Machine vision plays an important role in automated assembly. However, present vision systems are not adequate for robot control in an assembly environment where individual components have sizes in the range of 1 to 100 micrometers, since current systems do not provide sufficient resolution in the whole workspace when they are fixed, and they are too bulky to be brought close enough to the components. A small-size 3D vision system is expected to provide two decisive advantages: high accuracy and high flexibility. The presented work aims to develop a 3D vision sensor easily embedded in a micro-assembly robot. The paper starts by a screening of 3D sensing methods, performed in order to identify the best candidates for miniaturization, and that results in the selection of the multifocus principle (which elegantly avoids the depth of field problem encountered for example in stereo vision). Here, depth is measured by determination of sharpness maxima in a stack of images acquired at different elevations. Then, it presents a preliminary system configuration, that delivers images of a 1300×1000 micrometers field of view with lateral resolution better than 5 micrometers and vertical resolution better than 20 micrometers. Finally, future steps in development of a real-time embedded multifocus sensor are presented, with a discussion of the most critical tradeoffs.