Passive mold alignment for the fabrication of polymer through-holes using punching and double-sided hot embossing

Abstract

Aligning two mold inserts is one of the most important steps in the punching of through-holes for polymer microfluidic devices. Significant misalignment of the mold inserts could reduce device functionality or allow for interference between mold inserts. Active and iterative methods require repetitive experiments, characterization, and mold adjustments making the process tedious. Passive set-up alignment using a temporary kinematic coupling can be an alternative to the active and iterative methods. To do this, the three v-grooves on the primary mold insert mate with the three spheres set in dimples on the complementary mold insert. Once the mold inserts are aligned and secured, the spheres are removed, and face-to-face contact between the mold inserts can be achieved for the molding operation. This aligns the primary and complementary mold inserts without any repeated measurements or adjustments. To validate the proposed design, primary and complementary mold inserts were fabricated with alignment joints and features to conduct a punching process. Prior to assembling the mold inserts to the thermal press for punching, they were pre-assembled to inspect the innate misalignment due to the machining of the mold inserts. Along the X-Axis, the X-magnitude (∆Xi) of the mean misalignment ranged from 2 to 7 µm and the Y-magnitude (∆Yi,) of the mean misalignment were from 7 to 13 µm. The X- and Y-magnitude (∆Xj and ∆Yj) of mean misalignment along the Y-Axis ranged from 1 to 4 µm, and 5–12 µm, respectively. The mold inserts were aligned and subsequently mounted to the thermal press. Punching was conducted on a polymer substrate Misalignment was the displacement of the center-point of a die hole impression from the center point of a through-hole. The X- and Y-magnitudes of the mean misalignment (∆Xk and ∆Yk) along the X-Axis ranged from 12 to 82 µm and 32–72 µm, respectively. The X- and Y-magnitudes of the misalignment (∆Xl and ∆Yl) along Y-Axis were 11–71 µm and 32–70 µm, respectively. The results of experiments showed that the proposed passive alignment method is applicable to the punching of through-holes for polymer microfluidic devices.