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Method of fabrication for isolated differential signal vias in a solid metal core-based IC package

IP.com Disclosure Number: IPCOM000008592D
Publication Date: 2002-Jun-25
Document File: 4 page(s) / 117K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method of fabrication for isolated differential signal vias in a solid metal core-based IC package. Benefits include improved signal quality.

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Method of fabrication for isolated differential signal vias in a solid metal core-based IC package

Disclosed is a method of fabrication for isolated differential signal vias in a solid metal core-based IC package. Benefits include improved signal quality.

Background

              The goal of interconnect design for high-speed differential I/Os is to minimize discontinuities in the interconnect path. One way of doing this is to minimize the discontinuity presented by the core via in the package substrate. This can be achieved by placing vias in a differential pair so that maximum coupling is attained and by providing a nearby and continuous return path that isolates each differential pair from nearby pairs.  The discontinuity in the interconnect path caused by the core via in the package substrate is a key problem that must be addressed for server/workstation products and other products with high-speed I/O interfaces.

              Conventionally, differential signal lines are routed through a package core so that the signal vias for the differential pair are at the minimum via pitch. The pair of vias is surrounded as much as possible by VSS (ground) vias to isolate the pair (see Figure 1).  The distance to nearby signals is also maximized to reduce crosstalk among adjacent signals. 

General description

              The disclosed method reduces the discontinuity caused on differential signal lines by core vias, improving signal integrity. A metal core is punched, etched, or drilled (mechanical or laser) and then filled with a dielectric material, forming a clearance in the core. The fill is drilled (mechanical or laser), forming two holes within the original clearance which  are then Cu coated. The resulting structure is a via pair within a via, which is an ideal structure for differential signal pairs.

              The key elements include:

·        Two signal vias are drilled through a metal core sub...