From selective printing to using clear conductive ink, we use several techniques to ensure consistent backlighting with capacitive touch (PCAP) switches.

Projected capacitive (PCAP) touch technology has become a popular user interface option for many industries in recent years. Not only do they offer a sleek, intuitive user experience, but the possibilities for backlighting a capacitive touch circuit are nearly endless.

While capacitive touch technology incorporates well with a variety of backlighting options, the design of the circuit is an important consideration. If designed improperly, the switches can potentially impede parts of the lighting, resulting in an uneven or inconsistent look.

How Can Capacitive Touch Circuits Affect Backlighting?

Capacitive circuits work by projecting a capacitive field and measuring any changes to the capacitance. This capacitive field is most commonly generated using circuits printed with conductive ink. Standard conductive inks, such as silver, carbon, or dielectric ink, can pose challenges when printing backlit PCAP circuits. The opacity of the inks can block backlighting and result in uneven lighting or shadowing on the switch.

Fortunately, there are several methods to ensure that backlit capacitive touch circuits illuminate uniformly every time. Below, we’ll be going over the three most common techniques we use at Boyd to ensure consistent backlighting.

Selective Printing:

One of the simplest ways to backlight a PCAP switch is by selectively printing around any backlit areas or iconography. When using an inexpensive carbon or other opaque ink, icons or symbols can be left unprinted within the design. As the backlighting rises through the switch, the light only comes through the unprinted area, resulting in a user-intuitive illuminated icon.

However, there are a few requirements to employ this backlighting technique. First, the switch area needs to be large enough for iconography to be left unprinted. In addition, there needs to be enough conductive ink surrounding the unprinted area to complete the circuit and result in an effective switch. This method is ideal for large or geometrically simple switch designs.

Backlighting Through Clear Conductive Ink:

For smaller or more complex switch designs, a solution that has been recently gaining popularity is using clear, polymer-based conductive inks (such as PEDOT ink). These inks run from translucent to nearly transparent and allow the circuit to be lit from directly underneath. Unlike a switch that uses opaque ink that potentially blocks lighting, clear ink conducts electricity the same way but allows light to pass through the circuit unobstructed. While transparent inks are more expensive than opaque alternatives, they can be applied the same way through screen printing.

Another advantage of using these inks is that the translucency can be altered based on the type of ink and thickness of the deposition. Less transparent inks also act as a lighting diffuser, thereby eliminating hotspots.

Altering the Capacitive Touch Stack-Up

Another solution is to engineer the stack-up so that the backlighting source sits above the capacitive circuit. While most capacitive touch circuits are backlit from underneath, rearranging the backlighting source (typically light-guide film or fiber optic bundles) to sit above the PCAP switches can ensure that the circuits do not impede any lighting.

While this is an effective method, the sensitivity of the PCAP switch needs to be tuned to accurately register inputs through the backlighting layer. Lighting hotspots are also a potential concern as the backlighting sits directly underneath the overlay, but this can be easily solved by adding a diffuser.

The above solutions are often mixed and matched depending on the design to ensure that each part of the interface is consistently lit. Boyd offers a host of different backlighting solutions for nearly any project. To discuss your specific backlighting needs, schedule a consultation with our experts.

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.