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]>
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]>
> http://cipherengineering.com<http://cipherengineering.com/>
>
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