Current challenges in automated robotic breast ultrasound (US) acquisitions include keeping acoustic coupling between the breast and the US probe, minimizing tissue deformations and safety. In this paper, we present how an autonomous 3D breast US acquisition can be performed utilizing a 7DOF robot equipped with a linear US transducer. Robotic 3D breast US acquisitions would increase the diagnostic value of the modality since they allow patient specific scans and have a high reproducibility, accuracy and efficiency. Additionally, 3D US acquisitions allow more flexibility in examining the breast and simplify registration with preoperative images like MRI. To overcome the current challenges, the robot follows a reference- based trajectory adjusted by a visual servoing algorithm. The reference trajectory is a patient specific trajectory coming from e.g. an MRI. The visual servoing algorithm commands in-plane rotations and corrects the probe contact based on confidence maps. A safety aware, intrinsically passive framework is utilised to actuate the robot. The approach is illustrated with experiments on a phantom, which show that the robot only needs minor pre-procedural information to consistently image the phantom while relying mainly on US feedback.