MIL-R-93 Resistors, Fixed, Wire-Wound, Accurate, General Specification ForThis specification covers the general requirements for accurate, wire-wound, fixed resistors having a maximum resistance tolerance of 1 percent, with the winding protected against high humidity. The resistors are rated for continuous full load operation at any ambient temperature up to 125 Degrees C, and derated up to 145 Degrees C. They are not capable for application where alternating current ac characteristics are of critical importance. Performance characteristics are in accordance with table I.

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MIL-R-93F

6.7.3  Characteristics and terminal.  Resistors identified by temperature characteristic and lead type symbol "C" of this specification, are interchangeable with resistors with characteristic "C" of MIL-R-93C. Temperature characteristic "C" of this specification supersedes characteristics "A" and "C" of MIL-R-93B and covers the temperature range of 125°C to 145°C specified in MIL-R-9444A.

6.7.4  Supersession of styles.  The styles in this specification supersede the style of superseded MIL-R-93C, 12 June 1961, "Resistors, Fixed, Wire Wound (Accurate), General Specification for". and MIL-R-9444A, 20 July 1959, "Resistors, Fixed, Wire Wound, Precision High Temperature, General Specification for", as listed in table XIII.

*                                                      TABLE XIII.  Supersession of styles.

1/  Resistors in this specification are mutually interchangeable with resistors of the same type designation under MIL-R-93B (see 6.7.3) and MIL-R-93C.

2/  Cancel specification.

*                6.8  Environmentally preferable material.  Environmentally preferable materials should be used to the maximum extent possible to meet the requirements of this specification.  Table XIV lists the Environmental Protection Agency (EPA) top seventeen hazardous materials targeted for major usage reduction. Use of these materials should be minimized or eliminated unless needed to meet the requirements specified herein (see section 3).

TABLE XIV.  EPA top seventeen hazardous materials.

*        6.9  Tin whisker growth.  The use of alloys with tin content greater than 97 percent, by mass, may exhibit tin whisker growth problems after manufacture.  Tin whiskers may occur anytime from a day to years after manufacture and can develop under typical operating conditions, on products that use such materials. Conformal coatings applied over top of a whisker-prone surface will not prevent the formation of tin whiskers.  Alloys of 3 percent lead, by mass, have shown to inhibit the growth of tin whiskers.  For additional information on this matter, refer to ASTM-B545 (Standard Specification for Electrodeposited Coatings of Tin).

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