Failure mode of diodes - Page 1
Forum section: electronics / projects

author: trevortjes
author_rank: Contributor
timestamp: December 04, 2020, 06:30:01 pm
content: Hello everyone,For a project about reverse polarity protection, I'm trying to find out if diodes more often fail open or closed/shorted after being stressed with a DC current thats higher than the max ratings. So before I start killing 100 diodes to see what the average failure mode is, I wonder if anyone here has a more scientific reasoning, proof or personal experience which of the 2 failure modes occur more often. Diodes of interest: 1N400x series, 1N581x schottky series, 1N4148.Thanks in advance

author: madires
author_rank: Super Contributor
timestamp: December 04, 2020, 06:41:06 pm
content: In most cases they fail shorted.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 04, 2020, 08:52:44 pm
content: Yep. Specifically:Above rated forward current, the junction simply heats up until it melts. Junction welds together, short.It may actually be recoverable before actual physical damage occurs; as junction temp rises, silicon gets quite conductive (regardless of doping), which, in the instant, it might look like it's already failed (low resistance forward and backward). But it may return to normal if allowed to cool. This temperature is probably in the range of 200-300°C. Beyond that, it just ends up shorted both ways.Likewise, above breakdown voltage, they avalanche, and this can either cause excessive power dissipation (leading to the exact same failure sequence), or hot-spot failure (the overall device need not be running hot, just some microscopic part of it).Rectifiers tend not to be as robust against avalanche as proper zener or TVS diodes are, so this can happen at fairly low currents (~mA).In any case, once a diode fails shorted, if that short causes enough fault current to flow, it can be blown open again -- that is, raw fusing current. Examples are mains or battery powered applications. (Hopefully, there's a fuse at the input, which will blow first!)So, a diode can be operational, then shorted (recoverable), then shorted (unrecoverable), then open (fused), in the blink of an eye (this can all happen in 10s of milliseconds) -- but an eternity to the semiconductor!Tim

author: bdunham7
author_rank: Super Contributor
timestamp: December 04, 2020, 09:18:25 pm
content: To summarize,allcomponents eventually fail open if you give them enough juice. Unless you reach that point, diodes almost always will fail short--like most semiconductors.

author: james_s
author_rank: Super Contributor
timestamp: December 05, 2020, 05:54:51 am
content: Every failed diode I've ever seen was failed shorted. Technically it's possible for one to fail open, say due to thermal cycling but I don't think I've ever seen it happen. Usually they grenade before becoming open, most diodes have the chip directly between the metal leads rather than having a thin bonding wire like transistors and ICs.

author: wraper
author_rank: Unknown
timestamp: December 05, 2020, 06:07:28 am
content: Very low power diodes may sometimes fail open, but more powerful diodes almost always will fail short.

author: trobbins
author_rank: Frequent Contributor
timestamp: December 05, 2020, 08:35:01 am
content: So in summary, you need to define your over-current event, the diode mounting scheme and environment, and diode type, before making the effort to gather statistics.

author: DimitriP
author_rank: Super Contributor
timestamp: December 05, 2020, 09:59:38 pm
content: Many good words here :https://www.eevblog.com/forum/repair/need-help-identifying-this-diode/