Functional Printing

Equipped with an excellent infrastructure and long-standing expertise, Fraunhofer ISE offers a variety of services for challenging functional printing applications like silicon solar cells, printed circuit boards (PCBs), fuel cells, batteries, sensors, electronic devices and more. We support material, equipment as well as device manufacturers in selecting suitable printing technologies, developing functional materials or innovative processes. We offer a wide range of characterization methods covering all relevant aspects from material and surface characterization to an in-depth analysis of electrical, optical and functional properties.

Silicon solar cells serve as a well-known example for printed devices produced on an industrial level. Printing ultrafine line contacts with good conductivity on textured silicon surfaces is a supreme discipline of functional printing, in which Fraunhofer ISE has gathered extensive experience.

Our PV-TEC – Photovoltaic Technology Evaluation Center features a variety of different state-of-the-art printing technologies which can be applied for various applications. We can offer research services and in-depth knowledge covering the following printing technologies:

  • flatbed screen
  • stencil printing
  • rotary screen
  • flexographic printing
  • inkjet printing
  • multi-nozzle parallel dispensing
  • FlexTrail

The multi-nozzle dispensing activities have been recently commercialized successfully by our spin-off HighLine Technology GmbH. 

Our expertise and services in the field of "functional printing":

Screen and Stencil Printing

High-precision thick film coating of finest structures

Multi-Nozzle Dispensing

Efficient, flexible and ready for high throughputs

Rotary Printing

High-throughput rotary printing platform and shuttle transport for rotary screen and flexo printing

Inkjet and FlexTrail Technology

Innovative FlexTrail technology for ultra-fine line structures below 10 µm

Drying and Firing Equipment

Inline and offline drying, curing- and sintering devices for low and high temperature sintering pastes

Characterization Services

Thorough analysis of all process steps, including all relevant parameters

Screen and Stencil Printing

Functional Printing: Ultra fine line screen printed contact finger
© Fraunhofer ISE
Ultra fine line screen printed contact finger on textured Silicon surface.

Flatbed screen printing and stencil printing have been used for decades in many fields of technical printing. Specific application examples are the metallization of silicon solar cells, the printing of solder paste for the SMT assembly of printed circuit boards or the printing of antennas used in vehicles. The peculiarity of including even very fine structures with a high layer thickness on a wide variety of substrates means that screen and stencil printing belongs to various other processes. At Fraunhofer ISE, fine line contact fingers with a width of 19 µm will be screen printed on silicon solar cells.

Our infrastructure and services for Screen and Stencil Printing:

  • fully automated industrial screen printing lines for high-precision thick-film printing processes (i.e. solar cell metallization, functional layers)
  • inline inspection system with highprecision detection of printing quality and defects
  • semi-automatic high precision screen printer
  • in-house screen development

Multi-Nozzle Dispensing

dispensing nozzle tip
© Fraunhofer ISE
Finite elements simulation of dispensing nozzle tip.

Dispensing is used in many areas of industrial production as a method for precise dosing and precise positioning for the application of fluids.

Dispensing requires high-precision manufacture of the nozzles, fast and micrometer-precise control of the dispensing head over the substrate and intensive rheological optimization of the fluids used. Using dispensing, very homogeneous structures with almost perfect shape and uniformity can be created, for example ideal conductor structures with the finest line width and minimal deviations. A specialty is the multi-nozzle dispensing, which combines the advantages of the dispensing process in terms of precision with a high throughput. In the multi-nozzle dispensing process, the finest contact fingers e.g. for the front-side metallization of silicon solar cells with perfect geometry and high throughput can be transferred highly parallel. However, the process also offers great potential for other applications. Multi-nozzle dispensing was developed at Fraunhofer ISE using CFD simulations and has been commercialized by Highline Technology - a spin-off of Fraunhofer ISE - since 2020.

Our infrastructure and services for Multi-Nozzle Dispensing:

  • industrial platform with high-precision 3-axis positioning system and multinozzle dispensing print-head
  • high-throughput inline multi-nozzle parallel dispensing unit
  • lab devices for single-nozzle and multi-nozzle dispensing

Rotary Printing

Fine line front side metallization
© Fraunhofer ISE
Fine line front side metallization using rotary flexographic printing technology.

Rotary printing processes such as flexographic printing, rotary screen printing and gravure printing have been used in a large number of industrial applications in the graphic and technical field for decades. Rotary printing processes are unique in terms of speed, precision and flexibility. Usually rotary printing processes are used to print roll-to-roll.

Whereas printing on non-flexible piece goods such as e.g. Silicon solar cells, printed circuit boards, electronic components or chip cards is a lot more complex than roll-to-roll printing.  

Coating such substrates at high printing speeds requires a high-precision transport system and precise alignment of the rotary printing units.

Such a technology was developed by Fraunhofer ISE in cooperation with project partners as part of the "Rock-Star" project. The innovative rotary printing demonstration system in the PV-TEC – Photovoltaic Technology Evaluation Center of Fraunhofer ISE enables the high-precision transfer of the finest structures in flexographic and rotary screen printing with high throughput. In addition to the metallization of silicon solar cells, this technology offers great potential for a wide variety of applications in the field of functional printing.

Our infrastructure and services for Rotary Printing:

  • high-throughput shuttle-transport rotary printing platform for rotary screen printing and flexo printing
  • laboratory rotary printing device for flexo, rotary screen and gravure printing tests

Inkjet and FlexTrail Printing

Inkjet-printed dot array
© Fraunhofer ISE
Inkjet-printed dot array using hotmelt wax ink.

Inkjet is a digital printing process that enables the contactless and extremely precise application of drops of all kinds. Fraunhofer ISE has many years of experience in the development of printing processes, for example with inks based on nano-scale metal particles, wax-like etching masks (also UV-curing) and dopants. To make sure the desired substrate can be wetted by the ink, Fraunhofer ISE offers the complete portfolio for characterizing media with regard to viscosity and surface tension. By using inkjet printers in glove boxes, the environment can be adjusted in terms of wetting. The Fraunhofer ISE also offers plasma-assisted preliminary processes for the activation of surfaces.

Ultra-fine line
© Fraunhofer ISE
Ultra-fine line printed with Ag ink using FlexTrail.

The FlexTrail process is currently in development and enables the precise application of media of different viscosities with an extremely precise, minimal structure width. In this way, conductor tracks with a minimum structure width of less than 10 µm could already be printed stably on smooth substrates.

Our infrastructure and services for Inkjet- und FlexTrail Printing:

  • industrial inkjet printing equipment with modification for integrating various printheads
  • customized development of solutions for specific inkjet applications
  • innovative FlexTrail technology for ultra fine line structures below 10 µm

Drying and Firing Equipment

Fast firing process for Silicon solar cells
© Fraunhofer ISE / Dirk Mahler
Fast firing process for Silicon solar cells.

The printing of functional fluids not only requires high-precision printing and coating processes, but also suitable drying and sintering processes. Various highly specialized drying and sintering technologies are available at Fraunhofer ISE. In addition to classic continuous dryers based on IR radiation and convection, high-temperature sintering processes (contact firing) as well as innovative processes such as vertical-cavity surface-emitting laser (VSCEL) and intense pulsed light (IPL) can be realized in PV-TEC.

Our infrastructure and services for Drying and Firing Equipment:

  • inline and offline drying, curing and firing equipment for low and high temperature sintering pastes including inert high-temperature sintering
  • fast firing furnace with extended peak firing zone and integrated IR camera for process monitoring
  • special drying/firing technology (UV, intense pulsed light (IPL) and VCSEL-Technology).

Characterization Services

Image analysis tool for 3D characterization of front side contacts
© Fraunhofer ISE
Image analysis tool for 3D characterization of front side contacts.

The analysis of the geometric and electrical quality of functional structures such as conductor paths require special characterization procedures as well as corresponding and know-how for the correct implementation of measurements and assessment of the results.

At Fraunhofer ISE there are a number of special characterization methods for analyzing the printing process and the quality of the printed functional structures, e.g. 3D microscopy, scanning electron microscopy and high-speed cameras for direct optical printing process analysis are available. In addition, the flow behavior of relevant print media can be examined using ultra-modern rheology measuring devices and then modeled. Finally, based on these models, entire printing processes can be fully automated optimized within the framework of CFD simulation.

Our infrastructure and services for Characterization:

  • in-depth analysis of all relevant rheological parameters using rotational rheometer and capillary viscosimeter
  • contact angle measurement
  • laser beam reflection for measuring particle size
  • statistical analysis of 3D geometry of printed structures using laser-scanning 3D microscopy and image analysis algorithms
  • optical microscopes for all types of applications
  • scanning electron microscope (SEM) including EDX detector and FIB (Focused Ion Beam)
  • contact and sheet resistance measurements for printed structures
  • statistical measurement of metal-semi conductor contact resistance and lateral line resistance