Jonathan Newell looks at how additive manufacturing can help in complex EMC compliant flexible circuit production.
One of the hidden jewels in modern consumer electronics is the flexible circuit. Now considered essential enabling technology, having circuit boards which could be bent was first proposed even at the time when rigid PCBs were first appearing.
First developed as interconnect products to replace cable harnesses, advanced electronic devices mounted directly on flexi circuits first started to appear around 35 years ago when suitable materials and manufacturing techniques became available that could meet the demands of the electronics industry.
This significant step in the history of electronics gave us the capability to make such commonplace items as the laptop computer, disk drives, modern car instrument panels and mobile phones.
Now, the application landscape for flexible electronics is expanding rapidly with the Internet of Things (IoT) demanding the use of embedded antennas, connected vehicles requiring more circuitry in constrained spaces and consumer electronics probing further into the realms of wearable devices.
The flexi circuit technology of the last few years is now beginning to look too clunky to meet these new requirements so further development work is taking place in both materials and manufacturing technology.
One answer to the difficulties of multi-layered, 3D flexible circuitry is to apply the additive process of 3D printing to build up the circuitry rather than the subtractive process of etching the circuit.
New Mexico based Optomec specialises in 3D printing for the electronics industry and has produced its Aerosol Jet Technology for 3D micro-additive manufacturing of conformal sensors, passive components and on-circuit antennas.
A major user of this equipment is Carnegie Mellon’s Advanced Manufacturing and Materials Laboratory (AMML), where researchers are working on flexible microelectronics manufacturing for wearable and IoT applications, such as smart contact lenses, wearable electronic clothing, robotic skins and bio-patches.
According to Dr Rahul Panat of Carnegie Mellon, AMML uses the Aerosol Jet system to directly print nanoparticle inks and polymers over complex surfaces. “This has enabled us to fully print 3D antennas at the sub 100 micrometer scale and to conduct simulation studies to identify omnidirectional antenna designs,” he says.
One of the problems associated with the explosion of connected wireless devices is the common practice of having both transmitting and receiving functions on the same device.
According to Dr Kurt Christenson of Optomec, the rigid, sheet-metal “cans” traditionally used for electromagnetic shielding can’t be used with flexible circuits. “Aerosol Jet technology is able to deposit a film of conductive material around the perimeter of the die, contacts and connections to flex circuits to form printed electromagnetic shielding barriers,” he explains.
As well as conductive material, the Aerosol Jet system can print dielectric material enabling elements of the circuitry to bridge other elements, effectively creating a 2.5D circuit where multi-layer functions can be created on a single layer. The printer supports multiple inks in one process so can produce multi-layered circuitry as well as the required EMC shielding.
It can also print passive components such as resistors, capacitors and even sensors and antennas with values that can be varied using print parameters.
At the prototyping stage, since nothing is committed to tooling, circuitry can be produced in “final” manufacturing form and submitted for EMC testing at a very early stage with the opportunity still remaining to make design changes to meet conformance or functional requirements.