These reverse mount NeoPixel LEDs are an easy way to add a lot of small (but bright!) colorful LEDs to your project when you want the top of the PCB to be flat, or to keep manufacturing simplified by having only one side of components. They are just 3.1mm x 2.7mm x 1.7mm and can be soldered reverse mount-style using the top pads and a cutout in the PCB. Thanks to the long pads, they're not too bad to hand solder!
The driver chip is inside the LED and has ~12mA constant current drive, so the color will be very consistent even if the voltage varies, and no external choke resistors are required making your design minimal. Power each one with 5VDC, and you're ready to rock.
There are three LEDs inside, red, green, and blue. The RGB LEDs are controlled by a tiny chip that takes a 24-bit color level via the clock and data in and then does all the PWM control for you. So you just 'set' the color data once. Like all NeoPixels, you can chain them together, the output of one leading into the input of another for near-infinitely long strips.
We've been using these in our NeoKey boards, so that the LED shines through a cutout of the PCB - but there's many use cases for reverse mount LEDs. Note that a cutout is required and the body of the LED will nestle inside of the cutout. Comes in a package with 10 individual LEDs.
Our detailed NeoPixel Uberguide has everything you need to use NeoPixels in any shape and size. Including ready-to-go library & example code for the Arduino UNO/Duemilanove/Diecimila, Flora/Micro/Leonardo, Trinket/Gemma, Arduino Due & Arduino Mega/ADK (all versions)
Single LED Dimensions (excluding pads): 3.1mm x 2.7mm x 1.7mm