Electronic Design

Power ICs Migrate To Open-Frame Packaging

Long known for building high-power IC amplifiers in hybrid packaging, Apex Microtechnology is now offering products in open-frame packages. The new packages, which resemble open-frame dc-dc converters, cost significantly less than the hybrids, are easier to cool, offer more I/Os, and can save space in the user's application (see the figure).

While the open-frame packages sacrifice hermeticity, this is less of a concern these days. According to the vendor, many customers no longer require hermetic components because they're placing parts in hermetically sealed assemblies.

So far, Apex has released five open-frame-packaged products. The most recent, the MSA66 pulse-width-modulation (PWM) amplifier, serves as a motor-control driver IC. Operating from an 80-V motor supply and a 7.5- to 16-V logic supply, it delivers 5 A of continuous output or 10 A peak. The unit costs $38.30 each in lots of 1000, which is 75% less than equivalent hybrids.

Last year, Apex released four power op amps and two PWM amplifiers in open-frame packages. This year, the company plans to release six more open-frame products.

The new open-frame packages consist of plastic-packaged surface-mount components mounted (using conventional pc-board assembly techniques) to an insulated metal substrate (IMS). The IMS, which is thermally conductive but electrically isolated, contains layers of aluminum, insulation, and copper traces. This style of assembly lowers the material and labor costs of packaging versus those of hybrid construction.

Gone are the steps required for substrate printing of thick-film conductive layers and resistors, solder reflow of the substrate to the package header, and die attach and wirebonding steps. The new approach also eliminates package welding, pre-weld testing, and possible rework. In place of the hybrid assembly steps, the new packages require solder screening of the IMS substrate, component placement, reflow, and final test.

While hybrid packages like the TO-3 mount to the user's pc board through a heatsink, the open-frame packages can mount directly to the board. The heatsink then mounts to the exposed side of the open-frame package. Pulling the heatsink off the pc board saves space for components. So despite its larger footprint, the open-frame package can save more space in the application than the hybrid.

The open-frame package also gives designers much greater flexibility in choosing a heatsink, because the heatsink doesn't need to include space and mounting holes for the device package. Designers may opt to employ a more thermally efficient heatsink than would be possible with a hybrid device.

Because of their larger size, the open-frame packages permit greater numbers of I/O than hybrids. This may be exploited to bring more functionality into a power device. The company plans to introduce new power-amplifier devices with higher levels of integration as well.

Apex Microtechnology

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