Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – Fusible element actuated
Reexamination Certificate
2002-02-11
2004-09-28
Vortman, Anatoly (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
Fusible element actuated
C337S248000, C337S246000, C337S228000, C337S187000
Reexamination Certificate
active
06798330
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a miniature fuse of surface mount type. In particular, the present invention is suitable for a micro-miniature fuse of surface mount type which can be used for protection of apparatuses for communication and whose longitudinal length does not exceed 11 mm.
Apparatuses for communication to be connected to telephone lines and the like are liable to be subjected to high surge current due to indirect lightning strikes, or sudden and unusually high increases in voltage due to telephone lines accidentally coming into contact with power lines. Thus, fuses to be used for apparatuses for communication require both a strong time lag characteristic preventing the fuses from being melted by the surge current due to indirect lightning strikes as well as a high breaking capacity in the order of 60A at AC600V which assures a big fault current flow at the moment of the accidental power line contact to be safely switched off. Furthermore, as the apparatuses for communication become increasingly miniaturized, micro-miniature sized fuses are required to have a strong time lag characteristic and a high breaking capacity, they are also required to be of a surface mount type so that surface mounting of high density may be carried out. Thus far there have been provided inner soldered fuses which are constructed in such a manner as shown in FIG.
1
and
FIG. 2
, wherein a fusible member
102
is wound around a support member of insulating material made up of bundled glass fibers and the respective ends of the fusible member
102
are soldered to the recessed bottom of the conductive terminals
104
of cap-like configuration.
A disadvantage of the inner soldered type fuse is that the electrical resistances of produced fuses disperse widely from designed value so that the pre-arcing time may often be uneven. In accordance with an inner soldering type, when a soldering iron is placed from the outside of the cap-like terminal
104
so as to melt the solder
106
attached to the interior of the recess of the cap terminal
104
to solder the fusible member
102
wound around the bundled glass fibers
100
to the bottom of the recess of the cap terminal
104
, melted soldering material will be caused to flow along the fusible member
102
wound around the bundle of the glass fibers
100
, resulting in a clogging of the spaces between the adjacent portions of the wound fusible member
102
to make short-circuits between them. As a result, the length of the fusible member
102
which is in the short-circuit state may result in one-third of overall length of the fusible member, and thus the performance of fuses may be changed entirely. In addition to the above, it also often happens that at the time of breaking, the soldering material inside the cap terminal will be vaporized and arc will be sustained, making it impossible for the breaking to be performed, which is also a disadvantage.
Further, the conductive cap-like terminals
104
and the main body
108
made of an insulating material are secured by the frictional force caused by coagulation of the soldering material which has flowed into the space between the cap terminals and the main body. In the case of fuses of surface mount type, when such fuses are mounted on a substrate by means of soldering, the fuses are also heated to a temperature of soldering. Since the soldering temperature profiles differ from manufacturer to manufacturer, in the case of high temperature soldering, the soldering materials within the fuses, namely the soldering materials which have entered between the conductive cap-like terminals
104
and the main body
108
are caused to melt, whereby the conductive cap-like terminals
104
might possibly be detached from the main body
108
, which was considered a problem Furthermore, since the melting point of the soldering material which does not contain lead in view of problems associated with its use tends to be relatively high, the soldering temperature at the time of mounting fuses on a substrate is likely to be further increased, which is another problem that will have to be solved.
As shown in FIG.
1
and
FIG. 2
, the main body
108
has a columnar configuration and a through hole
110
is so provided as to extend between the opposite end faces of the main body in the longitudinal direction. Since a miniature fuse of surface mount type is so small, in the order of 11 mm in respect of the overall length, the diameter of such a through hole is also very small. Accordingly, since the support member
100
with the fusible member
102
wound therearound had to be inserted through a small inlet on the end face of the main body
108
, workability in the course of manufacturing was consequently poor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a miniature fuse of surface mount type which has a stable pre-arcing time-current characteristic without uneven performance and a strong time lag characteristic and, in addition, a large breaking capacity.
Another object of the present invention is to provide a miniature fuse of surface mount type which has a stable pre-arcing time current characteristic without uneven performance and a large breaking capacity.
A further object of the present invention is to provide a miniature fuse of surface mount type which is easy to manufacture.
The object of the present invention mentioned above may be accomplished by a miniature fuse of surface mount type according to the present invention including a fusible member, a support member adapted to support said fusible member, a main body made of heat resistant insulating material and a pair of conductive terminals, wherein said main body includes a pair of opposed end portions and a cavity defined inside of the main body between said pair of end terminals, the middle part of said fusible member is wound around said support member and, in this condition, disposed in said cavity between a pair of end portions, the opposite end portions of said fusible member are extended outwardly onto the peripheral surface of said main body from a pair of end portions of said main body or from the vicinities thereof, the respective conductive terminals are fit onto the respective end portions of said main body, and connected electrically and mechanically to the respective end portions of said fusible member, and wherein said support member is made of a material that has ease of shape formation, has pressure resistant strength, containing in terms of weight ratio Al
2
O
3
exceeding 96%, MgO exceeding 3%, and BeO less than 1%; said fusible member is made of a metallic material having a low melting temperature and containing in terms of weight ratio Ag equal to or exceeding 50%, Cu equal to or exceeding 20%, Zn equal to or exceeding 17% and Sn equal to or exceeding 5%; and said electrical and mechanical connection is executed by welding.
According to an aspect of the present invention, it is preferable that cut-out recessed portions are formed at two locations along the diagonal line on the outer peripheral surface at the opposite end portions of said main body in contact with the end surfaces of said main body, and the respective end portions of said fusible member are engaged with said cut-out recessed portions.
According to another aspect of the present invention, it is preferable that said main body has a columnar configuration; said conductive terminals are of cap-like configuration having recessed portions to be fit onto the opposite end portions of said main body; and lids of thin sheet made of insulating material and having a thickness smaller than the depth of said recessed portions are provided between the end surfaces of said main body and the bottom of the recessed portions of said conductive terminals.
The second object of the present invention mentioned above may be accomplished by a miniature fuse of surface mount type according to the present invention including a fusible member, a main body made of heat resistant insulating material, and a pair of conductive terminals, wh
Arikawa Hiroo
Ishimura Koh
Norisue Seiji
SOC Corporation
Vortman Anatoly
Wenderoth , Lind & Ponack, L.L.P.
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