Organic residue on a pad, at the bottom of a via, or on a contact bump can cause increased contact resistance, decreased contact strength, premature failure of the part and electrical opens. Thin coatings of organic residue are impossible to detect using reflected light illumination. The via structure shown in Figures 13a and 13b illustrates that even under ideal illumination conditions in which the via bottom is smooth, flat, and uniform in color, thin organic residue cannot be visually detected using reflected light. Figure 13a is the white light image of a 200 micron diameter via. Figure 13b is the Mscan image showing organic residue at the bottom of the via. Figures 14a and 14b are similar images for a 60 micron via from a flex circuit.

Organic residue as thin as an incredible 410 angstroms has been detected by the Mscan. Essential to this inspection is the ability to scan non-flat surfaces. Beltronics patented auto tracking system enables detection of extremely small defects on non-planar surfaces at high scanning speeds. The patented technology describing the inspection process is described in the technical section. Figure 16 shows a two dimensional topology map of a non-flat substrate with160 microns between the peaks and valleys.