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

5.7.2.1 Crevice corrosion. The mechanisms of crevice corrosion and pitting corrosion are very similar. A metal susceptible to pitting will also be susceptible to crevice corrosion, although the reverse is not true.

Crevice corrosion is usually characterized by intense localized attack in crevices of other shielded areas in contact with an electrolyte which, because of the shielding effect, is stagnant. Holes, gaskets, lap joints, crevices under bolt heads, rivet heads, and washers, as well as surface deposits are potential corrosion sites. Crevice corrosion is generally only a problem in stagnant crevices less than 0.125 inches wide. To prevent corrosion in crevices:

a. Eliminate sharp corners, re-entrant angles, pockets, or other conditions where solid or liquids could collect. Design equipment boxes and bays for complete drainage.

b. Insulating materials or other substances which can absorb or retain water should not be in contact with metallic surfaces. Use nonabsorbent, solid gasket materials.

c. Use butt-welded joints in place of riveted or spot welded lap joints. Seal all lap joints with solder weld metal, or caulking compound to prevent any trapping of corrosive agents.

d. When possible lower the relative humidity of the operating environment to reduce the occurrence of under-film corrosion.

e. Mechanical assembly components such as washers, threaded fasteners, and rivets shall be sealed with polysulfide, polyurethane, epoxy, silicone (non-acid

emitting) or a similar sealant during assembly.

5.7.3 Crimped and wrapped leads. When leads are crimped or wrapped, care shall be taken to prevent cracking the protective plating. Metals selected for crimped joints should be inherently resistant to corrosion and not dissimilar to each other.

5.7.4 Brazing. Brazing of steel, copper, copper alloys and nickel alloys shall be in accordance with MIL-B-7883. Flux residues shall be removed by cleaning after brazing.

5.7.5 Soldering. Soldering for non-electrical applications shall be in accordance with DOD-STD-1866. Soldering for all electrical and electronic applications shall be in accordance with MIL-STD-2000 unless otherwise approved by the procuring activity.

Soldered joints shall be protected with moisture-proof coating such as MIL-V-173 and MIL-I-

46058.

5.7.6 Welding, structural. Fusion and resistance welding shall be in accordance with MIL-STD-2219 and MIL-W-6858. All welded joints shall be cleaned of scale, oxidation, and rough areas which may hold moisture or contaminants. Resistance welded joints shall be sealed with sealant such as MIL-S-7124, except when the assembly is made through primer MIL-P-46105.