Micro-assembly becomes more important in industry every day, with many industries growing double digit every year. Dealing with micro components generates multiple issues. Some of the most common ones are component stiction, low positioning precision, surface damage or contamination and component destruction.
To solve the above issues, many approaches have been implemented. To detach components stuck to the tool an air stream blows away the component and, to correct the consequent positioning error, vision systems and robotic correction systems are usually implemented.
To deal with fragile or easily scratched components, such as components out of GaAs or HgCdTe, different materials are exploited for the tool, usually with lower lifetime. In most of the cases, these processes have anyway defect rate around 50%. Even for very mature component, defect rate around 5% can be found if fragile membranes or surfaces are present.
The root cause for most of these issues can be found in the manipulation steps, where usually a mechanical gripper or a suction unit grab the component to transport it.
The ultimate solution is to contactless manipulate the components, therefore removing the root cause.
Technological State of the art
To provide contatless manipulation, multiple approach have been developed. Nevertheless, the majority of those technologies presents important limitations and challenges.
Optical levitation is known to be able to suspend a particle up to 0.05 10-6 m3 by using laser radiation pressure. However, this type of manipulation must take place in a transparent environment in order to obtain stability. Furthermore, the particle must be transparent, a highly limiting factor for the target components.
Another solution is electromagnetic levitation, which uses an electric or magnetic field to manipulate a charged, polarized or magnetic object. However, this type of levitation is only applicable to objects sensitive to electric or magnetic fields. Moreover, there is a risk of degradation of the object placed in a magnetic or electric field. Finally, these techniques require specific installations depending on the object to be handled.
Aerodynamic levitation uses a gas flow to levitate an object, with two main categories: air bearings and Bernoulli devices. The air bearings expel a stream of air from below the object to levitate it. Conversely, the Bernoulli devices are positioned above the object, which must be between some sidewalls. Compressed air is projected onto the object, which is then evacuated by the space between the walls and the object. This generates an attractive force opposite the direction of the compressed air, called Bernoulli effect, which levitates the object. The main disadvantage of aerodynamic methods is that the levitated object has very poor lateral stability and is confined between the sidewalls.
Ultrasounds are also used to levitate components, exploiting acoustic standing waves. Systems using these waves require the presence of a reflector that faces the ultrasound generator. The generator emits waves that will reflect on the reflector and create equidistant nodes at λ/2 intervals, where the repulsive force is sufficient for an object to levitate. The main disadvantage of this technique is that the manipulations are limited to the area between the generator and the reflector, and those only at the nodes. Moreover, the object is kept necessarily at a minimum distance from the generator of λ/2 which is the distance of the first node. On the good points, this technology is suitable for any material and shape.
At last, methods of levitation using a combination of ultrasonic pressure and air aspiration are also known. Tools based on this technology are able to manipulate components of any material, with some limitations on component shape and lateral stability. Engineering efforts and ad hoc design of toolings and equipments can anyway almost completely solve all related issues.
Status of the market
In the latest years acoustic levitation have been able to raise some interest. These application seems anyway to be focused for laboratory or leisure and failed to find a proper industrial application.
The most promising technology seems to be the combination of ultrasonic pressure and air suction. This approach don’t show the same limitations of the others and could be easily implemented into industrial machinery.
Equipment based on this technology are beginning to be commercialised for the Semiconductor, Optoelectronics and Watchmaking industries, with very positive preliminary results.
The future rise of contactless manipulation could unlock design possibilities for microcomponents that are currently forbidden and could accelerate the implementation of materials that too brittle or soft to be held. Furthermore, with greatly improved production yields, components could become cheaper and less resources would be wasted during production.
The potential of this new technologies has been deemed by industry experts as revolutionary and potentially disruptive for many industries. The potential is there, will this really become the manufacturing Paradigm of the Future?
About the Author
Maurizio Migliore Currently serving as COO at Touchless Automation, he studied Nanotechnology Engineering (PoliTo, INPG, EPFL) and perfectioned his studies with an MBA (Collège des Ingénieurs).
Work experience as Project Manager at Comau (Industrial Automation, FCA group) and Operations Manager at Uber and UberEATS.
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