MIL-PRF-27G
4.
VERIFICATION
4.1 Classification of inspections. The examination and testing of transformers and inductors shall be classified as
follows:
Qualification inspection (see 4.4).
a.
b.
Conformance inspection (see 4.6).
4.2 Test equipment and inspection facilities. Test and measuring equipment and inspection facilities of sufficient
accuracy, quality and quantity to permit performance of the required inspection shall be established and maintained by
the inspection facility. The establishment and maintenance of a calibration system to control accuracy of the
measuring and test equipment shall be in accordance with ANSI/NCSL Z540.3, ISO 10012 or equivalent.
4.3 Inspection conditions. Unless otherwise specified herein, all inspections shall be performed in accordance with
the test conditions specified in the "GENERAL REQUIREMENTS" of the applicable DoD standard, i.e., MIL-STD-202.
When a test method is not specified, the standard test conditions of MIL-STD-202 shall apply.
4.3.1 Test voltage. For transformers and inductors (other than audio families), the rated rms voltage at the
minimum frequency of the specified frequency range shall be applied at the rated duty cycle (e.g., transformers rated at
50/60 hertz (Hz) shall be tested at 50 Hz; transformers and inductors rated at 60 Hz ±10 percent shall be tested at 60
Hz. When rated primary voltages are specified with a tolerance (see 3.1), the test voltage shall be the rated voltage
(e.g., 115 ±10 volts shall be tested at 115 volts). For two-terminal primary windings where the rated primary voltage is
specified as a range, the test voltage shall be the arithmetic mean of the range. For multitap primary windings where a
range of voltages is specified, the test voltage shall be applied to the highest voltage in the range and applied to the
appropriate terminals (e.g., 105 to 125 volts shall be tested at 125 volts). For dielectric withstanding voltage tests, the
peak of the voltage applied shall not exceed by more than 5 percent the peak of the pure sine voltage.
4.3.2 Test frequency. When a test frequency is specified herein, the frequency used shall be within ±2 percent
of the nominal value. The test frequency of audio transformers and inductors shall be the geometric mean of the
specified frequency range or a lower value selected by the manufacturer.
4.3.3 Specified mounting. When specified in the test procedure, surface mount devices (SMD) style products are
to be mounted on a suitable test substrate, which shall be a minimum of 95 percent alumina. The test substrate
material shall not contribute to, or cause any failure in any of the tests for which it may be used. If multiple parts are
mounted to the same substrate, a minimum separation of 1.0 inch (2.54 mm) will be used. The method of mounting
shall be as follows:
a.
All solderable terminations. Transformers/Inductors shall be mounted on the test substrate by soldering
the terminations directly to the test substrate metallized land areas in the following manner:
(1)
Solder and soldering flux, when used shall be selected to enable the parts to meet the
requirements of this specification. Additional information and guidance on solder and flux is
provided in paragraph 6.19.
(2)
All Transformers/Inductors shall then be placed across the metallized land areas of the test
substrate with contact between the terminations and substrate land areas only.
(3)
The test substrate with all transformer/inductors in position shall then be placed in or on a
suitable heat transfer unit (molten solder, hot plate, tunnel oven, etc.) with the temperature
maintained at 260°C +/- 5°C until the solder melts and reflows forming a homogenous solder
connection.
4.4 Qualification inspection. Qualification inspection when required and for listing on the QPL shall be performed
at a laboratory acceptable to the government (see 6.3) on sample units produced with equipment and procedures
normally used in production.
4.4.1 Qualification of transformers and inductors based on complete testing.
4.4.1.1 Sample size. The number of sample units comprising a sample of transformers or inductors to be
submitted for inspection shall be as specified in appendix A. Sample units shall have previously passed all the
requirements of a 100 percent screen to the appropriate Group A subgroup for the product level and grade for which
qualification is requested. Extension of qualification requirements are also specified in appendix A.
4.4.1.2 Inspection routine. The sample units shall be subjected to the inspections specified in table V, in the order
shown, and as specified in appendix A to this specification.
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