Hi Joe::
                Even the most moisture sensitive devices do not soak moisture as a sponge does. It takes hours or days for the moisture to seep in. The exposure to water during a wash is minutes and it is dried right a away. The key is to keep the components in a dry environment between operations.. Keeping the boards or reels in a dry room works really well and does not require N2. A 10' by 10' room that is heated at about 110 degrees does really well. Run the air through a dehumidifier if needed. Whole reel carts can be stored there. Have a big temp / humidity monitor that can be viewed from outside the room.
        Regards,
        Ramon

> -----Original Message-----
> From: Macko, Joe @ IEC [SMTP:[log in to unmask]]
> Sent: Thursday, March 18, 2004 8:31 PM
> To:   [log in to unmask]
> Subject:      [TN] double sided reflow and MSDs
>
> Fellow Techs,
>
> Some new designs have moisture sensitive devices (MSDs) such as BGAs on both
> sides of the pwb.  A lot of effort is put into making sure that the MSDs are
> properly packaged, not opened until ready for use so they stay within the
> allotted floor life, etc..  Some MSDs are level 5 sensitivity which only
> have a 24 hour floor life.
>
> What I would like to hear about is how assemblers handle MSDs when they are
> already mounted on 1 side of the board, maybe aqueous washed and then see
> another reflow cycle when the other side of the board is assembled/reflowed.
> Are the MSDs/boards rebaked which adds a lot of cycle time but maybe
> necessary?  Assembled within the allotted floor life for the most sensitive
> MSD - probably the most ideal situation?  Not washed until both sides are
> reflowed which doesn't make sense when using water soluble flux?  Or, stored
> in a dry-box until ready for the 2nd side reflow - which should work.
>
> Also, what impact does aqueous cleaning have on a mounted MSD?  Does it
> saturate the MSD with moisture requiring a bake out?
>
> I look forward to hearing how other users manage this problem.  thanks
>
> joe
>
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