Enabling Higher Performance Power Components with Packaging Innovations

July 15, 2014
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This is the first in a series of three blog posts written by Doug Ping, Principal Application Engineer at Vicor, which explain how packaging innovations play a critical role in the improvement of power system performance.

Packaging for power electronics has evolved from simple metal bending to advanced materials and thermo-mechanical design, and from freestanding supply to integrated power management. System-size reductions made possible by higher switching frequencies and semiconductor miniaturization drove the early part of this trend. The more recent improvements, however, have also depended on advances in thermo-mechanical design, particularly of power management components.

Beyond the Box

The last decades have witnessed aggressive advances in semiconductor miniaturization. During the 30 years from 1982 to 2012, commercial processes for fabricating CMOS logic shrank from the 1.5 μm node to the 22 nm node (Figure 1). The resulting increase in functional-density—more than 4,600:1—has altered the course of electronic product design, not just within computational cores or memory subsystems, but throughout the product as well.

Figure 1 - IC Geometries

Figure 1: In three decades, commercial semiconductor processes for fabricating digital circuits have moved from the 1.5 μm node to the 22 nm node, shown here on a logarithmic scale

At the start of this interval, typical electronic products provided low functional density and presented modest power demands. Power supply designs made use of discrete components and less than optimal cooling methods. Although supply efficiencies were poor by today’s standards, they were sufficient given their products’ low power requirements and large enclosure size.

Traditional open- and closed-box power subsystems

Figure 2: Traditional open- and closed-box power subsystems, including the ATX12V silver box power supply shown here, provide low power density and limited scaling potential.

Among the best-known examples of these designs that remain in use today are the silver-box supplies that power desktop computers. For example, a 400 W ATX12V features a largely discrete design (Figure 2). Individual heatsinks cool power MOSFETs and output rectifiers but the overall thermal design results in large thermal gradients, which are problematic at high ambient temperatures. With a typical efficiency of 80%, the 138 x 86 x 140 mm form factor provides a power density of only 0.24 W/cm3. ATX supplies meeting the 80-plus platinum criteria can almost double that number to 0.42 W/cm3 but are still insufficient in power density and not practical for most central office and data center applications.

The progression of semiconductor miniaturization imposed changes to power subsystem architectures. ICs fabricated at smaller process nodes require ever-lower operating voltages and tighter supply-voltage tolerances. Higher functional densities increase supply currents and highly variable resource schedules dramatically increase load-current dynamics. Under these load conditions, designs that separate power sources from their loads by significant lengths of copper cannot provide the performance that these small geometry ICs require.

The next post in this series discusses the impact of the brick packaging technology on power system design.

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