Earl,

Do you find the bottom side temperature of 250C to be consistent across all
the rework stations you mentioned?  I'm curious, because I have an SRT unit
and have been having some difficulty with some large TI DSPs with attached
heatsinks.  I've been working with 220 - 230.  Based on your experience, do
you think 250 might be something I should try?

Thanks,

I just went to 250 first out of frustration with large thermal masses as high layer
count MLB's and large devices. Then, I discovered how well the settings worked.
Within the first 80 seconds, I ramp the bottom side heater (750W, 3 element heater -
found no need to go to the 1200W type) to max (remembering it is 1.5" below
the board's bottom) and never look back.

Simply, I just want bottom heat input providing equillibrium to avoid thermal shock. I really
expect little difference in top side reflow process management (on a 16 layer board
I see abouy 160 -180 C as a result on the top side at reflow).

I remove heat sinks whenever possible. If glued, what can you do but replace the
entire device assembly - re-attaching the heat sink after rework.

Also, If not previously mentioned before, I allow the top side heater nozzle to board surface spacing
to range from 60 to 120 mils (SRT) preventing the board from being an air dam. It
provides, as I'm sure you're aware, significant air flow and heat improvement throughout
the BGA's ball and solder joint structure ensuring more effective reflow nearly 100% of
the time provided solder paste or paste flux is used. Again, no liquid flux please.

Enjoy,

Earl Moon