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

protected against electrolytic corrosion.  Special attention shall be given to the following problem areas, which can result in lower conductivity, "noise," short circuits or broken leads.

5.3.1  Surface contamination.  Where maximum conductivity is required on items exposed to the atmosphere (as on contacts), metals which are inherently resistant to oxidation and tarnish shall be selected, such as gold, rhodium and platinum.  When other metals are used, the surface shall be protected from oxidation by plating with the noble metals listed above or by suitable noninsulating coatings.

5.3.2  Intergranular and stress corrosion.  Preference shall be given to metals which are resistant to both intergranular and stress corrosion, especially for applications involving residual and induced stresses.  The alloys which are normally most resistant to intergranular corrosion are also more resistant to stress corrosion.  Preference shall be given these alloys, especially for applications involving residual and induced stresses.  In addition, all bending, forming, and shaping shall be performed on metal in the annealed condition.  Every effort

shall be made to use the lowest stress level practical.

5.3.3  Hydrogen embrittlement.  Preference shall be given to metals which are not susceptible to delayed fracture due to hydrogen pickup from acid cleaning or plating, such as the 300-series corrosion resistant steels and oxygen-free copper.  Where it is necessary to use metals which are susceptible to hydrogen pickup, coating methods shall be selected in accordance with restrictions in MIL-S-5002.  In addition, the following methods shall be used to minimize damage:

a.        Organic coating, vapor deposition, mechanical plating, metal spraying and other non-hydrogen-producing processes shall be used in preference to electroplating or chemical plating

b.         If plating is necessary, low-hydrogen-embrittlement baths shall be used

c.        Parts shall be embrittlement- relieved immediately after plating in accordance with the appropriate specification

d.        Where practical, parts shall be thermally stress relieved prior to plating, for a minimum of three hours at 190° ± 14°C

e.        Where practical, parts shall be mechanically stress relieved prior to plating, by shot peening in accordance with MIL-S-13165

f.        Neither acid nor alkaline cathodic cleaning shall be used on metals susceptible to hydrogen embrittlement.

5.3.4  Whisker growth.  The growth of metal whiskers on tin, cadmium, silver, or iron shall be minimized by the following techniques:

a.         Use of heavy, rather than thin, metal coatings

b.         Use of hot dip tin rather than electrodeposited tin c.         Reheating tin plating to relive stresses

d.         Maintaining a low level of humidity in the equipment

e.         Use of tin plating with 2 to 5 percent co-deposited lead

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