High <i>Q</i>-Factor PCB Embedded Flip-Chip Inductors With Multilayer CZTB Magnetic Sheet for Power Supply in Package (PwrSiP)

Abstract

This article investigates a novel approach to the integration of multilayer, thin film magnetics embedded in printed circuit board (PCB) for Power Supply in a Package (PwrSip) applications. A solenoid inductor structure is formed by sandwiching a multilayer CZTB magnetic sheet between two distinct PCBs with copper tracks on each which form the upper and lower windings of the device. A solder reflow process utilizing solder balls mounted on the exposed NiAu pads of one of the PCBs is used to create the electrical connection between the two boards, hence, forming closed current loops for the windings of the inductor. This novel inductor structure enables the use of about 4 oz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$140~\mu \text{m}$ </tex-math></inline-formula> ) of copper to enclose the multilayer CZTB magnetic sheet, and hence demonstrates very low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\text {dc}}$ </tex-math></inline-formula> . The multilayer CZTB magnetic sheet is characterized by using a Ryowa permeameter. The magnetic sheet exhibited a permeability of 367. The manufactured flip-chip inductor was electrically characterized by using a vector network analyzer (VNA). The device has a footprint of 7.25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and has an inductance of 52 nH. The fabricated PCB embedded inductor achieved a peak quality factor of 23 at 40 MHz.