The primary electrical function of an electronic module is to provide electrical interconnections among the inputs and outputs of its components. At the semiconductor single chip package level, these interconnections are from the pads on the silicon die to the pins/ball grids, which provide electrical connections to the next level of packaging. The board level interconnections are between the input/output terminals of ICs, ICs and components, and layers of board. There are also interconnections between boards through back-panel, motherboard, and connectors and cables.

 

The interconnections can be divided into two categories: signal interconnections and power/ground interconnections. The major electrical design objective of interconnections is to maintain the signal integrity (or fidelity) in signal paths and to minimize the transients in the power/ground structure.

 

The factors that contribute to the loss of signal integrity and the generation of transient (parasitic) phenomena on the power/ground lines include:

• parasitic resistance associated with interconnections;
• parasitic inductance associated with interconnections;
• parasitic capacitance associated with interconnections;
• non-uniform cross section of the signal path;
• proximity of other signal interconnections;
• sharing of return lines by various digital and analog signals.

 

Grounding Techniques

Grounding techniques apply to both multi-layer and double-layer/single-layer PCBs. The objective of grounding techniques is to minimize the ground impedance and thus to reduce the potential of the ground loop from circuit back to the supply. As know, a loop is made by a signal and the ground return path from the receiver device back to the signal source. Signal return paths present the most difficult design problem in PCB layout. Keeping signal tracks and its ground return close together will help to minimize the ground loop, thus, avoiding potential aerial loops or parasitic loops through other PCB structures, components, and interconnections.