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IntroductionThe trend for microelectronic devices has historically been, and will continue to be, toward a smaller feature size, faster speeds, more complexity, higher power, and lower cost. The driving force behind these advances has traditionally been microprocessors. With the tremendous growth of wireless telecommunications, rf applications are beginning to drive many areas of microelectronics that traditionally were led by developments in microprocessors. An increasingly dominant factor in rf microelectronics is electronic packaging, and the materials needed to create the package, because the package materials strongly affect the performance of the electronics. Many challenges remain for the packaging of microprocessors as well. These challenges include increased speed, the number of input/output interconnects, decreased pitch, and decreased cost. This article highlights the key issues facing the packaging of high-performance digital and rf electronics.

In early electronic technologies, circuit components were attached to circuit boards by mechanical means. The electrical leads were either twisted together or mechanically interlocked to a board prior to soldering. The possibility of an unreliable solder joint causing any kind of circuit failure was remote. Interconnections were made intrinsic to the board by applying solder to increase electrical and thermal conductance. Technological advances and the need for high-density electronics have since eliminated the luxury of mechanical interlocks. Soldering in advanced applications, like surface mount technology (SMT), provides electrical, thermal, and mechanical interconnections between the board and its electrical components. In SMT, solder joints are the only mechanical features on the board and must hold components in place in a wide range of environments. The solder joints themselves are decreasing in size as increased chip functionality and clock frequencies become available. The failure of a single solder joint can render a device, or an entire electrical system, inoperable. Therefore, as insignificant and innocuous as they may seem, solder joints have become a critical aspect of electronic circuit reliability.