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Method for package land designs for removing impedance discontinuities in the I/O signal path

IP.com Disclosure Number: IPCOM000006274D
Publication Date: 2001-Dec-19
Document File: 3 page(s) / 57K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for package land designs for removing impedance discontinuities in the I/O signal path. Benefits include reduced impedance discontinuities, improved bandwidth and improved I/O transmission speed.

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Method for package land designs for removing impedance discontinuities in the I/O signal path

Disclosed is a method for package land designs for removing impedance discontinuities in the I/O signal path. Benefits include reduced impedance discontinuities, improved bandwidth and improved I/O transmission speed.

Background

      Impedance discontinuity of about 30-35 Ohm before leaving the package occurs because of additional capacitance between the land and the previous metal build-up layer (see Figure 1). Impedance discontinuities lower transmission bandwidth and reduce transmission speed.

Description

      The disclosed method includes package land designs to reduce the additional capacitance between the land and the other metal in the package. Reducing the capacitance can remove the impedance discontinuity in the I/O signal path.

              The key elements include:

·        Air gaps under package lands to reduce the capacitance between the land and the other metal in the package because the relative dielectric constant of air is equal to 1 (see Figure 2).

·        Lands with irregular shapes to reduce the capacitance between the land and the other metal in the package (see Figure 3). Reducing the additional capacitance increases I/O signal impedance up to about 50 Ohm.

              For fabrication, the procedures for OLGA and FCPGA lands can be used.

Advantages

              The disclosed method provides new package pad designs to reduce the additional capacitance that caused an impedance discontinuity in the I/O signal path. Accordin...