Microelectronics Packaging:Package Parasitics

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Package Parasitics

Package parasitics are the electrical resistance, capacitance, and inductance associated with the electrical interconnection of a device package. The parasitics are determined by the geometries and properties of both the interconnect and the intermetal dielectrics.

Resistance refers to both DC and AC. The DC resistance of an interconnect is determined by of its cross-sectional area, length, and DC resistivity. The AC resistance depends on the frequency of the signal and is higher than the DC resistance because of the skin effect. Resistance in the power distribution path results in attenuation of input signals to the device and output signals form the device. This has the effect of increasing the path delay.

The parasitic capacitance is a property of interconnect area, the thickness of the intermetal dielectric, and the dielectric constant of the dielectric. Mutual capacitance can exist between circuit elements. This occurs because electric field from charges on one interconnect can attract or repel charge on another interconnect. It is convenient to consider the capacitance as two parts: capacitance with respect to ground, and capacitance with respect to other interconnections. The capacitance with respect to ground is referred to as the load capacitance. This is seen as part of the load by the output driver and thus can slow down the rise time of the driver. Interlead capacitance couples the voltage change on the active interconnect to the quiet interconnect. This is referred to as cross talk.

Inductance can be defined only if the complete current path is known. The package inductance will vary if the placement of the package in the system alters the current path in the package. The parasitic inductance consists of self-inductance and mutual inductance. Mutual inductance between two inter- connects generates a voltage in one when there is current change in the other. Inductive effects are the leading concern in the design of power distribution path in high-performance packages. They are manifested as “ground bounce” noise and “simultaneous switching” noise [1,2,8,11,12].

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