Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – Fusible element actuated
Reexamination Certificate
1999-09-16
2001-03-06
Thompson, Gregory (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
Fusible element actuated
C337S404000, C337S405000, C337S416000, C337S159000
Reexamination Certificate
active
06198376
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a safety device for preventing a trouble caused by an abnormal overheating of an electric circuit and more particularly, to a solder fuse, as a safety device, which can be easily formed with the same and normal solder as used for connecting electrical parts, has high reliability as a fuse, and can reduce manufacturing cost.
2. Description of the Related Art
For example, a voltage-dependent varistor is used as a conventional safety device for an electric circuit as proposed in Japanese U.M. Registration Application Laid-open No.1-129744.
In this safety device for an electric circuit, leads of the voltage-dependent varistor are bent in a right angle and are soldered to respective electrodes of first and second circuit patterns which are standoff-insulated each other on the circuit board, whereby the first and second circuit patterns are electrically connected.
In the above structure, the solder fixing the leads melts and then the voltage-dependent varistor falls due to its own weight when the ambient temperature of the first or second circuit pattern or of the voltage-dependent varistor has risen high, whereby the circuit between the first and second circuit patterns is broken. This prevents a trouble caused by an abnormal overheating of the electric circuit.
With respect to the above-described conventional safety device for an electric circuit, however, the voltage-dependent varistor is required and further the varistor requires to be held when the varistor is soldered to a circuit board, thereby consuming time and cost.
In order to solve this kind of problems, a number of safety devices for an electric circuit, in which a solder itself is used as a fuse, have been proposed.
Such a conventional safety device for an electric circuit is described with reference to
FIGS. 3 and 4
.
FIGS. 3A
to
3
C are plan views showing a conventional safety device for an electric circuit, which safety device utilizes a solder fuse. And, sectional views of
FIGS. 3A
to
3
C are shown in
FIGS. 4A
to
4
C, respectively.
As shown in
FIGS. 3A and 4A
, a first circuit pattern
110
and a second circuit pattern
120
are formed on a circuit board
100
, and electrodes
111
,
121
of the respective first and second circuit patterns
110
,
120
are standoff-insulated each other by arranging a gap
100
a
therebetween. And, as shown in
FIGS. 3B and 4B
, a solder fuse portion
101
is formed with a solder
30
bridging the electrodes
111
,
121
.
According to such a structure, when the ambient temperature of the first or second circuit pattern
110
,
120
or of the solder
30
has risen high, the solder
30
completely melts.
And then, as shown in
FIGS. 3C and 4C
, the melted solder
30
on the gap
100
a
is shed by the circuit board having no affinity with the solder
30
and separates on the electrodes
111
,
121
by surface tension.
Consequently, the circuit between the first and second circuit patterns
110
,
120
is broken, thereby preventing a trouble caused by an abnormal overheating of the electric circuit.
With respect to the above conventional solder fuse, however, when the solder fuse portion
101
is formed, the solder
30
shall be almost completely melted and is deposited over each of the electrodes
111
,
121
.
When the solder fuse portion
101
is formed, however, since the solder
30
is apt to be separated on each of the electrodes
111
,
121
, formation of the solder fuse portion
101
is difficult, thereby resulting in a low yield rate.
This is caused by form of the gap
100
a
between the electrodes
111
,
121
, that is, since the gap
100
a
continues in an arrow direction shown in
FIG. 3A
, the melted solder
30
on the gap
100
a
is shed.
However, since the characteristics that the melted solder
30
is apt to be separated onto each of the electrodes
111
,
121
can be utilized as a fuse, it is necessary that the melted solder
30
does not separate onto the electrodes
111
,
121
only when the solder fuse portion
101
is formed.
In order to solve the above problem, Japanese Patent Application Laid-open No.4-56028 proposes a safety device for an electric circuit wherein a solder fuse portion is formed with a porous solder layer having cavities and bridging electrodes of respective first and second circuit patterns, which electrodes are standoff-insulated each other on a circuit board.
With respect to the above conventional safety device having such a structure, however, a solder shall be melted incompletely so as to form the porous solder layer, thereby consuming time and cost, compared with formation of a solder fuse portion with the normal solder
30
.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a safety device for an electric circuit, wherein a solder fuse portion can be easily formed with the same and normal solder as used for connecting electrical parts, has high reliability as a fuse, and can reduce manufacturing cost.
In order to achieve the above-described object, as a first aspect of the present invention, a safety device for an electric circuit in accordance with the present invention includes: a circuit board; a first circuit pattern; a second circuit pattern; a first electrode connected to the first circuit pattern; a second electrode connected to the second circuit pattern, while enclosing the first electrode without a break, the second electrode being standoff-insulated from the first electrode; and a solder fuse portion made of a solder and formed over and inside the second electrode for bridging the first and second electrodes, wherein the solder fuse portion in a melted state separates onto the first and second electrodes by surface tension of the solder, whereby a circuit between the first and second circuit patterns is broken.
As a second aspect of the present invention, in the structure with the above first aspect, the first and second electrodes are arranged on the top of the circuit board and the first circuit pattern is arranged on the reverse side of the circuit board.
As a third aspect of the present invention, in the structure with the above first or second aspect, the first electrode is formed in a disk-shape and the second electrode is formed annularly.
According to the above-described structure, since the second electrode has no break, the second electrode can prevent the almost completely melted solder from spreading outward and simultaneously can leave the almost completely melted solder on the gap arranged on the top of the circuit board. That is, the solder fuse portion can be easily formed with the same and normal solder as used for connecting electrical parts.
Also, since the completely melted solder surely separates onto each of the first and second electrodes at an abnormal overheating of the electric circuit, the circuit between the first and second circuit patterns is broken, thereby achieving high reliability as a fuse.
Further, since the solder fuse portion can be formed with the same and normal solder as used for connecting electrical parts, a special manufacturing process conventionally required is not required, whereby the safety device for an electric circuit can be manufactured at low cost.
As described hereinabove, according to the safety device for an electric circuit in accordance with the present invention, a solder fuse portion can be easily formed with the same and normal solder as used for connecting electrical parts, has high reliability as a fuse, and can reduce manufacturing cost.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3334205 (1967-08-01), Griffin
patent: 4198617 (1980-04-01), Hara
patent: 4393432 (1983-07-01), Neuhaus et al.
patent: 4622534 (1986-11-01), Bowman
patent: 4652848 (1987-03-01), Hundrieser
patent: 5192940 (1993-03-01), Yajima et al.
patent: 5543774 (1996-08-01), Lof
patent: 5586014 (1996-12-01),
Ishikawa Satoshi
Soda Osamu
Armstrong, Westerman Hattori, McLeland & Naughton, L.L.P.
Thompson Gregory
Vortman Anatoly
Yazaki -Corporation
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