Oscar,
The answer is "It Depends".  Waterproofing can mean a lot of different
things, depending on the application.  Does it mean immersion to a certain
depth of water?  Does it mean that a stream of water running over the
electronics will not impede its function?  What are the consequences of
failure?

If you want to make something bulletproof against water, you pot it, either
with a waterproof gel like a silicone, or a waterproof foam.

Conformal coatings are OK for some applications, but it depends on the
application and what happens if the waterproofness fails.

What you are seeing for many of the consumer products is not what we
classically think of as conformal coatings.  These newer classes of
coatings are called by a variety of names: nanocoatings, ultra-thin
coatings, superhydrophobic coatings, etc.  Some are applied as very thin
liquids, others as chemical vapor deposition processes.  Hermetic sealing
is often a very expensive practice, so the expense is really justified if
it is a safety-critical or mission-critical item, certainly not for
consumer electronics.  For most consumer electronics, the cases are meant
to be very rugged, with the thin coatings sealing up up entrances to the
unit itself.  It can work a few times, but not regularly.

I know there are members on the forum who are examining the use of these
new materials as replacements for conventional coatings, or supplements to
coatings.  But in my experience, most of us have NDAs in place and won't
discuss them here.




Doug Pauls
Principal Materials and Process Engineer
Rockwell Collins

On Sun, Oct 9, 2016 at 5:54 PM, Oscar Fallah <[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?
> > >
> > >
> >
>