Chapter 19 - Hybrids

Abstract

In electronic terms, a hybrid consists of a collection of components mounted on a single insulating base layer called the substrate. A typical hybrid may contain a number of packaged or unpackaged integrated circuits and a variety of discrete components such as resistors, capacitors, and inductors, all attached directly to the substrate. Hybrid substrates are predominantly formed from alumina (aluminum oxide) or similar ceramic materials. Ceramics have a variety of characteristics that make them particularly well-suited to electronic applications. Hybrid substrates are usually created by placing ceramic powder in a mold and firing it at high temperatures. The two most common techniques used to create tracks and components on the surface of hybrid substrates are known as the thick-film and thin-film processes. The thick-film process is based on screen-printing. Resistors can be formed from a paste containing carbon compounds suspended in a solvent; the mixture of carbon compounds determines the resistivity of the final component. Thin-film processes typically employ either ceramic or glass substrates. The substrate is prepared by spluttering a layer of nichrome (nickel and chromium) alloy across the whole of its upper surface, then electroplating a layer of gold on top of the nichrome. Some hybrids contain only passive components such as resistor-capacitor networks; others contain active devices such as integrated circuits. Hybrids come in a tremendous variety of shapes, sizes, and packages. Many hybrids are not packaged at all, but simply have their external leads attached directly to the substrate.