Optical Interaction
Deviation of light rays from their original path when they encounter an irregular surface or a particle determines how an imaging system perceives the features of a board. This light scattering occurs because the microscopic roughness of the copper or the matte finish of the solder mask redistributes the incoming energy in multiple directions. Automated optical inspection systems must account for this behavior to avoid generating false alarms or missing genuine defects.
Inspection Accuracy
High-resolution cameras rely on controlled illumination to minimize the negative effects of light scattering on the clarity of the image. When the light hits a smooth, reflective trace, it bounces predictably, but a scratched or oxidized surface will cause the light to disperse. This dispersion can blur the edges of a feature, making it difficult for the software to measure the exact width of a conductor or the position of a component.
Advanced multi-angled lighting arrays help to normalize the reflection and improve the contrast between the board features and the background.
Surface Texture
Advanced algorithms filter out the noise created by these random reflections to focus on the geometric properties of the circuit. Controlling the angle and the wavelength of the light source can help to mitigate the impact of light scattering on the inspection results. Different materials like gold or tin-lead require specific lighting configurations to ensure the camera captures a clear and high-contrast image.
