Hi Oscar

It is possible to waterproof boards with thin films without hermetically
sealing. We are working a lot with LED boards and they have to be
submerged in water while completing exposed.

Waterproofing with any film is down to many things. However I have found
the two key areas are the coverage of the coatings and the permeability of
the material.

The coverage relates to achieving a homogeneous film. Not so easy with a
liquid conformal coating. Down to application method, number of layers
applied. But it can be achieved. Or, you put the material on very thick.
Eg encapsulate or pot. Again, relates to the key areas.

Finally, you can choose a CVD type process that gives you the homogeneous
coating. Something like Parylene or MVD. We are experimenting with new
alternatives to Parylene that are also hydrophobic and lower permeability
so you get the great uniform protection but it repels water too. They are
also lower cost to manufacture compared to XY so that helps too.

I am presenting a paper on the new and old different technologies and
their waterproofing nature at Apex in San Diego in February. You can
contact me offline any time and I would be happy to discuss the results.

Best Regards

Dr Lee Hitchens


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On 10/10/2016, 05:54, "TechNet on behalf of Oscar Fallah" <[log in to unmask]
on behalf of [log in to unmask]> wrote:

>Hi TechNetters.
>Is conformal coating the best option for waterproofing applications? I am
>wondering how some consumer products like phones and tablets are made
>waterproof? Are these units hermetically sealed (e.g., housing has gaskets
>or sealant/glue at all joints and interfaces) or do they rely on
>sealing/coating individual components that comprise the whole device
>(conformal coating individual flexible and rigid circuit boards and all
>other components with exposed pads and solder joints etc)?
>Would anyone on the forum have experience with "film" sealing a PCBA?
>Thanks much in advance for your replies and help.
>Regards,
>Oscar Mahinfallah
>Sourcing commodity manager
>On Thu, Oct 6, 2016 at 8:00 AM Wayne Thayer - EXT
><[log in to unmask]>
>wrote:
>
>> Well stated!
>>
>> There are gaps between the molecules of everything. Polymers are
>> particularly permeable, and vaporized solvent molecules are tiny. It
>>EASILY
>> goes through the cured material. So does water vapor, of course!
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
>> Sent: Thursday, October 06, 2016 6:13 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Silicone Conformal Coating supplier
>>
>> Nigel,
>> Whenever people discuss the impact of bubbles on reliability, the work
>> "hypothetically" is always involved.  Well, hypothetically, it could be
>>a
>> place for water to collect over time.  Well, hypothetically, the bubble
>> could pop in service allowing access.  Well, hypothetically, the bubble
>>is
>> a place for residual solvent to stay, hypothetically causing problems
>>in a
>> hypothetical end use environment for a hypothetical design life.  You
>>get
>> the picture.
>>
>> I have not really seen, either in field performance or my own research,
>>a
>> significant impact of bubbles on performance, with the possible
>>exception
>> of high altitude and high voltage applications.  In those cases, you
>>may be
>> relying on coating almost like a potting material and any loss of volume
>> can lead to loss of dielectric insulation.
>>
>> While bubbles can be a place for moisture to gather over time, as all
>> coatings have some degree of moisture permeability, people seem to think
>> coatings act like a diode, moisture only flows in and cannot flow out.
>>If
>> that were the case, I would simply apply the coating upside-down and all
>> the moisture would flow away from the board (tongue firmly in cheek).
>>
>> Bubbles usually form in coatings because you have solvent trying to
>>egress
>> from the coating faster than it wants to go.  Most of your organic
>>solvents
>> used with coatings are electrical insulators, so would not compromise
>> electrical performance and will slowly diffuse through the coating with
>> time.  So, while there may be a short term impact from entrapped
>>solvents,
>> there is probably not a long term issue with them, hypothetically.
>>
>>
>>
>>
>> Doug Pauls
>> Principal Materials and Process Engineer Rockwell Collins
>>
>> On Thu, Oct 6, 2016 at 4:59 AM, Nigel Burtt <[log in to unmask]>
>>wrote:
>>
>> > Are "solvent bubbles" a peculiar problem with this type of conformal
>> > coating or a generic problem for coatings?
>> >
>> > Hypothetically if coating penetrates under the body of a low stand-off
>> > component and a solvent bubble remains trapped under there after the
>> > cure/dry, could that bubble "pop" under thermal cycling or high stress
>> > service environment with enough force to fracture the solder joints on
>> > the part?
>> >
>> >
>>