Fabricating planar spiral inductances for a wireless charging module by using 355 nm ultraviolet laser ablation

Abstract

Inductive charging is one of the major wireless charging methods used to induce current through the coil inductances of a receiver. In this study, a 355-nm ultraviolet laser was used to create planar square-spiral inductances (PSSIs) on a copper-coated glass substrate. To obtain the optimal micromachining effect, coils with various line widths (0.5, 1.0, 1.5, and 1.9 mm) were developed on the substrate surface by laser direct writing technique and using a 3-W pulsed laser at various scanning speeds (200, 600, and 1,000 mm/s) and pulse repetition frequencies (60, 80, and 100 kHz). Scanning electron microscopy results revealed that a high pulse repetition frequency and fast scanning speed can reduce the oxidation degree of processed samples. Furthermore, the edge aspect ratio was dependent on the increasing scanning speed, but the increase in the aspect ratio was not substantial. Subsequently, a wireless charging module was used to evaluate the laser ablation quality of the PSSIs, which the induction capacity increased as the oxidation degree of the PSSIs decreased and demonstrated the highest induction capacity of 11.34 % when the scanning speed was 2,000 mm/s. However, because of the power loss during wireless charging and the oxidation degree of the coil surface, the actual inductance value was approximately 15 % of the value estimated using the modified Wheeler formula. In the future, these PSSIs can be applied in wireless charging modules and the results can serve as a reference for enhancing induction capacity in PSSI design.