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

3.4.1.2 Solderable terminals. Solderable terminals shall be treated to meet the requirements of solderability (see 3.9).

3.4.1.3 Weldable terminals. Weldable terminals shall be as specified in table II. The manufacturer shall verify by certification that the weldable leads meet all the applicable requirements of MIL-STD-1276 (see 3.1). The solderability requirement of 3.9 is not applicable to weldable terminals.

* 3.4.2 Pure tin. The use of pure tin, as an underplate or final finish is prohibited both internally and externally. Tin content of resistor components and solder shall not exceed 97 percent, by mass. Tin shall be alloyed with a minimum of 3 percent lead, by mass (see 6.9).

3.4.3 Protective coating or enclosure. Resistor assemblies shall be protected by a coating or enclosure of moisture resistant insulating material that shall completely cover the exterior of the resistance element, including connections or terminations. The coating shall not crack, craze, drip, run,

or form globules at any temperature up to and including 145°C, regardless of the mounting position of the resistor. This material shall afford protection against the effects of prolonged exposure to high humidities. The protective coating or enclosure shall be such as to minimize the establishment of leakage paths between the terminals resulting from collection of moisture film on the external surface of the resistor.

3.4.4 Solder dip (retinning) leads. The manufacturer may solder dip/retin the leads of product supplied to this specification provided the solder dip process (see appendix A) has been approved by the

qualifying activity.

3.4.5 Power rating. Resistors shall have a power rating based on continuous full load operation at an ambient temperature of 125°C (see 3.1). This power rating is dependent on the ability of resistors to meet the life requirements of 3.15. For temperatures in excess of 125°C, the load shall be derated in accordance with figure 1 (see 6.6).

FIGURE 1. Derating curve for high ambient temperatures.