Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-02-16
2004-08-31
Vo, Peter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S610100, C029S611000, C338S0220SD, C338S225000, C338S328000, C338S332000
Reexamination Certificate
active
06782604
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a chip PTC thermistor which uses a conductive polymer having a positive temperature coefficient (hereinafter referred to as “PTC”), and methods for manufacturing the same.
BACKGROUND ART
PTC thermistors have been used as the components to protect a device against an overcurrent. Exposure to an overcurrent in an electric circuit causes the conductive polymer having the PTC characteristics used in a PTC thermistor to heat up and expand by self heating. The thermal expansion increases resistance of the conductive polymer sheet in the PTC thermistor, and thus reduces the current to a safer level.
A conventional chip PTC thermistor is described below.
One known chip PTC thermistor is disclosed in Japanese Laid-open Patent No. H9-503097. The chip PTC thermistor is formed of a resistive material having the PTC characteristics, the chip thermistor having a first surface and a second surface. The chip thermistor comprises a PTC resistor element that specifies a space between the first surface and the second surface, a lateral conductive member provided within said space through the first surface and the second surface of PTC element, the conductive member being fixed to said PTC element, and a first layered conductive member connected physically and electrically to the lateral conductive member.
FIG. 14A
shows a cross sectional view of the conventional chip PTC thermistor, and
FIG. 14B
is the plan view. In
FIGS. 14A and B
, a resistor body
61
is formed of a conductive polymer having PTC characteristics, electrodes
62
a
,
62
b
,
62
c
,
62
d
are formed of a metal foil, conductive members
64
a
,
64
b
are formed inside the openings
63
a
,
63
b
by plating, and electrically couple the electrode
62
a
with
62
d
, and the electrode
62
b
with
62
c
respectively.
A method for manufacturing the conventional chip PTC thermistor is described below.
FIGS. 15A-15D
, and
FIGS. 16A-16C
illustrate the process steps for manufacturing the conventional chip PTC thermistor.
Polyethylene and conductive carbon particles are mixed to form a sheet
71
shown in FIG.
15
A. The sheet
71
is sandwiched by two sheets of a metal foil
72
, as shown in
FIG. 15B
, and these are heat pressed together to be integrated into a sheet
73
as shown in FIG.
15
C. After undergoing electron beam irradiation, the integrated sheet
73
is provided with through holes
74
in a regular pattern arrangement as shown in
FIG. 15D
, and then a metal film
75
is formed by plating to cover the inner surface of the through hole
74
and the metal foil
72
, as shown in FIG.
16
A. Then, as shown in
FIG. 16B
, an etched slit
76
is formed in the metal foil through a photo-lithographic process. And then, it is cut off along a longitudinal cut line
77
and a lateral cut line
78
to be separated into piece chips to obtain the conventional chip PTC thermistor
79
as shown in FIG.
16
C.
In the conventional chip PTC thermistor of the above configuration, however, the two electrodes
62
a
and
62
b
, or
62
c
and
62
d
, which are to be connected with a printed circuit board when the chip thermistors are mounted thereon, are disposed on only one surface of the chip thermistor (ref. FIG.
14
A). As a result, when the chip thermistors are mounted on a printed circuit board and reflow-soldered, solder fillets formed by the soldering are not visible from above because they are shadowed by the chip thermistors. Therefore, it is difficult to make sure of the state of soldering by visually inspecting the soldered portion. Furthermore, because the electrodes of the chip thermistors are not disposed at their sides, the flow soldering process is not applicable.
Furthermore, in the above described conventional manufacturing method, dislocation of the cut lines in relation to the location of a through hole is not avoidable because of dispersions in the accuracy of the sheet aligning and the cutting operations. This readily leads to a variation in the area of coupling between the conductive member formed within the through hole and the top/bottom electrodes.
FIG. 17A
shows a state wherein no dislocation exists between the through hole and the cut line, while
FIG. 17B
shows a state where there is a dislocation. In
FIGS. 17A and 17B
, numeral
81
denotes a through hole,
82
is a cut line,
83
is an electrode,
84
is an etched slit. In a case where a part of one through hole
81
, among the through holes located at both sides of a cut line, is cut as a result of the above described dislocation, as shown in
FIG. 17B
, the area at a contact section
85
making contact between the conductive member disposed within the through hole and the top/bottom electrodes becomes smaller, as compared with a case where there is no such dislocation. The case caused by a dislocated cut line is illustrated in
FIG. 17C. A
problem with the reduced contact area between the conductive member and the top/bottom electrodes is that the junction between the conductive member and the top/bottom electrodes is easily cracked due to stress caused thereon by repetitive expansion and shrinkage of the conductive polymer.
The present invention addresses the above problems and aims to provide a chip PTC thermistor, as well as a method of manufacturing the same, wherein the soldered portion can be inspected easily visually after the chip thermistors are mounted on a printed circuit board, and the chip PTC thermistor can be soldered by flow soldering. Furthermore, the coupling between the conductive member and the electrodes has only a small dispersion in the strength of connection against the stress that caused as a result of expansion and shrinkage of the conductive polymer.
DISCLOSURE OF THE INVENTION
A chip PTC thermistor of the present invention comprises:
a cuboidal form conductive polymer having the PTC characteristics;
a first main electrode disposed on a first surface of the conductive polymer;
a first sub-electrode disposed on the same surface as the main electrode, yet being independent from the first main electrode;
a second main electrode disposed on a second surface opposite the first surface of the conductive polymer;
a second sub-electrode disposed on the same surface as the second main electrode, yet being independent from the second main electrode;
a first side electrode disposed covering at least the entire surface of one of the side surfaces of the conductive polymer, which side electrode is electrically connected with the first main electrode and the second sub-electrode; and
a second side electrode disposed covering at least the entire surface of the other side surface opposing the one side surface of the conductive polymer, which side electrode is electrically connected with the first sub-electrode and the second main electrode.
In a method for manufacturing the chip PTC thermistors of the present invention, a conductive polymer having the PTC characteristics is sandwiched from the top and the bottom by a patterned metal foil and these are integrated by heat pressing into a sheet form, the integrated sheet is provided with openings, the integrated sheet having the openings is coated on the top and the bottom surfaces with a protective coating, a side electrode is formed at the side of the sheet having the protective coating and the openings, and the sheet provided with the side electrodes and the openings is divided into pieces.
With the chip PTC thermistors as configured above, solder fillet can be formed at the side of thermistor chips mounted on a printed circuit board because the side electrode is provided covering at least the entire side surface of the two side surfaces of the conductive polymer. Thus the chip PTC thermistors provide an advantage that the state of soldering of the soldered portions can be confirmed easily by visual inspecting after the chip thermistors are mounted on a printed circuit board a further advantage of the chip PTC thermistor is that they can be used in a flow soldering process.
In a method for manufacturing the chip PTC thermistors, wherein t
Ikeda Takashi
Iwao Toshiyuki
Kojima Junji
Morimoto Kohichi
Kim Paul D
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Vo Peter
LandOfFree
Method of manufacturing a chip PTC thermistor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of manufacturing a chip PTC thermistor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of manufacturing a chip PTC thermistor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3307921