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SHIM FOR A PRINTED CIRCUIT BOARD (PCB) EDGE WITH NON-ORTHOGONAL FIBER WEAVE

IP.com Disclosure Number: IPCOM000245424D
Publication Date: 2016-Mar-08
Document File: 5 page(s) / 307K

Publishing Venue

The IP.com Prior Art Database

Related People

Xiaogang Li: AUTHOR [+3]

Abstract

Provided herein is a shim that may be attached to the base tray of a printed circuit board (PCB). The shim provides an edge orthogonal to the rear edge of the PCB to assist with easy and clear insertion of a PCB into a slot in a chassis or other such device/assembly. With the shim, a PCB can be designed with non-orthogonal edges, which may allow the PCB to be optimized for performance at the high speeds now required for electrical transmission (e.g., 15Gbps with differential signaling) without increasing the risk of damage during insertion into a slot in a chassis. The shim may be used in lieu of adding wedges to a PCB that might require an increased PCB panel size. Since larger PCB panels are significantly more expensive, the shim may provide extensive cost savings.

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This is the abbreviated version, containing approximately 47% of the total text.

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SHIM FOR A PRINTED CIRCUIT BOARD (PCB) EDGE WITH NON-ORTHOGONAL FIBER WEAVE

AUTHORS:

  Xiaogang Li Rajesh Edamula Julian Ungureanu

CISCO SYSTEMS, INC.

ABSTRACT

    Provided herein is a shim that may be attached to the base tray of a printed circuit board (PCB). The shim provides an edge orthogonal to the rear edge of the PCB to assist with easy and clear insertion of a PCB into a slot in a chassis or other such device/assembly. With the shim, a PCB can be designed with non-orthogonal edges, which may allow the PCB to be optimized for performance at the high speeds now required for electrical transmission (e.g., 15Gbps with differential signaling) without increasing the risk of damage during insertion into a slot in a chassis. The shim may be used in lieu of adding wedges to a PCB that might require an increased PCB panel size. Since larger PCB panels are significantly more expensive, the shim may provide extensive cost savings.

DETAILED DESCRIPTION

    Typically, a printed circuit board (PCB) is made of an orthogonal weave/mesh of glass fibers with resin therebetween. More specifically, PCBs are usually cut orthogonal to a fiber weave pattern (e.g., edges of a PCB are cut along, adjacent, or otherwise parallel to a fiber strand included in the weave) and PCB artwork (e.g., copper traces) is designed largely along the orthogonal weave. In fact, for ease of implementation, PCB artwork designs in a computer-aided design (CAD) tool usually only includes orthogonal trace routes. Consequently, trace routes tend to be parallel to glass weave and/or may fall into the voids between the glass fibers and, thus, traces may be disposed in the dips and on the bumps formed from the intersection of the weave, as shown in Figure 1.

Copyright 2016 Cisco Systems, Inc.

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    When data is transmitted at high speeds on a printed circuit board (PCB), it becomes necessary to consider the
effects of the glass weave in order to ensure
optimum performance. For example, some
PCBs may provide a 15G SerDes
(Serializer/Deserializer) for the fabric
interface. At those speeds, even the PCB
material glass weave is something that cannot be ignored because signal routes which fall on weave will have different properties than the signal routes which fall in the 'dips' between the weave. As an example of a negative consequence, if the pair of traces shown in Figure 1 was a differential signal, it would cause an impedance mismatch with a common reference plane, thereby causing the performance of this transmission line to be worse, or at least different, from another set.

    One way to resolve this issue is to imprint the artwork with an angular rotation, which may ensure that routes fall evenly across the 'dip' and 'bumps.' However, once a PCB is angled, a bigger panel is required to get the entire artwork imprinted which, in turn, increases the costs of the PCB, as is demonstrated in Figure 2. In order to reduce the PCB back to its original size, such that it is properly dimen...