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Method for a centering notch for an LGA socket and package

IP.com Disclosure Number: IPCOM000020397D
Publication Date: 2003-Nov-19
Document File: 3 page(s) / 100K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a centering notch for a land grid array (LGA) socket and package. Benefits include improved functionality and improved support for future technology.

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Method for a centering notch for an LGA socket and package

Disclosed is a method for a centering notch for a land grid array (LGA) socket and package. Benefits include improved functionality and improved support for future technology.

Background

         Most conventional LGA sockets use the outer edges of the substrate for location reference. The tolerance variation of the substrate size has not been a problem because the contact pitch is relatively larger than the tolerance variation. However, as contact pitch decreases, the pad diameter must also shrink accordingly. As a result, the substrate size tolerance becomes critical.

                 The typical size tolerance for a small organic substrate is +/- 0.1 mm. As substrate size increases for high-end server products, the manufacturing tolerance increases accordingly. For example, the tolerance capability of a ceramic package is limited to +/- 0.5% linear size. For a 60x60-mm substrate, the size tolerance is +/-0.3 mm.

         The conventional LGA and package substrate are keyed together. The substrate floats inside the socket. As the substrate is moved toward one side, a small gap occurs between the substrate edge and the socket fence on the other side. The gap size, typically 0.5 mm, is relatively much smaller than the contact pitch (1.27-1.50 mm). Additionally, most of the conventional LGA socket contact designs are double compression type and have a very short contact travel distance. The combination of short contact travel distance and relatively longer pitch permits a larger gap.

         However, as substrate size increases (such as for high-end server products) and as the contact pitch decreases, the size tolerance that is acceptable today may become unacceptable for future technology. Tighter substrate size tolerance will require extra manufacturing steps, which may translate into higher cost, but may not necessarily meet the size accuracy required by future products.

         The industry is in a transition from a mPGA to a surface-mount LGA socket. The surface mount LGA contact design has a longer deflection range. Longer deflection ranges require longer wiping distances, which require more pad area to mate with. The combination of the LGA contact design with tighter contact pitch requires a very tight tolerance control of the substrate size, which may...