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

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.

Reply to
Terry
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I've seen chemically induced failures, particularly of low power relay coils.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

Do you have a snubber diode across the coil?

Reply to
Hellequin

"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

Reply to
Phil Allison

Got a link to the relay data sheet?

Are you using ultrasonic cleaning?

John

Reply to
John Larkin

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.

Reply to
Jamie

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

Reply to
Jon Elson

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.

Reply to
Hellequin

"Hellequin

** LOL

Could only cause insulation failure, not open copper .

..... Phil

Reply to
Phil Allison

In a car ignition coil, perhaps.

In a shit coil using shit magwire with less than even single strength shit insulation, it can fail with the coil open OR shorted (the coil).

One pulse could short it (via your insulation fail claim), and then the next 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.

Reply to
Hellequin

Doesn't it get boring, being AlwaysWrong?

John

Reply to
John Larkin

I note that you give no intelligent refutation.

Reply to
Hellequin

Of flyback voltage melting a relay coil? Why bother refuting anything that Wrong?

John

Reply to
John Larkin

I just got done dealing with a problem regarding early failure of crystal oscillators. Reflow temperatures are probably to blame. Parts that are hand soldered had no early failure problems, parts which went through 260°C reflow temps had very high failure (failure = dead, off frequency, intermittent) rate. If your process is using unleaded, be sure your relay can handle the higher reflow temp. Leaded process uses

230°, unleaded 260°.
Reply to
qrk

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