Intel's Packaging Databook Chapter 4: IC Packages Performance Characteristics: Packaging
As microprocessor speeds have increased and power supply voltages have decreased, the function of the microprocessor package has transitioned from that of a mechanical interconnect which provides protection for the die from the outside environment to that of an electrical interconnect that affects microprocessor performance and which must be properly understood in an electrical context. Inherent in understanding the electrical performance effects of the package is the need for electrical characterization of the package. The package is a complex electrical environment, and the characterization of this environment is a multi-faceted task that consists of models constructed from both theoretical calculations and experimental measurements.
In simple terms, a package electrical model translates the physical properties of a package into electrical characteristics that are usually combined into a circuit representation. The typical electrical circuit characteristics that are reported are DC resistance (R), inductance (L), capacitance (C), and characteristic impedance (Z_o) of various structures in the package. A package model consists of two parts, both of which are necessary for fully understanding the electrical performance effects of the package environment on Intel’s microprocessors.
The first is an I/O lead model that describes the signal path from the die to the board. Depending upon the complexity of the model required for simulation purposes, the I/O lead model can take the form of a simple lumped circuit model, a distributed lumped circuit model, a single-conductor transmission-line model, or a multiple-conductor transmission-line model. While lumped models can adequately model simple effects, such as DC resistive voltage drop, more sophisticated models like the multiple-conductor transmission-line model include effects such as time delay and crosstalk.
Read the full Packaging Databook, Ch. 4.