Riassunto
Excerpt from A Case-Based System to Support Electronic Circuit Diagnosis
Rapid changes in electronics product and process technology, such as smaller, surface mounted components, higher board densities. And more complex circuitry, have made circuit diagnosis more challenging. With fewer accessible connections and test pads, ih line functional testing can only identify the approximate area or block of components on theboard that is responsible for the malfunction. Detailed diagnosis must be done off-line through extensive probing and measurement.
Each component and connection on a circuit board is a potential defect site, and every site can have several possible defects such as an open or short circuit (due to poor soldering or component misalignment), component malfunction, inherent flaw in the circuit design, placement of the wrong component, or defect in the board's internal wiring. The failure rate of a board containing hundreds of components is, therefore, several orders of magnitude higher than the probability of a single defective component or operation, making testing and diagnosis inevitable even with highly capable placement and soldering operations. Isolating the root cause in such complex and dense circuits is arduous and time consuming. Annual expenses directly related to diagnosis and repair can exceed several hundreds of thousands of dollars even in a medium-sized facility. Work in process at the diagnosis stage and delayed feedback for process control further increase this cost. More importantly, the time and effort required to diagnose a faulty board is highly variable (from a few minutes to over 4 hours) depending on the type of defect, the analyzer's skill, the effectiveness of diagnostic tools, and the incentive and performance evaluation systems. Consequently, testing, fault diagnosis and repair Operations are often major bottlenecks in medium or high volume printed circuit board assembly facilities.
The cost and effort to train technicians is also becoming a significant concern for electronics companies. A new technician requires several months of training and experience with a particular board to understand the Circuit's cause-effect behavior and the potential root causes in its manufacturing process. As product life cycles shrink, the training costs must be amortized over smaller volumes for each board. Diagnosis bottlenecks are especially acute during the critical production ramp-up period following a new product introduction. Capturing market share early is essential for competitive survival in the electronics industry, but production facilities often cannot achieve the necessary rapid ramp-up because yields are low, and analyzers are least productive since they have not had significant experience with the new product.
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