NEMA grades

NEMA Grade G-11 Nemathelminthes Nematic liquid crystal Nemato cide Nemato cides... 

Prior information available on the irradiation behavior of organics and composites at higher temperatures was used to select materials that seemed likely to have the best behavior at 4 K, Screening was necessary to make the best use of limited reactor cold space. For example, the fluorine-substituted hydrocarbons, like polytetrafluoroethylene, show extremely poor radiation resistance near ambient temperature and therefore were not selected because of space limitations. Other materials of this sort are NEMA Grades CE and LE (textile-cloth composites), which are commonly used in magnets but are known to have poor radiation resistance. 

One of the first classifications of base materials for printed drcnits (and other electrical components) was completed by the National Electrical Manufacturers Association (NEMA). NEMA s industrial laminating thermosetting products standard documents many of the materials used in printed circuits as well as specifications for some of their properties. Historical NEMA grades are outlined in Table 6.1 and cross-referenced with IPC-4101 in Table 6.2. Some of the commonly used materials have been FR-2, CEM-1, CEM-3, and, of course, FR-4. 

TABLE 12.1 NEMA Grade Material Designations and Properties... 

NEMA grade Resin system Reinforcement Description... 

Material The principal printed board material discussed will be NEMA grade FR-4 or G-10, that is, epoxyfiberglass clad with 1.2-, 1-, or 2-oz. copper. Other materials will be briefly mentioned because they can significantly alter plating and related processes. 

NEMA grade Resin Reinforce- ment Description Use... 

The most widely used plastic materials in the printed wiring industry are epoxy resins based on bisphenol A. Epoxy-glass fabric laminates account for approximately 80% of the consumption of printed wiring substrates in the USA. In particular, laminates with specifications equal to or better than NEMA grade GIO or FR4, which combine very good dimensional stability with excellent electrical properties, are suitable for the fabrication of high density wiring that is required for computers and telecommunications equipment. 

NEMA Grade Description Reinforcement Resin Content, %... 

NEMA/ASTM Grade LE NEMA/ASTM Grade G-10 NEMA/ASTM Grade G-11... 

Asbestos fibers (crysotile) have been used in laminates to impart flame resistance and thermal stability. Used extensively in the past, they are listed in NEMA Laminate Standard Ll-1 as grade AA, but concerns about asbestosis limit their use, and they have now been phased out of the laminate industry. 

Nylon fabrics are used with phenolic resins to produce tough laminates with good electrical properties. They are listed as Grade N-1 in NEMA Standard LI-1. Creep or cold flow limits their application. 

Table 11.9. Standard Tolerance Guide for Punched Holes and Slots in High-Pressure Laminated Grades of Sheet Stock, Rods, and Tubes, as Classified by the National Electrical Manufacturers Association (NEMA)...

Table 15. NEMA LI-1 Laminated Thermoset Sheet Grades.

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