Peter,
I would add one more concern when choosing a coating and that is
maximum expected temperature. The Tg of various coatings will determine
which can be used for expected temperatures.
David A. Douthit
Manager
LoCan LLC
[log in to unmask] wrote:
> Hi, Matt,
>
> The commonly used coatings are either Acrylics, like Humiseal 1B31 which we
> use, Urethanes or Epoxies. All three have the same good resistance to
> moisture and salt fog, but the difference between them is that Acrylics are
> not very chemical resistant (which makes them great for rework), Urethanes
> are more difficult to rework and need much more sggressive stripping agents
> to remove them, and Epoxies are darned near impossible to shift. I remember
> the days of PC54, which was the common coating for military PCBA's up til
> the early 80's, and repairing boards nicely was a major pain.
>
> If it's purely Humidity and Salt Fog you're up against, use an acrylic
> conformal coating. It's easily applied by brushing, dipping or spraying.
>
> Peter
>
> "Gray, Matthew D HS-SNS" <[log in to unmask]> 22/05/2003 09:54 PM
> Sent by: TechNet <[log in to unmask]>
>
> Please respond to "TechNet E-Mail Forum."; Please respond to "Gray, Matthew
> D HS-SNS"
>
> To: [log in to unmask]
> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
> Subject: [TN] Conformal Coating Application Method for BGA
>
> Hello -
>
> I am requesting feedback to material and processes that have provided
> environmental performance protection for BGAs and other large array
> packages. The performance environment of consideration is corrosion and
> humidity.
>
> Can users provide particular details regarding application process spray
> (inclusion of steps used for flood/fill/etc), dip, other, and material that
> has provided a high amount of coverage and ability to protect electrical
> connections and components in humidity and salt fog environments. Ideally,
> these materials are below the parylene step. All feedback is appreciated.
>
> Regards - Matt
>
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