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June 2003

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From:
Mike Fenner <[log in to unmask]>
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Date:
Thu, 5 Jun 2003 15:23:49 +0100
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Could be the softening point of the new plastics/polymers is different to
the old. [Softening point is described on data sheets as glass transition
temperature or Tg]. Alternatively  the properties above the Tg are markedly
different.
Mechanical properties of polymers above the Tg are usually not documented
at all,  This is an easy overlook when looking at functionality of
materials. Above Tg things like strength and expansion coefficients are
different.

I'm tempted also to suggest  opaque covers...... :)


Regards

Mike Fenner

Applications Engineer, European Operations
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Pb-free: www.Pb-Free.com



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Rick
Thompson
Sent: Thursday, June 05, 2003 2:30 PM
To: [log in to unmask]
Subject: Re: [TN] Wave Solder Advice?


Peter,

Thanks for the feedback. We did find out from the vendor after a couple of
months of going back and forth on the issues that they had made what they
consider 'minor' changes to both the epoxy used to seal the relays and the
case/base materials as well. Unfortunately, after getting them to get make
us sample runs of the old configuration (another couple of months), we've
found similar problems with those parts as well. Venting is one thing we
haven't checked yet. We'll be checking it this week.

Regards,

Rick Thompson

Sr. SMT Process Engineer
SMTEK International, Inc.
+1 (805) 532-2800
[log in to unmask]




-----Original Message-----
From: peter tremewen [mailto:[log in to unmask]]
Sent: Wednesday, June 04, 2003 9:34 PM
To: [log in to unmask]
Subject: Re: [TN] Wave Solder Advice?


Rick,

        Double check the setup of the wave. After we moved factories, we had
unexpected trouble with the wave profiles due to the new "identical" exhaust
system that was installed. It caused the preheat to be about 10 to 20
degrees cooler, just enough to put off some of our profiles. Your new
instalation may be just diferant enough to cuase some unexpected or
unfamilliar problems, and the relays are sensitive to this change for some
reason. Like wise check that the vendor isn't spinning some "white lies",
thinking that some minor change wont effect the Relay in the wave. In my
limited experiance with this, some prety minor changes to manufacturing
process of the components can cause some prety major headaches. Something
obviously changed......

                Peter T

Rick Thompson wrote:

> We have a board with a safety relay on it that is exhibiting moisture
inside the relay case after we process it (aqueous process). After numerous
discussions with the relay vendor and several rounds of testing various
epoxies for sealing the case to the base of the relay, the vendor is
indicating they believe our wave solder process is heating the part too
much, causing expansion of the air inside and subsequent breaking of the
seal. I believe our wave solder profile is fairly standard and was developed
to ensure that all solder fillets on the top-side meet IPC-610 Class 3
standards.  I'm hoping some of you wave solder gurus can tell me if we're
way off base with our profiles.  We currently aim to acheive 90-100 C on the
topside of the board prior the board entering the wave.  This gives us the
wetting we're looking for as well as reduces the level of thermal shock on
bottom side components.  Is this temperature in line with what's being done
in wave soldering? Is there something I should be looking at to reduce this
topside temperature without sacrificing solder wetting?
>
> As an added note, we ran around 70,000 of these units without much
evidence of this problem occurring. Our process has not changed other than
to move to a new building. The vendor did change epoxy but tests with both
the old and the new epoxy yield similar failure rates.

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