So in general, the theory is more copper for a pad or trace will increase some level of self-inductance in the trace. Even though there is no “coil” per-say, it can still produce some level of inductance that could potentially change impedance values thus affecting EMI radiation or absorption. A through hole component has much higher levels of inductive coupling and inductance in general. Other forms of SMD devices with much larger pad area will produce more inductance in theory. So smaller pads (as small as you can go) is generally a good idea, but you are potentially looking at more complex issues like certain grounding practices and whatnot. There are a lot of variables here, but BGAs in general I can imagine have certain problems because the multiple pins are so close to each other. I think people are saying in general, compared to through hole or larger devices, SMD devices have much smaller levels of inductance considering pad size and trace size. I don’t have super detailed info on the whole process, so it is definitely more of an Engineering issue here.
