It is sort of a self answering question if you come in from the solder paste angle.
First....start gathering data. Check every day, or every new paste jar, for: Storage conditions (temp), paste expiration date, ambient temp and humidity where you are using the paste, warm up time, and a viscosity check. Maybe even some test print data. (SPI)
You might be able to start correlating the data against your soldering defects. Over time you may notice trends, for example, whenever it is warmer and more humid than normal, you might start to see more solder balling on the board. Things similar to that. The assumption here, of course, is that the paste is the issue for your defects.
From the other side, you might look at the defects from a process viewpoint. Solder balls are caused by X, or Y, or Z in your process. Eliminate those major things right up front.
In short, if you are taking good care of your solder paste, it should take pretty good care of you. If you don't take care of your paste, you could be chasing defects, (and collecting data)from here till sundown.
Hope that is of some help 'hege
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