Short answer: Depending on your definition of God, science either can't disprove God or disproved God long ago.
If God is defined as a being who created the universe, then God can't be disproved as God can always remain beyond detection.
However, if God is said to have left certain marks that we can see, marks that uniquely trace back to God, then science may be able to find evidence for or against this God's existence. As a result, modern evolutionary theory challenges the conception of God that created people ex nihilo (or out of dust), and modern brain science challenges the role of God as moral arbiter and so on.
There's some philosophical import to this. This same concept -- that a being otherwise unobservable could be known by traces -- can be seen as a motivation behind theodicy. That is, if there is an omnipotent, omnipresent, omnibenevolent being, then this being should leave a mark on the world -- namely, a lack of suffering. Yet, suffering exists.
Further, what does a lack of evidence mean? What if we postulate the existence of (to use Bertrand Russell's example) an invisible teapot? Would we take the idea of this teapot with the same seriousness as we do of God? Why keep an open mind about God and not the teapot? Are we perhaps revealing a bias towards God?
Then of course scientists have personal beliefs, and some believe in God and some don't. While the personal beliefs of scientists should not matter, some scientists may issue proclamations, perhaps as a result of over-enthusiasm for the methods and power of science or what certain findings imply.