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.

Pages 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - 20 - 21 - 22 - 23 - 24 - 25 - 26 - 27 - 28 - 29 - 30 - 31 - 32 - 33 - 34 - 35 - 36 - 37 - 38 - 39 - 40 - 41 - 42 - 43 - 44 - 45 - 46 - 47

MIL-STD-1250A

d. Freedom from outgassing

e. Compatibility with other materials in the assembly f. Resistance to flame and arc

g. For outdoor applications, ability to withstand weathering.

5.10 Moisture resistance. The deleterious effects of moisture on nonmetallic materials, shown in table VII, shall be avoided or minimized by the following techniques:

a. Materials shall have minimum moisture absorption, no greater than 1.00 percent b. Materials which "wick" or are hygroscopic shall not be used

c. Cut or machined edges of laminated, molded or filled plastics shall be sealed with impervious material

d. Parts shall have a sound, unbroken surface, free from cracks, holes, or other discontinuities which allow moisture to enter

e. Materials which undergo hydrolysis reaction shall not be used.

TABLE VII. Effect of moisture on nonmetallic materials.

Electrical Properties:

- Increases surface conductivity

- Increases loss angle

- Increases capacitance

- Increase dissipation factor

- Reduces volume resistivity

- Reduces dielectric strength

Physical and Mechanical Properties:

- Swelling

- Distortion

- Decomposition

- Change in strength

- Wicking and moisture retention

- Reversion

Fungal Resistance:

- Encourages fungal growth

5.11 Fungus resistant. Materials shall be selected which are funginert, in order to avoid the degradation (loss of insulation, short circuits, etched optics, corrosion and deteriorated seals) caused by fungal attack. Funginert materials are listed in table VIII and MIL-STD-454. If the design requires the use of nutrient material, prior approval shall be obtained from the procuring activity. The nutrient material shall be treated in accordance with MIL-T-152, using varnish in accordance with MIL-V-173 or other suitable coating approved