MIL-PRF-28776 Relays, Hybrid, Established Reliability, General Specification ForThis specification establishes the general requirements for relays that use a combination of solid state circuit input elements functioning with an electro-mechanical relay that performs the switching functions associated with control system applications \(see 6.1\). These relays are designed to operate in low and medium power switching circuits with contact ratings up to 1 ampere alternating current \(ac\) or direct current \(dc\). The failure rate level is established at a confidence level of 90 percent for qualification and 60 percent for maintenance of qualification based on 100,000 cycles at +125┬░C under rated load conditions specified herein. Excludes time delay relays. CAUTION: The use of any coil voltage less than the rated coil voltage will compromise the operation of the relay. CAUTION: Pick-up, hold, and dropout voltages are for test purposes only and are not to be used as design criteria. For additional application and caution information, see 6.1.

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MIL-PRF-28776F

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

shall be used which will enable the relays to meet the performance requirements of this specification. Materials used

externally shall be fungus inert, self-extinguishing, and shall not support combustion, nor give off noxious gases in

harmful quantities. Materials used internally shall not give off gases in quantities sufficient to cause explosion of

sealed enclosures, cause contamination of the contacts or other parts of the relay that will adversely affect life or

reliability, or form current-carrying tracks when subjected to any of the tests specified herein. Cotton-filled or wood-

flour-filled materials shall not be used. Ceramic used for external surfaces shall be glazed. The use of silicone (see

6.10) or silicone compounds for any purpose is prohibited. The selection of materials shall be such as to provide

maximum shelf life. Acceptance or approval of any constituent material shall not be construed as a guaranty of the

acceptance of the finished product.

3.4.1 Metals and plating. Metals shall be of a corrosion-resistant type or shall be plated or treated to resist

corrosion.

a. Use of pure tin, plating or otherwise, is prohibited internally and externally (see 6.7.1). Use of tin-lead

finishes are acceptable provided that the minimum lead content is 3 percent.

b. Use of zinc plating is prohibited internally and externally.

c. Use of cadmium plating is prohibited internally and externally.

d. The use of mercury or mercury compounds is prohibited.

e. The use of magnesium or magnesium alloys is prohibited (not applicable to contacts).

3.4.1.1 Dissimilar metals. When dissimilar metals are used in intimate contact with each other, protection against

electrolysis and corrosion shall be provided. The use of dissimilar metals in contact, which tends toward active

electrolytic corrosion (particularly brass, copper, or steel used in contact with aluminum or aluminum alloy), is not

acceptable. However, metal spraying or metal plating of dissimilar base metals to provide similar or suitable abutting

surfaces is permitted. Dissimilar metals should be as defined in 6.7. In hermetic seals, the 0.25 volt difference

between the header material and the housing material is not applicable.

3.4.2 Magnet wire. Magnet wire used shall enable the relay to meet the performance requirements of this

specification.

3.5 Interface and construction requirements. Relays shall meet the interface and construction requirements as

specified such as weight and physical dimensions (see 3.1).

3.5.1 Case. Unless otherwise specified (see 3.1), the case shall not be electrically connected to the contacts or

coil; however, it may be used as part of the magnetic circuit.

3.5.1.1 Case grounding. When specified (see 3.1), means for connecting the relay case to ground shall be

provided.

3.5.2 Sealing process. Relays shall be dried, degassed, and backfilled with an atmosphere and sealed by welding

such that the requirements of this specification are met. Adjunct sealant (see 6.10), if used, must comply with the

following characteristics:

Shall not extend above 20 percent of the length of the exposed terminals above the glass meniscus.

Trace color is permitted if it is a natural result of the sealant process.

Shall form, after curing, a permanent nonconductive, noncracking seal under all relay environments.

3.5.3 Contacts. Contacts shall have load ratings and arrangements (see MIL-STD-1285) as specified (see 3.1)

and unless otherwise specified (see 3.1), shall be capable of carrying the maximum rated current continuously as well

as making and breaking the specified current under all environmental conditions specified herein.