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Choose Proper Adhesive for Your Membrane Switch Assembly

Choose proper adhesive for your membrane switch is one of the more critical decisions you can make during the design process. Achieving a solid bond between your membrane switch and the surface to which it is adhered is vitally important to reducing failures and ensuring the long term reliability of your product.

 

Your choice of adhesive essentially comes down to identifying the appropriate family of adhesives and the proper adhesive thickness. There are two families of adhesive used for these applications: “acrylic” adhesives and “modified acrylic” adhesives.

 

Acrylic Adhesives

 

Acrylic adhesives are a popular choice, and generally considered the industry standard, for membrane switch attachment applications. They provide outstanding adhesion to metal and high surface energy plastics. These adhesives provide some initial re-positionability for placement accuracy when bonding to plastics. They also perform well after exposure to humidity and hot/cold cycles. Typical metals to which acrylic adhesives bond well to are aluminum and steel. Compatible high surface energy plastics are usually ABS, acrylic, and polycarbonate, to name a few. Acrylic adhesives offer outstanding temperature and chemical resistance, as well as excellent shear strength to resist slippage and edge lifting.

 

A popular acrylic adhesive choice is 3M™ High Performance Acrylic Adhesive 200MP adhesive, which offers the following performance characteristics:

 

Humidity Resistance: High humidity has a minimal effect on adhesive performance. Bond strength shows no significant reduction after exposure for 7 days at 90⁰F (32⁰C) and 90% relative humidity.

 

UV Resistance: When properly applied, membrane switches are not adversely affected by outdoor exposure.

 

Water Resistance: Immersion in water has no appreciable effect on the bond strength. After 100 hours at room temperature, the high bond strength is maintained.

 

Temperature Cycling Resistance: High bond strength is maintained after cycling four times through: 4 hours at 158⁰F (70⁰C) 4 hours at -20⁰F (-29⁰C) 4 hours at 73⁰F (22⁰C)

 

Chemical Resistance: When properly applied, nameplate and decorative trim parts will hold securely after exposure to numerous chemicals including oil, mild acids and alkalis.

 

Bond Build-up: The bond strength of 3M™ 200MP increases as a function of time and temperature

 

Temperature/Heat Resistance: 3M™ 200MP is usable for short periods (minutes, hours) at temperatures up to 400⁰F (204⁰C) and for intermittent longer periods (days, weeks) up to 300⁰F (149⁰C).

 

Lower Temperature Service Limit: The glass transition temperature for 3M™ 200MP is -31°F (-35°C). Many applications survive below this temperature (factors affecting successful applications include: materials being bonded, dwell at RT before cold exposure, and stress below the TG [i.e.expansion/contraction stresses, impact]). Optimum conditions are: bonding high surface energy materials, longer time at RT before cold exposure, and little or no stress below the TG. The lowest service temperature is -40°F (-40°C).

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