Joints and connections – Biased catch or latch – By separate spring
Reexamination Certificate
2001-10-15
2004-03-16
Browne, Lynne H. (Department: 3679)
Joints and connections
Biased catch or latch
By separate spring
C403S321000, C403S322100, C403S325000, C403S330000, C024S458000, C292S241000, C292S242000, C248S500000, C248S510000, C411S552000
Reexamination Certificate
active
06705795
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an attachment mechanism for mounting a cooling device to a component to be cooled. More specifically, the present invention relates to an attachment mechanism including a plate with a hinge and a pivotally mounted latch assembly for connecting a cooling device carried by the plate with a component to be cooled.
BACKGROUND OF THE INVENTION
It is well known in the electronics art to place a heat sink in contact with an electronic device so that waste heat generated by operation of the electronic device is thermally transferred into the heat sink thereby cooling the electronic device. With the advent of high clock speed electronic devices such as microprocessors (&mgr;P), digital signal processors (DSP), and application specific integrated circuits (ASIC), the amount of waste heat generated by those devices and the operating temperature of those devices are directly proportional to clock speed. Therefore, higher clock speeds result in increased waste heat generation which in turn increases the operating temperature of the device. However, efficient operation of the device requires that waste heat be effectively removed.
Heat sink devices came into common use as a preferred means for dissipating waste heat from electronic devices such as the types described above. In a typical application, a component to be cooled is carried by a connector that is mounted on a PC board. Efficient dissipation of heat from the component by the heat sink depends to a large extent on the thermal contact between the heat sink and the component and the contact pressure between the heat sink and the component. Ideally, an attachment device, such as a clip, positions the heat sink so that the a surface of the heat sink that is in contact with the component is substantially flat and the contact pressure between the heat sink and component acts along a load axis that is centered on the component.
There are, however, several disadvantages to prior clips for mounting a heat sink to a component. First, many of the prior clips are manufactured from a raw material such as spring steel or Stainless Steel, for example. The raw material that is ultimately selected must be of a punch and formable grade. Consequently, a spring rate of the material selected must be low and the hardness of the material must also be low so that a punch step and a forming step that are used to manufacture the clip can successfully punch and form the material into a clip. If the spring rate and hardness of the material are too high, then the material will be extremely difficult to punch and form. Additionally, a lifetime of a die that is used to punch and form the material will be reduced.
Second, the aforementioned spring rate of the material selected for the clip does not remain constant throughout the manufacturing process. Several factors contribute to variations in the spring rate including: variations in raw material sizing; variations in post process steps; and differences in elemental compounds that are used to form alloys of the material used for the clip. Because the objective of using a clip is to apply a load on the heat sink and the component such that heat is efficiently transferred from the component to the heat sink. As a result of the aforementioned variations, there are variations in a load characteristic of clips produced from different batches of raw materials and/or by different processing steps.
Third, another property of the clip that is directly related to the spring rate is a spring back property. If a clip is made from a material with a high spring back property, then it is more difficult to form and achieve a required profile in the clip as the tools used for forming those profiles require a substantial amount of spring back compensation. Another consequence of the high spring back property is that it makes it difficult to achieve a desired dimensional accuracy in the clip.
Fourth, a load center of the clip depends on accurate dimensions for each arm of the clip. However, due to the above mentioned spring back property, there will be variations in the arm lengths that result in the load center being offset from an ideal position. Consequently, the load center will not act on the required point with a resulting increase in a contact resistance between the heat sink and the component. The higher the contact resistance results in less efficient heat removal of waste heat from the component by the heat sink.
Fifth, to compensate for the spring back property associated with the material selected for the clip, in some cases, a soft material is selected for the forming process. After forming, the soft material is heat treated to harden the material. However, the material deforms during the heat treatment process and causes the load center to shift with the same results as described above.
Sixth, another disadvantage of prior clips is that they are difficult to install and difficult to remove. For instance, to install a prior clip, a latch portion on an arm of the clip must be tilted during insertion followed by pushing the latch portion back to attach the latch portion to a tab or the like on the connector that carries the component. On the other hand, to remove the prior clip, a special tool is usually required to tilt a handle on the clip so that the latch portion disengages from the connector. In some cases, the handle is so small that it is not easy to remove the clip using the special tool and is extremely difficult if not impossible to remove the clip by hand.
Finally, a typical prior clip that is made from a material such as sheet metal, for example, is designed to exert a total load force of about 25 lbs. To exert a higher load force requires either the thickness of the material be increased or the hardness of the material be increased to achieve a higher spring rate that will result in a higher load force. However, increasing the thickness and/or the spring rate of the material makes the material extremely difficult to punch and form and also reduces die life.
Consequently, there is a need for an attachment device that is made from a material that eliminates the aforementioned dependence on spring rate and material hardness, eliminates variations in spring rate due to variations in material properties or variations in processes used to form the material, and that eliminates variations in load characteristics. There exists a need for an attachment device that eliminates dependance on a materials spring back property and the resulting difficulties in manufacturing clip profiles that arise from the spring back property. Additionally, there is also a need for an attachment device that provides for an accurate load center that is free from offset due to the aforementioned variations in the spring back property caused by arm length variations and/or heat treating a soft material. There is a need for an attachment device that is capable of exerting a high total load force without increasing material thickness or material hardness to achieve a higher spring rate commensurate with the high total load force and that achieves the high total load force without reducing die life. Finally, there is a need for an attachment device that is easy to install and remove without the need for special tools and that can be installed or removed by hand.
SUMMARY OF THE INVENTION
The attachment mechanism of the present invention solves the aforementioned problems. The problem associated with the use of punch and formable materials such as steel or Stainless Steel with a low spring rate and a low hardness are solved by using a plate. The plate can be made from a rigid material, such as a metal, for example. The plate can be formed by die casting, injection molding, and stamping, for example.
Furthermore, the problems associated with variations in spring rate and the resulting variations in the load characteristics of the prior spring clips are eliminated by using a rigid material for the plate thereby providing for a consistent load characteristic. The plate is substanti
Browne Lynne H.
Denny III Trueman H.
Flandro Ryan M.
Hewlett--Packard Development Company, L.P.
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