or the phone in your back pocket went into the washing machine?
jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of John Burke
Sent: Tuesday, November 29, 2005 12:38 PM
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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