🏮 How to use reverse mounted LED in your PCB?

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This essay describes the application of reverse mount LEDs and shows actual examples of this technique ?.

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Revers mounted LED

Typically surface-mounted (SMD) light-emmiting diode (LED) mounted on the board with luminous flux up, relative to the footprint (base), but there are also reverse-mounted LEDs exist:

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How to search thus LED

For example on LCSC you can find such type of LED by filter (yes, Sytle) Mounting Sytle: Counterpost:

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Real example

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LTST-C230KRKT

  • Reverse mount Chip LED
  • Package: 1206
  • Pdiss: 75 mW
  • If = 30mA
  • If(peak) = 80mA
  • Vr = 5V

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Recommended layout

You can always grab footprint from EasyEDA:

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Based on the example from the datasheet:

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I design footprint in KiCad:

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It looks pretty impressive even as 3D model, so let's implement this in real design:

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Can you use ordinary LED for reverse mounting?

Here is the typical 1206 LED with transparent diffuser:

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You can mount ordinary LED manually (by hands).

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But you can't use ordinary LED for automatic mounting (with pick-and-place machine), because they have wider lends diffuser and they placed not reverse in the tape or reel.

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But for prototypes it's no problem, cause with hand soldering the LEDs could be used ?:

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How it looks like and lights?

The holes is oval, maybe rectangular will be better:

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But light in any case cool:

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Green LED on the right and orange LED on the left show the charge status.

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This is the same charger IC, that used in this Li-ion module:

? TP4056 Li-Ion USB Type-C charger

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RGB reverse mounted LEDs

Previously we considered only one-color LED, but RGB LED also available, and this give a chance to create custom beautiful colors:

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MPN: 156125M173000

MPN: XZMDKCBDDG45S-9

Addressable reverse mounted WS2812

In real project instead of connecting a large number of ordinary RGB LEDs, special LED chips (e.g. WS2812) are used, because this part give a change to make easiest connection only with one data wire and two power wires (positive and negative).

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MPN: SK6812

Another interesting technique

Another interesting approach to make cool lighting is to use side LED and textolite (board core) as diffuser, to make this just remove solder mask by placing figure on the both F.Mask and B.Mask layers.

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Conclusions

As you can see using reverse mounting technology for LED not difficult and could be very intresting.

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