In a message dated 4/8/99 1:19:50 PM Pacific Daylight Time,
[log in to unmask] writes:

<< Guys (and girls),

 Can anyone tell me whether or not polyimide boards need to be pre-baked
 before processing thru nitrogen reflow for solder melt?  We are doing it,
 which of course means added expense.  Is it really necessary?  We bake at
 110 C for four hours.  Is there evidence which suggests that it is
 necessary.
 Thanks for any replies,

 Bill Mengers
 Northrop Grumman Corp.
 Baltimore, Md. >>

Hello Bill!

      I can't think of any reason that you would HAVE to bake your boards
before processing. From my experience, I would bake boards if I were having
problems with entrapped moisture that outgases during wave solder giving me
blowholes, voids, etc..

      But even then, I wouldn't do it as a matter of course. The way I would
do it is; say I'd start waving a lot of PCB's, and if on the first few I see
blowholes and whatnot, I'd stop waving the assemblies, and then roll the
carts into a burn-in room to stay for about 3-4 hours to get rid of the
moisture. If I had a history of the FAB's being full of moisture from a
certain vendor, then I might bake them as a standard procedure until I
started getting boards that didn't.

      Bottom line in my opinion, you should get boards that are ready to rock
and roll as soon as you get them...you shouldn't have to bake anything unless
you're having some sort of problems. Baking increases the oxidation of your
solderable surfaces and may give you other problems...don't do it unless ya'
hafta...

-Steve Gregory-

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