Electrical resistors – With base extending along resistance element – Resistance element coated on base
Reexamination Certificate
2002-03-07
2004-04-20
Easthom, Karl D. (Department: 2832)
Electrical resistors
With base extending along resistance element
Resistance element coated on base
C338S313000, C338S314000, C338S328000, C338S332000
Reexamination Certificate
active
06724295
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chip resistor for surface-mounting on a printed circuit board and to a method of making the same.
2. Description of the Related Art
As is well known, various types of chip devices have been developed as components for constituting electric circuits. An example of such chip devices is a surface-mounting-type chip resistor (designated by a reference sign
21
as a whole) as shown in FIG.
15
. The resistor
21
includes a rectangular substrate
22
formed of alumina ceramic material. As shown in
FIG. 15
, the substrate
22
has an upper surface
22
a
, side surfaces
22
b
and a lower surface
22
c
. The resistor
21
includes a pair of first upper electrodes
23
formed on the upper surface
22
a
, side electrodes
24
formed on the respective side surfaces
22
b
, and lower electrodes
25
formed on the lower surface
22
c
. The upper surface
22
a
of the substrate
22
is formed with a resistor element
26
connecting the first upper electrodes
23
to each other. The resistor element
26
is covered with a protective coating layer
27
. Further, the protective coating layer
27
is covered with an overcoat layer
29
. Each first upper electrode
23
has an upper surface formed with a second upper electrode
28
.
The resistor
21
may be formed utilizing an aggregate board
11
as shown in
FIG. 16
, which is made of alumina ceramic material. The aggregate board
11
has a size capable of simultaneously providing a plurality of identical resistors. Specifically, the aggregate board
11
is sectioned into a plurality of rectangular regions
12
. Each of the rectangular regions
12
corresponds to one resistor
21
. In the figure, reference signs
13
,
14
indicate excess portions of the aggregate board
11
. The aggregate board
11
will be divided along the excess portions using a dicing cutter for example.
As shown in
FIG. 16
, the aggregate board
11
has an upper surface on which a plurality of conductor pieces
23
′ are arranged in a matrix. Each of the conductor pieces
23
′ extends across the corresponding cutting line
13
. Each rectangular region
12
is overlapped by two conductor pieces
23
′ which are spaced from each other along a cutting line
14
. The overlapping regions finally become the upper electrodes
23
shown in FIG.
15
.
After the conductor pieces
23
′ are formed, necessary parts such as a resistor layer corresponding to the resistor element
26
(
FIG. 15
) and a protective coating layer and the like are formed. Then, at an appropriate stage, the aggregate board
11
together with the conductor pieces
23
′ and the like formed thereon are divided along the cutting lines (excess portions)
13
.
Thereafter, side conductor layers (corresponding to the side electrodes
24
of
FIG. 15
) are formed on the cutting surface of the substrate
11
. By subsequently dividing the substrate
11
along the cutting lines (excess portions)
14
, the plural rectangular regions
12
are completely separated from each other. Finally, plating is applied to the electrodes
24
,
25
and
28
shown in
FIG. 15
, thereby providing the resistor
21
as a final product.
Although the above method is capable of making a plurality of resistors from one aggregate board and hence has a high manufacturing efficiency, it also has the following drawbacks.
As described above, in the manufacturing process, the aggregate board
11
(and the conductor pieces
23
′ and the like) are divided along the cutting lines
13
. At this time, the rotation of the dicing cutter may raise the conductor pieces
23
′. In such a case, as shown in
FIG. 17
, the first upper electrode
23
of the resistor
21
includes a rising portion at the edge thereof. As a result, the second upper electrode
28
formed on the first upper electrode
23
also rises.
Such a rising portion formed in the resistor
21
causes various problems. For example, the side electrode
24
may not be suitably connected to the first upper electrode
23
or the second upper electrode
28
. Further, in solder-plating the second upper electrode
28
, solder cannot be suitably applied to the rising portion.
SUMMARY OF THE INVENTION
The present invention is conceived under the circumstances described above. It is, therefore, an object of the present invention is to provide a chip resistor which is free from the rising of an electrode on the supporting substrate.
According to a first aspect of the present invention, there is provided a method of making a chip resistor. This method includes the following steps. First, an aggregate board is prepared which includes a first region and a second region which are spaced from each other via an excess portion. Then, a conductor pattern is formed which extends to bridge the first region and the second region. Subsequently, a resistor element is formed in each of the first region and the second region for connection to the conductor pattern. Then, the aggregate board is cut at the excess portion. The conductor pattern includes a thinner-walled portion extending across the excess portion and a thicker-walled portion connected to the thinner-walled portion and spaced from the excess portion.
According to the above structure, the conductor pattern is cut together with the substrate. However, since the conductor pattern is cut at the thinner-walled portion, the problem of rising as is in the prior art does not occur. Preferably, the thinner-walled portion has a thickness of 0.1-3.0 &mgr;m, whereas the thicker-walled portion has a thickness of 5-25 &mgr;m.
Preferably, the conductor pattern forming step includes a sub-step of applying a conductor paste for the thicker-walled portion and a sub-step of applying a conductor paste for the thinner-walled portion.
Preferably, the conductor paste for the thicker-walled portion and the conductor paste for the thinner-walled portion are baked simultaneously.
Preferably, the conductor paste for the thicker-walled portion and the conductor paste for the thinner-walled portion are made of a same material.
Preferably, the method according to the present invention further comprises the step of forming a resistance adjusting groove in the resistor element.
According to a second aspect of the present invention, there is provided a chip resistor comprising an insulating substrate having an upper surface and a side surface, a first conductor pattern formed on the upper surface, a resistor element connected to the first conductor pattern. The first conductor pattern includes a thinner-walled portion contacting the upper surface, and a thicker-walled portion connected to the thinner-walled portion and contacting the upper surface. The thinner-walled portion is spaced from the resistor element and extends up to the side surface. The thicker-walled portion contacts the resistor element and is spaced from the side surface.
Preferably, the resistor further includes a second conductor pattern extending on the first conductor pattern. The second conductor pattern contacts both of the thinner-walled portion and the thicker-walled portion.
Preferably, the thinner-walled portion has a thickness of 0.1-3.0 &mgr;m, whereas the thicker-walled portion has a thickness of 5-25 &mgr;m.
Other features and advantages of the present invention will become clearer from the description of the preferred embodiment given below with reference to the accompanying drawings.
REFERENCES:
patent: 5379016 (1995-01-01), Smith et al.
patent: 5966067 (1999-10-01), Murakami et al.
patent: 6153256 (2000-11-01), Kambara et al.
patent: 6242999 (2001-06-01), Nakayama et al.
patent: 6304167 (2001-10-01), Nakayama
Bednarek Michael D.
Easthom Karl D.
Rohm & Co., Ltd.
Shaw Pittman LLP
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