I am currently investigating a non destructive method of BGA profiling that is reliable. Here are the results of my first test.
Four thermocouples are attached to the same BGA (TOP, SIDE, INSIDE and BOTTOM surface), as pictured below. Conductive aluminium double sided tape is used along with Kapton. A KIC Explorer is the profiler.
To see more on Thermocouple attachment visit my post: http://profilingguru.com/tcs/thermocouple-attachment/
A hole was drilled out to attach the INSIDE TC.
Two tests were run, the first was running the board on the belt followed by running the same board on the chain/tab conveyor.
As you can see the delta for ramp and peak is the greatest, while soak is minimal. The inside TC runs the hottest and the underside bottom TC follows fairly closely the behavior of the inside TC.
This second profile was run on the belt with the same board but for a different BGA. Again we see similar behavior, where the INSIDE and BOTTOM TCs exhibit similar behavior.
This third profile was running the same board and same BGA as in the second example but this time on the chain/tab. Interestingly, all TCs were a good predictor of the INSIDE TC except when getting to the cooling zone. The BOTTOM TC was only a good predictor of the INSIDE TC.