U.S. patent application number 11/525167 was filed with the patent office on 2007-01-18 for current fuse and method of making the current fuse.
Invention is credited to Kazuyuki Kato, Satoru Kobayashi.
Application Number | 20070013472 11/525167 |
Document ID | / |
Family ID | 34131446 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070013472 |
Kind Code |
A1 |
Kobayashi; Satoru ; et
al. |
January 18, 2007 |
Current fuse and method of making the current fuse
Abstract
In order to provide a current fuse with high solderability
without containing harmful materials, solder chips containing 30 to
60 percent by weight of zinc, 0.1 to 2 percent by weight of copper,
0.1 to 1 percent by weight of nickel, and the remainder percent by
weight being tin, or further containing 0.01 to 0.5 percent by
weight of aluminum are inserted into the interior of the electrodes
before pressing the electrodes into the ends of the substrate of
the fuse, the exterior of the electrodes is heated to melt the
solder chips, thereby connecting between the electrodes and the
fuse wire.
Inventors: |
Kobayashi; Satoru;
(Komagane-shi, JP) ; Kato; Kazuyuki; (Kamiina-gun,
JP) |
Correspondence
Address: |
SMITH PATENT OFFICE
1901 PENNSYLVANIA AVENUE N W
SUITE 901
WASHINGTON
DC
20006
US
|
Family ID: |
34131446 |
Appl. No.: |
11/525167 |
Filed: |
September 22, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10883032 |
Jul 2, 2004 |
|
|
|
11525167 |
Sep 22, 2006 |
|
|
|
Current U.S.
Class: |
337/159 |
Current CPC
Class: |
H01H 85/0418 20130101;
H05K 3/3489 20130101; B23K 35/262 20130101; H01H 85/157 20130101;
B23K 35/282 20130101; H05K 3/143 20130101; H05K 3/1216 20130101;
H05K 3/3485 20200801; C22C 13/00 20130101; H05K 3/26 20130101; H05K
2203/043 20130101 |
Class at
Publication: |
337/159 |
International
Class: |
H01H 85/04 20060101
H01H085/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2003 |
JP |
2003-270614 |
Claims
1. A current fuse comprising a fuse wire and electrodes which are
soldered using lead-free solder, wherein said lead-free solder
contains at least 30 to 60 percent by weight of zinc, 0.1 to 2
percent by weight of copper, with the remainder percent by weight
being tin.
2. The current fuse according to claim 1, wherein said lead-free
solder further contains 0.01 to 0.5 percent by weight of
aluminum.
3. A current fuse, comprising: a fuse wire; a container for said
fuse wire; and cap electrodes that are attached to both ends of
said container; wherein said fuse wire is soldered to said
electrodes using lead-free solder that is provided in the interior
of said electrodes, and said lead-free solder contains at least 30
to 60 percent by weight of zinc, 0.1 to 2 percent by weight of
copper, with the remainder percent by weight being tin.
4. The current fuse according to claim 3, wherein said lead-free
solder further contains 0.01 to 0.5 percent by weight of
aluminum.
5. A method of making a current fuse by soldering a fuse wire and
electrodes using lead-free solder at a temperature between a solid
phase temperature and a liquid phase temperature of said lead-free
solder, wherein said lead-free solder contains at least 30 to 60
percent by weight of zinc, 0.1 to 2 percent by weight of copper,
with the remainder percent by weight being tin.
6. The method of making a current fuse according to claim 5,
wherein said lead-free solder further contains 0.01 to 0.5 percent
by weight of aluminum.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. Patent
Application Ser. No. 10/883,032 filed on Jul. 2, 2004, currently
pending. The disclosure of U.S. Patent Application Ser. No.
10/883,032 is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a lead-free current fuse,
which is suitable for electronic equipment and electronic
components, for example, and a method of making the current
fuse.
[0004] 2. Description of the Related Art
[0005] Various kinds of compact fuses, which are surface-mountable
on a printed circuit board or the like, have been proposed. For
example, a fuse in which a fuse element stretches in a hollow space
within a rectangular case formed by attaching a ceramic casing main
body and a lid has been disclosed in Japanese Patent Application
Laid-Open No. 8-222117.
[0006] In the case of this compact fuse, a fuse element and
tin-lead solder, which has been adhered to the interior of metallic
cap in advance, are soldered.
[0007] On the other hand, tin-lead solder is essential for
fabricating or assembling electronic equipment; however, it
contains lead which is harmful to the human body and the like.
Therefore, solder not containing harmful lead is desired by
electronic equipment industries or related industries, and various
kinds of lead-free solder have been proposed. For example, a
lead-free solder alloy containing 7 to 10 percent by weight of zinc
(Zn), 0.01 to 1 percent by weight of nickel (Ni), and the balance
consisting of tin (Sn) has been described in Japanese Patent
Application Laid-Open No. 9-94688.
[0008] On the other hand, a solder material that has been disclosed
in Japanese Patent Application Laid-Open No. 2000-15478 is
developed considering environmental issues after discarding
electronic equipment, and is a lead-free solder material containing
tin, 3 to 18 percent by weight of zinc in proportion to that tin
and a small amount of additives (e.g., nickel).
[0009] However, when solder containing 10 percent by weight of tin
and 90 percent by weight of lead is used to manufacture the fuse
described in Japanese Patent Application Laid-Open No. 8-222117, a
ceramic substrate absorbs heat generated when that solder melts.
Therefore, a temperature to heat metallic caps must be set at
approximately 400 degrees C., which is approximately 100 degrees C.
higher than the melting point of solder.
[0010] Such temperature degrades plating on the surface of metallic
caps, resulting in deterioration of solderability when mounting a
fuse on a substrate.
[0011] On the other hand, the above-described lead-free
tin-zinc-nickel solder is used for mounting a fuse on a substrate.
That solder used in the interior of component causes a problem of
deterioration of quality, such as break of a fuse element when the
solder within each component melts in a reflow process when
mounting the fuse on the substrate.
SUMMARY OF THE INVENTION
[0012] The present invention has been developed in view of the
above-described problems, and aims to provide a current fuse, which
has solderability suitable for electronic equipment and electronic
components, and does not have an adverse influence on the
environment including the human body, and a method of manufacturing
the current fuse.
[0013] The present invention has a configuration to achieve the
above-described objectives. In other words, a current fuse includes
a fuse wire and electrodes which are soldered using lead-free
solder, wherein the lead-free solder contains at least 30 to 60
percent by weight of zinc, 0.1 to 2 percent by weight of copper,
and the remainder percent by weight of tin.
[0014] Furthermore, a current fuse includes a fuse wire and
electrodes which are soldered using lead-free solder, wherein the
lead-free solder contains at least 30 to 60 percent by weight of
zinc, 0.1 to 1 percent by weight of nickel, and the remainder
percent by weight of tin.
[0015] Furthermore, a current fuse includes a fuse wire and
electrodes which are soldered using lead-free solder, wherein the
lead-free solder contains at least 30 to 60 percent by weight of
zinc, 0.1 to 2 percent by weight of copper, 0.1 to 1 percent by
weight of nickel, and the remainder percent by weight of tin.
[0016] Furthermore, a current fuse includes a fuse wire and
electrodes which are soldered using lead-free solder, wherein the
lead-free solder having any one of the above-described composition
further contains 0.01 to 0.5 percent by weight of aluminum.
[0017] Furthermore, a current fuse, including: a fuse wire; a
container for the fuse wire; and cap electrodes that are attached
to both ends of the container; wherein the fuse wire is soldered to
the electrodes using lead-free solder that is provided in the
interior of the electrodes, and the lead-free solder has any one of
the above-described compositions.
[0018] Even further, a current fuse includes a fuse wire and
electrodes which are soldered using lead-free solder, wherein the
lead-free solder contains at least 30 to 60 percent by weight of
zinc and the remainder percent by weight of copper and tin.
[0019] In addition, when manufacturing a current fuse, a fuse wire
and electrodes are soldered using lead-free solder at a temperature
between a solid phase temperature and a liquid phase temperature of
the lead-free solder. Alternatively, a fuse wire and electrodes are
soldered in an atmosphere of oxygen using lead-free solder.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is an exploded view of a chip-type fuse according to
an embodiment of the present invention;
[0021] FIG. 2 is an external view of a current fuse, which has a
substrate formed by combining a casing main body and a lid
according to the embodiment;
[0022] FIG. 3 is an external view of a current fuse when covered by
electrodes according to the embodiment;
[0023] FIG. 4 is a graph showing a comparison of changes in
resistance value of a fuse using tin-zinc type solder when changing
the zinc content ratio according to the embodiment;
[0024] FIG. 5 is a graph showing a comparison of changes in
resistance value of a fuse using conventional solder and a fuse
using solder according to the embodiment;
[0025] FIG. 6 is a table showing the evaluation results from
changing the content ratios of copper, nickel, and aluminum
included in tin-zinc solder according to the embodiment; and
[0026] FIG. 7 is a flowchart describing the steps of making the
current fuse according to the embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0027] An embodiment of the present invention is described in
detail forthwith while referencing the attached drawings. FIG. 1 is
an exploded block diagram of a chip-type fuse according to the
embodiment of the present invention. The chip-type fuse shown in
the drawing is configured by stretching a fuse in a hollow space of
a ceramic substrate. This substrate is formed by attaching a
ceramic lid 3 to a ceramic casing main body 2.
[0028] At the center of the casing main body 2, an opening 9 which
is opening upward is provided. At both ends of the casing main body
2, concave portions 11 communicating with that opening 9 are
provided.
[0029] On the respective bottoms of the concave portions 11, a
single-thread groove 8 is formed. A soluble fuse wire (fuse
element) 1 is aligned with this groove 8, and stretching across the
opening 9.
[0030] Note that when stretching the fuse wire 1 between the
concave portions 11, a constant tension is applied to that fuse
wire 1. In this case, the fuse wire 1 may be temporarily attached
to the groove 8 using a resin or the like in order to maintain that
tension.
[0031] In this way, the lid 3 is attached to the opening 9 in the
casing main body 2 in which the fuse wire 1 stretches. Both ends 13
of that lid 3 are shaped so as to fit in the concave portions 11
(the widths and the depths of the ends 13 are slightly smaller than
those of the concave portions 11). In addition, the center of the
lid 3 almost completely covers the opening 9 (the length and the
width of the center of the lid 3 are slightly smaller than those of
the opening 9).
[0032] In this way, the exterior of the substrate formed by
combining the casing main body 2 and the lid 3 is almost
rectangular. The exterior of the fuse in this case is shown in FIG.
2. As shown in FIG. 2, when the casing main body 2 and the lid 3
are combined, a bent portion 10 of the fuse wire 1 protrudes from
each end of the substrate, respectively. That bent portion 10 is
connected to a metallic cap as described later.
[0033] Each of metallic caps (electrodes) 4 is made of copper or a
copper alloy, for example, and has a shape where one side (which
faces the substrate) of a cube is opened so as to cap the end of
the substrate as shown in FIG. 2. In addition, solder chips 5, each
having a composition to be described later, are inserted into the
respective interiors 6 of the electrodes 4 before capping the ends
of the substrate with the electrodes 4 (see FIG. 1). The electrodes
4 into which the solder chips 5 are inserted, respectively, then
cap both ends of the substrate (by pressing in and attaching).
[0034] Note that not only solder chips may be provided to the
interior 6 of each electrode 4, but molten solder or creamy solder
may alternatively be provided to the caps.
[0035] FIG. 3 shows the exterior of the fuse over which the
electrodes 4 are fit as described above. As shown in FIG. 1, a
portion (heating position) 7 indicated by a dashed line in the
electrode 4 of the above-described fuse is heated using a heater,
for example, at a temperature of 350 degrees C. for approximately
three seconds to melt the solder chip 5, which has been inserted
into the interior of the electrode 4 in advance.
[0036] As a result, the solder chips 5 are soldered (fusion bonded)
to the above-described bent portions 10 of the fuse wire 1,
resulting in an electrical connection between the fuse wire 1 and
the electrodes 4.
[0037] As described above, the casing main body 2 and the lid 3 of
the chip-type fuse according to the embodiment are formed so that
the outer dimensions of the lid 3 are slightly smaller than the
internal dimensions of the casing main body 2. This facilitates
alignment therewith. More specifically, they are attached by
inserting the lid 3 perpendicularly to the casing main body 2
during assembling.
[0038] As a result, when the casing main body 2 and the lid 3 are
attached, the ends 13 of the lid 3 never protrude from the concave
portions 11 of the casing main body 2. This allows smooth pressing
in and attaching of the electrodes 4 to the ends of the substrate,
and establishment of electrical connections between the fuse wire 1
and the electrodes 4.
[0039] Note that the lid 3 is attached to the casing main body 2 by
bonding them together with an adhesive such as an epoxy and heating
at a given temperature for a given period of time (e.g., at a
temperature of 150 degrees C. for approximately 15 minutes). The
electrodes 4 are pressed in and attached after the adhesive has
hardened.
[0040] In addition, the electrodes 4 of the chip-type fuse
according to the embodiment are also soldered to land patterns on a
printed circuit board when mounting the fuse on the board.
Subsequently, to facilitate and secure soldering to the printed
circuit board when the fuse is mounted on that board, although not
shown in the drawing, the electrodes 4 are formed, for example, so
that one of the four sides of the pressed in and attached
electrodes 4 protrudes from the sides of the substrate of the
chip-type fuse for just the thicknesses of the electrodes 4. The
other three sides of the electrodes 4 are aligned with, that is, in
plane with the sides of the substrate of the chip-type fuse.
[0041] In this way, aligning the sides of the electrodes 4 with
those of the substrate and flattening them facilitates usage of a
vacuum chuck when mounting the chip-type fuse on the printed
circuit board, and also facilitates setting a seal on the fuse main
body.
[0042] Next, a solder chip used for the chip-type fuse according to
the embodiment is described in detail.
[0043] In the case of the fuse according to the embodiment, high
temperature tin-zinc type solder is used as a solder chip to
connect the fuse wire. Heat resistance (rate of change in the
resistance value) of solder, which contains 30 to 60 percent by
weight of zinc (Zn) considered to be an appropriate percentage of
zinc content, is measured. The exemplary measurement results are
shown in FIG. 4.
[0044] Note that a characteristic of the conventional tin-lead
solder (containing 90 percent by weight of lead) is shown on the
far-right portion of FIG. 4 for comparison. In FIG. 4, numerals
preceding Zn are percentages of zinc (Zn) content.
[0045] The higher the ratio of zinc (Zn) than tin (Sn), the higher
the melting point, resulting in improvement in solder heat
resistance. However, too much zinc (Zn) leads to difficulty in
working. On the other hand, shortage of zinc (Zn) leads to high
fluidity and deterioration of solder heat resistance.
[0046] As shown in FIG. 4, even considering the above-mentioned
conditions, high temperature tin-zinc type solder containing 30 to
60 percent by weight of zinc is available.
[0047] More specifically, lead-free solder containing 30 to 60
percent by weight of zinc, 0.1 to 2 percent by weight of copper,
0.1 to 1 percent by weight of nickel, and the balance consisting of
tin is used.
[0048] Alternatively, lead-free solder containing 30 to 60 percent
by weight of zinc, 0.1 to 2 percent by weight of copper, and the
remainder being tin, or lead-free solder containing 30 to 60
percent by weight of zinc, 0.1 to 1 percent by weight of nickel,
and the remainder being tin may be used.
[0049] In this way, inclusion of 30 to 60 percent by weight of zinc
makes tin-zinc-nickel type solder or tin-zinc-copper type solder
with a solid phase temperature of 199 degrees C. and a liquid phase
temperature of 360 degrees C. or greater, which are preferable for
a current fuse.
[0050] Incidentally, tin-zinc-nickel type solder and
tin-zinc-copper type solder have fluidity when reheated in the
reflow process for mounting the chip-type fuse on the printed
circuit board. Therefore, expansion of air inside the chip-type
fuse may cause malfunctions such as washing out the solder.
Accordingly, fluidity of solder must be reduced.
[0051] Since specific gravity of aluminum is low, aluminum
solidifies on the surface of a joint when it melts. In addition,
since aluminum is easily oxidized, a solid oxide film is formed on
the surface of the joint. Therefore, insulation of the fuse
increases when becoming an open-circuit, resulting in an
arc-suppressing operation.
[0052] In addition, since aluminum is effective in decreasing the
fluidity of solder, 0.01 to 0.5 percent by weight of aluminum is
added to solder in the present embodiment.
[0053] However, if the added amount of aluminum is less than 0.01
percent by weight, the influence on fluidity is small, resulting in
no prescribed effectiveness. On the other hand, if the added amount
of aluminum is greater than 0.5 percent by weight, conductivity
decreases due to oxidation of aluminum when the solder is left in a
high-temperature environment. From the above, with the embodiment,
a very small added amount of aluminum, which is effective for
fluidity, is used, and the amount of additive is determined based
on the solder use conditions.
[0054] In this way, inclusion of 30 to 60 percent by weight of zinc
leads to a preferable solid phase temperature for the current fuse.
Alternatively, it is preferable that tin-zinc solder containing 40
percent by weight of zinc with characteristics such as heat
resistance equivalent to those of the conventional tin-zinc solder
is used. Therefore, in the current fuse of the embodiment, tin-zinc
solder containing 40 percent by weight of zinc is used.
[0055] The evaluation results of various percentages of copper,
nickel, and aluminum contents to be contained in that tin-zinc
solder are shown in FIG. 6.
[0056] `Processability` in FIG. 6 means workability of inserting a
solder joint into an electrode cap. Moderate flexibility is
favorable because the solder joint fits to the interior of the
electrode cap. In addition, `solder manufacturability` means
workability of manufacturing a joint by melting a solder
material.
[0057] In addition, `heat resistance` means change in resistance
due to change in temperature; and `wettability` means adherability
of solder to a bonding target. Poor wettability causes solder to
peel off of the surface of the bonding target.
[0058] FIG. 5 is a graph showing the results of comparing the
changes in the resistance value of a fuse in which a conventional
solder is used and changes in the resistance value of a fuse in
which a solder according to the embodiment is used. A performance
test is carried out for the solder according to the embodiment,
which contains 40 percent by weight of zinc, 1 percent by weight of
copper, 0.5 percent by weight of nickel, and the balance consisting
of tin, and conventional solder, which contains 10 percent by
weight of tin and 90 percent by weight of lead.
[0059] Note that the rate of change in the resistance value is
examined under the conditions of immersion in molten solder at a
temperature of 260 degrees C. for ten seconds repeated five times.
As is seen from FIG. 5, in the case of the fuse using solder
according to the embodiment, the rate of change in the resistance
value is 2% or less at most. This is a characteristic almost
equivalent to that of the fuse using the conventional solder
containing lead (indicated by a dashed line in the drawing).
[0060] Such characteristic can be obtained based on the following
reasons. In short, the solder according to the embodiment has low
fluidity in a solid-liquid coexistence state. Therefore, even if
the solder is heated when the fuse is mounted on the printed
circuit board, the shape of solder (joint) connecting the fuse and
the electrode does not change, and the connection is
maintained.
[0061] This is because the solder according to the embodiment being
soldered in an atmosphere of oxygen steadily oxidizes the surface
thereof due to heat generated during soldering, and forms a solid
oxide film, resulting in decrease in fluidity thereof.
[0062] In addition, since the solder joint according to the
embodiment can never be exposed to oxygen due to a special flux,
progression of oxidation of the solder joint after being soldered
stops. This is one reason why the above-mentioned characteristic
can be obtained.
[0063] A method of manufacturing a current fuse with the
above-mentioned configuration is described forthwith while
referencing FIG. 7. FIG. 7 is a flowchart describing the steps of
manufacturing the current fuse according to the embodiment.
[0064] To begin with, in step S1, the fuse wire 1 is aligned with
the groove 8 at the bottoms of the concave portions 11 of the
casing main body 2 and stretched across the opening 9. At this
time, a certain tension may be applied to the fuse wire 1 in order
to temporarily adhere to the groove 8 using an adhesive resin. This
omits application of a certain tension after the temporary
adhesion. Note that there may not be need to temporarily adhere or
apply tension when providing the fuse wire in the groove 8
according to the shape of the fuse wire.
[0065] Next, in step S2, the lid 3 is attached to the opening 9,
and the exposed ends of the fuse wire are bent. This makes the
exterior of the current fuse shown in FIG. 2, in other words, the
bent portions 10 of the fuse wire 1 protrude from the ends of the
substrate. Note that in this case, the lid 3 and the casing main
body 2 are bonded together with an adhesive, and the adhesive is
hardened by heating at a given temperature for a given period of
time (e.g., at a temperature of 150 degrees C. for approximately 15
minutes).
[0066] Next, in step S3, the solder chips 5 with the
above-mentioned composition are aligned and inserted into the
interior 6 of the respective metallic caps (electrodes) 4 so as to
cover the bent portions 10 of the fuse wire 1, respectively, when
the electrodes 4 are fit over the substrate.
[0067] In addition, in step S4, the electrodes 4 into which the
solder chips 5 are inserted, respectively, are then pressed into
and attached to both ends of the substrate. At this time, it is
desirable that the solder chips 5 are provided at the bent portions
10. The exterior of the fuse over which the electrodes 4 are fit as
described above is shown in FIG. 3.
[0068] Next, in step S5, the center portion (indicated by a dashed
line 7 in FIG. 1) of each electrode 4 is heated by a heater at a
temperature between a solder solid phase temperature and a solder
liquid phase temperature, for example, at a temperature of 350
degrees C. for approximately 3 seconds. This melts the solder chips
5 which have been inserted into the electrodes 4 in advance.
[0069] As a result, the solder chips 5 are soldered (fusion bonded)
to the above-described bent portions 10 of the fuse wire 1, and the
fuse wire 1 and the electrodes 4 are soldered in an atmosphere of
oxygen, resulting in establishment of an electrical connection
therebetween (in step S6).
[0070] Note that the lid 3 is attached to the casing main body 2 by
bonding together with an adhesive such as an epoxy, and heating at
a given temperature for a given period of time (e.g., at a
temperature of 150 degrees C. for approximately 15 minutes). The
electrodes 4 are pressed in and attached after the adhesive has
hardened.
[0071] As described above, according to the embodiment, connection
between electrodes and a fuse wire can be secured by inserting a
solder chip into the interior of each electrode in advance before
pressing the electrodes into the ends of the substrate of the fuse,
and then heating the exterior of the electrodes to melt the solder,
and keeping a good electrical joint condition at the junctions
thereof.
[0072] In addition, usage of tin-zinc-nickel type solder that does
not contain harmful materials such as lead as the solder chip to be
inserted into the interior of each electrode for connection with
the fuse line, not only prevents adverse influence on the
environment and human health and also adverse influence on other
electronic components to be mounted together with the current fuse,
but also allows to maintain the internal condition of the current
fuse even if overheated when the fuse is mounted on the printed
circuit board.
[0073] Furthermore, addition of aluminum as a solder alloy material
improves heat resistance and fluidity of solder, resulting in
improvement of solderability, and prevention of change in the shape
of the solder joint due to reheating.
[0074] In addition, the fuse according to the embodiment allows a
sufficient joint between the electrode and the fuse wire by heating
the electrode at a temperature of 350 degrees C. As a result,
soldering is completed at a temperature less than the liquid phase
temperature even with consideration for heat radiation from the
ceramic substrate. Accordingly, soldering is possible even in a
solid-liquid coexistence state at a temperature between the solid
phase temperature and the liquid phase temperature, thereby
preventing degradation of plating on the surface of the
electrode.
[0075] Unavoidable impurities specified by Japanese Industrial
Standards (JIS) may be included in the composition of the lead-free
solder described above. However, even the case of such unavoidable
impurities being contained in the lead-free solder does not depart
from the scope of the appended claims of the present invention.
[0076] As described above, the present invention provides a current
fuse, which does not have an adverse influence on the environment
due to harmful materials, and has excellent characteristics such as
solderability on a printed circuit board, and a method of making
the same.
[0077] While the invention has been described with reference to
particular embodiments, further modifications and improvements
which will occur to those skilled in the art, may be made within
the purview of the appended claims, without departing from the
scope of the invention in its broader aspect.
* * * * *