If the guidelines within IPC-1601 are followed, there should be no grief, not even for PWB finishes other than ENIG and HASL.
A top-tier process engineer understands how to set up the optimum baking time and temperature schedule for any given PWB size and type, such that you can remove at least 80% of the saturated moisture content by weight with no compromise to the PWB solderability, for any PWB, for any finish. 

Just because the boards are stored in sealed bags means very little.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Grunde Gjertsen
Sent: Tuesday, December 10, 2013 5:23 PM
To: [log in to unmask]
Subject: Re: [TN] Moisture Level Determination of PCB

Hi

Without being too scientific about it.

1. For FR4 it is generally not that critical if storage and shop floor conditions is reasonably controlled and the boards are stored in sealed bags. J-STD-033 is not really relevant but if you can handle the logistics comfortably it seems like a good idea to me.
Be very careful about baking out anything other than HASL and ENIG, all sorts of grief can follow.
If what worries you are delamination and leadfree soldering the key is to choose a laminate that is suitable for the design, process and to some extent end user application. (Class 3) Anything polyimide/flex take much more care and bake out prior to soldering and for each thermal event according to manufacturers recommendations unless you can store the boards in a dry cabinet between. Do not trust the boards to be dry enough from the manufacturer.

2. Yes.

Best regards
Grunde

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of MaryJane Chism
Sent: 10.desember 2013 18:32
To: [log in to unmask]
Subject: [TN] Moisture Level Determination of PCB

Hi Group,

I have a question concerning the moisture level of a printed circuit board.

1) Does a printed circuit board have an MSL level? We have been treating the printed circuit as an MSL Level 3.
2) Should we consider the wave solder as a thermal event even though the wave carriers shield all areas of the printed circuit board except the specific through hole areas. We currently do but should we?

Any information you give will be helpful,

Thanks,

Mary Jane

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