Design and Characterization of Package Embedded Solenoidal Magnetic Core inductors for High Frequency and High Efficiency SIP Integrated Voltage Regulators
Abstract : In this article, the design and characterization of package-embedded solenoid inductors for a high-efficiency, four-phase system-in-package (SIP) buck-type integrated voltage regulator (IVR) switching at 100 MHz is discussed. The IVR enables three conversion ratios (5, 3, and 1.7–1 V) with a minimum inductance of 25 nH/phase and a load current of 10 A (2.5 A/phase). Two inductor designs (one with a rectangular core made of an epoxy dielectric/NiZn ferrite composite magnetic material/epoxy dielectric stack and one with an elliptical core of NiZn ferrite composite magnetic material only) were optimized and compared based on the highest achievable IVR efficiency. At high-load conditions (>5 A), the elliptical core inductor showed higher efficiency than the rectangular core inductor over the frequency range investigated (10–100 MHz). The elliptical core inductors were fabricated using a novel fabrication process combining core printing, noncontact photolithography, and copper electroplating. Two simple deembedding techniques which use a single thru structure and its equivalent circuit model as well as a cascade-based two-port analysis were introduced for the characterizations of the fabricated inductors. The accuracy of these deemebedding techniques was assessed using commercial, fixed-air core inductors and standard THRU and thru–reflect–line (TRL) deembedding for comparison purpose. Less than 5% difference was observed between the TRL and the introduced deembedding techniques for the inductance and ac resistance for both the fixed air core and package-embedded magnetic core inductors. The extracted electrical parameters of the fabricated inductors were compared with the modeling results and a good correlation was observed at 100 MHz.
? The technology of the power inductor has to be developed for enabling a future transfer into IPDiA’s production line, which means compatibility with PICS substrates: no electromagnetic interference (EMI) if 3D capacitors are placed below the inductor, the use of existing interconnection technologies for metal windings, a maximum thickness for the component to fit in the package.
? We gave the overall context of the work, i.e. DC/DC converter or POL converters and reviewed existing technologies and materials developed for small size and integrated inductors in commercial products and in research laboratories over the world.
? This approach can be easily adapted for realizing inductors on PCB, onchip or in-package using aluminum or gold bond wire of 25– 280 µm diameter.
? The printed core is degassed by vacuum in 30 minutes right after printing. It is verified that the problem of bubbles is eliminated by vacuum degas.
? Although simple and relatively low cost, the process is limited by the bondwire size, material (aluminum, gold) and inter-winding separation. Moreover, the hand-brushed core deposition lacks precision and can damage the bondwire windings.
? Geometric programming is another method to solve the inductor optimization problem .
? PSO uses the swarm intelligence method to solve the global optimization problem. PSO algorithm uses swarm of particles and each particle represents a potential solution.
• Considering the proposed magnetic materials in the literature, we see that although ferromagnetic metal alloys have big advantages of high saturation induction and low coercivity, they mostly show limited resistivity (< 200 µO•cm) which can result in high eddy current losses.
• To handle this problem, one solution proposed in is to add a serial resonant capacitor in the excitation winding. Similarly, one can extract losses as the product of current and voltage.
• Another technique to measure losses inspired from the principle of resonance is proposed in.
• The idea is to measure quality factor of the inductor as a function of alternating current, and then calculate indirectly the magnetic losses.
? In switched inductor dc–dc converters, inductors are the key power transfer elements, and therefore, optimizing their design for maximum performance is necessary.
? To deliver clean power to the load with high efficiency, the inductor needs to have the right inductance (to minimize current ripple) with minimum loss (both dc and dc).
? This paper examines the role of varying dimensions on inductor performance along with modelto-hardware correlation.
? Embedded inductors provide miniaturization through size reduction, provide performance enhancements due to lower parasitics, and are often more reliable since they are not assembled on the printed wiring board (PWB).
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