In reality, there is no such thing as perfect IR or perfect convection. No matter which system is used, if one does not take the time to develop the appropriate solder profile, changing to a newer machine is not going to solve the yield problem. Also, even after one has developed the appropriate solder profile, if the source of the problem is poor design, poor solder paste, misregistration or misplacement of components, to name just a few, a convection oven or any oven or profile for that matter, is not going to eliminate the problems caused by the other variables. Conveyor speed and panel temperatures are two variables in solder profile development. The solder profile is not only product specific, it is also flux dependent.
Different pastes require different profiles for optimum performance.
So it is important to consult the paste supplier before developing the solder profile. We should also note that panel temperatures for any setting will be very different from the temperature seen on the board and the component leads. For developing the profile, we need the loaded board for which the profile is being developed. We can start with a given belt speed and monitor the top-side board temperature using thermocouples. Most new reflow ovens have built-in thermocouples and software packages to record the thermal profile.