Summary:

Metal Matrix Cast Composites, LLC. (MMCC; Waltham, MA), is using its Advanced Pressure Infiltration Casting (APICTM) process, developed with BMDO SBIR funding, to make MetGraf™ copper and aluminum alloys for electronic thermal management. The composite heat sinks and thermal spreaders have controlled fiber orientations to achieve high thermal conductivity and matched thermal expansion required for direct solder bonds to semiconductor dies and substrate materials. The material is currently used on Boeing Company’s 702 satellite platform for DirecTV HDTV programming and the USAF Wideband Gapfiller system.

Technology Description:

Metal Matrix Cast Composites, LLC. (MMCC; Waltham, MA), is using its Advanced Pressure Infiltration Casting (APICTM) process to make MetGraf composites used for electronic thermal management. The composites, which are graphite preforms impregnated with aluminum or copper, are attractive for thermal management because they have high thermal conductivities approaching those of pure copper or aluminum but have low density and can be manufactured so that their coefficient of thermal expansion (CTE) matches that of the electronics they are being used to cool.

The most efficient way to remove heat from a chip is to directly attach, by brazing or soldering, a heatsink made of a thermally conductive metal like aluminum or copper. However, as the chip warms up during use, if it expands at a different rate than the metal, the metal heatsink will either detach from the chip, or the chip will crack. Some electronics, like PCs, use adhesives or pastes to prevent the different rates of expansion from causing damage, but adhesives do not transfer heat as well as heatsinks that use metallic bonds and are therefore not suitable for many high power applications. Other specialty alloys used in thermal management, such as kovar, Cu/W, and Cu/Mo, are not practical for weight sensitive applications and cannot adequately match very low CTE requirements needed for emerging SiC and GaN packaging technology.

MMCC’s Metgraf begins as porous carbon performs which are then infiltrated with aluminum or copper. Carbon has a high thermal conductivity, but it also has a negative CTE. By controlling the fiber architecture and the fiber to metal ratio, Metgraf can tailor composite products with CTEs from 2 to 10 ppm / ºK. In addition, super high thermal conductivity inserts of pyrolytic graphite (~1700 W/mK) can be cast in-situ into MetGraf products resulting in a CTE matched heat sink solution with exceptional thermal conductivity exceeding 1000 W/mK.

Standard Metgraf is cast as plate and block and machined using conventional CNC equipment to produce heat sinks to the customers specifications. MetGraf is a free machining material that is routinely milled, ground, lapped, drilled, polished, and plated.

For space applications, Metgraf has a key advantage over other low expansion alloys: machineability and density. Because carbon fibers are light weight (2.2 g/cc), the resulting composite is much lighter than a corresponding heatsink of aluminum or copper. This shaves important costs from launching satellites into orbit.

MDA Origins:

SDIO funded research and development of the process used to make Metgraf when it was being researched at MIT. Other agencies were involved, but according to Dr. James Cornie, CEO of MMCC, SDIO and BMDO were the primary funding sources through its research at MIT and now at MMCC. According to Dr. Cornie, “They [MDA] have really been instrumental and we really wouldn’t be here today without them.” Since 1994 MMCC has received more than 21 STTR and SBIR Phase I and Phase II contracts for both structural and thermal management materials.

Spinoff Applications:

MMCC’s Metgraf thermal management materials have a wide range of applications - primarily where low CTE and high thermal conductivity is required. The material can be used in any device where high reliability heatsinks, baseplates, and thermal spreaders are used to cool power semiconductor devices. For electronics, it could also be used in chip packaging, cooling microwave and millimeter wave electronics, and power semiconductor applications. The low density makes the material especially suited to airborne applications. In addition to electronics and communication equipment cooling, Metgraf could be used in welding equipment, elevators, hybrid cars, electric trains, or anywhere high currents are used.

Commercialization:

MMCC’s major commercial success is the inclusion of the material as part of Boeing Company’s Spaceway satellite platform. The satellite platform is being used as the basis for new DIRECTV HDTV satellites, and a series of military communication satellites, the Wideband Gapfiller System. On these satellites, Metgraf is used in the heat sink for cooling gallium arsenide transmit/receive electronics. Other programs either using or evaluating MMCC materials include the Non Line of Sight–Precision Attack Missile, Medium Extended Air Defense System, Wedgetail, TPS 59 USMC Radar, ECU converter heatsink, FAB-T (Family of Advanced Beyond-Line-of-Sight Terminals), and NMT. Commercial programs include semiconductor targets, power integrated gate bi-polar transistor heat sinks, thermo-electric cooler heat sinks, laterally diffused metal oxide semiconductor flanges, power amplifier modules, and solid oxide fuel cell interconnects.

Company Profile:

MMCC produces highly loaded particulate and continuous fiber-reinforced aluminum, copper, and magnesium alloy castings. MMCC has 15 employees and manufactures its products in a 15,000 square-foot facility in Waltham, MA.

Contact Information:

Dr. James Cornie
President
Metal Matrix Cast Composites, Inc.
101 Clemantis Avenue
Waltham MA 02453
Tel:781-893-4449
Fax:781-893-7230
email: jcornie@mmccinc.com
web: www.mmccinc.com