We been seeing some "random" LED failures and some someone suggested static electricity could be the cause. I've never heard static electricity is a problem with LEDs. Anyone have any comments?
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\$\begingroup\$ It's probably just your bad design. The number of poor designs for LED drivers seen on this site is beyond belief. Such a simple device yet time and time again, we see poor design. \$\endgroup\$– Andy akaOct 6, 2018 at 9:16
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2 Answers
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LED's are easily damaged by a differential reverse voltage much less than the Human Body Model of 1kV @ 100pF. Almost all discrete LEDs are rated for Vr = 5V max (meaning reverse biased) where leakage currents in uA rise rapidly and deform or burn out a much smaller semiconductor gap than the forward biased diode. This reverse polarity is the one that kills LED's. It can start with ones being dimmer and have higher junction capacitance then greater failure levels are too dim and short out.
You must observe all ESD/EOS precautions unless protected by design.
Anecdotal
It was about 10 yrs ago my client then, was saying "these LEDs are no good".
They had ramped up to ~100k / year annually of custom 5mm LEDs and they were seeing about 1~2% field failures. However, with 20 parts per unit that translated into 10% field rejects overseas in Swiss tunnels and furthermore, their customer had a 3 mos withholding clause to prove reliability and pay for their wireless powered LED sidewalk installation order.
It was a crisis. Yet I was confident the parts were perfect. So I flew "down under" to see what could be done immediately.
The parts I ordered were prepaid, custom-built-to-order with my detailed datasheet e.g. 20 Cd, "single bin" for voltage, intensity and dominant wavelength. They were better than anything else in the market and were "qualified" by the client. They were all 100% tested and sorted to my specs with yields that affect the cost.
My inspection of their evolving process changes found at least a 15 opportunities for improvement from incoming to outgoing. "shelf grounding, hand-solder thermal stress, plastic injection molding etc. The only thing I could not protect against was the injected hot plastic into the final assembly from hopper to conveyer, so I did the best thing possible. Order immediate replacements with Zener protection, and included in spec for all future buys. I was able to get them in 2 weeks with a rush order.
Problems solved. I suggest you do the same.
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1\$\begingroup\$ Just a side question ... can I just put a zener diode in front of a led strip and have it esd protected? Or should the led strip itself be protected (like every led separately)? \$\endgroup\$ Oct 5, 2018 at 20:29
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1\$\begingroup\$ Most LED static damage happens before being soldered into a board, so at my employer I traced the failure to miss-handling by stockroom. They had to use anti-static bins, have anti-static heel straps, and production had to use anti-static wrist straps along with anti-static trays. \$\endgroup\$– user105652Oct 5, 2018 at 22:11
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2\$\begingroup\$ The risk can occur anywhere the cathode or it’s conducting pads are high impedance and exposed to stray positive discharges or Anode to negative charges. In my case post solder with plastic injection moulding is huge tribolectric process of moving plastic particles, melted then injected into the mould. So Zener inside was the only best fix. \$\endgroup\$ Oct 5, 2018 at 23:44
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\$\begingroup\$ @TonyStewartSunnyskyguyEE75 -- Would you please consider adding a diagram of how the zener protects the LED, along with specifications for the Zener? I was just thinking that any diode paralleled in reverse polarity to the LED would work (as long as its response is fast enough). Why do we need a higher voltage breakdown? Thx. \$\endgroup\$ Nov 12, 2020 at 14:29
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1\$\begingroup\$ @MicroservicesOnDDD true a reverse diode can work except this is how LEDs are made with protection. Why, I am not sure, but if the anode wire breaks in a series current string, at least the rest of the LEDs will work. \$\endgroup\$ Nov 15, 2020 at 17:45
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LEDs can be damaged by electrostatic discharge (ESD). If proper handling procedures and workspace mitigation aren't in place, it might be your issue.
You can read about it in the following document from OSRAM
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\$\begingroup\$ Anecdotally, I've seen LED strips flash very briefly during handling, even with no power supply connected, due to ESD. I suspect that while a forward discharge may cause a brief visible flash, a reverse discharge is more likely to damage the device(s), since LEDs tend to have poor tolerance for reverse voltage. \$\endgroup\$– ajbOct 5, 2018 at 19:30
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\$\begingroup\$ @ajb Good point on the reverse discharge being more destructive, sounds plausible to me. Also, thanks for catching and correcting the bad link I posted. \$\endgroup\$– John DOct 5, 2018 at 19:32
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1\$\begingroup\$ LED’s are “diodes” in the forward bias mode and thus are inherently protected for that polarity against much higher levels than the hand or moving cart models. \$\endgroup\$ Oct 5, 2018 at 23:49