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March 2015

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From:
Robert Kondner <[log in to unmask]>
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Date:
Thu, 19 Mar 2015 15:38:28 -0400
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Hi,

 And I assume all the unused relays in stock had perfectly sealed vent
holes?

Bob K

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nutting, Phil
Sent: Thursday, March 19, 2015 3:22 PM
To: [log in to unmask]
Subject: Re: [TN] Sealed relays fail after water wash

Carl,

I'm assuming nothing else in the process changed.  What happens if you go
back to the original manufacturer?

Phil Nutting

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
Sent: Thursday, March 19, 2015 2:40 PM
To: [log in to unmask]
Subject: [TN] Sealed relays fail after water wash

Here is the first of two stories about recent relay failures caused by our
assembly process:

We have been selling an assembly that has 16 through-hole relays on 4-layer
FR-4 boards.  Our CM runs these boards through a wave soldering process,
using water-clean flux, and then washes the boards in a dishwasher using the
local water (quite pure).  We changed to a different (pin compatible,
customer approved) relay source for the last batch of 100 boards, and then
suffered some production test fallouts.  Upon analysis of the failed boards,
the relays seemed to be the cause.  With a little more work, I discovered
water inside the sealed relay packages.

We are using a subminiature power relay that states "Epoxy sealed for
automatic wave soldering" as one of the bulleted features on the datasheet.
I found another document on the vendor's website titled "Relay Technical
Notes", which covered cleaning, mentioning "Sealed relays can be safely
cleaned by immersion."  We sent several failed relays to the vendor for
analysis.  From their response, we learned more about the relay
manufacturing process, which includes a vent hole that allows for
outgassing.  The last step in the relay assembly process fills the vent hole
depression with a clear UV cure epoxy, followed by UV exposure to cure the
epoxy, sealing the relay.  Their failure analysis report indicated that the
relay seals had been compromised.

We are assuming that the epoxy seals (on the bottom of the relays) failed
during our product assembly process (in either the wave soldering, or the
washing processes), compromising the integrity of the seal.  Our guess is
that the epoxy didn't bond well to the relay vent hole (pick any reason you
like).  If the broken seal allows the internal heated air to escape while
the wash water is under the relay, when the air inside the relay cools,
water may be sucked into the relay.  This sequence of events would explain
the water discovered inside of relays that had failed our final assembly
testing.

To avoid field failures on the current batch of units, we decided to remove
all potentially damaged relays, replacing them with new parts (without a
final wash).  Analysis of the removed relays showed about half of the parts
had visibly defective seals, with several showing the vent plugs almost all
the way out of the vent.  (pictures available if there is interest and Steve
will host them)

Since the vendor says we are doing something wrong to break the vent seals,
we have decided to avoid the problem for any future units.  We now add the
relays after the initial board wash, using hand soldering with no-clean
solder.

Our conclusion: don't wash relays, regardless of the datasheet information.

Later,
Carl

p.s.  another relay story will follow . . .









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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