Browse Prior Art Database

PCB Tailoring Method for Reduced Via Stub Effects

IP.com Disclosure Number: IPCOM000028728D
Original Publication Date: 2004-May-27
Included in the Prior Art Database: 2004-May-27
Document File: 1 page(s) / 10K

Publishing Venue

IBM

Abstract

For increased board level frequencies and usage of high-speed serial links, board vias introduce excessive parasitic effects thereby limiting frequency for signal interface operation. The method presented here reduces the electrical parasitic effects associated with via interconnects by providing means of locally reducing board thickness thereby reducing parasitic effects associated with inter-plane vias. Current approaches individually back drill the vias to reduce the stubbing effects. This process is serial (each via is drilled individually, one after another) and it requires leaving some length for drilling depth tolerance. Other approaches include the use of blind and buried vias (which are shorter since they do not extend throughout the board like the Through Hole vias.

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PCB Tailoring Method for Reduced Via Stub Effects

     In the PCB lamination process, several cores (with etched copper on both sides) are laminated together and separated by a mix of fiberglass and epoxy resin (FR4). This forms the base upon which components such as discrete devices, chips, and connectors are mounted to create electronic products. The thickness of this board varies considerably depending on the application and rigidity requirements and for computer systems are typically from 60-70 MILs thick for simple computer boards up to 200-250 MILs for complex server boards and backplanes.

     Current approaches individually back drill the vias to reduce the stubbing effects. This process is serial (each via is drilled individually, one after another) and it requires leaving some length for drilling depth tolerance. This novel approach is much more manufacturing friendly because it addresses all the via stubs at once without having to individually drill each via. Other approaches such as blind and buried vias provide shorter vias at a much higher manufacturing cost. This approach uses conventional PCB technology without introducing additional equipment (such as precision drilling equipment, Laser via equipment, etc...) and/or materials.

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Via

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Conventional Method

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This Invention

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