Surface mountable electrical device

Details Surface mountable electrical device Surface mountable electrical device

2001-03-16

2001-09-04

Easthom, Karl D. (Department: 2832)

Electrical resistors

Resistance value responsive to a condition

Current and/or voltage

C338S327000, C338S328000, C338S314000, C338S312000

Reexamination Certificate

active

06285275

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a surface mountable electrical device, more particularly to a surface mountable electrical device that can serve as a circuit protection device, such as a fuse.
2. Description of the Related Art
FIG. 1
illustrates a conventional circuit protection device
10
disclosed in U.S. Pat. No. 5,852,397. The device
10
is prepared from a laminate having an array of drilled apertures. The laminate is cut into a plurality of the devices along intersecting cutting lines in two directions. The apertures are located at positions where the cutting lines intersect. The device
10
includes a planar PTC (positive temperature coefficient) resistive element
11
having opposite first and second surfaces
111
,
112
, and four apertures
113
of quarter circular cross-section that run between the first and second surfaces
111
,
112
at four corners of the PTC resistive element
11
, first and second electrode layers
12
,
13
respectively covering portions of the first and second surfaces
111
,
112
, third and fourth electrode layers
14
,
15
respectively covering other portions of the first and second surfaces
111
,
112
and spaced apart from the first and second electrode layers
12
,
13
, a first plating layer
16
having first and second portions
161
,
162
respective covering the first and fourth electrode layers
12
,
15
and two spaced apart first transverse portions
163
extending between the first and second portions
161
,
162
within two of the apertures
113
that are adjacent to the fourth electrode layer
15
, and a second conductive layer
17
having third and fourth portions
171
,
172
respectively covering the second and third electrode layers
13
,
14
and two second transverse portions
173
extending between the third and fourth portions
171
,
172
within another two of the apertures
113
that are adjacent to the third electrode layer
14
. The first and second transverse portions
163
,
173
have a quarter circular cross-section corresponding to those of the apertures
113
. Aside from being formed at the corners of the PTC resistive element
11
and having quarter cross-sections, the aforesaid apertures
113
can be formed at any other positions in the PTC resistive element
11
, and can have a closed cross-section, such as a circular, an oval, or a rectangular shape, or a reentrant cross-section that denotes an open cross-section which has a depth of at least 0.15 times the maximum width thereof and which has at least one part where the opposite edges of the cross section are parallel to each other in order to ensure that the first and second transverse portions
163
,
173
of the first and second plating layers
16
,
17
will not be damaged or dislodged during installation or use of the device
10
. However, since the maximum width of each aperture
113
is very small, which is normally designed to be within a range of 0.2 to 0.5 mm, there is a tendency for the first and second transverse portions
163
,
173
of the first and second plating layers
16
,
17
to be damaged or dislodged during the process of cutting the laminate to form the devices
10
with apertures of reentrant cross-sections, and there is a need for a relatively high accuracy to maintain the aforementioned cutting lines.
FIGS. 2 and 3
illustrate another conventional circuit protection device
8
disclosed in U.S. Pat. No. 5,884,391. The device
8
is prepared from a laminar sheet
9
having an array of strips
90
that includes a plurality of repeated units
92
that are to be processed into the devices
8
, and an array of elongated slits
91
at intervals of the strips
90
. The device
8
includes a PTC resistive element
80
with opposite first and second surfaces
801
,
802
, first and second electrode layers
81
,
82
respectively formed on portions of the first and second surfaces
801
,
802
, third and fourth electrode layers
83
,
84
respectively formed on other portions of the first and second surfaces
801
,
802
, first and second insulating layers
85
,
86
respectively formed on portions of the first and third electrode layers
81
,
83
and portions of the second and fourth electrode layers
82
,
84
, U-shaped first and second conductive layers
87
,
88
respectively formed on and interconnecting portions of the first and fourth electrode layers
81
,
84
and portions of the second and third electrode layers
82
,
83
, and U-shaped first and second end terminations
871
,
881
respectively superimposed on the first and second conductive layers
87
,
88
. Each of the U-shaped first and second conductive layers
87
,
88
has two lateral segments (
871
,
881
) that extend in lateral directions along the first and second surfaces
801
,
802
, and a transverse segment (
872
,
882
) that extends in a transverse direction relative to the first and second surfaces
801
,
802
at one side of the PTC resistive element
80
that faces a respective slit
91
. Since the transverse segment (
871
,
881
) of each of the first and second conductive layers (
87
,
88
) is only formed on one side of the PTC resistive element
80
, the device
8
still encounters the same problem of the previous device
10
disclosed in U.S. Pat. No. 5,852,397, and needs a relatively high accuracy when cutting the units of the laminar sheet
9
into the devices
8
.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a surface mountable electrical device that is capable of overcoming the aforementioned drawbacks.
According to the present invention, a surface mountable electrical device comprises: a PTC resistive element having opposite first and second surfaces and a plurality of planar lateral faces transverse to and interconnecting the first and second surfaces, each of two adjacent ones of the lateral faces defining a corner therebetween, the corner being indented relative to the two adjacent ones of the lateral faces and having a terraced face that interconnects the two adjacent ones of the lateral faces and that has a first tread face extending from one of the two adjacent ones of the lateral faces, a first rise face extending from and transverse to the first tread face, a second tread face extending from and transverse to the first rise face in a same direction as the first tread face, and a second rise face extending from and transverse to the second tread face in a same direction as the first rise face to connect with the other one of the two adjacent ones of the lateral faces; first and second electrode layers formed respectively on the first and second surfaces; a third electrode layer formed on the first surface and spaced apart from the first electrode layer; and a first conductive layer that has a first lateral segment formed on the third electrode layer, a second lateral segment formed on the second electrode layer, and a transverse segment transverse to and interconnecting the first and second lateral segments. The transverse segment is formed on the terraced face of one of the corners and has a terraced cross-section corresponding to the terraced face of said one of the corners.


REFERENCES:
patent: 5334968 (1994-08-01), Negoro
patent: 5572779 (1996-11-01), Adelman et al.
patent: 5852397 (1998-12-01), Chan et al.
patent: 5864281 (1999-01-01), Zhang et al.
patent: 5884391 (1999-03-01), McGuire et al.
patent: 6023403 (2000-02-01), McGuire et al.
patent: 4-357801 (1992-12-01), None

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