Electrical resistors – Resistance value responsive to a condition – Current and/or voltage
Reexamination Certificate
2000-09-15
2001-10-02
Easthom, Karl D. (Department: 2832)
Electrical resistors
Resistance value responsive to a condition
Current and/or voltage
C029S874000, C029S612000, C338S203000, C338S313000
Reexamination Certificate
active
06297722
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 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 in the aforementioned cutting lines.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a process for manufacturing surface mountable electrical devices that is capable of overcoming the aforementioned drawbacks.
According to the present invention, a process for manufacturing surface mountable electrical devices comprises the steps of: preparing a PTC resistive plate having first and second opposite surfaces; respectively covering the first and second opposite surfaces with first and second conductive layers to form a laminate; forming a plurality of spaced apart bores of cross-shaped cross-section in the laminate along intersecting cutting lines at locations where the cutting lines intersect; electroplating the first and second conductive layers and the cross-shaped bores; and cutting the laminate along the cutting lines to form a plurality of polygonal elements with each of the bores being divided into four parts, each having a substantially L-shaped cross-section.
REFERENCES:
patent: 5334968 (1994-08-01), Negoro
patent: 5572779 (1996-11-01), Adelman 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
Easthom Karl D.
Fuzetec Technology Co. Ltd.
Lee Richard K.
Merchanat & Gould P.C.
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