MIL-STD-981C
5.5.8.1 Pre-cap visual inspection. A pre-cap visual inspection shall be performed on all devices immediately prior to potting or encapsulation. The visual inspection, utilizing 1OX minimum to 3OX maximum magnification, shall be performed to ensure that the devices have been fabricated in accordance with good manufacturing practices and meet the requirements specified. Devices that fail to meet these requirements shall be removed from the lot and shall not be shipped.
5.5.8.1.1 In process color images. If DPA, per MIL-STD-158O is required, then the 4 stage color photographs may be substituted with consent from the acquiring activity. Color images shall be taken on a random sample of five parts per lot (or quantity specified on the contract or purchase order) during pre- cap inspection when solder joints/splices are still visible. Pre-cap images shall consist of the following:
a. One overall image of the part, using enough magnification so that the part fills the frame.
b. Close up images of each visible solder joint, using a minimum of 1OX magnification. Images may contain more than one solder joint.
c. A minimum of six images per device shall also be taken at 1OX minimum magnification, one in each orthographic plane, plus a sufficient number of views to assure that the devices are consistent with high-reliability construction and workmanship. For cylindrical objects (coils),
a minimum of four images shall also be taken at 1OX magnification, one end image plus three full length view images (O·, go· rotated, and 1ao· rotated), to assure that the devices are consistent with high-reliability construction and workmanship.
Images shall be identified with the contract or purchase order number.
5.5.9 Coil windings.
5.5.9.1 Tension. A suitable device shall be used to provide near uniform tension during the machine winding process of any coil of wire size AWG 18 or smaller diameter. For coils wound on square forms, special provision must be made to prevent excessive tension on the corners. This device and the winding machine used shall be inspected for proper operation a minimum of twice daily or once each lot whichever is more frequent. Tension control on larger wire is preferred but not mandatory. For machines which cannot accommodate any tension device, other criteria shall be established. Any portion of the device which contacts the magnet wire (pulleys, sliders, etc) shall be free of nicks, burrs, rough spots, or any
other anomalies that could cause damage to the coil wire.
5.5.9.2 W ire breaks. There shall be no wire breaks for any winding within the coil. The winding operation can be considered complete only when the coil has been made with an unbroken winding. Should the magnet wire break during winding operations, the magnet wire may be unwound and rewound. In no case may a broken coil wire be repaired. If magnet wire opens after assembly, the entire device shall be rejected. Those devices that are designed as multi-series connected windings are not to be identified as wire breaks within the definition of this paragraph.
5.5.9.3 Crossed wires. Winding shall be even and smooth. In insulated interleaved layer-wound coils, no uninsulated turns shall cross over other turns. In toroidal and cylindrical or random wound
bobbin coils wound in segments, there shall be no uninsulated cross-over of any one turn to the adjacent winding segment. All situations where voltage stress exceeds the ability of the magnet wire insulation to withstand it shall be avoided. Family 13, 14, 5O, 51 and 52 RF coils are often wound in a multilayer, progressive, or single pass (linear) wind pattern in order to achieve high Q and high SRF. These winding patterns shall not be interpreted as "crossed wires".
5.5.9.4 Kinks, nicks, and damaged insulation. The winding process shall not introduce any kinks, nicks, and insulation damage.
5.5.9.5 Tapes. The use of pressure sensitive adhesive tapes shall be kept to a minimum. The adhesive system must meet the outgassing requirements of 5.1.1.
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