Fastening device for tight attachment between two plates

A fastening device (10) includes a locking pin (12) and an associated pressing clip (14). The locking pin (12) includes a flat head (16) with ring-like shallow (18) therein for easy operational installation of the fastening device (12) unto the heat sink (100) and the PC board (200). A leg section (20) is provided below the head (16), including four locking legs (22) separated from one another by the slots (24) therebetween and extending downward from the head (16). Each leg (22) defines an enlarged tapered section (26) at the distal end with a shoulder section (28) thereabouts for latchable engagement with the back surface (201) of the PC board (200) around the corresponding hole (202) through which the locking pin (12) extends. A ring-like recess (30) is provided on the middle portions of the legs (22) for lowering the insertion force or preventing unnecessary excessive friction during insertion of the locking pin (12) into the corresponding holes (102, 202) of the heat sink (100) and of the PC board (200). A clip resting section (18) is positioned adjacent and under the head (16) with a step (38) therebetween for allowing the base (40) of the clip (14) to be mounted thereunto. Two wings or piers (44) of the clip (14) are provided by two ends of the base (40) of the clip (14).

BACKGROUND OF THE INVENTION 
1. Field of The Invention 
The invention relates to fastening devices for combining two plate-like 
pieces together, and particularly to the fastening device for tightly 
attaching a heat sink to a CUP mounted on a daughter board. 
2. The Related Art 
Traditionally, a CPU in the computer is installed unto a PGA (Pin Grid 
Array) socket which is mounted on a mother board, and a heat sink is 
attached to the CPU by a clip which is generally hooked unto the side 
edges of either the CPU or the socket, for example, U.S. Pat. Nos. 
5,381,305 and 5,436,798. Recently, the PGA sockets were replaced by the 
so-called the slot 1 connector with the associated retention means whereby 
a daughter board module with the CPU thereon is retained thereto wherein 
the heat sink is tightly fastened, by four screws, to the case or 
enclosure of the daughter board module for removal of heat generated by 
the CPU in the daughter board module. 
To lower down the cost of the daughter board module, an attempt is made to 
remove the enclosure of the daughter board module. Thus, it is required to 
have the a clip directly hooked unto the daughter board instead of the 
enclosure. One approach is taken that a plate-like clip with four hook 
legs on the four corners presses the back surface of the daughter board 
thus having the CPU on the front surface thereof abut against the heat 
sink wherein the four hook legs extend through the holes of the daughter 
board and are respectively latched to holes of the heat sink. Anyhow, it 
is not easy to make such plate like clip, and moreover, it requires to use 
a specific tool for simultaneously having the four hook legs latchably 
extend into the corresponding holes in the daughter board and in the heat 
sink. Further more, an excess tolerance of the positions or of the 
dimensions of the clip may prohibit clip from being expectedly evenly 
located, thus resulting in insufficient and bad combination between the 
heat sink and the CPU that substantially affects the heat transfer 
efficiency of the CPU and the corresponding signal transmission. 
Additionally, the main body of the plate directly presses against the back 
surface of the daughter board, and thus may damage the circuits 
thereabouts. 
Accordingly, it is known that another design is provided to use a locking 
pin with an associated surrounding coil spring wherein the distal end of 
the coil spring presses the bottom plate of the heat sink against the top 
surface of the CPU and the bottom end of the locking pin abuts against the 
back surface of the daughter board around the corresponding hole thereof 
through which the locking pin extends. Anyhow, the coil spring may 
provide, under some severe vibration situation, an unstable and unbalanced 
pressure on the heat sink that may jeopardize the securement between the 
heat sink and the daughter board, thus decreasing the heat transfer 
efficiency. 
Accordingly, an object of the invention is to provide a fastening device 
including a locking pin and an associated pier-like clip, thus reliably 
pressing the heat sink against the CPU on the daughter board. 
SUMMARY OF THE INVENTION 
According to an aspect of the invention, a fastening device includes a 
locking pin and an associated pressing clip. The locking pin includes a 
flat head with ring-like shallow therein for easy operational installation 
of the fastening device unto the heat sink and the daughter board. A leg 
section is provided below the head, including four locking legs separated 
from one another by the slots thereamong and extending downward from the 
head. Each leg defines an enlarged tapered section at the distal end with 
a shoulder section thereabouts for latchable engagement with the back 
surface of the daughter board around the corresponding hole through which 
the locking pin extends. A ring-like recess is provided on the middle 
portions of the legs for lowering the insertion force or preventing 
unnecessary excessive friction during insertion of the locking pin into 
the corresponding holes of the heat sink and of the daughter board wherein 
the diameter of the upper section and the lower section of the leg section 
are generally compliant with the holes of the heat sink and the daughter 
board. A clip resting section is positioned adjacent and under the head 
with a step therebetween for allowing the base of the clip to be mounted 
thereunto. Two wings or piers of the clip are provided by two ends of the 
base of the clip. When the fastening device is used with the heat sink and 
the daughter board, the locking pin is inserted into the corresponding 
holes of the heat sink and of the daughter board whereby the shoulder of 
the locking pin abuts against the back surface of the daughter board 
around the corresponding hole by mean that the heat sink is pressed 
against toward the CPU and the daughter board below by the spring forces 
generated by the deflected wings of the clip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
References will now be in detail to the preferred embodiments of the 
invention. While the present invention has been described in with 
reference to the specific embodiments, the description is illustrative of 
the invention and is not to be construed as limiting the invention. 
Various modifications to the present invention can be made to the 
preferred embodiments by those skilled in the art without departing from 
the true spirit and scope of the invention as defined by appended claims. 
It will be noted here that for a better understanding, most of like 
components are designated by like reference numerals throughout the 
various figures in the embodiments. Attention is directed to FIGS. 1-5 
wherein a fastening device 10 includes a locking pin 12 made by lathing 
and an associated pier-like clip 14 mad by stamping. 
The pin 12 includes a flat head 16 with a ring-like shallows 18 therein for 
allowing for using some tool to load the fastening device 10 to the heat 
sink 100 and the daughter board 200. 
A leg section 20 is integrally provided below the head 16, consisting of 
four legs 22 separated from one another by four axial slots 24. Each leg 
22 includes an tapered expansion section 26 forming an upward facing 
shoulder 28 for engagement with a back surface 201 of the daughter board 
200 around a corresponding hole 202 through which the pin 12 extends. It 
can be noted that the tapered configuration of the expansion section 26 
eases insertion of the locking pin 12 into the corresponding hole 102 of 
the heat sink 100 and hole 202 of the daughter board 200. 
A ring-like recess 30 is disposed around the leg section 20 to provide more 
resiliency and space thereof and prevent improper friction damage on 
either the heat sink 100 or the daughter board 200 during insertion of the 
locking pin 12 into the corresponding hole 102 in the heat sink 100 and 
hole 202 in the daughter board 200. 
It can be noted that due to ring-like recess 30, an upper section 32 and a 
lower section 34 are formed on two opposite ends of the recess 30 along 
the pin 12 wherein the diameter of the upper section 32 and that of the 
lower section 34 generally comply with the holes 102 of the heat sink 100 
and the hole 202 of the daughter board 200. 
A clip resting section 36 intermediates between the head 16 and the leg 
section 20, and forms a step 38 under the head 16 whereby a plane base 40 
of the clip 14 with a retention aperture 42 therein can be seated unto the 
step 38 wherein the aperture 42 of the clip 14 receivably engages the 
resting section 36 in an tight interference fit. A pair of wings or piers 
44 obliquely extend outward and downward from two opposite ends of the 
base 40 each with an opening 46 therein for increasing resiliency thereof 
and with a distal end 45 for abutment against a top surface 106 of the 
heat sink 100. 
Therefore, when used, the locking pin 12 extends through the corresponding 
hole 102 of the heat sink 100 and hole 202 of the daughter board 200 
wherein the expansion sections 26 of the legs 22 engage the back surface 
201 of the daughter board 200 around the corresponding holes 202, due to 
the reaction forces and the initial spring force which is generated from 
the wings 44 of the clip 14 and presses the base plate 104 of the heat 
sink 100 against the CPU 300 mounted on the daughter board 200. Thus, the 
heat sink 100 and the daughter board 200 can be tightly and stackably 
combined as one assembly. 
Referring to FIG. 4, the four slots 24 defining a cross-like configuration 
from a bottom view, provides adjustment in both the X and Y axes on a 
horizontal plane for efficiently forgiving any improper excess tolerance 
and mis-centered arrangement between the locking pins 12 and the 
corresponding holes 102, 202 or the heat sink 100 and the daughter board 
200, thus assuring proper and reliably tight attachment between the heat 
sink 100 and the CPU 300 on the daughter board 200. 
Referring to FIG. 5, the pair of wings 44 not only provides balanced and 
sufficiently strong spring forces against the heat sink 100 for obtaining 
the desired heat transfer efficiency between the heat sink and the CPU, 
but also is adapted to be compliantly received within a groove-like 
passageway 106, formed between the fins 108, of the heat sink 100, thus 
allowing for using the existing heat sink without additional reshaping of 
the heat sink. 
It is also noted that according to the invention, the sum of the 
thicknesses of the base plate 104 of the heat sink 100, the CPU and the 
daughter board 200, should be larger than the vertical distance between 
the end 45 of the wing 44 and the shoulder 28, and thus the wings 44 of 
the clip 14 may be upwardly deflected or deformed to provide the spring 
force against the heat sink 100 for firmly retaining the base plate 104 of 
the heat sink 100, the daughter board 200 and the associated CPU 300 
between the wings 44 and the shoulder 28.