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30 September 1996 Deformation measurements of surface mount assembly under power cycling using optical interferometry
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The reliability of solder joints has been regarded as one of the most critical problems in surface mount technology because of large stress developed at the joints due to thermal expansion mismatch between components and the substrate in operation. uNderstanding the deformation modes of surface mount assemblies and obtaining stress and strain values of joints allow the designer to predict the fatigue life of the solder joints. This study is directed toward a comprehensive evaluation of thermomechanical behavior through 3D deformation measurements of a typical surface mount assembly having gull-wing leads soldered on a printed circuit board by means of laser interferometric techniques. In this paper we describe the application of real-time holographic interferometry and Moire interferometry to measure the 3D formation of the device under power cycling. By combining the measured results of the out-of-plane and the in-plane displacements, together with the temperature distribution of the assembly, the stress distributions of the leads and solder joints were evaluated. It was estimated that the mechanical stress will exceed the yield stress of solder material when the PQFP assembly operates at the rated temperature of 75 degrees C. Then, the deformation of solder joints might change from elastic to plastic.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Kang Ming Leung and W. N. Wang "Deformation measurements of surface mount assembly under power cycling using optical interferometry", Proc. SPIE 2888, Laser Processing of Materials and Industrial Applications, (30 September 1996);

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