Hello Technetters,

There is very little concrete information concerning manufacturing of the
PCBs that are going to be mounted in high vacuum. I'm aware that the PCBs
got to be extremely clean. First of all there is the question of the
materials that are involved during the manufacturing process. Laminate that
printed board is build of, type of solder mask, type of finish, type of the
mounted parts and their properties, soldering paste, flux, residues,
cleaning chemicals, humidity et cetera.

There is need for a circular pad in the middle of the PCB that’s got to be
as plane as possible and has Ф25mm.
The designer has specified printed board with exposed copper alt. HASL
finish on the pads and the soldering mask should be founded only on one
side of the PCB. I believe that he want is to prevent or limit the
outgassing (Note that the whole PCB is going to be mounted in high vacuum).
I can't see why is better to have soldering mask only on one side. The
contamination degree is not that much different if there is the soldering
mask on the both sides. Aren't the laminates itself very porous and when
the soldering mask is on the PCB that you get less porosity?  Thereby,
should a minimum degree of contamination after the cleaning process, be
obtained.
This is how I'm thinking.
Printed board should have ENIG finish on the pads to obtain as plain pads
as possible and prevent the oxidation and also soldering mask on both sides
of the PCB to limit porosity of the PCB. Then, before mounting the PCB in
to the vacuum, wash (Zestron) and dry/bake the PCB in, we say, 8-10 hours.
This is followed by, we say, 8-10 hours in the vacuum chamber outgassing as
much as possible and at the same time preventing the oxidation on exposed
solder.
My general opinion about cleaning is that easiest way to clean something is
if that "something" doesn't exist. On the printed board in this case,
oxidation, contamination in the laminate, residues et cetera.

If there is anything that is wrong in my way of solving this problem or if
you have any expirience with PCBs in High Vaccum, please write a comment on
this.
I would appreciate getting any kind of answer.  :)

Thnx,
Sasha

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