Apr. 28, 1999 Adam Cohen is taking big steps to make very small things on a large scale.
The University of Southern California engineer is developing a process to mass-produce tiny mechanical and electromechanical devices with complex features smaller than the width of a human hair.
"Our process — called EFAB, for electrochemical fabrication — produces complex, three-dimensional microdevices quickly and economically without cleanroom facilities," says Cohen, a project leader at the USC School of Engineering's Information Sciences Institute. "Currently, micromechanical and microelectronic devices are limited in shape and must be manufactured manually in a costly cleanroom — often through a custom process that's expensive and difficult to develop."
Cohen points out that EFAB integrates micromechanics with microelectronics better than current technology because the temperature of the manufacturing process is relatively low, about 120 degrees Fahrenheit. "Thus," he says, "it would be ideal for producing sophisticated systems on a chip."
Cohen and a team of USC engineers recently used the EFAB process to fabricate a metal chain which, at 290 microns wide, may be the world's narrowest. All of its joints are fully articulated and movable. Instead of painstakingly assembling the chain one link at a time, the scientists used EFAB to make the entire 14-link chain in a single process.
EFAB is inspired by an industrial process called rapid prototyping. Instead of machining a model from a solid block, rapid prototyping uses an additive approach by stacking up a series of thin layers (usually made of plastic) that adhere to one another to form a three-dimensional object. Typically, objects made by rapid prototyping have dimensions measured in centimeters, with material deposited in layers tenths of millimeters thick.
EFAB creates much smaller objects with layers that are measured in thousandths of millimeters, and those layers are solid metal rather than plastic.
"You can make more complex designs by stacking layers than you can by machining or casting, and the EFAB process can be fully automated," says Cohen.
Currently, the USC team usually works with layers that are five to eight microns thick, but Cohen says they can make layers that are less than a micron. (A micron is a millionth of a meter, and human hairs are 50 to 100 microns in diameter.)
Each layer is made by depositing metal through a prefabricated patterned mask —similar to the way a printing plate applies ink to paper. The masks for all of the layers can be produced simultaneously from computer data, and the layers are then deposited one at a time.
"This is not like an assembly line which manufactures products one at a time from individual parts," says Cohen. "It's like a form of printing where an entire complex device is made by piling one slice on top of another until the unit is complete. With EFAB tens or even hundreds of thousands of finished products can be made at the same time using a single process."
Micromechanical devices have been limited to fabrications no more than five layers thick. The USC team has already made 12-layer devices. But when the process is fully automated, Cohen says, EFAB should be able to produce devices with hundreds or thousands of layers.
"When we finish automating the process, our manufacturing machine will be able to run unattended at high speed and it will be practical to do many more layers," he explains. "EFAB is also very versatile, like casting or machining. Manufacturers won't have to invent a new process for each new design, as is currently the case with microdevices."
Cohen says EFAB technology could manufacture many existing products faster and more economically through miniaturization and batch fabrication.
"For example, I think the mechanism for a bar-code scanner, which currently costs $50 to $100 to produce, could be mass- produced for less than $1 with EFAB," he says. "I believe we could make coronary stents, which are used to keep arteries open, for under $5 with EFAB mass-production technology. It costs about $100 to manufacture them now, because they're made one at a time by precision machining."
Cohen says that EFAB could facilitate the production of tiny devices that are practical only if large quantities can be produced at low unit costs. Examples include sensors for detecting the imminent failure of bridges, alleviating highway congestion or helping to predict weather or even earthquakes. Tiny wing actuators could reduce turbulence and cut aircraft fuel consumption.
Other members of the USC development team are senior mechanical engineer Uri Frodis, senior process development engineer Fan-Gang Tseng, and Gang Zhang, a doctoral candidate in materials science.
The Defense Advanced Research Project Administration's Defense Sciences Office is funding development of EFAB.
Early access to EFAB technology will be made available through USC/ISI's newly established EFAB Consortium, which will promote the technology and provide members with prototype devices, based on their own designs. Individuals or companies may contact the USC Office of Patent and Copyright Administration at (213) 743-2282 regarding licensing opportunities for the patent pending process.
For more information, point your browser to http://www.isi.edu/efab.
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