Inge, also look to see if there is a requirement that calls out (or expressly prohibits from) shaking the can prior to use. We use (different) coatings with either requirement, and not following it is sure to exhibit issues.
Regards,
Amol
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, August 20, 2009 3:17 PM
To: [log in to unmask]
Subject: Re: [TN] Manual spraying
Your advice is in the category 'common sense'. If i had over exposed photos
taken with an ordinary camera, and you showed me how to handle the ISO
setting, that had not been a sales trigging even if you were a camera
salesman.
Inge
----- Original Message -----
From: "Brian Stumm" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, August 20, 2009 9:04 PM
Subject: Re: [TN] Manual spraying
I sent this to Inge offlist because I was worried it would come across
as a sales pitch but since it goes along with what Gregg said I
decided to share. I cannot provide any experience for the
applications/spray side of conformal coatings but have *some*
experience on the curing side.
I've seen airflow from curing systems introduce bubbles in coatings.
I've also seen ovens that skin the coating on the outside trapping
solvent below the surface that later off-gases and bubbles and
sometimes blisters. These are usually much larger bubbles though. I
don't want this to sound like an advertisement (since we manufacture
ovens) but we build separate products for curing that use infrared
heaters and very low airflow whereas our reflow systems are
convection. Just recently I was on-site at a customer that was mixing
the coating very runny (3 parts solvent to one part coating compared
to recommended 1.5 to 1 ratio) and even the low flow rate of supply
air into the oven was causing the coating to flow which resulted in
uneven coating thickness and very tiny bubbles in the cured coating.
At least the customer believed the oven caused it. They used a robotic
spray cell which used compressed air to pressurize the 2 pots. After
reducing the airflow rate of the oven and switching to N2 instead of
compressed air the bubbles went away. Both changes were made at the
same time so I do not know for sure which was the culprit.
On Thu, Aug 20, 2009 at 11:52 AM, Temkin,
Gregg<[log in to unmask]> wrote:
> To continue with Brian's track, it's common with heavily solvent loaded
> conformal coatings (spray processes materials are often thinned with
> additional amounts of solvent) to see bubbling if the solvent if its not
> allowed to evaporate out of the coating prior to the outer surface curing
> curing. Excessive applied thickness will also promote bubbles. The sprayed
> boards should be allowed to sit and reach a handling cure before being
> heat cured.
>
> Gregg
>
> -----Original Message-----
> From: Inge [mailto:[log in to unmask]]
> Sent: Thursday, August 20, 2009 11:32 AM
> To: [log in to unmask]
> Subject: Re: [TN] Manual spraying
>
> Cured for one hour at +80 Centigrades. We have not done microscopy when
> wet
> (the cards).
> Inge
>
>
> ----- Original Message -----
> From: "Brian Stumm" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, August 20, 2009 8:21 PM
> Subject: Re: [TN] Manual spraying
>
>
>> How do you dry/cure the coating? Are you sure it is being introduced
>> during coating and not during drying?
>>
>> On Thu, Aug 20, 2009 at 11:17 AM, Inge<[log in to unmask]> 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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