MIL-STD-1250 Corrosion Prevention And Deterioration Control In Electronic Components And Assemblies S/S By Mil-Hdbk-1250This standard establishes minimum requirements for procedures, materials and systems for protecting electronic components in DoD systems and assemblies from adverse environments. Protective measures shall be sufficient to maintain performance characteristics within specified limits both during and after exposure to moisture, high and low temperatures, corrosive gases, chemicals and microbial fungal attack.

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MIL-STD-1250A

5. DETAILED REQUIREMENTS

5.1 Atmosphere in equipment. The design and construction shall minimize the corrosive effect of oxygen, moisture and airborne corrosives in the atmosphere within electronic equipment. Techniques to be used, as applicable, for prevention of deterioration include protective coating or encapsulation of components, evacuation and hermetic seals, filtering air and removal of moisture.

5.1.1 Evacuation. Materials which break down or outgas shall not be incorporated in components or devices which are evacuated and sealed. Partially cured or undercured organic materials shall be avoided.

5.1.2 Hermetic seal. For maximum protection against environments, components shall be evacuated and hermetically sealed by fusion of metals, glass or ceramics. Consideration shall be given to possible corrosion from condensation of moisture unless hermetically sealed units are evacuated before sealing, and to contamination of contact surfaces by outgassing materials.

5.1.3 Clean air. Precautions shall be taken to remove moisture, dust and contaminants from air which is inside, or which enters, compartments of electronic devices.

5.1.3.1 Cooling. When forced air cooling is necessary to maintain equipment at temperatures below the maximum permissible operating temperature, moisture and contaminants shall be removed, preferably externally, before cooling air passes over electronic components.

5.2 Moisture. Unless otherwise specified, the moisture level inside electronic equipment shall be maintained below 45 percent relative humidity at 20° Celsius (C). Moisture shall be excluded from electronic devices by adequate housings, seals, gaskets and closures. The following measures shall be taken:

a. Avoid pockets, wells, traps and sump areas where water and condensed moisture can collect, or provide drainage paths

b. Avoid hygroscopic materials

c. Desiccants shall not be used unless necessary for moisture level control, and then only where adequate surveillance schedules have been established for each specific application. In no case shall desiccant material be in contact with unprotected metallic parts. Unless otherwise specified, desiccants shall be in accordance with MIL-D-3464

d. Preclude condensation by keeping components at temperature above the dewpoint.

5.3 Selection of metals. Metals shall be selected which are suitable for the purpose and which are inherently resistant to corrosion or made corrosion resistant by coating or plating. Dissimilar metals shall not be used in contact or close proximity unless suitably