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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