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Subject:
From:
"Stadem, Richard" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard
Date:
Tue, 29 Nov 2005 12:09:11 -0600
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I saw nothing in GR 3108 to address that situation!  8~) 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Tuesday, November 29, 2005 11:38 AM
To: [log in to unmask]
Subject: Re: [TN] Humidity and enclosed RF board

You mean apart from the one where my daughter ran into the ocean with a
mobile phone in her pocket??........................8-)

John

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric CHRISTISON
Sent: Tuesday, November 29, 2005 9:34 AM
To: [log in to unmask]
Subject: Re: [TN] Humidity and enclosed RF board

Agree with Richard about the environment. Letting the enclosure breathe
is also a good plan; how many mobile phones fail due to humidity related
failures?

You might also consider adding a breathing desiccator to the enclosure
although they tend to be expensive and need replaced every six moths or
so.

Regards, 
  
  

Eric  Christison
Mechanical Engineer
Home, Personal, Communication Sector - Imaging Division
STMicroelectronics
33 Pinkhill
Edinburgh
EH12 7BF 

Tel:     +44 (0)131 336 6165 
Fax:    +44 (0)131 336 6001 



> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard
> Sent: Tuesday, November 29, 2005 5:25 PM
> To: [log in to unmask]
> Subject: Re: [TN] Humidity and enclosed RF board
> 
> 
> It also depends on the environment where the box will live. 
> If it is near the sea, there is a much higher probability of failure 
> if any moisture does enter from outside.
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls
> Sent: Tuesday, November 29, 2005 11:01 AM
> To: [log in to unmask]
> Subject: Re: [TN] Humidity and enclosed RF board
> 
> Well, it depends.
> 
> You say that the casing seals the electronics from the external 
> atmosphere. How well?  Is it a hermetic seal?  Are you using an 
> elastomeric gasket? Do you package with an inert cover gas?  What is 
> the design life of the product and what are the consequences of 
> failure?
> 
> In my experience, even those enclosures assumed to be "hermetic" are 
> not, and that usually means moisture will eventually get in and will 
> have a hard time getting back out.
>  So it all depends on how well insulated your case keeps the 
> electronics throughout the design life. Elastomeric gaskets willl wear

> out.  Field repair is often less than optimal.
> 
> If moisture gets inside the case, it will condense on your boards when

> you go through dew point.  Can it grow dendrites?
>  Yes.  What is the risk?  It Depends.  Dendrites have been observed to

> grow in as little as 3.5 volts DC.  There is no "safe" level of 
> humidity because the degree of risk is dependent on both humidity and 
> the amount of ionic soil.  The dirtier it is, the less humidity it 
> takes.  Some papers have suggested 70% RH as a threshold, but this is 
> usually SIR type of testing, not field trials.  In addition, if your 
> product is functioning in some of the more polluted areas of the 
> world, and the enclosure is not hermetic, then the pollutant gasses 
> also get into the enclosure and do nasty things.
> 
> Doug Pauls
> 
> 
> 
> 
>              "Tempea, Ioan"
>              <itempea@POSITRON
>              .QC.CA>
> To
>              Sent by: TechNet          [log in to unmask]
>              <[log in to unmask]>
> cc
> 
>  
> Subject
>              11/29/2005 10:43          [TN] Humidity and enclosed RF
> board
>              AM
> 
> 
>              Please respond to
>               TechNet E-Mail
>                    Forum
>              <[log in to unmask]>
>              ; Please respond
>                     to
>               "Tempea, Ioan"
>              <itempea@POSITRON
>                   .QC.CA>
> 
> 
> 
> 
> 
> 
> Hi Technos,
> 
> application: one RF board and one antenna, no conformal coating, both 
> sealed inside of a casing; outdoor unit, will see temp and humidity 
> variations.
> 
> question: assuming that the boards are well insulated from the 
> exterior, should I worry about long term rel of the boards? Otherwise 
> said, due to temp variations, can the residual humidity inside the 
> casing condensate on the boards and cause damage? Or can it make grow 
> dendrites?
> 
> And a general question:  For dendrites we need a potential difference,

> humidity and dirt; is there any threshold for the humidity level, 
> below which dendrites will not grow?
> 
> Thank you,
> Ioan
> 
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