Process optical inspection

Speckle shearing interferometry, or shearography, is a full field optical inspection teclmique that may be used for the nondestructive detection of surface and, sometimes, subsurface defects. Whilst being more sensitive in the detection of surface defects, it may also be considered for pipe inspection and the monitoring of internal conoslon. In contrast, laser ultrasound and other forms of ultrasound, are point by point measurement techniques, so that scanning facilities and significant data processing is required before information on local defects is extracted from any examination of extensive areas [1 - 3]. 

Subsequent to processing, an inspection is made for incomplete bonding, inside dirt, and glass quaUty. In the case of windshields, rigid optical standards must be met, and these must be evaluated for the completed windshield. Extensive test requirements are described in the appropriate codes (11,12,15,18—24), and they include light stabiUty, resistance to optical distortion, humidity, boil test, abrasion resistance, and assorted impact tests. 

Attachment No. 1700.30(H) OPTICAL INSPECTION REPORT IN-PROCESS CONTROL... 

The key point about assessing and defining process and product state similar to the machine operators way, is having objective information about the product quality. In the presented approach, the information from the optical inspection system was used to define characteristic situations based on the profile quality (the kind, distribution and quantity of defects) and the process parameters measured and stored by the automation system. A situation or case is thus characterized, among other things, by the aforementioned profile quality, the kind of profile that is produced, the used rubber-mixture, environmental data like air pressure or humidity, the values and latest progression of physical process parameters hke extruder-temperature, power of microwave heating or speed of conveyor-belts and the countermeasures that are taken by the machine operators. 

The physical size of some of the process-induced defects is beyond the physical resolution and detection limits of the traditional optical inspection techniques. The way in which each of the patterning processes contributes to defectivity in ArF-lithography-based device manufacture is related to the constituent materials in the photoresist and to the interaction of the photoresist with the substrate or ARC. 

Optical inspection has been discussed elsewhere. It is generally applied early in the fabrication process as a yield improvement and data collection tool, not as a means of final product qualification. However, with improvements in resolution, the type of defect that may escape undetected becomes somewhat more limited, and optical inspection is argued as a possible... 

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. 

Unimpeded inspection PCAs that have gone throngh a proper aqneous cleaning process are easy to inspect because there is no flux residue on the surface to interfere with solder-joint inspection by eye or automated optical inspection devices. 

There may be defects that do not show up as faults. Examples are insufficient solder, a misaligned component, a missing bypass capacitor, and an open power pin. Inspection systems such as automated optical inspection (AOI) and automated x-ray inspection (AXI) detect many of the defects and also some of the same faults as electrical test. The definition includes the phrase at the end of the manufacturing process, which is important when compared with potential defect. ... 

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. 

It may well be necessary to adapt an optical inspection system to accommodate the three-dimensional layout of MID process surfaces. Class 2l D MID can be inspected without additional kinematics and adaptation of the optical inspection system. This holds true only if the process surfaces are plane-parallel in the inspection plane of the sensor array. Classes n x 2D and 3D call for changes to the AOI system if the electronic components are widely spaced. This could well mean integrating an extra handling and positioning unit for MID, for example an automated workpiece carrier. 

Figure 6.5, left, shows a typical X-ray image of an MID by way of example. Suitable control and systems technology can extend X-ray processing to automated X-ray inspection (AXI), which can also be combined with automated optical inspection (AOI). 

Fiber-Optic Probes. Fiber-optic probes provide remote sampling capabilities to Raman instmmentation, are stable, and give reproducible signals. Their historical niche has been in environmental monitoring. More recently these probes have been used in chemical process control and related areas such as incoming materials inspection. 

Glass is one of the engineer s most useful and versatile materials. There are many types of glass to choose from to provide a wide range of physical, mechanical, electrical and optical properties for practically every type of environmental condition. The transparency of glass facilitates inspection of process operations and minimises the risk of failure due to unsuspected corrosion, while the hardness and smoothness contribute to easy cleaning. 

In this chapter, the motivations to adopt MLR systems for optical e-beam, x-ray, and ion-beam lithographic systems will be given, followed by a survey of published MLR systems. Specific practical considerations such as planarization, pinhole and additive defects, interfacial layer, etch residue, film stress, interference effects, spectral transmission, inspection and resist stripping will be discussed. The MLR systems will be compared in terms of resolution, aspect ratio, sensitivity, process complexity and cost. 

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