter by Dominique K. Numakura, DKN Research LLC Figure 1: After the circuit is printed.

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