Carbon fibre composites — stealth aircraft

Electronic baseboards are used for mounting the chips, transistors and other elements of electronic circuitry. They are generally made of either phenolic resin reinforced with cellulose (paper), or epoxy resin reinforced with glass fibre.Their principal purpose is to give physical support to the circuit elements while insulating them from 

The movement of ions along the surface of the dispersed cellulose or glass is a relatively slow process, and requires times around the order of seconds. As a result, a dielectric relaxation arises in the hertz frequency region. The amplitude of this relaxation depends on the number of ions formed, and so on the amount of water absorbed. This, in turn, depends on the relative humidity of the surrounding atmosphere. 

permittivities and losses a thousand times greater than those of unfilled polymers may be encountered. 

Although most ac electronic circuits function at frequencies much higher than these loss frequencies, failures have been experienced when high frequency signals are pulsed at these very low frequencies, since the pulse repetition frequencies may fall in the loss region. 

The absorption of water is greater in the cheaper cellulose-filled phenolic boards than in the more expensive glass-filled epoxy boards. Nevertheless, modern boards of both types are now fabricated with surface treatment of the filler to minimise rater absorption. 

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