MIL-PRF-28750F
3.6.1 Threaded parts. All threaded parts shall be in accordance with FED-STD-H28. Where practical, all threads
shall be in conformity with the coarse-thread series. The fine-thread series may be used only for applications that
show a definite advantage through their use. Where a special diameter-pitch combination is required, the thread shall
be of American National Form and of any pitch between 16 and 36, which is used in the fine-thread series. Terminal
threads shall be class 2A and class 2B for external and internal threads, respectively.
3.6.2 Envelope (case, cover, or enclosure). SSR's with metal cases shall be provided with means to permit
assured contact to ground. The enclosure shall not be electrically connected to any terminal, except one provided
specifically for grounding or as specified (see 3.1).
3.6.3 Sealing process. Sealed SSR's shall be dried, degassed, and backfilled (see 6.8) with an atmosphere and
sealed by welding such that the requirements of this specification are met (see 3.9). Adjunct sealant, if used, shall
comply with the following:
a.
Sealant shall not extend beyond 20 percent of the length of the exposed terminals above the glass
meniscus.
b.
Trace color is permitted if it is a natural result of the sealant process.
c.
After curing, sealant shall form a permanent nonconductive, noncracking seal under all relay environments.
3.6.4 Mounting means. Mounting means shall be as specified (see 3.1).
3.6.4.1 Socket. Plug-in SSR's shall be so designed that the weight of the SSR will be supported, and the stability
of the mounting will be provided by means other than the terminals.
3.6.5 Terminals (see 3.1). Terminals shall be as specified herein.
3.6.5.1 Solder-lug terminals. Solder-lug terminals shall be designed to accommodate two conductors, each rated
to carry the maximum rated current of the contact or coil terminated.
3.6.5.2 Wire leads. Wire leads shall be as specified (see 3.1).
3.6.5.3 Plug-in termination. Plug-in terminations shall conform to the arrangements or dimensions and interfaces
necessary for proper mating with the associated connectors or sockets as specified (see 3.1). The mounting
arrangement of the SSR and its corresponding socket shall be so designed that the entire weight of the SSR will be
suspended and the stability of its mounting will be provided by an auxiliary mounting means other than the electrical
terminals of the socket (see 3.1). During qualification, SSR's, with plug-in terminals shall have electrical tests of
section 4 and environmental tests of section 4 performed with the appropriate or specified socket or connector
assembled to the SSR. For further guidance on lead finishes, see 6.7.2.
3.6.5.4 Screw. Screw terminals shall be supplied with one nut, capable of engaging the screw by at least three full
threads, two flat washers and one lock washer. The size of screw thread and length shall be as specified (see 3.1).
At least three full threads of the screw shall visibly protrude with all hardware tightened in place.
3.6.6 Circuit diagram. The circuit diagram as specified (see 3.1), shall be a terminal view. Circuit symbols shall be
in accordance with IEEE-315A. For SSR's without an orientation tab, the circuit diagram as specified (see 3.1), shall
be orientated so that when the SSR is held with the circuit diagram right side up as shown in the appropriate
specification sheet (see 3.1), and rotated away from the viewer about a horizontal axis through the diagram until the
header terminals face the viewer, then each terminal shall be in the location shown on the circuit diagram.
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