Page 64 - Building A Succesful Board-Test Strategy

50 BUILDING A SUCCESSFUL BOARD-TEST STRATEGY

Figure 1-18 Control charts show process behavior over time, (a) Lot mean values over
time, comparing them to a universal mean or process specification, (b) The range of
individual measurements for expensive or low-volume products. (Oakland, John S., and
Roy F. Followell. 1990. Statistical Process Control—A Practical Guide, 2nd ed., Heinemann-
Newnes, Oxford.)

calibrate, adjust, or change the process. Requirements for SPC will also determine
some of the factors affecting test-strategy choices. Figure 1-19 presents a sample
technique for applying SPC to developing or improving an existing manufacturing
process.

A test strategy consists of all the steps that occur at any process stage that
help to ensure a quality product. Planning a strategy begins at product inception
and does not end until the last piece is retired. Many important test-strategy
decisions relate only indirectly to test activities.
Creating a successful strategy requires thoroughly understanding the product,
the manufacturing process, and the intended customer. Choice of specific strategic
elements depends on many interrelated factors, including who will perform
manufacturing and test, expected board-failure rates, likely fault spectrum, and
company size.
Throughout the planning stages, test engineers and engineering managers
must balance technical requirements with expected costs. A project's costs depend