IN MY OPINION

Future Sparkles for Aluminum-Diamond Heat Spreaders
By Nano Materials International Corp. (NMIC)

About three years ago, I published an article in MPD describing aluminum-diamond metal matrix composites (MMCs) and their unique benefits when used as heat spreaders for GaN devices.
Read More...

MILITARY MICROWAVE DIGEST


MMD March 2014
New Military Microwave Digest

ON THE MARKET


Band Reject Filter Series
Higher frequency band reject (notch) filters are designed to operate over the frequency range of .01 to 28 GHz. These filters are characterized by having the reverse properties of band pass filters and are offered in multiple topologies. Available in compact sizes.
RLC Electronics


SP6T RF Switch
JSW6-33DR+ is a medium power reflective SP6T RF switch, with reflective short on output ports in the off condition. Made using Silicon-on-Insulator process, it has very high IP3, a built-in CMOS driver and negative voltage generator.
Mini-Circuits


Group Delay Equalized Bandpass Filter
Part number 2903 is a group delayed equalized elliptic type bandpass filter that has a typical 1 dB bandwidth of 94 MHz and a typical 60 dB bandwidth of 171 MHz. Insertion loss is <2 dB and group delay variation from 110 to 170 MHz is <3nsec.
KR Electronics


Absorptive Low Pass Filter
Model AF9350 is a UHF, low pass filter that covers the 10 to 500 MHz band and has an average power rating of 400W CW. It incurs a rejection of 45 dB minimum at the 750 to 3000 MHz band, and power rating of 25W CW from 501 to 5000 MHz.
Werlatone


LTE Band 14 Ceramic Duplexer
This high performance LTE ceramic duplexer was designed and built for use in public safety communication and commercial cellular applications. It operates in Band 14 and offers low insertion loss and high isolation to enable clear communications in the LTE network.
Networks International

See all products in this issue


 

August 2014

Future Sparkles for Aluminum-Diamond
Heat Spreaders
By Kevin Loutfy, President,
Nano Materials International Corp. (NMIC)

About three years ago, I published an article in MPD describing aluminum-diamond metal matrix composites (MMCs) and their unique benefits when used as heat spreaders for GaN devices. From a technological perspective, much has changed since then as GaN spreads its wings from almost exclusive use in defense systems to wireless infrastructure. Significant advances have also been made in the performance, ruggedness, yield, and other characteristics of aluminum-diamond that are essential to its widespread acceptance.

For those of you not familiar with aluminum-diamond, the first point to remember is that low-cost, industrial-grade diamond has the highest thermal conductivity (ability to transfer heat) of any material on Earth, ranging from 1200 to 2000 W/mk. When used in an aluminum-diamond MMC, conductivity remains about 550 W/mK, far higher than common heat spreader materials such as copper tungsten (200 W/mK), copper molybdenum (250 W/mK), and copper-molybdenum-copper (350 W/mK).

In an aluminum-diamond MMCs, diamond particles are encapsulated in aluminum, the diamond providing the heat transfer mechanism and the aluminum providing structure as well as a very smooth surface for attachment. NMIC’s parent company has been developing aluminum-diamond MMCs since the 1990s in order to overcome the major obstacles preventing its use for dissipating heat in RF power devices as well as laser diodes and other heat-intensive semiconductors. Many organizations working toward the same end abandoned their efforts over the years, but as the benefits of aluminum-diamond are potentially so significant, NMIC has doggedly worked to eliminate these impediments. The result today is a viable alternative to traditional heat spreader materials that is both producible and affordable. Serendipitously perhaps, the timing could not be better.

The vast majority of current GaN RF power transistors employ copper, copper-molybdenum-copper, or copper-tungsten as their heat spreader material. This has proven to deliver acceptable performance at the RF power levels currently achievable by GaN devices. However, the promise of GaN continues to be delivering very high RF output power over wide bandwidths at higher frequencies than can be achieved by silicon or GaAs. In fact, applications such as electronic warfare and Active Electronically-Steered Array (AESA) radar will depend on GaN to deliver precisely these characteristics in future generations.

Higher RF power levels are where the characteristics of aluminum-diamond, especially thermal conductivity, begin to displace current materials. That is, as power output and thus heat dissipation increase, the need for better heat transfer increases with it, to a point at which only diamond has the thermal conductivity to effectively remove the heat. Consequently, it is likely that the use of aluminum-diamond MMCs will significantly expand in lockstep with advances in GaN performance.

For example, NMIC customers have demonstrated the ability to use aluminum-diamond in both hermetic and non-hermetic packages that are the result of advances in plating techniques made by the company. Plating is one of the most critical aspects of high-power packaging, as any voids between the die and heat spreader create pockets or hotspots at which temperature increases. As there is no solder available to move it safely away, the result is increased die temperature that results in reduced reliability and operating life. Solving plating issues was obviously a major achievement for aluminum-diamond, now placing it alongside traditional materials that have been used for many years.

Yield, which is intrinsically related to plating effectiveness, is arguably the most important determinant of manufacturability for any semiconductor device, and the role of the heat spreader plays a key role in establishing it. In multiple tests conducted by NMIC customers over the last three years, results have shown that aluminum-diamond can work efficiently with die-attach processes and has excellent yield. This has proven to be the case even in GaN devices with the highest RF output and destined for the most demanding environments. NMIC aluminum-diamond heat spreaders are already being used in hi-rel and space applications, the latter having especially stringent thermal cycling requirements.

Another factor is the stable coefficient of expansion (CTE) of aluminum-diamond when used in larger transistor packages that are increasingly employed in high-power GaN transistor modules. Aluminum-diamond’s CTE has always been the equal of other materials, but its stability in larger sizes sets it apart in devices with larger footprints. Weight may not seem terribly important as related to RF transistor packages that are smaller (or even much smaller) than a matchbook, and it isn’t—when only a few devices are used. However, large AESA arrays can have hundreds (or potentially thousands) of RF power transistors or MMICs, so any weight savings adds up. Weight reduction achieved at the device level is also important in smaller UAVs and platforms in which reducing size and weight is essential.

Taken together, the improvements made to aluminum-diamond MMCs have in a few short years transformed this technology into one that may well be the answer to dissipating heat from very-high-power GaN RF power transistors and MMICs, whose RF power outputs are increasing rapidly. While aluminum-diamond may never serve the needs of lower power devices that can achieve their performance requirements with traditional heat spreader materials, the thermal conductivity of aluminum-diamond seems certain to ensure it has a bright future at the “high end”.

Nano Materials International Corp. (NMIC)
Email this article to a friend!
 


 

SEARCH MPD’S EXTENSIVE DATABASE!

You Can
Search by Number:

   
  All ads, articles, and products in printed issues of MPD have a number. Just look for the red arrow in the ad or at the end of the article or product description.


FROM WHERE WE SIT

Uncertain Times for DefenseIn Defense of DARPA; Lamenting Bell Labs
By Barry Manz

A federal agency like DARPA is a sitting duck for politicians and assorted other critics. It has come up with some truly bizarre programs over years that ultimately either delivered no tangible results, were canceled before they could cause any damage, or attempted to answer questions that nobody was asking or needed answers to. Read More...


Home | About Us | Archives | Editorial Submissions | Media Kit (PDF) | Events | Subscribe/Renew | Contact Us
Copyright © 2014 Octagon Communication Inc. DBA MPDigest / MPDigest.com, All Rights Reserved.
Privacy Policy | Site Map