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Fundamentals of Functional Inks: Part 1

Last updated Dec 21, 2023 | Published on Apr 29, 2021

Depending on the application, there are several different kinds of functional inks used to print flexible circuits.

Functional inks are a cost-effective method to manufacture printed and flexible circuits. While the traditional technologies of etched copper flex circuits and printed circuit boards (PCBs) are still prevalent, functional inks have the advantage of being an economical alternative when it comes to printing on flexible substrates and mass-scale production of circuits. In this two-part blog series, we will broadly touch upon the essentials of functional inks Boyd uses in a wide range of manufacturing services.

Depending on the ink type and final product application, functional inks can be applied on a variety of both rigid and flexible substrates using various printing techniques including screen printing (sheet-fed and roll-fed), aerosol jet printing, and gravure printing. Functional inks are more environment-friendly than traditional technologies. While the subtractive process of etching copper on PCBs requires acid baths, the additive process of using functional inks does not produce any waste streams or involve any hazardous chemicals. Functional inks can be classified into two categories: conductive inks and non-conductive inks. In this blog, we will broadly explore the various types of conductive inks used at Boyd along with their properties and applications.

Conductive Inks at Boyd

Conductive inks are inks that conduct electricity. They are commonly seen in capacitive and membrane switches, Radio Frequency Identification (RFID) tags, touch screens, biomedical and electrochemical sensors, Positive Temperature Coefficient (PTC) heaters, electromagnetic interference/radio frequency interference (EMI/RFI) shielding, and more. Recent developments in stretchable conductive inks are also leading the evolution of wearable electronics.

For any given application, the two C’s that primarily govern the conductive ink selection process are Cost and Conductivity. Some other key factors that govern decisions include substrate compatibility, the ink’s molecular structure, final product application, and power efficiency requirements. Some of the conductive inks employed by Boyd include:

Silver and Silver Chloride Inks

Silver inks offer superior conductivity and low resistance. They are compatible with a broad range of substrates including polyester, polycarbonate, glass, and vinyl, and are resistant to abrasion, folds, and creases. Their high adhesion, high flexibility, and ease of printability have made them the ideal choice in medical electrodes and membrane circuits.

Carbon-Based Inks

Carbon inks offer higher resistance, lower conductivity, and superior durability as compared to silver inks. Carbon inks are often blended with silver inks to achieve the desired balance between resistivity, conductivity, and cost. They protect silver inks from silver migration, shield circuits from shorting, and are cheaper than silver inks. They also offer similar benefits as silver inks in terms of adhesion properties, ease of printability, and substrate compatibility. Typical applications at Boyd include cost-effective capacitive touch switches.

Gold and Platinum Inks

Given the huge cost hurdles associated with noble metals like gold and platinum, these inks are usually produced and utilized in very small quantities. Boyd occasionally employs them in the product development stage or in applications where performance benefits outweigh the cost barrier. For example, gold is used in applications where high oxidation resistance is crucial and platinum is seen in applications that demand high conductivity.

Other Metal-Based Inks

Copper ink can be used as a cheaper alternative to silver inks, given its high conductivity, but its low stability often poses limitations on its use. While nickel offers high durability, it is more expensive than carbon inks.

To learn about non-conductive functional inks, stay tuned for our next blog.

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