LGA771 Socket Mechanical Design Guide

Document Goals and Scope, LGA771 Socket Overview

This document describes a surface mount, LGA (Land Grid Array) socket intended for the Dual-Core Intel® Xeon® Processor 5000 sequence family for servers and workstations. The socket provides I/O, power, and ground contacts. The socket contains 771 contacts arrayed about a cavity in the center of th...e socket with solder balls for surface mounting with the motherboard. The LF-LGA771 Socket contains lead-free solder balls while the LGA771 Socket contains eutectic solder balls. This Design Guide will refer to the socket as LGA771 for simplicity, but its contents are applicable to both lead-free and eutectic solder materials unless otherwise specified. The socket contacts have 1.09 mm X 1.17 mm pitch (X by Y) in a 33x30 grid array with 15x14 grid depopulation in the center of the array and selective depopulation for keying features. A matching LGA package will be mated with the socket.

For board layout, the land pattern for the LGA771 socket is 43 mils X 46 mils (X by Y), and the pad size is 18 mils. The component dimensions are defined in metric so there is a slight round-off error when converting to mils, but it is a negligible amount, relatively speaking, when compared to the size of the ball and pad. There have been no reported manufacturing issues. The goals of this document are:
• To provide LGA771 socket information necessary for motherboard design to ensure the specified performance of the platform.
• To define the boundary conditions and design constraints within which the socket design must fit and perform.

Read the full LGA771 Socket Mechanical Design Guide.

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