OVERLAY MATERIALS
LASER CUTTING
 
A variety of overlay materials are used in membrane switch applications.The most commonly used base material is polyester. Polyester is a material that has superior life cycle and chemical resistance roperties in comparison to other flexible materials. In life cycle testing, polyester shows no signs of wear at 1,000,000 cycles. At one time, polycarbonate offered pricing advantages. Polycarbonate is still used for certain applications, however, the life cycle data shows that it begins to crack as early as 40,000 cycles. For this reason,Nelson recommends the use of polyesters in most applications. Both polyester and polycarbonate are available with a variety of textures and hardcoats. In their uncoated, glossy form both materials are very susceptible to scratching. For this reason gloss materials should always be hardcoated.
 

The various layers of a membrane switch can be cut out by using a numerically controlled laser. This technology offers two advantages. Tighter mechanical tolerances can be held, and no tooling is required. While laser cutting is a relatively expensive process, in many low volume applications it is cost effective. In most cases, if we are producing 100 parts or less, it is more cost effective to laser cut than to purchase steel rule dies.

 
EMBOSSING
 
DESIGNING
 
In many applications it is desirable to emboss or hydroform the keys of a switch. The embossing is used to describe keys that are raised and flat on the top.
 

ARTWORK: You can supply an electronic file in .ai (Adobe Illustrator), .cdr (Corel Draw),.dwg(AutoCad) or other vectored graphics program.

COLOR MATCHING: There are manysystems that a customer can use to communicate color requirements to us. Pantone Matching System (PMS) is the most popular color standard. RAL is available.

 

 
WINDOWS
 
Back Panels
 

The overlay materials used in membrane switches begin the process clear. Colors are screen printed on the back of the overlay material. Areas that do not have color printed on them become windows. As mentioned in the section on hardcoats, window areas can have a variety of hardcoats or textures added to them. It is recommended that small discrete LED enunciator windows have the same texture as the background.
Larger windows for LEDs, LCDs, or VFDs may need a
window with less light diffusing characteristics.
Window coatings in general are a trade-off between anti-glare characteristics and optical clarity. The closer the display is to the overlay the less effect the coating will have on display readability.

 

The most commonly used material for such back panels is aluminum. Aluminum back panels can be supplied with a variety of hardware installed. Other options include polycarbonate, galvanized steel sheet or acrylic backer panels. These can have chamfers or other features but normally do not use hardware.

 
CONNECTOR
 
MOUNTING ADHESIVES
 

TUK is tooled to crimp Nicomatic, AMP, HX, DM, and Molex connectors onto flex circuits.

 

In most cases flexible membrane switches are shipped to our customers with a pressure sensitive adhesive on the back side. The most commonly used adhesive is 3M's 467MP. This is an excellent adhesive for bonding to smooth metal and high surface energy plastic surfaces. For rougher surfaces we recommend 3M's 468MP.

 
Backlighting Options
 
ESD/EMI SHIELDING
 

Electroluminescent panels typically offer a brighter, more
even flow of light. Also, EL offers greater design flexibility
because the glowing element is discretely applied. EL, however, has a half-life of approximately 10,000 hours so marrying the technology with the proper application is critical. EL also requires an inverter to function properly. Fiber optic panels, on the other hand, are powered by LEDs that can
easily be replaced.

 

Several options are available for shielding membrane switches. The most common methods are printed carbon, printed silver, and aluminum foil. From a functional standpoint, the main difference among these materials is their conductivity. Both carbon and silver can be printed on the top side of the top circuit to act as a shield. Carbon shields are less expensive than silver shields. Silver is usually printed in a grid pattern to reduce cost. A foil shield has advantages both in conductivity and cost, particularly if the overall design does not need a printed top circuit. Another effective option for ESD shielding is a ground trace around the perimeter of the circuit layer. This adds very little cost and is often times effective for ESD shielding needs. The shield can be connected to the ground through the connector, or by means of a tab with a slot that can be mechanically connected to ground. The interconnect should be noted on the print.