Research On Integrated Inductor Embedding Technology Within Organic Packaging Substrate For Power Conversion System

With the increasing demands for integration and miniaturization,power conversion systems require the three-dimensional heterogeneous integration of power management chips with passive components to significantly reduce interconnect parasitics and volume.Inductors are vitally important for high-efficiency power conversion systems.By integrating inductors and other converter components onto chips or within packages,integrated power conversion systems can be realized,saving space and reducing power dissipation.Therefore,the development and integration of high-performance power inductors have become crucial technological bottlenecks in advancing high-density,high-efficiency integrated voltage regulators.There is an urgent need to develop innovative integration technologies and materials to overcome these limitations.The main research contents of dissertation are as follows.First,utilizing advanced lithographically defined vias technology,solid interconnected vias were fabricated on an organic packaging substrate for the first time.This innovative technology not only reduced the dc resistance of the power inductors but also enhanced the smoothness of the external walls of the vias,significantly improving the high-frequency performance of the devices.Concurrently,the design of the internal copper ring served as a sacrificial mold,enabling precise patterning of the composite magnetic core materials.This approach not only heightened the precision of integration but also safeguarded the performance characteristics of the composite magnetic materials.Subsequently,a composite magnetic core material fabrication process compatible with organic packaging substrate was developed,employing a blend of Fe Si Cr amorphous alloy powder and epoxy resin,resulting in composite magnetic core with superior electromagnetic properties,which achieved a low coercivity of 4.25 Oe,a saturation magnetization of 4.4 k Gauss,and a stable real permeability of 9.6 up to 1000 MHz,with a loss tangent of the permeability only 0.056 at 100 MHz.By coating the Fe Si Cr amorphous alloy particles with a layer of epoxy resin,the electrical resistivity of the composite cores was significantly enhanced,reaching 6.87 x 10~6Ω·m.Finally,employing semi-additive process flow and screen printing technology,a high quality factor solenoid magnetic-core inductor embedded within the packaging substrate was developed,achieving an inductance of 41.9 n H,a dc resistance of 60 mΩ,and an impressive inductance-to-resistance ratio of 0.7 n H/mΩ.Moreover,the saturation current is 3.81 A and the peak quality factor is 42.7@92.8 MHz.Secondly,in order to further enhance the current carrying capacity and efficiency of inductors,research has been conducted from four aspects:composite magnetic core materials,packaging substrate materials,inductor structural design,and fabrication processes.This approach aims to meet the stringent power supply requirements of high-performance computing.First,an interleaved windings style coupled inductor structure was implemented to achieve a higher negative coupling coefficient,thus effectively enhancing the inductor’s saturation current capability.Subsequently,a high-resistivity composite magnetic core material was introduced to reduce high-frequency losses in the magnetic-core and to enhance saturation current.Enhancements to photolithography vias technology,along with the use of an organic packaging substrate with high thermal conductivity,enabled the implementation of a solid micro-rectangular vertical interconnect structure which is designed to further reduce the dc resistance of the windings and improve heat dissipation capabilities.Finally,batch fabrication and testing were conducted on 16 types of packaged integrated coupled magnetic-core inductors.Analyzing from the perspective of applications in two-phase interleaved buck converter circuit with negative coupling,and considering the trade-off between inductor efficiency and size,the optimal choice was identified as a 2-turn inductor with a 1.3 mm magnetic-core width.Occupying only 2.9 mm~2 of area,the high efficiency above 95%is achieved for a wide current range of 0.11–2.32A operating at 100 MHz,demonstrating exceptional performance.Moreover,saturation current tests revealed the inductor’s extraordinary current carrying capacity,reaching up to 16.52 A.Finally,in response to the trends of reducing circuit area and thinning packaging substrates,this research originated from an integration strategy for a fully integrated voltage regulator system,designing and developing a coaxial lateral-transmission-line magnetic-core inductor based on an ultra-thin coreless package.This design aims to minimize parasitic interconnect effects and achieve a compact system thickness.Innovatively utilizing lithographic via technology to first create continuous trench vias,this approach provided high-throughput and precise patterning capabilities for composite magnetic sheets.It effectively addressed the issues associated with repetitive adjustments and time-consuming trial-and-error processes inherent in traditional laser cutting techniques used for patterning composite magnetic core sheets.Subsequently,simulation optimization,fabrication,and batch testing of the inductors were conducted.Test results demonstrated that the packaged integrated micro-coaxial transmission-line magnetic-core inductor exhibited a dc resistance of only 2.9 mΩand an inductance of 2.1 n H,with an inductance-to-resistance ratio of 0.724 n H/mΩ.At a switching frequency of 100 MHz,the inductor achieves a quality factor of 23.6 and an average quality factor of 103.6.Additionally,under a 5 A dc bias,the reduction in inductance was only 4.4%of the initial value.The performance of the inductor has been calculated for a single-phase buck converter circuit at 1.75 V to 1.08 V with a switching frequency of 100 MHz.The results demonstrate that the proposed inductor achieves the highest efficiency,surpassing 98%,for load currents exceeding 939 m A,and the peak efficiency reaches 98.7%.Additionally,the inductor demonstrates excellent electromagnetic interference suppression and current carrying capabilities,underscoring its substantial potential for deployment in high-efficiency integrated voltage regulators.