I don't have any practical examples of what happens if paste is left
sitting for long periods before placement, but with my CEM, we work on the
practice that all components must be placed within one hour. Longer than
that, the flux volatiles have sufficiently evaporated off that wetting
action is affected.

The actual time one can bank on before wetting action is affected may
depend on the particular solder paste you use and the acceptability
criteria of the finished product, but I would guess that 1 hour is probably
the max for most pastes. Just my opinion, but hope it helps.

Peter



Michael Bell <[log in to unmask]>     31/07/2002 12:26 PM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to Michael Bell

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: [TN] Paste sit time








Hi all,

Has anybody got any idea on how long it takes for paste, that has been
stenciled onto a PCB to start and degradate.  Our planning department is
trying to suggest we use one printer to feed two lines and I have had
little
success in advising otherwise.  It would basically mean that pasted PCB's
would sit for 10-60minutes before placement.  I have advised that this is a
bad idea, but I just need some form of information to back this up.  Has
anyone had any experiance in this???  Any information would be appreciated,

Cheers

Mike

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