[0001] This invention relates to an electrical terminal, particularly for an edgecard connector
for use in the electrical connector industry, for example in microcircuits technology
involving multiple circuit board terminations. More particularly, this invention relates
to elongate terminals which are press fit into circuit board apertures and which have
spring arm contacts adapted for receiving and making electrical contact with circuit
boards.
[0002] In the use of terminals for microcircuit applications there is an ever-present need
for structures which are inexpensive to manufacture, yet which possess inherently
high degrees of reliability. In the manufacture of press-fit terminals for mounting
in circuit board apertures, care must be exercised to insure that tolerances between
the board apertures and the mounting portions of the terminals are within certain
preset limits. The limits must be adequate to insure sufficient retention force, and
yet avoid injury to metallization plating in the aperture. Many structures have been
proposed for achievement of this objective without substantial sacrifice in manufacturing
costs and reliability of the terminations effected thereby.
[0003] For example, U.S. 4,066,326, issued to Lovendusky, discloses a circuit board contact
with an expanded mounting portion which will maintain a desired retention force over
a large circuit board aperture tolerance. Circuit board terminals having similar deformed
mounting portions are also described in U.S. 3,827,004 issued to Vanden Heuvel et
al. and U.S. 3,634,819 issued to Evans. These structures, although quite sufficient
for their intended purposes, do not provide sufficient retention force without solder
bonding when utilized in conjunction with wire wrap tail contacts wherein the terminal
may be subjected to substantial torsional forces. Additionally, some of the prior
art structures (e.g., U.S. 3,634,819) designed for high force retention do not sufficiently
insure accurate location of the central axis of the mounting portion within the circuit
board aperture upon termination.
[0004] Press-fit terminals with spring arm contacts are often used in edgecard connectors.
Unfortunately, such connectors built to provide high normal forces have been asociated
with undesirably high insertion forces, as most of them utilize cantilever spring
arm systems. In order to provide satisfactory mating between the board and spring
arms, a sufficient normal force must be created to assure firm electrical contact,
but high board insertion forces must be avoided. The typical edgecard connector contains
parallel opposing rows of terminals having spring arm contacts biased toward each
other so as to define a convex contact engaging surface for a mating board. The spring
arms function as cantilever beams, so that when a board is slidably inserted therebetween,
the ends of the spring arms are forced laterally apart. Thus, the higher the normal
force provided, the greater the insertion force. Various structures have been proposed
for achieving a reduced insertion force per a given normal force, but many do so only
marginally, and most involve the technique of preloading the opposing spring arm contacts
as disclosed in U.S. 3,963,293 issued to McKee and U.S. 3,671,917 issued to Ammon
et al.
[0005] Viewed from one aspect the present invention provides an elongate electrical terminal
for press fitting in a circuit board aperture, having a contact at each end and a
deformable mounting portion therebetween, said mounting portion comprising a generally
cylindrical body having symmetrically opposed generally oval-shaped voids impressed
therein, the major axes of said voids extending parallel to the longitudinal axis
of said body, the body having a generally bow-tie shaped cross-section with convex
surfaces at its ends and symmetrically opposed, dish-shaped impressions formed in
its sides by said voids to define a reduced centre portion in said cross-section,
whereby said mounting portion upon press fitting into a round circuit board aperture
in use has the convex surfaces at each end of the bow-tie shaped cross-section in
intimate contact with the inside surface of said round aperture and said reduced centre
portion plastically deformed.
[0006] Viewed from another aspect the invention provides an edgecard connector which comprises:
(a) a plurality of elongate terminals each having a contact at both ends and a deformable
mounting portion therebetween, said mounting portions being a press fit into apertures
in a supporting circuit board, one of said contacts of each terminal being a spring
arm having a free end, the second of said contacts being a wire wrap tail,
(b) an insulative housing mated with said supporting circuit board, said housing having
means to removably receive, edgewise, a mating circuit board, and being adapted to
fit over the spring arm contacts of said plurality of terminals, the terminals being
positioned in opposing rows in said apertures of the supporting circuit board, the
housing having a wall therein substantially parallel to the axes of the wire wrap
tails of inserted terminals, the wall being adapted to restrict the free ends of the
spring arms to movement only along a plane parallel to the axes of said tails when
a mating circuit board is inserted into the connector.
[0007] The elongate press-fit terminal of this invention has a mounting portion which provides
a high retention force under torsional stress without solder bonding. The mounting
portion also provides accurate central axis location in a circuit board aperture.
The edgecard connector of this invention provides a higi, normal force with proportionally
less insertion force than realized in cantilever systems, while requiring no preloading
of the terminals contained therein.
[0008] Some embodiments of the invention will now be described by way of example and with
reference to the accompanying drawings, in which:
Figure 1 is a side elevation view of a press-fit terminal of this invention attached
to a carrier strip;
Figure 2 is a front elevation view of the press-fit terminal of Figure 1, including
two such terminals attached to a carrier strip;
Figure 3 is a front elevation view of the deformed mounting portion of the terminal;
Figure 4 is a cross-section view of the deformed mounting portion of the terminal;
Figure 5 is a cross-section view of the deformed mounting portion after being press
fitted into a circuit board aperture;
Figure 6 is a broken perspective view of an alternate embodiment of the mounting portion
of the terminal;
Figure 7 is an exploded perspective view of an edgecard connector of this invention
which utilizes the terminal of Figures 1 and 2;
Figure 8 is a side elevation sectional view of the edgecard connector which shows
a pair of opposed terminals positioned therein; and
Figure 9 is a side elevation sectional view of the connector which depicts flexure
positions of the spring arm contact of the terminal.
[0009] An elongate terminal 10 according to this invention is shown in Figures land 2. The
terminal has a bifurcated spring arm contact 12 at one end and a wire wrap tail contact
14 at the other. Intermediate the contacts is a deformed mounting portion 16 adapted
for press fitting into an aperture in a printed circuit board. Intermediate the spring
arm contact and the mounting portion is a first shoulder 18, a neck 20, and a second
shoulder 22. The terminal 10 is integrally attached to a carrier strip 24 from which
it is severed at reduced section 26 for press fitting into a circuit board aperture.
The spring arm contact 12 when severed from a carrier strip has a free end 15 parallel
to and offset frcm the axis 17 of the wire wrap tail 14 as may be observed in Figure
1. The offset feature, however, is not essential to the operability of this invention.
[0010] Figure 3 is an enlarged view of the mounting portion 16 of the terminal 10. The body
of the mounting portion 16 is generally cylindrical with symmetrically opposed oval-shaped
voids 28 impressed therein by a die. The major axes 30 of the oval voids extend parallel
to the longitudinal axis 32 of the mounting portion 16. The cross-section 34 of the
mounting portion 16 is shown in Figure 4. It is generally bow-tie shaped with symmetrically
opposed dish-shaped sections 36 formed by the voids 28 to form a reduced centre portion
38. The reduced center portion 38 is designed to plastically deform upon the press
fitting of the mounting portion 16 into a circuit board aperture 40 as shown in Figure
5. Deformation of the center portion 38 occurs prior to the realization of injurious
pressure fitting forces. Thus, referring to Figure 5, the pressure exerted by the
contact'surface 42 of the mounting portion 16 against the metallization plating 44
in the aperture is thereby controlled to avoid (1) injury to the plating 44, and (2)
extreme deformation of the aperture 40. At the same time, the contact surface 42 is
large enough to afford high rates of retention force without solder bonding in terminations
subjected to substantial torsional forces as, for example, those encountered in the
use of wire wrap tails.
[0011] Although the mounting portion of this invention provides a high retention force without
solder bonding, the application of solder may be utilized for an even higher retention
force. Thus, Figure 6 is a broken perspective view of an alternate embodiment of the
mounting portion 16 in a cross section of the aperture 40. A mass of solder 46, shown
as a globule, is contained within a support hole 48 formed within the shoulder 22
of the terminal. As the shoulder 22 is contiguous with the mounting portion 16, the
mass of solder is positioned so as to flow into interspaces 50 (Fig. 5) between inserted
mounting portion 16 and the aperture 40 upon exposure to an external heat source,
such as an infrared heater.
[0012] The elongate terminal 10 of this invention is adapted for use in an edgecard connector
60 as shown in Figures 7 and 8.
[0013] Figure 7 is an exploded perspective view of the connector 60 which contains a plurality
of the terminals 10. The terminals are press fit into apertures 40 in a supporting
circuit board 52 in opposing parallel rows as shown. An insulative housing 70 fits
over the spring arm contacts 12 of the terminals 10 and is mated with the supporting
board 52 by mechanical fasteners not shown. The housing 70 has an opening 72 adapted
for removably receiving a mating circuit board 80 in edgewise fashion as depicted.
[0014] The circuit board 80 has metallization pads 82 printed thereon by conventional screen
printing techniques. The pads 82 are electrically connected to other electrical elements,
not shown. The edgecard connector 60 provides a mechanism by which mechanical and
electrical contact may be achieved between the metallization pads 82 and the spring
arm contacts 12 contained within the housing 70.
[0015] Figure 8 is an elevation sectional view of the assembled edgecard connector 60 which
shows a pair of opposed terminals 10 positioned within the housing 70 for receiving
mating circuit board 80. The housing 70 has an internal wall 74 parallel to the axes
17 of the wire wrap tails 14 of inserted terminals 10.
[0016] In Figure 9, one of the spring arms 12 is shown in both unflexed and flexed positions
(the latter in phantom). The free end 15 of the spring arm 12 maintains contact with
the wall 74 in both positions shown as well as between positions. The wall restricts
the free end 15 to slidable movement along a plane parallel to the axis 17 of the
wire wrap tail 14 of an inserted terminal 10. The spring arm 12 functions therefore
as a leaf spring instead of the typical cantilever spring used in most edgecard connectors.
Thus, as seen in Figure 8, since the free ends 15 of the spring arms 12 cannot move
laterally, they will not be forced apart upon insertion of a mating board so as to
produce the high rates of insertion forces associated with cantilever systems. Rather,
a much lower insertion force is realized for a given normal force value in the leaf
spring system of this invention.
[0017] The press-fit terminal and edgecard connector of this invention have wide applicability
in microcircuits applications involving electrical terminations between circuit boards.
For example, such devices are mounted in electronic backplanes of computers, telephonic
switching gear, and many other low voltage signal systems.
[0018] It should be noted that the reduced centre portion 38 of the mounting portion 16
of the terminal may be adapted to shear upon press fitting in a circuit board aperture,
rather than only plastically deforming as described above, with little or no reduction
in the advantages already set forth.
1. An elongate electrical terminal for press fitting in a circuit board aperture,
having a contact at each end and a deformable mounting portion therebetween, said
mounting portion comprising a generally cylindrical body having symmetrically opposed
generally oval-shaped voids impressed therein, the major axes of said voids extending
parallel to the longitudinal axis of said body, the body having a generally bow-tie
shaped cross-section with convex surfaces at its ends and symmetrically opposed, dish-shaped
impressions formed in its sides by said voids to define a reduced centre portion in
said cross-section, whereby said mounting portion upon press fitting into a round
circuit board aperture in use has the convex surfaces at each end of the bow-tie shaped
cross-section in intimate contact with the inside surface of said round aperture and
said reduced centre portion plastically deformed.
2. A terminal as claimed in Claim 1, which has a mass of solder adjacent said mounting
portion, said mass of solder being positioned so as to flow, upon exposure to an external
heat source, into interspaces between an inserted mounting portion and a corresponding
circuit board aperture.
3. A terminal as claimed in Claim 1 or 2, wherein one of said contacts is a spring
arm in line with the axis of the terminal.
4. A terminal as claimed in Claim 1 or 2, wherein one of said contacts is a wire wrap
tail, the other being a spring arm having a free end parallel to and offset from the
axis of the wire wrap tail.
5. A terminal as claimed in Claim 4, wherein said spring arm contact is bifurcated,
said terminal having a first shoulder, a neck portion, and a second shoulder all positioned
intermediate said spring arm contact and said mounting portion.
6. An edgecard connector which comprises:
(a) a plurality of elongate terminals each having a contact at both ends and a deformable
mounting portion therebetween, said mounting portions being a press fit into apertures
in a supporting circuit board, one of said contacts of each terminal being a spring
arm having a free end, the second of said contacts being a wire wrap tail,
(b) an insulative housing mated with said supporting circuit board, said housing having
means to removably receive, edgewise, a mating circuit board, and being adapted to
fit over the spring arm contacts of said plurality of terminals, the terminals being
positioned in opposing rows in said apertures of the supporting circuit board, the
housing having a wall therein substantially parallel to the axes of the wire wrap
tails of inserted terminals, the wall being adapted to restrict the free ends of the
spring arms to movement only along a plane parallel to the axes of said tails when
a mating circuit board is inserted into the connector.
7. An edgecard connector as claimed in Claim 6, wherein the said mounting portion
of each terminal has a generally cylindrical body with symmetrically opposed generally
oval-shaped voids impressed therein, the rajor axes of said voids extending parallel
to the longitudinal axis of said body, the body having a generally bow-tie shaped
cross-section with symmetrically opposed dish-shaped impressions formed therein by
said voids to define a reduced centre portion in said cross-section.
8. An edgecard connector as claimed in Claim 7, wherein the reduced portion of said
cross-section of said mounting portion is adapted to be plastically deformed upon
the press fitting of said mounting portion into a circuit board aperture.
9. An edgecard connector as claimed in any of Claims 6 to 8, including mechanical
fastener means for mating said insulative housing with said supporting circuit board.
10. An edgecard connector as claimed in any of Claims 6 to 9, wherein the spring arm
contact of each said terminal is bifurcated, the terminal having a first shoulder,
a neck, and a second shoulder all positioned intermediate said spring arm contact
and said mounting portion.
11. An edgecard connector as claimed in any of Claims 6 to 10, wherein the free end
of the spring arm of each terminal is parallel to and offset from the axis of said
wire wrap tail.