MIL-STD-981C
5.5.13.3 Curing. The cure schedule shall be sufficient to assure the complete cure of the impregnation and potting compound throughout the device. Impregnation, potting and bonding materials shall be cured to meet the outgassing requirements of 5.1.1.
5.5.13.4 Preparation of cups or molds. Cups or molds shall be prepared for potting or impregnation as follows:
a. Clean plastic or metal cups with solvents that will not contribute to the degradation of the part; such as commercial grades of isopropyl alcohol, acetone, stoddard solvent, or equivalent. Plastic cups shall be sandblasted or otherwise etched on the inside surface to assure good adhesion of the resin compound to the cups.
NOTE: Cleaned inner surfaces shall not be touched with bare hands or fingers and
cups or molds shall be stored in such a manner as to preclude atmospheric contamination.
b. Wipe molds with the same solvents, or equivalent, for removal of visible dust, dirt, and other undesirable matter.
c. Final rinse cups and molds with the same solvent used in b. above.
5.5.13.5 Impregnating and potting compounds. All impregnating and potting compounds must be degassed. Pot life of materials shall be controlled and shall be in accordance with manufacturer's recommendations. In addition, all potting materials shall be dated for expiration of shelf life, and shall not be used after this date.
5.5.13.6 Equipment. Vacuum chambers and other equipment shall have adequate automatic controls and shall be capable of maintaining the required pressure and temperatures for the time period specified by the applicable specification or source control drawing or by the product bulletin of the compound manufacturer. The inside of the chamber, chamber lid seal, resin containers and device holding fixtures shall be maintained free of dirt and other foreign materials that may inhibit proper operation of the equipment.
5.5.13.7 Voids. Units shall be potted or encapsulated in such a manner as to prevent voids, bubbles, and cracks.
5.5.13.7.1 Internal voids. There shall be no internal voids greater than 0.015 inch in the largest dimension located within 0.005 inch of any bare conductor, solder joint, or terminal. The total volume all voids, and the volume of any one void shall not exceed 10 and 5 percent respectively of the total volume of encapsulant within the device, and shall in no way jeopardize the mechanical or functional integrity of the device.
5.5.13.7.2 Surface voids and depressions. Surface voids and depressions shall not reduce the thickness of the covering over internal parts to less than what is shown in Figure B-4.
5.5.13.7.3 Extraneous material. Care shall be taken to ensure that extraneous material is not introduced during the potting process.
5.6 Quality assurance provisions. Unless otherwise specified, test and inspection methods and criteria shall be in accordance with MIL-PRF-27, MIL-PRF-15305, MIL-PRF-21038, MIL-T-55631, MIL- PRF-83446 or MIL-PRF-39010 as applicable.
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