Printed electronics as the key to compact and functional IoT devices
In the world of IoT device design, every decision is a balance between size, function, and fast production. Michał, an experienced engineer working on a new version of a diagnostic wristband, has a challenge. The client wants it to be light, waterproof, and have as few visible parts as possible. Using traditional PCBs, wires, and plastic panels is not helping – it’s a problem.
This is where printed electronics comes in. It allows you to combine HMI functions, sensors, and electrical connections in one flexible structure. This is not future tech – it’s already used by companies that want to build faster, cheaper, and with better quality. It helps engineers like Michał not only meet client expectations, but go beyond them, offering better and simpler products.
Imagine a PET film, 125 microns thick, with capacitive buttons, pressure sensors, printed graphics, and connection paths to the microcontroller – all in one. It weighs only a few grams, bends without breaking, and replaces many traditional parts. This isn’t just an idea – it’s something real that smart engineers use today.
Printed electronics using sheet-to-sheet (S2S) technology is one of the best tools a modern engineer can have. It lets you combine many functions in one printed layer. You need fewer wires, make fewer mistakes, and enjoy more design freedom and production control.
What can you include in one printed layer?
1. HMI interfaces
Modern touch buttons, sliders and control panels can be printed with screen printing or inkjet. They have no moving parts, are thinner, and are resistant to water and dirt. This makes them great for outdoor and industrial use.
A printed capacitive button has several layers. The functional layer includes silver electrodes (e.g. Henkel 725A) with resistance under 0.05 Ω/□. On top is a dielectric layer (e.g. Elantas PL 6051), 10–30 microns thick, resistant up to 120°C.
The whole is covered by a top film with printed graphics – icons or transparent windows. This multi-layer setup can be only 0.3–0.5 mm thick and can be directly integrated with flat surfaces. You can also add LED lighting through a diffusion window. Thanks to S2S technology, all layers are printed with ±20 µm precision.
2. Sensors
Pressure, temperature, proximity and humidity sensors can be printed as part of the same process. These layers can read data and send it to the microcontroller – no need for extra cables or connectors.
A common example is a Force Sensing Resistor (FSR), using carbon ink (e.g. ELCO 407C or EDAG 423SS). It changes resistance depending on pressure. The silver electrode and carbon layer are separated by a spacer with a hole. This design can detect pressure from a few grams to several kilograms, with resistance from 1 MΩ to a few hundred ohms.
These layers are usually printed on PET (125 µm) or TPU (100–150 µm). PET is stable and chemical-resistant; TPU is stretchy and better for soft materials like textiles.
The minimum bend radius for PET 125 µm is about 5 mm (for a single bend), but it depends on the number of layers. It’s important to use flexible inks that won’t crack after repeated bending – for example, carbon inks with elastomers or hybrid pastes.
These printed sensors can be used in wristbands, mats, car seat controls, rehabilitation systems, and smart labels that react to moisture. All these features can be printed on one sheet, giving engineers new creative options.
3. Graphic layer
Integrated graphics, colors, and lighting are key to modern user interfaces. The top layer uses UV inks for long life, weather resistance, and fine detail (up to 100 µm resolution). Offset inks are used when you need more colors or full backgrounds.
Diffuser films help spread light from LEDs placed below. These layers are 75–125 µm thick and transmit 80–90% of light. Icons, numbers and active zones are printed on the back of the top film (reverse printing), protecting them from damage. No need for extra labels or stickers.
Inks (e.g. from Nazdar or Marabu) must work with PET or PC films and be flexible, so they don’t crack during shaping or mounting.
The graphic layer becomes part of the device – it looks good, lasts long, and can be customized.
4. Conductive paths
Connections from sensors or buttons to the main board or microcontroller can be printed on the same layer. No need for wires, connectors, or flat cables. This makes assembly easier and removes possible failure points.
A standard path with Henkel 725A silver ink is about 10 µm thick, 0.3–1 mm wide, with resistance under 0.02 Ω/□. Even long paths (up to 150 mm) work without big voltage loss. Ends can be made for soldering, pressure contacts, or ZIF connectors.
These printed paths can be on flat or curved surfaces. Good material and design keep the electrical quality even after bending. S2S systems (like at LC Elektronik) allow printing multi-path structures with ±20 µm alignment – great for complex designs.
One printed functional layer can include electrodes, sensors, graphics, and signal paths. This reduces the number of components, shortens assembly time, and allows full preparation before the device is built.
Materials and construction
- Substrates: PET 125 µm (standard), TPU for flexible use
- Conductive ink: Henkel 725A (silver), < 0.05 Ω/□
- Insulating ink: Elantas PL 6051, heat resistance up to 120°C
- Printing: S2S, ±20 µm alignment, max size 500 × 700 mm
Benefits for engineers
- Fewer components and cables
- Simpler documentation and BOM
- Fewer connectors = fewer problems
- Easier assembly and prefabrication
Application examples
- HMI panels in home appliances and HVAC
- Pressure mats and seat sensors
- Integrated medical panels (e.g. for physiotherapy)
- Wearable wristbands with printed circuits
Conclusion
S2S technology lets engineers design full functional layers – not just electronics, but also mechanics and visuals. It puts more control into the designer’s hands. Fewer components mean cost savings and bett