The reason brakes squeal is because the pad is vibrating, my father in- lore worked at bindex brakes for about 20 years so I think he would know. That's also why you get a lot of cars now with the thin bits of flat spring steel on the pad this is to absorb the vibration from the brakes pad to stop the squealing sound.
And the other guys are right new pads can squeal to my brand new VE SSV Series 2 Squealed as I stopped before driving it out of the dealer.
One other tip if it's your wheel bearings you will hear a noise all the time when driving, or if it's not that far gone you may only get a slight vibration which starts at about 80ks
If you only hear it when you brake it's going to be the pads.
Could also be a stone stuck between your pad and disk check your disk for a mark or grove if there is a deep grove in the disk the stone could be still there.