Holographic Inspection Of Printed Circuit Board

Application of real-time holographic interferometry in the nondestructive inspection of electronic parts and assemblies

“…Enhancing the interaction of the stress with the defect improves detectability: the optimal method of stress application causes the greatest amount of distortion arising from the defect and the least amount of distortion to the normal surface contour. Fortunately, there are several good methods for making subsurface defects visible under holographic scrutiny, including thermal, vibrational, and pressure-induced stressing methods: 1) Thermal Stressing -This method involves raising or lowering the temperature of the part to induce a thermal expansion or contraction. Voids or debonds below the surface will exhibit different rates of heat transfer resulting in different rates of thermal expansion or contraction than the surrounding material, producing visible anomalies in the interferometric fringe pattern.…”

“…Two sensitivity enhancement techniques were adopted for use in this study: 1) Phase shift interferometry (PSI): PSI is commonly associated with quantifying interferometric data and makes use of the interferometry equations. Using PSI, a solvable set of independent equations is produced by phase shifting the argument of the original equations.…”