Jun 19, 2023

EIPC Technical Snapshot: Novel Laser

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“Summer is over, now it's back to work!” This was the opening line of the invitation to the 18th EIPC Technical Snapshot webinar, Sept. 14, following the theme of advances in automotive electronics technology, introduced and moderated by EIPC President Alun Morgan.

The first presentation, entitled "The fully printed smart component—combining additive manufacturing and sensor printing," came from Jonas Mertin, a thin-film processing specialist at the Fraunhofer Institute for Laser Technology.

He discussed how the properties and functionality of insulating and conducting coatings in printed electronics and embedded sensors can be enhanced by thin film processing and described two approaches: Laser-based modification of already-coated component surfaces, and the additive production of films by coating and thermal post-processing.

Considering the second approach in detail, he illustrated the succession of processing steps: surface pre-treatment, chemical solution deposition of sol-gels or nano-particulate dispersions, laser-based drying, and laser-based functionalisation. This procedure involves no batch or vacuum processes and is capable of automated in-line operation. It is resource-efficient, flexible, and low-cost. Functional material can be applied on selective areas of the substrate, enabling individualisation of mass products, and it is possible to work on temperature-sensitive substrates like polyester foil.

The demand for components with integrated functions continues to increase. Mertin showed several application and integration concepts for printed sensors and referred to Fraunhofer’s “Go Beyond 4.0” lighthouse project, which is working to combine traditional production methods with future-oriented technologies and digital manufacturing methods to develop new strategies and process innovations in market-relevant application areas such as automobile production. In his example, digital modules for additive printing and laser ablation of materials have been integrated into existing processes to incorporate piezo early-impact-warning sensors into the structure of a car door, using laser structuring for embedding printed layers, printing and laser drying of dielectric insulation layers, then printing and laser curing of electrical conducting layers onto the insulation. Further examples were embedded strain gauges and functional layers for high-power electronics. Direct printing of functionalities onto semi-finished or finished components is an easily automated approach to manufacturing, and can also be used to add various features to 3D-printed components. Not only final products, but tools as well—Mertin’s concluding example was a 3D-printed milling cutter with printed and laser-sintered strain gauges embedded behind the cutting tips.

A novel approach to the thermal management of power electronics components was introduced by Christopher Rocneanu, VP of business development with IQ evolution in Germany, who described the production and applications of liquid-cooled heatsinks, 3D-printed in stainless steel. Why stainless steel instead of copper or aluminium? The answer is not only its corrosion resistance, but the ability to form extremely thin-wall structures by selective laser melting. The tool-free manufacturing process involves the layer-by-layer melting of stainless-steel powder by a laser machine driven by a 3D-CAD file. Complex leak-free shapes with wall thicknesses of 150 microns can be achieved, whereas the equivalent geometries in copper or aluminium will require 800 microns or more.

The process not only enables rapid prototyping but is suitable for mass production. The metal powder is applied in very thin layers and melted by a laser beam, creating a homogeneous metal structure at the points where the laser melts the powder. Remaining areas of the powder remained unchanged and are removed at the end of the process. Geometry is a function of beam diameter, grain size of the powder, layer thickness, speed and power of the laser beam, and the selected pitch between successive scans. The resulting stainless steel heatsinks are capable of dissipating substantial thermal loads with very low thermal resistance.

Because of the flexibility of the 3D printing process there is effectively no such thing as a standard product, but he demonstrated many examples of commonly used cooler designs, in a range of industrial and automotive applications,

In automotive electronics there is a general requirement for heatsinks to operate at lower coolant pressures than in their industrial equivalents, so they have been adapted to enable substantially higher flow rates. Rocneanu showed a series of comparative performance graphs.

A key benefit in automotive applications is that these thin-wall stainless steel coolers offer a significant weight reduction. His example was capable of dissipating 1.5 kilowatts but weighed only 28 grams. And the stainless-steel material enabled the use of soldering or copper or silver sintering to attach modules to it.

An extreme example of weight and space saving is a DC/DC converter for a truck, with a total power of 210 kilowatts and a power dissipation of 4.4 kilowatts. A change from conventional cold plates to 3D printed heatsinks enables the converter to fit into a limited volume with a weight reduction of 97%.

Printing the unprintable using nozzle-free laser jetting technology was the intriguing subject of the final presentation from Ralph Birnbaum, director of business development at ioTech Group in Israel, in a paper entitled “Digital Mass Manufacturing of Electronics – Breaking the Mould.”

He reviewed a fundamental challenge that limits current additive manufacturing technologies. Because materials approved and certified for electronics manufacturing are generally too viscous, additive manufacturing is only used for prototyping.

He described the technique of continuous laser-assisted deposition, based on laser-induced forward-transfer technology and developed for additive manufacturing, which won the productronica innovation award in 2021.

In principle, this involves coating material of any viscosity on to a transparent carrier film, which is passed coated-side-down under a laser. Short pulses of focused laser energy striking the carrier from above release consistent droplets of material onto a substrate below, which can then be sintered or cured on-line.

The technique enables the high-resolution printing of otherwise unprintable industrial materials such as polymers, silicones, ceramics, metals, solders, and adhesives. Up to five materials, combining polymers, metals and ceramics, can be printed simultaneously at 7 million dots per hour with a line speed of 1 metre per second.

Birnbaum showed a long list of materials that have been successfully printed at resolutions as low as 25 microns and filler sizes ranging from 2 to 20 microns. On-line curing options are thermal or UV, with laser sintering or laser ablation available for finishing. He claimed that the eco-friendly technique offers the productivity of screen printing with the flexibility of dispensing and the precision of jetting, with low cost of ownership, simple maintenance, and no expensive consumables.

Discussing applications in printed circuit fabrication and electronics assembly, he showed a proof-of-concept single-layer PCB on an FR-4 substrate, with metal tracks and solder mask printed at the same station. He demonstrated die-bonding with silver paste applied at more than 10,000 droplets per second—significantly faster than dispensing—and SMT assembly with high-resolution printing of solder paste at more than 2,000 droplets per second, again significantly faster than dispensing.

A wide range of adhesives can be printed at resolutions down to 50 microns, and previously unprintable designs can be generated by overlapping equally distributed and fully registered droplets at 5 micron accuracy. Multiple adhesives can be incorporated in a single design if necessary.

As well as solder mask on bare PCBs, continuous laser-assisted deposition technology enables the selective deposition of multiple coating materials and encapsulants on PCB assemblies, with 50-micron accuracy.

Birnbaum’s concluding application example was the formation of conductive interconnect in cavities and on non-conformal substrates, in line widths down to 20 microns using standard commercial metallic pastes, with in-line laser sintering and combining dielectric and metal if required. Vias as small as 60 microns can be filled.

Bringing the proceeding to a close, Morgan thanked the speakers for their fascinating presentations, Kirsten Smit-Westenberg and Tarja Rapala-Virtanen for organising and managing another splendid event, and everyone who had attended.

The next Technical Snapshot is scheduled for Wednesday, Oct. 19.