MIL-PRF-19978 Capacitors, Fixed, Plastic \(Or Paper-Plastic\) Dielectric \(Hermetically Sealed In Metal, Ceramic Or Glass Cases\), Established And Non-Established Reliability General Specification ForThis specification covers the general requirements for established reliability \(ER\) and non-established reliability \(non-ER\), direct current \(dc\), plastic or paper-plastic dielectric, fixed capacitors, hermetically sealed in metal or ceramic or glass cases. Capacitors meeting the established reliability requirements specified herein have failure rate \(FR\) levels ranging from 1.0 percent to 0.001 percent per 1,000 hours \(see 1.2.1.9\). These FRLs are established at a 90-percent confidence level and maintained at a 10-percent producer\'s risk and are based on life tests performed at maximum rated voltage and maximum rated temperature. An acceleration factor of 5:1 has been used to relate the life test data obtained at 140 percent of rated dc voltage at the applicable high test temperature to the rated voltage at the applicable high test temperature. This specification also covers removable mounting retainers for use with applicable capacitors \(see 3.1\). A parts per million \(ppm\) quality system is used for documenting and reporting the average outgoing quality of ER capacitors supplied to this specification. Statistical process control \(SPC\) techniques are required in the manufacturing process to minimize variation in production of ER capacitors supplied to the requirements of this specification.

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MIL-PRF-19978K

3.5 Interface and physical dimension requirements. Capacitors and retainers shall meet the interface and

physical dimensions specified (see 3.1).

3.5.1 Case. Each capacitor shall be enclosed in a hermetically-sealed case (see 3.1) which will protect the

capacitor element from moisture, impregnant or filling compound leakage, and mechanical damage under all test

conditions specified herein.

3.5.2 Sleeving (when applicable, see 3.1). The sleeving material shall not soften, creep, or shrink to a point

where any part of the cylindrical portion of the case is left uncovered at any test temperature specified herein. The

sleeving shall not obscure the part marking.

3.5.3 Terminals.

3.5.3.1 Case as terminal. When the case is used as a terminal, any protective coating applied to the mounting

surfaces shall be such as to provide a direct conducting path for an electric current from the case to the surface on

which it is mounted.

3.5.3.2 Solder lugs and solder-lug terminals. Solder lugs and solder lug-terminals may be of any shape, provided

dimensional limits are met, and shall be solder coated.

3.5.3.3 Screw terminals. Screw terminals shall be supplied with one nut, one flat washer, and one Iockwasher.

3.5.3.4 Wire leads and pins. Leads and pins shall be solder coated.

3.5.3.5 Pure tin. The use of pure tin, as an underplate or final finish, is prohibited both internally and externally.

Tin content of capacitor components and solder shall not exceed 97 percent, by mass. Tin shall be alloyed with a

minimum of 3 percent lead, by mass (see 6.7). Lead-free, tin alloy high temperature solders may be used where

high temperature solder is necessary with approval by the qualifying activity. The tin content of lead-free high

temperature solders shall not exceed 97 percent by mass.

3.5.4 Threaded parts. All threaded parts shall be as specified (see 3.1) and in accordance with FED-STD-H28.

3.5.4.1 Engagement of threaded parts. All threaded parts shall engage by at least three full threads.

3.5.4.2 Locking of screw-thread assemblies. All screw-thread assemblies shall be rendered resistant to loosening

under vibration. Lockwashers shall be provided under all nuts.

3.6 Burn-in (ERs only. when applicable. see 3.1). When capacitors are tested as specified in 4.7.2, there shall be

no evidence of damage, arcing, or breakdown.

3.7 Radiographic inspection (ERs only. when applicable. see 3.1). When capacitors are tested as specified in

4.7.3, x-ray examination shall disclose no evidence of improperly made connections, misalignments of seals or

eyelets, substandard soldering or structural weakness, or solder particles or slivers attached to one end.

3.8 Thermal shock. When tested as specified in 4.7.4, capacitors and retainers shall withstand the extremes of

high and low temperatures without visible damage.

3.9 Seal. When capacitors are tested as specified in 4.7.5, there shall be no continuous visible stream of bubbles

or other evidence of leakage.

3.10 Dielectric Withstanding Voltage (DWV).

3.10.1 Capacitors. When capacitors are tested as specified in 4.7.6.1, there shall be no momentary or

intermittent arcing or other indication of breakdown, nor shall there be any visible evidence of damage.

3.10.2 Sleeving (when applicable. see 3.1). When capacitors are tested as specified in 4.7.6.2, the insulating

sleeve shall withstand the specified potential without breakdown.