Functional inks used to create printed and flexible circuits offer a cost-effective alternative to conventional methods such as etched copper flex circuits and printed circuit boards (PCBs). While the latter options are still widely used, functional inks make it possible for manufacturers to print on flexible substrates for mass-scale circuit manufacturing.
What are functional inks, and how do they work? Keep reading to learn everything you should know about this handy technology and harness its potential in your next project.
What are functional inks?
Functional inks are inks that can be applied to a broad range of rigid and flexible surfaces using different printing processes:
- screen printing (sheet-fed and roll-fed),
- aerosol jet printing,
- and gravure printing.
The choice of the printing technique depends on the ink type and ultimate product use. Functional inks are generally more environmentally friendly than traditional methods. Why is that? Because etching copper on PCBs requires the use of acid baths, while the additive process of employing functional inks generates no waste and uses no harmful chemicals.
We can divide functional inks into two categories: conductive and non-conductive. Let’s take a closer look at each to discover their benefits and drawbacks.
Conductive inks are inks that conduct electricity. You can find them in a broad range of applications – for example:
- capacitive and membrane switches,
- RFID tags,
- touch screens,
- biological and electrochemical sensors,
- Positive Temperature Coefficient (PTC) heaters,
- electromagnetic interference/radio frequency interference (EMI/RFI) shielding,
- wearable electronics (stretchy conductive inks).
What factors determine the selection of conductive ink over other options? It all boils down to cost and conductivity – but also other factors like substrate compatibility, ink molecular structure, ultimate product use, and power efficiency requirements are some of the other major elements that influence decisions. Conductive inks come in several variants.
Silver and silver chloride inks
Silver inks are very conductive and have low resistance. They work with a variety of substrates, including polyester, polycarbonate, glass, and vinyl, and are abrasion, fold, and wrinkle resistant. They’re suitable for medical electrodes and membrane circuits because of their great stickiness, flexibility, and printability.
In comparison to silver inks, carbon inks have stronger resistance, lesser conductivity, and longer durability. They prevent circuits from shorting, protect silver inks from silver migration, and are less expensive than silver inks. They also have comparable qualities to silver inks in terms of adhesion, printability, and substrate compatibility. To achieve the required mix of resistivity, conductivity, and cost, carbon inks are frequently combined with silver inks.
Gold and platinum inks
Due to the high cost of metals such as gold and platinum, these inks are typically manufactured and used in very limited amounts when the performance benefits outweigh the cost. Gold, for example, is used in applications that need a high level of oxidation resistance, whereas platinum is utilized in applications that need a high level of conductivity.
Because of its strong conductivity, copper ink may be used as a less expensive alternative to silver inks. However, the ink’s low stability limits its application. Nickel inks are extremely durable, but also more costly than carbon inks.
Non-conductive inks don’t conduct electricity but are used in a variety of important functional and ornamental applications: sensors, membrane switches, graphic overlays, and labels. Here are a few examples of non-conductive inks:
Graphic design inks
Graphic inks are used in a variety of components and brand identification products, including nameplates, labels, ornamental signs, decals, placards, elastomer keypads, and graphic overlays. Solvent-based inks, water-based inks, UV curable inks, epoxy inks, and air-dry inks are a few examples of graphic inks.
How to select the right graphic ink? Consider factors such as the substrate’s surface energy and surface tension, ambient conditions, and cost. At Melrose, we use techniques such as screen printing, digital printing, lithographic printing, UV inkjet printing, and UV flexographic printing.
Dielectric inks are electrically insulating inks that preserve conductive inks as they operate together. Dielectric inks prohibit the various layers of conductive ink from interacting with one other in a multi-layer circuitry design. They prevent electrical shorting and silver migration by forming insulating barriers.
Dielectric inks can be used on both stiff and flexible substrates, including bare or print-treated polyester, polycarbonate, and glass. They have excellent adhesive qualities, exceptional flexibility, moisture and abrasion resistance, and are unaffected by folds and bends. Membrane switches, Radio Frequency Identification (RFID) tags, antennas, and electrodes all employ dielectric inks.
Specialized inks are slowly creeping their way into common product development processes as well. Here are the most common types of specialized inks used today:
- Thermochromic inks – temperature-sensitive inks that change color when the ambient temperature rises over a set point. They come in a variety of colors, including neon, blue, purple, and other hues. Labels, print advertising, textiles, biomarkers, and sensors are all common use cases for thermochromic inks.
- Photochromic inks – when exposed to UV light, these inks change color immediately. These photochromic inks, like thermochromic inks, come in a variety of hues. They can be found in light-sensitive eyeglasses, body patches that sense sunlight exposure, and clothes.
- Hydrochromic inks – when this type of ink interacts with or is immersed in water, it changes color. Packaging, ornamental umbrellas, and apparel are all examples of common usage.
Melrose uses high-quality inks to deliver the most demanding components
We work with industry-leading ink compounders, which helps us to cut manufacturing lead times and decrease pricing volatility. Our engineers can match a broad range of production requirements related to unique ink and printing techniques while remaining flexible throughout product development. Schedule a meeting with our consultant to learn more about our offer and get specialized advice on inks and printing.
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