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Overcoming Challenges to Functional Test
Production Floor |
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Authored By:Craig T. Pynn SiFO Technologies, Concord, CA TranscriptFunctional circuit test of circuit boards and end products in a high volume production environment presents challenging technical, logistic and cost obstacles. Functional circuit test logistic challenges are even more significant when there is a high mix of different circuit types to be tested. It is not uncommon for production lines to routinely have fifty or more active board types, each with a difficult-to-forecast production schedule that must respond to varying customer demands. The demands of high volume production preclude the typical "one-off" functional testers or "product-minus-one" found in many production environments. A universal test system is required. However, most universal testers are typically large and expensive where cycle times may be several times longer than the line rate. Developing and maintaining revision control of application test programs for functional circuit test is a further complicating factor in a high product mix environment. The difficulty of developing a practical functional circuit test system to be used in the production line is exacerbated when the tests must include accurate and repeatable measurement of "outlier" electrical parameters such as very low or very high voltages and currents, and/or low level or very high frequency RF signals. This paper covers the development of a standardized functional circuit test system architecture, combined with fixturing interconnection solutions designed for the rigors of a high-mix, high volume production environment. This solution significantly reduces total cost compared to typical custom-designed functional circuit test systems. The paper also covers how this architectural and procedural approach meets functional circuit test technical, logistic and economic goals by studying the actual functional test of a high-mix, high volume AC driver product, which has more than 50 distinct variations, built in a volume exceeding one million units per year. SummaryFunctional circuit test (FCT) of circuit boards and end products in a high volume (>1000 units per day) production environment presents challenging technical, logistic and cost obstacles that are usually more complex than those encountered at the inspection (automated optical inspection) and the manufacturing process test step (in-circuit test). FCT "logistic challenges" are even more significant when there is a variety (high mix) of different circuit types to be tested. It is not uncommon for production lines to routinely have fifty or more active board types, each with a difficult-to-forecast production schedule that must respond to varying customer demand. The exigencies of high volume production not to mention the economics preclude the typical "one-off" functional testers or "product-minus-one" found in many production environments. A "universal test system" is required. However, most "universal testers" are typically large and expensive, where (1) cycle times may be several times longer than the line takt rate, and (2) complex fixturing and UUT connection requirements that are difficult to modify in line further impede throughput. Developing and maintaining revision control of application test programs for FCT is a further complicating factor in a high product mix environment. The difficulty of developing a practical FCT system to be used in the production line is exacerbated when the tests must include accurate and repeatable measurement of "outlier" electrical parameters such as very low or very high voltages and currents, and/or low level and/or very high frequency RF signals. We have developed a standardized FCT system architecture, combined with fixturing/UUT interconnection solutions designed for the rigors of a high mix, high volume production environment, significantly reducing total cost compared to typical custom designed FCT systems. We have also developed algorithmic programming techniques that have proven useful to minimize overall UUT test time. We will describe how this architectural and procedural approach meets FCT technical, logistic and economic goals by studying the actual functional test of a high mix, high volume AC driver product, which has more than 50 distinct variations, built in a volume exceeding one million units per year. The robustness of our technical test solution will be further illustrated by describing test requirements that included voltage measurements of up to 1200V and current measurements up to 40A. ConclusionsSo, what have we learned? First, that functional test takes on a dizzying array of different and challenging technical requirements. Engineering creativity and a willingness to think outside the proverbial box is needed to meet these challenges. Second, there must be awareness that the realities of the production environment are quite different than those of the development lab. Throughput and environmental ruggedness are mandatory. But perhaps the most valuable lesson is that standardization in as many areas as possible tester architecture, fixture interface and the fixtures themselves, the test software is the most rational and ultimately, cost effective approach to functional circuit test. This means sometimes operating counter intuitively such as adding in an additional test step or being willing to accept the higher price of a standardized test platform over the frequently illusory cost savings of multiple smaller custom-built testers. In the end, achieving a technically competent, logistically capable, cost-effective purpose-built functional test strategy follows a standardized path. Initially Published in the IPC Proceedings |
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