Electrical connector for direct connection to plated through holes in circuit board

A pluggable electrical connector is provided having contact elements with first ends soldered to a daughter board, midsections which are crimped and bent through ninety degrees, and second ends which have a converging portion and which terminate in bifurcated conical contact portions which make contact with the rims of contact-quality plated through holes of a mother board. By causing contact between the rim and the cone surface, normal forces greater than the mating force are generated. The connector housing includes self-centering funnel openings adjacent the mother board for centering the converging portions of the contact elements therein in a nominal position and for acting as a preloading stop. The housing also includes side-wall locking tabs which hold adjacent rows of contacts at identical fixing points relative to the ninety-degree bend to ensure identical spring parameters for all contact elements. By arranging the housing properly, the contact elements can be manufactured into preloaded spring contacts during assembly by bending and locking the first ends of the contacts past the side-wall locking tabs. Cams or retracting bars can be used with rows or individual contacts to create a ZIF connector and/or a selectively engaged pin enabled connector. Magnets, springloaded jack screws, or the like are used in conjunction with the connector to establish and maintain force during mating.

BACKGROUND 
1. Field of the Invention 
This invention relates generally to electrical connectors for connecting 
daughter cards to a backplane, midplane, harness card or the like 
(hereinafter referred to as a "mother board" or "mother card"). More 
particularly, the invention relates to a self-centering contact, high 
density connector for connecting a daughter card directly to the plated 
through holes of the mother card, where the high density connector may be 
configured as a standard connector, a zero insertion force connector (ZIF) 
or as a sequential/selectively engaging pin connector. 
2. Prior Art 
The electrical connector arts are crowded arts with many categories and 
subcategories of connectors. One such category are connectors which are 
used to connect two printed circuit boards (PCB). Within that category is 
a subcategory of connectors where the first PCB is a mother board, and the 
second PCB is a daughter board at right angles to the mother board, and 
the connection is a pluggable connection such that replacement or cards 
and/or expansion of the system is easily accomplished. The standard 
connectors for permitting such a non-permanent right angle interface 
require placing a first piece of hardware (e.g. in the case of 
conventional inverted DIN connectors, the pin or male part) on the mother 
board, and a second piece of hardware (e.g. the mating female receptacle 
of a right angle connector) on the daughter board. While such connectors 
are typically successful for their purpose, as these connectors grow in 
size with high pin counts, bowing may occur in the connector during mating 
due to the high insertion force required resulting in difficult mating 
between the male and female connector shells. Further, these standard 
connectors are costly as they essentially require the use of two connector 
parts (a mating pair) for accomplishing a single connection. In fact, 
systems are often sold with the mother board portion of numerous 
connectors already attached to the mother board where daughter cards are 
only to be optionally provided in the event the system is expanded. Thus, 
where daughter cards are not ultimately used, unnecessary cost is 
suffered. In any event, it is desirable to provide an arrangement where 
connectors fixed to a daughter card could make electrical contact with the 
mother board directly without the added cost of a mating pair. 
One solution to such a mother board/daughter board connection is proposed 
in U.S. Pat. No. 4,533,203 to Feldman et al., where a single connector 
having pins which are bent through a ninety degree turn and a two piece 
dielectric housing for housing the same are utilized in conjunction with 
contact pads on the mother board to establish contact. First ends of the 
pins are fixed to the daughter card while second ends are disposed at an 
oblique angle relative to the mother board to provide "wipe" action on the 
mating surface. Contact with the mother board is made between the angled 
second ends and contact pads on the mother board and aligning means are 
provided for aligning the angled pins and the pads. When contact is made, 
the bent portion of the pins deflects away from the mother board surface, 
and is permitted to do so by the housing which is enlarged around the area 
of deflection. With the provided arrangement, the two connector 
arrangement is obviated. 
While the Feldman et al. patent does overcome some of the problems in the 
art, it does not address several matters of importance. First, the patent 
does not provide an adequate manner of maintaining the contact between the 
connector and the mother board, particularly where contact density is 
high. While a "keying block" is provided to establish alignment and to 
permit keying, there is no indication that the keying block also provides 
a means for establishing and maintaining contact. Second, because of the 
geometric nature of the angled pins and the contact pads, it is very 
possible that good contact at a sufficient contact force ("normal force") 
is not establishable between the pins and the circuit board. Third, where 
contact density is high, the size of the "engagement" or "hold-in" force 
(also called "mating" or "insertion" force) necessary for holding down the 
daughter board so that it may be locked relative to the mother board may 
very well be prohibitive. This is so, because the Feldman et al. 
configuration transmits the spring force directly to the contact pad on 
the mother card without any mechanical advantage. Thus, the "hold-in 
force" which is equal to the spring force, is also equal to the normal 
force. Fourth, because of the geometry and nature of the keying block, 
precise geometries are required, and if not met, may result in 
malfunctioning of the connector. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a right angled 
connector for directly connecting a daughter board to plated through holes 
in a mother board where sufficient normal forces are maintained. 
It is a further object of the invention to provide a connector for printed 
circuit boards where the contact normal force obtained is greater than the 
hold-in force. 
It is another object of the invention to provide a connector for printed 
circuit boards which accommodates typical production tolerances. 
It is yet another object of the invention to provide a connector for 
printed circuit boards which is configurable for zero insertion force, and 
selective pin engagement embodiments. 
It is even a further object of the invention to provide a connector for 
printed circuit boards where the spring-loaded contacts are formed in and 
by the connector housing. 
In accord with the objects of the invention, a connector for connecting a 
daughter board to a mother board is provided with a plurality of contact 
elements which are bent over a radius of approximately ninety degrees, and 
a dielectric housing for housing the contact elements The connector is 
used in conjunction with a means for establishing and maintaining force on 
the contact elements so as to keep them engaged in plated through holes in 
the mother board The contact elements are pins with first ends which 
typically are soldered to through holes in the daughter board, 
mid-sections which are crimped and bent through ninety degrees, and second 
ends which have a converging portion and which terminate in contact 
portions which are tapered in cross section and which are used to make 
contact with the contact-quality plated through holes of the mother board. 
Electrical connection is made by having the tapered contact portion 
contact the mother board through holes at a plurality of points along the 
circumference of the hole at the surface of the PCB (i.e. along the rim). 
The dielectric housing is preferably a 16 single piece housing with a 
self-centering funnel-like arrangement on the end adjacent the mother 
board for causing the converging portions of the second ends of the 
contact elements to center themselves therein in a nominal position and 
for acting as a stop to cause the pins to be preloaded in a position such 
that they extend appropriately out of the housing. The housing also 
preferably includes side-wall locking tabs which hold adjacent rows of 
contacts at different fixing points relative to the daughter board but at 
identical fixing points relative to the ninety-degree bend in the contact 
elements, thereby causing all contact elements to have identical spring 
parameters. By providing appropriate holes and surfaces in the housing, 
the contact elements can be manufactured into preloaded spring contacts 
during assembly by inserting the contact elements in the housing, 
temporarily holding the contact elements at appropriate locations, and 
bending the elements so that the first ends are pushed past and locked 
into place by the side-wall locking tabs. The means for establishing and 
maintaining force on the contact elements for use in conjunction with the 
connectors may range from magnets, to spring-loaded jack screws, to 
bayonet locks, depending on the number of contacts required to be made and 
the contact force per pin desired. 
Additional preferred or alternative aspects of the invention include: 
arranging the contact elements in the form of compliant split cones for 
mating with the plated through holes of the mother board; the use of guide 
pins, at least one of which is grounded, and at least one of which is 
integrally formed as part of the connector assembly; the use of a 
stiffening element on the mother board to prevent warpage thereof where a 
spring loaded jack screw is used for maintaining force on the contact 
elements; the use of a laminated compliant layer atop a typical mother PCB 
to permit more effective mating; the use of a raised aligning grid on the 
mother board for permitting additional lateral tolerance; and the use of 
rods and/or cams for retracting contact elements (either individually, by 
row, or all) so as create a ZIF connector and/or a selectively engaged pin 
enabled connector. 
Other objects and advantages of the present invention will become evident 
upon reference to the detailed description in conjunction with the 
provided figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1, 2a, 2b, 3a-3c, and 4a-4c show a first preferred connector assembly 
of the invention. The connector assembly 10 typically comprises a 
plurality of contact elements 20, and a dielectric housing 30 for housing 
the contact elements. The contact elements 30 are spring pins with first 
ends 32, second ends 34, and a middle bend section 36. The first ends 32 
of pins 20 extend through holes 39 in the daughter board 40 and are 
preferably soldered to the back side 41 of the daughter board. At least a 
portion of the first ends 32 is preferably v-shaped to help align the 
first ends in the holes 39 of the daughter board 40. The shape of first 
ends 32 also provides stiffness, and helps in preloading the contacts as 
will be discussed hereinafter. 
The second ends 34 of the contact elements 30 are basically comprised of a 
neck portion 35 which may be channel shaped for stiffness, and a tapered 
contact portion 38. As seen in FIG. 3b, connecting the neck portion 35 to 
the contact portion 38 is an angled portion 37 which acts in conjunction 
with the housing to provide self-alignment and preloading as will be 
described hereinafter. 
The mid-sections 36 of pins 20 are preferably crimped to cause pins 20 to 
form a spring. As shown in FIG. 1, pins 20 are preferably crimped to first 
form a one hundred eighty degree bend and then a minus ninety degree bend, 
and are thus essentially bent through ninety degrees If desired, a simple 
bend of ninety degrees could be used, provided mid-sections 36 form spring 
elements As seen in FIG. 3a in phantom, when contact portions 38 of second 
ends 34 of pins 30 engage the mother board 50, the mid-sections 36 
resiliently deflect away from the mother board 50; i.e. the mid-sections 
36 are compliant along the mating axis. In so doing, the mid-sections 36 
provide pins 30 with a mating force. 
As seen in FIG. 4a, the contact portions 38 of the second ends 34 of 
contact elements 20 are tapered in cross section, with the cross section 
becoming larger further away from the end or tip of the contact element. 
The contact portions 38 are used to make contact with the plated through 
holes 51 of the mother board 50. Where the contact portions 38 of the 
second ends 34 are the preferred split (bifurcated) cones (as seen in 
FIGS. 4a and 4b), contact is made between the connector 10 and the mother 
board 50 at two points 53a, 53b (radius contact "points") for each contact 
element 20 and through hole 51. The contact is made between the tapered 
portion (i.e. the contact portion 38) of the contact element 20 and the 
rim of hole 51; i.e. the circumference of the hole 51 at the surface 55 of 
the mother board 50. In making contact, because contact portion 38 is 
bifurcated, it resiliently compresses as it is pushed into hole 51, and 
therefore extends into hole 51 further than it might have otherwise. As a 
result, the surface of contact portion 38 wipes along the rim of hole 51 
as it makes contact providing desired "wipe" and enhanced contact. 
As seen in idealized force diagram of FIG. 4c, the use of contact elements 
having tapered contact portions 38 which extend into plated through holes 
51 of a mother board magnifies the "normal" force relative to the axial 
holding or mating force. In particular, and by way of example only, if the 
axial mating force F.sub.A is fifty grams, the axial mating force at each 
of the two points of contact is seen as twenty-five grams (F.sub.A /2). Of 
course, the mother PCB must assert an equal but opposite force of 
twenty-five grams at each point. However, the equal but opposite force 
must be asserted as a component of a force which is perpendicular (i.e. 
normal) to the point of contact. Thus, at each of the two contact points, 
the mother board 50 provides a normal contact force F.sub.N /2 (shown as 
the hypotenuse of the triangle) Each normal contact force is the result of 
two perpendicular forces; an axial force of twenty-five grams opposite to 
the mating force (as required to provide an equal but opposite force to 
the axial mating force); and a force perpendicular to the axial force. As 
will be appreciated, the perpendicular forces to the axial forces are 
equal and opposite each other and therefore cancel. 
Assuming that the contact portion 38 tapers at an angle of fifteen degrees 
relative to the axial direction, in order for a twenty-five gram axial 
force opposite to the axial mating force to be generated at each point of 
contact, a resultant normal force (F.sub.N /2) of one hundred grams 
(twenty-five grams divided by the sine of fifteen degrees) is generated at 
each point. Thus, for a pin having a total axial mating force of fifty 
grams, the normal force generated is two hundred grams More generically, 
the normal force generated at each point of contact is equal to the axial 
force at that contact point divided by the sine of the taper angle .theta. 
of the tapered contact portion 38 of the pin 20. The smaller the taper 
angle .theta., the larger the normal force generated. Regardless of the 
taper angle, the total normal force generated by all the contact points is 
always greater than the axial insertion force as F.sub.N /F.sub.A 
=1/sin.theta.. 
Turning to FIGS. 5a1-5a3, . . . 5d1-5d3, it will be understood by those 
skilled in the art that the tapered contact portion 38 of pin 20 may take 
any of numerous embodiments. The most conventional candidates would be a 
sphere, a cone, a four edged pyramid, and a three edged pyramid or 
tetrahedron. As seen in FIGS. 5a2 -5b2, each such contact portion is 
tapered and would therefore contact the hole The contact, as seen in FIGS. 
5a3 -5d3, might range from a three point contact for the tetrahedron, to 
irregular annular contact for the sphere and cone. While a four point 
contact would be expected from the four-edged pyramid, it is possible that 
only two or three contact points would be made. Because of the exact 
geometries required of the plated through hole and the tapered contact 
portions of the pins to permit the exact contact points to be ascertained, 
the compliant bifurcated cone of FIG. 4a and 4b is the preferred 
embodiment, followed by the tetrahedron. 
Returning to FIGS. 1, 2a, 2b, and 3a-3c the preferred single piece 
dielectric housing 30 of the invention is seen. The housing 30 includes 
side walls 60 which separate and electrically insulate each column of 
contact pins 20; the side walls 60 extending perpendicularly from top wall 
62. Also extending perpendicularly from top wall 62 is front wall 64 
having a plurality of openings 66 for permitting at least a portion of 
tapered contact portions 38 (and preferably the entire tapered contact 
portion) of contact pins 20 to extend therethrough. Openings 66 are 
preferably tapered funnels which are arranged to interact with the angled 
portion 37 of the second ends 34 of the contact pins as will be 
hereinafter described. Extending rearward from the front wall 64 in a 
manner parallel to top wall 62 are a plurality of pin separation walls 68 
(also called "guide walls") which guide the second ends 34 and contact 
portions 38 of pins 20 into their preloaded position, and electrically 
insulate one pin contact from another. Because different rows of pins 20 
traverse different lengths (as seen in FIGS. 1 and 3a), the lengths of 
separation walls 68 are varied accordingly. Preferably, each guide wall 
extends slightly past the middle bent portion 36 of the pin contact below 
it, but only as far as the second end 34 of the pin above it. 
FIG. 3b explores the axial and lateral tolerances built into the connector 
contact pins relative to the plated through holes of the mother board. As 
shown, when the contact pins are not engaging the mother board, angled 
portions 37 contact the funnel-like openings 66 and thereby center 
themselves therein in a nominal position. By arranging openings 66 to be 
smaller in cross section than the cross section of the widest part of 
angled portion 37, the openings 66 act as a stop to the contact spring 
pins 20 to cause the spring pins to be preloaded in the housing, as will 
be discussed hereinafter. In the preloaded position, the contact portions 
38 of the pins 20 extend out of the housing 30 by a desired amount. When 
the contact pins 20 engage the mother board holes, the pins 20 are pushed 
backward (as seen in phantom) such that the angled portion 37 of the 
second ends 34 of the pins no longer contacts the funnel-like openings 66 
of the housing 30. As a result, lateral movement of the second end of the 
pin is expedited in all directions, as the passage for the second end of 
the pin defined by adjacent side walls 60 and adjacent guide walls 68 of 
the housing 30 is wider than the second ends 34 of the pins. As will be 
appreciated by those skilled in the art, the further pins 20 are pushed 
backward, the more second ends 34 can move laterally in any direction in 
the housing passage. As a result, a tolerance zone or range for the 
misalignment of a pin relative to a hole is provided which can approach 
the radius of the hole in size (provided the housing passage and 
funnel-like opening are large enough). Also, as seen in FIG. 3b, the 
tapering of the contact portion 38 of pin 20 provides tolerance relative 
to the hole diameter, as contact along the tapered surface of the contact 
portion 38 is guaranteed. 
As seen in FIGS. 1, 3a, and 3c, side walls 60 of housing 30 preferably 
include side-wall locking tabs 72 (preferably two per contact) which hold 
adjacent rows of contacts in a preloaded manner at different fixing points 
relative to the daughter board 40 but at identical fixing points relative 
to the ninety-degree bend portion 36 of the contact elements 20. The 
locking tabs 72 provide a restriction between adjacent side walls 60 
through which the v-shaped first end 32 of pins 20 are forced during 
assembly. After the v-shaped first end 32 deforms and passes through the 
tabs 72, they cannot return past the tabs 72. Thus, locking tabs 72 act to 
provide a preload to the spring contact elements 20 as the spring contact 
elements 20 are fixed in location on one end by the contact of angled 
portion 37 with the funnel-like opening 66, and on the other end by 
locking tabs. The locking tabs 72 also act to establish a fixing point 
which fixes a portion of first end 32 (the portion between the locking tab 
72 and the daughter board) against movement in the axis of insertion. As a 
result, the tabs 72 act as a strain relief for the first end 32 - daughter 
board solder joint, as the first end 32 will not substantially move below 
tab 72. The v-shape of first end 32 also helps to stiffen first end 32 and 
to prevent movement at the solder joint. 
By locating the locking tabs 72 such that pins of different rows have 
approximately the same spring length between the fixing point and the bend 
(as seen in FIGS. 1 and 3a), equal bearing forces between the contact 
portions 38 of pins 20 of different rows of the connector and the holes 51 
of the mother board 50 are assured. 
Housing 30 may also include at least one integral guide pin 74. Guide pin 
74 may act as a ground pin by having a ground wire (not shown) wrapped 
around it, and/or a make first pin for the connector. Typically, and as 
shown in FIGS. 2a and 2b, two guide pins 74 are located on either end of 
the connector and extend along the same axis as the second portion of pins 
20. Preferably, the guide pins extend out further than the contact 
portions 38 of pins 20 and thus act in a shielding or protective capacity. 
The guide pins 74 are preferably arranged such that they extend into 
mating holes in the mother board, with the diameter of the mating holes 
being as large as or slightly greater than the diameter of non-tapered 
section of the guide pin. While at least one guide pin is preferably 
integrally molded with the connector, other guide pins may have a threaded 
end, and are held in place in the housing 30 by nuts 76. If desired, first 
and second guide pins may be oval in cross-section and oriented 
perpendicularly with respect to one another. In this manner, one guide pin 
acts as a horizontal guide, while the other acts as a vertical guide. 
Where connectors are used in conjunction with a mid-plane, the guide pin 
arrangement is preferably altered. As seen in FIG. 4d a first connector 
10a with spring contact elements 20a, and a second connector 10b with 
spring contact elements 20b are mating with the midplane 50a via plated 
through holes. Midplane 50a includes a guide hole 137 which is slightly 
larger in diameter than typical guide holes, and connector 10a includes a 
hollowed guide pin 74a which mates with guide hole 137. Connector 10b is a 
connector according to the teachings of the invention with a standard 
guide pin 74b which mates with hollowed guide pin 74a. By providing an 
increased diameter guide hole 137 in the midplane, and by providing 
connector 10a with a hollowed guide pin 74a, conflict between the guide 
pins of connector 10a and 10b is avoided. Also, if guide pins 74a and 74b 
are arranged to be conductive, a first make arrangement is accomplished. 
As seen in FIG. 6b, the manufacture of the spring contacts for the 
preferred connector of the invention can be completed, and the spring 
contacts can be preloaded during the assembly of the connector. The 
contact element 20 of the invention is seen in FIG. 6a prior to its 
insertion into the housing 30. Contact element 20 includes contact portion 
38, angled portion 37, second end 34, middle portion 36, and first end 32. 
As shown, part of first end 32 is v or u shaped, and part of second end 34 
is ribbed or channel shaped Middle portion 36 is provided with a 
"dog's-leg" bend In manufacture/assembly, the contact element 20 of FIG. 
6a is inserted into housing 30 with side walls 60 and guide walls 68 
acting as guides, until angled portion 37 of the contact element 20 
engages funnel-like opening 66 of the housing. A bending fixture 140 is 
then preferably inserted between side walls 60 of the housing such that a 
rounded portion of the bending fixture engages the dog's leg bend in the 
contact element. With bending fixture 140 held in place, the first end 32 
of the contact element is forced downward by a press (not shown), with the 
v-shaped first end 32 being forced past locking tabs 72, until the first 
end 32 is brought into contact with the angled surface 142 of bending 
fixture 140. When the press is withdrawn, first end 32 springs back and 
bending fixture 140 is removed. However, first end 32 can only spring back 
to the vertical position of FIG. 6b because it is restrained by locking 
tabs 72. Hence, contact elements 30 are preloaded. Also, because the first 
end 32 of contact element 20 does not spring back to its original shape of 
FIG. 6a when locking tabs 72 are not present, but rather assumes the 
position of the spring contact elements of FIG. 1a, the process of bending 
the contact element 20 is seen to form the contacts into spring contacts. 
Thus, a connector whose preloaded spring contacts are actually partially 
manufactured during assembly is provided. 
Because contact elements 20 are preloaded spring contacts, with locking 
tabs 72 acting as fixing points, if the contact portions 28 of the spring 
contacts 20 are withdrawn into the housing 30, the resulting connector 
functions as a ZIF connector; i.e. the connector housing can be brought 
into contact with the mother board with the use of nominal force Two 
embodiments for retracting contact portions 28 are shown in FIGS. 7a and 
7b. In FIG. 7a, retracting cams 180 are provided and can be fixed to side 
walls 60. By rotating the cams as indicated, the middle portion 26 of the 
spring contacts 20 is forced backward (as shown in phantom), thereby 
drawing contact portions 28 back towards or into housing 30. After the 
connector is brought into contact or into close proximity with the mother 
board and locked into place, cams 180 may be further rotated to release 
spring contact 20 and permit mating. It will be appreciated that if a 
single cam is provided for each row of contacts, the rows may be 
selectively activated. If a cam is provided for each contact, each contact 
may be selectively activated. Similarly, in FIG. 7b, nonconductive 
retracting bars 185 which can move along the axis of the second portion 34 
of spring contacts 20 are provided to force middle portion 26, and hence 
contact portion 28, backward and provide a ZIF connector. If retracting 
bars 185 may also be perpendicularly retracted, sequential individual 
activation of contacts in a single row may be accomplished. 
Turning to FIGS. 8a, 8b, 9a and 9b, various means for establishing and 
maintaining force on the contact elements when they engage the holes in 
the mother board are provided. As shown in FIG. 8a, the daughter board is 
provided with a front panel 80, and a stiffening bar 82, with the 
stiffening bar preferably fastened to the connector housing 30 or bearing 
against the connector housing at the back face (the face opposite front 
wall 64) thereof. Also provided is a leaf spring 84 with ends abutting the 
stiffening bar 82 and a middle which bows away from the leaf spring in a 
direction away from the connectors. Midway along the front panel, the 
stiffening bar, and the leaf spring 84 are holes 86, 88, and 89 for 
accepting a rod or shaft 90 which extends past therethrough. On one end of 
rod 90 is a thumbscrew 92 or the like with an enlarged head which permits 
turning of the rod. Retaining rings 93 and 94 (which is shown in phantom) 
are also attached to rod 90, with the rings 93 and 94 located on the 
non-adjacent faces of stiffening bar 82 and leaf spring 84 respectively. 
The second end of rod 90 is threaded and terminates in a shoulder. The 
threaded section of rod 90 extends past the front face 64 of connectors 
10, through a hole in mother board (back plane) 50 and is arranged to 
engage a tapped bushing 95 located on a stiffening channel 97 which runs 
along the mother board 50. Stiffening channel 97 serves to stiffen the 
mother board 50 so as to prevent bowing of the same due to the large 
forces exerted by the leaf spring in keeping connectors 10 mated in the 
through holes of the mother board 50. The entire arrangement of FIG. 8a is 
particularly advantageous where there are a large number of contacts in a 
connector and the total force of engagement is appreciable as the 
connector is held to its portion of the mother board without putting undo 
stress on either the daughter card, the rest of the mother card, or the 
mother card cage structure. 
As seen in FIG. 8b, different spring arrangements could be used in 
conjunction with the preferred connectors for keeping the connectors 
engaged in the mother board. In FIG. 8b, instead of a leaf spring, a 
standard spring 84b is used between the stiffening bar 82a and retaining 
ring 94b. In essence, the system works in an identical manner to that of 
FIG. 8b. 
Other means of establishing and maintaining force on the connectors are 
shown in FIGS. 9a and 9b. In FIG. 9a, simple bar magnets 98a are attached 
to the daughter PCB 40, with one magnet on either side of the connectors 
10. Identical poles of each magnet are arranged to face the mother board 
(not shown) which is provided with one or more steel plates 99a as an 
attracting surface. In FIG. 9b, horseshoe magnets 98b are located 
alongside each connector 10. A steel strip 99b is provided on the mother 
board to provide an attracting surface for the magnets. 
Turning to FIGS. 10a, 10b, and 11, changes to the mother board are shown 
for enhancing the invention. In FIGS. 10a, and 10b, grid elements are 
provided on the surface 55 of the mother board 50 around each hole 51. The 
grid elements 105 are shaped so as guide the contact portion 38 of the 
contact elements 20 towards hole 51 without stubbing contact portion 38. 
As seen in FIGS. 10a and 10b, the preferred grid structure shape is 
substantially parabolic. However, many other shapes can be utilized. 
Grid elements 105 provide the connector invention with additional 
misalignment tolerance relative to the mother board which is particularly 
useful where relatively large spacing is used between mother board holes. 
Without the grid elements, the maximum misalignment tolerance of the 
spring elements 20 of connector 10 with a hole 51 is the radius of the 
hole. With grid elements 105, the maximum alignment tolerance of the pins 
to the holes is significantly increased to one half the distance between 
the holes 51. Such an alignment tolerance is very large compared to other 
connectors of the art. 
In FIG. 11, an additional compliant layer 110 is shown as an integral part 
of a specially laminated mother board 50. Compliant layer 110 is 
preferably laminated to a conventional FR-4 printed circuit board and 
provides an appropriate matching compliance for the contact elements 20. 
As seen, through hole 51 of the mother board 50 is provided with standard 
copper plating 112. Preferably, gold over nickel (although other 
contact-quality platings could be used) plating layer 114 is provided atop 
the copper plating 112 and serves to provide the mating contact surface 
for the spring contacts 20. The compliant layer 110 can be provided in 
situations where additional wipe is required, and/or where frequent 
insertion of daughter cards is expected. 
There has been described and illustrated herein electrical connectors for 
directly connecting daughter boards to plated through holes of a mother 
board. While particular embodiments of the invention have been described, 
it is not intended that the invention be limited thereby, as it is 
intended that the invention be broad in scope and that the specifications 
be read likewise. Thus, while a one part housing has been disclosed for 
use with preloaded spring contacts, it will be appreciated that the 
housing disclosed in U.S. Pat. No. 4,533,203 to Feldman et al. would 
suffice. Also, regardless of whether a one or two piece housing is used, 
it will be appreciated that the use of locking tabs is not mandatory. 
However, if fixing points are not provided, the characteristics of each 
contact will have to be different in order to create even mating forces 
across all of the pins. Further, while particular spring contacts, with a 
middle portions having a semicircular loops, first ends having v-shaped 
cross sections, contact portions of any of various tapered cross sections, 
etc. have been described, those skilled in the art will appreciate that 
the contact elements can take various other embodiments, provided, 
however, that they provide a spring force when mating In fact, while 
preloading of the spring elements is highly desirable, it is not mandatory 
for the invention to properly function. Also, while the first end of the 
spring contacts were described as being soldered to the daughter board, it 
will be appreciated that other manners of fastening such as compliant 
press fit, surface mounting, etc. could be used. Likewise, while the 
housing and second ends of the spring elements were respectively described 
as having funnel-like openings in a front wall, and angled portions of the 
spring element second portions which cooperate with each other, it will be 
appreciated that geometries other than that shown could be utilized. The 
funnel need not be conical (i.e. the term "funnel-like" being used in its 
broad sense to suggest a narrow opening and widening out to a large open 
mouth), while the angled portion need not be straight, providing it does 
converge. Moreover, the angled portion of the second end need not be 
circular in cross section, as fins could be utilized for centering 
purposes. 
It will also be appreciated by those skilled in the art that different 
means for maintaining sufficient forces to hold the connector to the 
mother board other than those illustrated may be provided. For example, 
numerous fasteners found in the Quarter Turn Fastener Section B of the 
Southco Fastener Handbook 39, published by Southco of Concordville, 
Pennsylvania, will suffice. Similarly, under many conditions, the 
fasteners of FIGS. 8a and 8b without the springs will suffice. Indeed, 
where the connectors of the invention are provided with ZIF capabilities, 
many additional fastener arrangements will suggest themselves It will 
likewise be appreciated that the connector invention will have application 
for connecting parallel PCBs as well as other applications. Therefore, it 
will be apparent to those skilled in the art that other changes and 
modifications may be made to the invention as described in the 
specification without departing from the spirit and scope of the invention 
as so claimed.