A study on thermoforming process of stretchable circuit and its performance in manufacturing of automotive lighting
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Date
2018-04-01
Authors
Mohamad Fikri Mohd Sharif
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Abstract
Printed circuits have been developed started from printed circuit board to flexible circuit and moulded interconnect devices (MID). The evolution of these kinds of circuit is due to limitation and highly demand of complex circuit design to fulfil the requirements of customers. However, manufacturing process of MID requires complex process since it involves advance equipment such as laser machine to produce printed circuit on 3-D part. In this research, an alternative manufacturing process was introduced to construct functional circuits using stretchable ink printed onto 2-D substrate and then transformed into 3-D shape by thermoforming process. A rear lighting product of national car was chosen as a reference product. Mould for the thermoforming process was fabricated based on reversed engineering technique where the lighting part dimensions were measured using coordinate measuring machine (CMM) and then transferred into 3-D drawing using Solidworks. The drawing was read computer numerical control (CNC) machine through coding generated by computer aided manufacturing (CAM) to manufacture the mould. The ink was initially printed on a flat thermoplastic substrate using screen printing technique. The printed ink was cured under 120oC for 30 minutes in an oven to form a highly conductive circuit. The circuit with the substrate were transformed into 3-D shape through thermoforming process according to the shape of mould which was designed similar to the existing design of automotive lighting. Light emitting diode (LEDs) were then assembled on the circuit by dispensing conductive adhesive at the LEDs joints and cured again in the oven at 120oC for 10 minutes to form strong bonding at the joints. Mechanical and electrical performances of the new design of automotive lighting were characterised and compared with the existing design using equipment such as multimeter, four point probes, spectrometer, scanning electron microscopy (SEM) and universal testing machine. Even the circuit of the new design had stretched and deformed that led to increase in circuit resistance, its electrical performance shows promising results. There was no significant difference between new design and existing design of automotive lightings in terms of power consumption by the system and luminous flux of LEDs. This new manufacturing process of printed circuit offers a future alternative method in manufacturing the automotive lighting product.