7.2.2 Vendor and Device
Major factors to consider when implementing a PMP is the
evaluation of vendors and the selection of components. It is imperative that
engineers select and use components from manufacturers in which they have
confidence. This confidence can be attained either empirically through
adequate past performance of the part manufacturer, or from verification that
the manufacturer is indeed producing high quality parts. The latter can be
achieved via evaluation of the part manufacturing processes through testing
and subsequent data analysis.
To ensure the supply of adequate parts, both vendors and
subcontractors must be effectively managed. A procedure is needed in which
each vendor/technology is evaluated, certified and qualified in a
cost-effective manner. Traditionally, this procedure was to test all devices
and audit all vendors. Due to the increased emphasis on quality (especially in
microcircuits), a more generic approach to vendor certification/qualification
of processes is recommended. Then, existing data from technology families can
be used for qualification by similarity. Ongoing vendor/customer testing
programs on representative products may be used to determine acceptability.
Procedures for performing and monitoring vendor/product testing and
incoming inspection are still necessary, but should be tailored to allow
each vendor to be handled on a case-by-case basis. For example, outgoing
vendor quality and user incoming inspection and board level testing can be
monitored to determine device quality and product design/manufacturing process
compatibility. Data analysis can then determine the need for vendor testing,
incoming inspection and increased vendor surveillance. These data can also
form the basis for determining whether a "ship to stock" program (i.e.,
acceptance of a product without incoming inspection) is feasible.
Parts must be selected based on a knowledge of both the
application environment in which the part is to operate and the conditions it
is exposed to during part manufacturing, assembly, handling and shipping. It
is equally important to understand how the failure rate during the partís
useful life, and its wearout characteristics (lifetime), are impacted by the
specific application conditions. Only with this understanding are robust
One specific area of importance is the continuity of production.
As mentioned earlier, facilities/production lines that manufacture parts on a
continuous basis often produce higher quality parts than those manufactured on
an intermittent basis. Intermittent production can be a characteristic of
custom, low usage parts. High volume, continuous production is usually
controlled in a statistical manner, whereas intermittent production may not be
able to implement SPC. Additionally, intermittent lines often run into
unanticipated problems associated with startup which can adversely affect the
quality, availability, and reliability of the part.
Many successful organizations have developed a qualified
manufacturers list (QML) on which procurement decisions are based. A QML lists
manufacturers who have proven that they can supply good parts with a high
degree of confidence. The DoD is also using this methodology in the
procurement of microcircuit devices, via the QML program (i.e.
Part manufacturers can be evaluated in many ways. For suppliers
of parts that have been manufactured for some time, analysis of historical
reliability/quality data is usually the optimum method. In many cases, these
data are readily available from the manufacturer and, in some cases, are
published in their data catalogs. To be meaningful, historical data must be
representative of the same, or a similar, part with few changes, and must be
for a similar application under similar operational stresses.
Vendor evaluation can be accomplished by analyzing design,
manufacturing, quality, and reliability practices. Figure 7.2-1 illustrates a
methodology to evaluate potential vendors.