Magnetic Inductor Integration in FO-WLP using RDL-first Approach

FO-WLP with integrated solenoidal magnetic core inductor in the RDL layer was proposed and developed in this work. This provide a packaging solution to integrate high performance inductors for high efficiency power conversion to the embedded device chips without sacrificing valuable chip estate as compared to integrating the inductors on the surface of device chip. Two photo-dielectric materials were evaluated and it was found that material with higher tensile strength and percent elongation was able to sustain the magnetic film deposition and patterning process without showing cracks or delamination. Different patterning methods of the magnetic film were explored. Wet etching method has residue issues on low lying features in valley and contact vias. The sidewall of the magnetic core was highly sloped for thicker magnetic film due isotropic nature of the wet process. Dry etching was inefficient to etch the thick magnetic film. A new patterning method was developed to overcome the wet etching issues to produce magnetic core with vertical sidewall with no residue issues. Electrical characterization was performed on the fabricated inductor. The inductor shows a flat inductance response up to its self-resonance frequency, and a quality factor of 14 can be achieved. These indicates that the inductor has low-loss and can be utilized in high-efficient power conversion.