Overview

The miniaturization of circuit boards and cards, made possible with higher-density integrated circuits and surface-mount technology (SMT), has been an ongoing trend in electronic packaging. The growing complexity of ICs as transistor densities increase has, to some extent, been offset by shrinking IC line widths or design rules. Semiconductor package sizes, profile heights, and pin spacing or pitch have been reduced to permit higher device populations per circuit board or card.

The use of standard size dual-in-line packages (DIPs) for ICs is declining as original equipment manufacturers (OEMs) turn increasingly to surface-mount packages that are reflow soldered to circuit boards without plated-through holes. These packages have permitted finer conductive traces on the circuit boards with narrower spacing between them. The elimination of most of the plated-through holes on circuit boards that must contain leaded components has also resulted in increased component population density. Some components such as transformers and power semiconductors do not lend themselves to SMT packaging. Lead-tin solder bonds might not reliably retain objects the size and weight of transformers, and they might not survive immersion in molten solder. Also, the heat dissipated by power semiconductors might cause the solder bonds to fail.

SMT construction is a requirement for the manufacture of many of the latest-generation electronics products such as notebook and palmtop computers, cellular telephones, pagers, CD players, and handheld GPS receivers. Moreover, miniaturized circuitry has made possible many plug-in computer peripherals that were, in earlier generations, separate products. Examples include modems and hard-disk, diskette, CD-ROM,...