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How to Properly Select LEDs for Your Keypad

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Manufacturing That Eliminates Risk & Improves Reliability
How to Properly Select LEDs for
Your Keypad
November 19th 2021

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Manufacturing That Eliminates Risk & Improves Reliability
2
Agenda
 Membrane & Keypad Overview
 LED Options for Keypads
...

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Manufacturing That Eliminates Risk & Improves Reliability
3
Membrane & Keypad Overview

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How to Properly Select LEDs for Your Keypad

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Many products we use every day involve some type of device equipped with buttons and small LED lights. Maybe it’s the power button on your computer monitor or the backlit switch on your car’s dashboard. Discrete LEDs are used everywhere to safely illuminate the products we rely on.

LEDs range in complexity and size and can include small discrete surface-mounted LEDs that are no larger than a flake of pepper to panel-mounted LEDs equipped with a lens and soldering wires.

In order to properly size an LED, engineers’ study both the mechanical and electrical considerations for mounting and energizing the LED. The direction, color, and intensity of the light emitted from the LED are equally important since when improperly sized, an LED may shine too bright or not bright enough for the application.

Early selection of LEDs is recommended since this can help finalize the overall system electrical design requirements, eliminating surprises later in the project. Spend the time to properly study and size the LEDs for your next keypad project.

In this webinar we review keypad backlighting option, LED choices, prototypes, production considerations, and more.

For more information on our custom human-machine interface solutions, visit https://www.epectec.com/user-interfaces.

Many products we use every day involve some type of device equipped with buttons and small LED lights. Maybe it’s the power button on your computer monitor or the backlit switch on your car’s dashboard. Discrete LEDs are used everywhere to safely illuminate the products we rely on.

LEDs range in complexity and size and can include small discrete surface-mounted LEDs that are no larger than a flake of pepper to panel-mounted LEDs equipped with a lens and soldering wires.

In order to properly size an LED, engineers’ study both the mechanical and electrical considerations for mounting and energizing the LED. The direction, color, and intensity of the light emitted from the LED are equally important since when improperly sized, an LED may shine too bright or not bright enough for the application.

Early selection of LEDs is recommended since this can help finalize the overall system electrical design requirements, eliminating surprises later in the project. Spend the time to properly study and size the LEDs for your next keypad project.

In this webinar we review keypad backlighting option, LED choices, prototypes, production considerations, and more.

For more information on our custom human-machine interface solutions, visit https://www.epectec.com/user-interfaces.

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How to Properly Select LEDs for Your Keypad

  1. 1. Manufacturing That Eliminates Risk & Improves Reliability How to Properly Select LEDs for Your Keypad November 19th 2021
  2. 2. Manufacturing That Eliminates Risk & Improves Reliability 2 Agenda  Membrane & Keypad Overview  LED Options for Keypads  Design Options to Reduce Risk  Case Study  How To Get Started With Your Custom Build
  3. 3. Manufacturing That Eliminates Risk & Improves Reliability 3 Membrane & Keypad Overview
  4. 4. Manufacturing That Eliminates Risk & Improves Reliability 4 Membrane Switch & Keypad Options  Membrane Switches – A momentary switch device in which at least one contact is on, or made of, a flexible substrate- ASTM – LEDs, dome switches, and adhesive  Silicone Rubber Keypads – Compression molded silicone elastomer – 40-60 Shore A hardness – Pair with dome switch or conductive carbon pill  High Reliability & Low Cost  LEDs for Backlighting – LED windows – Uniform backlighting Silicone overlay with circuit LED Locations
  5. 5. Manufacturing That Eliminates Risk & Improves Reliability 5 Membrane Switch & Keypad Options
  6. 6. Manufacturing That Eliminates Risk & Improves Reliability 6 Keypad Circuit Options  PET- Polyester Circuit – Silkscreened conductive ink – Flexible laminated layers, limited layer count – Typically, 0.007” – 0.025”  Rigid PCB – Etched copper traces with Laminated FR4 – Ideal for surface mounted components – Typically, 0.063” – 0.250”  FPC – Etched copper with polyimide base circuit – Fine pitch ZIF tails – Typically, 0.007” – 0.025” Circuit type will drive LED selection Flex FPC PET Circuit Rigid PCB
  7. 7. Manufacturing That Eliminates Risk & Improves Reliability 7 LED Options for Keypads
  8. 8. Manufacturing That Eliminates Risk & Improves Reliability 8 LED Design Options  Wikipedia LED Definition – A light-emitting diode (LED) is a semiconductor light source that emits light when current flows  Applications – Front panels & HMIs – Automobile headlights – Interior lighting – PCBAs  Electrical Operation – Most operate of 5VDC or less – Act as a diode - current flows one way – Must include a current limiting resistor LED polarity matters for custom installations Printed Circuit Board with LEDs LED Strip
  9. 9. Manufacturing That Eliminates Risk & Improves Reliability 9 LED Types to Consider  Leaded LEDs – Through-hole LEDs – Wide range of lenses and viewing angles – Must be used with rigid PCB base circuits  SMD LEDs – Surface Mounted Devices – No wires, solder direct to circuit – Wide variety of sizes and colors  Side-firing LEDs – Right angle surface mounted LED – Usually paired with Light Guide Film – Limited availability of sizes and colors Not all LEDs have drop in replacements Side-firing LED Rigid PCB with through-hole LEDs SMD LED Leaded LED Single surface mounted LED LGF backlit text
  10. 10. Manufacturing That Eliminates Risk & Improves Reliability 10 Light Guide Film  Use with Side Firing LEDs – Place LED outside the viewing window – LED is not visible to the user  Uniform Backlighting – Uniform brightness – Reduced hotspots  Selective Backlighting – Individually lit keys – Lightblock in strategic locations – Needs sufficient space Not all selective backlighting designs are manufacturable
  11. 11. Manufacturing That Eliminates Risk & Improves Reliability 11 LED Size and Color  Lots, and lots, and lots to chose from – Manufacturer – Package size – Electrical performance – Brightness and chromaticity  Design Flexibility – Specify high level requirements for non- critical applications – Add verbiage to drawing notes permitting alternate LEDs Not all LEDs have drop in replacements
  12. 12. Manufacturing That Eliminates Risk & Improves Reliability 12 LED Size and Color  Keep It Simple – What are you trying to accomplish? – Must Have’s vs. Nice To Have’s  Plan On Making Changes – Build samples quickly, then assess – Obsolescence risk Not all LEDs have drop in replacements
  13. 13. Manufacturing That Eliminates Risk & Improves Reliability 13 Other Keypad Backlighting Options  Fiber Optic Backlighting – Uses light source with glass or plastic fibers  Light Pipes – Uses injection molded plastics as an elongated lenses LEDs are the primary light source for most backlighting arrangements
  14. 14. Manufacturing That Eliminates Risk & Improves Reliability 14 Design Options to Reduce Risk
  15. 15. Manufacturing That Eliminates Risk & Improves Reliability 15 High Risk LED Choices  Small Package Sizes – Some membrane switch circuits are hand populated – Choose 0603 size and larger  Yellow vs Amber – Brightness must be tested – Can either color be used? Dual source all LEDs where possible Yellow LED vs Amber LED
  16. 16. Manufacturing That Eliminates Risk & Improves Reliability 16 High Risk LED Choices  ESD Threshold – Is there shielding? – Will these be used in ESD prone areas?  Bicolor & Tricolor LEDs – Bicolor & Tricolor LEDs are more scarce – Obsolescence risk – May require a respin to change Dual source all LEDs where possible Bicolored Red/Blue LED
  17. 17. Manufacturing That Eliminates Risk & Improves Reliability 17 Adjusting Keypad Brightness  Perceived Brightness – Must be tested at the end of assembly – Is it too late to make changes?  What Impacts LED Brightness? – Materials above the LED will change its intensity – Translucent silicone and graphic overlays Reduce risk by dual sourcing LED Driver ICs
  18. 18. Manufacturing That Eliminates Risk & Improves Reliability 18 Adjusting Keypad Brightness  Swap LEDs vs Modify Power – Potential for circuit respin  PWM Local Brightness Control – Pulse Width Modulation – Added to parent PCBA Reduce risk by dual sourcing LED Driver ICs 250 mcd luminance LED
  19. 19. Manufacturing That Eliminates Risk & Improves Reliability 19 Night Vision Imaging Systems (NVIS)  Mil-STD-3009 – Military specification that details the requirements for aircraft cockpit indicators and lighting systems. – NVIS Green A and Green B  NVIS Compliant LEDs – Use Off-The-Shelf LEDs – Pair white LEDs with caps – Consider NVIS films  Chromaticity – Requires specialty instrumentation – Transparent materials may filter NVG compatible LEDs are scarce and known for long leadtimes
  20. 20. Manufacturing That Eliminates Risk & Improves Reliability 20 LED Placement  Mounting locations and techniques are critical  Spacing Guidelines – Avoid placing LEDs within 4mm perimeter keep-out zone – 15mm keypad spacing for selective backlighting  Rear Mounted LEDs – Typically reserved for rigid PCBs – Optimize overall height – Necessary for backlit center hole domes  Location Drives Intensity – LEDs can be placed adjacent or behind switches Clever mounting arrangements can yield truly custom results Selective Backlighting Spacing
  21. 21. Manufacturing That Eliminates Risk & Improves Reliability 21 Case Study
  22. 22. Manufacturing That Eliminates Risk & Improves Reliability 22 Bezel Assembly- Case Study  Custom backlit bezel assembly  Narrow PCBA 0.75” wide  Local brightness and voltage control  6-week development timeline
  23. 23. Manufacturing That Eliminates Risk & Improves Reliability 23 Bezel Assembly- Case Study  PCBA Footprint and Layer Count Drives the Design – Limited circuit routing options with 4-layer PCB  Electrical Requirements – Aircraft power 28VDC – DC-DC converter necessary – 25 x LEDs in series  Local Brightness Control – PWM LED driver added to circuit LEDs mounted to PCBA
  24. 24. Manufacturing That Eliminates Risk & Improves Reliability 24 How to Get Started
  25. 25. Manufacturing That Eliminates Risk & Improves Reliability 25 Initial LED Backlighting Considerations  Backlit button vs discrete LEDs  Number of buttons to illuminate  Colors of the LEDs  Backlight uniformity requirements  LED package size  Overall height concerns  LED mounting arrangements  Are alternate LEDs allowed?  Dimmable brightness  Are LEDs in series with switches?  Will light guides be necessary?  Approval stakeholders Schematic and a dimensioned drawing are required to launch development
  26. 26. Manufacturing That Eliminates Risk & Improves Reliability 26 Development Timeline Most projects yield functional samples in 5 weeks Initial Concept Drawings & Schematic Samples Evaluation Production Typical Development Lead-Times Standard Keypad 4 - 6 weeks Complex Keypad 6 - 8 weeks SMART HMI 8 - 20 weeks
  27. 27. Manufacturing That Eliminates Risk & Improves Reliability 27 Summary
  28. 28. Manufacturing That Eliminates Risk & Improves Reliability 28 Summary  LEDs are widely available, reliable and inexpensive  Countless sizes, colors, and package sizes  Susceptible to long lead-times, high minimum order quantities  Circuit redesigns can be expensive  Clear delineation of Must Have vs. Nice To Have requirements
  29. 29. Manufacturing That Eliminates Risk & Improves Reliability 29 Our Products Battery Packs Flex & Rigid-Flex PCBs Cable Assemblies Printed Circuit Boards RF Products User Interfaces Flexible Heaters EC Fans & Motors
  30. 30. Manufacturing That Eliminates Risk & Improves Reliability 30 Q&A  Questions? – Enter any questions you may have in the Control Panel – If we don’t have time to get to it, we will reply via email
  31. 31. Manufacturing That Eliminates Risk & Improves Reliability 31 Thank You Check out our website at www.epectec.com. For more information email sales@epectec.com. Stay Connected with Epec Engineered Technologies Follow us on our social media sites for continuous technical updates and information:

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