April 30, 2014

(Nanowerk News) These days, no office is complete without a printer. But digital printing technologies also play an important role in microelectronics, microsystems engineering and sensor systems. Researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Bremen use various printing methods to produce electronic components and sensors. The tiny resistors, transistors, circuit paths and capacitors are first designed on screen and then deposited directly onto two- and three-dimensional substrates, for instance circuit boards. Instead of the usual paper inks, the scientists use what are known as “functional inks” – electronic materials in liquid or paste form.

The range of potential uses for printed electronics is wide – from the electronic circuits in digital thermometers to flexible sheets of solar cells and smart packaging with built-in sensors. To automate the process of applying printed electronics to components with flat and three-dimensional surfaces, the IFAM scientists have set up a robot-assisted production line that allows different printing methods to be combined in a single run. Modules for silk-screen, inkjet, dispenser, and aerosol-jet printing are integrated in the production unit.

Cylinder featuring functional surfaces acting as sensors. (Image: Fraunhofer IFAM)“The production line with its central robotic unit, component feeders, printing systems and heat treatment furnaces enables us to functionalize surfaces on a near-industrial scale,” says Dr. Volker Zöllmer, head of the Functional Structures department at IFAM.The availability of different technologies in one system makes it possible to print structures of different surface areas, widths, and thicknesses on the substrate. Aerosol-jet printing, for instance, enables the researchers to deposit extremely fine structures with a width of only 10 micrometers onto the component.

In this non-contact process, the conductive ink is transformed into an aerosol using compressed air (pneumatic spraying), and then fed to the print head through a fine tube. The print head focuses the aerosol jet on the surface of the substrate, which doesn’t necessarily have to be flat or smooth – even curved surfaces can be printed on using this method. It is also possible to vary the thickness of the printed features and create multilayer structures.“For example, as well as laying down circuits on a circuit board, we can also provide it with a corrosion-resistant coating,” says Zöllmer.

So how exactly does this printing process work? After the control software has been programmed for the desired end product, by defining the printing methods required and the order in which they are to be executed, the robot picks up the substrate, for instance a bare circuit board, and dispatches it to the first printing station. If the task requires integrating 200-micrometer-wide circuit paths in the substrate, it is first sent to the dispenser, a piezoelectric dosing system. The dispenser contains a valve that allows the precise volume and droplet size of the viscous medium – e.g. an electrically conductive adhesive – to be applied.

If the conductor is to be connected to a sensor, the circuit board is then routed to the aerosol-jet printer. This high-resolution device prints the sensors. The circuit board then passes through other printers, depending on the application, before finally undergoing heat treatment in the furnace, in order to obtain the desired performance characteristics. The system is capable of printing on substrates up to the size of a DIN-A3 sheet of paper, and can process components with a height of several centimeters.

Source: Fraunhofer Society

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