Assembled board testing Defects

Defects are most often detected by visual inspection or automated optical inspection (AOI). Other means of nondestructive evaluation (NDE) include electrical testing, x-ray inspection, and ultrasonic inspection. The preferred NDE inspection technique for BGA and CSP solder joints is x-ray inspection. Automated x-ray inspection equipment is often placed directly into the assembly process line for circuit board products having a large number of area-array components. 

The 2D x-ray systems are very effective in testing single-sided assemblies. With the use of a sample manipulator, an oblique view angle enhances inspection of both single- and doublesided assemblies with some loss of magnification due to increase in distance between source and detector. Experience is needed in discerning between bottom-side board elements and actual solder and component defects. This can be very difficult or impossible on extremely dense assemblies. As discussed previously, certain solder-related defects such as voids, misalignments, solder shorts, etc. are easily identified by transmission systems. However, even an experienced operator can miss other anomalies such as insufficient solder, apparent open connections, and cold solder joints. 

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