When I tell people that I started my career before carbon fibers were commercial (we had glass and boron), I get the same reaction as when I pull out my slide rule. For most of my career, aerospace structures and sports equipment were the dominant composites markets for carbon fiber reinforced resins. Recently, industrial applications — a catch-all category that includes everything but the other two — have become the number one market, with some of its segments attracting a good deal of attention. However, there are two areas with great growth potential that have not, in my opinion, received adequate consideration: mechanical engineering systems and electronics thermal management. Both have applications in the industrial and aerospace categories.
Mechanical engineering covers a wide range of products. The materials of construction used in the overwhelming majority of these products date from previous eras: aluminum (early 20th Century), steel (18th Century), cast iron (14th Century), and granite (stone age!) — used, for example, in coordinate measuring machine gantries.
Under the mechanical engineering umbrella, composites have made significant, widely publicized inroads in a few areas, such as natural gas vehicle tanks, wind turbines and conversion industry rollers. However, there are noteworthy applications that hardly anyone knows about, particularly in one large and important class of applications, machine parts. As a Distinguished Lecturer for the American Society of Mechanical Engineers (ASME), I have found that only a handful of engineers are aware that fiber-reinforced aluminum metal matrix composite (MMC) automobile engine parts have been in production since 1981. The benefits of composites in machine parts are increased productivity, improved accuracy, longer life, reduced downtime, and lower energy consumption. The world can ill afford to ignore the latter.
Examples of current inefficiencies resulting from use of what I call archaic materials include the gantry of a pick-and-place electronics assembly machine that positions a 1-mg/0.0000353-oz capacitor. It may have a mass of 100 kg/220 lb, for a mass ratio of 100 million to one. Similarly, the gantry of a large milling machine can have a mass of thousands of kilograms to support motors and tools with masses of only a few hundred kilograms. Because of the large thermal mass, the gantry never comes to thermal equilibrium, so distortion continually increases, reducing part accuracy. Moving the gantry consumes an unnecessarily large amount of energy.
The key materials of interest for machine parts include polymer matrix composites, MMCs and ceramic matrix composites (CMCs). Because stiffness is critical in many applications, high-modulus carbon fibers and silicon carbide particles are key reinforcements. For the many parts that must conduct heat, thermally conductive pitch fibers are of interest, because PAN-based fibers have low thermal conductivities. Ceramic fibers provide wear resistance. Some users report shortages of high-modulus PAN-based fibers, but other reinforcements appear to be in good supply.
Anyone with a laptop is familiar with the heat dissipation problem in modern electronics. In one recent case, a user required medical attention for burns. Thermal management and thermal stresses are critical issues in the $100 billion (USD) industry microelectronics and optoelectronics market: Intel has acknowledged that it has hit a "thermal wall" that could limit Moore's Law. And the new Apple Power Mac G5 has a pumped liquid cooling system similar to those used in automobiles.
In response to the inadequacies of traditional packaging materials, suppliers are developing an increasing number of new composites. Key properties are high thermal conductivity, low coefficient of thermal expansion (CTE) and low density. During an independent R&D project funded by the GE Aerospace Group in the early 1980s, I directed a team that was the first to use one of these materials, silicon carbide particle-reinforced aluminum (Al/SiC), in packaging. My estimate of current production of Al/SiC is about $50 million, with a 10 to 15 percent annual growth rate.
There are now over a dozen composites with low CTEs and thermal conductivities up to three times that of copper. For example, IBM now uses heat spreaders made of diamond particle-reinforced silicon carbide (a CMC). Because of short commercial development cycles, the rate of penetration of new composite materials of all types in electronic packaging has been an order of magnitude faster than anything I have seen in structures.
As for all applications, there are barriers to use of composites in machine parts and thermal management. Perhaps the greatest is that most mechanical engineers know little or nothing about these materials. To address this problem, ASME is presenting short courses on mechanical system applications, and the International Microelectronics and Packaging Society (IMAPS) has courses on thermal management.
For more information on the ASME or IMAPS course, e-mail me at email@example.com.