Intel S1155 User Manual download pdf (Page 23)

Thermal/Mechanical Specifications and Design Guidelines 23

LGA1155 Socket

3.3 Socket Components

The socket has two main components, the socket body and Pick and Place (PnP) cover,

and is delivered as a single integral assembly. Refer to Appendix C for detailed

drawings.

3.3.1 Socket Body Housing

The housing material is thermoplastic or equivalent with UL 94 V-0 flame rating capable

of withstanding 260 °C for 40 seconds which is compatible with typical reflow/rework

profiles. The socket coefficient of thermal expansion (in the XY plane), and creep

properties, must be such that the integrity of the socket is maintained for the

conditions listed in Chapter 5.

The color of the housing will be dark as compared to the solder balls to provide the

contrast needed for pick and place vision systems.

3.3.2 Solder Balls

A total of 1155 solder balls corresponding to the contacts are on the bottom of the

socket for surface mounting with the motherboard. The socket solder ball has the

following characteristics:

• Lead free SAC (SnAgCu) 305 solder alloy with a silver (Ag) content between 3%

and 4% and a melting temperature of approximately 217 °C. The alloy is

compatible with immersion silver (ImAg) and Organic Solderability Protectant

(OSP) motherboard surface finishes and a SAC alloy solder paste.

• Solder ball diameter 0.6 mm ± 0.02 mm, before attaching to the socket lead.

The co-planarity (profile) and true position requirements are defined in Appendix C.

3.3.3 Contacts

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.

3.3.4 Pick and Place Cover

The cover provides a planar surface for vacuum pick up used to place components in

the Surface Mount Technology (SMT) manufacturing line. The cover remains on the

socket during reflow to help prevent contamination during reflow. The cover can

withstand 260 °C for 40 seconds (typical reflow/rework profile) and the conditions

listed in Chapter 5 without degrading.

As indicated in Figure 3-6, the cover remains on the socket during ILM installation, and

should remain on whenever possible to help prevent damage to the socket contacts.

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Intel S1155 User Manual Page 23