Am i just unlucky or worldsemi ws2813 LEDs are crappy? - Page 1
Forum section: electronics / projects

author: hun_yeti
author_rank: Contributor
timestamp: February 17, 2019, 03:27:54 pm
content: I created a design with 20 ws2813 LEDs , and while programming the board, with minimal interaction of the board, i already had 3 LEDs fail, in different ways.on one just one color failed, on the other the brightness regulation failed, one has completely disabled. I just followed the schematic on the datasheet.Don't see anything obvious i could mess up. at first all LEDs worked correctly, all colors, all brightness settings. The started to fail after more then 24 hours of the assembly.The leds are supposedly genuine worldsemi products, ordered from LCSC. They where properly packed in anti static bags.Just as i was writing this, the board running in demo mode, i observed another LED to fail, so it makes 4 so far, and that's 2 LEDs in a row, so most of the leads don't work anymore.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 17, 2019, 03:31:27 pm
content: Do a Google search. Everyone's having reliability problems with these. Moisture is the most typical culprit for SMD LEDs, but the yield with these LEDs is poor even in careful, professional environment with moisture ruled out.

author: ebastler
author_rank: Super Contributor
timestamp: February 17, 2019, 03:36:34 pm
content: Quote from: hun_yeti on February 17, 2019, 03:27:54 pmSo you did include the filtering (series resistors and 100nF capacitors) on the power supply, individually for each LED? Could you post your overall schematic?

author: hun_yeti
author_rank: Contributor
timestamp: February 17, 2019, 03:41:55 pm
content: Attached the schematic. I just copied what was in the datasheet.But even if i didn't add the resistor and the capacitor it should not destroy LEDs right?The datasheet even states that it's okay to no add the resistor and capacitor.

author: ebastler
author_rank: Super Contributor
timestamp: February 17, 2019, 03:57:58 pm
content: Hmm... Have you had a look at your power supply rail with a scope? (Any spikes or oscillations, maybe?)Or are the LEDs mounted in a very confined space without airflow and heatsink? While the LEDs do not consume huge amounts of power, they can overheat if there is no sufficient convective or conductive cooling.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 17, 2019, 04:01:56 pm
content: The moisture indicator cards that were packaged with the LEDs - what did they say? Then, how did you solder the LEDs; profile, temp, time?

author: wraper
author_rank: Unknown
timestamp: February 17, 2019, 04:03:16 pm
content: Moisture popcorning during reflow and most are not even genuine ws2813.QuoteWas it a proper moisture barrier bag with a silica gel bag inside?

author: hun_yeti
author_rank: Contributor
timestamp: February 17, 2019, 06:18:44 pm
content: Quote from: ebastler on February 17, 2019, 03:57:58 pmThe supply rail looks fine, (or at least no oscillation in the sub Mhz range).They have an ample amount of space, there is at least 10mm between the LEDs. Also, during programming, the where mostly under 20% of the maximum output. Also, the pads where designed to be relatively large, to help cool the LED.Quote from: wraper on February 17, 2019, 04:03:16 pmQuote from: Siwastaja on February 17, 2019, 04:01:56 pmThere where not in a moisture bag.These where hand soldered, with my regular iron. I use the same iron at the same setting for thousands of components so i don't think the problem was there.

author: wraper
author_rank: Unknown
timestamp: February 17, 2019, 06:31:05 pm
content: Quote from: hun_yeti on February 17, 2019, 06:18:44 pmHand soldering SMT components stresses them more compared to reflow. LEDs are among most sensitive.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 17, 2019, 06:32:22 pm
content: Quote from: hun_yeti on February 17, 2019, 06:18:44 pmFound the issue. The supplier screw up the packaging.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 17, 2019, 06:34:38 pm
content: Quote from: hun_yeti on February 17, 2019, 06:18:44 pmDifferent components have different sensitivity, so the count doesn't matter. Many SMD LEDs are super sensitive to both moisture and proper soldering. Youcando it manually, but need to be super careful and super quick. Preheating both the board and the components help.

author: hun_yeti
author_rank: Contributor
timestamp: February 17, 2019, 06:55:17 pm
content: Fair enough, i didn't know that moisture control was so much important. I guess i would need to "dehydrate" them, on around 70c for many hours, to make sure everything is fine, right?I already ordered a rework station yesterday, that may help, but this has genuinely never happened to me, having multiple components fail, after they are being in use for a few hours.Come to think of it, it doesn't even look like the actual LED semiconductor have died, but the controller chip, since it's not transmitting the incoming data anymore.