New laser-based manufacturing processes in automotive electronics

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EIPC Technical Overview: New Laser-Based Manufacturing Processes in Automotive Electronics

“Summer is over, now it’s back to work!” This was the opening line of the invitation to the 18th EIPC Technical Snapshot Webinar on September 14 on the topic of Advances in Automotive Electronics Technology, presented and moderated by the President of EIPC , Alum Morgan.

The first presentation, titled “The Fully Printed Smart Component – Combining Additive Manufacturing and Sensor Printing”, was presented by Jonas Mertin, thin film processing specialist at the Fraunhofer Institute of Laser Technology.

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He explained how the properties and functionality of insulating and conductive coatings in printed electronics and embedded sensors can be improved by thin film processing and described two approaches: laser modification of already coated component surfaces and additive production of films by coating and thermal post-treatment.

By considering the second approach in detail, he illustrated the succession of treatment steps: surface pretreatment, chemical solution deposition of sol-gels or nanoparticle dispersions, laser drying and laser functionalization. This procedure does not involve any batch or vacuum process and is capable of online automated operation. It is resource efficient, flexible and inexpensive. The functional material can be applied to selective areas of the substrate, allowing individualization of mass products, and it is possible to work on temperature sensitive substrates like polyester sheet.

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

A new approach to thermal management of power electronics was presented by Christopher Rocneanu, VP Business Development at IQ evolution in Germany, who described the production and applications of liquid-cooled, 3D-printed heatsinks in stainless steel. Why stainless steel instead of copper or aluminium? The answer is not just its corrosion resistance, but its ability to form extremely thin-walled structures by selective laser melting. The tool-less manufacturing process involves the layer-by-layer fusion 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, while equivalent copper or aluminum geometries will require 800 microns or more.

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The process not only allows rapid prototyping, but is also 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. The remaining areas of the powder remained unchanged and are removed at the end of the process. The geometry is a function of the diameter of the beam, the size of the grains of the powder, the thickness of the layer, the speed and the power of the laser beam, and the pitch selected between successive scans. The resulting stainless steel heat sinks are capable of dissipating large thermal loads with very low thermal resistance.

Due to the flexibility of the 3D printing process, there is effectively no standard product, but demonstrated many examples of commonly used cooler designs, across a range of industrial and automotive applications,

In automotive electronics there is a general requirement for heat sinks to operate at lower coolant pressures than their industrial counterparts, so they have been adapted to allow for significantly higher flow rates. Rocneanu showed a series of comparative performance charts.

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

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

Printing the printable using nozzleless laser jet technology was the intriguing topic of the final presentation by Ralph Birnbaum, Business Development Manager at ioTech Group in Israel, in an article titled “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 usually too viscous, additive manufacturing is only used for prototyping.

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

In principle, this involves coating a material of any viscosity onto a transparent backing film, which is run coated face down under a laser. Short pulses of focused laser energy striking the substrate from above release coherent droplets of material onto a substrate below, which can then be sintered or hardened in line.

The technique enables 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 meter per second.

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

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

A wide range of adhesives can be printed at resolutions down to 50 microns, and previously unprintable designs can be generated by layering evenly distributed, fully registered droplets with 5 micron precision. Multiple adhesives can be incorporated into a single design if required.

In addition to solder mask on bare PCBs, laser-assisted continuous deposition technology enables the selective deposition of multiple coating materials and encapsulants on PCB assemblies, with an accuracy of 50 microns.

Birnbaum’s final application example was the formation of conductive interconnects in cavities and on nonconforming substrates, in linewidths down to 20 microns using standard commercial metal pastes, with inline laser sintering and combining dielectric and metal if necessary. Vias as small as 60 microns can be filled.

Concluding the proceedings, Morgan thanked the speakers for their fascinating presentations, Kirsten Smit-Westenberg and Tarja Rapala-Virtanen for organizing and running another splendid event, and everyone who was in attendance.

The next technical snapshot is scheduled for Wednesday, October 19.

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