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Do you really want to get rid of test costs?

Posted: 15 Oct 2015 ?? ?Print Version ?Bookmark and Share

Keywords:test engineering? failures? repair? test equipment? Penalty?

As a test engineering consultant, I frequently receive calls from clients who want to reduce their test costs. Is this the correct goal and are their test expenditures really excessive? My clients think they want to transform the "expensive test" into a "low cost test." What they really want is satisfied customers receiving fault free products at the lowest possible cost. While test is a factor in the overall cost of delivering good products, so are the cost of repair and the penalty cost incurred from selling bad products.

Wouldn't you love to have no failures and produce the perfect product that would work the first time and every time? In that ideal world, you wouldn't need test and thus no test costs. Because we don't yet live in manufacturing utopia, "No Test" has its own cost in added repair and penalty costs.

Without testing, we have the following alternatives to attempt to deliver fault free products:

Use exhaustive quality controls at each step of the manufacturing process. Because test is out of the equation, all these controls need to be done without test equipment or procedures. Feedback will be from customers but with a time lag while we continue to produce more faulty products, adding further to the cost. If the process fails to produce a sufficiently high yield, the company will not stay in business very long (and how much does going out of business cost?).

Overproduce and compensate customers with a brand new (albeit untested) replacement product. This may satisfy customers in the short term, but not if the replacement product also turns out to be faulty. Not knowing what to expect in terms of quality, you have no idea how much risk you're actually taking. (What if every product going out is faulty, or just every one built on Fridays?)

Use a final screening process whereby the product is turned on before it is shipped. If it looks OK, it's OK. (Yes, I know this really is a test, but will let this one slide because it's such a poor test.) You incur costs with faulty units escaping this process because you'll eventually have to replace them. You also incur costs with faulty units caught by the process. That is, you either have to fix them at a higher cost since you have no test or diagnostic information or else place them in a "bone pile" that awaits a future repair. After you've finally given up on repairing some units, you resign yourself to discarding them, which is becoming a potential hazardous waste issue.

Given some empirical data that you can readily collect from even a few days of production, you can calculate the cost of these alternatives to test, and the lowest of them will be the Cost of No Test. If adding test actually reduces the overall cost of "Test+Repair+Penalty Cost" over that of "0+Repair+Penalty Cost" the difference is a profit and you must call the test expenditure an investment. Investments are evaluated on the basis of their ability to provide a return on investment (ROI). To get a better ROI, you sometimes have to spend more in investment, and test investment is no different.

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