Hello,

We used to bake our bare boards prior to assembly at 60 degree C for 30min.
Recently, several mounted boards have delamination surfacing. One of them has
interesting fact that the delaminations are noticed when the inspector is
checking the fully populated board.

For these boards, the bare boards are baked at 60C for 30min and have BGAs
reflow. The rest of the components are manually assembled 1 day later. However,
the operator did not flag up any delamination until the QC inspector spotted
them when inspecting the fully mounted boards. The delaminations as big as 2cm
in diameter at several locations but at around pads.

I scan through IPC-HDBK-001 and it recommend 3 baking temp and time :
(a) 80C for 18 - 48hrs
(b) 100C for 8 - 16hrs
(c) 120C for 3.5 - 7hr

As our schedule is always very tight, I was told to take (c). My concerns are :
(1) Isn't it that (c) is too near the Tg of the laminate and will have impact?
(2) I interpret the above 3 requirement to be applicable during fabrication
process and not prior to assembly. Pls correct me if I mis-interpret.

On the other hand, I also come across IPC-PE-740 that recommends otherwise for
moisture and volatile removal : 100 - 125C for 2-4hrs.

Now,which temp and time should I adopt prior assembly as both temp in 001 and
740 are close to the laminate Tg (FR4).

For expert opinions will be greatly appreciated.

Regards,
Wee Mei

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