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Circuit Tracks on 3-D Thermoplastic Surfaces

Circuit tracks on the surface of flame retardant 3D thermoplastics give new possibilities for electronic design and for miniaturization of electronic devices. Many production stages of circuit pattern application on 3D thermoplastic devices set thermal and chemical resistance requirements for the plastic material. These material requirements depend on the manufacturing methods chosen. In our experiments the metallization of thermoplastics was done by using magnetron sputtering. A thin Ni/Cr layer (0.2 mum) with a subsequent copper layer (2-3 mum) was sputtered onto the thermoplastics. The final copper layer was grown electrolytically. Circuit patterns on the 3D thermoplastic surfaces were made by using an electro deposit (ED) photo resist. The Ni/Cr layer could be also utilized as a thin film resistance material. Thin film resistors were produced in the same manufacturing process by increasing the number of manufacturing stages with another photoimaging/etching stage. In this paper we investigated the suitability of several thermoplastics as a substrate for circuit patterns. The mechanical, thermal and electrical properties of the plastic substrates are essential in our evaluation. The capability of the magnetron sputtering process in metallization was evaluated by measuring the variation of the thickness of sputtered metal layers on different shapes. The adhesion of the sputtered metallic layer to the thermoplastics was measured with a peel strength test