I can put 1.4A through a 28Ga wire, and that's less than thirteen thousandths in diameter, or roughly two or three times the diameter of a black human hair! I don't know offhand what the current thickness of board traces is, but I would guess they have at least that cross-sectional area, and therefore at least that current capacity...
Not sure if I've read your wording right there Bilbat..

I've used 0.22mm(squared) 7/0.22 which is much thicker than a human hair and is rated at 1.4amp for internal equipment "hookup".

Also Motherboard PCB's use a multilayer approach, so you might not be able to see the "Print" (copper traces) that are being utilised anyway.

The Print "sandwich", is often formed like:-

Signal
Supply
Signal
Signal
Ground
Signal