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August 2009

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From:
Hernefjord Ingemar <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Hernefjord Ingemar <[log in to unmask]>
Date:
Fri, 21 Aug 2009 13:48:38 +0200
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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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