Page 59 - Building A Succesful Board-Test Strategy

What Is a Test Strategy? 45

personnel may already have expertise with particular tester types, managers may
be reluctant to experiment with new vendors or test technologies. Managers may
also feel pressured to include surplus test equipment from maturing, waning, or
discontinued manufacturing lines rather than make new capital purchases.
Adding a product to an existing product line may require conforming to
an established test strategy. Although slight tactical modifications may be possible,
in this circumstance the range of alternatives will likely be quite limited. Product
test may have to use excess capacity from existing equipment. Any new equipment
may have to conform to what is already on the factory floor. Test engineers
will have to justify carefully any requested changes using economic or quality
criteria or both.
Enhancing existing processes rather than introducing new products usually
occurs either because too many or too few products on the factory floor are failing.
Adding inspection or manufacturing-defects analysis, for example, may minimize
the number of simple failures that an in-circuit tester must catch. Similarly, intro-
ducing a functional tester may reduce or eliminate failures at system test and can
minimize the chance that a faulty board will escape into the field.
As a product matures, a manufacturing process may improve to the point
where early test steps, such as manufacturing-defects analysis, no longer find many
problems. An economic evaluation may show that the number of failures identi-
fied at that step does not justify equipment depreciation, labor, facilities, and other
costs. Transferring the equipment to a new product or even to another facility
might prove more cost-effective.
Based on the foregoing, a test strategy can include any of the steps outlined
in Figure 1-14. Few manufacturing operations would include them all. Incoming
inspection or vendor test verify bare boards or components. Prescreening can mean
an automatic shorts-and-opens test, or it could indicate some form of inspection
or manual test. The term simply indicates an effort to get out obvious problems
before the next test step, even if that step is as simple as manufacturing-defects

Possible test steps
*Incoming inspection or vendor test
*Prescreen
*In-circuit or manufacturing-defects analyzer
*Board-level burn-in or other ESS
* Functional or performance
*Hot mockup
*System burn-in
* System test
*Field test

Figure 1-14 A test strategy can include any of these steps. Few manufacturing
operations would include them all.