U.S. patent application number 10/656731 was filed with the patent office on 2004-09-23 for alloy type thermal fuse and material for a thermal fuse element.
This patent application is currently assigned to Uchihashi Estec Co., Ltd.. Invention is credited to Tanaka, Yoshiaki.
Application Number | 20040184947 10/656731 |
Document ID | / |
Family ID | 32322133 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040184947 |
Kind Code |
A1 |
Tanaka, Yoshiaki |
September 23, 2004 |
Alloy type thermal fuse and material for a thermal fuse element
Abstract
An alloy type thermal fuse of an operating temperature of 75 to
120.degree. C. is provided in which a fuse element of a Bi--In--Sn
alloy is used, excellent aging and heat cycle resistances for a
long term can be ensured, and satisfactory operating characteristic
can be ensured. A material for a thermal fuse element has an alloy
composition in which In is 15% or larger and smaller than 37%, Sn
is 5% or larger and 28% or smaller, and balance Bi, and in which,
with respect to each of reference points of ternary Bi--In--Sn
eutectic points of 57.5% Bi-25.2% In-17.3% Sn and 54.0% Bi-29.7%
In-16.3% Sn, a range of .+-.2% Bi, .+-.1% In, and .+-.1% Sn is
excluded.
Inventors: |
Tanaka, Yoshiaki; (Osaka,
JP) |
Correspondence
Address: |
AKIN GUMP STRAUSS HAUER & FELD L.L.P.
ONE COMMERCE SQUARE
2005 MARKET STREET, SUITE 2200
PHILADELPHIA
PA
19103-7013
US
|
Assignee: |
Uchihashi Estec Co., Ltd.
|
Family ID: |
32322133 |
Appl. No.: |
10/656731 |
Filed: |
September 4, 2003 |
Current U.S.
Class: |
420/577 |
Current CPC
Class: |
H01H 37/761 20130101;
C22C 12/00 20130101; H01H 2037/768 20130101 |
Class at
Publication: |
420/577 |
International
Class: |
C22C 012/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2002 |
JP |
P2002-361701 |
Claims
What is claimed is:
1. A material for a thermal fuse element wherein said material has
an alloy composition in which In is 15% or larger and smaller than
37%, Sn is 5% or larger and 28% or smaller, and balance Bi, and in
which, with respect to each of reference points of ternary
Bi--In--Sn eutectic points of 57.5% Bi-25.2% In-17.3% Sn and 54.0%
Bi-29.7% In-16.3% Sn, a range of .+-.2% Bi, +1% In, and .+-.1% Sn
is excluded.
2. A material for a thermal fuse element wherein 0.1 to 3.5 weight
parts of one, or two or more elements selected from the group
consisting of Ag, Au, Cu, Ni, Pd, Pt, Sb, Ga, and Ge are added to
100 weight parts of an alloy composition of claim 1.
3. An alloy type thermal fuse wherein a material for a thermal fuse
element of claim 1 is used as a fuse element.
4. An alloy type thermal fuse wherein a material for a thermal fuse
element of claim 2 is used as a fuse element.
5. An alloy type thermal fuse according to claim 3, wherein said
fuse element contains inevitable impurities.
6. An alloy type thermal fuse according to claim 4, wherein said
fuse element contains inevitable impurities.
7. An alloy type thermal fuse according to claim 3, wherein said
fuse element is connected between lead conductors, and at least a
portion of each of said lead conductors which is bonded to said
fuse element is covered with a Sn or Ag film.
8. An alloy type thermal fuse according to claim 4, wherein said
fuse element is connected between lead conductors, and at least a
portion of each of said lead conductors which is bonded to said
fuse element is covered with a Sn or Ag film.
9. An alloy type thermal fuse according to claim 5, wherein said
fuse element is connected between lead conductors, and at least a
portion of each of said lead conductors which is bonded to said
fuse element is covered with a Sn or Ag film.
10. An alloy type thermal fuse according to claim 6, wherein said
fuse element is connected between lead conductors, and at least a
portion of each of said lead conductors which is bonded to said
fuse element is covered with a Sn or Ag film.
11. An alloy type thermal fuse according to claim 3, wherein a pair
of film electrodes are formed on a substrate by printing conductive
paste containing metal particles and a binder, said fuse element is
connected between said film electrodes, and said metal particles
are made of a material selected from the group consisting of Ag,
Ag-Pd, Ag-Pt, Au, Ni, and Cu.
12. An alloy type thermal fuse according to claim 4, wherein a pair
of film electrodes are formed on a substrate by printing conductive
paste containing metal particles and a binder, said fuse element is
connected between said film electrodes, and said metal particles
are made of a material selected from the group consisting of Ag,
Ag-Pd, Ag-Pt, Au, Ni, and Cu.
13. An alloy type thermal fuse according to claim 5, wherein a pair
of film electrodes are formed on a substrate by printing conductive
paste containing metal particles and a binder, said fuse element is
connected between said film electrodes, and said metal particles
are made of a material selected from the group consisting of Ag,
Ag--Pd, Ag--Pt, Au, Ni, and Cu.
14. An alloy type thermal fuse according to claim 6, wherein a pair
of film electrodes are formed on a substrate by printing conductive
paste containing metal particles and a binder, said fuse element is
connected between said film electrodes, and said metal particles
are made of a material selected from the group consisting of Ag,
Ag-Pd, Ag-Pt, Au, Ni, and Cu.
15. An alloy type thermal fuse according to claim 3, wherein a
heating element for fusing off said fuse element is additionally
disposed.
16. An alloy type thermal fuse according to claim 4, wherein a
heating element for fusing off said fuse element is additionally
disposed.
17. An alloy type thermal fuse according to claim 5, wherein a
heating element for fusing off said fuse element is additionally
disposed.
18. An alloy type thermal fuse according to claim 6, wherein a
heating element for fusing off said fuse element is additionally
disposed.
19. An alloy type thermal fuse according to claim 7, wherein a
heating element for fusing off said fuse element is additionally
disposed.
20. An alloy type thermal fuse according to claim 8, wherein a
heating element for fusing off said fuse element is additionally
disposed.
21. An alloy type thermal fuse according to claim 9, wherein a
heating element for fusing off said fuse element is additionally
disposed.
22. An alloy type thermal fuse according to claim 10, wherein a
heating element for fusing off said fuse element is additionally
disposed.
23. An alloy type thermal fuse according to claim 11, wherein a
heating element for fusing off said fuse element is additionally
disposed.
24. An alloy type thermal fuse according to claim 12, wherein a
heating element for fusing off said fuse element is additionally
disposed.
25. An alloy type thermal fuse according to claim 13, wherein a
heating element for fusing off said fuse element is additionally
disposed.
26. An alloy type thermal fuse according to claim 14, wherein a
heating element for fusing off said fuse element is additionally
disposed.
27. An alloy type thermal fuse according to claim 3, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
28. An alloy type thermal fuse according to claim 4, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
29. An alloy type thermal fuse according to claim 5, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
30. An alloy type thermal fuse according to claim 6, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
31. An alloy type thermal fuse according to claim 7, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
32. An alloy type thermal fuse according to claim 8, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
33. An alloy type thermal fuse according to claim 9, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
34. An alloy type thermal fuse according to claim 10, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
35. An alloy type thermal fuse according to claim 11, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
36. An alloy type thermal fuse according to claim 12, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
37. An alloy type thermal fuse according to claim 13, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
38. An alloy type thermal fuse according to claim 14, wherein said
fuse element connected between a pair of lead conductors is
sandwiched between insulating films.
39. An alloy type thermal fuse according to claim 3, wherein a pair
of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
40. An alloy type thermal fuse according to claim 4, wherein a pair
of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
41. An alloy type thermal fuse according to claim 5, wherein a pair
of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
42. An alloy type thermal fuse according to claim 6, wherein a pair
of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
43. An alloy type thermal fuse according to claim 7, wherein a pair
of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
44. An alloy type thermal fuse according to claim 8, wherein a pair
of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
45. An alloy type thermal fuse according to claim 9, wherein a pair
of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
46. An alloy type thermal fuse according to claim 10, wherein a
pair of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
47. An alloy type thermal fuse according to claim 11, wherein a
pair of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
48. An alloy type thermal fuse according to claim 12, wherein a
pair of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
49. An alloy type thermal fuse according to claim 13, wherein a
pair of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
50. An alloy type thermal fuse according to claim 14, wherein a
pair of lead conductors are partly exposed from one face of an
insulating plate to another face, said fuse element is connected to
said lead conductor exposed portions, and said other face of said
insulating plate is covered with an insulating material.
51. An alloy type thermal fuse according to claim 3, wherein lead
conductors are bonded to ends of said fuse element, respectively, a
flux is applied to said fuse element, said flux-applied fuse
element is passed through a cylindrical case, gaps between ends of
said cylindrical case and said lead conductors are sealingly
closed, ends of said lead conductors have a disk-like shape, and
ends of said fuse element are bonded to front faces of said
disks.
52. An alloy type thermal fuse according to claim 4, wherein lead
conductors are bonded to ends of said fuse element, respectively, a
flux is applied to said fuse element, said flux-applied fuse
element is passed through a cylindrical case, gaps between ends of
said cylindrical case and said lead conductors are sealingly
closed, ends of said lead conductors have a disk-like shape, and
ends of said fuse element are bonded to front faces of said
disks.
53. An alloy type thermal fuse according to claim 5, wherein lead
conductors are bonded to ends of said fuse element, respectively, a
flux is applied to said fuse element, said flux-applied fuse
element is passed through a cylindrical case, gaps between ends of
said cylindrical case and said lead conductors are sealingly
closed, ends of said lead conductors have a disk-like shape, and
ends of said fuse element are bonded to front faces of said
disks.
54. An alloy type thermal fuse according to claim 6, wherein lead
conductors are bonded to ends of said fuse element, respectively, a
flux is applied to said fuse element, said flux-applied fuse
element is passed through a cylindrical case, gaps between ends of
said cylindrical case and said lead conductors are sealingly
closed, ends of said lead conductors have a disk-like shape, and
ends of said fuse element are bonded to front faces of said
disks.
55. An alloy type thermal fuse according to claim 7, wherein lead
conductors are bonded to ends of said fuse element, respectively, a
flux is applied to said fuse element, said flux-applied fuse
element is passed through a cylindrical case, gaps between ends of
said cylindrical case and said lead conductors are sealingly
closed, ends of said lead conductors have a disk-like shape, and
ends of said fuse element are bonded to front faces of said
disks.
56. An alloy type thermal fuse according to claim 8, wherein lead
conductors are bonded to ends of said fuse element, respectively, a
flux is applied to said fuse element, said flux-applied fuse
element is passed through a cylindrical case, gaps between ends of
said cylindrical case and said lead conductors are sealingly
closed, ends of said lead conductors have a disk-like shape, and
ends of said fuse element are bonded to front faces of said
disks.
57. An alloy type thermal fuse according to claim 9, wherein lead
conductors are bonded to ends of said fuse element, respectively, a
flux is applied to said fuse element, said flux-applied fuse
element is passed through a cylindrical case, gaps between ends of
said cylindrical case and said lead conductors are sealingly
closed, ends of said lead conductors have a disk-like shape, and
ends of said fuse element are bonded to front faces of said
disks.
58. An alloy type thermal fuse according to claim 10, wherein lead
conductors are bonded to ends of said fuse element, respectively, a
flux is applied to said fuse element, said flux-applied fuse
element is passed through a cylindrical case, gaps between ends of
said cylindrical case and said lead conductors are sealingly
closed, ends of said lead conductors have a disk-like shape, and
ends of said fuse element are bonded to front faces of said disks.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a material for a Bi--In--Sn
alloy type thermal fuse in which the operating temperature belongs
to a range of 75 to 120.degree. C., and also to such a thermal type
fuse element.
[0003] An alloy type thermal fuse is widely used as a
thermo-protector for an electrical appliance, a circuit element, or
the like.
[0004] Such an alloy type thermal fuse has a configuration in which
an alloy of a predetermined melting point is used as a fuse
element, the fuse element is bonded between a pair of lead
conductors, a flux is applied to the fuse element, and the
flux-applied fuse element is sealed by an insulator.
[0005] The alloy type thermal fuse has the following operation
mechanism.
[0006] The alloy type thermal fuse is disposed so as to thermally
contact an electrical appliance or a circuit element which is to be
protected. When the electrical appliance or the circuit element is
caused to generate heat by any abnormality, the fuse element alloy
of the thermal fuse is melted by the generated heat, and the molten
alloy is divided and spheroidized because of the wettability with
respect to the lead conductors or electrodes under the coexistence
with the activated flux that has already melted. The power supply
is finally interrupted as a result of advancement of the spheroid
division. The temperature of the appliance is lowered by the power
supply interruption, and the divided molten alloys are solidified,
whereby the non-return cut-off operation is completed.
[0007] 2. Description of the Prior Art
[0008] Conventionally, a technique in which an alloy composition
having a narrow solid-liquid coexisting region between the solidus
and liquidus temperatures, and ideally a eutectic composition is
used as such a fuse element is usually employed, so that the fuse
element is fused off at approximately the liquidus temperature (in
a eutectic composition, the solidus temperature is equal to the
liquidus temperature). In a fuse element having an alloy
composition in which there is a solid-liquid coexisting region,
namely, there is the possibility that the fuse element is fused off
at an uncertain temperature in the solid-liquid coexisting region.
When an alloy composition has a wide solid-liquid coexisting
region, the uncertain temperature width in which a fuse element is
fused off in the solid-liquid coexisting region becomes large, and
the operating temperature is largely dispersed. In order to reduce
the dispersion, therefore, the technique in which an alloy
composition having a narrow solid-liquid coexisting region between
the solidus and liquidus temperatures, or ideally a eutectic
composition is used is usually employed.
[0009] In a high-energy density secondary battery which is
generally used as a power source of a portable telephone, a
notebook personal computer, or a like portable electronic
apparatus, such as a lithium-ion battery or a lithium polymer
battery, a large amount of heat is generated in an abnormal state.
Therefore, a thermal fuse is attached to a battery pack, and, when
a battery reaches a dangerous temperature, the thermal fuse
operates to prevent abnormal heat generation from occurring. The
operating temperature of such a thermal fuse is set to be within a
range of 75 to 120.degree. C.
[0010] Because of increased awareness of environment conservation,
the trend to prohibit the use of materials harmful to a living body
is recently growing, and also an element for such a thermal fuse is
strongly requested not to contain a harmful element (Pb, Cd, Hg,
Tl, etc.).
[0011] As an alloy composition which can satisfy the requirement,
known is a Bi--In--Sn system. Conventionally, the following thermal
fuses which have an alloy composition of Bi--In--Sn, and which
satisfy the requirement of an operating temperature of 75 to
120.degree. C. are known: a thermal fuse in which a fuse element
has an alloy composition of 47 to 49% Sn, 51 to 53% In, and an
adequate amount of Bi, and which has an operating temperature of
105 to 115.degree. C. (Japanese Patent Application Laying-Open No.
56-114237); that in which a fuse element has an alloy composition
of 42 to 53% In, 40 to 46% Sn, and 7 to 12% Bi, and which has an
operating temperature of 95 to 105.degree. C. (Japanese Patent
Application Laying-Open No. 2001-266724); that in which a fuse
element has an alloy composition of 51 to 53% In, 42 to 44% Sn, and
4 to 6% Bi, and which has an operating temperature of 107 to
113.degree. C. (Japanese Patent Application Laying-Open No.
59-8229); that in which a fuse element has an alloy composition of
1 to 15% Sn, 20 to 33% Bi, and the balance In, and which has an
operating temperature of 75 to 100.degree. C. (Japanese Patent
Application Laying-Open No. 2001-325867); and that in which a fuse
element has an alloy composition of 0.3 to 1.5% Sn, 51 to 54% In,
and the balance Bi, and which has an operating temperature of 86 to
89.degree. C. (Japanese Patent Application Laying-Open No.
6-325670). Furthermore, a thermal fuse is known in which a fuse
element has an alloy composition of a Bi--In system not containing
Sn and of 45 to 55% Bi and the balance In, and which has an
operating temperature of 85 to 95.degree. C. (Japanese Patent
Application Laying-Open No. 2002-150906). Moreover, an In--Sn
eutectic alloy (52% In, 48% Sn) having a melting point of
119.degree. C. may be contemplated to be used as a fuse
element.
[0012] In view of increased power consumption and high capacity of
a battery due to enhanced functions of an electrical appliance, and
legislated product liability, also a thermal fuse is recently
requested to exhibit, for example, aging resistance and heat cycle
resistance for a long term, or to have high reliability. In the
above-mentioned conventional art examples, In which is a highly
reactive element is contained at a large amount or 50% or more.
When the fuse element is subjected particularly to long-term aging,
therefore, In in the surface of a fuse element reacts with a flux
to produce an In salt, and the rate of incorporation into the flux
is increased, so that the alloy composition of the fuse element is
changed in the direction of reduction of In. As a result, the
variation of the alloy composition shifts the operating
temperature, or increases the resistance of the fuse element,
thereby causing reduction of the operating temperature due to
self-heating. Furthermore, the function of the flux is reduced, and
the operation characteristic of the thermal fuse is inevitably
impaired. Therefore, the long-term aging resistance which is
requested in a thermal fuse is hardly ensured.
[0013] The aging resistance is requested to be set so that the
resistance of a fuse element is not largely changed or a thermal
fuse does not malfunction even when no-load, rated-load, and
humidified conditions are continued for a long term under an
environment of a high temperature such as the holding temperature
(which is the maximum holding temperature where the fuse does not
operate even when a rated current that is obliged to be set by the
safety standard is continued to be supplied for 168 hours, and
which is usually set to a temperature that is lower than the
operating temperature by 20.degree. C.). The conventional art
examples hardly adapt to the long-term aging resistance.
[0014] As a Bi--In--Sn eutectic alloy which can satisfy the
requirement of an operating temperature of 75 to 120.degree. C.,
and in which the weight of In is considerably smaller than 50%,
there are 79.degree. C.-eutectic (57.5% Bi, 25.2% In, and 17.3% Sn)
and 81.degree. C.-eutectic (54.0% Bi, 29.7% In, and 16.3% Sn). In
79.degree. C.-eutectic, as apparent from FIG. 12 showing a result
of a differential scanning calorimetry analysis [which is called a
DSC, and in which a reference specimen (unchanged) and a
measurement specimen are housed in an N.sub.2 gas-filled vessel, an
electric power is supplied to a heater of the vessel to heat the
samples at a constant rate, and a variation of the heat energy
input amount due to a state change of the measurement specimen is
detected by a differential thermocouple], however, solid phase
transformation occurs in a temperature zone of about 52 to
58.degree. C. which is considerably lower than the melting point.
In 81.degree. C.-eutectic, as apparent from FIG. 13 showing a
result of a differential scanning calorimetry analysis, solid phase
transformation occurs in a temperature zone of about 51 to
57.degree. C. which is considerably lower than the melting point.
As a result of a thermal hysteresis straddling the transformation
temperature zone, a fuse element receives repetitive distortion to
produce the possibility that the operating temperature is lowered
by an increased resistance or the fuse element is broken so as not
to operate. Therefore, the long-term heat cycle characteristic
which is requested in a thermal fuse is hardly ensured.
[0015] The long-term heat cycle characteristic is requested to be
set so that, even when a thermal fuse is subjected to a thermal
hysteresis between a high temperature (usually, the above-mentioned
holding temperature) which is lower than the operating temperature
and the room temperature or a below-freezing temperature (for
example, -40.degree. C.), the resistance of a fuse element is not
changed or a thermal fuse does not malfunction. However, the
79.degree. C.- and 81.degree. C.-eutectics hardly adapt to the
long-term heat cycle resistance.
[0016] The melting characteristic of an alloy can be obtained by a
DSC measurement. The inventor measured and eagerly studied DSCs of
Bi--In--Sn alloys of various compositions, and found that,
depending on the composition, the DSCs show melting characteristics
of the patterns such as shown in (A) to (D) of FIG. 14, and, when a
Bi--In--Sn alloy of the melt pattern of (A) of FIG. 14 is used as
fuse elements, the fuse elements can be concentrically fused off in
the vicinity of the maximum endothermic peak.
[0017] The pattern of (A) of FIG. 14 will be described. At the
solidus temperature a, an alloy starts to be liquefied (melted). In
accordance with progress of the liquidification, the absorption
amount of heat energy is increased, and reaches the maximum at a
peak p. After passing the point, the absorption amount of heat
energy is gradually reduced, and becomes zero at the liquidus
temperature b, thereby completing the liquidification. Thereafter,
the temperature is raised in the state of the liquid phase.
[0018] The reason why a division operation of the fuse element
occurs in the vicinity of the maximum endothermic peak p is
estimated as follows. In a BiIn--Sn composition showing such a
melting characteristic, all constituting elements have excellent
wettability so as to exhibit excellent wettability even in the
solid-liquid coexisting region in the vicinity of the maximum
endothermic peak p in which the liquid phase state has not yet been
completely established. Therefore, spheroid division occurs before
a state exceeding the solid-liquid coexisting region is
attained.
[0019] In FIG. 14, (B) shows the melt pattern of a eutectic
composition or a composition in the vicinity of the eutectic. In
the pattern, the solid-liquid coexisting region is zero or very
narrow.
[0020] In the melt pattern of (C) of FIG. 14 among (C) and (D) of
FIG. 14, the heat energy is slowly absorbed, and the wettability is
not suddenly changed. Therefore, the point of a division operation
of the fuse element is not deter-mined in a narrow range. In the
melt pattern of (D) of FIG. 14, there are plural endothermic peaks.
At any one of the endothermic peaks, a division operation of the
fuse element may probably occur. In both (C) and (D) of FIG. 14,
therefore, the point of a division operation of the fuse element
cannot be concentrated into a narrow range.
[0021] From the result of the above consideration, the followings
are effective for obtaining an environment adaptive alloy type
thermal fuse in which an excellent operation characteristic can be
ensured at an operating temperature of 75 to 120.degree. C. Because
of the unadaptability to the long-term heat cycle resistance,
Bi--In--Sn eutectic alloys of 79.degree. C.-eutectic (57.5% Bi,
25.2% In, and 17.3% Sn), and 81.degree. C.-eutectic (54.0% Bi,
29.7% In, and 16.3% Sn), and those in the range adjacent to the
compositions are excluded. Because of the long-term aging
resistance, furthermore, the amount of In is restricted, the
operating temperature of 75 to 120.degree. C. is satisfied, and the
melt pattern fulfills that of (A) of FIG. 14 or approaches that of
(B) of FIG. 14.
SUMMARY OF THE INVENTION
[0022] It is an object of the invention to, based on the
consideration result, provide an alloy type thermal fuse of an
operating temperature of 75 to 120.degree. C. in which a fuse
element of a Bi--In--Sn alloy is used, which exhibits excellent
heat cycle and aging resistances for a long term, and in which
satisfactory operating characteristic can be ensured.
[0023] It is a further object of the invention to thin a fuse
element to reduce the size and thickness of an alloy type thermal
fuse.
[0024] The material for a thermal fuse element of a first aspect of
the invention has an alloy composition in which In is 15% or larger
and smaller than 37%, Sn is 5% or larger and 28% or smaller, and
balance Bi, and in which, with respect to each of reference points
of ternary Bi--In--Sn eutectic points of 57.5% Bi-25.2% In-17.3% Sn
and 54.0% Bi-29.7% In-16.3% Sn, a range of .+-.2% Bi, .+-.1% In,
and .+-.1% Sn is excluded.
[0025] In the material for a thermal fuse element of a second
aspect of the invention, 0.1 to 3.5 weight parts of one, or two or
more elements selected from the group consisting of Ag, Au, Cu, Ni,
Pd, Pt, Sb, Ga, and Ge are added to 100 weight parts of the alloy
composition of the first aspect of the invention.
[0026] The materials for a thermal fuse element are allowed to
contain inevitable impurities which are produced in productions of
metals of raw materials and also in melting and stirring of the raw
materials, and which exist in an amount that does not substantially
affect the characteristics. In the alloy type thermal fuses, a
minute amount of a metal material or a metal film material of the
lead conductors or the film electrodes is caused to inevitably
migrate into the fuse element by solid phase diffusion, and, when
the characteristics are not substantially affected, allowed to
exist as inevitable impurities.
[0027] In the alloy type thermal fuse of a third aspect of the
invention, the material for a thermal fuse element of the first or
second aspect of the invention is used as a fuse element.
[0028] The alloy type thermal fuse of a fourth aspect of the
invention is characterized in that, in the alloy type thermal fuse
of the third aspect of the invention, the fuse element contains
inevitable impurities.
[0029] The alloy type thermal fuse of a fifth aspect of the
invention is an alloy type thermal fuse in which, in the alloy type
thermal fuse of the third or fourth aspect of the invention, the
fuse element is connected between lead conductors, and at least a
portion of each of the lead conductors which is bonded to the fuse
element is covered with a Sn or Ag film.
[0030] The alloy type thermal fuse of a sixth aspect of the
invention is an alloy type thermal fuse in which, in the alloy type
thermal fuse of the third or fourth aspect of the invention, a pair
of film electrodes are formed on a substrate by printing conductive
paste containing metal particles and a binder, the fuse element is
connected between the film electrodes, and the metal particles are
made of a material selected from the group consisting of Ag,
Ag--Pd, Ag--Pt, Au, Ni, and Cu.
[0031] The alloy type thermal fuse of a seventh aspect of the
invention is an alloy type thermal fuse in which, in the alloy type
thermal fuse of any one of the third to sixth aspects of the
invention, a heating element for fusing off the fuse element is
additionally disposed.
[0032] The alloy type thermal fuse of an eighth aspect of the
invention is an alloy type thermal fuse in which, in the alloy type
thermal fuse of any one of the third to sixth aspects of the
invention, the fuse element connected between a pair of lead
conductors is sandwiched between insulating films.
[0033] The alloy type thermal fuse of a ninth aspect of the
invention is an alloy type thermal fuse in which, in the alloy type
thermal fuse of any one of the third to sixth aspects of the
invention, a pair of lead conductors are partly exposed from one
face of an insulating plate to another face, the fuse element is
connected to the lead conductor exposed portions, and the other
face of the insulating plate is covered with an insulating
material.
[0034] The alloy type thermal fuse of a tenth aspect of the
invention is an alloy type thermal fuse in which, in the alloy type
thermal fuse of any one of the third to fifth aspects of the
invention, lead conductors are bonded to ends of the fuse element,
respectively, a flux is applied to the fuse element, the
flux-applied fuse element is passed through a cylindrical case,
gaps between ends of the cylindrical case and the lead conductors
are sealingly closed, ends of the lead conductors have a disk-like
shape, and ends of the fuse element are bonded to front faces of
the disks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a view showing an example of the alloy type
thermal fuse of the invention;
[0036] FIG. 2 is a view showing another example of the alloy type
thermal fuse of the invention;
[0037] FIG. 3 is a view showing a further example of the alloy type
thermal fuse of the invention;
[0038] FIG. 4 is a view showing a still further example of the
alloy type thermal fuse of the invention;
[0039] FIG. 5 is a view showing a still further example of the
alloy type thermal fuse of the invention;
[0040] FIG. 6 is a view showing a still further example of the
alloy type thermal fuse of the invention;
[0041] FIG. 7 is a view showing a still further example of the
alloy type thermal fuse of the invention;
[0042] FIG. 8 is a view showing an alloy type thermal fuse of the
cylindrical case type and its operation state;
[0043] FIG. 9 is a view showing a still further example of the
alloy type thermal fuse of the invention;
[0044] FIG. 10 is a view showing a result of a DSC measurement of a
fuse element of Example 1;
[0045] FIG. 11 is a view showing a result of a DSC measurement of a
fuse element of Example 2;
[0046] FIG. 12 is a view showing a result of a DSC measurement of a
79.degree. C. ternary Bi--In--Sn eutectic alloy;
[0047] FIG. 13 is a view showing a result of a DSC measurement of
an 81.degree. C. ternary Bi--In--Sn eutectic alloy; and
[0048] FIG. 14 is a view showing various melt patterns of a ternary
Sn--In--Bi alloy.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] In the invention, a fuse element of a circular wire or a
flat wire is used. The outer diameter or the thickness is set to
100 to 800 .mu.m, preferably, 300 to 600 .mu.m.
[0050] The reasons why, in the first aspect of the invention, a
thermal fuse element has an alloy composition in which In is 15% or
larger and smaller than 37%, Sn is 5% or larger and 28% or smaller,
and balance Bi, and in which, with respect to each of reference
points of 79.degree. C. ternary Bi--In--Sn eutectic point of 57.5%
Bi-25.2% In-17.3% Sn and 81.degree. C. ternary Bi--In--Sn eutectic
point of 54.0% Bi-29.7% In-16.3% Sn, a range of .+-.2% Bi, .+-.1%
In, and .+-.1% Sn is excluded (namely, the range of
55.5%.ltoreq.Bi.ltoreq.59.5%, 24.2%.ltoreq.In.ltoreq.26.2%, and
16.3%.ltoreq.Sn.ltoreq.18.3%, and that of 52%<Bi.ltoreq.56%,
28.7%.ltoreq.In.ltoreq.30.7%, and 15.3%.ltoreq.Sn.ltoreq.17.3% are
excluded) are as follows. In order to use a Bi--In--Sn alloy
because of the adaptability to the environment, and satisfy the
requirement that the alloy type thermal fuse has an operating
temperature of 75 to 120.degree. C., the following points are
satisfied with respect to the reference points of 79.degree.
C.-eutectic and 81.degree. C.-eutectic: (i) the two eutectic points
and the ranges adjacent to the eutectic points are excluded in
order to eliminate solid phase transformation appearing in the
eutectics; (ii) the amount of In is reduced in order to prevent In
which is highly reactive, from reacting with a flux in the surface
of the fuse element to be reduced, and reactive groups of the flux
from forming an In salt; and (iii) although the composition shows a
melt pattern having a wide solid-liquid coexisting region which is
considerably separated from the eutectic points, the alloy
composition exhibits a single maximum endothermic peak such as
shown in (A) of FIG. 14 (according to the alloy composition,
namely, the fuse element can operate in a concentrated temperature
zone, and dispersion of the operating temperature can be set to be
within an allowable range), and the maximum endothermic peak
satisfies the requirement of an operating temperature of 75 to
120.degree. C.
[0051] In the above, in interface zones respectively adjacent to
the eutectic points in the remaining region excluding the range of
.+-.2% Bi, .+-.1% In, and +1% Sn with respect to each of the
79.degree. C. ternary Bi--In--Sn eutectic point and the 81.degree.
C. ternary Bi--In--Sn eutectic point, the melting point is close to
the melting points of the eutectics (79 to 81.degree. C.), and also
the DSC melt pattern is close to the melt patterns of the
79.degree. C. ternary Bi--In--Sn eutectic and 81.degree. C. ternary
Bi--In--Sn eutectic. Therefore, requirement (iii) is satisfied. In
addition, solid phase transformation in a range which is lower than
the melting point can be eliminated, and hence requirement (i) is
satisfied. Since the amount of In is small, also requirement (ii)
is satisfied.
[0052] Each of the aboves will be further described.
[0053] (1) From a result of a DSC measurement of a 79.degree. C.
ternary Bi--In--Sn eutectic alloy shown in FIG. 12 and that of a
DSC measurement of an 81.degree. C. ternary Bi--In--Sn eutectic
alloy shown in FIG. 13, it is seen that the absorption amount of
heat energy is sharply changed in the vicinity of the melting point
because the solid phase is suddenly changed to the liquid phase,
and, in the temperature zones of about 52 to 58.degree. C. and
about 51 to 57.degree. C. which are lower than the melting point,
the heat energy is absorbed and transformation occurs while
maintaining the solid phase state. In the solid phase
transformation, distortion is generated in accordance with a change
of the phase state, and hence stress is produced in the fuse
element ends of which are fixed to lead conductors or electrodes. A
thermal fuse is exposed to a heat cycle at a temperature which is
lower than the operating temperature. As described above, a thermal
fuse is requested to have predetermined heat cycle resistance, and
to pass a heat cycle test in which one cycle is set to be between
the normal temperature (the operating temperature -20.degree. C.)
and the room temperature or a below-freezing temperature (usually,
-40.degree. C.). In the case of an operating temperature of 75 to
120.degree. C., one cycle is set to be between (55 to 100.degree.
C.) and -40.degree. C., and the solid phase transformation zones
(52 to 58.degree. C.) and (51 to 57.degree. C.) overlap with the
cycle. Therefore, stress due to solid phase transformation is
repetitively applied to the fuse element. When this state continues
for a long period, a remarkable change of the resistance, breakage,
or a malfunction is caused.
[0054] In the invention, therefore, the range of .+-.2% Bi, .+-.1%
In, and .+-.1% Sn with respect to each of the 79.degree. C. ternary
Bi--In--Sn eutectic point and the 81.degree. C. ternary Bi--In--Sn
eutectic point is excluded.
[0055] (2) In is more highly reactive than Bi and Sn, and reacts in
the surface of a fuse element with reactive groups of the flux to
produce an In salt. When the production rate is high, shift or
impairment of the melting characteristic of the fuse element due to
the reduced amount of In, and reduction of the activity of the flux
remarkably occur to impair the characteristics of the thermal fuse.
In a thermal fuse, it is requested to evaluate the aging
resistance, so that abnormality does not occur even when load,
no-load, and humidified conditions are continued for a long term
under an environment of a high temperature such as the holding
temperature. Because of the impairment of the characteristics of
the thermal fuse due to the reaction of In, however, it is very
difficult to maintain the operation stability for a long
period.
[0056] In the invention, therefore, the amount of In is set to be
smaller than that in Patent literatures 1 to 6 above or to be
smaller than 37%. In this case, since the range of In smaller than
15% is excluded, the requirement of an operating temperature of 75
to 120.degree. C. is satisfied, and thinning to 300 .mu.m.phi. can
be performed with a high yield.
[0057] (3) In Bi--In--Sn alloys, there is an alloy having a melt
pattern in which, even when deviated from a eutectic point or a
eutectic line, or when the solid-liquid coexisting region is
widened, the maximum endothermic peak is at one point in the wide
solid-liquid coexisting region as shown in (A) of FIG. 14. In such
an alloy, in the endothermic behavior in the melting process, the
heat absorption amount difference at the maximum endothermic peak
is very larger than that in another portion of the endothermic
process, and all constituting elements have excellent wettability.
Therefore, the wettability of the solid-liquid coexisting region at
the maximum endothermic peak is sufficiently improved even before
the completion of the liquidification, so that spheroid division of
the thermal fuse element can be performed in the vicinity of the
maximum endothermic peak.
[0058] In the invention, therefore, Sn is set to 5 to 28% so that,
although deviated from the 79.degree. C. ternary Bi--In--Sn
eutectic point and the 81.degree. C. ternary Bi--In--Sn eutectic
point, the operating temperature is set to the range of 75 to
120.degree. C. with dispersion of an allowable range (.+-.5.degree.
C.).
[0059] In the first aspect of the invention, one of the reference
alloy compositions is that In is 25%, Sn is 20%, and a balance is
Bi. The liquidus temperature is about 84.degree. C., the solidus
temperature is about 80.degree. C., a result of a DSC measurement
at a temperature rise rate of 5.degree. C./min. is shown in FIG.
10, and the maximum endothermic peak is at about 82.degree. C.
[0060] The other reference composition is that In is 30%, Sn is
15%, and a balance is Bi. The liquidus temperature is about
86.degree. C., the solidus temperature is about 81.degree. C., a
result of a DSC measurement at a temperature rise rate of 5.degree.
C./min. is shown in FIG. 11, and the maximum endothermic peak is at
about 82.degree. C.
[0061] In both the measurement results, an endothermic reaction is
not observed in a temperature region which is lower than the
melting points observed in the DSC measurement result of the
79.degree. C. ternary Bi--In--Sn eutectic alloy shown in FIG. 12
and that of the 81.degree. C. ternary Bi--In--Sn eutectic alloy
shown in FIG. 13, and there is no solid phase transformation which
may cause a serious problem.
[0062] In the invention, 0.1 to 3.5 weight parts of one, or two or
more elements selected from the group consisting of Ag, Au, Cu, Ni,
Pd, Pt, Sb, Ga, and Ge are added to 100 weight parts of the alloy
composition, in order to reduce the specific resistance of the
alloy and improve the mechanical strength. When the addition amount
is smaller than 0.1 weight parts, the effects cannot be
sufficiently attained, and, when the addition amount is larger than
3.5 weight parts, the above-mentioned melting characteristic is
hardly maintained.
[0063] With respect to a drawing process, further enhanced strength
and ductility are provided so that drawing into a thin wire of 100
to 300 .mu.m.phi. can be easily conducted. In the case where the
cohesive force of a fuse element alloy is considerably enhanced by
the inclusion of In, even when a fuse element is insufficiently
welded or bonded to lead conductors or the like, a superficial
appearance in which the element is bonded is produced. The addition
of the element(s) can reduce the cohesive force, so that this
defect can be eliminated, and the accuracy of the acceptance
criterion in a test after welding can be improved.
[0064] It is known that a to-be-bonded material such as a metal
material of the lead conductors, a thin-film material, or a
particulate metal material in the film electrode migrates into the
fuse element by solid phase diffusion. When the same element as the
to-be-bonded material, such as Ag, Au, Cu, or Ni is previously
added to the fuse element, the migration can be suppressed.
Therefore, an influence of the to-be-bonded material which may
originally affect the characteristics (for example, Ag, Au, or the
like causes local reduction or dispersion of the operating
temperature due to the lowered melting point, and Cu, Ni, or the
like causes dispersion of the operating temperature or an operation
failure due to an increased intermetallic compound layer formed in
the interface between different phases) is eliminated, and the
thermal fuse can be assured to normally operate, without impairing
the function of the fuse element.
[0065] The fuse element of the alloy type thermal fuse of the
invention can be usually produced by a method in which a billet is
produced, the billet is shaped into a stock wire by an extruder,
and the stock wire is drawn by a dice to a wire. The outer diameter
is 100 to 800 .mu.m.phi., preferably, 300 to 600 .mu.m+. The wire
can be finally passed through calender rolls so as to be used as a
flat wire.
[0066] Alternatively, the fuse element may be produced by the
rotary drum spinning method in which a cylinder containing cooling
liquid is rotated, the cooling liquid is held in a layer-like
manner by a rotational centrifugal force, and a molten material jet
ejected from a nozzle is introduced into the cooling liquid layer
to be cooled and solidified, thereby obtaining a thin wire
member.
[0067] In the production, the alloy composition is allowed to
contain inevitable impurities which are produced in productions of
metals of raw materials and also in melting and stirring of the raw
materials.
[0068] The invention may be implemented in the form of a thermal
fuse serving as an independent thermoprotector. Alternatively, the
invention may be implemented in the form in which a thermal fuse
element is connected in series to a semiconductor device, a
capacitor, or a resistor, a flux is applied to the element, the
flux-applied fuse element is placed in the vicinity of the
semiconductor device, the capacitor, or the resistor, and the fuse
element is sealed together with the semiconductor device, the
capacitor, or the resistor by means of resin mold, a case, or the
like.
[0069] The thermal fuse of the invention is useful particularly as
a thermoprotector for a secondary battery of a high energy density
such as a lithium battery or a lithium polymer battery, and
configured preferably as a thin thermal fuse of the tape type in
view of the accommodation space in a battery pack.
[0070] FIG. 1 is a view showing an embodiment of a thin thermal
fuse.
[0071] Referring to FIG. 1, 1 denotes flat lead conductors, and 2
denotes a fuse element of the first or second aspect of the
invention which is bonded between upper faces of tip ends of the
flat lead conductors 1 by welding or the like. In the welding
process, spot resistance welding, laser welding, or the like can be
used. The reference numeral 41 denotes a lower resin film, and 42
denotes an upper resin film. Front end portions of the flat lead
conductors 1, and the fuse element 2 are sandwiched between the
resin films 41, 42, and the peripheral portion of the upper resin
film 42 is sealingly bonded to the lower resin film 41 which is
horizontally held. The reference numeral 3 denotes a flux applied
to the periphery of the fuse element 2.
[0072] The thin thermal fuse is produced in the following manner.
The fuse element is bonded between the upper faces of the tip ends
of the flat lead conductors by spot resistance welding, laser
welding, or the like. Front end portions of the flat lead
conductors 1, and the fuse element 2 are sandwiched between the
lower and upper resin films 41, 42, the lower resin film 41 is
horizontally held on a platform, and end portions of the upper
resin film 42 are pressed by a releasable chip such as a ceramic
chip to cause end portions 421 of the upper resin film 42 to be in
press contact with the flat lead conductors 1. Under this state,
the flat lead conductors 1 are heated so that the contact faces of
the flat lead conductors 1 and end portions (portions pressed by
the releasable chip) of the resin films 41, 42 are fusingly bonded
together. Thereafter, faces of the resin films 41, 42 which are
directly in contact with each other are sealingly bonded together.
The timing of applying the flux 3 is set to that before the fuse
element 2 is sandwiched between the lower and upper resin films 41,
42, or that after the contact faces of the flat lead conductors 1
and end portions of the resin films 41, 42 are fusingly bonded
together and before faces of the resin films 41, 42 which are
directly in contact with each other are sealingly bonded
together.
[0073] The flat lead conductors can be heated by electromagnetic
induction heating, contact between a heat plate and the lead
conductors, or the like. In electromagnetic induction heating,
particularly, high-frequency magnetic fluxes cross tip end portions
of the lead conductors welded to end portions of the fuse element,
through the lower or upper resin film to concentrically heat the
tip end portions. Therefore, electromagnetic induction heating is
advantageous from the viewpoint of the heat efficiency. The seal
bonding between the faces of the lower and upper resin films 41, 42
which are directly in contact with each other can be performed by
ultrasonic fusion, high-frequency induction heating fusion, heat
plate contact fusion, or the like.
[0074] FIG. 2 is a view showing another embodiment of a thin
thermal fuse.
[0075] Referring to FIG. 2, 41 denotes a resin base film, and 1
denotes flat lead conductors in each of which a front end portion
is fixed to the rear face of the base film 41 and a part 10 of the
front portion is exposed from the upper face of the base film 41.
The reference numeral 2 denotes a fuse element of the first or
second aspect of the invention which is bonded between the exposed
portions 10 of the flat lead conductors 1 by welding or the like.
In the welding process, spot resistance welding, laser welding, or
the like can be used. The reference numeral 42 denotes a resin
cover film which is sealingly bonded in a peripheral portion to the
base film 41 that is horizontally held. The reference numeral 3
denotes a flux applied to the periphery of the fuse element 2.
[0076] The exposure of the portions 10 of the flat lead conductors
1 may be conducted by, for example, one of the following methods. A
projection is previously formed in the front end portion of each of
the flat lead conductors by a squeezing process, the front end
portions of the flat lead conductors are fusingly bonded under
heating to the rear face of the base film, and the projections are
protrudingly bonded to the base film. Alternatively, the front end
portions of the flat lead conductors are fusingly bonded under
heating to the rear face of the base film, and parts of the front
end portions of the flat lead conductors are caused to appear from
the surface of the base film by a squeezing process.
[0077] The thin thermal fuse is produced in the following manner.
On a platform, the fuse element 2 is bonded between the lead
conductor exposed portions 10 of the surface of the resin base film
41 by spot resistance welding, laser welding, or the like. The flux
3 is then applied to the fuse element 2. Thereafter, the resin
cover film 42 is placed, and the peripheral portion of the film is
sealingly bonded to the periphery of the resin base film 41.
[0078] The seal bonding of the peripheral portion of the resin
cover film 42 to the resin base film 41 can be performed by
ultrasonic fusion, high-frequency induction heating fusion, heat
plate contact fusion, or the like.
[0079] The thermal fuse of the invention may be realized in the
form of a fuse of the case type, the substrate type, or the
like.
[0080] FIG. 3 shows an alloy type thermal fuse of the cylindrical
case type according to the invention. A fuse element 2 of the first
or second aspect of the invention is connected between a pair of
lead conductors 1 by, for example, welding. A flux 3 is applied to
the fuse element 2. The flux-applied fuse element is passed through
an insulating tube 4 which is excellent in heat resistance and
thermal conductivity, for example, a ceramic tube. Gaps between the
ends of the insulating tube 4 and the lead conductors 1 are
sealingly closed by a sealing agent 5 such as a cold-setting epoxy
resin.
[0081] FIG. 4 shows a fuse of the radial case type. A fuse element
2 of the first or second aspect of the invention is connected
between tip ends of parallel lead conductors 1 by, for example,
welding. A flux 3 is applied to the fuse element 2. The
flux-applied fuse element is enclosed by an insulating case 4 in
which one end is opened, for example, a ceramic case. The opening
of the insulating case 4 is sealingly closed by sealing agent 5
such as a cold-setting epoxy resin.
[0082] FIG. 5 shows a fuse of the radial resin dipping type. A fuse
element 2 of the first or second aspect of the invention is bonded
between tip ends of parallel lead conductors 1 by, for example,
welding. A flux 3 is applied to the fuse element 2. The
flux-applied fuse element is dipped into a resin solution to seal
the element by an insulative sealing agent such as an epoxy resin
5.
[0083] FIG. 6 shows a fuse of the substrate type. A pair of film
electrodes 1 are formed on an insulating substrate 4 such as a
ceramic substrate by printing conductive paste. Lead conductors 11
are connected respectively to the electrodes 1 by, for example,
welding or soldering. A fuse element 2 of the first or second
aspect of the invention is bonded between the electrodes 1 by, for
example, welding. A flux 3 is applied to the fuse element 2. The
flux-applied fuse element is covered with a sealing agent 5 such as
an epoxy resin. The conductive paste contains metal particles and a
binder. For example, Ag, Ag---d, Ag--Pt, Au, Ni, or Cu may be used
as the metal particles, and a material containing a glass frit, a
thermosetting resin, and the like may be used as the binder.
[0084] The invention may be implemented in the form in which a
heating element for fusing off the fuse element is additionally
disposed on the alloy type thermal fuse. As shown in FIG. 7, for
example, a conductor pattern 100 having fuse element electrodes 1
and resistor electrodes 10 is formed on an insulating substrate 4
such as a ceramic substrate by printing conductive paste, and a
film resistor 6 is disposed between the resistor electrodes 10 by
applying and baking resistance paste (e.g., paste of metal oxide
powder such as ruthenium oxide). Lead conductors 11 are bonded
respectively to the electrodes 1 and 10. A fuse element 2 of the
first or second aspect of the invention is bonded between the fuse
element electrodes 1 by, for example, welding. A flux 3 is applied
to the fuse element 2. The flux-applied fuse element 2 and the film
resistor 6 are covered with a sealing agent 5 such as an epoxy
resin. In the thermal fuse having an electric heating element, a
precursor causing abnormal heat generation of an appliance is
detected, the film resistor is energized to generate heat in
response to a signal indicative of the detection, and the fuse
element is fused off by the heat generation.
[0085] The heating element may be disposed on the upper face of an
insulating substrate. A heat-resistant and thermal-conductive
insulating film such as a glass baked film is formed on the heating
element. A pair of electrodes are disposed, flat lead conductors
are connected respectively to the electrodes, and the fuse element
is connected between the electrodes. A flux covers a range over the
fuse element and the tip ends of the lead conductors. An insulating
cover is placed on the insulating substrate, and the periphery of
the insulating cover is sealingly bonded to the insulating
substrate by an adhesive agent.
[0086] Among the alloy type thermal fuses, those of the type in
which the fuse element is directly bonded to the lead conductors
(FIGS. 1 to 5) may be configured in the following manner. At least
portions of the lead conductors where the fuse element is bonded
are covered with a thin film of Sn or Ag (having a thickness of,
for example, 15 .mu.m or smaller, preferably, 5 to 10 .mu.m) (by
plating or the like), thereby enhancing the bonding strength with
respect to the fuse element.
[0087] In the alloy type thermal fuses, there is a possibility that
a metal material or a thin film material in the lead conductors, or
a particulate metal material in the film electrode migrates into
the fuse element by solid phase diffusion. As described above,
however, the characteristics of the fuse element can be
sufficiently maintained by previously adding the same element as
the thin film material into the fuse element.
[0088] As the flux, a flux having a melting point which is lower
than that of the fuse element is generally used. For example,
useful is a flux containing 90 to 60 weight parts of rosin, 10 to
40 weight parts of stearic acid, and 0 to 3 weight parts of an
activating agent. In this case, as the rosin, a natural rosin, a
modified rosin (for example, a hydrogenated rosin, an inhomogeneous
rosin, or a polymerized rosin), or a purified rosin thereof can be
used. As the activating agent, hydrochloride or hydrobromide of an
amine such as diethylamine, or an organic acid such as adipic acid
can be used.
[0089] As the resin film of the thin thermal fuse, useful is a
plastic film having a thickness of about 100 to 500 .mu.m, for
example, a film of: an engineering plastic such as polyethylene
terephtalate, polyethylene naphthalate, polyamide, polyimide,
polybuthylene terephtalate, polyphenylene oxide, polyethylene
sulfide, or polysulfone; an engineering plastic such as polyacetal,
polycaronate, polyphenylene sulfide, polyoxybenzoyl, polyether
ether ketone, or polyether imide; polypropylene; polyvinyl
chloride; polyvinyl acetate; polymetyl methacrylate; polyvinylidene
chloride; polytetrafluoroethylene; ethylene polytetrafluoroethylene
copolymer; ethylene-vinyl acetate copolymer (EVA); AS resin; ABS
resin; ionomer; AAS resin; or ACS resin.
[0090] Among the above-described alloy type thermal fuses, in the
fuse of the cylindrical case type, the arrangement in which the
lead conductors 1 are placed so as not to be eccentric to the
cylindrical case 4 as shown in (A) of FIG. 8 is a precondition to
enable the normal spheroid division shown in (B) of FIG. 8. When
the lead conductors are eccentric as shown in (C) of FIG. 8, the
flux (including a charred flux) and scattered alloy portions easily
adhere to the inner wall of the cylindrical case after an operation
as shown in (D) of FIG. 8. As a result, the insulation resistance
is lowered, and the dielectric breakdown characteristic is
impaired.
[0091] In order to prevent such disadvantages from being produced,
as shown in (A) of FIG. 9, a configuration is effective in which
ends of the lead conductors 1 are formed into a disk-like shape d,
and ends of the fuse element 2 are bonded to the front faces of the
disks d, respectively (by, for example, welding). The outer
peripheries of the disks are supported by the inner face of the
cylindrical case, and the fuse element 2 is positioned so as to be
substantially concentrical with the cylindrical case 4 [in (A) of
FIG. 9, 3 denotes a flux applied to the fuse element 2, 4 denotes
the cylindrical case, 5 denotes a sealing agent such as an epoxy
resin, and the outer diameter of each disk is approximately equal
to the inner diameter of the cylindrical case]. In this instance,
as shown in (B) of FIG. 9, molten portions of the fuse element
spherically aggregate on the front faces of the disks d, thereby
preventing the flux (including a charred flux) from adhering to the
inner face of the case 4.
EXAMPLES
[0092] In the following examples and comparative examples, alloy
type thermal fuses of the thin type shown in FIG. 1 were used. A
polybuthylene terephtalate film having a thickness of 200 .mu.m, a
width of 5 mm, and a length of 10 mm was used as the lower resin
film 41 and the upper resin film 42. A copper conductor having a
thickness of 150 .mu.m, a width of 3 mm, and a length of 20 mm was
used as the flat lead conductors 1. The fuse element 2 has a length
of 4 mm and an outer diameter of 300 .mu.m.phi.. A compound of 80
weight parts of natural rosin, 20 weight parts of stearic acid, and
1 weight part of hydrobromide of diethylamine was used as the
flux.
[0093] The solidus and liquidus temperatures of a fuse element were
measured by a DSC at a temperature rise rate of 5.degree.
C./min.
[0094] Fifty specimens were used. Each of the specimens was
immersed into an oil bath in which the temperature was raised at a
rate of 1.degree. C./min., while supplying a current of 0.1 A to
the specimen, and the temperature T0 of the oil when the current
supply was interrupted by blowing-out of the fuse element was
measured. A temperature of T0-2.degree. C. was determined as the
element temperature at an operation of the thermal fuse.
[0095] The heat cycle resistance was evaluated in the following
manner. Fifty specimens were used. A heat cycle test in which each
cycle is configured by (operating temperature -20.degree.
C.).times.30 min. and -40.degree. C..times.30 min. was conducted
1,000 cycles. The resistance was measured. When an abnormality such
as that the resistance is changed remarkably or by 50% or more,
that the fuse element is broken, or that, in an after-test
operation test, the operating temperature is deviated by
.+-.7.degree. C. or more from the initial operating temperature or
the thermal fuse does not operate was observed even in one
specimen, the heat cycle resistance was evaluated as unacceptable.
When an abnormality was not observed in all the specimens, the heat
cycle resistance was evaluated as acceptable.
[0096] The aging resistance was evaluated by a load aging test.
Fifty specimens were used. The specimens were exposed to a
high-temperature environment of (operating temperature -20.degree.
C.) for 20,000 hours while supplying a rated current. Thereafter,
the resistance was measured. When an abnormality such as that the
resistance is changed remarkably or by 50% or more, that the fuse
element is broken, or that, in an after-test operation test, the
operating temperature is deviated by +7.degree. C. or more from the
initial operating temperature or the thermal fuse does not operate
was observed even in one specimen, the aging resistance was
evaluated as unacceptable. When an abnormality was not observed in
all the specimens, the aging resistance was evaluated as
acceptable.
[0097] With respect to the drawability of a fuse element, a process
of drawing to 300 .mu.m.phi. under the conditions of an area
reduction per dice of 6.5%, and a drawing speed of 50 m/min. was
conducted. When the drawing process was conducted with satisfactory
yield without causing a constricted portion or a breakage, the
drawability was evaluated as .largecircle.. When a constricted
portion or a breakage was caused so that the sectional area was not
stabilized nor the continuity of the drawing was not ensured, the
drawability was evaluated as x.
Example 1
[0098] A fuse element having an alloy composition of 25% In, 20%
Sn, and balance Bi was produced. The wire drawability to a fuse
element was .largecircle..
[0099] FIG. 10 shows a result of a DSC measurement of the fuse
element. The liquidus temperature was about 84.degree. C., the
solidus temperature was about 80.degree. C., and the maximum
endothermic peak temperature was about 81.degree. C. Since the
alloy composition is close to the 79.degree. C. ternary Bi--In--Sn
eutectic point of 57.5% Bi-25.2% In-17.3% Sn, the DSC measurement
result belongs to the pattern of (B) FIG. 14. However, the solid
phase transformation zone does not exist in the temperature side
which is lower than the solidus temperature.
[0100] The fuse element temperature at an operation of a thermal
fuse was 82.+-.1.degree. C. Therefore, it is apparent that the fuse
element temperature at an operation of a thermal fuse approximately
coincides with the maximum endothermic peak temperature of about
82.degree. C.
[0101] The example passed both the load aging test and the heat
cycle test. The reason of the pass in the load aging test is
estimated as follows. Since the amount of In is as small as 25%,
the reaction of In with the flux was suppressed, and the variation
of the alloy composition and the reduction of the activity of the
flux were conducted at a very small degree. As apparent from the
DSC measurement result, solid phase transformation was not observed
in the temperature side which is lower than the solidus
temperature. Therefore, the pass in the heat cycle test coincides
with the estimation.
Example 2
[0102] A fuse element having an alloy composition of 30% In, 15%
Sn, and balance Bi was produced.
[0103] The wire drawability to a fuse element was
.largecircle..
[0104] FIG. 11 shows a result of a DSC measurement of the fuse
element. The liquidus temperature was about 86.degree. C., the
solidus temperature was about 79.degree. C., and the maximum
endothermic peak temperature was about 82.degree. C. Since the
alloy composition is close to the 81.degree. C. ternary Bi--In--Sn
eutectic point of 54.0% Bi-29.7% In-16.3% Sn, the DSC measurement
result belongs to the pattern of (B) FIG. 14. However, the solid
phase transformation zone does not exist in the temperature side
which is lower than the solidus temperature.
[0105] The fuse element temperature at an operation of a thermal
fuse was 82.+-.1.degree. C. Therefore, it is apparent that the fuse
element temperature at an operation of a thermal fuse approximately
coincides with the maximum endothermic peak temperature of about
82.degree. C.
[0106] The example passed both the load aging test and the heat
cycle test. The reason of the pass in the load aging test is
estimated as follows. Since the amount of In is as small as 30%,
the reaction of In with the flux was suppressed, and the variation
of the alloy composition and the reduction of the activity of the
flux were conducted at a very small degree in the same manner as
Example 1. As apparent from the DSC measurement result, in the same
manner as Example 1, solid phase transformation was not observed in
the temperature side which is lower than the solidus temperature.
Therefore, the pass in the heat cycle test coincides with the
estimation.
Examples 3 to 7
[0107] The examples were conducted in the same manner as Example 1
except that the alloy composition in Example 1 was changed as
listed in Table 1.
[0108] In all the examples, good wire drawability was obtained.
[0109] The solidus and liquidus temperatures of the examples are
shown in Table 1. The fuse element temperatures at an operation are
as shown in Table 1, have dispersion of .+-.3.degree. C. or
smaller, and are in the solid-liquid coexisting region.
[0110] The melt pattern of the fuse element of each example belongs
to the pattern of (A) of FIG. 14, and the solid-liquid coexisting
region is wide. However, the single endothermic peak exists and is
sharp. As a result, dispersion of the operating temperature can be
set to be .+-.3.degree. C. or smaller.
[0111] The examples passed the load aging test. The reason of the
pass in the load aging test is estimated as follows. Since the
amount of In is as small as 15 to 30%, the reaction of In with the
flux was suppressed, and the variation of the alloy composition and
the reduction of the activity of the flux were conducted at a very
small degree in the same manner as Example 1.
[0112] The examples passed also the heat cycle test. From results
of DSC measurements, it was confirmed that solid phase
transformation does not exist in the temperature side which is
lower than the solidus temperature. This coincides with the
estimation.
[0113] [Table 1]
1TABLE 1 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 In (%) 15 20 25 30 35 Sn (%)
5 5 5 5 5 Bi Balance Balance Balance Balance Balance Solidus
temperature 79 79 79 80 84 (.degree. C.) Liquidus temperature 194
171 144 109 105 (.degree. C.) Element temperature 85 .+-. 1 84 .+-.
1 92 .+-. 2 95 .+-. 3 98 .+-. 3 at operation (.degree. C.) Heat
cycle resistance Passed Passed Passed Passed Passed test Load aging
test Passed Passed Passed Passed Passed
Examples 8 to 11
[0114] The examples were conducted in the same manner as Example 1
except that the alloy composition in Example 1 was changed as
listed in Table 2.
[0115] In all the examples, good wire drawability was obtained.
[0116] The solidus and liquidus temperatures of the examples are
shown in Table 2. The fuse element temperatures at an operation are
as shown in Table 2, have dispersion of .+-.1.degree. C. or
smaller, and are in the solid-liquid coexisting region.
[0117] The melt pattern of the fuse element of each example belongs
to the pattern of (A) of FIG. 14, and the solid-liquid coexisting
region is wide. However, the single endothermic peak exists and is
sharp. As a result, dispersion of the operating temperature can be
set to be .+-.1.degree. C. or smaller.
[0118] The examples passed the load aging test. The reason of the
pass in the load aging test is estimated as follows. Since the
amount of In is as small as 15 to 35%, the reaction of In with the
flux was suppressed, and the variation of the alloy composition and
the reduction of the activity of the flux were conducted at a very
small degree in the same manner as Example 1.
[0119] The examples passed also the heat cycle test. From results
of DSC measurements, it was confirmed that solid phase
transformation does not exist in the temperature side which is
lower than the solidus temperature. This coincides with the
estimation.
[0120] [Table 2]
2TABLE 2 Ex. 8 Ex. 9 Ex. 10 Ex. 11 In (%) 15 20 25 35 Sn (%) 15 15
15 15 Bi Balance Balance Balance Balance Solidus temperature
(.degree. C.) 79 80 80 69 Liquidus temperature (.degree. C.) 158
134 105 84 Wire drawability .largecircle. .largecircle.
.largecircle. .largecircle. Element 86 .+-. 1 86 .+-. 1 83 .+-. 1
79 .+-. 1 temperature at operation (.degree. C.) Heat cycle
resistance test Passed Passed Passed Passed Load aging test Passed
Passed Passed Passed
Examples 12 to 16
[0121] The examples were conducted in the same manner as Example 1
except that the alloy composition in Example 1 was changed as
listed in Table 3.
[0122] In all the examples, good wire drawability was obtained.
[0123] The solidus and liquidus temperatures of the examples are
shown in Table 3. The fuse element temperatures at an operation are
as shown in Table 3, have dispersion of +3.degree. C. or smaller,
and are in the solid-liquid coexisting region.
[0124] The melt pattern of the fuse element of each example belongs
to the pattern of (A) of FIG. 14, and the solid-liquid coexisting
region is wide. However, the single endothermic peak exists and is
sharp. As a result, dispersion of the operating temperature can be
set to be .+-.3.degree. C. or smaller.
[0125] The examples passed the load aging test. The reason of the
pass in the load aging test is estimated as follows. Since the
amount of In is as small as 15 to 35%, the reaction of In with the
flux was suppressed, and the variation of the alloy composition and
the reduction of the activity of the flux were conducted at a very
small degree in the same manner as Example 1.
[0126] The examples passed also the heat cycle test. From results
of DSC measurements, it was confirmed that solid phase
transformation does not exist in the temperature side which is
lower than the solidus temperature. This coincides with the
estimation.
[0127] [Table 3]
3TABLE 3 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 In (%) 15 20 25 30 35
Sn (%) 25 25 25 25 25 Bi Balance Balance Balance Balance Balance
Solidus temperature 79 79 79 78 77 (.degree. C.) Liquidus
temperature 126 107 107 107 104 (.degree. C.) Wire drawability
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. Element temperature 94 .+-. 3 83 .+-. 1 82 .+-. 1 81
.+-. 1 80 .+-. 3 at operation (.degree. C.) Heat cycle resistance
Passed Passed Passed Passed Passed test Load aging test Passed
Passed Passed Passed Passed
Example 17
[0128] The example was conducted in the same manner as Example 1
except that an alloy composition in which 1 weight part of Ag was
added to 100 weight parts of the alloy composition of Example 1 was
used as that of a fuse element.
[0129] A wire member for a fuse element of 300 .mu.m was produced
under conditions in which the area reduction per dice was 8% and
the drawing speed was 80 m/min., and which are severer than those
of the drawing process of a wire member for a fuse element in
Example 1. However, no wire breakage occurred, and problems such as
a constricted portion were not caused, with the result that the
example exhibited excellent workability.
[0130] The solidus temperature was 79.degree. C., and the maximum
endothermic peak temperature and the fuse element temperature at an
operation of a thermal fuse were lowered only by about 1.degree. C.
as compared with those in Example 1. Namely, it was confirmed that
the operating temperature and the melting characteristic can be
held without being largely differentiated from those of Example
1.
[0131] The example passed both the heat cycle test and the load
aging test. It is estimated that the consideration results were
maintained because the addition amount of Ag is as small as 1
weight part.
[0132] It was confirmed that the above-mentioned effects are
obtained in the range of the addition amount of 0.1 to 3.5 weight
parts of Ag.
[0133] In the case where the metal material of the lead conductors
to be bonded, a thin film material, or a particulate metal material
in the film electrode is Ag, it was confirmed that, when the same
element or Ag is previously added as in the example, the metal
material can be prevented from, after a fuse element is bonded,
migrating into the fuse element with time by solid phase diffusion,
and local reduction or dispersion of the operating temperature due
to solid phase diffusion can be eliminated.
Examples 18 to 25
[0134] The examples were conducted in the same manner as Example 1
except that an alloy composition in which 0.5 weight parts of
respective one of Au, Cu, Ni, Pd, Pt, Ga, Ge, and Sb were added to
100 weight parts of the alloy composition of Example 1 was used as
that of a fuse element.
[0135] It was confirmed that, in the same manner as the metal
addition of Ag in Example 17, also the addition of Au, Cu, Ni, Pd,
Pt, Ga, Ge, or Sb realizes excellent wire drawability, the
operating temperature and melting characteristic are not largely
different from those of Example 1, the examples passed the heat
cycle test and the load aging test, and solid phase diffusion
between metal materials of the same kind can be suppressed.
[0136] It was confirmed that the above-mentioned effects are
obtained in the range of the addition amount of 0.1 to 3.5 weight
parts of respective one of Au, Cu, Ni; Pd, Pt, Ga, Ge, and Sb.
[0137] [Comparative Example 1]
[0138] The comparative example was conducted in the same manner as
Example 1 except that the composition of the fuse element in
Example 1 was changed to 25.2% In, 17.3% Sn, and the balance
Bi.
[0139] The wire drawability was satisfactory. The fuse element
temperature at an operation of a thermal fuse was 81.+-.1.degree.
C. FIG. 12 shows a result of a DSC measurement. It was expected to
produce excellent thermal fuses in which the solid-liquid
coexisting region is narrow and the operating temperature is less
dispersed. However, solid phase transformation was observed between
temperatures of 52 to 58.degree. C.
[0140] The resistances of specimens which were subjected to 1,000
cycles of a heat cycle test (in which each cycle is configured by
60.degree. C..times.30 min. and -40.degree. C..times.30 min.) were
measured. As a result, a resistance change of 50% or more, and a
breakage often occurred, and the result of the heat cycle test was
x. This was caused by the following reason. The solid phase
transformation zone overlaps with the temperature zone of the heat
cycles, and stress due to solid phase transformation was
repetitively produced.
[0141] [Comparative Example 2]
[0142] The comparative example was conducted in the same manner as
Example 1 except that the composition of the fuse element in
Example 1 was changed to 29.7% In, 16.3% Sn, and the balance
Bi.
[0143] The wire drawability was satisfactory. The fuse element
temperature at an operation of a thermal fuse was 81+1.degree. C.
FIG. 13 shows a result of a DSC measurement. It was expected to
produce excellent thermal fuses in which the solid-liquid
coexisting region is narrow and the operating temperature is less
dispersed. However, solid phase transformation was observed between
temperatures of 51 to 57.degree. C.
[0144] The resistances of specimens which were subjected to 1,000
cycles of a heat cycle test (in which each cycle is configured by
60.degree. C..times.30 min. and -40.degree. C..times.30 min.) were
measured. As a result, in the same manner as Comparative Example 1,
a resistance change of 50% or more, and a breakage often occurred,
and the result of the heat cycle test was x. This was caused by the
following reason. In the same manner as Comparative Example 1, the
solid phase transformation zone overlaps with the temperature zone
of the heat cycles, and stress due to solid phase transformation
was repetitively produced.
[0145] [Comparative Example 3]
[0146] The comparative example was conducted in the same manner as
Example 1 except that the composition of the fuse element in
Example 1 was changed to 40% In, 20% Sn, and the balance Bi.
[0147] The wire drawability was satisfactory. As a result of a DSC
measurement, the solid-liquid coexisting region is narrow. As a
result of the measurement of an operating temperature, dispersion
of the operating temperature was within the allowable range. The
result of a heat cycle test was acceptable.
[0148] The resistances of specimens which had been subjected to a
load aging test for 7,000 hours were measured. A remarkable
increase of the resistance which is 50% or more was observed. The
operating temperature was measured. As a result, in many specimens,
the operating temperature was largely deviated from the range of
the initial operating temperature .+-.7.degree. C. The reasons of
the above are estimated as follows. In was consumed by the flux,
and the specific resistance of the fuse element was increased.
Since the amount of In in the alloy was reduced, the operating
temperature was varied. Since the reactive groups were used for
producing an In salt, the activity of the flux was reduced, so that
spheroid division of the molten alloy was not satisfactorily
conducted.
[0149] [Comparative Example 4]
[0150] The comparative example was conducted in the same manner as
Example 1 except that the composition of the fuse element in
Example 1 was changed to 10% In, 20% Sn, and the balance Bi.
[0151] A process of drawing to 300 .mu.m.phi. was attempted.
However, breakage frequently occurred, and the wire drawability was
x.
[0152] A thin wire of 300 .mu.m.phi. was obtained by the rotary
drum spinning method to be formed as a fuse element.
[0153] The DSC measurement result of the fuse element belongs to
the melt pattern of (C) of FIG. 14. The fuse element temperature at
an operation was measured. As a result, dispersion was larger than
the allowable range of +5.degree. C., and the fuse element was not
able to be used as a thermal fuse.
[0154] The reasons of the large dispersion of the operating
temperature are estimated as follows. The heat energy is slowly
absorbed. The wettability is not suddenly changed. The point of a
division operation of the fuse element is not determined in a
narrow range.
[0155] [Comparative Example 5]
[0156] The comparative example was conducted in the same manner as
Example 1 except that the composition of the fuse element in
Example 1 was changed to 20% In, 35% Sn, and the balance Bi.
[0157] A drawing process was smoothly conducted, and the wire
drawability was .largecircle..
[0158] In the result of a DSC measurement, the solid-liquid
coexisting region is wide, the heat energy is slowly absorbed in
the solid-liquid coexisting region, and the wettability is not
suddenly changed. The DSC measurement result belongs to the melt
pattern of (C) of FIG. 14.
[0159] The fuse element temperature at an operation was measured.
As a result, dispersion was larger than the allowable range of
.+-.5.degree. C., and the fuse element was not able to be used as a
thermal fuse.
[0160] The reason of the large dispersion of the operating
temperature is identical with that of Comparative Example 4.
[0161] [Comparative Example 6]
[0162] The comparative example was conducted in the same manner as
Example 1 except that the composition of the fuse element in
Example 1 was changed to 52% In and the balance Bi.
[0163] The wire drawability was satisfactory. As a result of a DSC
measurement, the solid-liquid coexisting region is narrow. As a
result of the measurement of an operating temperature, dispersion
of the operating temperature was very small. The result of a heat
cycle test was acceptable.
[0164] The resistances of specimens which had been subjected to a
load aging test for 7,000 hours were measured. A remarkable
increase of the resistance which is 50% or more was observed. The
operating temperature was measured. As a result, in many specimens,
the operating temperature was largely deviated from the range of
the initial operating temperature .+-.7.degree. C. The reasons of
the above are estimated as follows. In was consumed by the flux,
and the specific resistance of the fuse element was increased.
Since the amount of In in the alloy was reduced, the operating
temperature was varied. Since the reactive groups were used for
producing an In salt, the activity of the flux was reduced, so that
spheroid division of the molten alloy was not satisfactorily
conducted.
[0165] [Comparative Example 7]
[0166] The comparative example was conducted in the same manner as
Example 1 except that the composition of the fuse element in
Example 1 was changed to 52% In and the balance Sn.
[0167] The wire drawability was satisfactory. As a result of a DSC
measurement, the solid-liquid coexisting region is narrow. As a
result of the measurement of an operating temperature, dispersion
of the operating temperature was very small. The result of a heat
cycle test was acceptable.
[0168] The resistances of specimens which had been subjected to a
load aging test for 7,000 hours were measured. A remarkable
increase of the resistance which is 50% or more was observed. The
operating temperature was measured. As a result, in many specimens,
the operating temperature was largely deviated from the range of
the initial operating temperature .+-.7.degree. C. The reasons of
the above are estimated as follows. In was consumed by the flux,
and the specific resistance of the fuse element was increased.
Since the amount of In in the alloy was reduced, the operating
temperature was varied. Since the reactive groups were used for
producing an In salt, the activity of the flux was reduced, so that
spheroid division of the molten alloy was not satisfactorily
conducted.
[0169] [Effects of the Invention]
[0170] According to the material for a thermal fuse element and the
thermal fuse of the invention, a small and thin alloy type thermal
fuse can be provided in which a Bi--In--Sn alloy that does not
contain a metal harmful to a living body is used as a fuse element,
the operating temperature is 75 to 120.degree. C., the initial
operating characteristic is maintained, and excellent heat cycle
and aging resistances are attained for a long term.
[0171] According to the material for a thermal fuse element and the
alloy type thermal fuse of claim 2 of the invention, since a fuse
element can be further thinned because of the excellent wire
drawability of the material for a thermal fuse element, the thermal
fuse can be advantageously miniaturized and thinned. Even in the
case where an alloy type thermal fuse is configured by bonding a
fuse element to a to-be-bonded material which may originally exert
an influence, a normal operation can be assured while maintaining
the performance of the fuse element. Therefore, the thermal fuse is
particularly useful as a thin thermoprotector for protecting a
secondary battery which is requested to be thinned because of
attachment to a battery pack.
[0172] According to the alloy type thermal fuses of claims 3 to 10
of the invention, particularly, the above effects can be assured in
a thin thermal fuse of the tape type, a thermal fuse of the
cylindrical case type, a thermal fuse of the substrate type, a
thermal fuse having an electric heating element, a thermal fuse or
a thermal fuse having an electric heating element in which lead
conductors are plated by Sn, Ag, or the like, and a thermal fuse of
the cylindrical case type in which endsof the lead conductors have
a disk-like shape, whereby the usefulness of such a thermal fuse
can be further enhanced.
* * * * *