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Advancing Microelectronics • Volume 29, No. 5 • September/October, 2002
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Considering AOI?
Here’s what it might do for you:
It’s obvious that IBM has learned to use its AOI systems productively and profitably. However, many organizations now using manual inspection systems (people and microscopes) could also benefit from this technology to help increase yields, enhance quality, lower raw material use and labor costs, speed throughput, and improve process efficiencies.
AOI systems used for production of ceramic packages (MLCCs, HTCCs, and LTCCs, for example) are ideal for inspecting - and documenting - defects on laser drill vias, conductor/resistor lines, missing, clogged, or misaligned vias, shorts, smears, opens, pattern misalignment, circuit contamination, voids, bumps, and other imperfections.
In general, yield deterioration correlates directly with increased package densities. For example, single layer circuit processing typically exhibits yield rates as high as 95%; yields would be reduced to about 60% with ten layer circuits. That number could be increased significantly with AOI technology (see Figure 2 - Yield deterioration due to layer count). With higher density packaging technology being developed constantly, yields - along with reliable performance and lower costs - will become even more important. These characteristics are direct functions of accurate inspection procedures which ultimately lead to lower processing costs and higher circuit reliability.
The ability that AOI provides to precisely locate defects as a result of process variations or other imperfections in the production cycle also become more important as costs for labor and materials increase. And when circuits are mass produced, AOI helps add scheduling efficiency to eliminate production downtime and thus reduce costs as well. When you consider return on investment (ROI) you could easily see a payback period as short as 3 weeks in some applications. Using statistical process control (SPC) techniques, AOI equipment can provide precise characterization of process capabilities with unbiased feedback to the user as well as automated data collection.
AOI systems similar to those used by IBM can detect defects with resolution to .002” including voids, vias, shorts, contamination, bleeds/smears, etc. They also can measure conductor/resistor line widths and area ratios, print/via alignment and diameter, and print/tape stretch, vital characteristics for producing quality circuits at highest possible yields.
When considering AOI systems, you should also look into their data collection capabilities with regard to report generation and formatting structures to document defect data on location, size, measurements, registration, line width, etc. Accuracies should be programmable to minimum print/via size and should typically be .001” with other programmable tolerances possible to meet changing processing requirements. Also consider the size (footprint) of the AOI equipment, since it most likely must fit into an existing circuit process line. Simplified setup time (with minimum downtime) and low maintenance are other issues to think about.
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