U.S. patent number RE35,549 [Application Number 08/135,461] was granted by the patent office on 1997-07-01 for solderable lead.
This patent grant is currently assigned to North American Specialties Corporation. Invention is credited to Jack Seidler.
United States Patent |
RE35,549 |
Seidler |
July 1, 1997 |
Solderable lead
Abstract
A solderable lead is fashioned with a C-shaped contact portion
along its length. The interior of the C-portion is dimensioned to
receive and resiliently contact a substrate at a predetermined
contact pad. A layer of solder is provided on the exterior of the
C-shaped contact portion and extends around its edge. During
heating, the solder migrates to the interior of the C-portion by
capillary action to the area between the contact pad of the
substrate and the interior of the C-portion. While the solder is
liquid, the C-portion maintains engagement with the substrate.
Inventors: |
Seidler; Jack (Flushing,
NY) |
Assignee: |
North American Specialties
Corporation (Flushing, NY)
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Family
ID: |
24652817 |
Appl.
No.: |
08/135,461 |
Filed: |
October 12, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
661252 |
Feb 26, 1991 |
05090926 |
Feb 25, 1992 |
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Current U.S.
Class: |
439/876;
29/843 |
Current CPC
Class: |
H01R
12/57 (20130101); H05K 3/3405 (20130101); H01R
4/02 (20130101); H01R 43/02 (20130101); H05K
3/341 (20130101); H05K 3/3457 (20130101); H05K
3/403 (20130101); H05K 2201/10386 (20130101); H05K
2201/10984 (20130101); Y10T 29/49149 (20150115) |
Current International
Class: |
H05K
3/34 (20060101); H01R 4/02 (20060101); H05K
3/40 (20060101); H01R 004/02 () |
Field of
Search: |
;439/83,876 ;29/843
;228/6.2,56.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"High Purity Precision Alloys", Semi-Alloys Corp, Tech. Bull.
CM-64, 4 pp, 1968..
|
Primary Examiner: Abrams; Neil
Attorney, Agent or Firm: Darby & Darby
Claims
What is claimed is:
1. A solderable lead for connection to a device having a conductive
area, comprising:
a substantially flat elongated body, said body having a curved
contact portion having an interior and an exterior, said interior
being adapted to receive said device and to resiliently contact
said conductive area of said device; and
a layer of solder overlying said curved portion exterior and having
a portion extending around the edge thereof and immediately
adjacent said curved portion interior, but without having solder in
said interior of the curved portion, whereby upon heating, said
layer of solder will liquefy and migrate to form a soldered joint
between said interior and said conductive area.
2. A solderable lead according to claim 1, wherein said curved
contact portion is a C-shaped clip portion having top, rear and
bottom walls.
3. A solderable lead according to claim 2, wherein said portion of
said solder layer covers an edge of one of said top and bottom
walls.
4. A solderable lead according to claim 3, wherein portion of said
clip portion under said solder layer is curved toward said curved
portion interior.
5. A solderable lead according to claim 3, wherein said C-shaped
portion has a burr at the edge thereof, said solder layer extending
over the edge of said burr.
6. An assemblage of leads, each as in claim 1, each lead being
integral with a carrier strip and said leads being uniformly spaced
along said carrier strip.
7. The method of producing a lead soldered to a conductive pad of a
substrate comprising the steps of:
providing a lead as in claim 1;
resiliently maintaining said curved portion interior in contact
with said substrate conductive area;
heating said lead to melt said solder layer and cause said solder
to flow around the edge of said lead into the region between said
curved portion interior and said conductive area;
whereby on cooling, said conductive pad is soldered to said curved
portion interior. .Iadd.
8. A solderable lead for connection to a device having a conductive
area, comprising:
a substantially flat elongated conductive body having a body
portion intended for soldering to said conductive area, said body
portion having a first surface facing said conductive area and a
second surface opposite said first surface;
a plating-like substantially uniform thickness layer of solder
formed from a band of solder overlying said body portion on said
second surface, said solder layer having a portion extending around
the edge of said body portion and covering substantially the entire
thickness of said edge, to be immediately adjacent said first
surface, but not covering said first surface;
whereby upon heating said body in juxtaposition to said conductive
area said solder will liquify and migrate to form a soldered joint
between said body portion and said conductive area.
.Iaddend..Iadd.9. A solderable lead according to claim 8, wherein a
portion of said body portion under said
solder layer is curved toward said first surface.
.Iaddend..Iadd.10. A solderable lead according to claim 8, wherein
said body portion has a burr at the edge thereof, said solder layer
extending over the edge of said burr. .Iaddend..Iadd.11. An
assemblage of leads, each as in claim 8, each lead being integral
with a carrier strip at one end of each lead and said leads being
uniformly spaced along said carrier strip. .Iaddend..Iadd.12. A
method of producing a lead soldered to a conductive area of a
substrate comprising the steps of:
providing a lead having an elongated body with a body portion
intended for soldering to said conductive area, said body portion
having a first surface for facing said conductive area and a second
surface opposite said first surface, with a plating-like layer of
solder of substantially uniform thickness overlying said body
portion on said second surface and extending around the edges of
said body portion but short of said first surface;
maintaining said first surface in contact with said substrate
conductive area,
heating said lead to melt said solder layer and cause said solder
to flow around the edge of said lead adjacent the region between
said first surface and said conductive area;
whereby on cooling, said conductive area is soldered to said one
surface. .Iaddend..Iadd.13. A solderable lead for connection to a
device having a conductive area, comprising:
an elongated body, said body having a substantially flat contact
portion having a first surface and a second surface, said first
surface being adapted to contact said conductive area of said
device; and
a plating-like substantially uniform thickness layer of solder
overlying said second surface and having a portion extending around
the edge thereof and immediately adjacent said first surface, said
solder layer overlying substantially the entire thickness of said
edge, but without having solder on said first surface, whereby upon
heating, said layer of solder will liquefy and migrate to form a
solder joint between said first surface and said conductive area.
.Iaddend..Iadd.14. A method of producing solderable leads soldered
to conductive areas of a substrate, comprising the steps of:
providing a substantially flat sheet of conductive material having
a band of solder thereon,
stamping from said sheet a series of leads, each lead having an
elongated body with a body portion intended for soldering to said
conductive area, said body portion having a first surface for
facing said conductive area and a second surface opposite said
first surface, with a layer of solder overlying said body portion
on said second surface,
said stamping including causing solder from said band to extend
around the edge of the body portion of each lead.
.Iaddend..Iadd.15. A method as in claim 14, wherein said step of
stamping further comprises forming a carrier section of said sheet
joined to each lead at one end thereof. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to solderable terminals and leads,
particularly solder clips intended for connection to contact pads
on edges of substrates.
Several leads exist in the market in the form of a clip adapted
resiliently to engage the edges of a substrate, while a mass of
solder is held on the clip adjacent the position of a conductive
area or pad on the substrate. Upon heating the substrate/terminal
assembly, the solder mass melts and is drawn, usually by capillary
action, to the area of contact between the terminal and the
substrate conductive area. Examples of such solderable clips are
shown in U.S. Pat Nos. 4,120,558; 4,019,803; 4,203,648; 4,357,069;
4,367,910; 4,592,617; 4,605,278; 4,697,865; 4,728,305; and
4,780,098. Unfortunately, these terminals generally involve complex
structures, such as curved fingers or tabs, for forming the lead
and holding the solder mass in place until the assembly is heated,
requiring specialized tooling and production techniques.
A device disclosed in U.S. Pat. No. 4,900,279 to Dennis partially
solves this problem. This devices uses a basically C-shaped clip
that is coated on the interior of the C with solder. The substrate
is inserted into the interior of the C, bringing the contact pads
of the substrate in contact with the solder, which is then melted,
forming when re-solidified a mechanical and electrical connection
between the clip and the substrate. Unfortunately, when the solder
melts, the significant layer of liquid solder between the clip and
the substrate create an unstable hold on the substrate. The
substrate tends to float or slide around in relation to the clip
during this period. This can potentially lead to a solder
connection of the clip to an area partially or completely off of
its desired contact pad, which may cause a short-circuit to an
adjacent, closely spaced contact pad.
SUMMARY OF THE INVENTION
Thus, it is an object of the invention to provide an improved
simple solderable terminal having an easily applied and relatively
nearby source of solder, while providing a firm grasp on a
corresponding substrate throughout the soldering process.
It is a further object of the invention that the solder terminal be
easily and simply fabricated with a minimum of manufacturing
steps.
In accordance with the invention, a solderable lead is fashioned
with a C-shaped contact element formed along its length. The
interior of the C-element is dimensioned to receive and resiliently
engage a substrate at a predetermined contact point such as a
contact pad on the substrate. A layer of solder is provided on the
exterior side of the C-element. During heating, the solder migrates
to the interior of the C-element by capillary action to the area
between the contact pad of the substrate and the C-element. Thus,
while the solder is liquid, the resilient C-element holds the lead
engaged with the substrate. To aid in the migration of the solder,
the side edges of the layer of solder are curved toward the
interior of the C-element by simple expedients during
manufacture.
The foregoing and other objects and advantages of this invention
will become apparent to those skilled in the art upon reading the
detailed description of a preferred embodiment in conjunction with
a review of the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of a fragment of a conductive strip shoWing
two solderable leads according to the invention connected to a
carrier strip.
FIG. 2 is a side view of a solderable lead according to the
invention, taken along the line 2--2 of FIG. 1.
FIG. 3 is a rear view of a fragment of a conductive strip during
manufacture of solderable leads according to the invention.
FIG. 4 is a cross-section of the contact portion of the solderable
lead, mounted on a substrate, viewed along line 4--4 of FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 and 2 show a preferred embodiment of the invention in the
form of a series of leads 10 each having a C-clip 12 for receiving
and grasping a substrate 50 (such as a printed circuit board,
integrated circuit, chip carrier or the like). The leads 10 are
formed from a continuous strip 11 of semi-resilient conductive
material through a series of steps, such as by progressive
stamping, including punching and bending.
FIG. 3 shows a fragmentary portion of the strip 11 from which the
leads 10 are formed. The semi-resilient conductive material (such
as beryllium copper) has two bands of solder 28 secured thereto,
such as by cold welding the solder bands 28 to the conductive strip
11. Other methods of applying the solder bands 28 to the strip 11
may of course by used.
The strip 11 is punched at lines 15 to form the individual lead
bodies 17. Indexing holes 16 are also punched along the edge of
strip 11 to form a carrier strip 14.
During manufacture, the leads 10 remain connected to the carrier
strip 14. The indexing holes 16 are used to move the leads 10
through a manufacturing apparatus such as a progressive stamping
machine, and to maintain the precise inter-lead spacing necessary
for the leads 10 to mate with respective similarly spaced contact
pads 18 on the substrate 50. Extending from the carrier strip 14
for each lead 10 is an elongated body portion 20 for eventual
connection of the lead 10 to other electronic components.
Adjacent the end of the body portion 20 remote from the carrier 14
is the C-clip 12. The C-clip 12 is formed of four generally right
angle bends, the two outer bends being convex with respect to the
front of the lead 10, while the two inner bends are concave. The
bends may be formed at the lines marked "a", "b", "c", and "d" on
FIG. 3. The lengths of the top and bottom walls 22,24 of the C-clip
12, as well as the length of the rear wall 26 are determined by the
thickness of the substrate 50 on which the clip 12 is to be mounted
and the positioning of the contact points 18 thereon.
As pointed out above, preferably before the leads 10 are punched
from the sheet 11 of stock material, the bands of solder 28 are
deposited on the back side of the leads 10 in the area that is to
be bent into the C-clip 12. Alternatively, the solder bands 28 may
be formed in a single band, adapted to cover not only the top and
bottom walls 22,24 of the C-clip 12, but also its rear wall 26.
Where connection is desired to only one contact pad 18 on one side
of substrate 50, a corresponding one of the solder bands 28 may be
omitted. The solder bands 28 are thick enough to provide a
sufficient amount of solder to positively connect the C-clip 12 to
the contact pad 18 of the substrate 50 after heating.
According to a feature of the invention, the flow of solder to the
contact pad is facilitated by specially forming the solder band or
bands 28 on the individual lead 10. Thus, when the lead 10 is
punched from the sheet 11, a portion of solder 30 is caused to
extend laterally beyond the width of the body 20 and is curved
toward the interior of the C-clip 12, to cover not only the
exterior face of the C, but also the edges on either side. This may
be done by causing the punch/die combination that forms the leads
10 as shown in FIG. 3 to have a slightly larger than normal
tolerance, which creates a burr 30 at the edges of the lead 10. In
so doing, the malleable solder curves around the lead 10 to cover
the sides of the lead 10 as shown at 30 in FIG. 4. Depending on the
actual tolerance of the punch/die combination, some of the sheet
material 11 may also be bent in a burr 32 toward the interior of
the C-clip 12. As can be seen in FIG. 4, this may cause the main
area of the C-clip 12 to be held slightly away from the surface of
the contact pad 18 of the substrate 50 to form a very narrow gap
34.
In assembly, a comb-like section of the carrier strip 14 with a
desired number of leads 10 (for example, 10 to 50 in various
applications) is engaged over the edge of a substrate 50. The leads
10 are spaced in correspondence with the spacing of the contact
pads 18 on the substrate 50, which may be on either side or both
sides of the substrate 50. Each C-clip 12 then resiliently engages
a corresponding substrate contact pad 18, and the leads 10 are
thereby held in proper position with respect to the substrate 50
for further operations.
After the substrate is engaged with the C-clip 12, as shown in FIG.
4, the clip/substrate assembly is moved through a heater, which
melts the solder layer 28. The liquid solder will migrate by
capillary action into the intervening gap 34 between the C-clip 12
and the contact point 18. The gap 34 caused by a burr 32 on the
lead edges improves the capillary action causing the solder to flow
between the C-clip 12, and contact point 18 to improve the soldered
bond. However, even without any significant burr 32, the solder
will still sufficiently migrate into the space between the C-clip
12 and the contact pad 18 because of inevitable irregularities
between the C-clip 12 and the contact pad 18 when they are
engaged.
While the solder migrates, the top and bottom walls 22,24 of the
C-clip 12 or the burrs 32 will remain in contact with the contact
point 18, retaining the clip in engagement with the substrate 50.
On cooling, the solder will re-solidify, forming a solid solder
joint between the C-clip 12 and the substrate 50. In this way,
difficulties of relative movement of clip and substrate, which may
be caused in the arrangement shown in the prior Dennis U.S. Pat.
No. 4,900,279, are avoided, and the lead 10 is fixed to the
substrate 50 at the desired point.
After joining the set of leads 10 to the substrate contact pads 18,
the carrier strip 14 is cut off. When this is done adjacent the
point where the lead body joins the carrier strip, the end of the
body 20 previously near the carrier 14 may be used as a terminal.
This terminal portion may take any desired configuration. It may,
for example, be formed as a pin to be received in a connector or in
an opening of a further printed circuit board or the like, so as
for example to be soldered thereto, or as a wire-wrap post.
Alternatively, the portions of lead 10 beyond the C-clip (above it
in FIG. 2) may be configured to be used as the terminal
portion.
As an optional improvement, small apertures 52 may be formed in the
lead 10 underneath the solder layer 28, which will facilitate flow
of molten solder into the gap 34, by capillary action, without
significantly weakening the lead 10.
It will be understood that instead of forming a burr at the edge of
the C-clip portion, that portion of the lead body may be bowed
slightly above a longitudinal axis, to be slightly concave facing
inwardly to provide the space 34 between the C-clip interior and
the substrate conductive pad.
While the embodiment of the invention shown and described is fully
capable of achieving the results desired, it is to be understood
that this embodiment has been shown and described for purposes of
illustration only and not for purposes of limitation. It will be
apparent to those skilled in the art that variations and
modifications can be substituted herein without departing from the
principles and true spirit of the invention, which is defined by
the accompanying claims.
* * * * *