How to Choose the Right Dome for a Membrane Switch

How to Choose the Right Dome for a Membrane Switch

Choosing the “right” dome for a membrane switch may seem daunting, but rest assured, it is more straightforward than you might initially think. Firstly, what are metal domes? Metal domes are used in membrane switches and keypads to enable and facilitate the electrical connection from the keypad to the product itself. Or in other words, how the user of a device initiates a specific electrical function on the product. 

Electrical switches are necessary in almost every HMI (human-machine interface) device or product. No membrane switch is the same and all are used in a unique environment, therefore it is critical that the most suitable dome is chosen for the specific application and environment. For instance, if the product is used in an industrial setting and the user will be wearing gloves: a dome larger in size with a higher force & stronger tactile feedback would be ideal. Or if the membrane switch will be used in a nursing home setting and the user will typically be older in age: a dome with a lighter force (easier to press) would be best suited.

Our CSI engineers will work closely with you in deciding which dome is best for your application. We understand that the tactile feel of a key is very subjective, so typically will mock up multiple sample keypads with different dome options in the prototype stage of the design. This allows our customers to make a decision through a more “hands-on” approach. It’s also important to understand that the dome happens to be one of the easiest components of the membrane switch design to change-out & replace throughout the design cycle and even after the keypad is in production (ie so you are never stuck with a specific dome).

Dome Characteristics & Options:

Size: 

Measured in diameter and height of the dome. The size of the keys on the membrane switch will ultimately determine the size of the dome required for the application. Domes sizes range from 6mm up to 20mm. Height is dependent on size and ranges from .25mm up to 1.45mm.

Shape:

  • Four legged
  • Triangle
  • Round 
  • Oblong
  • Custom
 

Actuation Force: 

The actuation force is one of the most critical characteristics when choosing a dome. Actuation or trip force is the minimum force needed to depress the dome and is measured in grams. Actuation forces range from 40g up to 2250g. 

Lifecycles: 

Domes have come a long way since their inception. Originally, domes were only rated for thousands of cycles. The standard for domes is now at least one million cycles, with specialized domes rated for at least five million cycles. No matter the application, there is a dome that can meet your lifecycle requirements.

Dimple or Non-Dimpled: 

Looking at a variety of domes for different applications, users may notice a little dimple located in the center of the dome (see pictures to the right). The dimple is a small concave feature located on top of the dome, and can be as deep as 0.2 mm (0.008 in.). The purpose of the dimple is to provide better electrical characteristics and to reduce contact bounce..

What is a Dome Switch Keypad?

What is a Dome Switch Keypad?

CSI Keyboards designs domes into the majority of our membrane switches. Dome switch keypads use two circuit board traces in conjunction with a metal dome. Metal domes, which are typically made of stainless steel, are momentary switch contacts that provide tactility or “snap” when pressed. The domes become normally-open tactile switches when actuated on the circuit. 

The main advantage of dome switch keyboards is the tactile snap or feedback when actuated. When pressing the key, the user realizes they have actually actuated or successfully pressed the switch due to the feel and sound feedback received from the dome.

Another major benefit of the dome switches are the the long lifespan and reliability. Standard dome switch keypads are now rated from one million to even five million cycles. They are still the most reliable type of switch available in the membrane switch space. 

Dome Options:

  • Dome plating: can be plated in other metals such as nickel, silver or gold
  • Dome shapes: four legged, triangle, round, oblong
  • Dome sizes: standard sizes are 6mm, 7mm, 8.5mm, 10mm, 12mm, 14mm, 16mm
  • Dome forces: standard forces range from 85g to 700g
  • Other options: dimpled, hole in center (for backlighting key), double-contact closure domes. 
 
Understanding Dome Actuation Forces:

Actuation force is the amount of force required to make the dome snap. Or in other words, how much force is required to change the dome from the open position to the closed position. Dome actuation force is typically measured in grams. 
 
Internal Venting for Dome Switches:
 
A critical aspect to keep in mind when designing a dome switch keypad is internal venting. When the dome is actuated, air is trapped underneath the dome with nowhere to go. It is therefore recommended that venting is incorporated in the membrane switch design. Not properly venting the dome will result in poor tactile response, key failure and potential issues with air entrapment under the membrane surface.
 

How Do I Choose the Right Dome for my Membrane Switch?

The CSI engineers will work very closely with you in deciding which dome is best for your application. Typically the decision is based on the force of the dome (how soft or hard of a press it takes to actuate the dome) and is extremely subjective. CSI can mock up different sample keypads with different dome options so the customer can decide through a more “hands-on” approach.

Dome Arrays