FUNCTIONAL INKS FOR PRINTED ELECTRONICS – DEMYSTIFIED

Screen printing is the dominant process for printed electronics manufacturing. Screen printing is capable of multilayer patterning of materials with different functionalities. These include conductive, resistive and insulating layers. This method of printing is used to manufacture various electronic components and circuits. For example, printed touch switches for control panels, displays, lighting, flexible heaters, printed antennae and medical electrodes. Additionally, various sensors used in environmental monitoring, wellness and healthcare monitoring and even medical diagnostics.

Traditional high-speed printing methods – such as flexography and gravure – are rarely used in electronics manufacturing. These methods are typically used for low power interconnects and sensors in niche and speciality applications. They include electronic medical adherence packaging, smart adult incontinence products and, in some cases, wearable medical electrodes.

For some electronics applications – such as in organic light-emitting diode (OLED), organic photovoltaic (OPV) – inkjet printing can be appropriate. It offers an opportunity to displace vapour deposition processes, rather than compete with screen printing for more traditional printed-electronics applications.

“Screen printing is the dominant process for printed electronics manufacturing”

Many of today’s functional inks are based on polymer thick film (PTF) technology. This combines screen printing with polymer-based pastes filled with functional particles to create electronic components and circuits on plastic substrates. PTF technology found its commercial success in membrane touch-switch applications back in the 1970s. Its use is now widespread in other printed electronics applications. The term ‘functional inks’ expands beyond PTF inks. It also covers a broader scope of printing materials suitable for variety or printing methods designed to provide specific properties for electronic component or circuit functions. 

Depending on the level of electrical resistivity – the material’s ability to resist electric current to flow – functional inks are divided into three main types (see Table 1). Primarily, these inks are used to make passive electronic components, such as interconnect wires, electrodes, resistors and capacitors. The opposite of electrical resistivity is electrical conductivity. Therefore low-resistivity material is considered conductive and very high resistivity material does not conduct electric current and is thus considered electrically insulating.

There are other types of functional inks designed for speciality uses. Among these are ferric inks for inductors, semi-conducting inks used as active layers in transistors and diodes. In addition, other forms of these inks are used for light-emitting materials for displays and lighting, light-absorbing materials for solar cells, various sensing and catalyst inks.

There is a constant push for higher-performance functional inks. This is to increase adoption of printed-electronics technologies in automotive, consumer, industrial and healthcare electronics markets. 

Ink formulators are currently pursuing many targets for advancement. For example, better electrical performance (higher conductivity, higher insulation and reliability) and improved mechanical properties (flexibility, folding endurance, conformability, stretchability, thermoformability). Additionally, better environmental stability and operational reliability. Formulators are also looking for more cost effective, faster or lower-energy curing capabilities, as well as biocompatibility and eco-designed materials with a lower carbon footprint. 

While there are advancements in all categories of functional inks, large development effort revolves around conductive inks. These are the key materials for any printed electronics application.

“Ink formulators are currently pursuing many targets for advancement”

The primary functional filler for conductive inks is silver (Ag) because of its high conductivity, stability and high-volume manufacturability. Silver is highly reliable and stable to handle in ambient conditions. In contrast, other metals – such as copper or aluminium – form surface oxides that hinder conductivity. There are some copper inks on the market, however, they typically require special handling and processing. Other conductive fillers include silver chloride, silver-plated gold, platinum, copper particles and nickel. 

Silver-based conductive inks utilise the metal in a range of forms, shapes and sizes (see Figure 1). Silver micro-flakes and powders are commonly used in PTF silver inks. However, there are also silver nanoparticles, as well as reactive silver salts or metal-organic precursors (transient metals). These are sometimes used either by themselves, or as an additive, to increase conductivity of particle-based silver inks (hybrid or semi-sintering).

Formulators typically consider aspects such as particle-size distribution, particle morphology, tap density and lubricant chemistry. All of these affect ink properties, such as dispersibility in polymer matrix, processability, particle-packing density and, ultimately, ink conductivity. The radar graph (see Figure 2) compares the main attributes for various types of silver-conductive inks available on the market. Advances in particle and polymer binder technologies have led to a dramatic increase in electrical, mechanical performance and compatibility with various substrates and processing methods. In addition, compatibility with various substrates and processing. The price of conductive silver inks is highly dependent on silver bullion market price. Because of this, it is very important to balance ink cost and performance. 

“Many of today’s functional inks are based on polymer thick film (PTF) technology”

Sun Chemical has a long history of supplying traditional printed circuit board (PCB) manufacturing materials, functional inks for printed electronics, including biosensors, and material solutions for solar cells and Li-ion batteries. 

Performance targets, operational and environmental reliability, safety and cost are all important considerations when designing materials for electronics applications. As new applications and markets emerge, ink formulators rise to the challenge. Sun Chemical works in partnership with leading original equipment manufacturers (OEMs) and partners to develop functional ink solutions for a range of electronics applications areas. At Sun Chemical, value-chain partnerships and extensive fit-for-purpose testing capabilities are key. These aspects allow for development and optimisation of materials addressing the needs and new requirements of this exciting field. SunTronic and SunSens functional inks product lines offer a broad selection of conductive, resistive and insulating inks for printed electronics and biosensors.

The Sun Chemical team will be on Stand B0.201 at LOPEC 2026 (24–26 February in Munich, Germany).