U.S. patent application number 12/483754 was filed with the patent office on 2010-04-15 for thermally decoupling fuse holder and assembly.
This patent application is currently assigned to Littelfuse, Inc.. Invention is credited to Gordon T. Dietsch, Vincent Minh-Tu Tran, Stephen J. Whitney.
Application Number | 20100090792 12/483754 |
Document ID | / |
Family ID | 36943607 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100090792 |
Kind Code |
A1 |
Whitney; Stephen J. ; et
al. |
April 15, 2010 |
THERMALLY DECOUPLING FUSE HOLDER AND ASSEMBLY
Abstract
In one aspect of the present invention, subminiature fuses are
soldered to a PCB via clips attached to the fuse end caps. The
clips are physically attached to the PCB pads, enabling the fuse to
be replaced if needed and providing thermal decoupling between the
fuse and the heating sinking solder/PCB pads. The fuse and clips
can also be picked and placed in one operation. In another aspect,
improved fuse clips are provided that include tabs that separate
the housing portions of the clips from the heating sinking
solder/PCB pads. Such improved clips further enhance thermal
decoupling. In a further aspect, an improved fuse is provided, in
which the thermal decoupling tabs just described are provided
directly with the fuse. In yet a further aspect, a thermally
insulative fuse body is provided to further decouple the fuse
element from its surroundings.
Inventors: |
Whitney; Stephen J.; (Lake
Zurich, IL) ; Dietsch; Gordon T.; (Park Ridge,
IL) ; Tran; Vincent Minh-Tu; (Arlington, TX) |
Correspondence
Address: |
Duane Morris LLP (Littlefuse, Inc.)
P.O. Box 5203
Princeton
NJ
08543-5203
US
|
Assignee: |
Littelfuse, Inc.
Chicago
IL
|
Family ID: |
36943607 |
Appl. No.: |
12/483754 |
Filed: |
June 12, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11072553 |
Mar 3, 2005 |
7564337 |
|
|
12483754 |
|
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|
Current U.S.
Class: |
337/251 |
Current CPC
Class: |
H05K 2201/10946
20130101; Y02P 70/613 20151101; H05K 2201/062 20130101; H01H
85/0418 20130101; H05K 2201/1031 20130101; H01H 2085/2085 20130101;
H05K 2201/10636 20130101; H05K 3/3426 20130101; H05K 2201/10181
20130101; Y02P 70/611 20151101; Y02P 70/50 20151101; H05K 3/301
20130101; H05K 2201/10386 20130101; H01H 2085/0414 20130101; H05K
2201/10757 20130101; H01H 85/202 20130101 |
Class at
Publication: |
337/251 |
International
Class: |
H01H 85/22 20060101
H01H085/22 |
Claims
1. A fuse assembly comprising: a first clip holding a first
terminal of a fuse; and a second clip holding a second terminal of
the fuse, wherein the first clip, second clip and fuse are
configured such that (i) they may be picked and placed when
assembled and (ii) the fuse spaces the first and second clips apart
as needed according to a distance that a plurality of conductive
pads or a printed circuit board ("PCB") are spaced apart.
2. The fuse assembly of claim 1, wherein the first and second clips
include first and second thermally decoupling tabs, respectively,
the fuse spacing the first and second tabs apart as needed
according to the distance that the plurality of conductive pads on
the PCB are spaced apart.
3. The fuse assembly of claim 2, wherein the first and second clips
each include a base and at least one wall angled therefrom, the
tabs each extending (i) in at least a substantially parallel
direction with respect to the corresponding base or (ii) in at
least a substantially perpendicular direction with respect to the
corresponding base.
4. The fuse assembly of claim 2, wherein the first and second tabs
are soldered to the PCB such that fuse housing portions of the
first and second clips (i) contact the PCB or (ii) are spaced apart
from the PCB.
5. The fuse assembly of claim 1, wherein the fuse is of a type
selected from the group consisting of: midget, 2AG, 3AG, 3AB,
5.times.20 mm, Nano.sup.2.RTM., Pico.RTM. SMF and chip fuses.
6. The fuse assembly of claim 1, wherein the first and second clips
are soldered to the PCB via a process selected from the group
consisting of: wave soldering and reflow soldering.
7. A fuse for a printed circuit board ("PCB") comprising: a body; a
fuse element located within the body; first and second conductive
end caps coupled to the body and in electrical communication with
the fuse element; and a first tab extending from the first end cap
and a second tab extending from the second end cap, the tabs
configured so that when assembled to the PCB the end caps are at
least partially thermally decoupled from first and second solder
joints connecting the tabs to the PCB.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to circuit protection and more
particularly to fuse protection. Miniature cartridge fuses commonly
include a main insulating housing, conductive end caps secured to
the housing and a fuse element or wire extending across the end
caps. The cup-shaped or open end caps include a skirt portion that
extends over the ends of the housing. The fuse element may be
electrically and physically secured to the end caps via a body of
solder in each of the end caps. The solder can also extend into
small clearance spaces between the skirt of the end caps and the
electrically insulative housing.
[0002] Miniature or subminiature cartridge fuses are typically
soldered directly to a printed circuit board ("PCB") via a process
called reflow soldering. The miniature fuse is typically picked and
placed onto conductive pads of the PCB, which have been coated or
printed with a solder paste. The PCB carrying the fuse is sent
through an oven called a reflow oven. The reflow oven heats the PCB
and fuse to a temperature that melts the solder paste beneath the
miniature fuse. The solder paste melts or reflows at a temperature
of, e.g., 180 to 186.degree. C. as the PCB travels through the
oven. Afterward, the PCB and associated components cool, allowing
the solder paste to harden and fix the miniature fuse to the
PCB.
[0003] Larger surface mounted or PCB fuses can be placed in clips
that are soldered to the PCB. Prior art FIG. 1 shows one example of
a pair of such clips 12, which are manufactured by the assignee of
the present invention. The fuse can be, e.g., a 1/4 inch (6.35 mm)
fuse that is clipped into spring-like walls 14 and 16 of clips 12.
Clips 12 are spaced apart on the PCB so that walls 14 and 16 extend
around and connect electrically with the end caps of a replaceable
fuse.
[0004] Clips 12 are soldered to the PCB via an alternative process
called wave soldering. Here pins 18 extending downwardly from walls
14 and 16 are fitted into holes formed in the PCB. The PCB is sent
through a machine called a wave soldering machine, which can have
one or more waves of flowing solder. The solder from the waves
wicks up through the holes in the PCB into which pins 18 are
inserted as the PCB is conveyed over the one or more waves. After
the PCB passes the solder bath, the solder cools and creates solder
joints holding clips 12 to the PCB. The fuse may then be inserted
into clips 12.
[0005] Prior art FIGS. 2 and 3 illustrate another surface mountable
fuse holder, which is also manufactured by the assignee of the
present invention. Here, a plastic housing 40 is provided in
assembly with a fuse 42. Plastic housing 40 includes side walls 44
and end walls 46. Terminals 48 are attached to housing 40.
Terminals 48 communicate electrically with the end caps of fuse 42
and are soldered to the PCB via the above-described reflow
soldering process. The fuse end caps and clips have surface
finishes which facilitate solder attachment of the clips to the
circuit board pads, but will not reflow the fuse end caps to the
clips during the soldering operation. Fuse 42 is replaceable as is
the fuse used with clips 22 of FIG. 1.
[0006] Both reflow and wave soldering form solder joints between
conductive pads provided on the PCB and the directly mounted fuses
or the fuse clips. The solder and pads act as a heat sink,
potentially preventing the fuse from reacting as quickly as desired
to an overcurrent condition because heat generated by self-heating
of the fuse element in response to the overcurrent condition is
conducted away from the fuse element via the end caps to the
circuit board pads and traces, either via the clips, or directly in
the case where the fuse is attached directly to the PCB. This
conductance of heat away from the fuse element can prevent the
element from reaching its melting temperature, thus interrupting
the overload condition as intended.
[0007] Further, as discussed above, some surface-mounted fuses are
mounted directly to the PCB. If such fuses open, the PCB must be
reworked, which entails diagnosis, removal of the PCB from the
application, possible shipping or transport of the PCB and
potentially harmful hand-soldering to remove and replace the
fuse.
[0008] Accordingly, a need exists for an improved surface mount
fuse assembly.
SUMMARY OF THE INVENTION
[0009] The present invention provides an improved circuit
protection device and assembly. The present invention includes
several inventive aspects. In one aspect of the present invention,
an improved apparatus and method of mounting a miniature or
subminiature PCB fuse is provided. As discussed above, miniature
PCB fuses are mounted directly to the PCB. This causes two
problems, potential PCB rework and thermal coupling with the solder
and PCB pads.
[0010] The present invention in one embodiment provides small fuse
clips that are packaged with the miniature or subminiature fuse to
form a fuse assembly. The fuse assembly is picked and placed onto
the PCB and thereafter reflow or wave soldered to the PCB. The
clips, not the fuse, are soldered to the board. The clips can have
leaf-spring type walls, or the walls may have indents or detents to
hold the fuse end caps and fuse in place frictionally but
replaceably. The clips provide two benefits: (i) they enable an
opened miniature fuse to be removed and replaced, preventing costly
and potentially damaging rework and (ii) they thermally decouple
the fuse from the solder and pads of the PCB. The fuse of the
assembly also provides a benefit by spacing apart separate fuse
clips so that the clips automatically align with the PCB pads when
placed onto the PCB.
[0011] In a second aspect of the present invention, the
above-described assembly is further improved through the addition
of tabs or standoffs to the clips. The tabs or standoffs space the
fuse end caps even further away from the solder joints and PCB
mounting pads, providing enhanced thermal decoupling. The tabs can
be formed integrally with the clips or be attached to the clips.
The tabs can extend outwardly sideways from the clips so that the
clips sit on the PCB, or extend downwardly from the clips so that
the clips and fuse are propped up from the PCB. Accordingly, the
resulting solder joints may extend laterally or vertically away
from the clips. The clips in an embodiment are finished with a
material, such as gold flash that will not reflow in the soldering
operation.
[0012] In any embodiment, the clips may hold any suitable PCB fuse
and are not limited to holding subminiature cartridge fuses. For
example, the fuses may be of any of the following types: midget,
2AG, 3AG, 3AB, 5.times.20 mm, Nano.sup.2.RTM., Pico.RTM. SMF or
chip fuses.
[0013] The clips may be reflow or wave soldered to the PCB. For
example, the thermally decoupling extension tabs described above
may terminate in pads that are reflow soldered to pads on the PCB
or pins that extend through the PCB for attachment via wave
soldering.
[0014] In a third aspect of the present invention, the
above-described thermal decoupling tabs or standoffs extend from
the end caps of the fuse, not from the separate clips. Here, the
tabs or standoffs space the fuse end caps away from the solder
joints and PCB mounting pads, providing enhanced thermal
decoupling. The tabs can be formed integrally with the end caps or
be attached to the end caps. The tabs can extend outwardly sideways
from the end caps so that the end caps sit on the PCB, or extend
downwardly from the end caps so that the end caps and fuse are
propped up from the PCB. To those ends, the resulting solder joints
may reside laterally or vertically away from the clips.
[0015] It is therefore an advantage of the present invention to
provide an improved PCB fuse assembly.
[0016] It is another advantage of the present invention to provide
an improved PCB fuse assembly clip.
[0017] It is a further advantage of the present invention to
provide an improved PCB fuse.
[0018] Moreover, it is an advantage of the present invention to
improve thermal characteristics and response time for surface
mounted fuses.
[0019] It is yet another advantage of the present invention to
provide an improved method and apparatus for assembling a fuse to a
PCB.
[0020] Additional features and advantages of the present invention
are described in, and will be apparent from, the following Detailed
Description of the Invention and the figures.
BRIEF DESCRIPTION OF THE FIGURES
[0021] FIG. 1 is a perspective view of prior art printed circuit
board ("PCB") mountable fuse holding clips.
[0022] FIG. 2 is a front view of another prior art PCB mountable
fuse holder with installed fuse.
[0023] FIG. 3 is a side view of the prior art fuse holder with
installed fuse of FIG. 2.
[0024] FIG. 4 is a perspective view of one embodiment of an
assembled and thermally decoupled fuse and associated fuse clips of
the present invention.
[0025] FIGS. 5 and 6 are perspective views of one embodiment of a
pair of improved fuse clips and associated fuse assembly, which is
similar to the embodiment described in connection with FIG. 4.
[0026] FIG. 7 is a perspective view of another embodiment of a pair
of improved fuse clips of the present invention.
[0027] FIG. 8 is a perspective view of the fuse clips of FIG. 7
assembled with a fuse and PCB.
[0028] FIG. 9 is a perspective view of a further embodiment of a
pair of improved fuse clips and associated fuse assembly of the
present invention.
[0029] FIGS. 10, 11 and 22 are perspective, front and side views,
respectively, of another embodiment of a pair of improved fuse
clips and associated fuse assembly, which is similar to the
embodiments of FIGS. 7 to 9.
[0030] FIG. 13 is a perspective view of one thermally decoupling
fuse of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention provides an improved electrical
device. More specifically, the present invention provides an
improved PCB fuse assembly, fuse clip and fuse. In one aspect,
subminiature fuses are soldered to a PCB via clips attached to the
fuse end caps. The clips are physically attached to the PCB pads,
enabling the fuse to be replaced if needed and providing thermal
decoupling between the fuse and the heating sinking solder/PCB
pads. The fuse and clips can also be picked and placed in one
operation. In another aspect, improved fuse clips are provided that
include tabs that separate the housing portions of the clips from
the heating sinking solder/PCB pads. Such improved clips further
enhance thermal decoupling. In a further aspect, an improved fuse
is provided, in which the thermal decoupling tabs just described
are provided directly with the fuse.
[0032] Referring now to the drawings and in particular to FIGS. 4
to 6, various embodiments for thermally decoupled fuse clips and
associated fuse assemblies are illustrated. Each of the assemblies
10a and 10b includes a fuse 20, a pair of fuse clips 50, 60 and a
printed circuit board ("PCB") 100. In one embodiment, fuse 20 is a
so-called "cartridge fuse," which is a small fuse that is typically
surface mounted to a PCB. The smallness of the fuse and the method
of its attachment to the PCB create a number of manufacturing and
operational issues that have led to the apparatus and method of the
present invention.
[0033] Fuses 20 include an electrically insulative body 22. A pair
of end caps 24 and 26 is fixed to or attached to electrically
insulative body 22. Electrically insulative body 22 includes a top,
a bottom, a front and a back in the illustrated embodiment. In
other embodiments, body 22 is round or has another suitable
cross-sectional shape. Body 22 can initially be open on its ends,
which are capped with caps 24 and 26. Body 22 may be made of any
suitable insulating material, such as a ceramic material, glass
material or a relatively high temperature electrically insulative
polymer. A glass or polymer body is less thermally conductive than
ceramic and has the advantage of yet further thermal decoupling of
the fuse element from its surroundings. For example, a
boro-silicate or soda-lime material may be used for the body
22.
[0034] End caps 24 and 26 may be made of any suitable conductive
material, such as copper, tin, nickel, gold, silver, brass and any
combination thereof. End caps 24 and 26 may include any suitable
one or more coatings, such as a nickel, gold, tin, silver, copper,
intermediate or finish coating. The intermediate or finish coatings
may be selectively applied, so that only intended portions of the
clips are coated. Further, alloys of the above metals may also be
used for the base and plating materials of end caps 24 and 26.
Still further, the end caps may not have any plated coatings.
[0035] In an embodiment, caps 24 and 26 are open five-sided
structures, including an end plate and a four-walled skirt
extending from the end plate. In an alternative embodiment, end
caps 24 and 26 are at least substantially cylindrical, and the end
plates are at least substantially circular. Other suitable shapes
for the end caps, housings and fuses are also within the scope of
the present invention.
[0036] In one embodiment, end caps 24 and 26 are pre-plated or
pre-prepared internally with solder. In one implementation, the
inner surfaces of the end plates are plated or pre-prepared with an
area of solder. The solder areas may additionally or alternatively
extend to the inner surfaces of the skirts of end caps 24 and
26.
[0037] Caps 24 and 26 in one embodiment fit over electrically
insulative body 22 so that a small amount of clearance exists
between inner surfaces of the skirts of end caps 24 and 26 and the
outer surfaces of electrically insulative housing 22.
Alternatively, the skirts of end caps 24 and 26 are sized such that
their inner surfaces create an interference fit with the outer
surfaces of housing 22. Here, the inner surfaces of the skirts of
end caps 24 and 26 may be plated or pre-prepared with solder to
ensure that solder resides between the caps 24 and 26 and body 22
upon assembly.
[0038] A fuse element or wire of fuse 20 (not seen, located inside
body 22) is attached to the above-described solder areas and thus
to end caps 24 and 26 in one of a variety of ways. In one way,
after end caps 24 and 26 are placed over housing 22, the fuse
element is fitted through small holes in the relative centers of
the end plates of caps 24 and 26. In another embodiment, the fuse
element 32 is fixed to one of the end caps 24 and 26 and is fused
or connected to the other cap 24 or 26 during the soldering
process. In still a further embodiment, the fuse element extends
diagonally within housing 22 and is bent at both ends around the
outside of electrically insulative housing 22 before the end caps
24 and 26 are placed on the housing. The press-fit or soldering
process then holds the fuse element in place. The fuse element may
be for example a fast opening element.
[0039] The fuse elements can have a variety of forms and shapes.
The fuse element can be a spirally wound conductive wire on an
electrically insulative or conductive substrate. The fuse element
is alternatively a braided or a single strand of wire. The fuse
element further alternatively has a serpentine shape. Any of the
above fuse elements may include a core conductive material, such as
copper, which is plated for example with tin, gold or silver. The
fuse elements can also be coiled or spiral-wound or have any other
suitable configuration. In an embodiment, the fuse elements are
sized and dimensioned to open or melt upon a certain current or
energy threshold.
[0040] As described above, end caps 24 and 26 may make an
interference fit with body 22. Alternatively or additionally, body
22 may include indents or recesses (not illustrated), which accept
tabs or detents (not illustrated) that extend inwardly from the
skirts of caps 24 and 26. The adhesion that the solder areas create
between the housing 22 and end caps 24 and 26 can also provide cap
retention.
[0041] It should be appreciated that each and every teaching
described for fuse 20 is equally applicable for fuse 30 described
below.
[0042] Clips 50 of assembly 10a of FIG. 4 each include a bottom
wall (not seen), side walls 52 and a rear wall 54. Side walls 52
and rear wall 54 in the illustrated embodiment include or define
indents or detents 56 (referred to collectively herein as indents).
Indents 56 hold fuse 20 removeably in place. Specifically, indents
56 press fit onto end caps 24 and 26 of fuse 20 and make electrical
contact with same. The bottom wall of clips 50 can also have an
indent (see e.g., FIG. 6). Indents 56 serve further to thermally
isolate or decouple fuse 20 from the surrounding heat sinking. That
is, they reduce the amount of surface area contact between clips 50
and end caps 24 and 26 of fuse 20.
[0043] Assembly 10a in one embodiment is picked and placed onto PCB
100. One clip 50 is placed onto PCB conductive pad 104a, while
another clip 50 is placed onto PCB conductive pad 104b. The length
of fuse 20 spaces clips 50 apart a determined distance
corresponding to the distance between pads 104a and 104b. Pads 104a
and 104b connect respectively to traces 106a and 106b, which lead
to desired electrical locations.
[0044] Clips 50 (like all other clips described herein) in an
embodiment are made of brass, spring brass, copper,
beryllium-copper, phosphor-bronze, steel, nickel or alloys thereof,
possibly with an intermediate barrier layer of nickel, and a finish
layer of tin, tin-lead, nickel, silver, gold, palladium, palladium
alloys or rhodium. The intermediate and finish layers may be
applied selectively so that only certain portions of the clips are
coated. Pads 104a, 104b and traces 106a, 106b (for each embodiment
described herein) are made of copper and are etched onto PCB 100 in
one embodiment. PCB 100 (for each embodiment herein) can be rigid,
e.g., be of an FR-4 material or other glass-epoxy composite,
ceramic, polymer material, or be made of a flexible material, e.g.,
a polyimide, Kapton.TM. material, or other material.
[0045] Once clips 50 are soldered to pads 104a and 104b, fuse 20
may be removed if opened from clips 50. A replacement fuse 20 can
then be placed into clips 50 without the extensive rework
associated with directly mounted fuses. In the illustrated
embodiment, clips 50 are reflow soldered to pads 104a and 104b. In
an alternative embodiment, clips 50 include pins that extend
through holes drilled in PCB 100. The pins are then wave soldered
to PCB 100 and associated pads 104a and 104b. Clips 50 may directly
contact pads 104a and 104b, wherein, e.g., solder flows around
sides 52 and back 54 of clips 50 to seal the sides to pads 104a and
104b. Clips 50 may alternatively indirectly contact pads 104a and
104b, wherein, e.g., the solder provides an interface
(intermetallic bonding) between clips 50 and pads 104a and
104b.
[0046] Clips 60 of assembly 10b of FIGS. 5 and 6 each include a
bottom wall 68, side walls 62 and an end wall 64. Bottom walls 68
in the illustrated embodiment include or define indents or detents
66b. Indents 66b serve further to thermally isolate or decouple
fuse 20 from the surrounding heat sinking. Here, indents 66b prop
end caps 24 and 26 of fuse 20 up from the larger surface area of
bottom walls 68.
[0047] Assembly 10b in one embodiment is picked and placed onto PCB
100. One clip 60 is placed onto a first PCB conductive pad, while
the other clip 60 is placed onto another PCB conductive pad. The
length of fuse 20 spaces clips 60 apart a determined distance
corresponding to the distance between pads.
[0048] As illustrated, walls 62 and 64 extend individually from
base 68. Walls 62 and 64 are leaf-spring like and enable fuse 22 to
snap into and out of clips 60. Walls 62 and 64 each include bent
portions 66a that snap over end caps 24 and 26 to hold fuse 20
within clips 60. In an embodiment, walls 62 and 64 do not contact
or completely contact end caps 24 and 26, rather, bent portions 66a
contact walls 62 and 64. Such configuration enhances the thermal
decoupling characteristics of clips 60 for reasons discussed above,
while still providing a firm fit. Bent portions 66a and indent 66b
in essence provide a four point (or edge) contact with end caps 24
and 26.
[0049] Once clips 60 are soldered to the pads of PCB 100, fuse 20
may be removed if opened from clips 60. A replacement fuse 20 can
then be placed into clips 60 without the extensive rework
associated with directly mounted fuses. In the illustrated
embodiment, clips 60 are reflow soldered to the pads of PCB 100. In
an alternative embodiment, clips 60 include pins that extend
through holes drilled in PCB 100. The pins are then wave soldered
to PCB 100 and associated pads. Clips 60 may directly contact the
pads, wherein, e.g., solder flows around sides 62 and back 64 of
clips 60 to seal the sides to the pads. Clips 60 may alternatively
indirectly contact the pads of PCB 100, wherein, e.g., the solder
provides an interface (intermetallic bonding) between clips 60 and
the pads.
[0050] Clips 70 of FIG. 7 and assembly 10c of FIG. 8 each include a
bottom wall, side walls 72 and a rear wall 74. Side walls 72 and
rear wall 74 in the illustrated embodiment include or define
indents or detents 76. Indents 76 hold fuse 20 removeably in place.
Specifically, indents 76 press fit onto end caps 24 and 26 of fuse
20 and make electrical contact with same. The bottom wall of clips
70 can also have an indent (see e.g., FIG. 6). Indents 76 serve
further to thermally isolate or decouple fuse 20 by creating point
contact as described herein.
[0051] As seen in FIGS. 7 and 8, clips 70 each include tabs 78.
Tabs 78 extend from a housing portion of clips 70, which is made up
of the bottom wall and walls 72 and 74. Tabs 78 separate the
housing portion of clips 70 and thus the fuse 20 residing within
clips 70 horizontally from the heat sinking solder pads 104a and
104b and associated solder. Tabs 78 may be formed integrally with
the housing portions of clips 70 or be attached, e.g., welded to
the housing portions. Tabs 78 may be made of the same or different
material as the material of the housing portions of clips 70. Tabs
78 may have any suitable shape as needed to maximize their thermal
decoupling and rigidity.
[0052] Assembly 10c in one embodiment is picked and placed onto PCB
100. One tab 78 is placed onto PCB conductive pad 104a, while the
other tab 78 is placed onto PCB conductive pad 104b. The length of
fuse 20 and tabs 78 spaces the ends of tabs 78 apart a determined
distance corresponding to the distance between pads 104a and 104b.
Pads 104a and 104b connect respectively to traces 106a and 106b,
which each lead to a desired electrical location.
[0053] Once tabs 78 of clips 70 are soldered to pads 104a and 104b,
fuse 20 may be removed if opened from clips 70. A replacement fuse
20 can then be placed into clips 70 without the extensive rework
associated with directly mounted fuses. In the illustrated
embodiment, tabs 78 of clips 70 are reflow soldered to pads 104a
and 104b. In an alternative embodiment, tabs 78 include pins that
extend through holes drilled in PCB 100. The pins are then wave
soldered to PCB 100 and associated pads 104a and 104b. Tabs 78 of
clips 70 may directly contact pads 104a and 104b, wherein, e.g.,
solder flows around the sides of tabs 78. Tabs 78 may alternatively
indirectly contact pads 104a and 104b, wherein, e.g., the solder
provides an interface (intermetallic bonding) between tabs 78 and
pads 104a and 104b.
[0054] Assembly 10d of FIG. 9 illustrates an alternative embodiment
of assembly 10c of FIG. 8. Each of the features and embodiments
described above for assembly 10c of FIG. 8 is applicable here,
except as follows. Here, clips 80 each include a housing portion
having bottom walls, side walls 82 and a rear wail 84. Tabs 88
extend downwardly from the housing portions of clips 80. Tabs 88
separate the housing portion of clips 80 and thus the fuse 20
residing within clips 70 vertically from the heat sinking solder
pads 104a and 104b and associated solder. Tabs 88 may be formed
integrally with the housing portions of clips 80 or be attached,
e.g., welded to the housing portions. Tabs 88 may be made of the
same or different material as the material of the housing portions
of clips 80. Tabs 88 may have any suitable shape as needed to
maximize their thermal decoupling and rigidity.
[0055] Assembly 10e of FIGS. 10 to 12 illustrates one preferred
embodiment of the present invention. Assembly 10e employs clips 90.
Clips 90 each include a housing portion having side walls 92 and a
bent rear wall 94. The housing portion of clips 90 is similar to
clips 60 of FIGS. 5 and 6 in that walls 92 and 94 extend
individually from a base of clips 90. The base may have an indent
that creates a point contact with the bottoms of end caps 24 and
26. Walls 92 and 94 are leaf-spring like and enable fuse 22 to snap
into and out of clips 90. Walls 92 and 94 each include bent
portions 96 that snap over end caps 24 and 26 to hold fuse 20
within clips 60. In an embodiment, walls 92 and 94 do not contact
or substantially contact end caps 24 and 26, rather, bent portions
96 contact walls 62 and 64. Such configuration enhances the thermal
decoupling characteristics of clips 90 for reasons discussed above,
while still providing a firm fit. Bent portions 96, the lower edge
of bent rear wall 94 (see FIG. 11) and the indent of the base in
essence provide a four point or edge contact with end caps 24 and
26.
[0056] Like assemblies 10c and 10d, clips 90 include decoupling
tabs 98. Tabs 98 extend from the bent rear walls 94 of housing
portions of clips 90. Tabs 98 separate the housing portions of
clips 90 and thus the fuse 20 residing within clips 90 horizontally
from the heat sinking solder pads and associated solder on PCB
100.
[0057] Tabs 98 as illustrated are formed integrally with the
housing portions of clips 90. Alternatively, tabs 98 are attached,
e.g., welded to the housing portions. Tabs 98 may be made of the
same or different material as the material of the housing portions
of clips 90. Tabs 98 may have any suitable shape as needed to
maximize their thermal decoupling and rigidity.
[0058] Assembly 10e in one embodiment is picked and placed onto PCB
100. One clip 90 is placed onto a first PCB conductive pad, while
the other clip 90 is placed onto another PCB conductive pad. The
length of fuse 20 and tabs 98 space clips 90 and tabs 98 apart a
determined distance corresponding to the distance between pads.
[0059] Once tabs 98 are soldered to the pads of PCB 100, fuse 20
may be removed if opened from clips 90. A replacement fuse 20 can
then be placed into clips 90 without the extensive rework
associated with directly mounted fuses. In the illustrated
embodiment, tabs 98 are reflow soldered to the pads of PCB 100. In
an alternative embodiment, tabs 98 include pins that extend through
holes drilled in PCB 100. The pins are then wave soldered to PCB
100 and associated pads. Tabs 98 may directly contact the pads,
wherein, e.g., solder flows around sides of tabs 98. Tabs 98 may
alternatively indirectly contact the pads of PCB 100, wherein,
e.g., the solder provides an interface (intermetallic bonding)
between clips 90 and the pads.
[0060] Referring now to FIG. 13, assembly 10f illustrates fuse 30
of the present invention. Fuses 30 includes an electrically
insulative body 32. A pair of end caps 34 and 36 is fixed to or
attached to electrically insulative body 32 as described above for
fuse 20. Electrically insulative body 32 includes a top, a bottom,
a front and a back in the illustrated embodiment. In other
embodiments, body 32 is round or has another suitable
cross-sectional shape. Body 32 can initially be open on its ends,
which are capped off with caps 24 and 26. As discussed above, each
of the alternative embodiments and features discussed with fuse 20
is applicable to fuse 30.
[0061] End caps 34 and 36 of fuse 30 include tabs or tab portions
38. Tabs 38 extend downwardly from the housing portions of fuse 30
in the illustrated embodiment. Alternatively, tabs 38 extend
horizontally from end caps 34 and 36. Tabs 38 separate the end caps
34 and 36 and thus the fuse 30 vertically (alternatively
horizontally) from the heat sinking solder pads 104a and 104b and
associated solder. Tabs 38 may be formed integrally with end caps
34 and 36 or be attached, e.g., welded to the end caps. Tabs 38 may
be made of the same or different material as the material of end
caps 34 and 36. Tabs 38 may have any suitable shape as needed to
maximize their thermal decoupling and rigidity. A glass or polymer
body is less thermally conductive than ceramic and has the
advantage of yet further thermal decoupling the fuse element from
its surroundings.
[0062] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art.
[0063] Such changes and modifications can be made without departing
from the spirit and scope of the present invention and without
diminishing its intended advantages. It is therefore intended that
such changes and modifications be covered by the appended
claims.
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