| The best way to design the molded keypads for | | | | expected to last for five million activations. |
| your equipment is to understand each component | | | | High-use molded keypads from TV remotes to |
| and how it contributes to keypad function. In this | | | | ATM interfaces benefit from the durability of |
| entry we look at the materials Si Tech uses in | | | | carbon pills. Carbon also provides low resistance to |
| our keypad contacts. | | | | the circuit, on the order of 200 ohms or less. |
| Understanding Contacts | | | | Although carbon pills are a reliable technology |
| Underneath the surface of molded keypads is the | | | | there are limits to how small the contacts can be. |
| circuit board that controls the device's operation. | | | | A standard pill is about 0.5 millimeters thick, but |
| Beneath each key is an open circuit. Pressing a | | | | that can be far too much if you are trying to |
| key causes the contact underneath the key to | | | | make a wafer-thin device. If your application |
| come into contact with the circuit board, closing | | | | needs an unusual contact shape, carbon is difficult |
| the circuit. When choosing a contact material the | | | | to form into anything but the simplest forms. |
| two most important factors are conduction | | | | SiCoat V Conductive Coating |
| resistance and activation life. | | | | For custom silicone keypads that need an |
| Every component in an electrical circuit adds | | | | alternative to carbon pills, our SiCoat V conductive |
| some resistance and for most components that | | | | coating provides a flexible and low-cost option. |
| resistance should be kept to a minimum. Contacts | | | | Conductive coatings can be used to make |
| add several hundred ohms of resistance and the | | | | contacts of any size or shape, greatly expanding |
| greatest amount of resistance the circuit can | | | | design options for custom silicone keypads. The |
| handle is based on the power in and type of | | | | coating layer is very thin, on the order of 10-20 |
| circuit. | | | | microns, so is perfect for the slim electronics |
| Although contacts in molded keypads have a long | | | | modern consumers demand. |
| life, over repeated use the material wears out. | | | | Although SiCoat V contacts have worked for |
| The best case is to have contacts that last longer | | | | over a million cycles in independent laboratory |
| than the device so customers never have to deal | | | | tests, they will wear out a little faster than carbon |
| with keypad failure. Engineers measure switch life | | | | pill contacts. The thinness of the layer gives it a |
| in the number of activations expected. | | | | higher resistance, approaching or passing 1000 |
| Durable Carbon Pills | | | | ohms for the slimmest molded keypads. |
| Most of the molded keypads we produce use | | | | As you can see both options have strengths and |
| carbon pills as contacts. Other materials can be | | | | weaknesses and each is suited for different |
| used as well but carbon is the ideal choice for | | | | equipment. The best choice for your keypad will |
| most applications. | | | | depend on the characteristics of your device. |
| Carbon is a durable material and contacts can be | | | | |