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86 SMT Magazine • June 2016 Since the solder joint area is defined by three plans, the inspection area without the ambient light reflection can now be given by (11). 11 where 12 Figure 5 shows the obtained image after re- moving the ambient light reflection from the initial image. Specular Light Reflection The Phong model allows calculating the specular light reflection based on the knowl- edge of the specular light intensity, the observa- tion and illumination angles and the character- istics of the reflector material (13). 13 The value used in the observation angle po- sition was 90°, and the illumination angles used in the structured light system are given in Table I. These parameters are determined initially and remain constant during the procedure of solder inspection. As in the case of the ambient light reflec- tion, the specular light reflection has three plans corresponding to the red, green and blue components (14). 14 The specular light intensity for each LED light ring is obtained by finding the maximum intensity value of each specular light reflection plan (15). 15 The nShiny parameter is a constant value that depends on reflective material only. Table II shows the nShiny value for the two different solder pastes, with and without lead. With all constants (∅i,∅o,ia,id,is,nShiny) calculated previously for the AOI system, the calculation of specular light reflection Is, will depend only on surface angle ∅s,as shown on (16). 16 Figure 5: Inspection area without the ambient light reflection. Table I: Light Ring Parameters. Table II: nShiny Parameter. 3D SOLDER JOINT RECONSTRUCTION ON SMD BASED ON 2D IMAGES