PCB-embedded solenoid inductors with different magnetic cores

The design, modeling, fabrication, and characterization of three types of printed circuit board (PCB)-integrated solenoid inductors using air core and two embedded magnetic cores are demonstrated in this paper. The fabrication applies a double-side PCB process to form the inductor windings. A cavity for accommodating the magnetic cores is created in the middle of the PCB. Two types of magnetic cores fabricated using in-house developed proprietary processes are applied as magnetic cores for the inductors. One of these cores is made out of FeSiAl magnetic powder, while the other is made out of laminated NiFe thin films. The size of the inductor is 5 mm × 3 mm × 1.56 mm. The quality factor of the FeSiAl powder core inductor reaches its peak value of 36.6 at 40 MHz. The NiFe multilayer thin-film core inductor obtains the highest inductance (22.48 nH) at 10 MHz but has a lower quality factor compared with the two other inductors. The tested saturation current of both magnetic core inductors is greater than 3 A. The inductors are also tested in a Buck converter switching at 10 MHz with an input voltage of 4 V, output voltage of 1 V, and load current of 1 A. The FeSiAl powder core inductor has the lowest loss of 115 mW, thereby suggesting that embedding the pre-made powder cores or multilayer thin-film cores is a good option for manufacturing PCB-integrated inductors. The powder core approach tends to yield an excellent high frequency performance, while the multilayer thin-film core option allows the integration of the magnetic thin-film process into the PCB fabrication flow to reduce costs and improve reliability for volume production.