MIL-C-25F
6.7 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).
6.8 Voltage derating with temperature. The applicable dc voltage-derating factor depends upon the characteristic
and the energy content of the capacitor fully charged. Voltage-derating factors for various temperatures are
determined from the curves shown. The permissible operating voltages, while based on incomplete data, are the
capacitor supplier's best estimate to provide a life expectancy of 8,800 hours of continuous operation at high ambient-
temperatures. Longer life can be expected of all types by operation at still lower voltages; for example, a life
expectancy of approximately 44,000 hours may be obtained by operation at 70 percent of the voltage specified in
1.2.1.5. Also, a life longer than 8,800 hours may be expected at the voltage specified in 1.2.1.5, if the high ambient
6.8.1 DC capacitors. The energy content of a dc capacitor when fully charge is determined by use of the following
formula:
CV 2
Where: W = energy content in watt-seconds.
W=
C = nominal capacitance in farads.
2
V = rated dc voltage in volts at +40ºC.
When the characteristic and watt-second group have been determined (see below), the voltage-derating factors for
Watt-second grouping:
Group I:
Group IA: 0 to 0.08 watt-second.
Group IB: 0.08 to 0.5 watt-second.
Group II:
0.5 watt-second to 5 watt-seconds.
Group III: 5 to 50 watt-seconds.
Group IV: 50 watt-seconds and greater.
6.9 DC voltage. A dc voltage is a unidirectional voltage in which the changes in value are either zero or so small
that they may be neglected (see 1.2.1.5).
6.10 Black (ultra-violet) light. Black (ultra-violet) light is not to be used during the seal test (see 4.6.13).
6.11 Liquid-filled capacitor. A liquid filled capacitor is a capacitor in which a liquid impregnant occupies
substantially all of the case volume not required by the capacitor element and its connections. Space may be allowed
for the expansion of the liquid under temperature variations (see 3.3.1).
6.12 Liquid-impregnant capacitor. A liquid impregnant capacitor is a capacitor in which the impregnant is
dominantly contained within the foil-and-paper winding, but does not occupy substantially all of the case volume not
required by the capacitor element and its connections (see 3.3.1).
6.13 Noninductive construction. Noninductive construction means a construction which reduces, but usually does
not eliminate completely, the effective inductance of the capacitor. This result is obtained by so routing the currents
in the electrodes that the magnetic fields tend to cancel each other, or by making the current paths very short (see
3.4.2.1).
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