How laser sintering can transform printed electronics production

In the electronics industry, printing technologies have become increasingly ubiquitous in recent years, and for good reason. Printing processes like screen printing and inkjet use deposition techniques to selectively deposit conductive materials onto a substrate, unlike more traditional electronics production methods like etching and lithography, which are subtractive by nature and are highly complex. The printing approach has numerous benefits, such as lower production costs and less material waste. Printed electronics are also more versatile, opening up possibilities for miniaturized circuits, flexible electronics, and more.

Electronics printing workflows comprise several vital steps, starting with pre-printing steps like circuit design and material and substrate selection. After the printing stage, where conductive inks are selectively deposited onto a substrate, the next step is sintering (sometimes called curing). The importance of sintering can’t be overstated, as it is responsible for fusing the metal nanoparticles in the ink to create durable circuits with low resistivity and thus enhanced conductivity.

How laser sintering of conductive inks works

In printed electronic post-processing, sintering is typically carried out using heating ovens, infrared emitters, or broadband flash lamps. While each of these processes has specific strengths, they are all burdened by challenges, like being energy-intensive or challenging to scale. That’s where laser sintering comes in. 

Hamamatsu Photonics, a Japan-based specialist in semiconductor lasers, is aiming to transform how printed electronics are post-processed, positioning its hardware,like the SPOLD LD irradiation light source,as a more economical, sustainable, scalable, and versatile solution for printed electronics manufacturers. As we’ll see in more detail, semiconductor lasers can effectively overcome bottlenecks associated with conventional sintering equipment and create opportunities for more types of electronic devices.

Before we dive deeper into the benefits of laser sintering, let’s take a closer look at how it works in a printed electronics workflow. With inkjet printing, for example, print heads selectively deposit ink to create a pattern on a substrate. These inks are filled with nanoparticles of a conductive material, such as silver, held in a polymeric binder. The sintering process fuses the conductive nanoparticles to create dense traces with low resistivity, enabling the smooth flow of electrons through the circuit for optimal performance. Laser sintering stands out among other sintering processes because it uses laser light technology (laser spot optics or line optics) to selectively sinter the ink without heating the substrate.

The benefits of laser sintering printed electronics

Compared to more conventional sintering methods used to process printed electronics, like sintering ovens, lasers offer a number of advantages that enable circuit manufacturers to overcome scalability bottlenecks, minimize production costs, and develop more sophisticated electronics. These benefits include:

Faster post-processing speeds

There are a couple of factors that make laser sintering a significantly more rapid post-process than conventional sintering ovens. For one, near-infrared (NIR) lasers are capable of sintering metal nanoparticles in conductive ink in just milliseconds. By contrast, the post-processing step can take several minutes with sintering ovens. On top of that, Hamamatsu’s semiconductor laser modules can be integrated in-line with printing workflows, scanning and sintering freshly printed circuits in a conveyor-like manner. According to the company, its laser technology can process printed electronics at a speed of several hundred millimeters per second in roll-to-roll production. 

Less energy consumption

Among the various methods for sintering conductive ink traces, laser sintering is the most energy efficient, since semiconductor lasers have a high conversion rate from electrical power to light power. For example, the Hamamatsu SPOLD laser only requires about 1kW of electrical power for roll-to-roll sintering. The next most efficient sintering technique, flash lamps, require 5kW of electrical power or more. Ovens are the most energy-intensive, requiring over 60kW of energy to reach the necessary temperatures for sintering the metal nanoparticles.^[1]

More compact footprint

As mentioned, laser sintering solutions can be integrated seamlessly into roll-to-roll printing workflows using a conveyor system for scalable post-processing of printed circuits. This approach also has another important benefit: it means printed electronics manufacturers can scale without significantly increasing the footprint of their hardware. Whereas sintering ovens take up substantial space, sintering laser modules are very compact, facilitating their adoption and enabling manufacturers to maximize their factory floor. On top of that, Hamamatsu’s lasers are coupled with an extendible fiber, allowing the laser source to be positioned away from the laser light without impacting performance.

Wider material compatibility (substrates and inks) 

One of the biggest advantages of choosing laser sintering for printed electronics is that the post-processing hardware is compatible with a greater range of substrate materials and conductive inks. With other sintering processes, it is not possible to use heat-sensitive substrates since the heat required to sinter the inks can damage and even melt the underlying material (such as PET or paper). Laser sintering makes it possible to use these materials by selectively heating the conductive traces using line beams or circular beams, leaving the substrate untouched.^[2] More specifically, Hamamatsu’s lasers can be tuned to specific wavelengths so that the light is only absorbed by the ink. This has a big impact on facilitating the production of flexible electronics, such as wearable displays, at scale. 

Laser sintering can also allow the use of different types of conductive inks, including low-cost copper and aluminum inks. These inks, which have comparable conductivity properties to silver, have been limited due to their sintering requirements. Fortunately, Hamamatsu has been working closely with ink manufacturers to develop optimized sintering parameters for a variety of inks, leading to more validated material options.

Application support 

To date, the widespread implementation of laser sintering has been limited by a lack of understanding of the process and as Hamamatsu says “anxiety about reliability and quality control.” To overcome this hurdle, the Japanese company has a team of application engineers who work with customers to develop the optimal parameters for their printed electronics sintering applications. 

This application support facilitates the integration of its laser sintering solutions in existing workflows and new printed electronics production lines, giving customers confidence in the process and ensuring greater efficiency in terms of performance, cost, and throughput.

Conclusion

Ultimately, printed electronics manufacturers can only seek to benefit from the integration of laser sintering in their circuit post-processing. The technology is not only more energy efficient and scalable than more conventional sintering ovens, it also has less restrictions in terms of the substrates it can process, opening the doors to industrial-scale processing of flexible electronic devices, such as conformable displays, thin-film transistors, wearable sensors, and photovoltaic cells. 

Hamamatsu’s laser sintering solutions, like the SPOLD LD irradiation light source, are engineered for easy integration into printed electronics workflows and offer the reliability and consistency necessary for everything from R&D to industrial-scale production.

Resources

[1] Optimize printed electronics manufacturing with laser sintering. Hamamatsu Photonics Europe, August 30, 2024. https://www.hamamatsu.com/eu/en/news/featured-products_and_technologies/2024/optimize-printed-electronics-manufacturing-with-laser-sintering.html 

[2] Mitra D, Mitra KY, Buchecker G, Görk A, Mousto M, Franzl T, Zichner R. Laser Sintering by Spot and Linear Optics for Inkjet-Printed Thin-Film Conductive Silver Patterns with the Focus on Ink-Sets and Process Parameters. Polymers. 2024 Oct 14;16(20):2896. https://pmc.ncbi.nlm.nih.gov/articles/PMC11510878/