What is Conductive Ink Technology and How Is It Used?

Conductive ink is a fantastic material that actually lets you draw working circuits on various materials like paper or textiles. There has been a lot of hype in recent years about how it will eventually replace traditional circuits. 

But is this true?

Here we'll explore what conductive ink is, how its made, its pros and cons, and see in which industries it is currently being used.

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What is conductive ink?

Conductive ink, as the name suggests, is a form of ink that can conduct electricity. In most cases, the ink is infused with a conductive material, like graphite or silver, to enable electrical conduction. 

For some, it is a technological panacea that may, one day, enable electrical circuits to be printed on paper or other flexible surfaces. It could even be used using inkjet technology. 

As well as inks, some companies, like Bare Conductive in the UK, have produced paint products that can also conduct electricity. Working much like conductive inks, conductive-paint can be used as a cold solder, to repair PCBs and many more other applications.

But we are not there yet. They are, for example, not without their downsides (like when washing textiles for instance).

"There are already some simple circuit boards made using conductive inks. For example, some subway and train systems use them to print circuits onto disposable passes. But the downside to conductive ink circuits is their resistance. Solid, pure metal will always be more conductive than the flakes or powder in conductive ink, so solid copper circuits will be more efficient with electrical energy and generate less heat," according to scienceline.ucsb.edu. 

That being said, they have some great advantages for many industries.

"Conductive inks can be a more economical way to lay down a modern conductive traces when compared to traditional industrial standards such as etching copper from copper plated substrates to form the same conductive traces on relevant substrates, as printing is a purely additive process producing little," notes Wikipedia.

This ink has several uses today and is commonly used in printing metallic structures. Yet, in its early days, the biggest push behind its development was in the wearable technology and e-textile industries. 

"Conductive ink is the most important component in [the] printing of metallic structures. Several conductive materials could be considered for this purpose, such as conductive polymers, carbon, organic/metallic compounds, metal precursors, and metal NPs. Most conductive inks are based on metal NPs," according to sciencedirect. 

Conductive inks have a variety of advantages over other existing solutions. One of the most important is that it can be easily customized to cater to a broad spectrum of industry requirements. 

For e-textiles, for example, conductive inks are a great option as they can be applied after the main product has been produced. In other words, it can be added later without interfering with the textile production process. 

This is made possible because inks can be laminated, and heat transferred much as graphics are today. There is also ongoing innovation on the use of sacrificial layers.

What is conductive ink used for?

Conductive inks have a variety of applications.

For example, silver-infused conductive inks tend to be used for printing RFID tags as used in modern transit tickets. They can also be used to improvise or repair circuits on printed circuit boards. 

These inks can also be used in computer keyboards that contain membranes with printed circuits that 'sense' when a key is pressed.

Windshield defrosters consisting of resistive traces applied to the glass can also include conductive inks.

Many newer cars have conductive traces printed on a rear window, serving as the radio antenna. 

But they do have other uses. For example, they have applications in the following markets and industries (credit to idtechex.com):

• Photovoltaics
• Power electronics
• EMI shielding
• In-mold electronics (automotive, home appliance, etc.)
• Electronic textile and wearable electronics
• 3D antennas and conformal printing
• Flexible hybrid electronics (FHE)
• Touch screen edge electrodes, automotive (defoggers, seat occupancy sensors, seat heaters, etc.)
• 3D printed electronics
• Multi-layer ceramic capacitors (MLCC)
• ITO replacement (hybrid, direct printing, etc)
• Printed piezoresistive 

• Capacitive and biosensors
• PCB (DIY/hobbyist, professional, seed-and-plate)
• RFID (HF, UHF)
• Printed TFT and memory
• OLED and large-area LED lighting
• Flexible e-readers and reflective displays
• Large-area heaters (battery, plant, seat, etc.)
• Conductive pens
• Digitizers

Is conductive ink a good conductor of electricity?

In short yes it is, but not as much as more traditional materials used for making electrical circuits, at least for now.

In order for a material to conduct electricity, it must allow the movement of electrons through it. Conductive materials, therefore, allow an electric current to flow through them.

Some materials are naturally able to do this with the prime example being metals. But metals tend to be, in their 'natural' form solid at room temperature and pressure - with the notable exception of mercury. 

In order to get around this to produce ink, conductive materials (like metals) need to be included within a liquid medium whilst still retaining as much conductive potential as possible. 

One common solution is to produce metal nanoparticles that are entrained with a liquid medium. 

"These nanoparticles are tiny spheres of metal, so small that you could fit over 5 million in the period at the end of a sentence. Each nanoparticle can conduct electricity, and when strings of nanoparticles form, like pearls in a necklace, electrons can travel from one nanoparticle to the next," according to scienceline.ucsb.edu. 

When the ink finally dries, the chain of interconnected nanoparticles is locked. This forms a permanent conductive route for electricity to travel through the dried ink. 

However, this relies on the random, or near-random, creation of paths of metal nanoparticles in the ink when used. By virtue, thicker films of ink increase the probability that enough paths of nanoparticles will form for sufficient electrical conduction.

While still highly conductive, they are inherently less conductive than the use of non-conductive ink solutions. Presently, most microchip fabrication, for example, requires thicknesses much smaller than the required amount of conductive ink needed for the job.

For this reason, it is unlikely that this method of creating electrical circuits will replace the current method of producing circuit boards. Of course, as conductive ink technology improves, we may see a time when conductive ink can challenge conventional solutions.

How do you make graphite conductive paint?

We have already touched in this a little above, but effectively they are made by mixing tiny particles of conductive materials with non-conductive liquid mediums. The idea is to use a liquid medium that can flow relatively freely whilst building a chain of conductive materials behind it. 

Once the liquid medium dries, it should, in theory, lock the conductive particles (or inclusions) in place leaving a completed circuit. 

There are various ways of manufacturing it and you can even make a basic DIY batch of it for yourself. For example, IEEE has a handy little tutorial if you want to have a crack at it yourself. 

Obviously, take all the necessary safety precautions if you wish to attempt this!