When designing a custom rubber keypad for your device, it’s important to make sure that the keys don’t stick. Sticky rubber keypads not only detract from the efficiency of a device, but they can cause aggravation and frustration on the part of the user.
Sticky keys can cause a multitude of problems, from activating a feature on a device too many times to preventing other features from being used while the first one is engaged. For example, a simple key stick on QWERTY computer keyboard can produce some crazy words while typing. One letter sticking can prevent other letters from being used. A spell check can typically fix this problem, but it’s time-consuming and should be unnecessary. More serious key-stick problems occur in designs where the button activates a more complex action, such as medical devices or heavy machinery.
When your device’s users press the buttons on your custom rubber keypad, how the keys feel as they respond is described as the tactile feel. When the key pops back up, it needs to have a minimum return force to avoid sticking and to reassure the user that the button is doing its job. A suggested industry minimum is 30 grams of force.
While the design of the key is important in preventing a malfunction, the quality of silicone keypad manufacturing is another factor. Poor quality materials and processing produce inferior rubber keypad molding. The keys can degrade before their average life expectancy is anywhere near complete, causing them to stick. If the silicone rubber keypad isn’t installed on the device correctly, this can also cause problems for users. Some silicone keypad manufacturing companies offer keypad assembly with membrane circuits and printed circuit boards for a complete product.
Prevention Tips By Design
There are several design considerations that engineers can use to prevent keys from sticking. Here are 6 design tips to minimize the chances of keys sticking on the user and lowering the effectiveness of your product.
1. The bezel is the cover or faceplate that secures the silicone rubber keypad to a switch or printed circuit board. Use a minimum of .0125 inches between the bezel and each key for good clearance to avoid sticky keys.
2. An anti-wobble device included in the design underneath the key provides stability and prevents sticking. An unbalanced load on the key can force one side against the surface underneath, causing it to stick.
3. Use the liquid silicone injection molding process to ensure superior quality workmanship and durability.
4. Separate the bases of two key diaphragms by at least .0125 inches.
5. Consider using a rattail to hold the keypad in place.
6. Consult an application guide from the silicone keypad manufacturing company you plan to have do the work to make sure that all tolerances are the right minimum dimensions.