a. Select one of the three environmental categories
(Protected, Normal or Severe) that best fits the application
b. Select parts for the required application and
c. Decide if the part is environmentally (temperature
limits, vibration, pressure, moisture, etc.) and electrically compliant, and
reliable for the application.
d. If the selected part is non-compliant according to
the manufacturer’s specifications, assess the non-compliance(s) in light of the
application requirements. Examples of possible non-compliances are the part’s
temperature limits, functionality, and EMI, vibration, pressure, moisture and
salt resistance. If the part fails the assessment, re-select another part. If
the part passes the assessment, perform part qualification.
e. Qualification is an acceptance of a manufacturer’s
part and its process control. All parts should be qualified. There are a number
of ways to qualify a part for an application. When performing part
qualification, a customer should sample test-assess, not 100% screen. If a
customer needs to 100% screen the part, this implies the part or process is not
controlled well enough. Examples are:
1. Monitor the part manufacturer and review data.
This can be accomplished by monitoring the manufacturer website and freely
sharing data/ information with other system manufacturers. If the part is
compliant to the application, this may be all that is needed. If the part is
non-compliant to the application, an assessment of the non-compliance will also
be needed, as a minimum.
2. Use QML parts. QML parts should not need further
qualification than provided by the part manufacturer; that is, if the correct
QML level is selected for the application.
3. Non-military parts that meet the application
requirements should need no further testing beyond what the part manufacturer
performs for qualification. It is suggested the part manufacturer be monitored,
as a minimum, as noted in “a.” above. Additional reliability testing may be
needed for new package styles or certain critical
4. Non-compliant selected parts that pass the
application non-compliance assessment may only need the assessment for the parts
5. Some applications require ESS (environmental
stress testing). This is usually performed at the board or power supply level.
ESS tests are usually a combination of thermal shock and vibration. ESS does not
take the place of a non-compliance assessment but may for a part
f. The compliant part, or the part that passes
the non-compliance assessment and passes the part qualification, then goes to
part approval. An application compliant part should only need approval of the
internal engineering department. A non-compliant part that passes the
non-compliance assessment and part qualification should get approval from
internal engineering, the customer (OEM), and, if used in a critical
application, the application’s Program Office representative. In addition, the
part manufacturer’s opinion is important and should be solicited, especially for
critical applications. Disapproved parts should be re-assessed, re-qualified or
re-selected. Approved parts can be used in the