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September 2006

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Subject:
From:
"Ingemar Hernefjord (KC/EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ingemar Hernefjord (KC/EMW)
Date:
Thu, 14 Sep 2006 10:10:14 +0200
Content-Type:
text/plain
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text/plain (143 lines)
Agree,

Black magic...

We had a hysterical implementation of all kind of MIL environmental
testing years back. Cost a fortune and one could not see clear
connection between these tests and report from the field. If you temp
change a product and you get e.g. One failed gate and two interrupts in
a relay, what does that tell about all the parts that you sell and which
are spread and used on one hundred different conditions? In fact, we
have left nearly all these tests behind and instead we study each
component's properties. And the suppliers reputation. And general
physical terms. Etc. Even so called burn-in tests begin to be
aquestioned... 
Interesting topic, because testing is oftenly very expensive and one
saves money skipping...with sence

Inge


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of
[log in to unmask]
Sent: den 13 september 2006 21:21
To: [log in to unmask]
Subject: Re: [TN] Temp Testing

Tom,

     You picked up on an obvious issue....the lithium battery temp
limits.  You'll need to check temp specifications for all the components
on the board to find out what the design temp limits for the board will
be.  A common temperature range for board Environmental Stress
Screen(ESS) would be -10C to +70C, special case component population
withstanding(lithium battery).

     In order to determine your board temp stress limits you'll need to
know what the objective of testing will be....infant mortality issues,
board process validation, board design/functionality verification,
Highly Accelerated Life Test(HALT)?  

     Since the customer is asking for a specific temperature range and
electrical test to be completed after stress, you should be sure none of
the product components storage temp specs are beyond the temp the
customer wants.  Hopefully they did that homework but anyone who has
seen a lithium battery go up in flames would understand your concerns to
double check the specs.

     Time of temp stress should be at least long enough to get the board
to the stress temp or into a valid soak and based on board process
specs.  Some board processes can take cold with no issues while other
board processes will develop cracked vias at cold.  Too much time at
heat can cause board delamination.  Ideally you should perform a
destructive level test on a small board sample to determine limit
baseline after you think you have the right temp limits/time picked.

     The customer is not asking for electrical test during temp stress,
so it seems as though they are looking more for process related issues
than design related issues.  

     The product stress field is kinda like black magic and you almost
have to develop a feel based on stress test experience.  Just thought
I'd trow in my two cents.  Hope all goes well for you.

Barrie Fraley
EMC Corporation
Engineering HWQA
Electrical DVT/HALT
1-508-249-4472

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tom Parkinson
Sent: Wednesday, September 13, 2006 2:38 PM
To: [log in to unmask]
Subject: [TN] Temp Testing

Hello DN & TN people

We have a customer that wants us to thermally stress a completed PC
assembly (all the SMT & THT parts are soldered in).

The question comes up as to the temp range and time.

They are suggesting:  
Room temp to +150F to -40F to room temp.
I'm concerned because of the populated parts (one is a lithium battery).
Not
to mention I have no idea on the time periods from extreme to room temp.

Following this test, an electrical test would be performed.

Any suggestions / Comments??

Thanks

Tom



Tom Parkinson
Quality System Manager - CIT
WinTronics, Inc.
Phone: 724-981-5770 - extension 235

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