Watts Current - Volume 39

ULTRAMIC 600 heaters can be operated up to 600°C (1112°F) with a ramp rate of up to 150°C (270°F) per second depending on the application, heater design and process parameters. The heater contains a unique integrated thermocouple configuration that improves the reliability of the sensor/heater interface to ensure fast responsiveness during high ramp rate applications.

This heater can be designed and manufactured in two-dimensional flat or ring forms, and can be machined to meet specific design requirements found in challenging industrial applications. The construction technique of the ULTRAMIC 600 is to sinter the ceramic at elevated temperatures to create a monolithic, geometrically stable structure that offers high dielectric strength, low leakage current, uniform temperatures, high durability at low mass, a rapid ramp rate and a low coefficient of thermal expansion.

High performance aluminum nitride ceramic heaters offer significant advantages in terms of fast ramping and cooling, as well as temperature uniformity. Plus, they are ideal for the most demanding applications.

Dr. Hongy Lin, principal scientist and program manager of the ULTRAMIC development team and Ray Derler, the director of Watlow's Single Iteration, share insight into the development of this important new product.

What drove the development of ULTRAMIC 600?
From conversations with customers in a variety of markets, it was clear that the increasing adoption rate of ceramic heaters presented an opportunity for Watlow to expand its product offering beyond the existing Watlow product portfolio. This potential warranted the investment in developing a ceramic heater. Therefore, a development team was established within the Watlow research and development group to develop what is now known as the ULTRAMIC 600 heater.

ULTRAMIC 600 is an "advanced" ceramic heater. What does that mean?
Ceramic is a generic term associated with a particular type of chemical composition. In common terms, if a material is not a plastic or a metal, then it is a ceramic. The clay in our soil is a naturally occurring ceramic raw material that, when baked at a high temperature, becomes very hard. As such, it has been used for centuries as baking pots, figurines and floor tiles. By contrast, "advanced ceramics" do not occur naturally. Like many materials we are familiar with, such as plastic, they are man-made. Unlike plastics, which are derived from hydrocarbons, ceramics are inorganic compounds and are produced with exceptional purity. Examples include alumina (Al₂O₃), zirconia (ZrO₂), silicon nitride (Si₃N₄) and aluminum nitride (AlN) - of which the ULTRAMIC 600 heater is constructed. The well controlled purity and chemistry of advanced ceramic allows a highly organized microsturcture after sintering, which makes the superior mechanical, electrical and thermal properties of ceramic possible.

What is it about ceramic that makes it such a good material for use as a heater?
The various advanced ceramic materials all have slightly different performance characteristics relative to one another. Each is unique with respect to temperature limits, heat conduction properties, durability, electrical characteristics, hardness and geometric stability. Depending on the application demands, these properties then become the selection criteria to determine which advanced ceramic material is appropriate for a particular heating requirement. Watlow has chosen aluminum nitride as the first ceramic material in its ULTRAMIC product line because, for the majority of applications, it has superior properties. The main features that make AlN an excellent material are:

1. High thermal conductivity - The AlN construction enables the heater to be constructed with a high watt density, giving it the ability to heat up at a rate of 150°C/second.
2. Clean, non-contaminating material - The manufacturing process of high heat and pressure results in a heater that is very hard and dense with virtually no porosity or surface roughness. This means for applications requiring a "clean" heater, AlN is an ideal choice.
3. Resistance to chemical degradation - AlN is resistant to many acids and is impervious to moisture unlike many alternative insulation materials.
4. High dielectric strength and high insulation resistance - AlN is a very good electrical insulator that offers low leakage current, a highly sought after characteristic for many applications.

What industries or applications are most appropriate for ULTRAMIC 600?
Natural fits for advanced ceramic heaters are those that value six critical characteristics: ramp rate, uniformity, low leakage current, compact size, cleanliness and chemical compatibility. The packaging segment of the semiconductor industry is particularly interested in the ramp rate, uniformity and dimensional stability that the ULTRAMIC delivers. Integrated circuits are tested by subjecting them to rapid temperature cycling where the faster the cycle the more throughput and test results can be achieved. Similarly, die and wire bonding processes benefit from the cycle times that can be achieved. In the plastics packaging market, special high volume sealing needs are met with the same product benefits of thermal speed coupled with the benefit of a non-stick surface.

The ULTRAMIC 600 manufacturing process involves pressing the material in a high pressure press followed by heating, or sintering, at high temperatures. This results in a very high density material that is resistant to chemical attack and impenetrable by water. The combination of these effects means that the heater does not degrade and does not release particles. Some segments of the analytical instrumentation market require samples that are heated by a clean, non-degrading heat source. ULTRAMIC 600 meets that requirement and as such, sophisticated instrumentation techniques like mass spectroscopy, which can detect concentrations as low as part per trillion - think testing of athletes for performance enhancing chemicals - are excellent candidates for an advanced ceramic heater. This same cleanliness of operation is valued when heating gases in front-end processes in semiconductor manufacturing. Another market would be medical device that could take advantage of low leakage current.

What would you say to engineers who may feel like the old technology is sufficient for their needs?
This heater may be an opportunity to improve an existing solution. Without realizing it, a legacy heating solution may contain hidden costs associated with assembly labor, reliability or simply unrealized performance. Should these potential improvements exist, then the benefits of the ULTRAMIC heater may be worth exploring.

Are you able to customize ULTRAMIC heaters or are they all "off the shelf" products? We are manufacturing a small suite of standardized off-the-shelf products so customers can quickly and easily get and test the performance of the heater in their engineering facilities. However, we have designed our manufacturing approach to accommodate the need for custom configurations. Heaters with holes, grooves, notches and even circuit patterns that provide no-heat zones can be rapidly delivered despite being custom.