Hi Ap,

In point of fact, it is a fortuitous artifact of the Infrawave oven I use that the top and bottom elements heat disparately (one set appears to be ceramic, the other quartz). Or perhaps it was done intentionally by the designers. In either case, the two different temperatures seem to create circulation via thermal currents of the disparately heated air masses, resulting in more uniform heating.

I haven't measured it, but from memory I can tell you that once my solder joints begin to reflow, they all reflow within a window of seconds (approximately 10 or so). For me a typical board dimension is approximately 6".

I'm sorry, but I haven't tried to do any BGAs. I don't have any xray equipment, nor do I plan to get any. In my case, I've just made a point of avoiding BGAs altogether. That said, I will say this. I don't see that BGAs would be any more challenging in my oven than in any other. Make the dwell (or "soak" if you prefer) and reflow periods as long as you can and then measure the result.

Good luck,

Joe