A membrane switch gives a visually pleasing human-machine interface that is easy to use, low profile, and electronically stable. They are well known to stand up to harsh conditions. Flex circuitry is resilient and can be used in many different environments. Once you know what the end use will be for the flex circuit, the appropriate overlay material can be selected for the part.
Polycarbonate and polyester are the two most used materials for membrane switches. The overlay starts out as a clear material and then is printed on the back side. This protects the graphics and increases durability.
Indoor or Outdoor
Where your membrane keypad will be located is important to know for the designer. For outdoor use we use Autotex XE which is a polyester film with special hard coat and primer layers. This material is designed to resist ultraviolet light, moisture and temperatures from -40C to 80C. If you try and use a regular indoor film outdoors the material can get brittle and yellow pretty quickly.
The XE material is UV and humidity resistant (85% RH). We use the Fine version (f). It can also be embossed if needed to enhance tactile usability. Our XE polyester has an estimated flex life of 5 million actuations for non-embossed switches.
Adhesive Layers
A membrane keypad is made of about 6 layers and each layer serves a unique function. The Graphic Overlay is on top and provides the actual interface buttons and controls. It is mounted to the rest of the keypad with pressure sensitive adhesive.
The PSA (adhesive) forms a strong body when pressure is applied. It doesn’t need any heat or other solvents to activate. This is also sometimes called cold laminating.
These adhesives will give a certain amount of sealing properties to the rest of the membrane switch. Small amounts of liquid and dust are kept out of the switch by the membrane construction. However, this durability is not good enough for severe settings.
The membrane switch may have problems if dropped into water or other liquids and is submerged for any length of time. The edges of a keypad, which protect the circuitry for most normal day to day operation environments, will be insufficient to keep water out if submerged.
Other Contaminants
- Certain abrasive and corroding cleaners may degrade the quality of an Overlay over time.
- Dust can be a problem with outdoor use.
- High humidity.
- Very high or low temperatures.
- High altitudes.
Sometimes, the membrane switch can function less reliably when exposed to extreme conditions mentioned above.
Contact us at Almax-Rp to get a membrane switch quote today!