Which material is better for membrane switches

A membrane switch typically consists of six parts: the panel, surface adhesive, upper circuit (spring plate fixing layer), isolation layer, lower circuit, and back adhesive. The selection of materials for each layer must be determined at the beginning of engineering design based on user requirements, product characteristics, and usage environment.

The commonly used panel materials include polycarbonate (PC), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). PC material is heat-resistant (-60~120℃), environmentally friendly, and exhibits excellent heat resistance, cold resistance, electrical insulation, and atmospheric aging resistance. It also boasts superior bending, tensile, and compressive strength. However, it has poor chemical resistance (organic solvents), poor fatigue resistance, and is prone to stress cracking. It is also susceptible to air oxidation, gradually forming a peeling layer and eventually decomposing completely. Due to its decomposability, PC is widely used in the environmental protection field and can meet the requirements of membrane switch panels. Highly transparent PC is often used as the lens for display windows.

PVC is stable to acids, alkalis, and salts at room temperature, possesses good wear resistance, self-extinguishes in case of combustion, reduces noise and vibration, has good electrical insulation properties, but has poor thermal stability (-20~60℃). PVC is rarely used for membrane switches and is occasionally employed only for panel labeling.

PET exhibits good resistance to chemicals, acids, and alkalis, and is insoluble in common organic solvents. It possesses excellent insulation properties, heat resistance (-30~160℃), and wear resistance, particularly exhibiting high flexural strength and toughness, as well as high dimensional stability. It is the most ideal substrate for the production of membrane switch panels and circuits. Commonly used frosted PET for membrane switch panels includes the Autotype F series (F150, F200) and V series (V150, V200), while the glossy versions are the Autotype EBG and EBA series.

Many manufacturers of circuit substrates choose Toray (imported) and Dongfang (domestic) PET materials. The thickness is mostly 0.125mm, and for many light-touch types, sometimes 0.10mm or even 0.075mm thickness is chosen. The spring-loaded fixing layer generally uses the same series of 0.075mm or 0.05mm thick PET. When the membrane switch wire spacing is less than 1.00mm, the circuit will consider using FPC or PCB.

The tactile feel of a membrane switch often depends on three major factors: the size, force, and travel of the dome (or switch). The design of the ventilation slots in the isolation layer and surface adhesive also affects the tactile feel. Commonly used domes include stainless steel, nickel-plated, and gold-plated varieties. Typically, nickel-plated domes are selected for membrane switches, while gold-plated domes are preferred when particularly sensitive button presses and very stable circuit resistance are required. The force applied is generally proportional to the diameter of the dome. For example, a dome with a diameter of 8mm requires a force of 180~220 grams, a dome with a diameter of 10mm requires a force of 220~280 grams, and a dome with a diameter of 12mm requires a force of 280~350 grams. A too low travel distance can result in a poor tactile feel, while a too high travel distance can make pressing difficult and prone to the dome not conducting when pressed lightly.

Terminals are generally chosen as 2.54mm female terminals (1.27mm is rarely used), and occasionally, male terminals are adopted by users. The pin spacing is divided into two types: 2.54mm and 5.08mm. Terminals with a 2.54mm pin spacing are convenient for production and offer high efficiency, but it is necessary to check whether the terminals are securely fastened. If necessary, destructive testing should be conducted to check whether the terminals are prone to peeling off. Terminals with a 5.08mm pin spacing are relatively more securely pressed together and will not loosen even when used in vibrating environments. For automotive electronics applications.

There are special requirements for the reliability of connections. Sometimes, connectors from Japan's FCI and DuPont are chosen. The connections at both ends of the terminals are required to be locked with latches. In special cases, the connection points are sealed securely using a potting process.

For membrane switches, there are many double-sided adhesive options available, with the most commonly used being Durofix

For products requiring waterproofing, it is recommended to use double-sided adhesive tapes without substrate or with PET substrate (such as 3M's 467, 468, and 9495Le) from brands like Nihon Gohsei, Crown, and 3M. If necessary, the 3M series GTM920 or GTM940 can also be considered.

When selecting materials for membrane switches, the best choice is the one that suits the user's requirements.