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

5.7.7 Welding, electrical purposes. Resistance welding of electrical interconnections shall be in accordance with MIL-W-8939, using component leads in accordance with MIL- STD-1276. Other welding processes such as electronbeam welding, laser welding, pressure welding, and thermocompression bonding shall be in accordance with high quality industry practice, and subject to the approval of the procuring activity. Care shall be taken to prevent formation of a gold-aluminum intermetallic (Purple Plague) by one of the following techniques: use silver or copper instead of gold; deposit aluminum upon the gold before bonding; or remove the gold plate from the post or other item before bonding.

5.8 Electrical bonding and grounds. Consideration shall be given to obtaining an electrical ground through use of a bus-strap or a shear-splice joint, adequately insulated on the exterior. Surface finishes for metals which are to be electrically bonded to provide electromagnetic compatibility are listed in table II. The surfaces to be bonded shall be free from all oxides and contaminants. Protective finish (organic coating, sealant, paint system) shall be applied to the joint area after making the electrical bond or ground. Attention is directed to table IV.

TABLE IV. Checklist for electrical bonding.

(1) Provision shall be made to assure electromagnetic compatibility in the original design.

(2) Insofar as possible, materials shall be selected which are compatible, such as cadmium or tin plate on steel with aluminum.

(3) If bonding dissimilar metals is unavoidable, the joint area shall be coated after bonding with organic sealant such as silicone, epoxy or polyurethane.

(4) Metal surfaces shall be clean before bonding and shall be free from oil, dirt, moisture, or other contaminants.

(5) Bond shall be made by means of a bus-strap or shear-splice joint when practical. (6) Bonds made by conductive gaskets or adhesives, and involving dissimilar metal

contact, shall be sealed with organic sealant.

(7) A combination environmental and electromagnetic seal, such as wire or other metal form in an elastomer, shall be preferred.

(8) When strippable coating is used to preserve a clean surface for later bonding, compatibility of coating and surface shall be established prior to use.

5.8.1 Aluminum surfaces to be bonded. When aluminum is to be electrically bonded, preference shall be given to the use of clad alloys or the 6000 series alloys. If the part is anodized, the bond areas should be masked before the anodic process or spot-faced after anodizing to remove the insulating anodic layer. Chemical film treatment for electrically