There are several methods of creating the backlit legends.
Laser Etched Legends
With a laser etched backlit keypad you need to overspray the translucent keypad using the colour that you would like your keypad to be in such as black, then the legends are laser etched through to the base material. The benefit of this process is that by spraying the keypad black and laser etching the legends the light from the LED is concentrated through the legends offering clear crisp backlighting. If you did not completely overspray the keypad then light would transmit through all areas of the button rather than just the legends. The laser etching method is slower however and so more expensive.
For a low cost solution to backlighting you can print the entire surface of the button using a negative print, this means the normally printed legend is clear and the areas around the legend are printed. Although this is cheaper it does mean that the sides of the buttons are still translucent and can allow light to escape. You are also unable to print to the very edge of the button so you end up with a ‘halo’ of clear around the perimeter of the button that also transmits light. For many situations this can be an attractive design feature.
Standard Positive Printing
The other method and most simple method of backlighting your keypad is to print a standard positive legend onto a translucent keypad, this illuminates the entire keypad and will offer enough transmitted light for you to see the printed legends. Although this is a simple solution and low cost it is generally not preferred as you are not making the legends stand out as much from the keypad as the other two options do.
Each of the methods achieves backlit legends in different ways, all are effective but it depends upon the design brief as to which method is best for your application.
It may be best to ask your supplier if they have samples of each option that they can send you for trials before you finalise your keypad design, this would allow you to evaluate each option without any costs.
Rubbertech have been manufacturing silicone rubber keypads for over 20 years. Our keypads can be found in test instruments, chip and pin devices, hospital call alarms, fire alarm panels and many more electronic control systems.