Background of the Invention
Field of the Invention
-
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°C, and also to such
a thermal type fuse element.
-
An alloy type thermal fuse is widely used as a thermoprotector
for an electrical appliance, a circuit element,
or the like.
-
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.
-
The alloy type thermal fuse has the following operation
mechanism.
-
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.
Description of the Prior Art
-
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.
-
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°C.
-
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.).
-
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°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°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°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°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°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°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°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°C may be contemplated to be
used as a fuse element.
-
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.
-
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°C). The conventional art examples
hardly adapt to the long-term aging resistance.
-
As a Bi-In-Sn eutectic alloy which can satisfy the requirement
of an operating temperature of 75 to 120°C, and in
which the weight of In is considerably smaller than 50%,
there are 79°C-eutectic (57.5% Bi, 25.2% In, and 17.3% Sn)
and 81°C-eutectic (54.0% Bi, 29.7% In, and 16.3% Sn). In
79°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 N2 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°C which is considerably
lower than the melting point. In 81°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°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.
-
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°C), the resistance
of a fuse element is not changed or a thermal fuse
does not malfunction. However, the 79°C- and 81°C-eutectics
hardly adapt to the long-term heat cycle resistance.
-
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.
-
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.
-
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 Bi-In-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.
-
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.
-
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 determined
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.
-
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°C. Because of the unadaptability to the long-term
heat cycle resistance, Bi-In-Sn eutectic alloys of
79°C-eutectic (57.5% Bi, 25.2% In, and 17.3% Sn), and 81°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°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
-
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°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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
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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.
-
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.
-
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.
-
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
-
- Fig. 1 is a view showing an example of the alloy type
thermal fuse of the invention;
- Fig. 2 is a view showing another example of the alloy
type thermal fuse of the invention;
- Fig. 3 is a view showing a further example of the alloy
type thermal fuse of the invention;
- Fig. 4 is a view showing a still further example of
the alloy type thermal fuse of the invention;
- Fig. 5 is a view showing a still further example of
the alloy type thermal fuse of the invention;
- Fig. 6 is a view showing a still further example of
the alloy type thermal fuse of the invention;
- Fig. 7 is a view showing a still further example of
the alloy type thermal fuse of the invention;
- Fig. 8 is a view showing an alloy type thermal fuse of
the cylindrical case type and its operation state;
- Fig. 9 is a view showing a still further example of
the alloy type thermal fuse of the invention;
- Fig. 10 is a view showing a result of a DSC measurement
of a fuse element of Example 1;
- Fig. 11 is a view showing a result of a DSC measurement
of a fuse element of Example 2;
- Fig. 12 is a view showing a result of a DSC measurement
of a 79°C ternary Bi-In-Sn eutectic alloy;
- Fig. 13 is a view showing a result of a DSC measurement
of an 81°C ternary Bi-In-Sn eutectic alloy; and
- Fig. 14 is a view showing various melt patterns of a
ternary Sn-In-Bi alloy.
-
Detailed Description of the Preferred Embodiments
-
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 µm, preferably, 300 to 600 µm.
-
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°C ternary Bi-In-Sn
eutectic point of 57.5%Bi-25.2%In-17.3%Sn and 81°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% ≤ Bi ≤ 59.5%, 24.2% ≤ In ≤ 26.2%, and 16.3% ≤ Sn ≤
18.3%, and that of 52% ≤ Bi ≤ 56%, 28.7% ≤ In ≤ 30.7%, and
15.3% ≤ Sn ≤ 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°C, the following points are satisfied with respect to
the reference points of 79°C-eutectic and 81°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°C.
-
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°C ternary Bi-In-Sn eutectic point and the 81°C
ternary Bi-In-Sn eutectic point, the melting point is close
to the melting points of the eutectics (79 to 81°C), and
also the DSC melt pattern is close to the melt patterns of
the 79°C ternary Bi-In-Sn eutectic and 81°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.
-
Each of the aboves will be further described.
- (1) From a result of a DSC measurement of a 79°C ternary Bi-In-Sn
eutectic alloy shown in Fig. 12 and that of a DSC
measurement of an 81°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°C and about 51 to 57°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°C) and the room temperature or a below-freezing temperature
(usually, -40°C). In the case of an operating temperature
of 75 to 120°C, one cycle is set to be between (55 to
100°C) and -40°C, and the solid phase transformation zones
(52 to 58°C) and (51 to 57°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.
In the invention, therefore, the range of ±2%Bi,
±1%In, and ±1%Sn with respect to each of the 79°C ternary
Bi-In-Sn eutectic point and the 81°C ternary Bi-In-Sn eutectic
point is excluded.
- (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.
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°C is satisfied, and thinning
to 300 µm can be performed with a high yield.
- (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.
In the invention, therefore, Sn is set to 5 to 28% so
that, although deviated from the 79°C ternary Bi-In-Sn
eutectic point and the 81°C ternary Bi-In-Sn eutectic point,
the operating temperature is set to the range of 75 to 120°C
with dispersion of an allowable range (±5°C).
-
-
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°C,
the solidus temperature is about 80°C, a result of a DSC
measurement at a temperature rise rate of 5°C/min. is shown
in Fig. 10, and the maximum endothermic peak is at about
82°C.
-
The other reference composition is that In is 30%, Sn
is 15%, and a balance is Bi. The liquidus temperature is
about 86°C, the solidus temperature is about 81°C, a result
of a DSC measurement at a temperature rise rate of 5°C/min.
is shown in Fig. 11, and the maximum endothermic peak is at
about 82°C.
-
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°C ternary Bi-In-Sn eutectic alloy shown in
Fig. 12 and that of the 81°C ternary Bi-In-Sn eutectic alloy
shown in Fig. 13, and there is no solid phase transformation
which may cause a serious problem.
-
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.
-
With respect to a drawing process, further enhanced
strength and ductility are provided so that drawing into a
thin wire of 100 to 300 µm 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.
-
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.
-
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 µm, preferably,
300 to 600 µm. The wire can be finally passed through
calender rolls so as to be used as a flat wire.
-
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.
-
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
-
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.
-
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.
-
Fig. 1 is a view showing an embodiment of a thin thermal
fuse.
-
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.
-
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.
-
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.
-
Fig. 2 is a view showing another embodiment of a thin
thermal fuse.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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-Pd, 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.
-
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.
-
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.
-
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 µm or
smaller, preferably, 5 to 10 µm) (by plating or the like),
thereby enhancing the bonding strength with respect to the
fuse element.
-
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.
-
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.
-
As the resin film of the thin thermal fuse, useful is
a plastic film having a thickness of about 100 to 500 µm,
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.
-
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.
-
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]
-
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 µm, 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 µm,
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 µm. 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.
-
The solidus and liquidus temperatures of a fuse element
were measured by a DSC at a temperature rise rate of
5°C/min.
-
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°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°C
was determined as the element temperature at an operation
of the thermal fuse.
-
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°C) × 30 min. and -40°C × 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°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.
-
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°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°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.
-
With respect to the drawability of a fuse element, a
process of drawing to 300 µm 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 ○. 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 ×.
[Example 1]
-
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 ○.
-
Fig. 10 shows a result of a DSC measurement of the
fuse element. The liquidus temperature was about 84°C, the
solidus temperature was about 80°C, and the maximum endothermic
peak temperature was about 81°C. Since the alloy
composition is close to the 79°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.
-
The fuse element temperature at an operation of a
thermal fuse was 82 ± 1°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°C.
-
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]
-
A fuse element having an alloy composition of 30% In,
15% Sn, and balance Bi was produced.
-
The wire drawability to a fuse element was ○.
-
Fig. 11 shows a result of a DSC measurement of the
fuse element. The liquidus temperature was about 86°C, the
solidus temperature was about 79°C, and the maximum endothermic
peak temperature was about 82°C. Since the alloy
composition is close to the 81°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.
-
The fuse element temperature at an operation of a
thermal fuse was 82 ± 1°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°C.
-
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]
-
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.
-
In all the examples, good wire drawability was obtained.
-
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°C
or smaller, and are in the solid-liquid coexisting region.
-
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°C or
smaller.
-
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.
-
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.
[Table 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 (°C) |
79 |
79 |
79 |
80 |
84 |
Liquidus temperature (°C) |
194 |
171 |
144 |
109 |
105 |
Element temperature at operation (°C) |
85 ± 1 |
84 ± 1 |
92 ± 2 |
95 ± 3 |
98 ± 3 |
Heat cycle resistance test |
Passed |
Passed |
Passed |
Passed |
Passed |
Load aging test |
Passed |
Passed |
Passed |
Passed |
Passed |
[Examples 8 to 11]
-
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.
-
In all the examples, good wire drawability was obtained.
-
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°C
or smaller, and are in the solid-liquid coexisting region.
-
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°C or
smaller.
-
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.
-
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.
[Table 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 (°C) |
79 |
80 |
80 |
69 |
Liquidus temperature (°C) |
158 |
134 |
105 |
84 |
Wire drawability |
○ |
○ |
○ |
○ |
Element temperature at operation (°C) |
86 ± 1 |
86 ± 1 |
83 ± 1 |
79 ± 1 |
Heat cycle resistance test |
Passed |
Passed |
Passed |
Passed |
Load aging test |
Passed |
Passed |
Passed |
Passed |
[Examples 12 to 16]
-
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.
-
In all the examples, good wire drawability was obtained.
-
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°C
or smaller, and are in the solid-liquid coexisting region.
-
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°C or
smaller.
-
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.
-
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.
[Table 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 (°C) |
79 |
79 |
79 |
78 |
77 |
Liquidus temperature (°C) |
126 |
107 |
107 |
107 |
104 |
Wire drawability |
○ |
○ |
○ |
○ |
○ |
Element temperature at operation (°C) |
94 ± 3 |
83 ± 1 |
82 ± 1 |
81 ± 1 |
80 ± 3 |
Heat cycle resistance test |
Passed |
Passed |
Passed |
Passed |
Passed |
Load aging test |
Passed |
Passed |
Passed |
Passed |
Passed |
[Example 17]
-
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.
-
A wire member for a fuse element of 300 µm 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.
-
The solidus temperature was 79°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°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.
-
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.
-
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.
-
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]
-
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.
-
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.
-
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.
[Comparative Example 1]
-
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.
-
The wire drawability was satisfactory. The fuse element
temperature at an operation of a thermal fuse was 81 ±
1°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°C.
-
The resistances of specimens which were subjected to
1,000 cycles of a heat cycle test (in which each cycle is
configured by 60°C × 30 min. and -40°C × 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 ×. 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.
[Comparative Example 2]
-
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.
-
The wire drawability was satisfactory. The fuse element
temperature at an operation of a thermal fuse was 81 ±
1°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°C.
-
The resistances of specimens which were subjected to
1,000 cycles of a heat cycle test (in which each cycle is
configured by 60°C × 30 min. and -40°C × 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
×. 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.
[Comparative Example 3]
-
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.
-
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.
-
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°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.
[Comparative Example 4]
-
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.
-
A process of drawing to 300 µm was attempted. However,
breakage frequently occurred, and the wire drawability
was ×.
-
A thin wire of 300 µm was obtained by the rotary drum
spinning method to be formed as a fuse element.
-
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°C, and
the fuse element was not able to be used as a thermal fuse.
-
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.
[Comparative Example 5]
-
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.
-
A drawing process was smoothly conducted, and the wire
drawability was ○.
-
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.
-
The fuse element temperature at an operation was measured.
As a result, dispersion was larger than the allowable
range of ±5°C, and the fuse element was not able to be
used as a thermal fuse.
-
The reason of the large dispersion of the operating
temperature is identical with that of Comparative Example
4.
[Comparative Example 6]
-
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.
-
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.
-
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°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.
[Comparative Example 7]
-
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.
-
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.
-
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°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.
[Effects of the Invention]
-
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°C, the initial operating characteristic is
maintained, and excellent heat cycle and aging resistances
are attained for a long term.
-
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.
-
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 ends of the lead conductors
have a disk-like shape, whereby the usefulness of such a
thermal fuse can be further enhanced.