Earl, Brad,

Thank you for the answers. Obviously, there is no a lots of experiences on
this area among TechNetters or the question itself wasn't interesting
enough. :)
However I just want to follow up this subject with the experiences that I
gained during the testing of the PCB in vacuum chamber. I hope that this is
going to help someone in the future.
I found that the best solution was to add two extra layers (top and bottom)
to the PCBs that are only containing pads and annular rings for the plated
holes. Pads are connected with the layers with hidden vias. That way, I
minimised the amount of the exposed copper/ENIG on the surface of the PCB.
There is no coating on the laminate at all, which minimises outgassing (I
wouldn't believe this if I haven't seen it myself).
I'm washing the flux residues away directly after the reflow, first with
Zestron and than with not-ionised water. After this, the PCBs are baked and
stored in the nitrogen atmosphere. Before mounting the PCBs in to the
vacuum the PCBs are stored in the vacuum chamber during the 8 hours period,
outgassing as much as possible. When this procedure is finnished and the
PCBs are mounted in to the vacuum, make little prayer and hope for the best
when you push "ON" button. :)

Sasha Miladinovic


**********************************************************************
Sasha Miladinovic - Production Engineering
Amersham Biosciences, PCB Production, Umeå
Tel:      +46 (0) 90 150 232
Fax:     +46 (0) 90 138 372
E-mail: [log in to unmask]
**********************************************************************

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