Characterizing Geometric Effects of Thermal Forming Mold Using Taguchi Method

Abstract The production of In-Mold Electronics (IME) involves applying heat and pressure to soften a polymer film with printed circuits, allowing it to conform to a mold shape. The geometrical features of the mold, such as draft angle, draw depth, and fillet radius, influence the axial strain distribution of the polymer film, which in turn affects the electrical performance of the printed circuits. This study investigates the deformation behavior of a 0.25 mm polycarbonate (PC) film during the thermal molding process, considering its temperature dependent viscosity. Two different molds configurations-one with a single protrusion and the other with dual protrusions were analyzed. The draft angles for the bump features were set at 25°, 30°, and 35°, while the fillet radii were 0.4 mm, 0.6 mm, and 0.8 mm, and the draw depths were 1 mm, 2 mm, and 3 mm. For the dual protrusions mold, the spacing between each protrusion was varied at 3 mm, 4 mm, and 5 mm. During the thermal forming process, the film temperature was raised to 200 °C, and a 3 kPa pressure was applied. Using Polyflow commercial software, the maximum axial strain in the PC film after forming was determined. The influence of mold geometry on strain distribution was then analyzed using Taguchi method, and analysis of variance (ANOVA) was conducted to quantify the contribution of each geometric factor. Results indicated that for the single protrusion mold, draw depth had the most significant impact on maximum tensile strain, followed by fillet radius and draft angle. In the dual protrusions mold, spacing had a minor influence compared to other geometric parameters. These findings highlight the importance of draw depth and fillet radius in thermal forming mold design for IME applications.