IPC 2141A

Abstract

This guide is intended to be used by circuit designers, packaging engineers, printed board fabricators, and procurement personnel so that all may have a common understanding of each other&#8217;s area.<br>The goal in packaging is to transfer a signal from one device to one or more other devices, through a conductor. High-speed designs are defined as designs in which the interconnecting properties affect circuit performance and require unique consideration.<br>The term &#8216;&#8216;high-speed&#8217;&#8217; as applied to logic or digital designs needs clarification in its usage. The three most common interpretations of high-speed are as follows. (1) High-speed as a reference to the rate of change of signal amplitude with time (frequently called the edge rate of a pulse) constitutes the most important usage. The edge rate puts the greatest performance demand on interconnecting structures. (2) High-speed as a reference to the data transmission rate (bits or bytes per second) is often used to describe the &#8216;&#8216;speed&#8217;&#8217; of a system. However, high data rates can be achieved with parallel bus architectures that do not necessarily require improved performance of an interconnecting structure. (3) High-speed as a reference to the speed (distance per unit time) of a signal propagating between devices has the smallest usage and, in many cases, is not important to the application.<br>Controlled impedance is the maintenance of some specified tolerance in the characteristic impedance of an interconnect line (transmission line) that is used to connect different devices on a circuit. Controlled impedance is often a design consideration for high-speed digital or high-frequency analog circuits. However, the reverse is not true, that is, high-speed digital or high-frequency analog circuit designs may not need to consider controlled impedance. The purpose of this document is to help the designer understand when controlled impedance should be considered in his/her circuit design and to describe concepts important to controlled impedance design.