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

used under gold or rhodium on contacts and for applications requiring high mechanical strength and hardness. Electrical connectors with finishes of nickel plating shall not be used.

5.3.6.6 Palladium plating. Palladium plating shall be in accordance with MIL-P-

45209. The use of palladium plating in enclosed assemblies containing organic materials shall be avoided, to prevent polymerization of organic compounds.

5.3.6.7 Silver plating. Silver plating shall be in accordance with QQ-S-365. Silver plating may be passivated for temporary protection, or may be over-coated with rhodium in accordance with MIL-R-46085 to prevent tarnish. Silver plating shall be protected from sulfurous fumes during storage, and shall be cleaned immediately prior to soldering. Attention shall be given to prevention of silver migration (see 5.3.5). Silver plating shall not be used for contacts without prior approval from the procuring activity.

5.3.6.8 Tin coating. Tin coating shall be applied by hot dip or electrodeposition in accordance with MIL-T-10727. For maximum protection, tin shall be reflowed (diffused) after coating. Where desired for electrical bonding, tin-cadmium plating shall be in

accordance with MIL-P-23408. Care shall be taken to prevent formation of metal whiskers on tin surfaces during storage (see 5.3.4).

5.3.6.9 Tin-lead coating. Tin-lead (solder) coating shall be applied by hot dip or electrodeposited for solderability or purposes of electromagnetic compatibility, in accordance with MIL-STD-2000 or MIL-P-81728.

5.3.6.10 Zinc plating. Zinc plating may be used as an alternate coating for cadmium where it meets the requirements for the component or system. However, cadmium plating is the preferred choice for avionics and systems used in marine environments. Zinc plating shall not be used without prior approval from the procuring activity.

5.3.6.11 Metallic coatings on nonmetals. Metallic coatings may be applied to nonmetallics to provide a conductive surface. Although problems of dissimilar metal corrosion are thereby minimized or eliminated, other corrosion reactions of the metal coating shall be considered in the same manner as for plated or solid metals.

5.3.6.12 Vapor deposited coatings. Metallic coatings may be applied by vapor deposition to either metallic or nonmetallic surfaces for electrical conductivity. Vapor deposited coatings shall not be used for any mechanical application because of their extreme thinness, fragility and susceptibility to damage. Aluminum coatings shall be applied in accordance with MIL-C-83488.

5.3.7 Castings. Surface porosity in castings shall be impregnated in accordance with MIL-STD-276 before receiving appropriate surface finish. Impregnants for aluminum castings shall be in accordance with MIL-I-17563.