Product category: Power Supply ICs and Controllers
News Release from: International Rectifier | Subject: DirectFET power packaging
Edited by the Electronicstalk Editorial Team on 29 January 2002

SM power package
cracks two-way cooling conundrum

International Rectifier is claiming a breakthrough in surface-mount power MOSFET packaging technology with its DirectFET power packaging

International Rectifier is claiming a breakthrough in surface-mount power mosfet packaging technology with its DirectFET power packaging. The DirectFET packaging is the first surface-mount package in an SO-8 footprint designed for efficient top-side cooling. In combination with improved bottom-side cooling, the new package can be cooled on both sides to cut mosfet part count by up to 60% and shrink board space by as much as 50% compared with an SO-8 type solution.

This effectively doubles current density.

A dual-side cooled DirectFET chipset enables DC/DC convertors capable of 30A per phase with a single pair of mosfets, at a lower total system cost when compared to single-side cooled SO-8 designs and at a current density of over 24A/in2, double that of the standard SO-8 solution.

The new devices are designed for high-frequency, high-current DC/DC convertors used to power next generation Intel and AMD microprocessors found in high-end notebooks and servers, as well as advanced telecom and datacom systems.

Multiphase synchronous buck converters that power these CPUs must deliver currents of 20A per phase and above in reduced footprints.

Managing heat loads in high power microprocessor systems is a true challenge when the PCB is the main source of heat dissipation.

Standard SO-8 packages, as well as proprietary SO-8 derivatives such as bottomless and leadless SO-8, can only effectively be cooled on one side through their connection to the PCB due to their poor top-side thermal resistance, adding to the thermal challenge.

"The DirectFET technology is the first surface-mount package designed from the ground up to be a power semiconductor package.

It is also the first surface-mount package designed for dual-side cooling where the use of heatsinks or thermal pads removes the heat away from the PCB and provides tremendous system benefits", said Carl Blake, DC-DC Marketing Manager for Computing at International Rectifier.

DirectFET packaging can be leveraged to reach high current levels without paralleling mosfets, adding an additional phase in multiphase converters, using heat pipes or fans, or adding copper throughout the whole PCB, all of which reduce current density and add system cost.

When comparing DirectFET solutions to these alternative designs, DirectFET is the most economical solution, with at least a 50% reduction in the cost of heat removal, and provides the smallest space requirement.

In the DirectFET package, the silicon die is contained into a copper housing.

The bottom of the package consists of a die specifically designed with source and gate contact pads that can be soldered directly to the PCB.

The copper "can" forms the drain connection from the other side of the die to the board.

The large-area contacts combined with the copper housing significantly improve heat dissipation compared to a plastic molded package: the junction-to-PCB thermal resistance is reduced to 1C/W max, compared with 20C/W max for a standard SO-8 package.

The copper housing provides a heatsink surface, improving junction-to-case thermal resistance to 3C/W compared with 18C/W for a standard SO-8.

With the use of heatsinks and cooling air flow, the DirectFET package dissipates 50% more heat through the top of the package than a plastic-molded package SO-8, reducing operating temperatures by up to 50C and enabling more than doubled system currents.

The DirectFET package has a height of 0.7mm, while the SO-8 is 1.75mm, which is a further advantage in space-constrained applications such as notebook computers and 1U servers.

The DirectFET package is bromide and lead-free.

The devices are compatible with existing high-volume manufacturing equipment and processes.

Samples are available immediately.

Production release is in the third quarter of 2002.

Pricing starts at US $0.77 each in 10,000-unit quantity.

(This was Electronicstalk's Top Story on 29 January 2002)

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