A quick test is to spray a laminate not connected with the product. If
you get a perfect finish it pushes you towards a surface finish issue on
the board.
Best Regards
Dr Lee Hitchens
SCH Technologies
On 01/03/2017 04:58, Steve Gregory wrote:
> Hi Phil,
>
> We've been using Shercon KD Kwiky Dot Discs which are supposed to have an
> acrylic adhesive:
>
> http://www.all-spec.com/Catalog/Adhesives-Sealants-Tapes/Tapes/Dots-Discs/KD00312-45075
>
> Those aren't the ones you are using are they?
>
> Steve
>
> On Tue, Feb 28, 2017 at 2:35 PM, Nutting, Phil <[log in to unmask]>
> wrote:
>
>> 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,
>>>>>> 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.
>>>>>>
>>>>>
>> --
>>
>>
>> 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.
>>
|
