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This application is related to U.S. Ser. No. 321,329, filed this same date,
Oct. 11, 1994.
BACKGROUND OF THE INVENTION
The present invention relates to an electrical connector and, in
particular, a zero insertion force, pin grid array socket.
Integrated circuits (ICs) have become the world's standard for electronic
circuits. These range from basic transistor networks to complex memory,
microprocessor and multi-chip module circuits. The common denominator to
all such circuits is that they are produced en mass on a substrate such as
silicon and then separated into individual units commonly known as chips.
The majority of chips are then mounted in a carrier for subsequent
incorporation into end products. The basic size, shape and construction of
the carrier is commonly known as the package and many standard packages
have emerged. Some examples are commonly known as DIP, SOJ, PLCC, QFP and
PGA. Chip packages have developed to accommodate both circuit function,
i.e., number and placement of leads, and assembly trends, i.e.,
through-board and surface mount solder assembly. While the majority of IC
devices are hard soldered in place, several factors such as device
availability, testing, upgrades, etc., have traditionally shown that there
is a need to socket ICs regardless of their package. IC sockets are known
in the art for receiving pin grid array (PGA) packages. Previous PGA
sockets required a high insertion force. Such sockets resulted in lead
damage due to the high insertion and withdrawal forces. Presently, IC
packages have increasingly larger pin counts due to the continued
miniaturization of the ICs. Such increased pin counts require zero
insertion force (ZIF) sockets. For example, Intel, Inc. OverDrive.TM.
Processor Sockets are known in the art. Generally, the contacts used in
these sockets are referred to as normally closed contacts. Such ZIF PGA
sockets are known in the art but include complex and expensive contact
designs. Such contact designs are stressed greatly as the insertion forces
increase. Also, such common contact designs have large plating areas which
increase cost. Further, such socket designs do not provide for adequate
cooling of the IC packages. Accordingly, there is desired a ZIF PGA socket
design which overcomes the aforementioned shortcomings.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a socket
which includes a contact design which is quickly and inexpensively
manufactured.
It is another object of the present invention to provide a socket having a
contact design which provides for a selective plating area.
It is a further object of the present invention to provide a socket having
a contact design which provides for low stress-strain upon increase of
normal force.
It is another object of the present invention to provide a contact design
providing for great elastic range upon insertion.
It is a further object of the present invention to provide a contact which
may be generated on a die having small centers to reduce material usage.
It is another object of the present invention to provide an air-gap to
provide additional cooling of the IC package.
Accordingly to the above object of the present invention, a zero insertion
force, pin grid array IC socket comprises a cover slidably engaged to a
base and the cover having an array of holes formed therethrough
corresponding to an array of passages in said base for receiving a
corresponding array of IC pins. The passages of the base including
contacts having a generally tuning-fork shape, having a tail portion and a
U-shaped portion having a pair of torsional beams. The U-shaped portion
has an open side including retention arms being bent at a
45.degree.-90.degree. angle to the plane of the tail and U-shaped portion.
The open portion of the contact includes a pair of wipe surfaces and
shoulders. The wipe surfaces being at the stamped edge of the contact.
The contact includes a pair of continuous torsional beams having a surface
area of at least forty percent of the surface area of the entire contact.
The torsional beam provides for a low stress/swain force ratio.
The contact includes a pair of wipe surfaces along the stamped edge or
first side of the open end of the contact. This arrangement provides for a
reduced selective plating area. A selective plating area includes an area
less than an eightieth of the size of the entire contact.
Further, an air-gap means is provided including a stand-off hole through
the cover for receiving an IC package pin having a stand-off thereon
wherein insertion of the stand-off pin in the stand-off hole causes the
stand-off to abut the top surface of the cover.
These and other features of the invention are set forth below in the
following detailed description of the presently preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the socket of the present invention;
FIG. 2 is a partial side elevation cut-away view of FIG. 1 taken at line
2--2;
FIG. 3 is a plan view of the socket of FIG. 1;
FIG. 4 is a plan view of the socket of the present invention having the
cover removed;
FIG. 5 is an enlarged plan view of Area A of the socket of FIG. 4;
FIG. 6 is a side elevation cut-away view of the socket of FIG. 5, taken at
line 6--6;
FIG. 7 is a side elevation cut-away view of the socket of FIG. 5, taken at
line 7--7;
FIG. 8 is a perspective view of a contact of the present invention; and
FIG. 9 is a perspective view of a contact of the prior art.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
An embodiment of the zero insertion force, pin grid array socket of the
present invention is best understood by FIGS. 1-8. Turning to FIG. 1,
socket 10 is shown in perspective view, having base 20 and cover 40. The
cover includes an array of holes 42 for receiving pins of an IC package.
The holes 42 generally are beveled in order to assist in the insertion of
the pins of the IC package. The socket 10 includes actuator 60 for sliding
the cover 40. FIG. 1 shows the actuator 60 in an intermediate position. By
moving the actuator 60 in direction of arrow 61, the cover 40 will be slid
in direction of arrow 41 to move the cover 40 into the opened position. In
this position, the IC package will be mounted to the socket 10 via
insertion of the IC package pins through the corresponding array of holes
42 of the cover 40. The array of pins of the IC package are inserted
through the array of holes 42 of the cover 40 and into the corresponding
array of passages of the base 20. Due to the design of the contacts and
the passages of the base 20, the insertion of the pins requires a zero
insertion force. Following full insertion of the pins into the holes 42
and passages of the base 20, the actuator 60 is moved in direction of
arrow 62 causing the cover 40 to slide in direction of arrow 43, forcing
the pins into their fully mated position with the contacts mounted in the
passage of the base 20.
The cover 40 is mounted to the base 20 via outer latches 51 which engage
hooks 53 of the base 20. As well, the cover 40 includes inner latches 52
which engage inner hooks 54. In a preferred embodiment, the latches 51,52
are integrally molded with the cover 42 and the hooks 53,54 are integrally
molded with the base 20. The latches include an opening 55. The opening 55
has a sufficient width greater than the hooks 53,54, so that the cover 40
may slide freely in direction of arrows 41,43 without abutting the hooks
53,54. While the latches 51,52 act to retain the cover 40 onto the base
20, they also provide a means for limiting warpage of the cover 40. The IC
packages which are mounted to the socket 10 can undergo great changes in
heat dissipation. Such heat may cause the warpage of the socket 10. To
avoid such warpage in a preferred embodiment, four outer latches 51 are
oriented in each comer of the socket 10 and a pair of inner latches 52 are
oriented on either side of the inner portion of the socket 10.
The socket 10 includes on its cover, stand-off hole 46. The stand-off hole
46 receives a stand-off mounted on selected pins of the IC package.
According to specific industry specifications, each IC package includes
four stand-off pins adjacent the center of the package. The stand-offs are
received by the stand-off holes 46 of the present invention and maintain
an air-gap between the cover 40 of the socket 10 and the IC package (see
FIG. 2). The actuator 60 of the present invention, in its preferred
embodiment, includes an end portion 64 which is bent at an angle of
approximately 15.degree.-30.degree. from the axis of the shaft 65 of the
actuator 60. The bent end 64 of the actuator 60 allows for the actuator to
be easily grasped to move the actuator from its closed position to the
open position. Especially when an IC package is mounted to the socket 10,
the bent end 64 of the actuator 60 is easily grasped. The actuator 60 is
mounted in channel 67 of the base 20. The channel 67 has an open end 68
and a closed end 69. At the closed end 69, a retaining wail 70 extends
from the edge of the base 20 and is perpendicular to channel 67. A
retaining wail 70 retains the actuator 60 within channels 67 upon
attachment of cover 40 over the actuator 60 and onto the base 20.
FIG. 2 shows a partial side elevation cut-away view of FIG. 1, taken at
line 2--2 and also shows an IC package 80 mounted to the socket 10. Base
20 includes passages 22. Mounted within most passages 22 are contacts 30.
Mounted to base 20 is cover 40. The cover includes holes 42. Generally,
these holes are beveled to allow the easy insertion of pins 81 of the IC
package 80. However, in a preferred embodiment at four positions on the
cover 40, stand-off holes 46 are not beveled and are only a through-hole
having a diameter slightly larger than the pins 81 of the IC package 80.
As the stand-off 82 has a diameter which is larger than the diameter of
the stand-off hole 46, the stand-off 82 prohibits the pin from being
inserted any further into the socket 10. As the stand-off 82 of the pin 83
is spaced between 0.200 inches to 0.180 inches from the base of the IC
package 80, there is provided an air-gap 85 of equal spacing. This air-gap
provides for the circulation of air between the IC package 80 and the
socket 10. The air-gap allows for heat reduction to occur for the IC
package 80 and the socket 10.
FIG. 3 is a plan view of the socket 10 of FIG. 1 having cover 40 and base
20. The cover 40 includes holes 42 which include a beveled opening for
receiving the pins of a IC package. Stand-off holes 46 are through-holes
which do not have a beveled opening. Actuator lever 60 is mounted in
channel 67 of housing 20 and is retained to the socket 10 via retention
wall 70. The actuator 60 may be mounted on either the right or left side
of the socket 10. Outer latches 51 engage hooks 53. Inner latches 52
engage hooks 54.
FIG. 4 is a plan view of the socket 10 having the cover removed. The base
20 is shown having an array of passages 22. Contacts 30 are mounted in
passages 22. Channel 67 is shown having the actuator removed. In a
preferred embodiment, the socket 10 houses two hundred and thirty-six
contacts on 0.100 inch spacing. Generally, the socket 10 has an overall
dimension of 1.940 inch.times.2.430 inch.times.0.320 inch. In a preferred
embodiment, the housing of the cover and base are injection molded from a
polymeric material.
Turning to FIG. 5, an enlarged plan view of Section A of FIG. 4 is shown.
Base 20 includes passages 22 having contact 30 mounted therein. Upon
initial insertion of the pins of an IC package, the pins are inserted
through the cover and are received in zero insertion force bore 25. The
zero insertion force bore 25 has a diameter greater than the diameter of
the pin of the IC package. The pin is then slid in direction of arrow 24
and is moved from zero insertion force bore 25 into passage 22 via the
movement of the cover. The pin first contacts shoulders 31,34 of the
retention arms 35 of contact 30. The pin then continues past shoulders 31
to arrive in its fully mated position against wipe areas 32,33.
FIG. 6 is a side elevation cut-away view, taken at line 6--6 of FIG. 5. The
base 20 includes passages 22 having contacts 30 mounted therein. The
contact includes tail 38 and U-shaped section 37 at the opposite end from
the tail 38. U-shaped section 37 has at its open end retention arms 35.
The retention arms 35 are bent at approximately a right angle to the plane
of the tail 38 and U-shaped section 37 and parallel to the stamped edge of
the contact 30. The tails 38 of the contacts 30 are inserted into
apertures 29 of the base 20.
FIG. 7 is a side elevation cut-away view of FIG. 5 taken at line 7--7. Base
20 is shown having passages 22 having contacts 30 mounted therein. The
contacts 30 have tail potion 38 and at the end opposite end, U-shaped
section 37. The U-shaped section 37 has at its open end retention arms 35.
The contacts 30 also include wings 26 for providing a friction fit of the
contact 30 within passage 22.
Turning to FIG. 8, contact 30 includes tail 38 at one end and U-shaped
section 37 at the other end. U-shaped section 37 includes an open end
having torsional beams 27,28. At the end of the torsional beams 27,28 are
retention arms 35. The retention arms 35 are bent at an angle to the
U-shaped section 37 and tail portion 38 of the contact 30. The angle at
which the retention arms 35 are positioned may vary from between
45.degree.-90.degree.. The retention arms 35 of the contact 30 include
shoulders 31,34 and wiping areas 32,33.
The insertion of the pin of the IC package into the contact 30 is
represented by pins 81a, 81b. Generally, contact 30 is a stamped contact
of a copper alloy or phosphor bronze. The contact is stamped on a die in a
unitary plane. The unitary plane is that of the tail 38 and U-shaped
section 37. The stock that the contact 30 is stamped from, in a preferred
embodiment, has a stamped edge or a first side 11 which generally has a
thickness of 0.005 inch and a wipe area 33 which is approximately 0.030
inches long, providing a total wiping surface area of 0.00036 square
inches compared to the total contact surface area which is 0.031 square
inches or approximately eighty-six times the wiping surface area. This
small wiping area allows for selective plating of a small area of the
contact 30. Prior to the forming of the retention arms 35 at approximately
a right angle, the contact in its unitary plane is plated at this
selective wiping area 33 or target area. A method of forming the socket
includes preparing a plurality of contacts on a die in a unitary plane
plated generally at the selective wiping area 33. It can be seen that the
overall design of this contact allows for a great reduction in the plating
materials required for this contact 30. In a preferred embodiment, gold
plating is adhered to wipe areas 32,33 and due to the small area, the
plating costs are greatly reduced. Such plating techniques may include
mask plating or controlled depth plating. Such plating techniques may be
applied either before or after bending of the retention arms 35. As well,
the contact design of the present invention allows for the contacts to be
spaced on the die on 0.100 inch spacing so that they may be quickly and
easily inserted into the passages 22 of the base 20 and providing for
minimal material usage.
The IC package pin 8 la is initially inserted into the zero insertion force
bore and is then slid in direction of arrow 24. The pin 81a is slid
between the retention arms 35 of the contact 30. The pin 81a initially
contacts shoulders 31,34 of the retention arms 35. As the pin 81a slides
past shoulders 31,34, the greatest mount of force is received by the
contact 30. Because each retention arm 35 is a unitary member with the
entire torsional beams 27,28 and U-shaped section 37, the entire force
received at shoulder 31 is spread along the entire length of the torsional
beams 27,28 of the U-shaped section 37. The force of the pin 81a against
shoulders 31 causes the torsional beams 27,28 including the retention arms
35 to deflect in a torsional manner in direction of arrow 39. Each
torsional beam 27,28 of the contact 30 receives this torsional deflection
upon insertion of the pin 81a.
The present contact design provides for the contact being stamped from a
sheet of material having a narrow Z dimension or thickness or first side
11. The rolled surface of the material is of sufficient width and length
for the X-Y dimensions of the contact and define a second side 12 and a
third side 13. The retention arms 35 are bent at an angle to the second
side 12 or third side 13 of the contact 30. Such bending along the
relatively lengthy crease 15, as compared to the thickness of first side
11, provides for a large surface area of the contact 30 for the torsional
motion 39 induced by the normal force of pins 81a, 81b to be transferred
beyond the retention arms 35 and to the entire torsional beam 27,28. Such
torsional beams 27,28 provide for the advantages of the present invention
of a low stress/strain force ratio and a great elastic range, as compared
to the straight cantilever designs of the prior art (see FIG. 9). The
prior art contact designs have the retention arm 92 bent (or stamped) at
an angle to the first side 11' which provides only the narrow thickness of
the contact to receive the torsional forces of the retention arm; which
are not transferred to the beam 93 of the contact 90. Due to the
dispersion of the normal force of the pin 81a of the present invention
along the entire torsional beams 27,28 length, the stress-strain
measurement is lessened for this contact design. Thus, the torsional beams
having a surface area of at least forty percent of the entire contact
surface area, provide for greater elastic range than the contacts of the
prior art, while maintaining sufficient normal forces.
After the pin 81a is slid passed shoulders 31 of each retention arm 35, it
attains its final mating position against wiping areas 32,33. Pin 81b is
shown in the final mated position abutting wiping areas 32,33 of the
retention arms 35 of the contact 30. The distance between wipe areas 32,33
is only slightly greater than that between shoulders 31,34, and the force
of the contact 30 against the pin 81b is a sufficient normal force to hold
the pin 81b therein.
FIG. 9 shows a prior art contact 90 of a generally straight cantilever
design. The contact 90 includes only a single wipe area 94 and includes a
retention arm 92 which is formed at an angle to the first side 11' or
thickness of the contact 90. Pin 91a is moved to its mated position 91b
next to wiping area 94. Upon such movement, the entire force is taken up
by only the retention arm 92. The majority of the body of the contact 90
including beam 93 is not acted on by the normal force of the pins 91a, b.
As well, the prior art contact design requires a large area to be plated.
Due to the shape of the contact 90, it is generally necessary to plate the
entire retention arm 92 and sometimes the whole upper portion of the
contact 90. Such prior art contacts do not have the advantage of the
contact of the present invention in that two wipe areas are not provided,
insertion forces are not deflected throughout the majority of the contact
surfaces and selective plating of small areas cannot be undertaken.
It should be understood that various changes and modifications to the
presently preferred embodiments described herein will be apparent to those
skilled in the art. Such changes and modifications may be made without
departing from the spirit and scope of the present invention and without
diminishing its attendant advantages. It is, therefore, intended that such
changes and modifications be covered by the appended claims.
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