Low insertion-force socket for IC device

A socket for an integrated circuit device, particularly of the "Small Outline" type, includes a receptacle having a base and a pair of opposing side walls. A row of spaced-apart, generally vertical guide members extending inwardly from the interior surface of each side wall defines a row of generally vertical slots adjacent the interior surface of each side wall. Near the bottom of each slot is an electrical contact, comprising a pair of elongate, overlapping wire loops, each having a leg interposed between the legs of the other loop. The contact has one end conductively connected to an interior portion of a conductive pin which extends through the base of the receptacle. The other end of the contact is a free end that exhibits a resilient flexibility. A cover is provided with two opposed rows of downwardly-extending fingers, each of which is registrable with, and receivable in, one of the slots. The slots are spaced and dimensioned so that each lead of the IC device is received in a separate slot when the device is placed in the receptacle. When the cover is then placed on the receptacle, each lead of the device is firmly engaged between a finger of the cover and the resilient electrical contact in the slot.

BACKGROUND OF THE INVENTION 
This invention relates generally to the field of sockets for electronic 
components and devices. More particularly, it relates to a socket for 
integrated circuit devices, especially those of the so-called "small 
outline" type, in which the device can be installed or "socketed" with 
little or no insertion force applied to the body of the device, and with 
subsequent retention forces applied substantially only to the leads of the 
device. 
The use of integrated circuit ("IC") devices has become commonplace in the 
electronics field. One type of IC device which has recently gained 
popularity is the "small outline" or "SO" device. The SO device resembles 
the standard dual-in-line package ("DIP") device, but it is substantially 
smaller in size, with short, stubby pins with horizontal end tabs, as 
opposed to the long, thin, generally vertical pins of the standard DIP 
device. 
In many applications, the IC device is "surface-mounted", that is, soldered 
or otherwise permanently fastened directly onto a circuit board. In some 
applications, however, a permanent installation is not desired, due to a 
need, for example, to remove the device periodically. This is true, for 
example, in testing and "burn-in" procedures. In such applications, a 
socket is necessary for the temporary installation of an IC device into a 
testing or burn-in circuit. 
Small outline devices pose particular socketing problems because of their 
small size. For example, the pin configuration of the SO device is not 
suitable for standard DIP sockets, and maintaining good electrical contact 
between SO device pins and socket contacts is difficult. Compounding this 
problem is the relatively delicate nature of SO devices, which mandates 
the use of sockets that require relatively little force on the body of the 
device to insert the device into, and remove it from, the socket. 
Accordingly, specialized sockets have been devised specifically for use 
with SO devices. An example is disclosed in U.S. Pat. No. 4,461,525 to 
Griffin. The Griffin device employs hinged "clamp wings" mounted on the 
sides of the socket. Each clamp wing includes conductive leads having 
terminal contacts which make contact with the SO device pins when the 
clamp wings are pivoted into their upright position. With this 
arrangement, the clamp wings provide electrical contact with the SO device 
pins, while also retaining the device within the socket. 
The Griffin device has the desirable characteristic of low insertion force. 
Nevertheless, the need to combine the low insertion force feature with 
good physical retention, simplicity of design, and durability of 
electrical contact integrity has led to a search for further improvements 
in the design of SO device sockets. 
SUMMARY OF THE INVENTION 
Broadly, the present invention is an IC device socket, comprising a 
receptacle having a pair of side walls extending upwardly from a base, a 
row of spaced-apart vertical slots along the interior surface of at least 
one of the side walls, an electrical contact near the bottom of each slot, 
and a cover element or lid having a plurality of downwardly-extending 
fingers, each of which is registrable with, and receivable in, one of the 
slots. The receptacle is dimensioned to receive the IC device, and the 
slots are spaced and dimensioned so that each lead is individually 
received in a separate slot. The device is placed in the receptacle with 
the leads received in the slots, and when the cover element is placed on 
top of the receptacle, the fingers extend into the slots so that the leads 
of the IC device are each engaged between one of the fingers and one of 
the electrical contacts. 
More specifically, the slots are formed by a row of substantially vertical 
guide members extending inwardly from the interior side wall surface and 
upwardly from the base at least part of the way up the side wall, with the 
slots being defined between adjacent guide members. The electrical 
contacts are, preferably, of the multi-wire type, and are each 
conductively attached to the interior portion of a socket pin extending 
through the base. In the preferred embodiment described in detail below, 
the receptacle and its associated slots are dimensioned and configured to 
accommodate a small outline (SO) device, and the cover element is 
configured with a recess in its interior surface conforming to the outline 
of the SO device body. Also, in the preferred embodiment, the socket pins 
are provided with barbs along their shank portions where they pass through 
the base, to restrain vertical movement of the pins through the base 
during handling and assembly, and to prevent the pins from being loosened. 
The present invention offers a number of advantages over prior art sockets, 
especially when it is specifically configured as a socket for an SO 
device. The use of fingers on the cover element, in conjunction with 
contacts at or near the bottom of the slots in the receptacle, allows each 
lead of the device to be firmly and securely engaged between the finger 
and the contact, even if the leads of the device have non-coplanar 
terminations. This engagement assures secure device retention and positive 
electrical contact with low contact resistance. These qualities are 
enhanced by the use of multi-wire contacts, especially if the contacts are 
mounted on the socket pins in a cantilevered manner that provides them 
with a spring-like resilience which tends to push upwardly against the 
device leads. The use of the cover element to secure lead engagement with 
the contacts provides for low insertion force and easy removal of the 
device from the sockets. The entire socket assembly is relatively compact; 
in fact, it can be dimensioned only slightly larger than the device it is 
to receive. Also, the socket is of a design that is relatively simple and 
economical to manufacture, not requiring any moving parts (other than the 
removable cover, which may, if desired, be hinged to one end or side of 
the receptacle). 
These and other advantages of the present invention will be best 
appreciated from the detailed description which follows.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, an IC device socket assembly in accordance 
with a preferred embodiment of the invention is designated by the numeral 
10. The socket assembly 10 comprises two major subassemblies: a receptacle 
12 and a cover 14. The receptacle 12 comprises a generally rectangular 
base 16 (FIG. 2) having a central vent opening 17 for heat dissipation and 
drainage of condensation. From each of the longer sides of the base 16 
extends a generally vertical side wall 18. Each of the shorter sides of 
the base 16 is advantageously provided with a generally vertical end wall 
20. The receptacle 12 formed by the base 16, the two opposed side walls 
18, and the two opposed end walls 20 is dimensioned and configured, in the 
preferred embodiment, to receive and enclose a typical small outline IC 
device 22 (FIG. 3). 
Extending inwardly from the interior surface of at least one side wall 18 
is a row of guide elements 24, each of which extends partway up the side 
wall 18 from the base 16. The guide elements 24 are spaced apart to define 
slots 26 between adjacent ones of the guide elements. Advantageously, the 
guide elements 24 have tapered tips 28, so that the slots 26 are wider at 
their tops than at their bottoms. 
Disposed at the bottom of each slot 26 is an electrical contact 30. As best 
shown in FIG. 6, each of the contacts 30 is of a multi-wire type, 
comprising a pair of elongate wire loops 31a and 31b of two different 
lengths, and arranged in overlapping relationship so that each loop has 
one leg interposed between the legs of the other loop. The closed ends of 
the loops 31a and 31b are thus "staggered", to present adjacent wire 
elements or legs of alternating lengths. Each leg of each of the loops 31a 
and 31b is advantageously provided with an upwardly extending hump 32 near 
the closed end thereof. 
The contacts 30 are each conductively attached to an interior tab portion 
33 of a socket pin 34, each of the latter having a shank 36 which extends 
through the base 16 of the receptacle. The tab portion 33 is preferably 
bent downwardly so as to form a slightly acute angle (e.g., approximately 
80 degrees) with the shank 36 of the pin 34. The portion of each contact 
30 that includes the closed ends of each of the wire loops 31a and 31b, as 
well as the humps 32, extends away from the interior tab portion 33 of the 
associated pin 34 to provide a cantilevered, resiliently flexible free end 
for each of the contacts 30, the advantage of which will be made apparent 
below. With the aforementioned "staggering" of the wire loops 31a and 31b, 
it can be seen that the closed end of one loop extends away from the tab 
33 farther than does the closed end of the other loop. 
As shown in FIG. 5, the shank 36 of each pin 34 is provided with barbs 40 
which engage the base 16 around the holes 42 in the base through which the 
pin shanks 36 pass. The barbs 40 lock the pins 34 in place and restrain 
them from being vertically displaced when the socket is being handled, 
used, or assembled. The barbs 40 also minimize any loosening of the pins 
34 through repeated use of the socket, or through forming of the pins in a 
surface-mount configuration after the socket is assembled. 
The cover element 14 is preferably provided with heat dissipation vents 43, 
and it has an exterior perimeter conforming to the interior shape and size 
of the receptacle 12. Thus, when the cover 14 is placed on the receptacle, 
its sides fit flush against the interior surfaces of the side walls 18. 
Extending downwardly from the bottom surface of the cover element 14, 
along each of its longer sides, is a row of elongate prongs or "fingers" 
44. The fingers 44 are registrable with, and receivable in, the slots 26. 
The socket assembly of the present invention can be made with only a 
single row of guide elements 24 and interspersed slots 26 and contacts 30, 
and with only a single row of fingers 44 on the cover 14 to accommodate IC 
devices having leads on only one side. The preferred embodiment, however, 
has a row of the appropriate elements on each of the longer sides of the 
receptacle 12 and cover 14, in order to accommodate IC devices, such as 
small outline devices, wbich have leads on two opposed sides. It should be 
noted from FIGS. 2 and 3 that the drawings illustrate the preferred 
embodiment, even though FIG. 1 is taken from a perspective that shows only 
a single row of guide elements 24. 
Referring now to FIGS. 3 and 4, the operation of the socket will now be 
readily understood. With the cover 14 removed, an IC device 22 is placed 
in the receptacle 12. The device 22, if it is the small outline (SO) type, 
has a plurality of generally step-shaped leads 46 extending from each side 
of its body, each ending a short horizontal tab 48. The tabs 48 register 
with, and are received in, the slots 26, one tab to a slot, with the tabs 
engaging the contacts 30 near the bottoms of the slots. The cover 14 is 
then installed on the receptacle 12, with the fingers 44 being received in 
the slots 26, as described above. As best seen in FIG. 4, the fingers 44 
engage the tabs 48, urging them into intimate contact with the 
cantilevered free ends of the electrical contacts 30. The engagement of 
the tabs 48 by the fingers 44 tends to push the contacts downwardly, while 
the previously-mentioned resilient flexibility of the contacts' free ends 
biases them upwardly against the tabs 48, thereby assuring that a 
positive, low resistance electrical connection is maintained between the 
leads 46 and the contacts 30. This coaction of the fingers 44 and the 
cantilevered contacts 30 also allows good electrical contact to be 
maintained with all of the leads 46, even if their end tabs 48 are not 
exactly coplanar. The use of multi-wire contacts is advantageous because 
of their durability and their ability to withstand repeated flexing due to 
insertion and removal of IC devices without acquiring a "set". Moreover, 
the use of the overlapping loops 31a and 31b to form each of the contacts 
30 assures that good electrical contact is maintained at a number of 
points on each device lead 46, and provides a strong, box-like spring 
configuration that resists lateral movement ("splaying") of the wire 
elements of the contacts as a result of their engagement with the leads. 
Also, by using looped wire elements, the total effective resistance of the 
lead/contact interface is somewhat lowered, as compared to unlooped, 
straight wire elements. 
The positive locking action provided by the fingers 44 of the cover also 
provides good mechanical durability, allowing the device to be retained in 
the socket with positive electrical contact maintained even if the socket 
is subjected to vibrations and physical shocks. Furthermore, the 
electrical and mechanical characteristics of the socket are maintained 
despite extended periods of repeated use. 
The positive locking action of the cover 14 is advantageously enhanced by 
several specific features. For example, as shown in FIGS. 2 and 3, the 
inside surface of the cover is preferably provided with a recess 50 
conforming to the perimeter of the body of the IC device 22. Also, as 
shown in FIG. 1, the ends of the cover 14 are each provided with a thinned 
edge or flange 52 (only one of which is shown in the drawing). The flanges 
52 are engaged by inwardly-extending retention members or prongs 54 
provided at the tops of the receptacle end walls 20, and this engagement 
between the flanges 52 and the prongs 54 positively locks the cover 14 in 
place. The prongs 54 are advantageously provided with sloped inner faces 
56 to facilitate the insertion and removal of the cover 14. 
Removal of the IC device from the socket is facilitated by the provision of 
a pair of vertical slots 58 in the end walls 20, on either side of the 
prongs 54. The slots 58 allow the end walls 20 to be bent slightly 
outwardly to disengage the prongs 54 from the cover flanges 52, thereby 
allowing the cover 14 to be easily removed. The slots 58 can also provide 
access for a suitable tool (not shown) which may be used to remove the 
device. 
From the foregoing description, it can be appreciated that the present 
invention provides an IC socket that is particularly adapted to 
accommodate SO devices, and which provides good physical retention of the 
device, while maintaining good electrical contact and thus low contact 
resistance. The socket is durable in its ability to maintain good physical 
retention and integrity of electrical contact in the face of long-term 
repeated use, as well as adverse physical conditions (e.g., vibration and 
shocks). The present invention provides these advantages with a structure 
that is easily and economically manufactured and which is easily used, 
lacking, as it does, any complex and costly moving parts (except for the 
removable cover). The present invention can also be made in a size that is 
not substantially bigger than a typical SO device, a feature which is 
highly advantageous in certain applications. 
As previously mentioned, the socket pins 36 can be formed into a surface 
mount configuration after assembly of the socket. This can be done by 
bending the exterior (distal) ends of the pins outwardly to form 
horizontal tabs or "feet". If desired, these surface-mounting tabs can be 
configured to give the socket essentially the same "footprint" as the 
device contained in it, so that the socket and the device can use the same 
circuit board pads, if it is later desired to surface mount the IC device 
directly. 
While a preferred embodiment of the invention has been described herein, it 
should be noted that many modifications may suggest themselves to those 
skilled in the pertinent arts. For example, the receptacle 12 and cover 14 
may be made square, instead of rectangular, and may be provided with guide 
members 24, slots 26, contacts 30, and fingers 44 on all four sides to 
accommodate IC devices with leads on all four sides. Furthermore, the 
receptacle and cover can be configured to accommodate IC devices with any 
number of leads on a side. In addition, the cover may be removable by any 
of a variety of means. For example, it may be attached at one end or side 
to the receptacle 12 by a hinge or the like. Other modifications may be 
made, for example, in the configuration of the contacts 30, to accommodate 
IC devices having a variety of lead shapes and sizes. For example, the 
angle of the tabs 33 on the pins 36 can be varied to provide more or less 
cantilever action, and the number of wire loops forming each contact can 
be increased to three or more, if desired, to accommodate larger IC 
packages. These and other modifications should be considered within the 
spirit and scope of the invention, as defined in the claims which follow.