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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.