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March 2017

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From:
Craig Sullivan <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Craig Sullivan <[log in to unmask]>
Date:
Wed, 1 Mar 2017 14:35:25 -0500
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You'll also see this phenomenon with acrylic adhesive depending on how the tape is slit or the dots are made. Most slitters use a 1-2% silicone solution on their blades so the adhesive doesn't stick.

Craig Sullivan
Manufacturing Engineer
IT Administrator
Phone:  (607) 266-0480 x115
Fax:  (607) 266-0482
Email: [log in to unmask]
Web:  www.mplinc.com

MPL, Inc. 
41 Dutch Mill Road  |  Ithaca  |  NY  |  14850
An ISO 9001:2008 Certified and ITAR Registered Company
IPC member since 2004 




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nutting, Phil
Sent: Tuesday, February 28, 2017 4:35 PM
To: [log in to unmask]
Subject: Re: [TN] Baking before conformal coating

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_l
> ight_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, dissemination, distribution or other disclosure of 
>>>> the contents of this 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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