Shala,
We perform a vacuum bake for 6 hours at 200 deg. F. @ 724mmHg vacuum on all
boards prior to rework.  Thick Master Interconnect boards (10-15 layers)
require 16 hours bakeout.  In either case, the "dry" period is good for only
4 days max. if left at room conditions (40-60%rh).  After four days, the
bake must be repeated.  The dry condition can be prolonged day for day if
the board is kept in a dry nitrogen box after baking.

Hope this helps,

Rainer Blomberg
Honeywell - Space Systems
Staff Production Engineer


-----Original Message-----
From: Burdette, Shala [mailto:[log in to unmask]]
Sent: Thursday, February 24, 2000 1:14 PM
To: [log in to unmask]
Subject: [TN] Polyimide Board Rework & Repair


Hello everyone!

Our company is currently considering setting up standard guidelines for
Polyimide Board Rework & Repair.  I have checked the latest IPCs (7711 &
7721), but neither give a clear cut answer to my questions.  I was wondering
if maybe some of you could let me know what procedures you are following or
recommend.

Primarily, we want to know if preheating or baking out a board prior to
rework is required.  If so, what temperature and for how long?  (This is a
component loaded board, so we cannot exceed 85C).  How long is considered
too long out of  "dry" storage before another bake-out is required to drive
off any moisture absorption?  And lastly, does anyone have any diffusion
coefficient data for different types of Conformal Coating (i.e. Conathane
CE-1175)?

Any information would be greatly appreciated.

Thank you!
Shala Burdette

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