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May 2009

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From:
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Inge <[log in to unmask]>
Date:
Wed, 27 May 2009 20:46:41 +0200
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Better you quit, and I take your job and get your salary, I become rich = 10 
times what I have now. It's so much , that I can be generous and give you 
one half back= you get money without doing nothing.
Inge

----- Original Message ----- 
From: "Werner Engelmaier /*" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, May 27, 2009 7:59 PM
Subject: Re: [TN] humidity test failure


No, if you quit and become a consultant, you become richer—the up-side. The 
down-—you are on the job 24/7/365.

Werner







-----Original Message-----
From: Inge <[log in to unmask]>
To: [log in to unmask]; [log in to unmask]
Sent: Wed, 27 May 2009 1:45 pm
Subject: Re: [TN] humidity test failure
















So, if I quit, you become richer, can we share your
extras?


Inge




----- Original Message ----- 


From:
  [log in to unmask]


To: [log in to unmask] ; [log in to unmask]


Sent: Wednesday, May 27, 2009 7:08
  PM


Subject: Re: [TN] humidity test
  failure






Hi Inge,
"Why do we repeat all failures that have
  been known for decades?"
Easy, most companies get rid of their experienced
  people. And the new hires simply do not have the time to learn about 
anything
  that happened previously.
——sure keeps consultants busy,
  though.

Werner









-----Original Message-----
From: Inge <[log in to unmask]>
To:
  [log in to unmask]
Sent: Wed, 27 May 2009
  1:02 pm
Subject: Re: [TN] humidity test failure



We
  had an awful lot of environmental test chambers, and we followed MIL-STD 
like
  a blind klinging to his stick. With time, we have realized the 
questionable
  relationship between those tests and the unpredictable mother Nature. The
  exact repetition of temperature up, temp down, dwell, temp down=2
0etc does not
  always correspond to the erratic reality with endless variations and
  combinations of condensation and vibration, heat and salt, power switching 
and
  deep freeze, sun irradiation and sand blast , very short exposure followed 
by
  extremly long one etc etc. I listened to a guy who was a successful design
  manager, whose motto was 'skip all testing, do the right design or process
  from the beginnin g' . Easy said, but still interesting topic. Am brought 
up
  with MIL-STD, so I'm little ambivalent, but I try to think like him. And, 
in
  fact, with all billion hours of testing everything on this planet, should 
we
  not have background enough for avoiding all disasters..like corroded 
ceramic
  caps, for instance. Why do we repeat
  all failures that have been known for
  decades?

Inge

----- Original
  Message ----- From: "Chris Mahanna" <[log in to unmask]>
To:
  <[log in to unmask]>
Sent:
  Wednesday, May 27, 2009 6:34 PM
Subject: Re: [TN] humidity test
  failure

Hi Wayne,

Agreed. The DUT
  probably slipped close to, or below dew. Close can be just as bad. And, 
surely
  there is trapped ionics. But, I suspect a correlation ranking might show 
those
  non-wetted solderable surfaces as your real
  culprit.

Ability to control the chamber and DUT is highly
  dependent on absolute humidity. 85/85 is very tough. Anything higher is 
crazy.
=2
0 The common 25-65C, 90% is quite difficult without good multi loop control. 
If
  you're cycling a heavy assembly you will probably want to use the surface 
temp
  as an input to your controller.
IPC-9201A is a good source of info.
  NPL has several papers.

Fully processed comb patterns can
  'survive' 85/85 or 25-65/90 SIR/ECM tests for 1000 hours without cc, but 
it's
  not
  easy.

Chris



-----Original
  Message----- 
From: TechNet [mailto:[log in to unmask]] On Behalf Of
  Thayer, Wayne
Sent: Tuesday, May 26, 2009 10:01 PM
To: [log in to unmask]
Subject: [TN]
  humidity test failure

Hi Technet
  Gurus!

I have attached a picture of a part responsible for
  excess current draw during an extended humidity/temperature cycling test. 
(I
  copied Steve so he can hopefully post!)

The board was
  carefully solvent cleaned, but no SIR test validating the process strips 
all
  ionic contamination. The board is in an enclosure where plenty of ionic
  contaminants are available.

Humidity was supposed to not
  exceed 90% and was to be non-condensing during cycling. There were a 
handful
  of components which displayed similar deposits on the same circuit board.
  These were the only parts biased during the humidity test. I believe the
  evidence suggests at least some condensation occurred. To me the deposits 
look
  like salts. But what do
 "the experts" think?

Is there any
  rule of thumb as to humidity levels where we are nuts to try to survive
  without conformal coating? Part of the adjacent circuitry contains RF 
devices
  and those guys get panic-stricken when told we probably n eed to conformal
  coat!

Wayne Thayer

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