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

bonded areas shall be chromate type in accordance with MIL-C-5541, Class 1A. It is thin, fragile and easily damaged by abrasion, so bond should be made immediately after application of the chemical film.

5.8.2 Bonding dissimilar metals. Where electrical bond is made between dissimilar metals the surface of one or both shall be coated with a metal compatible to both, where possible. Special care shall be taken to assure complete sealing of any joint between dissimilar metals.

NOTE: If a bond is made by use of a conductive gasket in which the conductive metal is protected from the atmosphere by resin or elastomer, this precludes contact of the dissimilar metal bond with moisture, and galvanic corrosion is not likely to occur. However, it should be sealed where possible.

5.8.3 Bonding at a later time. If it is necessary to make an electrical bond at some later time than at original fabrication, the metal surface to be bonded shall be treated in accordance with table V and then coated with strippable plastic coating in accordance with MIL-C-16173. At the time bond is made, this coating shall be removed and the joint area shall be protected after bonding.

5.8.4 Conductive adhesives. When conductive adhesives are used to make an electrical bond, all resultant fumes shall be thoroughly dissipated before incorporation into the next assembly. Special care shall be taken that the conductive metal (usually silver) does not constitute a dissimilar metal contact, or that adequate moisture-proofing protects the joint. When conductive adhesives are used, their location shall be identified to the procuring

activity.

5.8.5 Conductive gaskets. When conductive gaskets are used, provision shall be made in design for both environmental and electromagnetic seal. Where practical, a combination gasket with conductive metal encased in resin or elastomer shall be preferred. Attention is drawn to possible moisture retention when sponge elastomers are used. Because of the

serious loss in conductivity caused by corrosion, special precautions such as environmental seals or external sealant bead shall be taken when wire mesh caskets of monel or silver are used in conjunction with aluminum. When conductive gaskets are used, their locations shall be identified to the procuring activity.

5.9 Selection of nonmetallics. To assure reliability of electronic devices, nonmetallic materials shall be selected for their ability to maintain desired electrical and mechanical properties within specified limits during and after exposure to anticipated environments. In addition to suitability for the intended application, nonmetallic materials shall be selected which have the following characteristics:

a. Low moisture absorption

b. Resistance to fungi and microbial attack

c. Stability throughout the temperature range