Hi Werner
I agree that one of the characteristics of the straight-ramp (or "tent")
profile is that there is potential for a larger gradient at peak than with the
classic ramp-soak-spike (since the soak portion allows for a reduction of
gradient prior to the reflow thermal excursion) but the choice is application
specific.  Many applications will be able to attain a low gradient with the straight
ramp profile and a moderate rate of heating (< 2 deg. C/sec) even with the
much tighter process window imposed by the lead-free alloys.  Some more complex
assemblies (in terms of mass and surface geometry) will do better, as you
imply, with the ramp-soak-spike profile.
And for those real "mother" boards, there's always vapor phase !

Phil Zarrow
ITM Consulting
Durham, NH  USA
www.ITMconsulting.org

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