My build configuration -

     2300kv cobra motors
     20a BeLhi opto esc
     Cc3d flight controller.
     Cheap 250 carbon fiber Chinese frame
     Zippy 2200mah 45c lipo battery

The only problem I m facing is that sometimes after a good 3 min flight time the quad just falls off from the sky. I don't know if the ESC don't match with the cobra motors or the flight controller is not able to handle the motors. Other than that it just flies great!

What's your max Amp rating of your Motor? Your esc should be having higher amp rating. And does the esc or motor get hot?

No it doesn't get that hot. Not the ESC nor the motor. But it does get a little heated up. The maximum continuous current for my motors are 17 amps.

Are my esc's too low on the quality? Or do I need to upgrade my FCB?

Your escs are fine, try testing your quads without props on and tell me whether it happens when not flying.

I also run a similar configuration but with 30a blheli_s ESC and 210 frame, never faced such issues.
From my testing continuous 10 mins of run, the temperature of any component never raised above 100~F.
2300KV motors i use, maximum load current is 19.2A. As per experts here, in realty this can be little higher. That's the reason I went for 30A ESC to get some breathing space.

What kind of props do u use?

N I guess my flight control board is faulty going to change the FCB let's see if I face the problem again.

It maybe due to your fc or your firmware.