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Socket Cooling Using External and Internal Heat Sinks, Forced Air Convection, and Underfill for the Socket-Motherboard Interface

IP.com Disclosure Number: IPCOM000101733D
Publication Date: 2005-Mar-16
Document File: 5 page(s) / 634K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for removing heat from the socket and socket pins by using heat sinks on external moldings and internal cavities, using forced air convection, or by applying underfill to the socket and motherboard interface around the solder ball array. Benefits include improving thermal performance.

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Socket Cooling Using External and Internal Heat Sinks, Forced Air Convection, and Underfill for the Socket-Motherboard Interface

Disclosed is a method for removing heat from the socket and socket pins by using heat sinks on external moldings and internal cavities, using forced air convection, or by applying underfill to the socket and motherboard interface around the solder ball array. Benefits include improving thermal performance.

Background

Current densities are increasing with every product generation, thereby increasing socket pin temperatures. The maximum socket pin temperature (~ 100oC) is used as the threshold for various failure modes that occur between the socket pin and the LGA land. Reducing the maximum socket temperature requires the reduction of the overall board temperature and/or the maximum total current running through the power and ground pins.

Currently, no dedicated cooling solution for a socket exists.  The heat from the pins and solder balls flows into the socket mold and motherboard, which are exposed for natural convection. Some heat is also lost from the outer perimeter of the socket molding by natural convection. Figure 1 shows the top view of an LGA package. The socket mold surrounding the pins and the capacitors on the motherboard are clearly visible. Figure 2 shows the schematic illustration of the cross section of a socket showing all the details.

General Description

The disclosed method proposes three different approaches for removing heat from the high-current carrying socket pins:

External and Internal Heat Sinks

Figure 3 shows a heat sink on the outside molding of the socket; this achieves a very high heat transfer coefficient by regulating the air flow. There are many heat sink designs that can be used with the disclosed method. The present generation socket current maps predict current flow of around 0.5 amperes in the peripheral pins.

Figure 4 shows a heat sink on the inside molding of the socket. Since this region is directly under the die shadow, it carries a very high current (i.e. more than one ampere) and has higher temperature boundary conditions. Since the heat sink is attached inside the cavity, there is no air flow, and the heat can only move to other regions of the socket if a significant temperature difference exists. Therefore, the heat sink tends to act more as a heat slug rather than a heat sink. However, an encapsulated Phase Change Material (PCM) can be used to accommodate the transient current variation between die activities.

The internal heat sink can be attached to the socket mold cavity using epoxy or using an internal wire frame (see Figure 5) within the socket molding. Epoxy is easier from a manufacturing point of view, but a wire frame decreases the thermal resistance of the socket molding and may lead to more benefits. The wire frame...