Here’s a fact about membrane switches that might surprise you: multiple component parts of any given membrane switch are printed rather than assembled or constructed. The same is true of many sensors, input devices, and other printed electronics.
A membrane switch is a thin on-off switch that activates or deactivates an electric circuit when pressed (learn more about how membrane switches work). “Within a membrane switch, there are different components that need to be printed, including the underlying circuits, their casing and the graphics display on top,” Hiroshi Ono, group product manager of Roland DGA Corp., which makes industrial printers, tells Sign and Digital Graphics Magazine.
Manufacturers have a couple of options when it comes to printing components for these devices, including screen printing and digital printing. Both screen and digital printing refer to the application of special inks to a substrate, but they differ in the mechanisms by which they work. The key difference is how the image is mapped.
- With screen printing, the printer uses a fine wire mesh (typically a layer of polyester or silk) fashioned into a stencil with open areas through which ink will be pressed onto the substrate below. If the final design requires multiple colors, multiple screens will be required.
- With digital printing, the image is translated into a digital file that maps where small drops of ink that will, in aggregate, create the final image once applied to the substrate.
The printing method used can affect cost, usability, and durability. For example, the graphic overlay is part of the user interface and experience. It guides the user in engaging with the device in helpful ways. A poor print job will make the device less usable or, if the print job deteriorates over time, will reduce the functional lifespan of the device. Thus, the print method can strongly impact the quality of the final device.
This is particularly true of the circuit layer, which is crucial to the functionality of a membrane switch. Ono says, “To print directly on the underlying circuits, typically screen printing processes are employed. In fact, traditional screen printers have dominated this market. This is because the inks used to print the metallic, conductive items within the switch are very specialized, high viscosity inks that are not well suited for inkjet printing.”
Admittedly, digital printing is a fast-evolving field, and it offers numerous advantages that make it suitable in certain applications. Digital printing is user-friendly and cost-effective, and it dovetails nicely with small volume runs and “just-in-time manufacturing” methodologies. But it also faces some shortcomings that have left screen printing as the dominant choice for most membrane switches.
For one thing, screen printing offers much higher throughput per hour with a more extensive color range that extends beyond digital’s four-color CMYK system. In fact, some colors are achievable only with screen printing, and screen printing yields thicker ink deposits, which can add to color vibrancy and ink durability. The result is a printed electronic device that’s appealing, long-lasting, and functionally excellent.
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Technical wordsmith and guest blogger for Hoffmann + Krippner.