IPC-7530 "Guidelines for Temperature Profiling for Mass Soldering Processes (Reflow & Wave)"
As you observe, the temperature you measure will depend on what you are measuring. For instance: * Hottest temperature in the oven - air in the oven * Hottest spot on the board - PCB laminate * Coldest spot on the board - largest component or a ground plane.
R Prasad talks about "Bandwidth of Profile". Where in addition to meeting the shape of the profile, the oven settings must also show a narrow band width (5*C to 10*C). The band width is defined as the total temperature difference across the board in any given zone. The tighter the bandwidth, the more consistent is the yield. If the shape of the profile does not meet the desired shape or if the bandwidth is too wide (more than 10*C), adjust the panel settings.
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