5. Avoid designs which create sump areas.
防止采用可能造成积水区域的设计。
6. Provide drainage and/or drain holes for all parts which would become natural sumps.
对于可能成为积水区域的所有部件，应提供排水孔和（或）排水口。
7. Provide dessicants for parts which will include sumps but cannot be provided with drain holes. Dessicant filters can also be provided for air intake.
对于带有积水区域，但无法做排水孔的部件，应提供干燥剂。还可在进气口处提供干燥过滤器。
8. Avoid sharp edges or protrusions. 避免利边或外伸部
9. Select proper protective finishes. The definition of a “safe“ level of galvanic activity must clearly be expanded to include the requirements of the design. If all traces of corrosion must be prevented (e.g., airframe applications) the structure must be properly finished or must be made of materials which will not corrode in the use environment. In these cases, the outside edges of EMI-gasketed flanges might also require peripheral sealing as defined in MIL-STD-1250, MIL-STD-889 or MIL-STD-454. MIL-STD-1250 deserves special mention. Although it was developed many years prior to the availability of CHO-SEAL 1298 conductive elastomer and CHO-SHIELD 2000 series conductive coatings, it offers the following useful corrosion control methods applicable to electronic enclosures:
选择适当的保护性表面。必须将电化反应的“安全”等级定义扩展至包含设计要求。如果必须防止出现任何腐蚀迹象（如机身应用），则必须对结构进行正确的表面处理，或采用在使用环境中不会发生腐蚀的材料加工该结构。在这些情况下，还应按 MIL-STD-1250、MIL-STD-889 或 MIL-STD-454 MIL-STD-1250 中规定，对安装有 EMI 垫片的凸缘的外缘进行外围密封。其中，特别值得一提的是 MIL-STD-1250。尽管 MIL-STD-1250 在 CHO-SEAL 1298 导电橡胶和 CHO-SHIELD 2000 系列导电涂层之前很多年就已经推出，其可提供多种适用于电子器件外壳腐蚀控制的有效方法：
1 Bonds made by conductive gaskets or adhesives, and involving dissimilar contact, shall be sealed with organic sealant.
对于由导电垫片或粘合剂形成的接合，包括相异金属接触，应使用有机密封剂对其进行密封。
2 When conductive gaskets are used, provision shall be made in design for environmental and electromagnetic seal. Where practical, a combination gasket with conductive metal encased in resin or elastomer shall be preferred.
当使用导电垫片时，设计中应考虑到环境和电磁密封问题。在可行处，宜采用垫片和树脂或橡胶封装导电金属组合。
3 Attention is drawn to possible moisture retention when sponge elastomers are used.
当采用海绵体橡胶时，应尽可能地注意持水性。
4 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 gaskets of Monel or silver are used in conjunction with aluminum or magnesium.
由于腐蚀会造成严重的导电性丧失，当蒙耐合金或银制金属丝网垫片与铝或镁一起使用时，应考虑采用特殊的防范措施，如采用环境密封或外部密封条。
5 Cut or machined edges of laminated, molded, or filled plastics shall be sealed with impervious materials.
层压、模制或填料塑料的切割或机加工边缘应使用密封材料对其进行密封。
6 Materials that “wick” or are hygroscopic (like sponge core mesh gaskets) shall not be used.
不应使用具有毛细作用或吸湿性的材料（如海绵芯金属网垫片）。
7 In addition to suitability for the intended application, nonmetallic materials shall be selected which have the following characteristics:
除了考虑是否适用于目标用途外，应选择具有以下特性的非金属材料：
a. Low moisture absorption; 低吸湿性；
华译网上海翻译公司曾经翻译过大量有关海绵体橡胶的资料文件，Beijing Chinese Subtitling Translation Service Agency has translated many technical documents about Sponge elastomers.
b. Resistance to fungi and microbial attack;
耐发霉和耐微生物影响；
c. Stability throughout the temperature range;
在整个温度范围内保持稳定；
d. Freedom from outgassing; 不会排出气体；
e. Compatibility with other materials in the assembly;
与组件中的其他材料相容；
f. Resistance to flame and arc;
耐火和电弧；
g. For outdoor applications, ability to withstand weathering.
对于室外应用，还应具有耐风化的能力。
Selection of Seal Cross Section
密封截面的选择
Selection of the proper conductive elastomer gasket cross section is largely one of application, compromise, and experience with similar designs used in the past. Some general rules, however, can be established as initial design guidelines in selecting the class of gasket to be used.
导电橡胶垫片截面的选择主要依据于目标用途、综合考虑各要求及在以前类似应用中积累的经验。不过，有些一般性原则可在选择垫片等级时作为初始设计准则。
1. Flat Gaskets
1. 平垫片
When using flat gaskets, care must be taken not to locate holes closer to the edge than the thickness of the gasket, or to cut a web narrower than the gasket thickness.
当使用平垫片时，必须注意孔与边缘之间的距离不得小于垫片的厚度，或是注意不要切割宽度小于垫片厚度的肋板。
This is not to be confused with the criteria for punching holes in sheet metal parts discussed earlier.
此点不要与前面所述的板金件冲孔准则相混淆。
Keep in mind also that flat gaskets should be deflected typically 10 percent, compared with 15 to 18 percent for molded and solid extruded gaskets and 50% inside diameter for hollow gaskets. Standard thicknesses for flat gaskets are 0.020, 0.032, 0.045, 0.062, 0.093 and 0.125 in. (see General Tolerances, Table 4.)
同时，切记平垫片变形一般不要超过 10％，模制和实心挤制垫片一般不要超过15 至18%，同时，对于空心垫片而言，不可超出内径的 50%。平垫片的标准厚度为0.020、0.032、0.045、0.062、0.093 和 0.125 英寸（见一般公差表 4）。
Where possible, the flange should be bent outward so that the screws or bolts do not penetrate the shielded compartment (see Figure 9a). If the flange must be bent inward to save space, the holes in the gasket must fit snugly around the threads of the bolts to prevent leakage along the threads and directly into the compartment. This calls for closely toleranced holes and accurate registration between the holes in the flange and the holes in the gasket, and would require machined dies (rather than rule dies) to produce the gasket. An alternate solution can be achieved by adding an EMI seal under the heads of bolts penetrating the enclosure, or by using an insert similar to an acorn nut that has been inserted in the flange and flared to make the joint RF-tight. “Blind nuts” can also be welded or attached with a conductive epoxy adhesive (see Figure 9b).
在可能处，凸缘应向外弯，以使螺钉或螺栓不会穿透被屏蔽的部件（见图 9a）。如果凸缘必须向内弯，以节约空间，则垫片内的孔在螺栓螺纹周围必须紧密配合，以防止沿螺纹直接泄漏至舱体内。这要求孔的公差紧密，凸缘内的孔和垫片内的孔精确对齐，同时，要求使用机加工模具（而不是使用刀模）加工垫片。另外可以在穿外壳螺栓的螺栓头下加 EMI 密封垫实现上述要求，或是使用法兰中已插入的类似盖帽螺母的插入件，形成防 RF 的连接。“盖螺母”还可通过焊接或导电环氧胶的方式固定（见图 9b）。 |
