Assembly inspection Optical

To facilitate maintenance, gas turbines used for aircraft and those modeled after ffiese have a modular design so that the individual components such as compressor, combustor, and turbine can be taken out of the assembly individually. Those gas turbines allow also for a borescopic inspection of their insides by an optical tube with lens and eyepiece. Heavy industrial gas turbines are not designed for borescopic inspection and must be dismantled for inspection and maintenance. Preventive maintenance is very important for gas turbines. 

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. 

Automated optical inspection systems also image only a small portion, or view, of the assembly at a time. These systems normally can use somewhat bigger views than the 3-D solder paste systems because the features being extracted often do not require as much magnification as do measurements of solder paste depositions. However, inspection of components, such as 0402, 0201, and 01005 passive components, or very-fme-pitch deposits, can require the same level of magnification and therefore views as small as the 3-D solder paste inspection systems. 

Examples of optical and SEM inspection of tin-lead and lead-free solder joints are presented before and after exposure to environmental conditions. Assemblies include both conventional leaded and leadless packages, as well as CSP leadless packages. 

Optical inspection, along with nondestructive evaluation systems having finer feature selection capabilities, such as x-ray and C-SAM, become critically important as electronic package/ assembly become more complex, feature sizes decrease, and hidden interconnects such as EGAs are used. X-ray systems have improved signihcantly however they shll have limitations. Many features of area array package as-... 

Lead-free solder has a rougher surface finish and generates a different-shaped fillet. It also is more prone to voids and tombstoning. These and other deviations can require adjustments to commonly used inspection techniques, such as automated optical inspection (AOI). While the results of a National Physical Laboratory (NPL) study confirm that AOI systems can be used to inspect lead-free surface mount assemblies, many defects created by lead-free processes are not visible. The added loss of visual and electrical access due to the growing complexity of PCBAs compounds the problem. 

Implementation of the MID application in series production necessitated the development of a fully automated assembly solution by a manufacturer of special-purpose machines. The 3D placement of the SMDs, the switch elements, and the contact pins is only one of the functions discharged by the system. Others include incoming-goods inspection, electrical testing of the conductor tracks, dispensing the solder paste with optical process monitoring, and final inspection. [116]... 

The test rig employed in this study consisted of a high-pressure cylindrical steel vessel with a length of 1.8 m and an internal diameter of 0.28 m (see Chap. 2). Visual inspection and accessibility of the reactor assembly was achieved via a 50 mm diameter quartz window at the rear flange of the vessel and two 350 mm long and 50 mm high quartz windows at the vessel sides. Experiments were performed in two different reactors. The first reactor was the optically accessible, channel-flow reactor presented in Sect. 2.1 therein, the use of in situ laser diagnostics (Sect. 2.2) allowed for the assessment of the catalytic reactivity of propane on platinum. The second reactor was a honeycomb subscale unit of the desired catalytic combustor (see Sect. 2.3), and was used for the evaluation of combustor performance characteristics. 

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