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High Density Integration of High Frequency High Current Point-of-Load (POL) Modules with Planar Inductors

Fig. 1.Fabrication process of PCB-embedded planar inductor.
This work provides detailed information regarding the development of new fabrication techniques using two different magnetic materials for the integration of high frequency high current POL converters. Mixed low-fire ferrite laminates and metal-flake composite materials were chosen for the fabrication of planar inductors and further high density integration of POL modules based on a comparison of core loss density and permeability with other candidate magnetic materials. The first POL module with a multilayer ferrite inductor substrate was fabricated using modified LTCC processing and hybrid integration techniques. The second module with a PCB-embedded metal-flake inductor was prepared using PCB processing techniques. The electrical performance and thermal reliability were then tested on both integrated high power density POL prototype modules. This demonstrated that both selected magnetic materials and associated integration techniques are desired for the integration of high frequency high current POL modules. The PCB-embedded inductor module may have a cost advantage due to the easy integration process and the feasi-bility of mass-production.

Planar inductors made by mixed laminates of low-temperature sintered Ni-Cu-Zn ferrite tapes and metal-flake composite materials are used for high density integration of point-of-load (POL) modules. Incremental permeability and core loss density were characterized on toroidal samples under high dc bias to demonstrate that both materials are suitable for application in high frequency high current POL converters. In order to realize a high power density POL module, a multilayer ferrite inductor laminated with alternating layers of ESL 40010 and ESL 40012 in a 1:1 ratio was fabricated and integrated with the active layer. Meanwhile, standard printed circuit board (PCB) processing was adopted for the POL integration with a PCB-embedded inductor using NEC-TOKIN's metal-flake composite materials. These developed 3-D integration approaches can be used to reduce the footprint and increase the power density for POL converters. This demonstrated that the power efficiency of both POL modules with integrated planar inductors can achieve above 87% at an operating frequency of 2 MHz and an output current of 15 A. Additionally, no obvious efficiency degradation was observed on the integrated POL modules after a certain number of thermal cycling from -40 °C to 150 °C.

Fig. 2. SEM micrographs of laminated PCB substrate with embedded metal-flake composite inductor.