Intel LGA 771 3.2.2 Socket Actuation Mechanism

LGA 771 Socket Mechanical Design Guide 13

Mechanical Requirements

3.2.1.4.2 Lot Traceability

Each socket will be marked with a lot identification code to allow traceability of all

components, date of manufacture (year and week), and assembly location. The mark

must be placed on a surface that is visible when mounted on the motherboard.

The socket has a total of 771 contacts, with 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 alignment features. For board layout, a 43 mils x 46 mils pitch

(X by Y) can be utilized.

Base material for the contacts is high strength copper alloy.

For the area on socket contacts where processor lands will mate, there is a 0.381 µm

[15 µinches] minimum gold plating over 1.27 µm [50 µinches] minimum nickel

underplate.

No contamination by solder in the contact area is allowed during solder reflow.

A total of 771 solder balls corresponding to the contacts are on the bottom of the

socket for surface mounting with the motherboard.

Two versions of the socket, leaded and lead-free, will be available with the following

materials for the solder balls:

•Eutectic Solder

— Sn63 Pb37 (± 0.5% Sn).

— Socket marking will be LGA771 for sockets comprised of eutectic solder.

•Lead-free Solder

— Composition must be lead free and have a melting point temperature in the

range of 217-220°C (for example: Sn Ag 3.0 Cu 0.5).

— Socket marking will be LF-LGA771 for sockets comprised of lead-free solder.

The co-planarity (profile) requirement for all solder balls on the underside of the socket

is defined in Appendix A.

The solder ball pattern has a true position requirement with respect to applicable

datum’s in order to mate with the motherboard land pattern. See Appendix A.

3.2.2 Socket Actuation Mechanism

The socket actuation mechanism is made of the load plate and the load lever. These

components are made of stainless steel SUS 301. Both components need to be fully

actuated to ensure electrical contact. When correctly actuated, the top surface of the

processor IHS is above the load plate allowing proper installation of a heatsink. The

post-actuated seating plane of the package is flush with the seating plane of the

socket. Movement will be along the Z direction, perpendicular to the motherboard.

When combined with the socket body and load lever, the load plate distributes the force

necessary to achieve the required socket contact resistance values. The load from the

load plate is distributed across two sides of the package onto a step on each side of the

IHS. It is then distributed by the package across all of the contacts.