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August 2009

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Graham Naisbitt <[log in to unmask]>
Date:
Sun, 23 Aug 2009 17:35:20 +0100
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Inge

All from the same can?

If no, then I suspect some incomplete curing or "residual board  
contaminants" might be the problem.

Try baking the problem boards for around 8 hours at 80C, leave them to  
revert to room temp and try again. If problem persists, then there you  
probably need to run FTIR to figure what is there causing the problem.

Also, are they from the same board fabricator? If not, check ROSE to  
see if there is a difference.

If yes, then have the batch checked - it is possible that there has  
been a labelling issue.

Let me know

Regards

Graham Naisbitt

Email: [log in to unmask]
Phone: +44 (0)12 5252 1500
Web: www.gen3systems.com

On 21 Aug 2009, at 12:48, Hernefjord Ingemar wrote:

> Nick,
> we have done tests today, same operator, same boards, same cans,  
> same everything. Most boards get a clear, deep and nice look, but  
> suddenly we get a greyish coating, quite matte!
>
> Q1: what spray angle do you recommend?
> Q2: what spray pattern do you recommend? Zig-zag, up-and-down, side- 
> to-side or what?
> Q3: is the room RH of importance?
> Q4: is the process sensitive to laminar flow and if so, what level  
> is critical?
>
> Inge
>
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Nicholas  
> Redgrave-Plumb
> Sent: fredag 21 augusti 2009 12:31
> To: [log in to unmask]
> Subject: Re: [TN] Manual spraying
>
> The only way I can see for the propellant causing this kind of  
> problem is if the nozzle of the spray can is too close to the  
> substrate whilst spraying. I note several suggestions in the posted  
> responses of expensive elevated IR curing ovens etc. for IB31 but  
> these are really not necessary as this material is dry to the  
> touch/"tack" dry in only minutes, dry in 24 hours and cured/fully  
> optimised in 7 days. This would undoubtedly be accelerated by an  
> elevated cure but it shouldn't really be necessary. So all you  
> should really need is simple drying cabinet at ambient temperature  
> just to take the solvent vapours away.
>
> Otherwise, it could be "champagning" or "solvent-popping" which are  
> terms to describe a condition where the surface of the coating  
> material partially cures leaving solvent still trapped inside the  
> wet- film. The solvent has to go somewhere so it finds it's way out  
> through the surface and in doing so makes multiple small holes.
>
> To avoid this problem should be a matter of going back to basics.
> Review the coating procedure, make sure the operators are properly  
> trained (and not getting the spray nozzle too close to the substrate).
> If the volumes justify the use of a purpose-built spray booth for  
> conformal coating with intrinsic safety features and laminar air- 
> flow/ extraction then it might be worth going in that direction.
>
> But there should be a simple solution to this problem because the  
> usage of HumiSeal 1B31 globally, in both liquid and aerosol cans is  
> massive.
>
> Nick Plumb
> Gen3 Systems Limited
> Farnborough, United Kingdom
>
> _________________________________
>
>
> On 20 Aug 2009, at 19:17, Inge wrote:
>
>> Good Evening,
>> we use small cans filled with 1B1 conformal coating for handspraying
>> boards. The guys are not satisfied with the result, because sometimes
>> the result is matte. Microscope photos show thousands of microscopic
>> bubbles in the coating. I suspect that it's included driving gas. Or
>> wrong handling the spray can.Anyone out there with experience? How do
>> you avoid this problem?
>> /Inge
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