>From the EMPF HelpLine in Indianpolis:

In my experience, the reasons for prebake have usually been the result of
storage or fabrication problems related to the pwb.  If you know that you
have good product coming in the door from the pwb vendor, and the boards are
properly stored, then prebake should not be a requirement for achieving good
quality assembled pwb's.  This assumes that the pwb's are used at a rate
that minimizes the opportunity for moisture absorbtion.  The fabrication of
the pwb's by the pwb vendor must also be monitored to insure that the
opportunities for moisture absortion are held to a minimum.

In the situation described in this request, I would suggest a side by side
comparison of finished quality between prebaked and non prebaked boards.
The quantity of assemblies in the test should be high enough that any trends
or occurances related to time would be observed.

The handling and usage interval of the pwb's are the two most critical
parameters to control.  If these are properly monitored, then there appears
to be no reason that eliminating the prebake cycle from this process should
not yield favorable results.

Pat Kane
Manufacturing Research Engineer
EMPF

At 10:56 AM 5/13/96 -0500, you wrote:
>>X-POP3-Rcpt: crawfoj@ginger
>>Resent-Date: Mon, 13 May 1996 09:12:19 -0700
>>Resent-Sender: [log in to unmask]
>>Old-Return-Path: <[log in to unmask]>
>>Date: Mon, 13 May 96 08:27:53 EST
>>From: "Hollandsworth, Ron" <[log in to unmask]>
>>To: [log in to unmask]
>>Subject: Board Bake
>>Resent-From: [log in to unmask]
>>X-Mailing-List: <[log in to unmask]> archive/latest/4086
>>X-Loop: [log in to unmask]
>>Precedence: list
>>Resent-Sender: [log in to unmask]
>>
>>     We are manufacturing PWBs using SMD, PTH, and Mixed
>>     Technology.  Run rates are relatively high and cycle
>>     time of product flow is relatively fast.  Boards range
>>     from double sided (minimal) to multilayer (most) in
>>     single, half panel, and full panel configuration.  Some
>>     PWBs, obviously see IR, some flow solder, and some
>>     mixed technology both IR and flow solder.  Some parts
>>     are commercialized some MIL spec.  Our plant
>>     environment is somewhat controlled (air conditioned).
>>     Humidity is not high, yet somewhat humidity controlled
>>     (ESD reasons).
>>
>>     We are currently observing no adverse affects at IR as
>>     a result of not baking PWBs prior to IR.  We are
>>     considering eliminating pre-wave bake.  The question is
>>     "What experience can you share from eliminating your
>>     bake cycle at pre-wave." Positive and negative will be
>>     well accepted and appreciated.
>>
>>
>>
>
>          Jack Crawford
>      HelpLine Manager
>              EMPF
>       317.226.5616
>  Visit our homepage at:
>   http://www.empf.org
>
>
>