Why WS2812/SK6812 failures after SMT Soldering?


There so many WS2812 LED used, most of them are soldered on a separated board for displaying.  Many makers use the WS2812 LED in their own projects, but , no one will tell that there a big mistake in your prototyping& small batch production.

Yes, you will get astonishing failure rate,after the reflow soldering as this man:

So recently, myself and another fellow from work ordered some of these WS2812's (neopixels) from Adafruit. We ordered them loose, so we could build our own boards here in our shop and run them through our reflow oven. We use pneumatically dispensed solder paste and a conveyer style reflow oven. The reflow curve is calibrated frequently and does not exceed 250 degrees Celsius. Upon testing the WS2812's, approximately 30 percent of the LED's had failures (missing R or G or B LED diode).

Makerfabs encountered an alike problem, that we found almost all the WS2812 LED do not on as intended, really nightmare:

This is one of our customer’s design, 16 pcs of WS2812 LED are serial connected to the controller module ESP12. If any LED got destroyed, all the LED follow will not be on as the 1 wire communication protocol.

The result is: there 120 pcs PCBA produced, and almost NONE of them works.

The LED quality problem?  seems NO. We checked some sample new LED, all works.  After checking the datasheet, the datasheet shows us:  soldering temperature: 240 °C, and indeed our soldering temperature 240°C ~!



Without any other solution, we asked the WS2812 producer, they feedback us: the soldering temperature suggested  is < 230 °C … , and the Medium temperature solder paste suggested.  

Got ~ The datasheet bad. Normally, to ensure the SMT soldering quality, especially for components that is tall, the High-temperature solder paste would be more safe to keep the soldering quality. But for the WS2812 LED, or alike LED SK6812, high-temperature solder paste, which need soldering temperature >240 °C, will lead to serious damage to the LEDs

Makerfabs’s suggestion on WS2812/SK6812 LED design& soldering:

1. Using the Medium temperature solder paste,  to ensure the soldering temperature <230 °C;

2. Do not use height components, such as SMD electrolytic capacitor, together with WS2812/SK6812 LEDs in the same boards.  The SMD electrolytic capacitor soldering temperature need to be high, which will leads to LED damages, unless you will solder them manually. . 

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