small SMD sealed relays are having high rate of coil open failures?

Question

Can anyone shed some light on why about 50% of my small SDM relays fail with the coil going open circuit in the first few days of normal operation? There is nothing unusual about the application, the drive circuit, and the load on the contacts is very light.

Reflow temperatures too high maybe?

I read warnings about not to use ultrasonic cleaning on relays specifically becuase of coil damage or contacts sticking, but no specific reasons why are given. What kind of coil damage? They don't come off the production line open circuit, as the failure happens often during first power up, minutes later, but can also be after a few days of operation.

Please limit responses to ACTUAL PRACTICE EXPERIENCE with this topic, as I already have lots of specualtive input from many sources already.

Spehro Pefhany · Accepted Answer

I've seen chemically induced failures, particularly of low power relaycoils. Best regards, Spehro Pefhany-- "it's the network..."                          "The Journey is the reward"             Info for manufacturers:  software/hardware/analog  Info for designers:

Hellequin · Answer

Do you have a snubber diode across the coil?

Phil Allison · Answer

"Terry"** The time delay is the BIG clue  !!Not until DC voltage is applied to the coil does it fail and it fails OPEN !!This is strong evidence of electrolysis causing wasting of the fine copper wire -  likely just where it attaches to the terminals and is bare of protective enamel.Electrolysis implies that water is entering the relay package during PCB cleaning -  possibly a tiny entry is created during soldering due to local shrinkage of the moulding material.A possible solution is to heat the PCB for a considerable time after washing to drive off all trapped moisture.YOU have to try this out, no absentee analysis is gonna help.....  Phil

John Larkin · Answer

Got a link to the relay data sheet?Are you using ultrasonic cleaning?John

Jamie · Answer

I assume you have tested one of those out side the box on the bench?  assuming that past? Is this relay mounted next to a high B field device?  Jamie.

Jon Elson · Answer

Well, I think it is time for a post-mortem! Most of these relays can be cut open with a new X-acto blade, just gently scribing the surface until you poke through and then peeling the cover away from the body. Most likely, once you get inside, the nature of the damage will be obvious. Either heat has melted the internal soldering, or ultrasonic cleaning has migrated dirty water inside the housing through leaks in the external termination penetrations.

Jon

Hellequin · Answer

If they are failing open, it is very likely the coil itself that is failing. I say it is back EMF slamming back into the coil, killing it. Place snubber diode across the coil, and the problem goes away.

Phil Allison · Answer

"Hellequin** LOLCould only cause insulation failure, not open copper ......  Phil

Hellequin · Answer

In a car ignition coil, perhaps.  In a shit coil using shit magwire with less than even single strengthshit insulation, it can fail with the coil open OR shorted (the coil).  One pulse could short it (via your insulation fail claim), and then thenext firing pulse could fuse it open.  You need to think things through, LOL boy.  You lost this one.  Right now, you are in a LULL.

John Larkin · Answer

Doesn't it get boring, being AlwaysWrong?John

Hellequin · Answer

I note that you give no intelligent refutation.

small SMD sealed relays are having high rate of coil open failures?

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