The failed Omron relays appeared to be sealed well, with no obvious water entry points. With only a small sample, I decided to skip right to the conclusion: Water can get into sealed relays . . . Never wash them.
Addendum to water in relay stories:
Having experienced 2 different types of water-in-sealed-relay problems in the last 2 months, I was primed with paranoia. Last week, while working with a third product that uses 12 relays (a different type and vendor) on each board, I found a failure that was traced to one of the relays. Replacing the relay cured the problem. With the Hitchhiker phrase of “Oh, no, not again” going through my mind, I carefully opened up the sealed relay case, expecting to find water. I was relieved to see no drops of water evident inside. I verified that the problem (no electrical contact when activated) was still present by using a beeper while manually activating the armature. I could see no reason for the non-contact, so I carefully pried the contacts apart. Upon very careful examination (under the microscope), I found a hair-like fiber attached to the armature contact. That fiber was preventing the metal-to-metal contact, causing the relay to fail. I’m sending the picture for you to add to the “broken relay” list.
Thanks,
Carl
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
[log in to unmask]<mailto:[log in to unmask]> http://cipherengineering.com<http://cipherengineering.com/>
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Friday, March 20, 2015 11:50 AM
To: TechNet E-Mail Forum; Carl VanWormer
Subject: Re: [TN] Sealed relays fail after water wash - story #2
Hi Carl!
Dang, I got busy this morning! Sorry I didn't get your pictures posted earlier, but I have them up now:
http://stevezeva.homestead.com/Omron_corrosion_1.jpg
http://stevezeva.homestead.com/Omron_corrosion_2.jpg
http://stevezeva.homestead.com/Omron_corrosion_3.jpg
http://stevezeva.homestead.com/Omron_corrosion_4.jpg
http://stevezeva.homestead.com/Omron_Water_in_Case.jpg
http://stevezeva.homestead.com/Omron_corrosion_case_3.jpg
http://stevezeva.homestead.com/Omron_water_on_contacts_1.jpg
Your story interests me because we build a lot of relay modules here, but they are from a different manufacturer. We do selective solder and not wave, and then the PCB assembly gets potted into a plastic case with some Epic Resin polyurethane potting compound:
http://stevezeva.homestead.com/Relay_Module.jpg
I looked at the bottom of the relays we use (CIT) and they seem well sealed to me:
http://stevezeva.homestead.com/CIT_Relay.jpg
This is something that I will surely keep my eye on! Thanks for sharing!
Steve
On Thu, Mar 19, 2015 at 2:46 PM, Carl VanWormer <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Here is the second of two stories about relay failures caused by our assembly process:
We have another product with mostly surface mount parts, along with one through-hole relay and some 48-pin through-hole connectors. After the SMT parts are reflowed, the boards go through a wave soldering operation to attach the four connectors and the relay. Our first batch of 50 boards had 6 fallouts that were traced to "bad" relays. Since I had recently been burned by water in "sealed" relays (another style, from another manufacturer), my paranoia kicked into high gear.
The datasheet shows these relays as "Fully sealed", with a note to "Contact your OMRON representative for the ratings on fully sealed models." Searching the relay manufacturer's website turned up a few more documents. One document, titled Electromechanical Relays Technical Information shows that for Fully Sealed relays:
Boiling cleaning and immersion cleaning are possible. Ultrasonic cleaning will have an adverse effect on the performance of relays not specifically manufactured for ultrasonic cleaning. The washing temperature is 40°C max.
My guess is that our wash process (and probably yours, too) is above 40°C. This is probably how I screwed this one up . . .
Opening up the 6 failed relays showed significant water inside. Since these boards were produced last month, they had been sitting on the shelf for several weeks, with the water and other chemicals causing problems, including mechanical binding. My real fear was that other boards that tested "good" might have water inside and would soon go bad. The failed boards showed several different problems, but a common feature attracted my attention. During the initial board testing, as I ramped up the DC power supply (that activated the 24V rated relay coil), all of the good boards made a little "tick" sound as the relay armature took up slack in the system, but didn't have enough force to overcome the return-spring force. This sound occurred at about 8V, except for the "bad" boards. I touched a 9V battery to the coil drive pins while holding a bad relay against my ear. I could only hear a slight "tick" sound. Holding a good (new, never been washed) relay up to my ear, then touching the battery to the pins gave a louder, stronger "tick" that had a little ringing character that was not present in the bad relays. The difference was subtle, but similar to the difference in sound from dropping an old (Copper) penny and a new (Zinc) penny. I cut the top from a good relay, listened to the sound as I touched the coil terminals to a 9V battery (reference, good). I ran water over the exposed (good) relay, and shook off the excess. Activating the dampened "good" relay gave a sound that was more muffled, lacking the "ring" of the little vibrating parts as the water film damped the vibrations. With this test, I was able to check all of the "good" boards, finding that they all had the "ring" of goodness (hopefully with no significant internal water).
I'll send some pictures to Steve for his wonderful picture hosting service.
Once again, our planned solution to the problem is to add the relays after the final board cleaning, using a no-clean flux solder.
Once again, our conclusion is: don't wash relays, regardless of the datasheet information.
Later,
Carl
p.s. there will be no follow-up water-in-relay stories from me because I'll never allow a relay to run through a wash system. This goes for potentiometers, too, since I've had "sealed" pots fail after washing.
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
[log in to unmask]<mailto:[log in to unmask]><mailto:[log in to unmask]<mailto:[log in to unmask]>> http://cipherengineering.com<http://cipherengineering.com/>
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