NEMI's Test Strategy Project Releases Cost Model that Allows PCA Manufacturers to Compare Costs of Alternate Test Strategies


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Herndon, Va. — The Test Strategy Project of the National Electronics Manufacturing Initiative (NEMI) has released a manufacturing test strategy cost model designed to help printed circuit assembly (PCA) manufacturers determine the financial impact of selecting a particular test strategy.

The model, which uses an Excel-based spreadsheet format, is intended for use on post-reflow PCA test strategies. It is available to industry (free of charge) on the NEMI Web site at www.nemi.org/projects/TSCM/test_strat_cost_model.html.

The NEMI Test Strategy Project was organized to address the loss of physical access and fault coverage at in-circuit test (ICT) caused by the physical space constraints of increasingly dense interconnections and packaging designs. Project activities were organized into three working groups: test coverage analysis, test vehicle analysis and test strategy cost model.

Reduced fault coverage, combined with limited diagnostic resolution at ICT and functional test (FT), can lead to excessive debug times. Electronics manufacturers are finding that they can no longer use a single method of test for PCAs and are increasingly combining ICT with AOI (automated optical inspection) and AXI (automated x-ray inspection) techniques. However, it is often difficult to know which method — or combination of methods — will provide the best results.

Six companies participated in the test cost model project team: Agilent Technologies Inc., Delphi Delco Electronics Systems, HP, Intel Corp., Solectron Corp. and Teradyne Inc. The cost model they developed estimates the cost of finding and repairing manufacturing assembly defects using various types of test and inspection strategies. Users of this model should be able to define the potential advantages and disadvantages of each test technique, and to understand the impact of removing test stages vs. sampling strategies vs. 100 percent inspection or test methods.

The NEMI test strategy cost model is intended to enable companies to make trade-off analyses and decisions based on the financial impact that a strategy may have on an organization. The model has the ability to compare two different PCA test strategies and, for each strategy, provide cost, yield enhancement savings, defects escaping out of the strategy, DPMO or yield for each test stage, ROI (return on investment) metrics and time-to-market savings.

Several cost variables are considered in the model, including equipment, maintenance, scrap, repair and field return costs. To determine the ROI, the tool uses the initial investment, payback, net present value and internal rate of return calculations. For the time-to-market analysis, investments in R&D, cost of goods sold (COGS), sales and marketing, and general administrative costs are factored into the equation. A detailed user's guide (also available on the NEMI Web site) walks users through all of the steps and the inputs required for the calculations.

The output of the model provides a description of the yield and defect levels achieved at each test stage, a summary of costs, a graphical cost comparison of the strategies, ROI metrics and time-to-market savings.

The National Electronics Manufacturing Initiative's mission is to facilitate leadership of the North American electronics manufacturing supply chain. For more information, visit www.nemi.org.

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