[time-nuts] wwvb weak on east coast especially when the pre-amps under wa...

[Tom Knox]

What type of coating do you recommend? What is the downside of coating all electronics?

Thomas Knox



> From: K3WRY at aol.com
> Date: Mon, 14 May 2012 21:16:15 -0400
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] wwvb weak on east coast especially when the	pre-amps under wa...
> 
> If you can keep the boards in a vertical mount position, and they have been 
>  sprayed with a conformal coating, the heat from the components and the 
> coating  will keep any moisture from forming on the boards in a vertical 
> position.   We do this in several products we supply to the military.
>  
> Dr Joe Palsa k3wry
>  
>  
> In a message dated 5/14/2012 9:03:13 P.M. Eastern Daylight Time,  
> GandalfG8 at aol.com writes:
> 
> The  other option of course is to pressurise the box with dry air to ensure 
>   
> a positive pressure differential, such that the net flow is always  
> outwards 
> at  all points, but it's probably easier just to provide a  drain hole:-)
> 
> However, whilst a drain hole will prevent the build up of  a lake inside 
> the 
> enclosure it still doesn't prevent condensation forming  on circuit boards, 
> and  powered circuit boards and condensation don't  really go well  
> together.
> 
> As per earlier comments, it's quite  difficult to keep any externally  
> mounted enclosure totally moisture  free, so it's much easier to accept the 
>  
> inevitable and allow for  it.
> 
> In a past life I designed quite a few circuit boards that   were required 
> to 
> be fitted in externally mounted vented enclosures, so  not  a great deal of 
> pressurisation there then:-), and I usually  specified that  both sides 
> should be sprayed with a plastic coating  following final test.
> 
> I can't remember now exactly what this stuff was  called, but it  was 
> readily available in the UK from both RS and  Farnell as an aerosol plastic 
>  spray 
> that provided a good barrier but  was a bit more flexible than the  usual 
> MOD 
> spec conformal  coatings.
> It melted easily under a soldering iron, albeit with a foul   pong:-), so 
> reworking was no problem, and resisted moisture  remarkably  well.....
> 
> problem  solved:-)
> 
> Nigel
> GM8PZR
> 
> 
> 
> 
> 
> In a message dated  14/05/2012 23:10:30 GMT Daylight Time,  
> arnold.tibus at gmx.de  writes:
> 
> The only  solutions I think:
> Apply air pressure tight  boxes having a breathing hole  an the bottom,
> mount the
> box that no  rain and water can penetrate from  the top or sides. If the
> hole is  big enough,
> eg. 2mm, no pressure  difference is possible and no  pumping effect will
> occur.
> (If the hole is  too wide, small animals  may penetrate).
> Or,
> when using a pressure tight  box, it must be  stiff and sealed to
> withstand under all
> temperature  conditions  more then 1 bar/ 100 kPa. Do not forget that  all
> feed
> throughs  must be of real hermetic type, normal coaxial  connectors are
> not  tight!
> Don't route cables directly in, because no  cable braid or mesh  is   vapor
> tight.
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