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?
> >
> >
>