Note: Descriptions are shown in the official language in which they were submitted.
1293-7 21 70436
SURFACE MOUNT ELECTRICAL CONTACTS
BACKGROUND OF THE INVENTION
The invention generally relates to electrical contacts,
and more specifically, to surface mounted electrical contacts
that can be mounted on the surfaces of printed circuit boards
by automated surface component mounting equipment, capable of
sequentially picking up the electrical contacts, one at a time,
and transferring them from a pick-up station to a mounting
station for accurately mounting on a printed circuit board.
Numerous electrical contact designs have been proposed for
mounting on printed circuit boards. Many of these are for pins
or posts that are formed by stamping flat sheet stock. In many
cases, the pins or posts are initially connected to each other
by a carrier strip to allow automated mounting on a printed
circuit board. The aforementioned pins or posts take on
different shapes, including relatively flat shapes as shown in
U.S. Patent No. 5,073,132. Thin flat posts are shown in U.S.
Patent No. 3,864,014. Box-type male connectors are illustrated
in U.S. Patent No. 3,375,486. Relatively large cross-section
pins are also disclosed in U.S. Patent Nos. 4,017,142 and
3,428,934.
In U.S. Patent Nos. 4,395,087 and 3,663,931, substantially
square, solid pins are utilized for the electrical contacts.
In the '087 patent, the pins are mounted on a carrier strip
while in the '931 patent a unitary pin is shown formed
integrally with a socket contact, presumably formed out of
stamped material. In U.S. Patent No. 4,369,572, a
substantially solid rectangular pin is shown welded to the
carrier strip. However, none of the known designs disclose pin
connectors formed from flat sheet stock adapted or suitable for
surface mounting on a printed circuit board.
It is also known to provide single loose surface mount pin
terminals each packaged in individual plastic pockets carried
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by a plastic pocket carrier or tape. However, the
aforementioned ~pproach has a number of problems and has not
found wide acceptance in the industry. To begin with, the
additional plastic pockets or envelopes increase the per unit
costs of the surface mounted components. Additionally, because
the surface mounted pins are contained within a normally
oversized pocket or enclosure, the components have at least
some degree of freedom of movement therein and this has made
it difficult and impractical to precisely align the components
at the pick-up stations of the automatic pick-and-place
equipment with the vacuum nozzles used for this purpose,
notwithstanding the sprocket or pilot holes intended to
accurately align the pins. Such machinery demands very
accurate alignment of the parts during pick-up and even small
misalignments from the required positions may cause damage to
the parts and/or to the nozzles themselves.
In view of the foregoing, although significant
advancements have been made in the design and use of pick and
place equipment, such machinery has primarily been used to
pick and place components that have a sufficiently large flat
surface to provide a suction area for engagement by the
nozzles. As such, such machinery has primarily been used to
pick and place transistors, ICs, capacitors, and numerous other
electrical components that provide the requisite surfaces.
However, because electrical posts, test points, IDC's and other
electrical receptacles have not always exhibited the requisite
geometries suitable for pick and place equipment, it has not
always been possible to automate the mounting of such
components utilizing surface mount technology.
Until now, therefore, surface mount posts were packaged
in header form utilizing a plastic body to hold a row of
components and placed on the board by a pick-and-place robot.
If there was a need for test points, tabs, IDCs or any other
type of single terminal, the board and the manufacturing
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process had to be a combination of surface mount technology and
through-hole technology, because those terminals were only
available for through-hole technology.
On electrical packaging, quite often, traces on the
printed circuit board have to cross each other. This can be
easily done on a double sided PC board, by utilizing a via
(plated through hole) to connect traces from one side of the
board to the other side of the board. Using this method, the
need to cross two conductive traces on the top side of the
board is done by going underneath the board with one trace
through two vias. This practice is not possible with the
increasingly popular aluminum printed circuit boards or other
single sided boards. In those cases, the common industry
practice is to use zero ohm surface mount resistors or jumpers.
Those components must be taped to lend themselves to automatic
placement utilizing a vacuum component placement system.
The taping of surface mount components is a widely used
industry practice. The components are placed in little buckets
which are part of a continuous plastic tape and they are sealed
in place with a tape over it. The continuous tape winds on a
reel. The reel is placed on a tape feeder. Several tape feeders
are mounted on a vacuum component placement system. The feeders
will unwind, index, and peel off the top tape from the strip
to expose the component to the vacuum pick-up nozzle which in
turn picks up the component from the tape bucket and places it
on the proper location on the surface mount circuit board. The
above mentioned taping process is very expensive, quite often
costing more than the component.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to
provide surface mount electrical connectors that do not possess
the disadvantages inherent in prior art surface mount
connectors.
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.
It is another object of the present invention to provide
surface mount electrical connectors that are simple in
construction and economical to manufacture.
It is still another object of the present invention to
provide a surface mount electrical connector that can readily
be used with pick-and-place automated surface mount equipment.
It is yet another object of the present invention to
provide surface mount electrical connectors that can be
efficiently mounted on printed circuit boards while
substantially eliminating all waste due to damage to such
connectors.
It is a further object of the present invention to provide
surface mount electrical connectors of the type mentioned in
the previous objects that can be in the forms, for example, of
mounting posts, test points, IDCs, female receptacles and
jumpers.
It is still a further object of the present invention to
provide surface mount electrical connectors of the type
aforementioned that can be inexpensively produced by using
continuous stamping technology and without the need for
individual packages or tapes to carry the conductors.
The present invention provides a new family of surface
mount terminals that can readily and efficiently be utilized
with associated feeders for use with pick-and-place equipment
to eliminate the need for the combination surface
mount/through-hole technologies.
In accordance with the present invention, a surface mount
contact for surface mounting on a generally flat conductor
surface of a printed circuit board comprises a base defining
a plane and having a generally flat surface suitable for
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contact with and attachment to an associated flat conductive
surface of the printed circuit board. The contact has at least
one portion projecting from said base in a direction
substantially normal to said plane defined by said base. At
least one bent intermediate connecting portion integrally
connects said at least one portion to said base, said at least
one portion, base and at least one bent intermediate connecting
portion all being integrally formed of a generally flat sheet
of conductive material. Said at least one portion of the
contact may be in the form of an electrical pin, a test point,
an electrical female receptacle, an electrical insulation
displacement connector (IDC) or a conductive link or jumper.
In order to provide a positive engagement between a vacuum
nozzle of a surface mounting machine and the surface mount
contact to be place on the printed circuit board, the surface
mount contact comprises a first conductive portion arranged in
a plane and dimensioned to be positioned on a conductive pad
on which the contact is to be mounted. A second conductive
portion is integrally formed with said first conductive portion
and extends to one side of the plane, at least one of said
portions being provided with a generally flat pick-up surface
that can be engaged by the vacuum nozzle of the surface
mounting equipment for positive engagement of the contact by
the vacuum nozzle. Typically, connecting means are provided for
connecting said surface mount contacts in a continuous strip
of series-connected surface mount contact A. The connecting
means is severable to permit selective detachment of one
surface mount contact from said continuous strip by the surface
mounting equipment for surface mounting on the conductive pads
by engagement of said pick-up surface by the vacuum nozzle.
Such contacts are made in the form of surface mount jumpers or
other surface mount connectors.
When used with automated pick-and-place machinery, a strip
of series connected surface mounted contacts are provided with
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frangible connecting means between each two adjacent contacts.
In this manner, a strip of contacts can be advanced to an
automated mounting station and a contact at the downstream end
of the strip can be separated from the strip by severing said
frangible connecting means between said contact at the
downstream end and the adjacent immediately succeeding contact
in the strip. Preferably, the series connected surface mount
contacts are helically wound on a spool or bobbin so that the
strip can be unwound and advanced to an automated mounting
station.
The present invention also contemplates blanks for forming
a surface mounted contact and a plurality of series-connected
surface mounted contacts in accordance with the present
invention, as well as the method of forming such contacts.
This invention consists of a specially designed jumper to
eliminate the need for taping of the jumpers. The jumpers are
stamped in a continuous strip form. There is a small connecting
tab which connects the individual jumpers to each other to form
a continuous strip. This connecting tab is an integral part of
the jumper. Other contacts are disclosed that also provide flat
pick-up surfaces for positive engagement with a vacuum pick-up
nozzle and which can be produced from a continuous strip of
conductive sheet material and formed into coiled reels for
automated use on pick-and place machines.
The continuous strip is wound on a reel. The reel is
mounted on a special feeding system which shears off one single
jumper or other contact from the continuous strip and presents
it to the vacuum pick-up nozzle at the proper place and time.
That special feeding system is described in detail in U.S.
Patent Application, Serial Numbers 08/196,864.
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,.
BRIEF DESCRIPTION OF THE DRAWINGS
This and other objects and features of the present
invention will become clear from the following description
taken in conjunction with preferred embodiments thereof with
reference to accompanying drawings, in which:
Fig. 1 is a perspective view of a surface mounted
connector in the nature of a test point or male contact pin in
accordance with the present invention, shown in its individual
form after being severed from a strip of such connectors and
ready to be surface mounted on a printed circuit board;
Fig. 2 is a plan view of a blank for a plurality of
series-connected surface mounted connectors of the type shown
in Fig. 1, showing one connector in solid outline, while
downstream and upstream connectors in relation thereto are
shown in phantom outline;
Fig. 3 is a perspective view of another embodiment of a
surface mounted connector in accordance with the present
invention, also in the form of a contact pin, and schematically
illustrating a vacuum pick up nozzle positioned over the
connector at the downstream end of the strip for picking up the
connector after being severed from the strip;
Fig. 4 is a bottom perspective view of the connector shown
in Fig. 3, showing the details of the base construction as well
as the manner in which the connectors are joined to each other
by means of connecting tabs or carrier strips;
Fig. 5 is similar to Fig. 3, but showing a still further
embodiment of a surface mounted connector in accordance with
the present invention, in which adjacent connectors in the
strip are joined to each other at a portion of the contact pins
instead of at the bases;
Fig. 6 is yet a further embodiment of a surface mounted
connector in accordance with the present invention, in which
adjacent connectors are joined to each other by a double set
of carrier strips and illustrating a construction for
stabilizing the contact pin;
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Fig. 7 is similar to Figs. 3 and 5, but illustrating a
surface mounted connector in accordance with the present
invention in the form of an insulation displacement connector
(IDC);
Fig. 7A is similar to Fig. 7, but showing a configuration
of an IDC and supporting base to permit passage of a vacuum
nozzle through an opening in the IDC connector to positively
engage a flat pick-up surface on the surface mount base;
Fig. 8 is similar to Fig. 7, but illustrating a female
receptacle for surface mounting in accordance with the present
invention;
Fig. 9 is a bottom perspective view of the connector shown
in Fig. 8 to illustrate details of the base and the manner in
which adjacent connectors are joined to each other;
Fig. 10 is similar to Fig. 3, but showing a variant form
of the connector which includes a downwardly extending post;
Fig. 11 is a bottom perspective view of the connectors
shown in Fig. 10;
Fig. 12 is an exploded perspective view showing a surface
mounted connector of the type shown in Figs. 10 and 11 just
prior to mounting on a printed circuit board which includes a
through opening for the post of the connector;
Fig. 13 is a perspective view of a rolled strip of
connectors of the type illustrated in Fig. 1, illustrating the
orientations of the connectors helically wound on a reel and
an interleaf or spacer member for separating adjacent layers
of the helical winding;
Fig. 14 is an enlarged perspective view of a section of
the spacer member used in the rolled strip shown in Fig. 13;
Fig. 15 is a front elevational view of a further
embodiment of a surface mounted connector in accordance with
the present invention in the nature of a fuse holder;
Fig. 15A is a top plan view of a pair of fuse holders of
the type shown in Fig. 15, illustrating how the connectors are
joined to each other in a strip and illustrating holes formed
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in the bases of the connectors to enhance capillary action
during soldering on a printed circuit board;
Fig. 15B is a perspective view of the fuse holder shown
in Fig. 15, showing the manner in which a vacuum nozzle can
pass between appropriately spaced fuse holder clips to
positively engage a flat pick-up surface on the surface mount
base;
Fig. 16 is a perspective view of a continuous strip of
series-connected jumpers in accordance with the invention shown
wound on a dispensing reel;
Fig. 17. is a perspective view of one of the jumpers,
after being separated from the strip shown in Fig. 16,
positively engaged by a vacuum nozzle just prior to being
placed on a printed circuit board; and
Fig. 18 is a perspective view of a spool of surface
mounted pins in accordance with the prior art wherein
individual pins are contained within pocket carriers serially
mounted on a tape helically wound on a reel.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to Figure 18, this shows a known method
of packaging single loose surface mount pin terminals. Each
terminal is separately packaged in individual pockets carried
in plastic pockets P carried by a plastic pocket carrier or
tape T. Since the pockets are normally oversized, the separate
components each have some degree of movement therein,
notwithstanding the sprocket or pilot holes H intended to
accurately align the pins. In pockets of this type it is
difficult and impractical to precisely align the components at
the pick-up stations of the automatic pick-and-place equipment
with the vacuum nozzles used.
Referring now to the Figures 1 through 17, in which
identical or similar parts are designated by the same reference
numerals throughout, and first referring to Fig. 1, an
electrical connector or contact suitable for mounting on the
21 70436
surface of a printed circuit board (PCB) is generally
designated by the reference numeral 10.
The connector 10 includes a base 12 which defines a plane
and has a generally flat surface suitable for contact with and
attachment to a flat conductive surface of a printed circuit
board frequently referred to as a "land" or "pad". An
electrical contact pin 14 has at least one portion projecting
from the base 12 in a direction substantially normal to the
plane defined by the base. At least one bent intermediate
connecting portion integrally connects the contact 14 to the
base 12. In the construction shown in Fig. 1, two intermediate
bent connecting portions 16a and 16b respectively connect the
first contact portion 14a to a first base portion 12a and a
second contact portion 14b to a second base portion 12b.
The uppermost ends of the first and second contact
portions 14a, 14b, which are juxtaposed to each other as
indicated, are joined to each other by an integral bent
bridging portion 14c. The juxtaposition of the contact
portions 14a, 14b as shown creates a narrow gap or space 14d
which permits the surface mounted pin design to take advantage
of capillary action during solder reflow. At least one of the
two thin strips of 14a, 14b are plated and when the base 12 of
the pin terminal is exposed to melted solder paste, the
capillary attraction makes the liquid solder rise up inside the
gap 14d to solder the two halves 14a, 14d together forming a
solid pin that can be used either as a contact pin or test
point. The designs of other surface mounted connectors in
accordance with the invention that promote capillary action and
the advantages thereof will be discussed below.
An important feature of the present invention is that the
electrical contact, such as the contact pin 14 in Fig. 1,
including the base 12 and the intermediate connecting portions
16a, 16b, is formed of a generally flat sheet of conductive
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material, as will now be discussed in connection with Fig. 2.
Such construction allows for the economical manufacture of the
surface mount electrical connectors and, equally importantly,
it allows the connectors to be produced in elongate strips, as
will be discussed hereafter, which facilitates the accurate
positioning of the electrical connectors in pick-and-place
equipment and to make such connectors viable and practical to
use with such equipment.
Referring to Fig. 2, a blank 19 is illustrated from which
the connector 10 of Fig. 1 is made. The blank 19 is preferably
for a plurality of series connected surface mounted connectors,
as shown, which is formed as a stamping from an elongated strip
of a flat sheet of electrically conducted material which
includes like blank portions successively stamped along the
strip as shown. Only the center blank l9a is shown in solid
outline, a downstream immediately adjacent blank l9b and an
upstream adjacent blank l9c being illustrated in phantom
outline. All the blanks are similarly constructed and joined
to each other by a frangible connecting tab strip or carrier
18 which connect adjacent blanks to each other. Each blank
generally includes a base suitable for attachment to an
associated surface of a printed circuit board, a contact and
at least one intermediate connecting portion integrally
connecting the contact to the base, as aforementioned in
connection with Fig. 1. In connection with the specific blank
shown in Fig. 2, utilized to produce the contact pin 14 of Fig.
1, the first base portion 12a is shown to include a generally
U-shaped member having two parallel segments 12c on opposite
sides of the contact portion 14a, and each having inwardly
projecting protuberances 12d as shown. The two parallel
segments 12c are joined to a transverse segment 12e, which is
also joined, at its center, with the contact portion 14a by
means of the intermediate connecting portion 16a. The bridging
portion 14c is shown as a narrowed or necked down portion
between the first and second contact portions 14a, 14b. At the
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upper or free ends of the contact portions, as viewed in Fig.
2, the second base portion 12b is provided as an outwardly
tapered portion provided with opposing or lateral indentations
12f. As is clear from Fig. 1, the dimensions of the second
base portion 12b are selected so as to be received within and
substantially fill the area between the segments 12c when the
base portions 12a, 12b are all moved into a common plane of the
base 12.
Once the blanks have been formed, as shown in Fig. 2, the
surface mounted connector 10 is formed by deforming the blank
so as to impart an approximately 90 bend in the first
intermediate connecting portion 16a, thereby moving the first
base portion 12 into a plane substantially normal to the first
contact portion 14a. The second contact portion 14b is then
bent 180 in relation to the first contact portion 14a about
the bridging portion 14c so as to bring the contact portions
14a and 14b into juxtaposed position as shown in Fig. 1.
Finally, the second base portion 12b is moved into the plane
of the first base portion 12a by imparting a bend of 90 to the
second intermediate connecting portion 16b, and positioning the
protuberances 12d into the indentations of 12f as shown in Fig.
1. Other surface mounted connectors can be formed by the steps
of forming a blank as described or by slightly modified steps
as will be from the description that follows to those skilled
in the art to apply the present invention to numerous other
surface mounted connector designs.
It will be appreciated that the combination of
protuberances 12d and indentations 12f provide a locking
mechanism which prevents the first and second base portions
12a, 12b and first and second contact portion 14a, 14b from
separating, particularly prior to assembly or mounting on a
printed circuit board. The design maintains the integrity of
the contact pin or test point in its desired configuration
during processing in the pick and place equipment, including
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severing a connector from the strip, gripping the connector at
the pick up point, and placing the connector on a land on the
printed circuit board to which it is to be soldered.
Therefore, even though the connector is stamped from flexible
sheet material, which exhibits some resiliency or "memory," the
connector enjoys the advantages of a solid pin. Of course,
after the connector 10 has been soldered to a printed circuit
board, the contact portions 14a, 14b effectively become a solid
pin by virtue of the capillary action of the solder which flows
into and fills the gap or space 14d.
The flat base 12 of the embodiments of Figs. 1 and 2 is
preferably square in configuration, to conform to lands or pads
on printed circuit boards which frequently are also square.
However, this is not a critical feature of the present
invention and it should be clear that the area defined by the
flat base 12 can be any desired or selected area by selecting
by appropriate dimensions for the various base portions which
have been described. Also, with the base configuration shown
in Figs. 1 and 2, it will be appreciated that with exception
of the central area, the flat base 12 presents a substantially
solid surface for providing significant contact and adhesion
to a land or pad on the printed circuit board. However, there
are provided at least some open regions S in the center of the
base. As suggested above, the solder will, by capillary
action, rise into the open spaces "S" and into the pin 14 and,
therefore, also provide adhesion to the printed circuit board
in that central region. Preferably, in all the designs
utilizing the present invention, the bases of the connectors
exhibit substantial solid metal surfaces provided with openings
or apertures S that are relatively small to take full advantage
or benefit from capillary action, so that the connectors can
be drawn to and attached to the printed circuit board when the
solder reflows into the spaces S. This generally occurs with
minimum float or lateral shifting because the rising of the
reflowing solder draws the base towards the surface of the PCB
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with an effect not unlike a suction-cup effect. This is
important because the pick-and-place equipment provides the
greatest precision in the surface mounting process and the
undesired shifting of components during reflow of the solder
may misalign a component after accurately placed by the
machine. The flow of solder into spaces S of the bases or into
the space or gap 14d of the contact pin 14 (Fig. 1), which
effectively "absorb excess solder, to draw the bases to the PCB
surfaces, has the additional advantage of rendering tolerances
of the base and PCB land or pad dimensions less critical.
The spaces S (or gap 14d) should have dimensions that will
provide capillary action, as aforementioned. Such dimensions
will depend on numerous factors, including the nature of the
solder paste, how clean and large the board and/or the contact
surface area is, how level the board is, etc. Numerous
technical papers have been written about the properties of
solder that deal with the related topics of surface tension,
wetting angles and capillary action. See, for example,
"University Physics," Sears and Zemansky, 2nd Edition, Addison-
Wesley Publishing Company, Inc., 1957, pages 231-235; "Testing
SMDs for Solderability," B. M. Allen, "Surface Mount
Technology" October 1988, pps 17-18; "The Assessment of the
Solderability of Surface Mounted Devices Using the Wetting
Balance", Yoshida et al, International Tin Research Institute
Report. Those skilled in the art can, knowing all the relevant
factors, determine what those dimensions should be. The number
of spaces S, their dimensions, and/or their arrangement is not
critical as long as they provide the desired capillary action.
Referring to Figs. 3 and 4, another embodiment in
accordance with the invention is shown in the form of a contact
pin 20. The contact pin 20 includes an upper contact member
20a which is advantageously provided with a bevelled upper or
free end 20b to facilitate insertion into a female contact
receptacle. The base 22, as with the embodiment shown in Figs.
14
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1 and 2, is generally U-shaped and includes parallel spaced
portions 22a, 22b, transverse portion 22c and solder absorbing
space S as shown. The upper contact member 2Oa, in the region
of the base 22, flares out or widens to the width of the base
22 as shown and defines a plurality of depending portions which
are substantially co-planer with the central contact member
20a. In Figs. 3 and 4, the enlarged shoulder 20c includes
first and second side depending portions 20d, 20e and a center
depending portion 20f. A separate bent intermediate connecting
portion connects each of the depending portions with an
associated base portion. Thus, the first side depending
portion 20d is connected to the base portion 22a by connecting
portion 24a, which includes first and second bent portions 24c,
24d. Similarly, connecting portion 24b connects the side
depending portion 20e to the base portion 22b. In order to
maximize the area or contact surface of the base with the
printed circuit board and provide a solder-receiving space S,
the center base portion 22d, which is an extension of the
center depending portion 20f, joined at the bent portion 24e.
Bent portions 24c and 24e are bent 90, while bent portions 24d
are bent 180 as shown. As with the contact pin 14, the bases
are joined to each other by means of connecting or carrier tabs
18 which are selectively severed when the connector at the
downstream end of the strip is about to be picked up by the
mounting equipment, as suggested by the vacuum pick up nozzle
N in Fig. 3.
In Fig. 5, a pin generally similar to that shown in Figs.
3 and 4 is illustrated, except that only two base portions are
provided. Thus, the enlarged shoulder portion 20c is
configured as shown in order to provide a first depending
portion 20g and second depending portion 20h. While the
connecting portions 24a are both arranged on the same side of
the contact pin 20 in Fig 3, the connecting portions 24a are
arranged on opposite sides of the contact pin 20a in Fig. 5.
Thus, only two base portions 22e and 22f are provided, each
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respectively joined to one of the two depending portions and
joined thereto by means of bent portions 24d and 24e which are
respectively bent 180 and 90 as with the connecting portions
in Fig. 3.
With the embodiment shown in Fig. 5, the total width of
the two depending portions 20g and 20h are less than the width
of the enlarged shoulder portion 20c to provide lateral
connecting tabs or carrier strips 18', so that adjacent
connectors are severed by severing them at the shoulder
portions instead of at the bases as is the case with the
embodiments shown in Figs. 1-4. It should be clear, therefore,
that the specific locations of the connecting tabs or carrier
strips is not critical for purposes of the present invention,
and the specific locations of the carrier strips or connecting
tabs will least to some extent be a function of the pick and
place equipment and, in particular, the design of the feeder
used to feed the connectors to the pick and place equipment.
In Fig. 6, a still further contact pin design is
illustrated which is similar in certain respects to the pins
shown in Figs. 3-5. However, in Fig. 6, the base 26 is formed
of a solid portion of the strip and defines a pair of opposing
sides (at the bent portions 28a, 28b). The contact pin 20 is
positioned generally centrally of the rectangular area defined
by the base 26. One bent intermediate connecting portion 26a
extends from one side of the base 26, as shown, to the contact
pin 20 and another intermediate connecting portion 26b extends
from the other side of the base to a point proximate to the
contact pin 20. A tab or collar 30 is provided which is
crimped about the contact pin 20 as shown. In this manner, the
intermediate connecting portions 26a, 26b stabilize the
position of the contact pin 20. Also in Fig. 6, the bases 26
are shown to include a pair of spaced connecting tabs or
carrier strips 18a, 18b, although, clearly, one or more such
carrier strips can be provided depending on the equipment to
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be used and the manner in which the tabs are to be fed to the
pick and place equipment. Shown in phantom are optional holes
S in the base 26 to absorb solder during reflow, for reasons
discussed above.
The present invention is not limited to generally elongate
contact pins, posts or test points of the type described in
Figs. 1-6. Fig. 7 illustrates an embodiment of the invention
in which the contact is in the form of an insulation
displacement connector (IDC) 32 connected to the solid base 26
by means of intermediate bent connecting portion 32a. The
construction of the IDC portion 32 is well known to those
skilled in the art. Similarly, in Fig. 8, another type of
surface mounted connector is illustrated in the form of a
female tab receptacle 36 which includes first and second
resilient prongs 36a, 36b spaced from each other as shown to
provide a flat tab receiving space 36c. The prongs 36a and 36b
are joined to the base 34, as best shown in Fig. 9. The base
34 is I-shaped and includes transverse base portions 34a, 34b
and a center base portion 34c. Each of the prongs 36a, 36b are
joined to the center base portion 34c, each of the transverse
base portions 34a, 34b carrying two connecting tabs or carrier
strips 18a, 18b, as shown.
Referring to Figs. 10-12, a variant of the surface mounted
connector in the form of a contact pin is illustrated which is
similar in construction to the pin connector shown in Fig. 3.
However, instead of the center depending portion 20f being bent
as shown in Fig. 3 to provide a center base portion 22d, the
center dependent portion 20f extends straight downwardly co-
extensively with the contact pin 20 to form a downwardly
extending post 20f' which can be received within a through
opening 38 formed in a conductive land or pad of a printed
circuit board 42, as shown in Fig. 12. The post or anchor pin
protrudes downwardly from the flat mounting base. The solder
pads 40 of the PCB must have a hole in the center 38 as shown.
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When the terminal or connector is placed on the side of the
paste covered solder pad the anchor post 20f' enters into the
hole or opening 38 and limits the terminal from floating while
the solder is reflowed. In most cases, undesired floating is
almost totally eliminated as a result of the absorption of
solder into spaces S by capillary action as described above.
In Fig. 13, a rolled strip of series-connected surface
mounted connectors for automated mounting on a surface of a
printed circuit board is illustrated and generally designated
by the reference numeral 44. The spool or reel 44 includes a
rotatable support member 45 which has an axis of rotation 46.
As shown, the surface mounted connectors 48 are oriented so
that the directions of the contacts 49 are substantially
parallel to the axis of rotation 46 while the bases of the
individual connectors are substantially arranged in a common
or in parallel planes. The frangible connecting means in the
form of connecting tabs or carrier strips are sufficiently
flexible without breaking to allow the connectors 48 to be
arranged along circular arcs when helically wound about the
support member 45.
Since the radial dimensions of the elongate contact pins
(when wound on the spool or reel 44) are generally less than
those of the bases of such connectors, it is preferred that a
suitable spacer element be provided which is interleafed with
the continuous helically wound strip of connectors for
maintaining the electrical contacts in the desired parallel
orientations as shown. Referring to Fig. 14, there is shown
one form of spacer that can be used for maintaining the
contacts 49 in adjacent layers spaced from each other at a
distance to define a spiral connector-receiving space which has
a radial dimension substantially equal to the radial dimension
of the bases of the connectors. A suitably dimensioned spiral
connector receiving space minimizes contact interference
between the bases in adjacent layers. The illustrated spacer
21 70436
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includes a continuous flat strip of flexible material 50a, and
an undulating wave-like or corrugated strip of material 50b
which is attached to the flat strip of material 5Oa as shown.
The wave-like strip of material 50b has a peak-to-peak distance
50c along the length of the flat strip 50a which substantially
corresponds to the distance between successive contacts 48 on
the strip, and a peak-to-peak height 50d along a radial
direction normal to the longitudinal direction of the flat
strip which is substantially equal to the difference between
the radial dimension of the bases and the dimension of the
contacts 49 in the radial direction when helically wound on the
rotatable support member 45. The spacer 50 normally secures
the contacts on the reel. By unwinding the spacer during use,
a section of the continuous strip can be unwound and fed to a
pick and place machine. A spool or reel of the type shown in
Fig. 13 can be mounted on a feeder of the type shown and
described in U. S. Patent application Serial Numbers
08/196,864. The specific construction of the spacer 50 is not
critical and, in theory, the continuous strip of surface
mounted connectors can be helically wound without the use of
a spacer or simply separated by a continuous strip of flat
sheet material. However, the use of the spacer maintains the
desired orientations of the connectors 48 and prevents the
connecting tabs or carrier strips from becoming damaged or
severed.
In Figs. 15 and 15A a further embodiment is illustrated
which incorporates the invention and is in the form of a fuse
holder 60. The fuse holder 60 has a base 62 similar to the
base shown in Figs. 8 and 9. Spring clips 60a, 60b extend
normally from the base and integrally joined thereto at bent
portions 64a, 64b as shown. As with the other surface
connectors, the bases are preferably provided with apertures
or opening S for receiving solder by capillary action. Some
solder will also enter the spaces S' in the regions of the bent
portions 64a, 64b.
19
21 70436
While a number of the aforementioned surface mount
contacts are dimensioned and configurated to require a
generally large Nozzle (e.g. see Figs. 7 and 8) in order to
receive the upwardly projecting or contact portions which
project from the bases on which the contacts are mounted on the
printed circuit board, a class of surface mount contacts can
take advantage of generally smaller nozzle sizes and provide
a more positive pick-up by providing a generally flat pick-up
surface on the contact that can be engaged by the vacuum nozzle
of the surface mount equipment. In its broadest aspects, such
surface mount contacts comprise a first conductive portion
arranged in a plane and dimensioned to be positioned on a
conductive pad on which the contact is to be mounted. A second
conductive portion is integrally formed with said first
conductive portion and extends to one side of the plane, at
least one of said portions being provided with a generally flat
pick-up surface that can be engaged by the vacuum nozzle on a
surface mounting equipment. One example of such contact is a
surface mount jumper. Referring to Figs. 16 and 17 a continuous
strip of series-connected jumpers of this type is generally
indicated by the reference numeral 100. The jumpers are wound
in a coil on a reel 102 for automated feeding to surface mount
equipment. Each individual jumper is designated by the
reference numeral 104 which includes spaced leg portions 106
dimentioned to correspond to the dimensions of two spaced
conductive pads 118 on a printed circuit board 116 on which the
jumper is to be mounted. A second conductive portion 108 is in
a form of a conductive linking portion generally offset from
the plane of the leg portion 106 and arranged in a plane
generally parallel to the plane of the leg portions 106 as
shown and extending between the leg portions. The conductive
linking portion 108 provides a generally flat pick-up surface,
as illustrated in Fig. 17.
Preferably, the individual jumpers 104 are arranged in a
continuous strip of series-connected surface mount jumpers, as
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illustrated, by means of suitable connecting means. In the
embodiment illustrated, the connecting means are in the form
of two spaced connecting tabs 114 which extend between adjacent
jumpers. The tabs 114 are severable to permit selective
detachment of one jumper from the continuous strip by the
surface mounting equipment so that one of the jumpers can be
mounted on the printed circuit board by its engagement by a
pick up vacuum nozzle N. The stubs 114' are illustrated on the
jumper following its severance from the rest of the strip by
a suitable feeder of such continuous strip of electrical
contacts or connectors to pick and place or surface mount
equipment, as disclosed in U.S. Patent Application Serial
Numbers 08/196,864.
While the illustrated jumpers 104 include two leg portions
for being mounted on two spaced conductive pads 118, as shown
in Fig. 17, it should be clear that jumpers with more than two
legs are possible, in which case the legs would be arranged in
a selected configuration within a plane to be set on a
corresponding number of pads or lands on the printed circuit
board, and the conductive linking portion would assume a
suitable configuration to extend between and bridge the various
leg portions to provide a common electrical contact
therebetween.
The method of forming the continuous strip of jumpers 104
includes the steps of advancing a continuous strip of
conductive sheet material. A plurality of transverse slits 110,
112 arranged in successive lines generally transverse to the
advancing direction are formed as shown. The transverse slits
110, 112 are arranged to define the spaced leg portions 106 and
the conductive linking portion 108 extending between the leg
portions to generally arrange the leg portions in a common
plane and the linking portions 108 in a plane offset from and
generally parallel to said common plane.
21
2 1 70436
Referring to Fig. 7A, a surface mount contact in the form
of a surface mount IDC 120 is illustrated, wherein a first
conductive portion comprises a generally flat base 122
dimensioned to correspond to a conductive pad on which the IDC
connector is to be mounted. The IDC portion 124 of the contact
is integrally formed with the base 122 at 126, and includes two
IDC contact portions 130, 132 as shown which are spaced from
each other to provide a conductor receiving opening 134. The
upper surface of the base 122 provides a generally flat pick-up
surface, the central opening 134 being dimensioned to permit
the vacuum nozzle N to pass through it to engage the generally
flat base portion 122.
A surface mount fuse clip 136 is illustrated in Fig. 15B
which likewise includes a generally flat base 138 dimensioned
to correspond to a conductive pad on which the clip contact is
to be mounted and which provides a generally flat pick-up
surface. Tabs 140 on the base represent the severed connecting
strips between adjacent contacts when first formed as a
continuous strip and fed to the surface mount equipment. The
two clip contacts 142, 144 are sufficiently spaced from each
other to provide access to the vacuum nozzle N to the base to
permit engagement with the generally flat base portion 138.
Therefore it is clear that a whole class of surface mount
contacts exist which can use relatively small pick-up nozzles,
because the pick-up nozzles contacts or abuts against a flat
pick-up surface, which enhances the vacuum suction. Not only
are such smaller pick-up nozzles more conventional but they are
more effective when contacting a small flat surface.
Although the present invention has fully been described
in connection with the preferred embodiments thereof with
reference to the accompanying drawings, it is to be noted that
various changes and modifications are apparent to those skilled
in the art. Such changes and modifications are to be
2 1 70436
understood as included within the scope of the present
invention as defined in the claims that follow.
