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Engineering Change Methodology for LGA Compression Connector

IP.com Disclosure Number: IPCOM000015691D
Original Publication Date: 2002-Aug-21
Included in the Prior Art Database: 2003-Jun-20
Document File: 4 page(s) / 150K

Publishing Venue

IBM

Abstract

As higher density connectors are implemented on systems, there is a growing demand for connector schemes that permit significant I/O densities while at the same time provide for excellent signal integrity interconnection to the next level of packaging. With the advent of Land Grid Array (LGA) compression connectors as defined by Cinch, Thomas and Betts, etc., the density and signal integrity problems are addressed. A new problem for providing a suitable method of Engineering Change (EC) for rewiring or repairing system boards is required. In the early stages of hardware build, there are times that engineering changes are needed for the system boards. These modifications are due for a number of reasons including architecture changes, added function, or early user availability from imperfect hardware. The LGA connector requires an electrically insulated backing structure to counterbalance the forces used to compress the chip carrier (i.e., Multi-chip Module (MCM) or Single-chip Module (SCM) to the system board. In the common application of this arrangement, an insulator sheet of FR4 and metal plate are used, which by nature of their design, entirely covers the access to the connector area on the board and hence the I/O’s of the chip carrier. In most applications, this is permissible but when access is needed for Engineering Changes it is necessary to provide space for the repair wires (both DC and high frequency coaxial cable) while maintaining excellent electrical measurement characteristics provided by the LGA connector.

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Engineering Change Methodology for LGA Compression Connector

    As higher density connectors are implemented on systems, there is a growing demand for connector schemes that permit significant I/O densities while at the same time provide for excellent signal integrity interconnection to the next level of packaging. With the advent of Land Grid Array (LGA) compression connectors as defined by Cinch, Thomas and Betts, etc., the density and signal integrity problems are addressed. A new problem for providing a suitable method of Engineering Change (EC) for rewiring or repairing system boards is required. In the early stages of hardware build, there are times that engineering changes are needed for the system boards. These modifications are due for a number of reasons including architecture changes, added function, or early user availability from imperfect hardware. The LGA connector requires an electrically insulated backing structure to counterbalance the forces used to compress the chip carrier (i.e., Multi-chip Module (MCM) or Single-chip Module (SCM) to the system board. In the common application of this arrangement, an insulator sheet of FR4 and metal plate are used, which by nature of their design, entirely covers the access to the connector area on the board and hence the I/O's of the chip carrier. In most applications, this is permissible but when access is needed for Engineering Changes it is necessary to provide space for the repair wires (both DC and high frequency coaxial cable) while maintaining excellent electrical measurement characteristics provided by the LGA connector.

Two basic approaches have been employed previously to facilitate the addition of the EC wire. The first is the custom machining of the insulator to facilitate routing of the wire between the Printed Circuit Board (PCB) and the insulator. This routing is unique per repair and provides the necessary clearance for the EC wire to prevent mechanical loading of the wire by the LGA actuation for...