MIL-PRF-39035 Resistor, Variable, Nonwirewound \(Adjustment Type\), Nonestablished Reliability, And Established Reliability, General Specification ForThis specification covers the general requirements for nonestablished reliability \(non-ER\) and established reliability \(ER\), multiturn lead-screw actuated, and single-turn, nonwirewound, variable resistors with a contact bearing uniformly over the surface of the entire resistive element, when positioned by an actuator. These resistors are capable of full-load operation \(when the maximum resistance is engaged\), at a maximum temperature of 150 Degrees C, with a resistance tolerance of ??10 percent. The ER resistors will have life failure rate levels ranging from 1.0 to 0.001 percent per 1,000 hours \(see 1.2.1.5\). These failure rate levels are established at a 60 percent confidence level maintained at 10 percent producer\'s risk on the basis of the life tests.

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MIL-PRF-39035E

3.3.2 PPM system. As part of the overall MIL-STD-790 QPL system, the manufacturer shall establish a ppm

system for assessing the average outgoing quality of lots in accordance with EIA-554-1 and 4.6.4. Data exclusion, in

accordance with EIA-554-1, may be used with approval of the qualifying activity. The ppm system shall identify the

ppm rate at the end of each month and shall be based on a six month moving average. PPM and total resistance

shall be assessed for each style. Style reporting may include both non-ER and ER style combinations.

3.4 Material. The material shall be as specified herein. However, when a definite material is not specified, a

material shall be used which will enable the resistors to meet the performance requirements of this specification.

Acceptance or approval of any constituent material shall not be construed as a guaranty of the acceptance of the

finished product.

3.4.1 Ferrous materials. Unless specifically approved by the Government, the use of ferrous material, with the

exception of corrosion-resistant steel and resistance-element material, is prohibited.

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 6.12.1).

3.5 Interface and physical dimension requirements. The resistors shall meet the interface and physical dimensions

specified (see 3.1).

3.5.1 Resistance element. The resistance element shall be nonwirewound on a form which shall not char or break

down as a result of the tests specified herein. The element shall be characterized by a continuous nature of the

surface area, or multiple paths of the resistance element to be contacted. Contact must be made over a continuous

and unbroken resistance path.

3.5.2 Protective housing or enclosure. The resistance element of completed resistors shall be protected by a

housing, or an enclosure, or both, which shall completely cover the exterior of the resistance element. The protective

enclosure shall be free from holes, fissures, chips, or other faults, and shall be such as to minimize the establishment

of leakage paths between the terminals, resulting from collection of moisture film on the exterior surface of the

housing or enclosure. If the housing is made from a metal or metal alloy, it shall be properly protected against

corrosion and all fasteners shall be plated. Unplated copper-alloy metals shall not be used in contact with aluminum.

3.5.3 Terminals. Terminals shall be as specified in table II. Connections of terminals to the resistance element

shall be mechanically strong. All terminals shall be fastened securely. Terminals shall be protected by a corrosion

resistant metallic coating, and all terminals or exposed portions of insulated wire shall be treated to facilitate soldering.

3.5.3.1 Terminal identification and circuit diagram.

3.5.3.1.1 Terminal identification.

3.5.3.1.1.1 Terminals (applicable to all terminals except L). Terminal identification shall be by one of two methods:

The numerals designating terminal identification may be marked adjacent to the terminals, or circuit diagram (see

3.5.3.1.2) may be used, provided that such identification clearly indicates the applicable terminals.

3.5.3.1.1.2 Terminal L type resistors. For terminal type L resistors, the insulation of the flexible leads shall be

color-coded as shown on figure 1.

3.5.3.1.2 Circuit diagram. The circuit diagram shall be marked on any surface of the resistor in a legible manner,

as shown on figure 1.