Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-08-09
2003-08-26
Vidovich, Gregory (Department: 3726)
Metal working
Method of mechanical manufacture
Electrical device making
C029S619000, C029S620000, C029S025420, C338S307000
Reexamination Certificate
active
06609292
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of making a chip resistor for surface mounting on a printed circuit board for example.
2. Description of the Related Art
Recently, for enhancing a mounting density on a circuit board, various electronic components are being replaced with chip-type components which can be surface-mounted. As a typical example of chip-type electronic component, there exists a chip resistor of the type as shown in FIG.
26
. Specifically, the chip resistor includes a substrate
70
made of a ceramic material for example, film electrodes
71
formed to cover the opposite side surfaces and some parts of the upper and the lower surfaces of the substrate
70
, a film resistor
72
bridging the film electrodes
71
on the upper surface of the substrate
70
, and a protective coating
73
for protecting the film resistor
72
.
The chip resistor is made generally in the following manner. Specifically, as shown in
FIG. 27
, use is made of a mother substrate
74
which is substantially flat and prepared by baking a ceramic material. The mother substrate
74
is formed with a plurality of longitudinally-dividing grooves
75
(hereinafter referred to as BB slit which is an abbreviation of bar break slit) arranged at a regular pitch, and a plurality of transversely-dividing grooves
76
(hereinafter referred to as CB slit which is an abbreviation of chip break slit) arranged at a regular pitch. The respective slits
75
,
76
define generally rectangular unit substrates
77
which are finally formed into chip resistors.
Subsequently, as shown in
FIG. 28
, film electrodes
71
as electrode terminals are collectively formed on the upper surface of the mother substrate
74
. Specifically, the film electrodes are formed at opposite ends of each of the unit substrates
77
by printing and baking. Thereafter, film resistors
72
are collectively formed on the unit substrates
77
by printing and baking.
The mother substrate
74
is then divided widthwise along the BB slits
75
to provide intermediate products each in the form of a narrow strip. Subsequently, after predetermined electrode material is printed and baked on the side and the lower surfaces of each of the intermediate products, the intermediate product is divided along the CB slits
76
.
The resistance of each of the film resistors
72
is adjusted by so-called laser trimming in the state of the mother substrate
74
. Specifically, a trimming groove is formed on each film resistor
72
by laser application for providing a predetermined resistance while measuring the resistance with a measurement probe brought into contact with film electrodes
71
provided at opposite ends of the film resistor
72
.
In forming the film electrodes
71
and the film resistors
72
by the above-described chip resistor making, a print mask
79
as shown in
FIG. 29
, which includes openings
78
formed in accordance with the printing pattern of the film electrodes
71
or the like, is disposed on the mother substrate
74
. In this state, by moving a squeegee on the print mask
79
for example, printing paste is applied and printed on the mother substrate
74
through the openings
78
of the print mask
79
.
However, when the mother substrate
74
made of ceramic material is baked, the mother substrate
74
may shrink widthwise or longitudinally to some extent. Therefore, when the above-described print mask
79
is disposed on the mother substrate
74
, the pitch of the openings
78
of the print mask
79
does not coincide with the pitch of the BB slits
75
and CB slits
76
, thereby causing print deviation.
Hitherto, therefore, a plurality of (practically no less than 100 kinds of) print masks
79
are prepared which are identical in printing pattern but slightly different in position of openings
78
. Thus, for applying printing paste on the mother substrate
74
to form film electrodes
71
or the like, a print mask
79
having openings
78
which correspond to the slits
75
,
76
of the shrunk mother substrate
74
is selected and disposed on the mother substrate
74
. However, preparation of a multiplicity of print masks
79
in accordance with shrinkage of the mother substrate
74
is uneconomical.
Further, in recent years, size-reduction of a chip resistor is increasingly demanded. However, there is a limitation on and a difficulty in reducing the size of a chip resistor by the above-described method which utilizes the print mask
79
for forming the film electrodes
71
and the film resistors
72
.
On the other hand, JP-A-63-224305 discloses another method of making a chip resistor. This method comprises the steps of extruding a substrate material into a non-baked green substrate bar, printing electrodes and resistors on the green substrate bar, simultaneously baking the substrate bar together with the electrodes and the resistors, and finally dividing the substrate bar into unit substrates.
With this method, since the substrate bar together with the electrodes and the resistors are simultaneously baked, it is possible to alleviate the printing deviation of the electrodes and the resistors relative to the substrate bar, or the printing deviation of the resistors relative to the electrodes.
However, the above-described method includes the step of forming, by extrusion, a non-baked green substrate having a cross section which corresponds to the cross section of an aimed chip resistor. With this method, however, it is very difficult to form extremely small chip resistors of a dimension of, for example, no more than 1 mm so as to have uniform cross sections. This is partially because it is very difficult to adjust a substrate material, which is a suspension of ceramic particles and a solvent so as to have viscosity suitable for extrusion. Further, it is not practical to form a green substrate bar of a uniform cross section by continuously extruding the substrate material through a very small nozzle hole.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of making a chip resistor which is capable of realizing size reduction of a chip resistor and enhancing production efficiency.
In accordance with the present invention, there is provided a method of making chip resistors each of which comprises a unit substrate which is rectangular as viewed in plan and has a predetermined thickness, a resistor element provided on an upper surface of the substrate, and electrodes provided at opposite ends of the unit substrate, the method comprising the steps of:
continuously forming a green sheet;
obtaining from the green sheet an intermediate product in the form of a narrow strip on which electrodes and resistor elements are printed, at least the resistor elements being printed at a pitch corresponding to the unit substrates;
forming slits on the intermediate product for dividing the intermediate product into the unit substrates, each of the slits extending perpendicularly to the longitudinal direction of the intermediate product;
simultaneously baking the intermediate product together with the printed electrodes and the printed resistor elements; and
dividing the baked intermediate product along the slits into the unit substrates.
In a preferred embodiment, the step of obtaining the intermediate product is performed by cutting the green sheet into a narrow substrate strip of a predetermined width extending longitudinally of the green sheet followed by printing thereon the electrodes and the resistor elements.
In a preferred embodiment, corners of the substrate strip are rounded in cutting the green sheet into the narrow substrate strip of the predetermined width.
In a preferred embodiment, an upper surface of the narrow substrate strip is formed, at widthwise opposite edges thereof, with longitudinally extending stepped portions of a predetermined width.
In a preferred embodiment, an upper surface of the narrow substrate strip is formed, at a widthwise central portion thereof, with a longitudinally extending recess having a predetermined
Bednarek Michael D.
Kenny Stephen
Rohm & Co., Ltd.
Shaw Pittman LLP
Vidovich Gregory
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