| 摘要 |
<p>Switching noise within an LGA-packaged or PGA-packaged IC Vdd and IC Vss nodes is reduced by spreading the electrical current in the bypass path to reduce the effective current loop area, and thus reduce the energy stored in the magnetic field surrounding the current path. This result is achieved by minimizing the horizontal components of the linkage paths between the IC nodes to be bypassed and the bypass capacitor. Since effective inductance Leff seen by the bypass capacitor is proportional to magnetic energy, Leff is reduced over a broad band of frequencies. For each bypass capacitor, a pair of conductive vias is formed. A first via is coupled to the LGA package Vcc plane and to the IC Vdd node, and a second via is coupled to the LGA package Vss plane and to the IC Vss node. These vias preferably are spaced-apart a distance DELTA X corresponding to the distance between first and second connections on the bypass capacitor although sub-mm offsets in a via at connections may be used to accommodate differing connection pitches. The bypass capacitor connections are coupled to the lower surfaces of the first and second vias, at the lower surface of the LGA package. When the package is inserted into a socket, the bypass capacitor extends into at least some of the otherwise unused recess in the socket. Multiple bypass capacitors are accommodated by forming additional spaced-apart vias that may be electrically parallel-coupled.</p> |
