MIL-PRF-27G
3.4.5 Internal wire leads. Internal wire leads shall be attached to the coils and other internal components and
terminals or case by soldering, welding, brazing, or other method (e.g., lead-sweating of nylon-coated wires) in such a
manner as to provide adequate electrical connection and mechanical strength. Where soft solder is used to provide
the electrical connection, wire leads shall be anchored mechanically. In addition, for class T product, wire leads shall
be attached in order to meet the radiographic inspection requirements of Appendix B.
3.4.6 Core and coil mounting. Cores and coils shall be secured rigidly to prevent any permanent change in the
relative position of the parts. When the total volume of the case or inner case of multiple-cased units (such as shielded
units) exceeds 6.5 cubic inches, the means of securing the core and coil to the devices for mounting the transformer or
inductor in the equipment (e.g., studs, lugs, inserts, brackets, etc.,) shall not depend on soft solder alone for
mechanical strength, nor shall the transmission of the mechanical load of the core to the mounting device depend only
on soft solder. When rigid thermosetting material is used, or when the total volume of the case or the inner case of
multiple-cased units (such as shielded units) does not exceed 6.5 cubic inches, the potting or filling compound alone
may be used to prevent movement provided the compound does not tend to flow at the specified maximum operating
temperature (see 3.1). When specified (see 3.1), the core shall be grounded to the case or shall be electrically
accessible.
3.4.7 Paint color. When a paint finish is specified (see 3.1), the color of the paint shall be in accordance with
FED-STD-595, gray, 26307 Unless otherwise specified (see 3.1), the manufacturer shall omit paint from the mounting
area surface and terminal surface.
3.4.8 Potting, filling, or encapsulating material (grades 4 and 5). The amount and coverage of potting, filling, or
encapsulating material used shall be essentially the same for all units of a specific design. Potting, filling, or
encapsulating material shall not flow from the case of the transformer or inductor during any of the applicable tests.
3.4.9 Weight. Transformers and inductors shall not exceed the weight specified (see 3.1).
3.5 Solderability. When the transformers and inductors are tested as specified in 4.7.2, they shall meet the
applicable criteria for terminal evaluation in the test method.
3.6 Resistance to solvents. When the transformers and inductors are tested as specified in 4.7.3, there shall be no
evidence of mechanical damage and the markings shall remain legible. The paint or exterior finish shall not soften,
peel, or show other signs of deterioration.
3.7 Thermal shock screening and thermal shock test.
3.7.1 Thermal shock screening (Product level T only). This test is applicable only when specified (see 3.1) and
shall be performed in the qualification tests in group II and the group A inspection in subgroup I. When transformers
and inductors are tested as specified in 4.7.4.1 there shall be no evidence of filling material and no evidence of other
physical damage such as cracks, bursting or bulging of the case or corrosion affecting the mechanical or electrical
operation. When continuity monitoring is specified there shall be no evidence of electrical discontinuity greater than
100 microseconds.
3.7.2 Thermal shock test. When transformers and inductors are tested as specified in 4.7.4.2 there shall be no
evidence of filling material damage or leakage and no evidence of other physical damage such as cracks, bursting or
bulging of the case or corrosion affecting the mechanical or electrical operation.
3.8 Resistance to soldering heat. When the transformers and inductors are tested as specified in 4.7.6, there shall
be no softening of the insulation or loosening of the windings or terminals.
3.9 Terminal strength. When the transformers and inductors are tested as specified in 4.7.7, there shall be no
evidence of loosening or rupturing of the terminals, or other mechanical damage. Bends shall not be considered as
damage unless surface cracking is evident. Except for flexible leads, there shall be no rotation of the terminals.
Rotation of the external portion of the metallic portion of a "hook" type terminal exceeding 10 degrees shall not
constitute a failure.
3.9.1 Bond strength. Bond strength for leadless "chip style" units shall be specified in the individual specification
sheets (see 3.1).
3.10 Seal (grade 4) (see 4.7.8).
3.10.1 Liquid-filled units. When the transformers and inductors are tested as specified in 4.7.8.1, there shall be no
evidence of liquid leakage.
3.10.2 Gas-filled units. When the transformers and inductors are tested as specified in 4.7.8.2, the leak rate shall
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not exceed 1 x 10 standard atmosphere cubic centimeter per second (atm cm /s).
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