PCB with ATmega168 fully soldered and all bridges removed

RGB LED Ring Assembly

I finally finished soldering an RGB LED ring after eight hours of hard labor with the giant Hakko soldering iron tip. It was my first SMD soldering job! The RGB LED ring was from http://blog.spitzenpfeil.org/wordpress/2012/01/11/rgb-led-ring-v2-sequels-dont-have-to-be-bad/

I ordered it on his online shop for $26 and a few days later, I had a nice box from Germany with all the parts in it: a PCB, eight LEDs, and a bunch of resistors and capacitors.

PCB and 5050 SMD LEDs

PCB and 5050 SMD LEDs

I had to do a lot of heating with the solder wick to remove bridges on all the ICs. If there is one thing I got out of this, it is buy liquid flux for SMD soldering. After I applied liquid flux, the bridge on the TQFP32 package evaporated instantly.

PCB with ATmega168 fully soldered and all bridges removed

PCB with ATmega168 fully soldered and all bridges removed. You can still see where I brushed on the flux.

I was almost sure I burned LEDs because the blue ones would never turn on. I soldered  one blue LED first and it never turned on regardeless of the sketch I put on the microcontroller. Then I soldered more and it was the same story: all green and red only. Encouraged by the consistency, I continued to solder on all the LEDs. I got a little careless at the end and misaligned some of the LEDs, so the contacts are not that robust, but they work.

Later, as I did continuity tests over and over on the blue current sink, I could not seem to find a problem. I eventually realized though that I was touching a pad in my continuity tests and not the actual leg of the IC. Pin 15 was not connected to the pad even though it looked like it was. I eliminated the cold solder joint on the blue current driver (pin 15).

I am really surprised that the LEDs did not burn out. I did my best to keep the iron under 250 C, but I still touched the LEDs a lot when removing bridges. Same for the ICs. Both the microcontroller and the current sinks withstood a lot of my 650 F poking with the iron. It was a little frustrating soldering and removing bridges by hand, but the satisfaction of the lights shining bright white at the end was worth it. Next time I should really do it with solder paste and hot air.

Finished RGB Ring

Finished RGB Ring and programmer. In the real world you can see the discrete RGB LEDs, but even with a 2/255 duty cycle, the camera still blends them to white.

Discrete RGB LED painting

Now you can see the 2/255 duty cycle discrete LEDs. It’s an RGB rainbow!

And as if just seeing the lights shine was not enough, now I get to program them!

Summary:

  • Use flux for SMD work.
  • Perform continuity tests with legs of ICs and not pads.
  • I’m amazed that all the components withstood the heat from the iron.
  • Soldering was a success but next time I’m using paste.
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One thought on “RGB LED Ring Assembly

  1. robert

    Glad you liked it. The chips are very sturdy as far as temperature is concerned, the RGB LEDs aren’t. Staying at or below 250°C saved them 😉

    Reply

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