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Advances in AOI and AXI Result in Increased Quality and Speed
December 31, 1969 |Estimated reading time: 5 minutes
Vast improvements in both automated optical (AOI) and X-ray inspection (AXI) result in simultaneous speed and depth of inspection, and a combined system can improve yields and lower defects.
By Paul J. Handler
AOI and AXI advances are ongoing and proceeding at a pace that may catch the average electronics manufacturer by surprise. For example, AOI is much faster these days up to in-line speed. Additionally, the old tradeoff of speed vs. depth of inspection is gone because now one may have both. Similarly, in AXI, technological advances have improved performance and speed vastly. Combined AOI/AXI systems can provide the best of both worlds, making these technologies key allies in the drive for higher yields and lower defect levels.
Figure 1. Soldering defects such as insufficient solder, solder wicking or poor wetting can result in defective joints.
Applying AOIAOI systems are, in simplest terms, image-processing systems. An AOI system's cameras identify the characteristics of a good solder joint. The system registers a defect when the solder joint under inspection does not conform to these characteristics sufficiently. Naturally, for this process to be acceptable for a manufacturing production environment, the process must be fast, accurate and automatic. AOI systems are integrated into manufacturing lines as standalone units or as inspection modules, and can operate using visible light or X-ray analysis. In electronics manufacturing, AOI is used in solder paste print analysis (SMT assemblies, for example) as well as the inspection of finished solder joints or connections in a post-soldering capacity (Figure 1). As with so many different technologies, greater speed often is obtained at the cost of accuracy, and vice versa. With AOI, the price of increased speed and flexibility used to be loss of depth of inspection, (i.e., at higher speeds one may detect gross defects, but finer ones may escape the system's scrutiny). This tradeoff, however, is no longer acceptable in a global manufacturing environment desiring zero-defect levels. One solution to the speed vs. depth of inspection tradeoff is the use of multiple high-performance sensors. These give the AOI system the ability to combine high speed with full-depth, high-resolution printed circuit board (PCB) inspection. This includes not only solder joints but also the assemblies themselves (missing/misplaced components, loose or skewed components, etc.) as well as solder paste prints. It also is possible to add or subtract sensors depending on the speed and depth of inspection required. In an AOI system, these sensor modules provide both angular and orthogonal views. Camera resolutions between 5 and 20 μm per pixel allow effective inspection of fine-pitch components as well as standard-pitch SMT and through-hole. Various inspection window types facilitate soldered connection inspection across the entire spectrum of standard components. A graphic MFC-based user interface facilitates program optimization. A graphic template editor gives the user the ability to expand and modify the inspection template library.
Mega-pixel technology dramatically increases inspection speed because it increases resolution (e.g., up to 1,300 x 1,024 pixels, yielding nearly four times the information provided by conventional CIR cameras). This reduces analysis time by up to 75 percent, satisfying the requirements for electronic production with continuously decreasing line cycle times.
Figure 2. Defective joints can be detected quickly and readily using AOI systems.
Alternately, the higher pixel count can be used to increase image resolution, thereby guaranteeing high defect recognition reliability even in the fine-pitch range (Figure 2). Additionally, the ability to add capability because of modular design and flexibility is key to increasing inspection speed without sacrificing depth of inspection. For example, in some systems, a sensor head can be equipped with up to 12 new generation sensor modules, operating in parallel, to achieve in-line inspection speeds at optimum quality.
X-ray BenefitsAOI and AXI work hand-in-hand, and often are combined. The benefits of X-ray technology for seeing "inside" components, solder connections, etc. are well known; however, continuing improvements in X-ray technology not only maintain X-ray's relevance in the world of ever-changing electronics technology (and thus challenges), but also make it an even more powerful tool and ally in the struggle for highest yields with fewest defects.
Microfocus X-ray SystemsNew microfocus X-ray inspection systems offer powerful microfocus X-ray inspection capability combined with automatic failure analysis to bring nondestructive inspection to the early stages of the electronics manufacturing process. This helps boost yields by lowering reject rates, solving process problems upstream and maintaining an optimized process. Such systems are capable of providing fully automated inspection of electronic components. For example, one may detect glue defects in surfaces with different material depths (shading). It also is possible to execute range measurements and detect predefined structures (pattern recognition). These systems can be combined with a vision inspection/repair station, creating a powerful off-line inspection center that coordinates defect data and enables paperless repair.
TAF Improves X-rayA significant improvement in X-ray inspection technology, which has been implemented universally on some machines since the beginning of 2001, has been true auto focus (TAF) technology*. TAF ensures optimum image quality under all circumstances, instead of resorting to stored factory curves, as was necessary in the past. Combined with automatic start-up features and automatic centering already available on some equipment, TAF technology provides the convenience of a closed X-ray tube with the specifications and possibilities of open microfocus tubes.
Combining AOI and AXISystems already are available that combine classic visible light inspection with microfocus X-ray inspection technology to create a powerful inspection tool that can detect both visible and hidden defects. Such systems are designed for automatic inspection and verification of single- and double-sided circuit boards, for reliable inspection and quality control of hidden areas, components, and solder joints. Advanced package designs and circuit assembly configurations that have concealed areas, connections and components are becoming more commonplace. These hidden connections often cannot be inspected reliably using traditional optical inspection alone. With the combination of X-ray and visible-light pictures, all typical faults in surface mount devices, ball grid arrays (BGA) and plated through-hole components can be detected in one inspection operation.
The High-mix Challenge During the next year (and beyond), electronics manufacturers are going to be faced with an increasing volume of high-mix inspection applications. This means BGAs, SMT, wavesoldered through-hole products and more, often with multiple technologies combined on the same board. This growing challenge will place increasing demands on the flexibility of AOI and AXI systems. The challenge to makers of AOI systems will be to provide inspection systems even with combined AOI/AXI technology that can accommodate this varied product mix with speed, precision, depth of inspection, reliability and flexibility, while maintaining a reasonable product footprint.
- Developed and implemented by Viscom AG.
Paul J. Handler, vice president of N.A., may be contacted at Viscom Inc., 3290 Green Point Pkwy., Suite 400, Norcross, GA 30092; (678) 966-9835; Fax: (678) 966-9828; E-mail: Ph@ViscomUSA.com.