Hey guys,
So I’ve just spent the last week investigating this topic as I’ve recently learned that a couple thousand dollars worth of our inventory is defective because of bad WS2812B LEDs.
Story Time: Discovering the Issue
(Feel free to skip to How to Identify Smart LEDs)
For a while we’ve been sourcing Smart LED flexible strips from various sources: eBay, Amazon, Aliexpress, Alibaba with varying results. All searches were done using the term WS2812B which is a 4 pin integrated smart RGB LED. It only needs V+, GND rails and Data in/out using a daisy chain structure and sending data down the line sequentially.
We now rely on a very stable supplier http://www.shiji-led.com/ who I’ve now purchased about 800m worth of LEDs without issue.
However, we also needed to make some custom double sided LED PCB bars so I went and sourced WS2812B LEDs directly from WorldSemi. These we spent about $800 worth on discrete LEDs, ~$100 on pcbs, and then another $1200 to have them assembled by a local fab. After everything was made we did some QC tests and found that the LEDs were failing in a weird way. Basically 1/10 LEDs had one or more internal diodes failing. Typically the blue diode, but occasionally red or green and in rare cases multiple or all three diodes failed.
Here are a couple videos of the behavior we were seeing:
Test 1: https://www.youtube.com/watch?v=_Gt5VzD8Di4
Test 2: https://www.youtube.com/watch?v=cQURSWLKLFU
The failure seems to be temperature sensitive, and in extreme cases pressure sensitive too. Being temperature sensitive means that from a cold start running full brightness white, in about 30 seconds you’ll start to see issues, but after it’s warmed up (~1-5min) those issues will disappear. If poked (pressure) it’s very likely you can permanently damage it. In the second video that one LED I poked never worked again and in fact the data line has been severed so subsequent LEDs will not work either.
This raised a lot of questions as to why our flexible strip LED supply was so reliable, but the LEDs bought directly from WorldSemi were not.
After investigating bad WS2812B chips and variations of the chip, we discovered there is a clone called the SK6812. And I’ve since confirmed that our stable flexible strip supplier has been selling these since early 2016 without telling their clients. Since they’re directly clones they felt there was no need to change the name of their product since it uses the same WS2812B protocol. However the main reason they switched was because they’re way more reliable than the WS2812B. There is also some slight improvements in the electrical characteristics, namely double the PWM frequency on the diodes (making them better for persistence of vision projects).
###How to Identify (4 pin) Smart LEDs
I’ve compiled a imgur album, but I will summarize the main points:
- WS2812(S) is the 6 pin grandfather of the 4 pin smart LED, which follows a stupid naming convention. WS2812 is the name of the Smart LED with RBG diodes and an integrated IC. The name of that IC is WS2811. The reason this IC has 6 pins is because the WS2811 has separate power rails which is rather pointless. 6 Pins makes this easy to identify on it’s own.
- WS2812B is the next evolution with 4 pins. From the images you’ll see I’ve found at least 3 different variations of it. To identify this IC you’ll need a microscope to look at the bonding wires. I’m mainly focusing on the IC itself because of the bonding wire pad placement. You’ll see that it has 3 closely place pads along the short edge of the IC and on the opposite side 3 spaced out pads. Other indicators for variations of the LED package are the placement of the blue diode and shape of the pads inside the package.
- SK6812 is the clone Smart LED and is most easily identified by the IC being rotated 90°. Under a microscope you’ll also see that the 3 closely placed bonding wire pads are now along the long edge of the IC.
One other way to differentiate the ICs is the size:
- WS2811 is 0.8x1.05mm
- WS2812B is 0.7x0.9mm
- SK6812 is 0.6x0.8mm
###Summary
If you’re buying this type of smart LED, make sure you get the good stuff. Verify with your supplier which IC is being used in the product because it seems like most manufacturers aren’t bothering to tell people they’ve switch to clone.
###Credits
I’ve done most of this investigation through discussion on a few blogs. For more information on bad WS2812B LEDs and other failure modes check out:
For more information on the SK6812 go here:
And for a summary on the differences between WS2811 and WS2812B, go here:
###After Credits
WorldSemi has yet to respond to my inquiry of the failed ICs but I expect with a small order (on their scale) I expect they’re probably not going to bother compensating me in any way.
Shiji has been very helpful and offered to supply me with the SK6812 discrete LEDs in tape/reel. I’m not sure if we’ll do that though because the cost of rebuilding the inventory is far higher than falling back to an old design using old inventory we already have.
Other things to note:
There are also a new generation of smart LEDs if you’re interested in looking them up. Some have RGBW diodes with varying white color temperatures. The next generation of ICs WS2813 and SK6822 which have dual data lines, this is a redundancy so that if one dataline breaks, you can still have signal going through. Interestingly WS2813 also incorporates the decoupling capacitor inside the LED package too allowing you to cram more LEDs closer together.
Another few other names to throw out: APA102 and SK9812. I haven’t looked into these in detail but I believe they’re also 6 pin packages with different protocols or data line redundancy.
