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Method for a variable-size directional antipad

IP.com Disclosure Number: IPCOM000101579D
Publication Date: 2005-Mar-16
Document File: 4 page(s) / 48K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a variable size and directional antipad. Benefits include improved functionality and improved performance.

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Method for a variable-size directional antipad

Disclosed is a method for a variable size and directional antipad. Benefits include improved functionality and improved performance.

Background

      Substrate and board manufacturing processes define features within a layer through various methods. However, all methods are subject to defects. Larger spacing between features provides additional benefit to most methods as the chance for incomplete feature definition decreases. For example, a process that uses a dry film to define different features requires adhesion to the layer prior to chemical processing, which ultimately defines all features on that layer. The adhesion of the film increases as a function of cross-sectional area. Larger spacing provides more cross-sectional area and better yields.

              Conventionally, a minimum spacing requirement between the reference plane and the passing signal is applied to designs sensitive to signal integrity issues. However, all designers are encouraged to align to larger preferred spacing.

      The physical design of the conventional antipad (see Figure 1, [1]) is comprised of a minimum of two design layers. The first layer has the target signal trace [2]. The second layer has the reference plane [3] where the signal also passes. The signal passes through the second layer through an interconnect microvia or through-hole via [4]. The interconnect is  designed with lands, which capture the interconnect microvia [5]. The antipad is formed around the capture land of the passing signal microvia.

      Interconnect layout strongly influences the effective impedance. The effective impedance incorporates all coupling effects, including crosstalk. The sensitivity of effective impedance to simultaneous switching of nearby signals is greatly influenced by the relationship of these traces to their coupled reference planes. A discontinuity between signal and reference plane is inherent in the design [6] as the signal passes through the reference plane. The objective of any good design is to minimize such discontinuities.

      Dry film resist (DFR) requires process steps, such as pasting and etching...