RMQSI Answers ForumCategory: Electrical Component ReliabilityResistor short circuit failure modes/FMD-97
Guest Forum User asked 17 years ago

In RAC’s Failure Mode/Mechanism Distributions 1997 (FMD-97), the failure mode “Shorted” is given for Resistors (I’m specifically looking at “Resistor, Fixed, Wirewound” here). My EEs are telling me this is completely impossible, but every FMEA I’ve ever seen has considered “Resistor Shorted” as a possible failure mode.

Unfortunately, many many web searches on the possible combinations of keywords here have yielded almost no results; I’ve seen as many people saying shorted resistors are a failure to consider as saying that it is impossible (and I can count them each on one hand).

So I’m hoping somebody can shed some more light on this situation. Are the failures listed in FMD-97 only manufacturing defects (ie, not a result of an operational situation)? Is it possible to say for sure that, if you drive too much current through a resistor, it *won’t* fail shorted? [I would assume knowledge of the physical construction of resistors would tell us that.]

Thanks!

5 Answers
RMQSI Technical Staff Member Staff answered 17 years ago

FMD-97 does have 3% short condition. It also has 27% open failure condition. From a failure mode analysis point of view, many wire wound resistors fail due to insulation breakdown. This condition usually results in a short condition that ends in an open circuit or if contamination exists the resistor could

tmweber answered 12 years ago

In the same vein, but more specific, is it possible to show that a wire wound resistor will not fail short in an overstressed condition. I’m looking to show that a fault won’t cascade. Specifically, if another failure causes 28V to be placed over a 165Ohm, 2W resistor putting it at 4.76W. Is is possible to show by analysis, that this resistor will not fail short? I know instinctively that a short is unlikely in this case, but I’m not very well versed on the physics of failure for resistors.

smorris answered 12 years ago

As you note, intuitively it probably will not fail short, at least for long; however, overheating may cause a momentary short. This would arise , from an initial short condition that ends in an open circuit. I know of no way to prove by analysis that this resistor will not fail short, at least for some short time duration.

robin48gx answered 11 years ago

I am very interested in finding a good source for the ratio of OPEN to SHORT failures
for resistors.

I am using probablistic trees to calculate the overall FIT value for a simple electrical circuit.

I have MIL1991 (public domain MIL reliability standard).
I can obtain FIT values for resistors on this, but it only gives me a FIT
for the resistor as a whole. Not one FIT for OPEN and one for SHORT.

Can anyone help me with this ?

Currently I am feeding in 90% OPEN 10% SHORT into my models.

norbyzuka answered 10 years ago

MIL-HDBK-338B/FMD91:

Resistor fixed film
59% open
36% drift
5% short