Page 16 - Building A Succesful Board-Test Strategy

What Is a Test Strategy? 3

1.1 Why Are You Here?

What drives you to the rather daunting task of reading a textbook on board-
test strategy? Although reasons can vary as much as the manufacturing techniques
themselves, they usually break down into some version of the following:
• The manufacturing process is getting away from you,
« Test represents your primary bottleneck, and
• Test has become part of the problem rather than part of the solution.
The design-and-test process must treat "test" as an ongoing activity. Its goal
is to furnish a clean product to manufacturing by designing for manufacturability
and testability, while encouraging the highest possible product quality and relia-
bility. (Product quality means that it functions when it leaves the factory. Reliabil-
ity refers to its resistance to failure in the field.)
The purpose of manufacturing is to provide:
• The most products
• At the lowest possible cost
• In the shortest time
• At the highest possible quality

Debate has raged for years over the relative importance of these goals. Cer-
tainly, test people often maintain that quality should be paramount, while man-
agement prefers to look first at costs. Nevertheless, a company that cannot provide
enough products to satisfy its customers will not stay in business for very long.
Suppose, for example, that you have contracted to provide 100,000 personal-
computer (PC) motherboards over some period of time, and in that time you can
deliver 50,000 perfect motherboards. Despite superior product quality, if you
cannot meet the contract's volume requirements, the customer will fly into the arms
of one or more of your competitors who can.
Using similar reasoning, the purpose of "test" is to maximize product
throughput, reduce warranty failures, and enhance your company's reputation—
thereby generating additional business and keeping jobs secure. We get there by
designing the best, most efficient test strategy for each specific situation.

1.2 It Isn't Just Testing Anymore

Therein lies part of the problem. What is "test"? Unless we broaden the
concept to include more quality-assurance activities, verifying product quality
through "test" will soon approach impossible.
Inspection, for example, is usually considered part of manufacturing, rather
than test. Simple human nature suggests that this perception tends to make test engi-
neers less likely to include it in a comprehensive strategy. Yet inspection can identify
faults—such as missing components without bed-of-nails access or insufficient solder
that makes proper contact only intermittently—that conventional test will miss.