Hi,

We have received some handling instructions from our board supplier, it
said prebake prior to assembly 4 hours at 130?C, between the first run and
the second run the boards should be stored at a temperature of 80?C. Since
we store our boards in a oven with a temperature of 30?C this would mean we
need three ovens.
(1) Is this a normal procedure for everyone
(2) or can we store our boards at 30?C between the first and second run.
(3)  is there a maximum time for the boards out of the oven (first run)
until assembly (reflow_

I did find the following table on the net, but this is only for one run.

RECOMMENDATIONS FOR PRE BAKING OF PCB's BEFORE SOLDERING

Rigid and Rigid/Flex PCB's FR-4 and Polyimide:

PCB's up to 1.0 mm thickness: minimum 2 hours at 120? C
PCB's up to 1.8 mm thickness: minimum 4 hours at 120? C
PCB's up to 4.0 mm thickness: minimum 6 hours at 120? C

Rigid and Rigid/Flex PCB's with Polyimide/Thermount(r):

All PCB thicknesses: minimum 6 hours at 135? C

Dwell time between baking and soldering is depending on the storage
conditions.
At 50 % relative moisture the recommended time is max. 8 hours.
After baking the PCB's can be kept in vacuum or in an oven at 35?C, which
will increase the dwell time.




Hilbrand




Hi Tech Net,

In the near future we will start flow production of flex-rigid boards. The
boards are going to be double-sided smt so we will have two runs on our
production line. We use an oven for storage with a temperature of 30?C. I
have read that we should prebake the boards at 130?C four hours before
production.

Since this is a double-sided board I would like to know if there are there
any requirements for storage between the two runs.

Can anyone share his or her experience on the subject?

Thanks in advance.

Hilbrand

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