Screen Printing on a Micro Scale
By Julia Goldstein, Ph.D.
It wasn’t exactly the Roadshow, but I visited a fascinating start-up company and spoke with Arthur Chait, CEO; and Anwar Mohammed, VP of manufacturing and operations, about EoPlex Technologies, headquartered in Redwood City, CA. They’re pioneering a technology that uses screen printing to extrude layers of metals, ceramics, or polymers to produce components for a wide variety of applications.
Figure 1. CEO Arthur Chait in his office.
Chait explained that his company aims to fill the gap in the market between nanoscale and large-scale components, changing the design rules to enable new products. They consider their technology an alternative to micromachining or injection molding. Multiple materials can be printing within a single component, and products are designed to contain active elements that do mechanical, chemical, or electrical work. While Chait can envision an array of possible applications, EoPlex is making prototypes in four areas: fuel cells, energy harvesting, micro-reactors, and thermal energy management.
One critical application is fuel cells for emergency radios. EoPlex has designed a “chemical plant” contained within a square of ceramic about 2" on a side and ¼" thick. The part doesn’t look impressive, but the internal structure consists of 300 layers that include catalyst, ceramic, and metal materials. When alcohol is introduced through an external port, a reaction begins that can power a radio without the use of batteries. An emergency worker need only carry a squirt bottle of alcohol to keep a radio going for a week.
Figure 2. Loc Tran, process technician; and Alex Mandaliya, senior process engineer, examining parts in the microscope
Micro-reactors, using similar technology to fuel cells, can be used to manufacture drugs or chemicals. Gases enter through one port and the product comes out through another. Though each reactor can produce only a small amount of material at a time, multiple micro-reactors could be linked together to scale-up manufacturing.
Energy harvesting is another application – harnessing, for example, the vibration energy from automobile tires to self-power a tire pressure sensor using piezoelectricity – eliminating the need for a battery. The sensor could be the size of a dime and embedded in the tire tread, sending a wireless signal to the car’s computer.
The application closest to the concerns of packaging engineers is thermal management. A heat spreader or micro-fluidic structure can be built into an IC, limiting the need for heat dissipation at the package level. The current focus is on high-power LEDs, but other types of devices could make use of the technology. A thin square of diamond could be fired within a ceramic structure, positioned directly under the hot spot in a microprocessor, at an estimated cost of 36 cents.
Figure 3. Heatsink.
EoPlex’s manufacturing process starts by forming “inks” – pastes based on metal, ceramic, or polymer powders that are then extruded through specially designed printing plates to form layers 10- to 25-µm thick in a large panel format. This is the “active” material. Each layer needs to form a planar surface, so a fugitive, or sacrificial material, is extruded in a pattern that is the negative of the active material design. Fugitive materials must be individually tailored to match the properties of the active material in the layer, since the two must be cured together. Subsequent layers are applied, up to several hundred for a finished component, and then the entire assembly is sintered. Firing can be done in air, nitrogen, hydrogen, or vacuum, or some combination of these, depending on the material set. The fugitive materials evaporate or diffuse through the active materials during the sintering process while the active material densifies, leaving a structure that can include a wide range of geometric features, even moving parts. Since the entire component is sintered in a single step, the set of materials needs to be compatible in terms of coefficient of thermal expansion (CTE), shrinkage, and other properties. Most of EoPlex’s IP is in materials development, and as Mohammed said, “every week new materials are being created.”