Note: Descriptions are shown in the official language in which they were submitted.
~773~
CIRCUIT BOARD PIN
This invention relates to circuit board pins.
Soldering has traditionally been accepted for
providing electrical connections. Certain electrical
connections are, however, made difficult to form by the use
of soldering techniques. For instance, it has been found
that soldering imposes restrictions in design of printed
circuit boards because of problems associated with inserting
circuit board pins into holes in the boards and connecting
the pins to electrically conductive surfaces of the holes.
The development of circuit board pins having
compliant portions has overcome the soldering problems, but
has introduced other problems. The compliant portions of
these pins are oversize for the holes in boards into which
they are to be fitted. To assemble the pins and boards, the
compliant portions are forced into the holes by press-fit
techniques which deform the compliant portions inwardly of
the pins. Resilient deformation ensures a tight fit of the
compliant portions in the holes and a good metal-to-metal
contact between the pins and the surface material forming the
holes. Unfortunately, certain pin designs have compliant
portions with surfaces which meet at junction positions to
form corners in cross-section of the pins. These corners
tend to cut into the conductive lining material of the holes
under the outward resilient pressure of the inwardly deform-
ing compliant portions. Cutting or wearing action also
occurs when the compliant portions provide relatively small
contact surface areas with the conductive lining material of
the holes. The wall thickness of lining material is normally
around 0.0015 inches and the lining material may be complete-
ly cut through by a compliant portion of a pin. After a
cutting action, copper material of the lining may then break
away to expose the surface of the board material. This
results in less contact area between the lining material of
the hole and the pin and resultant decrease in passage of
current. In the case of multi-layer boards, aging, tempera-
ture changes and temperature cycling and presence of moisture
are known to cause delamination and breaking away of the ~
~7734
boar~d material following breaking away of the copper lining
material. Oxidization of the conductive layers between the
multi-layers increases resistance to passage of the current.
one pin design has a compliant portion which is of
C-shaped cross-section and has an outer continuously convex
surface. Resilient deformation occurs at all positions
around the compliant portion to produce movement towards each
other of the ends of the C-shape and its accompanying reduc-
tion in radius. The convex outer surface of the compliant
portion provides a large contact area with the conductive
lining material of the hole and thus more even distribution
of the pressure than is obtainable with other pin designs.
As a result, there is a reduced tendency for the C-shaped
compliant portion to cut into the conductive lining material
of the hole.
However, compliant pins having C-shaped compliant
portions require a multitude of incremental forming steps
performed by press tools to produce them. The tooling for
these consecutive operations is extremely expensive and
precise and is intended to produce precisely shaped compliant
portions. Tooling expense is partly due to the tool design
required to precisely control the shape of transition zones
between the compliant portions and wire terminal portions of
the pins. Nevertheless, symmetry problems do occur and in
some pins, the compliant portions are weaker at one side of
the C-shape than at the other. This may result in twisting
of asymmetrical pins as they are forced into the holes and
gouging into conductive lining material. Also, the incremen-
tal forming steps sometimes produce random flashes of metal
between press tools and this leads to assembly and conduction
problems. In addition, the transition zones between the C-
shaped compliant portions and wire terminal portions o~ the
pins are axially short and are inclined to be weak ~uch that
breakage may occur when the pins are inserted.
The present invention seeks to provide a compliant
pin designed to have a large contact area with conductive
lining material or holes into which it is to be fitted while
overcoming problems associated with a pin having a C-shaped
7773~
compliant portion. The invention also seeks to provide a
method of forming a compliant pin which overcomes problems
associated with other pin forming methods.
Accordingly, the present invention provides a
circuit board pin having a compliant portion extending along
part of its length and another section extending from the
compliant portion, the pin comprising two beams extending
along the compliant portion, the beams extending laterally
from and integrally joined together by a concentrated
resilient hinge region of the compliant portion for resilient
movement towards each other of the beams, the beams also
increasing in thickness laterally away from the hinge region
and having opposing inner surfaces diverging from the hinge
region to define an inwardly tapering groove between the
beams, the compliant portion having a convex continuously
smooth outer surface which extends around the beams and hinge
region, and the beams merging at one end into the other pin
portion at a transition zone.
The circuit board pin according to the invention
operates to provide a gas tight fit within a hole by resili-
ent deformation of the hinge region to move the opposing
surfaces of the beams towards each other. This resilient
deformation is concentrated at the thinner hinge region and
negligible, if any, resilient deformation occurs at thicker
parts of the beams. The beams have considerable mass away
from the hinge region whereby merging of the beams together
and into the other pin portion does not result in drastic
changes in mass or cross-sectional dimensions of the pin
whereby the pin is not unduly weakened at the transition
zone.
The pin according to the invention may be made
simply by a combined cold worked molding and coin punching
process. In this process, a mold is closed around part of
the pin to form the compliant portion to provide a mold
cavity with cavity parts unoccupied by the pin, and a coining
punch is moved across the cavity to apply pressure to the pin
and deform it to cause it to be displaced into unoccupied
parts of the cavity. Such a process may be performed
77734
incrementally in stages, but may easily be performed in a one
or two stage operation. Displacement molding into a mold
cavity also closely controls the shape of the compliant
portion to provide symmetry to the structure. Also, as mold
closure occurs before the deformation process, the formation
of flash is avoided.
Accordingly, the invention also provides a method
of forming a circuit board pin having a compliant portion
along part of its length and another portion extending from
the compliant portion, comprising forming the compliant
portion by disposing mold parts around said part of the
length of the pin to provide a mold cavity containing said
length part with the length part firmly stabilized in
position laterally while providing cavity portions unoccupied
by said length part, and with the mold cavity defined, moving
a tapered coining punch partly across the mold cavity to
reduce the volume of the cavity and displace material of the
length part to each side of the punch and into empty cavity
portions:- a) to provide two beams of the compliant portion,
one at each side of the punch which forms an inwardly tapered
groove between the beams, the punch terminating on its
working stroke a distance from an opposite wall of the mold
cavity to provide a concentrated resilient hinge region
integral with and between the two beams and to provide the
beams with an increase in thickness as they extend laterally
away from the hinge region: and b) to provide the compliant
portion with a continuously smooth outer surface which
extends around the beams and hinge region with the beams
merging at one end into the other portion of the pin at a
transition zone.
With the process according to the invention,
displacement molding minimizes any possibility of asymmetry
of the compliant portion. Also, because the compliant
portion is formed within a mold cavity, the production of
flash is minimized.
In the inventive method, formation of the compliant
portion may take place in one operation, i.e. the beams and
hinge region are formed by a single displacement operation
127~7734
within the mold cavity from a shaped preform which will fit
within the cavity while being positionally stabilized.
In the method, however, a preform is provided in
which two beams are already partially formed and a preform
groove exists between the beams. The tapered coining punch
moves partly across the mold cavity to displace material to
complete both the inwardly tapering groove and the beams.
Preferably, before the tapered punch is moved across the
cavity, the preform is disposed within the cavity with the
outer surface of the preform engaging over an area of the
mold surfaces for a distance at each side of a parting line
of the mold parts. This has been found to completely avoid
flash or render it negligible, because material is only
displaced by the punch into empty mold portions spaced from
the parting line. The overall engagement between mold parts
and the preform at each side of the parting line substantial-
ly prevents any displacement of material in this region
during operation of the punch.
In a preferred manner of performing the method, in
the transition zone between the compliant portion and the
other portion o~ the pin, material at the two end regions of
the compliant portion i8 displaced longitudinally of the pin
in an uncontrolled and unrestricted manner. This lack of
restriction on the flow of material provides the advantage
that the beams and the hinge region are allowed to merge
naturally with the other portion of the pin without placing
undue stresses and strains upon the transition zone as by the
use of mold surfaces.
The invention further includes an apparatus for
making a circuit board pin comprising a plurality of mold
parts relatively movable into and out of mold cavity forming
positions, the mold parts in their cavity forming positions
defining a mold cavity having a mold surface to provide a
convex continuously smooth outer surface of a compliant
portion of the pin, a coining punch having a tapered end, the
mold parts in their cavity forming positions defining a
passage for movement on the punch on a working stroke to
allow for movement of the tapered end of the punch partly
~277734
across the mold cavity, and means for moving the mold parts
into and out of the mold cavity forming positions and for
moving the punch on its working stroke.
In a preferred practical arrangement, the apparatus
includes a means for intermittently moving strip material
along the feedpath, a compliant portion forming station at a
certain position on the feedpath with the mold parts, coining
punch and moving means operably disposed in the compliant
portion forming station, a compliant portion preform forming
station upstream along the feedpath from the compliant
portion forming station, and a forming means in the preform
forming station for forming a preform for the compliant
portion.
It is also to be preferred that the mold parts in
the mold cavity forming positions define an opening at each
end of the mold cavity. With this arrangement, material at
the two ends of the compliant portion may be displaced longi-
tudinally of the pin in an unrestricted and uncontrolled
manner so as to allow for the natural merging of the beams
and hinge region with the other pin portion at the transition
zone. Also, the provision of an opening to each end of the
mold cavity simplifies the manufacture of the mold parts
while reducing their cost. For instance, in a particularly
preferred arrangement, each mold part has a mold surface with
a shape and dimensions which remain constant from cross-
section to cross-section between the ends of the mold part
with the mold surface extending in rectilinear fashion in any
section taken longitudinally along the mold part. This shape
for the mold surface enables it to be made economically by a
simple straight machining operation from end-to-end of the
mold part. This simplicity in mold part manufacture avoids
the difficult and expensive machinery operations in the
manufacture of the ends of press cavities for the manufacture
of compliant portions for circuit board pins of other
designs.
Embodiments of the invention will now be described,
by way of example, with reference to the accompanying
drawings, in which:-
~;~77734
Figure 1 is a plan view of a circuit board pin
according to a first embodiment;
Figure 2 is a plan view of a compliant portion of
the pin and to a larger scale;
Figure 3 is an isometric view of the compliant
portion of the pin;
Figure 4 is a cross-sectional view of the compliant
portion taken along line IV-IV in Figure 2 and to a larger
scale;
Figure 5 is a plan view of the compliant portion of
the pin showing it mounted in a pin receiving hole of a
printed circuit board;
Figure 6 is a cross-sectional view through the
assembled pin and board taken along line VI-VI in Figure 5
and to the same scale as Figure 4;
Figure 7 is a diagrammatic representation of
apparatus of a first embodiment, showing an automated process
for the progressive forming of circuit board pins of Figure
l;
Figure 8 is a side elevational view of part of the
apparatus of the first embodiment with the apparatus in an
open position;
Figure 9 is a view similar to Figure 6 showing the
part of the apparatus in closed position;
Figure 10 is a cross-sectional view through the
apparatus of the first embodiment in the direction of Figure
8 and to a larger scale, and shows the apparatus in an open
position and in greater detail;
Figure 11 is a cross-sectional view through the
apparatus taken along line XI-XI in Figure 10;
. Figures 12, 13 and 14 are cross-sectional views in
the direction of Figure 8 and to a much larger scale, showing
apparatus parts in succeeding operational positions during
formation of a compliant portion of the pin; and
Figures 15 and 16 are cross-sectional views, to the
same scale as Figures 12 to 14, taken along lines XV-XV and
XVI-XVI respectively in Figures 12 and 14:
Figures 17, 18 and 19 are cross-sectional views, in
~77734
the direction of Figure 8, and to a larger scale than Figures
12, 13 and 14, showing the sequence of forming operations in
the first embodiment in greater detail; and
Figures 20 to 24 are cross-sectional views similar
to Figures 17, 18 and 19, of the operation of apparatus
according to a second embodiment.
In the embodiment of a pin as shown in Figure 1, a
circuit board pin 10 comprises a compliant portion 12
extending along part of its length. The compliant portion
lo extends at one end into an end portion 14 of the pin and at
the other end into a neck portion 16 of the pin which is
integral with an intermediate wider portion 18 and a wire
terminal portion 20 at the other end of the pin. As shown by
Figure 3, the end portion 14 and neck portion 16 are of
rectangular cross-section. The wire terminal portion 20 is
of similar cross-section. The intermediate portion 18 is
wider in plan view as shown in Figures 1, 2 and 3 to provide
two shoulders 22. The compliant portion 12 of the pin
comprises two beams 24 which extend along the compliant
portion. These two beams lie side-by-side, as shown in
Figure 4, and are integrally joined together along one edge
of each of the beams by a concentrated resilient hinge region
26 of the compliant portion. The beams increase in thickness
away from the hinge region, as shown particularly in Figure
4, and have planar opposing inner surfaces 28 which diverge
as they extend laterally away from the hinge region. The
compliant portion also has a convex continuously smooth outer
surface 30 which extends around the two beams and the hinge
region to a junction with the surfaces 28 at edges of the
beams remote from the hinge region. Because of the increas-
ing thickness of the beams laterally from the hinge region,
then the beams themselves have greater lateral stiffness than
the hinge region thereby ensuring that the resiliency of the
structure is confined to the hinge region. The hinge region
allows for relative resilient movement towards each other of
the two beams so that the angle between the surfaces 28
decreases as will be described below.
The depth and width of the compliant portion are
~7~3~
greater than those of the end and neck portions 14 and 16.
The compliant portion tapers at each end into the end and
nec}c portions at a transition zone 32. As can be seen from
Figures 1 to 3, along the transition zone the two beams
graaually change shape so as to merge together and also merge
into the rectangular shapes of the end and neck portions. As
indicated above, each of the beams 24 has a greater thickness
laterally from the hinge region 26 and this thickening of the
beams provides substantial mass to the compliant portion with
the cross-sectional area of the compliant portion being at
least substantially equal to, but in this embodiment, greater
than that of each of the portions 14 and 16. Thus, as there
is no area reduction at the compliant portion there is no
weakening of the structure. A V-shaped groove 34, which is
formed between the inner surfaces 28, reduces progressively
in depth together with a reduction in the width of the groove
at each of its ends 36 in the transition zone so as to allow
for progressive change in shape from the compliant to the end
and neck portions.
The circuit board pin 1~ is intended to be as-
sembled into a conductively lined hole of a circuit board.
For instance as shown in Figures 5 and 6, a multi-layer
circuit board 38 comprises three layers 40 through which are
provided a plurality of holes 42 (one only being shown).
Each of the holes 42 is lined in conventional manner with a
conductive lining material 44 and conductive layers 46 of an
electrical circuit are provided extending away from the
material 44, at each side of the multi-layer board and also
between the board layers themselves.
The pin lo is inserted into its respective hole 44
by passage of the end portion 14 through the hole and then
the adjacent transition zone 32, followed by the compliant
portion 12. As the transition zone moves through the hole,
it engages the conductive material 44, and as insertion
proceeds, the conductive material 44 bears upon the transi-
tion zone and then upon the two beams to apply a radial
pressure to cause resilient inward movement of the beams.
Because the beams are laterally rigid at their thickened
~ ~7773~
sections, then such inward deformation may only take place by
movement of the beams towards each other caused by resilient
deformation at the hinge region 26. This has the effect of
sign,ificantly reducing the width of the groove 34, as shown
in Figure 6, accompanied by compression placed in the
material at the hinge portion directly beneath the base of
the groove and tension in the material at the hinge region
closer to the outer surface 30. This is shown by the
direction of the arrows in the hinge region in Figure 6. The
shape of the outer surface 30 is predetermined so that in the
assembled condition of the pin into its hole, there is a
substantial arc of contact 48 between each beam and the
conductive material 44. This is clear from Figure 6.
As can be seen from the above description, two
effects are provided by the cross-sectional area of the
compliant portion being greater than the end and neck
portions and by the thick beam structure away ~rom the hinge
region 26. The one effect is that the resilient deformation
of the compliant pin takes place substantially completely in
the hinge region and as a second effect, there is a resultant
strengthening to the transition zones at the ends of the
compliant portion. As a result of this, the possibility of
the pin shearing in the compliant portion or in the transi-
tion zones is minimized to produce a negligible amount of pin
failures during and after assembly into printed circuit
boards.
The compliant portion of the pin also has a
substantial degree of symmetry about a longitudinal median
plane 50 (Figure 4) passing along the groove 34 and through
the center of the compliant portion. This high degree of
symmetry is produced by the method and apparatus to be
described, and ensures that during insertion of the pin, no
undesirable pin twisting or rotation will occur.
Figure 7 shows diagrammatically the main parts of a
first embodiment of apparatus used in making pins 10 consecu-
tively by a continuous process. As shown by Figure 7, a
strip 52 of conductive material is fed in intermittent
fashion along a passline by a moving means (not shown). The
~2~
11
moving means is a conventional drive mechanism for controll-
ing the forward movement of the strip. In an upstream
posiition along the passline, the apparatus comprises pilot
hole punches 54 on one side of the passline and pilot hole
pierce inserts 56 on the other for forming pilot holes 58
along the two edges of the strip as it moves along the
passline. Downstream from the pilot hole punches at a
subsequent station, are located a contact trim punch 60 and
contact trim insert 62, one at each side of the passline for
punching out shaped apertures 61 in the strip 52 to provide
basic pin preform shapes 63. As can be seen from Figure 7,
these preform shapes 63 are already provided with the
substantially finished end portions 14 and also wider
portions 65 lying adjacent to the port ons 14. Each portion
65 is for forming a compliant portion 12 and, as will be
appreciated, as each portion 65 is wider than, but of the
same thickness as, its associated end portion 14, then the
lateral cross-sectional area through each portion 65 i5
greater than that for an end portion 14~ As will be clear
from the following description, all of the material in each
portion 65 is used for making a compliant portion 12 of its
respective pin with the result that the cross-sectional area
of the finished compliant portion is always greater than that
of the end portion 14 as has previously been discussed.
Downstream from the punch 60 and the insert 62 are
located parts of the apparatus for forming the compliant
portions of the successive pins. These parts of the ap-
paratus are disposed in two stations, namely a compliant
portion preform forming station 64 downstream from the punch
60 and insert 62, and a compliant pin forming station 66
which lies further downstream. With reference to Figure 7,
in the station 64, a preform forming means comprises a
preform forming punch 68 on one side of the feedpath and a
preform forming die 70 on the other side of the feedpath. At
the compliant portion forming station, there is disposed a
mold comprising upper and lower mold parts 72 and 74,
disposed at each side of the passline, and a coining punch 76
which, as will be described, is movable through the mold part
~77734
12
72 to displace material of a preform and form it into a
compliant portion 12.
The parts of the apparatus disposed in stations 64
and 66 will now be described in greater detail with reference
to ~igures 8 through 16.
As shown in Figures 8 and 9, both the preform
forming punch 68 and the coining punch 76 are vertically
slidably movable within a punch block 78 disposed above the
passline and urged downwardly from a ram 80 upon compression
springs 82. The punches 68 and 76 are secured at their upper
ends to the ram so that, after the punch block has reached
its lower limit of travel illustrated in Figures 9 and 13,
then continued downward movement of the ram will urge the
punches through the punch block. Beneath the passline is
disposed a die block 84 which securely holds in position the
forming die 70 and the lower mold part 74.
As is shown in more detail in Figure 10, the mold
part 72 is provided by a downwards extension from a stripper
plate 85 which extends across both stations 64 and 66 and
acts as a guide for the lower ends of the punches 68 and 76.
The stripper plate 85 is secured to the punch block 78. The
mold part 72 defines a concave upper surface 86 for a mold
cavity, and the lower surface 88 for the cavity is provided
by an upper projection 90 of the mold part 74. With the
punch block and thus the stripper plate 85 in its lower
position, as seen from Figure 12 onwards, edges of the strip
of material 52 are gripped and also the strip accurately held
in position by the entrance of pilot pins (not shown) into
the preformed pilot holes 58. The use of pilot pins in this
regard is conventional for forming circuit board pins and
needs no further description. In addition to this, with the
punch block in its lower position, the mold part 72 substan-
tially engages the projection 90 of the lower mold part.
There may be a nominal gap of approximately 0.005 inches
between the mold parts which is dictated by the downward
limit of movement of the stripper plate 85. This gap is
provided to prevent the ram pressure acting directly on the
lower mold part. The pressure is applied from the punch
~2~73~
13
block 78 to the die block 84 instead. Hence in the lower
position, the surfaces 86 and 88 define a mold cavity 94
(Figure 12) for the formation of compliant portions of the
circuit board pins as they are moved through station 66. The
lowe~r end 96 of the coining punch 76 is tapered and the
stripper plate 85 is provided with a tapered passage 98 which
opens through the surface 86 into the mold cavity 94. Thus
when the punch block 78 and the mold part 72 have reached
their lower positions shown in Figures 9 and 12, continued
downward movement of the ram moves the tapered end 96 of the
punch 76 downwards into and partly across the mold cavity 94.
This is illustrated by a comparison of Figures 12, 13 and 14.
The surfaces 86 and 88 are of simple construction
and are formed as straight through cavities from end-to-end
of the mold parts. Thus in the closed condition, the mold
cavity 94 has two open ends 99 as can be seen from Figures 15
and 16. Hence, each mold surface 86 and 88 is of constant
cross-sectional shape from end-to-end of its mold part and
extends rectilinearly from end-to-end of the mold part.
The preform forming punch 68 is formed with a lower
forming groove 100 which iB of V-shape and the die 70 is
formed with a similar groove 102 which lies directly below
the groove 100.
In use of the apparatus, the punch block is in its
upper position and the strip 52 is moved intermittently from
one position to another along its feedpath in the direction
of the arrow in Figure 8. After each intermittent movement
of the strip, the ram descends to move the punch block into
engagement with the die block so as to hold the strip
accurately in position during the forming operations. Upon
the punch block engaging the die block 84, the mold part 72
engages the upper portion 90, as shown in Figure 12, and a
previously made preform 104 is disposed within the cavity 94.
This is also shown more clearly in enlarged section of Figure
17. The dimensions of the preform are such that, with the
mold closed, the preform engages surface parts of the mold in
spaced positions as shown in Figures 12 and 17 so as to
stabilize ~the preform accurately in position laterally while
~X7'7734
14
providing empty cavity portions (unoccupied by the preform)
as shown clearly by those figures. Also, in this position of
the apparatus, the punch 68 is spaced upwardly from the die
70 and the portion 68 of a succeeding circuit board pin is
located above the groove 102.
As the ram continues to move downwardly, the punch
68 descends until the groove surface 100 engages the portion
68. Continued downward movement then deforms this portion
into a succeeding preform 104 as shown in Figure 14. In an
intermediate stage (Figure 13) a partly formed preform 104a
is shown. During the downward movement of the ram, the punch
76 also descends so that the lower tapered end 96 enters the
mold cavity 94 and moves partly across the cavity. During
this movement, the lower end 96 of the punch engages the
upper surface of the preform 104 for substantially the whole
length along the preform and displaces material of the
preform laterally and to each side of the punch, as il-
lustrated in successive stages in the punching operation in
Figures 13 and 14. See also enlarged sections of Figures 18
and 19. This movement forces the material into previously
empty portions of the mold cavity whereby the two beams 24
are formed (see Figures 14 and 19) with an intermediate stage
for the beams 24a shown in Figures 13 and 18. The punch
terminates on its working stroke a distance from the lower
wall or surface of the mold cavity. Material between the end
of the punch and the surface 88 provides the concentrated
resilient hinge region 26 of the compliant portion being
formed. As can also be seen from Figures 12 to 14, the whole
of the surface 88 becomes engaged by the material being
displaced which conforms to the surface 88 and to most of the
surface 86 so as to provide the continuously smooth outer
surface 30 of the compliant portion.
It is an important part of the method that material
displaced at the ends of the compliant portion 104 and in a
longitudinal direction of the pin should be displaced in an
unrestricted manner. This lack of restriction is convenient-
ly provided by the open ends 99 to the cavity 94 as provided
by the simple straight through rectilinear forms of the
~:~7`7734
surfaces 86 and 88. As can be seen from Figure 15, as the
punc:h 76 descends, it enters into the preform 104 (Figure 16)
to clisplace the material as described above and, with the
assistance of inclined corners 106 of the end of the punch
76, some of the preform material is also displaced longi-
tudinally. A comparison of Figures 15 and 16 shows that the
finished compliant pin 12 extends further towards the ends 99
of the mold cavity 94 than does the preform 104. This
allowance for unrestricted movement of the material at the
ends of the preform in a longitudinal direction of the pin,
has the effect not only of allowing for a simple and economic
structure for the mold parts, but also enables a natural flow
of the material to be produced. Hence the transition zones
38 are more naturally and smoothly formed than would be the
case with a completely enclosed mold cavity. Thus the
transition zones, which are of acceptable strength, are
easily formed without difficultly formed mold shapes.
In the formation of each compliant portion 12, the
grain flow in the strip material automatically extends in the
longitudinal direction so that grain flow will extend from
bead to bead around the hinge region 26 of each of the
compliant portions. This grain flow is increased during the
displacement of the material of the preform 104 into the
formation of the compliant portion by the lateral movement of
the material at each side of the punch. Thus, a particularly
strong compliant portion is produced. In addition, some
grain flow is also introduced in a longitudinal direction in
the transition zones 32 by the tapered corners 106 of the
coining punch which displace the material longitudinally.
This also adds to the strength of the pin in the transition
zones. Further to this, as has previously been mentioned,
the cross-sectional area of each compliant portion is greater
than that of its associated end portion 14 and neck portion
16. This is to ensure no undue weakening at the transition
zone such as would be occasioned by a reduction in the area
in the compliant portion from that found in adjacent regions
of the pin. It will be noted that the portion 68 of each pin
which is formed prior to the formation of the preform 104 is
~Z~773~
16
of greater cross-sectional area than the end portion 14 (see
above). According to the process, as each preform is made
and each compliant portion is subsequently made from each
preform, there is substantially no removal of material except
for the slight amount of material which is caused to flow
into the transition zones during downward movement of the
punch 76. As a result, the cross-sectional area of each
compliant portion is only slightly less than the cross-
sectional area of the portion 68 from which the compliant
portion has been made. Thus the process ensures that the
cross-sectional area of a compliant portion is greater than
the cross-sectional area of adjacent regions of the as-
sociated pin.
As can be seen from the above embodiment, the
apparatus for manufacture of each circuit board pin is
relatively simple and provides a method of displacement
molding of compliant portions which avoids the series of
steps normally provided for formation of the conventional C-
shaped circuit board pins. Thus, very little work hardening
of the compliant portion results such as would produce
brittleness and thus weakening of the structure during
deformation in use. In fact, while a little work hardening
may result during formation of the groove 34, this will
mainly occur in the hinge region 26 of each compliant portion
and will result in a strengthening of the structure as a
whole.
Further to this, because the mold parts are
substantially closed around the preform before deformation by
the punch 76, then the material does not tend to flow between
two mating parts (such as may occur in formation of more
conventional compliant portions) whereby the flash at the
sides of the compliant portions is minimized. This is the
case even though there is a nominal gap of perhaps about
0.005 inches between the mold parts and the material during
displacement flows past this gap. The gap 108 is shown in
enlarged views of Figures 17, 18 and 19. Thus, any problems
associated with flash in the use of circuit board pins is
substantially avoided. In addition to this, because of the
~7 773~
17
lateral stability of each compliant portion within the mold
cavity 94 and the symmetrical downward movement of the punch
76, the chance of asymmetry in the finished compliant portion
is minimized. It follows that there is a reduced tendency
for circuit board pins made by the method and apparatus of
the first embodiment to rotate or distort when assembled to
circuit boards.
Further, if it is required to strengthen or weaken
the compliant portion of circuit board pins as described
above and according to the invention, so as to produce a
compliant pin having specified strength requirements, then
this can be easily achieved by simply altering the lowest
position of movement of the punch 76. As can be seen from
this, the lower end 96 of the punch can be varied in its
distance from the mold surface 88 whereby the total depth of
the hinge region 26 and thus the thickness of each of the
beams 24 can be controllably varied.
The above advantages are also obtained by the
manufacture of pins 10 by a second embodiment of apparatus
now to be described. The apparatus of the second embodiment
operates basically as described for the first embodiment of
apparatus and has two stations, i.e. a compliant portion
preform forming station and a compliant pin forming station
for forming the pins from portions 65 of the pin preform
shapes 63 discussed in the first embodiment. With the
understanding that all of the forming parts for these two
stations are carried by a stripper plate and die block (as
for all of the parts in the first embodiment), the second
embodiment will be described with reference to Figures 20 to
24 which show forming parts only. Parts of the apparatus of
the same construction as in the first embodiment will carry
the same reference numerals.
In a first station, Figure 20, the portions 65 of
the pins are fed in succession into the compliant portion
preform forming station 110. In this stati~n, each portion
65 is disposed completely within a preform forming groove 112
formed in a die 114. A preform forming punch, in the form of
a coining punch 116, descends symmetrically onto the portion
~.X~773~
18
65 which is stabilized laterally between parallel side walls
111 of the groove 112. The punch 116 performs a first
coining operation in which it shapes the portion 65 into a
pref'orm 118 (Figure 21). The punch 116 is tapered at its
lower end 120 which contacts the portion 65 during downward
movement of the punch and displaces material laterally and to
each side of the punch to provide partially formed beams 24b
at each side of a V-shaped groove 122 of the preform. The
preform lies completely within the groove 112 with material
also displaced downwardly and outwardly substantially into
intimate contact with a base surface 126 and side,walls lll
of the groove. The base surface and side walls blend
together to form an unbroken smoothly concave groove surface
which produces a smoothly convex outer surface 127 of the
preform.
After raising of the punch 116, the strip of
conductive material carrying the preform ~hapes for the pins,
i8 intermittently advanced to bring the preform 118 into the
second station, i.e. the compliant pin forming station 128
(Figure 22). In this station is located a mold comprising
lower and upper mold parts 130 and 132 and a coining punch 76
which is as described in the first embodiment. The lower
mold part 130 has a mold surface 133 which conforms closely
to the lower section of the smooth outer surface 127 of the
preform with the upper parts of this surface projecting above
the mold surface 133. The upper mold part has a concave mold
surface 134 which, with the mold parts brought together,
forms a continuation of mold surface 133 with a n~minal gap
136 ~Figure 23) between mold parts as described in the first
embodiment. The preform 118 is wider across the upper parts
of the partially formed beams 24b than the mold surface 134
so that as the mold parts are moved together (Figure 23), the
partially formed beams are engaged by the surface 134 at the
upper parts of surface 127 and the beams are then urged
towards each other by the interaction with the mold surface
134. Thus the upper ends of the surfaces 127 are deflected
inwards from the chain dotted position of prefo~m 118 to the
full outline position shown in Figure 23. The mold surface
3~
19
134 is shaped so that, in the mold closed position, the outer
surface 127 is engaged over an area of the mold surface for a
distance above the parting line for the mold, the parting
line of course lying at the gap 136. As a result, the outer
surface 127 is engaged over an area of both mold surfaces for
a distance at each side of the parting line with the lower
mold surface conforming closely to the lower section of the
smooth outer surface 127. As shown by Figure 23, at this
stage, the mold cavity is unoccupied by preform material not
only in the region of groove 122, but also above the tops of
the partially formed beams 24b.
The punch 76 is caused to descend and firstly
enters the groove 122 and then proceeds further into the
preform to produce the finished groove 34. This is accom-
panied by further displacement of preform material laterallyof the punch so that the partially formed beams 24b expand
upwardly into the previously unoccupied cavity regions
thereby forming the completed beams 24 and finalizing the
shape of the pin 10 ~Figure 24). As in the first embodiment,
material i5 also displaced longitudinally of the pin during
downward movement of punch 76, this displacement being
unrestricted.
In the use of the apparatus of the second embodi-
ment, the outer surface 127 of the preform is formed as a
smooth curving surface against a single preform forming
groove 112 to avoid discontinuity in surface 127. The
preform is then located against the closely conforming
surface 132 and to ensure close conformity of the upper parts
of surface 127 with surface 134, this s-urface deflects the
surfaces 127 inwards as described. This action produces no
discontinuity in surface 127, but produces its final curved
shape by a simple deflecting movement before the punch 76
descends. When the punch descends, there are no significant
spaces in the mold cavity for a substantial distance at each
side of the parting line and into which the preform material
can be moved. The overall support for the surface 127 has
been found to prevent any outward movement of material in the
region of the parting line of the mold parts so that no flash
is formed into the narrow gap between the mold parts.
Instead, the preform material moves more readily into mold
cavity parts where there is no resistance to movement, i.e.
at the top of the cavity at each side of the punch 76.
Hence, with the outer surface of the preform being shaped
against a single forming groove and then supported closely
ancl intimately by two mold surfaces which hold the outer
surface 127 in finished shape before the coining operation of
punch 76 commences, the production of flash between the mold
parts is completely avoided.
