Something else to throw into the equation is the sharp temp rise when going from ambient to hot wash tank. Gas inside the cavity expanding could compromise the seal if the adhesion is marginal. As it enters the cooler rinse stage the gas contracts, inhaling the water through the compromised seal.

Ed Popielarski
Engineering Manager


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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce Koo
Sent: Thursday, March 19, 2015 3:27 PM
To: [log in to unmask]
Subject: Re: [TN] Sealed relays fail after water wash - story #2

immersion clean: you mean it specified as in-line water clean with top spray type?  the contact time for the venting hole possibly is much less time and not much chemical attack on its sealing epoxy (most likely, acrylic type... although it called epoxy - Few good UV curable true epoxy =chemically speaking, electronic grade out there... you need short wavelength UV cure = lamp is more expansive than your standard 365 nm curing lamp).  if you use dish washing machine, possibly with some chemical additive as agent, it might weaken the "epoxy".  the contact time, and chemical may not be compatible to your parts.  Just wondering, you should be able to pull out of the qualification of those parts and review the process evaluation and see if any reliability test being done = so much water, with large population of parts exhibit water ingress, you got see some performance indicator when you qual... unless someone skip the whole parts qual process.  (proper cured UV epoxy top surface is heavily oxidized - if it is true epoxy, it should be hydrophobic, short time in contact to a spray water of DI followed by air knife and drying process should not be a problem in the cleaning process, if the design intent is for in-line immersion clean).
my 2 cents.
            joyce
On Mar 19, 2015, at 4:46 PM, Carl VanWormer 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
>      
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