| Summary: | 博士 === 國立成功大學 === 航空太空工程學系 === 103 === Three Dimensional Molded Interconnect Devices, also known as 3D-MID, integrate both mechanical and electrical functions on plastic substrates. The products are characterized with mechanical structures and electric circuits. This research is based on In-Mold Decoration, also known as IMD, process for 3D-MID. IMD process prints electric circuits on plastic films which are subsequently thermoformed to 3D surface for final products. The thermoformed 3D plastic film is then trimmed and inserted into mold cavity for injection molding to make the final 3D-MID product with electric circuits and mechanical structures.
In the first phase of printing ink on plastic films, it ran into an issue of high cost by using conductive silver ink paste for printing. In this research, a new process had been developed to increase the conductivity and lowered the cost by using conductive ink with electroplating process. Experiment results showed that after adding 20% of conductive carbon black, the resistance was 104 for printed lines of 0.9mm in width 40mm in length on PC films. The resistance dropped to 1.3 if treated with electroplating.
The issue of phase 2 was the deformation of the plastic films during thermoforming because of the high temperature of punch and die. The film was then deformed by tensile stress and the printed circuits were distorted. A semispherical thermoforming die with a diameter of 100 mm had been developed for the study. PC films with 0.178 mm thick were used to investigate the transformation of 2D electric circuits to 3D surface and the mapping from 3D to 2D. The experiment results showed that the deformation is sever along the sides. The deformation ratio from the experiment was 47.6% versus 49.4% from the simulation of deformation model. The errors of the deformation model were 10.3 ＆ 5.8% in X- ＆ Y- directions; respectively, while the errors of T-SIM, a commercially available deformation model, were 17.2 ＆ 20.0% in X- ＆ Y- directions, respectively.
The challenge was burrs on the cutting edge of the plastic films in phase 3 for trimming. A trimming die was developed to study the phenomenon with PC films of 1 mm thick. The results showed that there were four distinctive areas in the cross section of film cutting edge (1) Roll-over; (2) Shear zone or burnish; (3) Rupture zone or fracture; (4) Burr. There were always burrs of 63±17.4 m long on PC-film edges after trimming. The burr’s length increased with film temperature or the clearance between die and film. When the clearance became small, the zones of burnish and fracture had bigger portion. If it got large, the zones of burnish and fracture became narrow.
In phase 4, there were warpage of the plastic films during heating and cooling because of the difference of surface temperatures. The product was then hard to assemble. A round-plate die and 80% PC ＆ 20% ABS had been used to study the effect. PC films of 0.178 mm was inserted in mold cavity for injection molding. Control of the mold temperature was the major factor that affected the warpage. The experiment results showed that material temperature of 250℃ would cause short shots and the worst warpage of 3.2 mm. Warpage was improved to 0.63 mm if mold temperature dropped to 90℃.
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