TECHNET Archives

March 2015

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Thu, 19 Mar 2015 12:54:22 -0600
Content-Type:
text/plain
Parts/Attachments:
text/plain (113 lines)
Hey Carl, if you want to send the pictures I'll post them. I'd be
interested to see them because we wave and inline clean a lot of relays
here, and I'm the one who determines what gets waved and cleaned and what
gets hand soldered with no clean. Haven't had any of our customers complain
of relay failures from water getting inside them, but that doesn't mean
it's never happened.

Steve

On Thu, Mar 19, 2015 at 12:40 PM, Carl VanWormer <[log in to unmask]
> wrote:

> 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/>
>
> This message may contain confidential and/or proprietary information, and
> is intended for the person/entity to whom it was originally addressed. Any
> use by others is strictly prohibited.  If I sent this to you by mistake,
> please be nice and delete it, and then tell me of my mistake so I can send
> it to the right person.
>
>
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>

-- 


This email and any attachments are only for use by the intended 
recipient(s) and may contain legally privileged, confidential, proprietary 
or otherwise private information. Any unauthorized use, reproduction, 
dissemination, distribution or other disclosure of the contents of this 
e-mail or its attachments is strictly prohibited. If you have received this 
email in error, please notify the sender immediately and delete the 
original. 


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2