This design guide is intended to offer basic information on keypad design and offer guidelines for you to follow as your project develops.
Silicone rubber keypads are the most widely used form of switching technology today. They offer reliability, long life and design flexibility. If you are currently deciding between various user interface materials, please review some of the benefits that silicone offers.
Silicone Rubber Benefits
Silicone rubber is an excellent material for several reasons;
Resistance to both high and low temperatures (-55° C to 250° C)
Minimal noise generation due to soft and elastic contact structure
Minimal abrasion and high resistance to SO2 and oxidation even in heavy humidity
In addition, silicone rubber offers several features that make its design and usage flexible;
Design both tactile and linear feedback
Translucent color is excellent for backlighting
Multi-color designs easily accommodated
Water and contamination resistant
It will be helpful to familiarize yourself with the following diagram and the Dictionary of Terms Used prior to reviewing the rest of this design guide.
Dictionary of Terms Used
Basic Key Considerations
Key design will vary with the functional and aesthetic requirements of the application. It is possible to mold a key in almost any shape and to fit almost any configuration. It is important to remember that the key shape will affect the feel of the key. While a circular shaped standard key will have a consistent feel across the entire surface a half moon shaped key will respond different depending upon where the key is pressed.
Once you have decided upon a key shape and layout; the next item to consider is the method for marking the rubber and creating legends. There are three common methods for marking keypads; printing, laser etching, and plastic key caps.
Printing is the most common method of marking rubber. The rubber is fixtured to flatten the key top then screen printed. There is no limit to the number of colors available. The arc of the key top determines how far printing must be set back from the edge of the key.
There are currently several options available for improving legend life with printed rubber.
Plastic Key Caps - custom molded clear plastic is adhered over the legend or molded into the rubber
Oil or Epoxy Coating - coating is deposited on the top surface of the key over printing, available in matte, semi-gloss, or gloss finish
Drip Coating - drip coating can be hard or flexible. It adds a glossy layer over the key top. It can not be used on some keys with sharp angles. Hard coatings are subject to cracking if the key has large surface areas.
Parylene Coating - offers the highest level of protection for a non-plastic coating. Parylene bonds to the rubber at the molecular level.
Laser etching is especially well suited for applications where the keypad is backlit. Etching typically involves three production steps.
Translucent rubber (any color) is sprayed with a translucent base coat ink which will be the legend color that is visible to the user.
Rubber is sprayed with an opaque top coat ink which will be the overall color of the keypad.
The top coat of ink is laser etched away using high speed etchers to reveal the base coat.
Alternatively, you can decide to use a single translucent or opaque rubber ink and laser etch the legends revealing the color of the rubber that is used.
Plastic Key Caps
The longest lasting legend type is custom molded plastic. Plastic legends will not wear out. Many cell phone keypads are designed with plastic keys over rubber.
Ratio & Tactile Feel
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