For applications that require high reliability, the resistor production process includes MIL-style testing consisting of electrical and environmental stresses to screen out and identify any parts or lots that exhibit performance variations. The level of testing needed depends on how critical the circuit is to the overall objective of the project. Microhm Electronics metal film resistor EE series meeting standard MIL-R-10509 are widely used in precision instruments.

 
Parts testing may vary depending on the specification’s requirements. However, the tests are usually separated into groups. Some undergo screening tests performed on 100% of a production lot, while other lots undergo destructive tests performed on a sample of units from within a specific lot to guarantee the performance of the rest.
 
For space-project applications (or even military and avionics), a more specific and relevant testing pattern developed by NASA may be used as a basis. The EEE-INST-002 guidelines titled “Instruction for EEE Parts Selection, Screening, Qualification, and Derating” are used as a basis for the development of several specifications that use foil resistors. Subjecting the resistors to the aforementioned sequence of tests can improve the confidence level of a part to perform in a critical space application. NASA developed the EEE-INST-002 guidelines to be flexible enough to accept any technology and part type. Consequently, there are foil devices with a number of different specifications suitable for these types of critical projects.

 
Some military applications require a part that’s not qualified to a QPL specification. The Defense Supply Center of Columbus also maintains several up-screening plans oriented around high-demand products that haven’t been QPL-qualified. These specifications, known as DSCC specs, consist of a 100% screening test (Group A testing) and a destructive series of tests (Group B testing). DSCC specifications are easily recognized by engineers, distributors, and QA organizations and come in a wide variety of part types. Hermetically sealed precision foil-resistor networks are available with screen/test flow in compliance with EEE-INST-002 (Tables 2A and 3A, Film/Foil, Level 1) and MIL-PRF-83401.