I've never seen an issue with MSD during a second reflow but...

If you do feel you are having an issue, look at the data sheet for the
aqueous flux contained in your solder paste. I have seen 24 - 48 hours
specified as the maximum time before wash. Your risk of scrap due to
planning errors or machine down time is high, but it would eliminate the
need for the first wash.

Jason 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Macko, Joe @ IEC
Sent: Wednesday, September 06, 2006 12:31 PM
To: [log in to unmask]
Subject: [TN] Populated board bake out after 1st side reflow/DI wash

Fellow techs,



Hello.

A general question came up about the need to re-bake a double sided
board after 1st side reflow/DI wash before starting 2nd side assembly.
The concern is that the board (or mounted MSDs) may absorb enough
moisture going through the high-pressure DI water in-line cleaner to
potentially cause a problem during 2nd side reflow. There are some MSDs
mounted on the 1st side but both sides are assembled before exceeding
any of the component's floor life. It has been suggested that some level
of bake out should be performed after 1st side cleaning to prevent
potential problems during 2nd side reflow but the push back is that this
adds cost, handling, etc... that may introduce its own associated
problems and is not really necessary.



Thanks again. It is great to have a knowledgeable forum such as TechNet.



Joe






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