Fault source of a short circuit

[rumpumpel1]

I have a mainboard with a short circuit (approx. 0 Ohm) on the 3.3V rail. As usual, I injected current and observed the mainboard with the thermal camera. Instead of individual components becoming warm, I observed that an area of several square centimeters became evenly warm from approx. 2A.
Has anyone ever seen anything like this? Is it possible that there is a short circuit between two layers of the mainboard? The visual inspection of the mainboard did not reveal any abnormalities.

[reformatt]

Yes, I have had inter layer shorts on quite a few laptops. It most commonly seen when there is carbonisation of the PCB in that area so the layers breakdown and one or more layers short to an intermediate ground plane. Seen it happen on a MAC motherboard with corrosion on a main rail decoupling capacitor. It carbonised the pad and layers underneath causing the main power to be shorted.

But it can also be due to a manufacturing defect when the VIA's are installed. If the VIA carries a lot of current, and the VIA has some level of resistance, then it will generate heat over time (remember that P=I2R). As the laptop ages, the heat from this small resistance will slowly cause damage to the VIA and it's resistance will continue to go even higher over time. Eventually the resistance is high enough that there is sufficient heat generated for the PCB to carbonise around it, causing an interlayer short.

I had this on a Razer R209 laptop recently near the fan connector. 4 VIA's with nothing else around them, no liquid damage, you could see the board was burnt. Main power rail was shorted to the ground plane and I can only assume that was a manufacturing fault.

[rumpumpel1]

interesting, the Wikipedia article about VIA explains it quite well.
These are pictures of both sides of the mainboard.