24.0 INTRODUCTION

Surface mount technology (SMT) is at the leading edge of assembling high-pin-count components. However, small as they are when compared with their through-hole counterparts, SMT components can be reduced in size considerably by reducing their lead pitch. Today, the lead pitch of the most common SMT packages is at 0.050-in (0.65-mm) centers. The availability of some fine-pitch 0.020-in (0.5-mm) lead spacing and below enables designers to make more efficient use of printed wiring board (PWB) real estate. The trend is toward SMT packages with lead spacing as small as 0.012 in (0.3 mm). The majority of the fine-pitch SMT components are called quad flat packs (QFPs). The QFP has input and output pins on all four sides of the component. This type of component is called a perimeter array package because all the input and output points are on the perimeter of the component. The QFP packages are used for active components. Several new active component packages have been introduced over the last few years, such as ball grid arrays (BGAs) and micro ball grid arrays. The BGAs and micro-BGAs are called area array packages because they use the entire bottom of the device for the input and output points. The requirement for smaller and lighter portable products such as cell phones and laptop computers has introduced the use of nonpackaged components. There are several types of nonpackaged components such as the flip chip (FC) and chip-on-board (COB).