Zero insertion force electrical connector and terminal

A zero insertion force electrical connector for use with a device having an array of pin terminals including a lower connector housing having a top surface and a plurality of cavities in the top surface corresponding to the array of pin terminals. Each of the cavities includes a base wall spaced from the top surface. A plurality of resilient terminals are mounted in the cavities. Each of the terminals includes a mounting portion for securing the terminal in the base wall, a free end portion, a contact structure adjacent the free end portion and a spring arm portion between the base wall and the contact structure. The pin terminals are moved in the cavities in a first direction along a path of travel between an unmated position wherein the pins are spaced from the contact structures in the cavities and a mated position wherein the pins are fully mated with the contact structures. The contact structure includes a pin engagement surface at least partly inclined with respect to the path of travel. The spring arm portion of each of the terminals is a generally flat and planar leaf region oriented generally parallel to the first direction. The leaf region includes a first side edge at a side of the terminal where the pin first engages the contact structure and a second side edge extending from the mounting portion to the contact structure at the opposite side of the terminal. Notch means is provided in at least one of the side edges for increasing the flexibility of the leaf portion.

FIELD OF THE INVENTION 
The present invention relates to electrical connectors and more 
particularly to an improved zero insertion force electrical connector for 
high frequency pin grid array devices. 
BACKGROUND OF THE INVENTION 
A pin grid array (PGA) device such as a microprocessor may have many pin 
terminals, numbering in the hundreds. Electrical connectors are used to 
mount PGA devices on a printed circuit board and establish electrical 
connections between the pin terminals of the PGA device and conductors of 
the printed circuit board. A typical electrical connector permits the PGA 
device to be removed for repair or upgrade purposes. Another beneficial 
result is that the PGA device is not subjected to heat when the connector 
is soldered to a printed circuit board. 
In some known electrical contact systems, when a pin terminal is inserted 
into a cavity of the connector, it contacts and resiliently deforms a 
mating terminal. As a result forces are required to mate and unmate such a 
contact system. Mating forces are not desirable in electrical connectors 
for devices such as PGA devices because the large number of contacts 
results in large cumulative forces that could damage some of the pins of 
the PGA device. When there is a need to eliminate mating forces, a 
connector known as a zero insertion force (ZIF) connector can be used. 
A typical zero insertion force connector for PGA devices includes a lower 
housing with numerous cavities corresponding to the array of pin terminals 
of a PGA device. A resilient electrical terminal is mounted in each 
cavity. An upper housing includes numerous openings through which the pin 
terminals of the PGA device extend. The upper housing can be moved 
relative to the lower housing between a first free or unmated position and 
a second locked or fully mated position. In the free position, the PGA 
device can be placed with no contact insertion force upon the upper 
housing with the pin terminals extending through the upper housing and 
into regions in the cavities of the lower housing where they are spaced 
from the resilient terminals. The upper housing is then moved relative to 
the lower housing, causing the pin terminals to move into contact with the 
resilient terminals in the cavities. 
U.S. Pat. Nos. 4,498,725 to Bright et al. and 4,750,891 to Egawa at FIGS. 5 
and 7 disclose zero insertion force connectors with resilient terminals 
having contact structures in the form of a pair of spaced apart resilient 
opposed fingers between which a pin terminal may be received. 
U.S. Pat. Nos. 3,315,212 to Peterson, 4,674,811 to Corwin, 4,750,891 to 
Egawa at FIGS. 8A and 8B and 4,887,974 to Ichimura et al. disclose zero 
insertion force connectors with terminals having free ends with contact 
structures and spring portions that flex in the same direction as the pin 
terminals move in order to provide a contact force. 
U.S. Pat. No. 4,988,310 to Bright et al. discloses a zero insertion force 
connector having terminals with an upstanding beam, a cantilever beam 
portion extending laterally from the upstanding beam and a contact area 
upon the cantilever beam acting to cause torsional deflection of the 
cantilever beam in the mated condition. 
U.S. Pat. No. 5,342,214 to Hsu discloses a zero insertion force connector 
having two upstanding terminal portions, one including a laterally 
extending guide portion 430 and a noninclined contact portion 43. 
Pending U.S. patent application Ser. No. 08/367,566 filed on Jan. 3, 1995 
discloses and claims a zero insertion force connector with flexible 
terminals each having a mounting portion, a leaf spring portion and a 
contact structure at a free end. The leaf spring portion flexes in a 
direction perpendicular to the direction of movement of the pin terminal 
relative to the flexible terminal, and the contact structure includes an 
inclined ramp surface generally disposed within the lateral bounds of the 
leaf spring portion. 
The zero insertion force connector of said U.S. patent application Ser. No. 
08/367,566 has advantages including small contact pitch or spacing, a 
simple sturdy shape and minimum contact plating requirements. However, in 
some applications it is desirable to reduce the inductance when used with 
PGA devices operating at very high speeds or frequencies. 
Shortening the length of the terminal would reduce the inductance but could 
lead to other problems such as large contact mating forces or 
overstressing of the terminal beams. In addition, the terminals of that 
connector are inserted from the top of the connector housing and the 
terminal mounting force may need to be applied to the free end of the 
terminal and not directly to the mounting portion. 
SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide an improved zero 
insertion force connector and terminal having low impedance and suited for 
use in high frequency applications. Another object is to provide a zero 
insertion force connector with a terminal having a small length between a 
mounting portion and a free end and having low contact mating force, low 
mechanical stress and substantial normal contact force when fully mated. 
Other objects are to provide a terminal for zero insertion force 
connectors that is loaded from the bottom of a housing with a loading 
force applied directly to the terminal mounting portion, and to provide a 
terminal having structure for preventing the wicking of solder through an 
enlarged mounting opening used to facilitate loading the terminal from the 
bottom of the housing. 
In brief, in accordance with the invention, there is provided a zero 
insertion force electrical connector for use with a device having an array 
of pin terminals. The electrical connector includes a lower connector 
housing having a top surface and a plurality of cavities in the top 
surface corresponding to the array of pin terminals. Each of the cavities 
includes a base wall spaced from the top surface. A plurality of resilient 
terminals are mounted in the cavities. 
Each of the terminals includes a mounting portion for securing the terminal 
in the base wall, a free end portion, a contact structure adjacent the 
free end portion and a spring arm portion between the base wall and the 
contact structure. The pin terminals are moved in the cavities in a first 
direction along a path of travel between an unmated position wherein the 
pins are spaced from the contact structures in the cavities and a mated 
position wherein the pins are fully mated with the contact structures. The 
contact structure includes a pin engagement surface at least partly 
inclined with respect to the path of travel. The spring arm portion of 
each of the terminals is a generally flat and planar leaf region oriented 
generally parallel to the first direction. The leaf region includes a 
first side edge at a side of the terminal where the pin first engages the 
contact structure and a second side edge extending from the mounting 
portion to the contact structure at the opposite side of the terminal. 
Notch means is provided in at least one of the side edges for increasing 
the flexibility of the leaf portion. 
In brief, in accordance with another feature of the invention, there is 
provided a zero insertion force electrical connector including a connector 
housing having a top surface and a plurality of cavities in the top 
surface corresponding to an array of pin terminals. Each of the cavities 
includes a base wall spaced from the top surface and terminal retention 
openings in the base wall. A plurality of terminals are mounted in the 
cavities. Each of the terminals is a stamped and formed segment of flat 
and planar metal stock including a mounting portion substantially in the 
plane of the stock, a free end portion, a contact structure adjacent the 
free end portion and a spring arm portion between the mounting portion and 
the contact structure. The pin terminals are moved in the cavities between 
an unmated position wherein the pins are spaced from the contact 
structures in the cavities and a mated position wherein the pins are mated 
with the contact structures. The terminal mounting portion of each 
terminal is received in one of the terminal retention openings for 
securing the terminal in the cavity. The contact structure includes a pin 
engagement surface raised from the plane of the stock. The terminal 
retention opening has an enlarged portion permitting entry of the contact 
structure into the cavity through the base wall. The mounting portion has 
a projection extending out of the plane of the stock and substantially 
blocking the enlarged portion when the mounting portion is received in the 
terminal retention opening.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Having reference now to the drawings, FIG. 1 illustrates a zero insertion 
force connector designated as a whole as 20 used with a PGA device 22. In 
a preferred arrangement the PGA device may be a microprocessor having 
hundreds of pin terminals 24 (FIG. 3) typically in a staggered array. 
Connector 20 is mounted by soldering to a printed circuit board (not 
shown) and releasably receives the device 22 in order to make electrical 
connections between the pin terminals 24 and conductive areas of the 
printed circuit board. 
In general, the zero insertion force connector 20 includes a lower housing 
26 and an upper housing 28. Latch and guide structures 30 are provided on 
the housings 26 and 28 in order to removably secure the upper housing 28 
on an upper surface 32 (FIGS. 3, 5 and 6) of the lower housing 26. The 
housings 26 and 28 are relatively movable in the plane of the surface 32 
in the direction indicated by an arrow 34 in FIGS. 1 and 3. An operating 
lever 36 is rotatably supported by the lower housing 26 and engages the 
upper housing 28 to move it between a first free or unmated position and a 
second locked or fully mated position. In these respects, the housings 26 
and 28 and the lever 36 may be conventional, and reference may be had to 
U.S. Pat. No. 4,498,725, incorporated herein by reference, for a 
disclosure of one conventional arrangement. 
Upper housing 28 includes an upper surface 38 upon which the device 22 is 
mounted and a lower surface that slides across the upper surface 32 of 
lower housing 26 in response to manipulation of the operating lever 36. 
Numerous openings (not shown) extend through the upper housing 28 from the 
upper surface 38 and the openings are arrayed in the same pattern as the 
array of pin terminals 24 so that the device 22 can be placed upon the 
surface 38 with male pin terminals 24 extending through the openings of 
the upper housing 28. A further disclosure of one suitable form of upper 
housing 28 is found in pending U.S. patent application Ser. No. 08/367,566 
filed on Jan. 3, 1995, incorporated herein by reference. 
The lower housing 26 has a lower surface 40 generally parallel to the upper 
surface 32. A plurality of cavities 42 extend from the upper surface 32 
toward the lower surface 46. Cavities 42 correspond to the array of pin 
terminals 24 such that an individual cavity may be provided for each pin 
terminal 24 or a single cavity may receive more than one pin terminal 24. 
A portion of one cavity 42 is seen in FIGS. 3, 5 and 6. 
The cavity 42 extends down to a base wall 44 having an upper surface 46 
spaced from the lower surface 40. A generally T-shaped terminal mounting 
opening 48 extends through the base wall 44 between the upper and lower 
surfaces 46 and 40. The cavity 42 is also defined by an upstanding side 
wall 50 defining a pin terminal receiving region 52 and a terminal contact 
region 54 (FIG. 3). Side wall 50 includes a pin terminal guide ramp 56 and 
a pin terminal backing wall 58 (FIG. 3). 
Numerous resilient terminals 60 are mounted in the lower housing 26 for 
contacting the pin terminals 24 of the PGA device 22. Each resilient 
terminal 60 includes a mounting portion 62 received in the terminal 
mounting opening 48 of the base wall 44. Extending downward from the 
mounting portion 22 is a solder tail portion 64 for connection to a plated 
through hole of the printed circuit board (not shown) upon which the 
connector 20 is mounted. Alternatively, a surface mount tail or other tail 
configuration could be used. Extending upward from the mounting portion 22 
is a flexible and resilient spring arm portion 66 in the form of a flat 
and planar leaf region. A contact structure 68 is located above the spring 
arm portion 66 near a free end 70 of the terminal 60. The terminals 60 are 
small enough to permit terminals formed in a stamping and forming 
operation from a single sheet of flat planar sheet metal stock to be 
inserted at close spacings before the terminals are severed from a single 
carrier strip. 
In the free or unmated position of the housings 26 and 28, the pin 
terminals 24 are initially received without a mating or insertion force in 
the pin terminal receiving regions 52 of the cavities 42. The initial, 
unmated pin terminal position is seen in solid lines in FIG. 3. When the 
lever 36 is used to move the housings to the fully mated position, each 
pin terminal 24 moves in the direction of the arrow 34 in FIG. 3 relative 
to the lower housing 26 into the terminal contact region 54 of the cavity 
48. The fully mated position of the pin terminal in cavity 42 is seen as 
24A in broken lines in FIG. 3. The guide ramp 56 and backing wall 58 guide 
the pin terminal 24 into the fully mated position. 
The contact structure 68 is formed to project above or out of the plane of 
the metal stock from which the terminal 60 is made. As the pin terminal 24 
moves relative to the resilient terminal 60 in the direction of the arrow 
34 in FIG. 3, it engages a raised pin engagement surface 71 of the contact 
structure 68 and the spring arm portion 66 resiliently flexes to apply a 
contact mating force to the contact interface as the contact structure 68 
moves away from the wall 58 in a direction perpendicular to the direction 
of the arrow 34. The contact structure 68 is preferably as described in 
pending U.S. patent application Ser. No. 08/367,566 filed on Jan. 3, 1995, 
and reference may be had to that application for a further description of 
the structure, operation and advantages of the contact structure 68. 
Because PGA devices such as microprocessors operate at increasingly higher 
frequencies, it is important to reduce the impedance of associated 
electrical connectors. The physical size of the resilient terminal 60 
affects the high speed electrical performance. Increased length of the 
spring portion 66 increases inductance. Decreases in cross sectional area 
of spring portion 66 can also degrade high frequency electrical 
performance. It is desirable to decrease the spring length to reduce 
inductance while minimizing reduction of cross sectional area, and to 
maintain a desired predetermined normal resilient contact force of the 
mated contacts without a substantial increase in the cam forces incurred 
as the mating contacts engage and move relative to one another. 
The spring arm portion 66 includes a pair of arc-shaped notches or 
indentations 72 and 74 in opposed side edges 76 and 78 of the spring 
portion 66 as best seen in FIGS. 2 and 6. The center of the radius of each 
arc is located outside the side edges 76, 78 of the terminals 60. The side 
edge 76 is located at the side of the terminal 60 where the pin engagement 
surface 71 is initially contacted by the pin terminal 24, and the opposite 
side edge 78 is adjacent the fully mated contact interface location. 
Notches 72 and 74 are not vertically aligned with one another but rather 
are offset from one another along the length of the spring portion 66. The 
notch 74 is relatively closer to the contact structure 68 and the notch 72 
is relatively closer to the mounting portion 62. 
This notch configuration has important advantages. The spring portion 66 is 
made relatively short, thereby minimizing inductance. The notches 72 and 
74 increase the flexibility of the spring portion 66 so that excessive 
normal mating forces are avoided even though the spring length is 
decreased. Because the notches 72 and 74 are not aligned, they do not 
result in a narrow neck region that would have electrical and mechanical 
disadvantages including increased impedance, concentration of mechanical 
stress and susceptibility to plastic deformation. Furthermore, the notches 
are preferably arc-shaped in order to reduce stress concentrations in the 
beam. 
The offset notches 72 and 74 impart a somewhat diagonal or slightly S 
shaped configuration to the spring portion 66. This has the beneficial 
effect of making the spring portion 66 act as a relatively short member 
electrically but as a relatively longer beam member mechanically. Spring 
portion 66 serves primarily as a cantilever leaf spring, flexing in the 
direction perpendicular to the contact mating direction of arrow 34. 
However, the notch 74 adjacent to the contact structure 68 and underlying 
the region where the pin terminal 24 first contacts the contact structure 
permits a limited and transitory torsional deflection, increasing 
flexibility as contact is initiated near the side edge 76. The contact 
structure is permitted to rotate slightly as contact is made. Then as the 
fully mated position is approached closer to the side edge 78 of the 
contact region, the contact structure rotates back. In the fully mated 
position, substantially pure cantilever flexing occurs with no significant 
torsional deflection. 
A further advantage of the connector 20 is that the resilient terminals 60 
are loaded into the lower housing 26 from beneath the base wall 44. In 
connectors of the same type where the terminals are loaded from above, the 
terminal insertion tooling may apply some of the terminal mounting force 
to the free end of the terminal because there is not sufficient room 
within the terminal receiving cavity for the tooling. Forces applied to 
the free end of the terminal can damage the contact structure or the 
spring arm portion. 
The mounting portion 62 of the terminal 60 is generally a flat, planar 
element in the plane of the stock of the metal from which the terminal 60 
is made. A pair of positioning feet 80 are formed on the portion 62 for 
increasing the force with which the terminal is retained and for 
accurately locating the terminal in the cavity 42. Mounting portion 62 is 
pressed with a frictional, interference fit into a correspondingly shaped 
portion of the terminal mounting opening 48. Once positioned within 
terminal mounting opening 48, the lateral edges of the mounting portion 62 
engage end walls of the opening 48 and feet 80 and the surface of mounting 
portion 62 opposite feet 80 engage the sidewalls of mounting portion 62 in 
order to securely hold the terminals on all sides. 
The mounting portion 62 of the terminal 60 has downwardly facing shoulders 
82 that can be directly engaged by tooling for forcing the mounting 
portion 62 upward into the terminal mounting opening 48. Sloped entry 
surfaces 84 are formed on the upper corners of the mating portion 62 to 
guide and facilitate movement of the portion 62 into the opening 48. 
Because the resilient terminal 60 is installed from below, the contact 
structure 68 must pass through the terminal mounting opening 48. Contact 
structure 68 projects above or out of the plane of the sheet metal stock 
from which the terminal 60 is made. To provide clearance, the terminal 
receiving opening 48 has an enlarged portion 86 seen in FIGS. 3-5. 
As such, it can be seen in FIG. 4 that the terminal receiving cavity 48 is 
generally T-shaped. The base or stem of the T-shape is slightly longer 
than the distance the contact structure 68 projects out of or above the 
plane of the sheet metal stock from which it is formed in order to permit 
the contact structure to pass through the cavity 48. As stated above, the 
cross member of the T-shape receives mounting portion 62 of the terminal 
in an interference fit. As a result, the cross member of the T-shape is 
slightly smaller than the mounting portion 62. 
When the pin contact portion 64 of the terminal 60 is soldered to a printed 
circuit board, molten solder can flow or wick upward along the metal 
surfaces of the terminal. The enlarged portion 86 of the terminal 
receiving opening 48 could provide a path for the flow of solder through 
the base wall 44 and into the cavity 42. To prevent such solder wicking, a 
projection 88 is formed on the mounting portion 62 of the terminal 60. As 
best seen in FIGS. 4 and 5, the projection 88 is approximately at least as 
large as the contact structure 68 and substantially blocks or fills the 
enlarged portion 86 leaving only clearances too small for the flow of 
solder. The projection 88 is formed as a tab struck from the mounting 
portion 62, but other configurations of projection could be used. By 
striking the projection 88 from mounting portion 62, a hole is created in 
mounting portion 62. As the terminals are soldered to a printed circuit 
board, if solder attempts to wick up the terminal, the solder will attempt 
to fill the opening 89 created when projection 88 was formed rather than 
continuing up the terminal 60 into the contact structure 68. 
While the present invention has been described with reference to the 
details of the embodiment of the invention shown in the drawing, these 
details are not intended to limit the scope of the invention as claimed in 
the appended claims.