SPECIAL REPORT/ADVANCED CERAMICS: Put the Metal to the Ceramic

Advanced ceramics offer engineers a unique set of physical, chemical, electrical and thermal characteristics that place them among the "miracle materials" of modern technology. Simply put, ceramics possess a full range of properties that metals lack, and vice versa.

Such mutually exclusive material properties produce a common engineering dilemma: we are often confronted with the need to combine the characteristics of metals and the characteristics of ceramics into a single component. Though this challenge may be akin to mixing oil and water, a solution can often be obtained by metallizing the ceramic material-attaching a metal alloy to a ceramic surface through a process of chemical or mechanical bonding. Done properly, metallized ceramics can offer engineers the best of both material worlds in a wide range of challenging applications.

The basic technologies for metallizing ceramic have been known for more than 60 years. In today's society of rapid change, this long history may suggest a mature technology in declining demand. In fact, the opposite is true. Many of today's hottest and most promising fields depend on metallized ceramics. Examples include the revolution in wireless communication, high-speed optical Internet technology, advanced medical diagnostic equipment, implantable medical devices, scientific test and measurement equipment, and even research into high-energy particle physics and nuclear fusion energy.

Major Features

Suppliers of metallized ceramic solutions can provide a range of products and services, including bare ceramics and substrates for a variety of applications, metallized ceramics for customers that attach metal assemblies via brazing or welding, brazed ceramic sub-assemblies for customers who weld or braze the component into a final assembly, and full-service metallized and brazed solutions for customers who prefer to outsource all processing. In all cases, metallized ceramic components offer critical, high-added-value performance characteristics that may otherwise be unattainable using conventional material technologies.

Selective Electrical Conductivity
Although ceramic materials are electrically non-conductive, metallization allows electrical contacts to be printed onto a ceramic surface. This property is invaluable in the field of passive electronic components, where the ability to metallize ceramic has created a revolution in leadless, "surface-mountable" capacitors, resistors, filters and other devices. As a result, new generations of electronic equipment can occupy the same footprint while offering significantly greater functionality; or, conversely, equipment offering equivalent functionality can be made significantly smaller. These leadless devices have been among the main drivers allowing manufacturers to miniaturize all types of electronic equipment, from palmtop computers to cellular phones.

In addition to basic electrical contacts, specially formulated metallic inks can be applied to a ceramic surface using an automated screen-printing process to produce high-precision circuit patterns. After firing the ceramic component, these printed areas can be electroplated with nickel or gold for outstanding electrical conductivity, while maintaining the material's electrical insulating properties in the unprinted areas. As a result, metallized and multilayer ceramics play an indispensable role in semiconductor packaging, including many of the industry's most demanding applications.

The metallization of ceramic can also permit resistive circuitry to be printed onto a ceramic substrate to create an effective heating element in applications ranging from gas igniters to diesel glow plugs.

High-Voltage Insulation
Metallized ceramics can be designed for high-voltage feed-through applications involving up to 100 kV (100,000 volts). The numerous applications for this feature include equipment for high-energy physics research, where particle accelerators are facilitating new discoveries in many fields of science (see the "Metallized Ceramics at Japan's SPring-8 Synchrotron Lab" sidebar). In addition, high-voltage metallized ceramic components are also widely used in medical diagnostic and radiation therapy equipment, such as that used in treating many cancers; in mass spectrometers; and in a wide range of other test and measurement equipment.

Hermetic Sealing
High-performance semiconductors, laser devices and crystal units require complete protection from moisture, dust and gases. In housing these devices, hermetic seals are generally recognized as the best form of protection against the external environment. Plastics and epoxy materials-widely used for components in low-cost consumer equipment-are inherently moisture-permeable, leading to reliability issues over time.

In contrast, the extreme physical and chemical stability of advanced ceramics allows them to offer extremely durable hermetic sealing, both for these devices and for a full range of other critical applications that require ultra-high vacuum conditions. Metallized ceramics play an essential role in such applications, including optical communications infrastructure, where 25 years of trouble-free duty is the industry standard.

Enhanced Thermal Performance
As electronic technology advances, so does demand for miniaturization, integration and operating speed, resulting in an unprecedented need for thermal management. In fact, thermal limitations are now a major limiting factor in the performance of advanced electronic equipment. Ceramics generally offer better thermal conductivity than other materials, and metallization can enhance this performance further by facilitating the attachment of metal heat sinks to transmit very high levels of heat away from sensitive devices.

Hardware Attachment
As a general rule, engineers employ advanced ceramics only where the material's unique properties are necessary to achieve specific performance goals. At some point, the ceramic component must interface with another component within a system, and some kind of attachment or joint is necessary at this point of interface.

Ceramic materials are inherently difficult to join, either to themselves or to other materials, which limits some potential applications. Fortunately, this challenge can be overcome through metallization, which allows durable metal mounting hardware to be soldered, brazed or welded onto a metallized ceramic component-essentially moving the ceramic away from the direct point of interface.

A Promising Future

Metallized ceramics have a promising future in many cutting-edge technologies where rising performance goals require a super-material. In communications, for example, the diffusion of wireless phone technologies is allowing developing regions of the world to adopt 21st century infrastructure at relatively low costs.

In developed regions, the expansion of broadband technology using fiber optic networks is already allowing low-priced, high-speed Internet access to be bundled with TV and phone services. Future advancements may make the typewritten e-mail message obsolete in favor of video messaging, and enable full-length feature movies to be downloaded to your home theater system within seconds.

New medical diagnostic equipment, including advanced X-ray systems, can provide detailed, 3-D views inside a patient for better analysis of treatment options before any incisions are made. Implantable devices like pacemakers, defibrillators, neurostimulators and drug delivery devices are offering life-saving medical solutions to millions of people each year.

High-energy particle physics research is helping to advance the most exciting realms of science. And continued research into nuclear fusion offers the long-term potential for a limitless source of affordable, renewable energy, with none of the nuclear waste associated with today's fission-based reactors.

The introduction of metallized ceramics into so many fields provides an example of the broad opportunities available for the advanced ceramics industry as a whole.

For additional information regarding metallized ceramics, contact Kyocera Industrial Ceramics Corp. at 220 Davidson Ave., Suite 104, Somerset, NJ 08873; (732) 563-4340; e-mail johnmastrogiacomo@kyocera.com; or visit www.kyocera.com.

SIDEBAR: Metallized Ceramics at Japan's SPring-8 Synchrotron Lab

A synchrotron radiation facility consists of an injector, which generates an electron beam and accelerates electrons, and a storage ring, where electrons are accumulated. SPring-8, located in Japan's Harima Science Garden City, is the world's largest "third generation" synchrotron radiation facility. It features 62 beamlines and an 8 billion electron-volt (8 GeV) storage ring measuring 1.4 kilometers in diameter. Researchers worldwide use SPring-8 for exciting work in materials science, spectroscopic analysis, earth science, life science, environmental science and industrial applications.

The electron beams that circulate at near-light-speed inside SPring-8's massive storage ring need to run smoothly and efficiently at all times. To facilitate this, a minute electrical current generated by the flowing electron beams is constantly measured and analyzed to continuously correct the beam's position in the center of the ring's cross-section. This is accomplished through the use of 1300 metallized ceramic beam positioning monitors (BPMs)-four at each of 325 locations within the ring. Each BPM measures an electrical signal equivalent to a 25-picosecond pulse, requiring both excellent high-frequency operating characteristics and strong hermetic sealing to maintain the super-high-vacuum environment within the ring.