Inge,
It almost sounds like what I was seeing back in Feb, archive search subject "coating material". The end result for my problem was glycol which came from the solder resist process. The difficult task was that it was intermittent, effected multiple lots and the only way to find it was coat the boards. The work around was to use MEK as a career agent in the CC. The problem didn't go away but we were able to process all of the WIP and still pass the UV inspection process. There were still some areas that appeared to coat poorly but was class II compliant and had customer buy off.
By the way we were using 1B73AP at the time.
Ted T.
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Sun Aug 23 15:53:05 2009
Subject: Re: [TN] Manual spraying
Not likely, it's a fact that the weather is a bit unstable these days, but
the barometric pressure, temperature and RH does not (fortunately) vary
within minutes or even hours just now. The cans are weight checked and are
all marked with same symbols on the bottom. I'm little disturbed by the
abscense of the traditional steel ball, which use to be in most spray cans
for painting or coating. Too much shaking, what do you mean?
Inge
----- Original Message -----
From: "Roger Stoops" <[log in to unmask]>
To: "'TechNet E-Mail Forum'" <[log in to unmask]>; "'Inge'"
<[log in to unmask]>
Sent: Sunday, August 23, 2009 9:31 PM
Subject: RE: [TN] Manual spraying
> 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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