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

f. Avoiding organic brighteners

5.3.5 Electrolysis and silver migration. The movement of metal from one conductor in a circuit to another which is at a different voltage potential under humid conditions, across ceramic or plastic insulation, is especially liable to occur when one of the metals is silver. This phenomenon of electrolysis or silver migration shall be minimized by use of the following methods, as applicable:

a. The spacing between conductors at different voltage potentials shall be as wide as possible;

b. Conductors shall be protected by an organic moisture barrier coating such as

MIL-I-46058

c. Contaminants shall be removed from conductor surface by careful cleaning followed by rinsing with deionized water, and thorough drying prior to conformal coating;

d. Where practicable, gold, platinum, or tin-lead coatings shall be used in lieu of silver;

e. Humidity shall be maintained at a level which precludes condensation under anticipated environments;

f. Nonhygroscopic insulation shall be used.

5.3.6 Metallic coatings. Metallic coatings shall be selected for their suitability for the application involved. Attention shall be given to problems of aging, cracking, diffusion and corrosion. When metallic coatings are applied by electroplating, special care shall be taken to avoid hydrogen embrittlement. In selecting metallic coatings, the recommendations shown in table I for preventing corrosion shall be given consideration.

5.3.6.1 Cadmium plating. Cadmium plating shall be in accordance with type II, class

2 of QQ-P-416; AMS 2401-4; type II of MIL-C-81562; or vapor deposited in accordance with type 2, class II of MIL-C-8837. Parts-plated in accordance with AMS 2401-4 shall be given supplementary chromate treatment in accordance with MIL-T-12879. Cadmium and

cadmium-plated parts are susceptible to attack by corrosive vapors. Cadmium shall not be used in enclosed assemblies with materials such as acid, ammonia, adhesives, coatings, plastics, varnishes or other organic materials which give off corrosive vapors. Cadmium plating shall not be used in space applications.

5.3.6.2 Chromium plating. Chromium plating shall be in accordance with QQ-C-320. It shall be used for applications involving wear or requiring hardness, and not for corrosion prevention.

5.3.6.3 Copper plating. Copper plating shall be in accordance with MIL-C-14550.

5.3.6.3.1 Plating over copper. Copper oxide corrosion products (Red Plague) which occur at pinholes or porosity in other metallic plating over copper, may be precluded by the interposition of a layer of nickel between the copper and the top metallic coating.