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Subject:
From:
"Nutting, Phil" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Nutting, Phil
Date:
Tue, 28 Feb 2017 21:35:02 +0000
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With our acrylic conformal coating I noticed a blooming effect around the masking tape dots.  It turned out that the tape dots had changed from acrylic adhesive to silicon adhesive.



Phil



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory

Sent: Tuesday, February 28, 2017 4:19 PM

To: [log in to unmask]

Subject: Re: [TN] Baking before conformal coating



I don't know what the heck is going on here, but try these links!



Arrrrrrrrrgh!



http://stevezeva.homestead.com/Conformal_dark_spots.jpg



http://stevezeva.homestead.com/Conformal_dark_spots_close.jpg



http://stevezeva.homestead.com/Conformal_dark_spots_close_reflected_light.jpg



Steve



On Tue, Feb 28, 2017 at 2:14 PM, Steve Gregory <[log in to unmask]> wrote:



> Oh shoot, I sent thumbnail links! Here try these:

>

> http://stevezeva.homestead.com/Conformal_dark_spots.jpg

> <http://stevezeva.homestead.com/Conformal_dark_spots_thumb.jpg>

>

> http://stevezeva.homestead.com/Conformal_dark_spots_close.jpg

> <http://stevezeva.homestead.com/Conformal_dark_spots_close_thumb.jpg>

>

> http://stevezeva.homestead.com/Conformal_dark_spots_close_

> reflected_light.jpg

> <http://stevezeva.homestead.com/Conformal_dark_spots_close_reflected_light_thumb.jpg>

>

>

> Steve

>

>

> On Tue, Feb 28, 2017 at 2:07 PM, Steve Gregory <[log in to unmask]> wrote:

>

>> Hi Doug, Lloyd and everyone,

>>

>> Here are some photos:

>>

>> Area under UV light (BTW, that's my Ray-O-Vac pet pee-pee detector light

>> I bought at Walmart):

>>

>> http://stevezeva.homestead.com/Conformal_dark_spots_thumb.jpg

>>

>> Close-up of area under UV light:

>>

>> http://stevezeva.homestead.com/Conformal_dark_spots_close_thumb.jpg

>>

>> Close-up of the same area under reflected light:

>>

>> http://stevezeva.homestead.com/Conformal_dark_spots_close_

>> reflected_light_thumb.jpg

>>

>> So you can see that the area is indeed coated. This is Humiseal 1B73....

>>

>> Steve

>>

>> On Tue, Feb 28, 2017 at 1:51 PM, Douglas Pauls <

>> [log in to unmask]> wrote:

>>

>>> Argggh Steve, we know ye to be a pirate anyways......

>>>

>>> I had the same question come to mind as Lloyd asked.  Pinholes or

>>> dewetting?  Pinholes can be due to moisture coming out of the board, but is

>>> most often point sources of contamination, like droplets of oil or some

>>> other adulterating contaminant in the coating.  A picture would help.

>>>

>>>

>>> Doug Pauls

>>> Principal Materials and Process Engineer

>>> Rockwell Collins

>>>

>>> On Tue, Feb 28, 2017 at 2:20 PM, Steve Gregory <[log in to unmask]>

>>> wrote:

>>>

>>>> Hi all,

>>>>

>>>> I'm not trying to hijack this thread, but since we're talking conformal

>>>> coating here, what could cause an acrylic to appear that there are tiny

>>>> little fisheyes in the coating, but when you hold the board at an angle,

>>>> you can clearly see that the area is coated. I know pictures would help,

>>>> I'll see if I can get some....

>>>>

>>>> Steve

>>>>

>>>> On Tue, Feb 28, 2017 at 12:59 PM, lduso - Diamond-MT.com <

>>>> [log in to unmask]> wrote:

>>>>

>>>> > We do not pre-bake as an internal rule and never a complaint. Obvious

>>>> > exceptions: We are washing or cleanliness testing the boards. Then we

>>>> will

>>>> > bake them dry before masking and coating. Or the customer specifically

>>>> > requires a pre-bake on the drawing. (I always then ask the question;

>>>> "How

>>>> > long after the bake do I have to coat them before they need to be

>>>> baked

>>>> > again?" Strangely, only a few have an answer for that.)

>>>> >

>>>> > I have visited many facilities that conformal coat and I have

>>>> witnessed it

>>>> > both ways but mostly on the "no pre-bake" side. One customer even

>>>> pre-baked

>>>> > their boards before coating with a water based acrylic.

>>>> >

>>>> > Lloyd Duso

>>>> > Plant Manager

>>>> > Diamond-MT

>>>> > (814) 535-3505

>>>> > www.Diamond-mt.com

>>>> >

>>>> > On Tue, Feb 28, 2017 at 2:39 PM, Douglas Pauls <

>>>> > [log in to unmask]> wrote:

>>>> >

>>>> > > Lee,

>>>> > > It Depends.

>>>> > >

>>>> > > We have one facility that has never baked prior to coating

>>>> application.

>>>> > No

>>>> > > evidence of any conformal coating related problems.  We have several

>>>> > > facilities that bake religiously prior to coating application, also

>>>> for

>>>> > > acrylic.  No evidence of any conformal coating related problems.

>>>> > >

>>>> > > I think the biggest factor is how much residual water you have.  I

>>>> don't

>>>> > > think your assemblies have to be bone dry before coating.  We do a

>>>> lot

>>>> > with

>>>> > > in-line aqueous cleaners, which have heated air knifes that remove

>>>> the

>>>> > bulk

>>>> > > of the water.  Now, there might still be some entrapment areas, but

>>>> if

>>>> > so,

>>>> > > we find them and then blow out those entrapment areas with ionized

>>>> air.

>>>> > >

>>>> > >

>>>> > > Doug Pauls

>>>> > > Principal Materials and Process Engineer

>>>> > > Rockwell Collins

>>>> > >

>>>> > > On Tue, Feb 28, 2017 at 10:20 AM, Lee Hitchens <

>>>> > > [log in to unmask]

>>>> > > > wrote:

>>>> > >

>>>> > > > Hi all

>>>> > > >

>>>> > > > I've recently been asked about baking pcbs before conformal

>>>> coating and

>>>> > > > whether there is any quantified data on the effect on coating

>>>> > > performance.

>>>> > > >

>>>> > > > Does anyone know of any public studies on this or can shed some

>>>> light

>>>> > on

>>>> > > > its effectiveness beyond anecdotal experience ? I would be very

>>>> > grateful

>>>> > > to

>>>> > > > you on this.

>>>> > > >

>>>> > > > Best Regards

>>>> > > >

>>>> > > > Dr Lee Hitchens

>>>> > > >

>>>> > > > SCH Technologies is a Division of SCH Services Limited

>>>> > > >

>>>> > > > www.conformalcoating.co.uk

>>>> > > > Skype: leehitchens

>>>> > > >

>>>> > >

>>>> >

>>>>

>>>> --

>>>>

>>>>

>>>> This email and any attachments are only for use by the intended

>>>> recipient(s) and may contain legally privileged, confidential,

>>>> proprietary

>>>> or otherwise private information. Any unauthorized use, reproduction,

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>>>> e-mail or its attachments is strictly prohibited. If you have received

>>>> this

>>>> email in error, please notify the sender immediately and delete the

>>>> original.

>>>>

>>>

>>>

>>

>



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