Page 33 - Building A Succesful Board-Test Strategy

What Is a Test Strategy? 19

unfavorable conditions without breaking down. Service people's experiences can
help designers make new products more reliable.
For companies whose manufacturing operations are half a world away from
design teams, concurrent engineering makes the transfer of responsibility much
smoother. Disk-drive manufacturers often develop their boxes and perform early
production in their own country, then send the entire package to Asia (for example)
for high-volume production. The single biggest impediment to this arrangement
is a lack of communication across many time zones and thousands of miles. If
manufacturing and test engineers participate in the design, the Asian side of the
operation can become relatively self-sufficient.
Picture a Texas company with a manufacturing facility in south Asia running
30,000 boards a day. The Asian arm must be capable of dealing with most problems,
from the trivial to the fairly serious, independently. Phone calls, faxes, and e-mails
could take days to achieve results, during which time the production line is idle or
showing unacceptable quality levels. If a stateside engineer has to hop an airplane
to Asia to address the problem, delays get much worse and costs skyrocket. Unfor-
tunately, a problem with the design itself may necessitate such drastic steps.
Perhaps the least disruptive time to introduce concurrent engineering into an
existing facility is during new-product development. Extending the practice to
other product lines can occur gradually later. The first step must document the
capabilities and constraints of the existing manufacturing process. Eliminating
redundant or superfluous operations and optimizing what remains represent a
good beginning. Unfortunately, this step can be very difficult. Some organizations
do not fully understand their manufacturing processes because the processes
evolved over long periods and follow no master plan.
As stated earlier, one way to reduce the impact of increasing product com-
plexity on test is to take advantage at each step of information that previous steps
have generated and to avoid looking for faults that previous steps have already
found. The principal drawback to this approach, however, is that test-program-
generation tools often cannot automatically know what faults or fault mechanisms
to ignore. Therefore, engineers must allow the tools to generate complete test pro-
grams and eliminate redundant sections later or generate the programs manually—
neither alternative being particularly attractive. Fortunately, new tools are emerging
that keep track of which test-and-inspection steps identify which fault types. These
tools, properly implemented, can drastically reduce test-generation efforts as well
as test times without sacrificing product quality.
Designers must be sure that CAD/CAE information transfers easily into
manufacturing and test terms, reducing data-translation times and minimizing
transcription errors. In addition, design requirements must not include specifica-
tions that manufacturing or test activities cannot achieve.
Part of the concurrent-engineering effort must include statistical process
control (SPC), an online technique for determining whether the process is likely to
create high-quality products and whether quality problems result from consistent
process failures or random variations. Statistical process control is discussed
further in Section 1.9.