AMD 1207 manual Spring Clip, Chemical Element of SK7 Spring Steel

32800 Rev. 3.02 August 2006 Thermal Design Guide for Socket F (1207) Processors

5.3.2Spring Clip

The spring clip is designed to apply 75 lbs of force to the center of the heat sink. This force is necessary to help prevent the heat sink from lifting off of the package during shock or vibration- induced events. Lifting the heat sink away from the processor can result in damage to the processor contact pads, the socket contacts, or the socket solder-ball joints. Maintaining the spring force is important for the life of the processor and for repeated installations and upgrades of the processor.

The spring clip material is heat-treatable spring steel, SK7. AMD strongly recommends using SK7 or an equivalent material for the spring clip. The clip should be plated after heat treatment for cosmetic and anti-corrosive reasons. Table 9 gives the chemical composition of SK7. The heat treatment used should bring the ultimate strength of the material to a minimum of 1,300 megapascals (MPa) or 189 kilopounds per square inch (kpsi), and it should bring the yield strength to 940 MPa (or 136 kpsi).

Other materials commonly used for heat sink spring clips have been shown to yield under the high load of the initial spring-clip deflection and become deformed so that the spring clip can no longer apply the same load.

Table 9.	Chemical Element of SK7 Spring Steel
	Element	Percentage of the Element
	C	0.60-0.70
	Si	Maximum 0.35
	Mn	0.80-0.90
	P	Maximum 0.030
	S	Maximum 0.030
	Fe	Remaining balance

5.3.3Retention Frame

The plastic retention frame, made of 20% glass-filled Lexan, is a two-piece implementation rather than the single-piece frame used for socket 940. This change accommodates the larger foot-print of socket F (1207) processors.

The retention frame serves multiple purposes. The retention frame aligns the heat sink and provides a stop for the heat sink in large shock-force events. The retention frame and backplate are attached to the motherboard by the motherboard vendor. Two screws securely hold the backplate and retention frame together. The two mounting tabs on the retention frame serve as attachment points for the heat sink spring clip.

5.3.4Heat Sink

Figure 10 on page 34 shows a picture of the reference design heat sink for 2U-4P systems. The footprint of the reference design heat sink is 92 mm x 58 mm. The heat sink weighs 378 g and has an aluminum fin stack soldered to the copper base. The copper base tapers from a thickness of 7 mm at

Chapter 5 Thermal Design of Custom 2U-4P Systems 33