The Basics of Tactile Switches

The tactile switch is a well-recognized type of electrical switch that, like its fellow mechanical switch counterparts, completes or breaks an electrical circuit via manual actuation. Originally getting their start in the early 1980s as membrane or screen-printed switches for keyboards and keypads, these types of switches were initially met with resistance due to their poor performance and lack of tactile feedback. However, in the late 1980s versions with metal domes incorporated into the design gained more widespread adoption thanks to their improved feedback, robust actuation, and enhanced longevity. These changes gave us the tactile switches commonly used and seen today in a wide range of consumer and commercial applications.

As mentioned above, a key differentiator of tactile switches is that when pressure is applied to the actuator, it provides a perceptible “click” or haptic bump in response to indicate that the switch has successfully operated. As momentary action devices, once pressure is no longer applied by the user, the switch is released, and the current flow is cut off. While commonly found as normally open devices, tactile switches are also available in normally closed versions where current is turned off when the actuator is pressed and begins to flow once released.

The Basics of Tactile SwitchesFigure 1: Example of common tactile switches (Image source: CUI Devices)

Tactile or pushbutton?

Two types of switches that often get mixed up or have their names used interchangeably are tactile switches and pushbutton switches. While similar in nature and function, pushbutton switches are built with traditional switch contact mechanisms. In contrast, tactile switches utilize membrane switch type contacts in their construction.

Although most pushbuttons can operate as momentary action switches, all tactile switches are momentary. Tactile switches typically offer smaller package sizes than pushbutton switches, along with generally lower voltage and current ratings. Their audio or haptic feedback is also a key differentiator compared to pushbuttons and, while pushbuttons offer panel or PCB mounting styles, tactile switches are only designed for direct PCB mounting. To learn more about pushbutton switches, read CUI Devices’ Pushbutton Switches 101 blog.

Basic structure and operation

One key area that leads to a tactile switch’s simplicity and robustness compared to other mechanical switches is its limited number of internal components to achieve its intended function. A typical tactile switch design usually includes four total parts listed below:

  1. Top cover: this protects the internal mechanism of the switch and can consist of metal or other materials, depending on the intended function. Covers can further offer a ground terminal to protect the switch from static discharge.
  2. Plunger: sitting underneath the cover and on top of the contact dome, the plunger is the component that is pressed by the user to flex the dome, thereby activating the switch. Plungers can be either flat or raised.
  3. Contact dome: this component with its arched shape fits into the base and deflects or reverses shape when contacted by the plunger. This flexing process creates the audible and haptic click while connecting two fixed contacts in the base to complete the circuit. Once force is removed, the contact dome returns to its original shape and disconnects the circuit. The material used for both the contact dome and plunger (metal, rubber, etc.) will help determine the tactile feel and sound of the switch.
  4. Molded resin base: the final piece of the switch houses the terminals and contacts to connect the switch to the PCB.

The Basics of Tactile SwitchesFigure 2: Typical tactile switch structure (Image source: CUI Devices)

Key Benefits and Specifications

Proper tactile switch selection is more than just evaluating specifications on a product datasheet. Outside of several general features and benefits, such as momentary actuation, lower power and current ratings, robustness due to fewer moving parts, and lower cost, a tactile switch’s perceptible feel and sound can have a large influence on component selection. This can be a difficult feature to quantify because the force needed to activate the switch as well as its haptic feedback will vary depending on the intended use and function. For instance, a tactile switch used in an automotive application might need more actuation force to avoid accidental inputs from vibration compared to a switch used in a home or office setting. Often the best way to determine the proper characteristics of a switch is via prototyping and testing.

With all of that being said, here are several key specifications to still keep in mind during the selection process:

  • Voltage Rating: maximum voltage that the switch can withstand when open or closed.
  • Current Rating: maximum current in amps that a switch can carry before damage.
  • Activation Force (or operating force): amount of force or pressure (expressed in gram force or gf) that is needed to move an actuator on a switch.
  • Deflection (or actuator travel): overall travel distance of a depressed switch.
  • Contact Force: amount of force or pressure (expressed in grams) required for the switch to connect the terminals.
  • Actuator Height: the height of the actuator above the switch body. (See Figure 3)
  • Lifecycle Range: expected duration of a switch under normal operating conditions.
  • Temperature Range: operating temperatures within which the switch will perform to specifications.
  • Mounting Style: the method used to mount the switch on the PCB, either through-hole or surface mount.
  • IP Rating: an international standard that classifies the degrees of protection of a switch (or other product) against the intrusion of dust and liquids. See CUI Devices’ IP67 rated tactile switches.

The Basics of Tactile SwitchesFigure 3: Common actuator heights of tactile switches (Image source: CUI Devices)

Tactile switch wiring

Most tactile switches contain four pins to help provide stability during PCB mounting. These four pins are internally connected into two sets. While technically only two of the leads are needed for wiring, it is best practice to use all of the possible pins. There are also tactile switch models with only two available pins as well as 5-pin versions that allow for joystick-like control in a very minimal package.

The Basics of Tactile SwitchesFigure 4: Common 4-pin tactile switch configuration (Image source: CUI Devices)

Conclusion

Due to their small size, low height, and long life, tactile switches fit many needs in a variety of consumer and industrial products, including newer applications in wearable technology and more. When low-power, momentary actuation is needed, tactile switches will remain a go-to switch solution with the added benefit of tactile and auditory feedback. To assist in the selection process, CUI Devices offers a line of tactile switches featuring compact packages, a range of actuator heights, and multiple configuration options.