Packaging Innovations: As Slick as a Brick

July 22, 2014
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This is the second 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.

The first post in this series discussed early power supplies built from discrete components and housed in bent-metal “silver boxes”. The need for better performance led to the rise of a number of alternative structures that attempted to optimize power subsystems for various physical arrangements of loads. For example, high up-time applications, such as communication line cards, replaced large, inefficient, multi-output supplies with distributed power architectures. These designs begin with redundant single-output AC-DC converters to ensure that the reliability of the distributed voltage, typically 48 V, meets the system’s uptime requirements. Line cards usually use on-board brick converters followed by a number of small non-isolated point of load (POL) regulators to power individual resources.

Largely discrete, forced-air-cooled power subsystems present uneven surfaces to the cool-air source resulting in turbulent airflow, which can lead to thermal shadowing and hotspots. Encapsulated brick converters use potting compounds to form essentially isothermal devices. Within the encapsulant, power devices thermally couple to an aluminum baseplate, which provides a single cooling surface. Cooling can proceed by conduction, forced-air convection, or a combination of both.

The baseplate surface provides a large contact area for heat-sink attachment. This thermo-mechanical design allows a 600 W max output power from a 117 x 55.9 x 26 mm package and 12.7 mm heatsink (inclusive) for a power density of 3.5 W/cm3—an order of magnitude improvement over closed-frame silver-box designs.

Fractional Brick Power Generations

Figure 3: Fractional brick power management components offer decreasing baseplate surface areas while successive generations increase power density. Thermal challenges result when designs reach practical limitations of single-sided cooling methods.

As product functional densities continued to increase, the brick form factor quickly gave rise to fractionally sized versions—half, quarter, and eighth-brick—while successive generations provided increasing power capabilities. The fractional-brick’s shrinking cooling surfaces constituted a thermal challenge for system designs pushing both functional and power densities (Figure 3). This challenge was exacerbated in applications for which typical ambient temperatures were on the rise as was the case, for example, in server farms and communication hubs.

The final post in this series describes how the double-sided cooling capabilities of the ChiP platform have enabled a dramatic increase in power density.

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