Fast on-line electro-optical detection of wafer defects by illuminating with a short light pulse from a repetitively pulsed laser, a section of the wafer while it is moved across the field of view of an imaging system, and imaging the moving wafer onto a focal plane assembly, optically forming a continuous surface of photo-detectors at the focal plane of the optical imaging system. The motherboard has a motherboard connector extending from a planar surface of the motherboard. Light is emitted onto the object surface region under different illumination conditions, in particular different light incidence directions, and in each illumination condition a sequence S1 to Sn of camera images B is recorded. The inner porous layer has a higher porosity than the outer porous layer.