Sorry I'm late on this, and I haven't read all of the thread, but
Sounds like the variation may be in the environment (temp, RH, barometric
pressure and such), or the can is almost empty/almost full/not shaken
enough/too much. Are these parameters being followed as well? Devil's
always lurking in those itty-itty details. If already checked, then pardon
this ole' geezer...
Roger
(BTW, back to work doing board design again! Woo-hoo!)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Sunday, August 23, 2009 3:07 PM
To: [log in to unmask]
Subject: Re: [TN] Manual spraying
Yes, variations with same cans.
OK, will try baking.
Yes, from same fabricator.
Mystery.
One of our old foxes, experienced process engineer, you've met him, made a
try,
At first, the wet coating was crystal clear, but successively throughout
room drying, the
coating changed character, and became matte.
Will let you know.
Inge
----- Original Message -----
From: "Graham Naisbitt" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, August 23, 2009 6:35 PM
Subject: Re: [TN] Manual spraying
> 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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