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By Steve Baker | Jun 16, 2017
GMN's membrane switch assembly for Welch Allyn.

GM Nameplate’s (GMN) Singapore Division supported Welch Allyn, a medical company, to develop and manufacture a membrane switch panel with backlit indicators for their resting electrocardiogram (ECG) device. As a device used to test a patient’s heart activity, it is critical that the backlighting appropriately indicates how much battery power the device possesses.

GMN offers an array of backlighting options including discrete LEDs, fiber optic weave, light guide film, and electroluminescence. The part had strict spacing requirements between its tactile buttons, which influenced GMN to choose discrete LEDs. Discrete LEDs are cost-effective and ideal for lighting up small indicators.

Instead of using three different colored LEDs, GMN installed one bi-color LED to occupy as little space as possible and reduce costs. The two colors within the LED were green to indicate the battery was charged, and red to indicate the battery was dead. To create the amber color that indicates when the device needs charging, the LED was positioned off-centered from the indicator window to effectively blend the red and green colors together.

Another factor GMN had to consider was the material for the overlay. GMN utilized polyester (PET) film, a common overlay material for devices in the medical industry due to its resistance to abrasion and harsh chemicals. As an extremely durable, long-lasting material, PET film is ideal for applications with tactile switches because it’s abnormal for the material to crack. 

Co Nguyen, GMN
By Co Nguyen | May 15, 2015
Fiber optic weave backlighting

Another common backlighting solution is fiber optic weave.  Similar to light guide film, it takes LED light and distributes it across a larger area.  In fact, it usually only requires a single LED to backlight an entire assembly. It should be noted that the LED used is a bullet LED, which requires a PCB as a base because we cannot place bullet LEDs onto our printed membranes.  Using only a single LED, this leads to one if its greatest drawbacks; it isn’t very bright and may not be a good solution if the device will primarily be used in ambient light. 

There are other important considerations as well.  First, the fiber optic weave and fiber optic bundle are quite large and need to be accommodated in the design. In addition, the thick construction diminishes the tactile feedback of buttons.  Combined with the weak light, there are few projects to which this backlighting technology is suited.  While we see this option to continue in existing models, we anticipate that this solution will soon give way to thinner backlighting solutions as devices become smaller and lighter.  

Read our other backlighting blogs: 

Co Nguyen, GMN
By Co Nguyen | May 5, 2015
Backlit touchscreen

This month we are kicking off a five-part blog series on backlighting.  The series will begin with an overview of how to approach a backlighting project and then each subsequent blog will review one of the four most popular options in backlighting: discrete LEDs, light guide film, fiber optic weave and electroluminescence.  

GMN frequently works with customers to integrate backlighting solutions into products including membrane switches, displays, and even branding pieces such as nameplates. We’ve developed applications for industries as diverse as appliance, medical, automotive, and more.

To establish the best backlighting solution without hotspots (uneven brightness, usually due to the location of LEDs) or light bleed (light coming through where it shouldn’t), the first step is to create a list of necessary requirements and assess the proposed design.  Start by asking these questions:

  • In what type of light will the device be used? Will the backlighting need to be visible in bright sunlight, the ambient light of offices, dark hospital rooms, etc.?
  • What needs to be backlit?  Is it a full screen, keypad, specific buttons, status or discrete indicators, a combination?
  • What colors will be used and where? 
  • What are the power requirements? 
  • What are the space constraints?
  • If there is a keypad or buttons, what type of tactile feedback is required? 

Based on the responses to these questions, you should be able to evaluate which backlighting solution, or combination of backlighting solutions could work with your device. 

Learn more about backlighting from one of our other blogs: