Why did European scientists become atheists in the Renaissance period?

European's obtained their scientific knowledge in the middle-ages from the Moslems in Spain where they used to go to the Universities there in as much as we go to Harvard,or Oxford.The famous Moslem scientists like Razes,Ibn Sina were also very religious and believed in God.But the European scientists opted to drop the belif in God and became atheists on their return to their country.