AMD ClawHammer Thermal Design - Socket 754 Design

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More commonly now are newsbits about AMD's upcoming 64bit central processing units. It was brought to my attention that they have a tech white paper which describes two different heat sinks and mounting methods for the new CPU. The new connector for Hammer processors will be called Socket 754. Read more to learn all about the new guidelines about 8th generation cooling.

Heatsink - Backplate design: The heat sink installers do not have to assemble each individual component. The heat sink vendors package the parts with some of the components already assembled. The logical breakdown consists of the components that reside on the topside of the motherboard, the heat sink, and the components that reside on the bottom side of the motherboard, the backplate. Due to the high load required to attach the heat sink to the processor, a backplate is used on the backside of the motherboard to minimize possible warping of the motherboard due to clip forces on the heat sink. requires a screwdriver to install the heat sink. The mechanical advantage of the screw is that it applies a large force to the clip. Minimizing installer fatigue was a significant factor in selecting the use of screws in this thermal solution. Rentention mechanism design: The components are shipped as subassemblies so the heat sink installer does not have to assemble each individual component. The retention frame and backplate are shipped preinstalled on the motherboard. The heat sink unit has the components assembled so the installer can remove it from the packaging, remove any thermal interface material protection, hook the clip onto the retention frame, and then actuate the cam. the installer needs no tools for the heat sink installation process. Specific Functions: The backplate assembly prevents excessive motherboard warpage in the area near the processor. Without using a backplate, the warpage could cause serious damage to electrical connections of the processor socket and integrated circuit packages surrounding the processor. The reference backplate is made from a ΒΌ-inch hard-milled steel and incorporates three stiffening ribs to meet stiffness requirements. There is also a square hole in the center of the backplate with the center rib partially cut away. This region is for decoupling the capacitors on the backside of the motherboard. It is important to not cut entirely through the center rib, as that would compromise the stiffness of the backplate. There are two PEM standoffs used in the plate. The standoffs serve multiple purposes, mainly as attachment points for the retention frame screws and aligning the backplate easily and properly to the motherboard. Features in the retention frame slide over the standoffs and allow the screws to be installed with very little chance of cross-threading. The insulator also serves multiple purposes. The primary function of the insulator is to prevent the backplate from electrically shorting to the motherboard. Additionally, a pressure-sensitive adhesive in the insulator keeps the backplate in place against the motherboard during assembly. Also, the insulator is thick enough to prevent any significant capacitive coupling between the motherboard and backplate. The spring clips used for both thermal reference design solutions were designed to apply 75 lbs of force to the heat sink. This force is necessary to prevent a large mass heat sink from lifting off of the package during shock or vibration induced events. Any lifting of the heat sink away from the processor could result in damage to the processor pins, the socket contacts, or the socket solder ball joints. This spring force is greater than required in previous processor generations. Maintaining the spring force is important for the life of the processor and for repeated installations and upgrades of the processor. The retention frame serves multiple purposes. During installation, the retention frame provides a stop for the spring clip ends used in the thermal reference design solution 1. The retention frame also aligns the heat sink and provides a stop for the heat sink in large shock-force events. The retention frame serves to hold the solution 1 heat sink assembly together as a single unit for shipping and assembly, and aligns and helps to retain the EMC shield. The retention frame serves the same function for the thermal reference design solution 2, but it is implemented in a different way. The retention frame and backplate are joined to the motherboard by the motherboard vendors. Two screws securely hold the backplate and retention frame together. The six mounting tabs on the retention frame serve as an attachment point for the heat sink spring clip. The thermal reference design solution 2 utilizes only two of the mounting tabs, but the flexibility of the design is increased with the additional mounting tabs. The footprint of the reference design heat sink is 77x68 mm. The highest-power processors may require solutions incorporating copper in the base of the heat sink to spread heat, taller fins, increased fin density to increase surface area, and higher flow fans to increase cooling capacity. Because the processor mounting surface extends above the surface of the cam box on the socket, the heat sink bottom can be flat. The heat sink must have a flat surface of at least 40x40 mm centered over the processor as specified in the reference design drawing. Because of the high clock frequencies of the ClawHammer processors, an EMC shield has been designed and incorporated into the thermal solution. This shielding is an optional component that may or may not be necessary for meeting regulatory agency requirements, depending on the system. However, the shielding has been designed as a component that can be added to the heat sink assembly either during assembly of the heat sink components or during final assembly of the system. The heat sink retention frame has features for aligning and retaining the EMC shield. Reference Heatsink: AMD uses aluminum for their reference heat sinks. The final design is not yet complete or more likely there will be more than one solution. AMD is going to use 60mm or preferably 70mm fans for cooling. The heat sink makes contact with the top surface of the processor package utilizing the thermal interface material between the processor lid and the heat sink. AMD recommends using a high-performance grease. Furthermore cheap coolers will be 100% aluminium while higher performance coolers have a copper base or are manufactured completely of copper. More interestingly it seems that AMD is working on heat sink designs that allow attachment of external thermal diodes. See pictures below. Socket 754: Here a three-dimensional view of the Socket 754, which is a socket based on surface mount technology. The pin array is 29x29 on a 1.27 mm pitch with a 9x9 depopulation in the center. In addition, three pins are removed from the A1 corner of the package, and a single pin is removed from the other three corners. The electrical and mechanical connection to the motherboard is made with a small solder ball at each socket contact. This type of connection does not allow for a large mass, like a heat sink, to be attached to the socket. Therefore, independent support structures are required for mounting the heat sink. Source: AMD