2/4 NL Villian leads again

[maranello11]

Playing 2/4 NL 6-Max on Empire. I have about 600, Villian has abut 400. Im in the CO and raise to 15 with black 77.
Villian calls from the small blind. Seems to be a standard player have not seem much from him.

FLOP: 6 4 3 rainbow. He bets 10. I raise to 40. He thinks and then calls.

TURN: Q completes rainbow. He bets 20.

I know this is a standard raise, but how much. I have seen Villian's lately bet these small bets when out of position to build pots for them when they have a strong holding. I just dont want to put a bet of 120 into the pot and face a re-raise. And I dont want to give him a chance to a cheap draw incase he has AK or something like A5. Seems to be a leak in my game, is this more read dependent, anyone else see this type of play from Villian's.
Thanks