Hi Myke,

>My understanding of OSP is that it is designed for use in a two sided SMT
>process.  With bare copper, when it goes through the first reflow (with
>components and paste on the other side) it will oxidize.
>
>The purpose of OSP is to protect the copper during the first pass and burn
>off in time for the second pass.

I see.

>I don't understand your question with regards to water.  Your board should
>not be exposed to any water until the assembly process has completed (both
>sides and wave solder) and you are washing the board.

The question is: Can I use OSP to add a water (humidity) protection to the
circuit after assembly and during its operational life ?.

From your fine explanation of the process guess that this is just an
intermediate process and not a final work in the PCB manufacturing.

Have tested the solderable varnish to achieve this water protection and it
works very well. The varnish Covers all the PCB, IC pins, etc and if you
have any component that can be damaged if covered by varnish (connectors,
jumper pins, etc) you can solder them after varnish application. Then of
course will be exposed to oxidation but you can change them there after.

Didn't have so much luck with liquid epoxy. For mechanicaly complex circuits
you need to pot the circuit in a mould, something hard to manufacture and
most of the time needing "hand trimming" the resultant body to make it fit
correctly in its working place. If you use a more dense material (a kind of
paste, silicone, etc) there will be a lot of cavitys between components wich
will fill with liquid if exposed to any humidity/water. Water takes longer
to evaporate from there and oxidation will cause problems.




Luis Fernandez Cormenzana
RadioBit Sistemas, S.L.
        Vehicle fleet control systems
        Patrol presence controllers

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