Additive manufacturing, 3D printing in the world of mass production

The use of printing technologies for industrial manufacturing processes in microfabrication has long been considered the holy grail of 3D printing. Companies have certainly tried, but existing technologies such as traditional inkjet printing haven’t been able to deliver the ultra-high resolution and placement accuracy needed to be efficient and affordable.

Fast forward to today and there is a wide range of new technologies on the horizon that have the potential to transform many markets, most notably the semiconductor and display industries. Clearly, we have entered the era where digital printing has successfully transitioned from graphic printing to 3D printing of geometric objects and is now poised to make the next quantum leap by enabling the functional printing of microelectronic products.

Limits of traditional inkjet printing

As microfabrication-based industries such as the display market begin to realize the benefits of additive manufacturing, producers of printing machinery are being urged to deliver printing technology that can produce 100 times greater detail. thinner than those of conventional graphic printing. In the case of inkjet printing, the diagram on the left below illustrates how conventional technology works: liquid is squeezed out from inside fine nozzles, creating tiny droplets of ink.

Figure 1 The image above highlights the performance parameters and differences between conventional piezo-based inkjet printing and the new electrostatic technology. Source: Scrona AG

The problem with the traditional actuation process is that it only allows the ejection of thin inks, which are then flattened onto the substrate due to their high fluid content. The actuated droplets are not smaller than the size of the nozzle from which they were ejected. This conventional thrust concept physically limits nozzle size to a few tens of micrometers and thus makes it difficult to achieve the ultra-high resolution needed for microfabrication.

A new and alternative approach is to use an electrostatic force which pulls the liquid out of the nozzle, forming a pointed cone and concentrating all the energy at the tip of this cone. It is from this tiny tip that small droplets are ejected, accelerated and guided downward. Due to the force focusing effect, the droplets are no longer limited to the size of the nozzle, but can actually shrink more than 10 times.

Since no force needs to be guided to the nozzle exit from inside the nozzle, the technology becomes essentially independent of ink thickness, allowing both thin and thick fluids to be treated almost equally. Small droplets can be precisely placed on the substrate and small volumes dry quickly and form 3D projects smaller than 1 µm.

Because the electrostatic ejection principle is more or less independent of the ink, it opens the door to the use of a wide variety of inks. These inks can be at least 100 times more viscous than the inks used in today’s conventional inkjet printheads. In theory, it might even be possible to print with honey. This ability to print with many types of fluids expands use cases in addition to typical metallic nanoparticle inks in a wide range of materials, such as:

• Salt molecules and solutions
• Microparticles and proteins
• Fluxes, waxes and epoxies

Thanks to this new process, costly treatments of inks to make their rheology compatible with inkjet printheads become obsolete. While a single nozzle already demonstrates unprecedented performance for microfabrication, economical use only becomes viable by replicating these nozzles 1,000 times using a single microfabricated MEMS chip.

This enables the digital microfabrication of functional elements printed from multiple materials in a resolution invisible to the naked eye. This, in turn, enables the development of products we have only envisioned. An example is an invisible touch screen that could be printed as quickly and economically as printing an image on a typical desktop printer today. This capability has the potential to revolutionize the manufacturing of semiconductors, displays, and many other similar products.

Implications for semiconductor manufacturing

The ability to print on any material, at scale, can improve the speed, accuracy and cost of producing innovative products today and tomorrow. The semiconductor and display manufacturing industries are ideal targets for additive manufacturing to reduce their complexity, high cost as well as high water and energy consumption while delivering the high resolution needed.

As shown in the graph below, this could reduce the manufacturing steps of some solid-state back-end components by 10 times, while significantly reducing the consumption of materials, energy and water. With multiple steps (more than 20 needed for a single component on a semiconductor device), manufacturing can take up to 15 weeks, with 11-13 weeks being the industry average. Additionally, a semiconductor plant can use between 2 and 4 million gallons of ultra-pure water (UPW) every day, which is roughly equivalent to the water usage of 40,000 homes.

Figure 2 Additive manufacturing functional printing can reduce the manufacturing steps of certain semiconductor back-end components by a factor of 10, for example the microfabrication of redistribution layers (RDL).

Other markets can also be transformed by this type of technology. For example, the yet unseen resolution and layer thickness control can enable the printing of quantum dot RGB color filters for high-brightness color micro-LED displays in augmented reality glasses for gaming applications. and metaverse. It can also be used for circuit boards/printed electronics, MEMS and sensors, life science and security printing.

Electrostatic Benefits

By exploiting the principles of electrostatic ejection, it is possible to achieve simultaneous printing from a large array of nozzles, with the following advantages over conventional inkjet:

• Ultra high resolution printing with 100x higher resolution
• High-speed printing with 10x higher ejection frequency
• Smaller droplets not only for greater precision but also for faster drying
• 3D printing with aspect ratios >10:1 possible with nanoscale layer thickness control
• Customization of the MEMS printhead, dynamically and fully programmable
• Nozzle clogging prevention with proprietary Environmental Control System (ECS)

The unique combination of high resolution and high throughput has the potential to reinvent microfabrication for mass production, accelerating product invention in a cost-effective and environmentally friendly way. This is a quantum leap for a wide range of industries, from semiconductors to molecular printing in biotechnology.

Walter Brown is COO of Scrona AG.

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