Patent Description:
Patent Literature <NUM> discloses an invention that relates to a resistor, and a method of manufacturing the resistor. The resistor disclosed in Patent Literature <NUM> includes a resistive body, electrode plates which are positioned at both sides of the resistive body, respectively, and bent toward the lower surface side of the resistive body, and an electrically non-conductive filler interposed between the resistive body and the electrode plates.

The filler serves to adhere the resistive body to the electrode plates. In the resistor as disclosed in Patent Literature <NUM>, heat propagates from the resistive body to the electrode plates via the filler to secure a heat dissipation property.

Further prior art could be found in documents <CIT>, <CIT>, <CIT> and <CIT>.

In Patent Literature <NUM>, the filler in the uncured and unsolidified state is disposed on the surface of the resistive body, and the electrode plates are bent to be in contact with the filler. Thereafter, the filler is cured and solidified.

In Patent Literature <NUM>, as the filler in contact with the bent electrode plates is uncured, the filler exhibits high fluidity. The high fluidity is likely to cause the thickness variation of the filler between the resistive body and the electrode plates. Accordingly, the resistor disclosed in Patent Literature <NUM> has a problem that the heat dissipation property or adhesive strength is likely to vary.

The present invention has been made in consideration of the above-described problem. Especially, it is an object of the present invention to provide a resistor manufacturing method as disclosed in claim <NUM> for suppressing the thickness variation of the thermally conductive layer intervening between the resistive body and the electrode plates.

A resistor manufacturing method according to the present invention as set forth with the appended claims includes a step of forming an uncured thermally conductive layer on a surface of a resistive body, a step of bringing the thermally conductive layer into a semi-cured state, and a step of bending electrode plates respectively disposed at both sides of the resistive body, further curing the thermally conductive layer, and performing adhesion between the resistive body and the electrode plates via the thermally conductive layer.

Unlike the generally employed method, a resistor manufacturing method according to the present invention ensures that the thickness variation of a thermally conductive layer between a resistive body and electrode plates is suppressed. The method allows manufacturing of a resistor while suppressing variation in the heat dissipation property and the adhesive strength.

An embodiment according to the present invention (hereinafter simply referred to as an "embodiment") will be described in detail. The present invention is not limited to the following embodiment, but may be implemented in various modifications within a scope of the present invention as set forth with the appended claims.

Referring to the drawings, a resistor manufacturing method of the embodiment will be described in the order of the manufacturing steps.

In steps as shown in <FIG>, a resistive body <NUM> and a plurality of electrode plates <NUM> are prepared. Each of the resistive body <NUM> and the electrode plates <NUM> has a flat plate shape or a belt-like shape. In the embodiment as shown in <FIG>, each of the resistive body <NUM> and the electrode plates <NUM> has the belt-like shape.

In the step as shown in <FIG>, the electrode plates <NUM> are bonded to both sides of the resistive body <NUM>, respectively through laser welding, for example, to produce a bonded body <NUM>. Besides the laser welding as an exemplified case, the existing bonding process may be executed. As <FIG> shows, the bonded body <NUM> may be constituted by bonding the resistive body <NUM> and the electrode plates <NUM> into the belt-like shape. The above-described bonded body <NUM> is wound in a roll, and placed on a production line. This makes it possible to execute the subsequent manufacturing steps automatically for mass-production of the resistors according to the embodiment.

In the embodiment, each thickness of the resistive body <NUM> and the electrode plate <NUM> is not limited. For example, the resistive body <NUM> may be formed to have the thickness ranging from several tens of µm to several hundreds of µm approximately. The resistive body <NUM> may be formed to have substantially the same thickness as, or different thickness from that of the electrode plate <NUM>.

In the embodiment, existing material may be used for forming the resistive body <NUM> and the electrode plate <NUM> in a non-restrictive manner. For example, it is possible to use metal resistance material such as copper-nickel and nickel-chrome, a structure formed by applying a metal film onto the surface of an insulating base, a conductive ceramic substrate and the like for forming the resistive body <NUM>. For example, it is possible to use copper, silver, nickel, chrome, and composite material thereof for forming the electrode plate <NUM>.

When bonding the electrode plates <NUM> to both sides of the resistive body <NUM>, respectively, each end surface of the resistive body <NUM> may be brought into abutment on the corresponding end surface of the electrode plates <NUM> as shown in <FIG>. Alternatively, the resistive body <NUM> and the electrode plates <NUM> may be bonded while having the respective surfaces partially overlapped with each another.

The resistive body <NUM> and the electrode plates <NUM> may be integrally formed. That is, it is possible to use the single metal resistance plate as the same material for forming the resistive body <NUM> and the electrode plates <NUM>. Alternatively, plating of the metal material with low resistance is applied to the region to be formed as the electrode plate <NUM> on the metal resistance plate so that the electrode plate <NUM> is formed on the surface of the metal resistance plate.

In the steps as shown in <FIG>, an uncured thermally conductive layer <NUM> is formed on the surface of the resistive body <NUM>. Preferably, the thermally conductive layer <NUM> is an electrically insulating thermosetting resin with high thermal conductivity. For example, the thermosetting resin such as epoxy and polyimide may be used for forming the thermally conductive layer <NUM>.

The uncured thermally conductive layer <NUM> may be in the form of a film or a paste. In the case of the film, the uncured thermally conductive resin film is stuck on the surface of the resistive body <NUM>. In the case of the paste, the uncured thermally conductive resin paste is applied to or printed on the surface of the resistive body <NUM>. Alternatively, the thermally conductive layer <NUM> may be formed by executing the inkjet process.

In the embodiment, the thickness of the thermally conductive layer <NUM> is not limited. The thickness may be arbitrarily specified in consideration of the thermal conductivity of the resistor as the finished product, and secure fixation between the resistive body and the electrode plates. For example, preferably, the thickness of the thermally conductive layer <NUM> is in the range from approximately <NUM> to <NUM>.

The term "uncured" refers to the state where the layer is not cured completely. Specifically, the uncured state where the layer has not been completely cured represents that curing reaction hardly proceeds to exhibit fluidity at the same level as that in the initial formation stage, or the state of the purchased product for shipment. The term "cured (completely cured)" refers to the state where the layer has lost the fluidity owing to accelerated polymerization due to linkage of molecules. For example, when the thermally conductive layer <NUM> is formed as the thermally conductive resin film, the pre-processing (temporary crimping) is executed after placing the thermally conductive layer <NUM> on the resistive body <NUM> as shown in <FIG>. In this case, the state after executing the pre-processing is defined as being the "uncured" state. That is, in the pre-processing, heat is applied (equal to or lower than the application temperature) for a short time (for example, approximately several minutes) to adhere (temporary crimping) the thermally conductive layer <NUM> to the resistive body <NUM>. The state after heating in the pre-processing is still in the "uncured" state.

When using the thermally conductive resin film for the thermally conductive layer <NUM>, the thermally conductive layer <NUM> is in the uncured and solidified state. The term "solidified" refers to the state of having become solid.

Meanwhile, when using the thermally conductive resin paste for the thermally conductive layer <NUM>, the thermally conductive layer <NUM> is in the uncured and unsolidified state. The term "unsolidified" refers to the state where the solid component is partially or entirely dispersed in the solvent such as slurry and ink.

In the embodiment, the thermally conductive layer <NUM> may be formed only on the surface of the resistive body <NUM> as shown in <FIG>. However, it is possible to form the thermally conductive layer <NUM> on the entire surface from the resistive body <NUM> to the electrode plates <NUM> as shown in <FIG>. Alternatively, although not shown, it is possible to form the thermally conductive layer <NUM> on the surface from the resistive body <NUM> to a part of each of the electrode plates <NUM>. Alternatively, in the manufacturing step to be described below in which the electrode plates <NUM> are bent, it is possible to form the thermally conductive layer <NUM> on the region except the bent parts. That is, the thermally conductive layer <NUM> may be formed in three divided parts on the respective surfaces of the resistive body <NUM> and the electrode plates <NUM> except the boundary therebetween.

As <FIG> shows, the thermally conductive layer <NUM> is formed not only on the surface of the resistive body <NUM> but also on the surfaces of the electrode plates <NUM>. This makes it possible to facilitate formation of the thermally conductive layer <NUM>. When using the thermally conductive resin film for the thermally conductive layer <NUM>, for example, as <FIG> shows, the thermally conductive resin film does not have to be positioned to the resistive body <NUM>. The thermally conductive resin film that is large enough to cover the resistive body <NUM> and the electrode plates <NUM> may be stuck on the surfaces of the resistive body <NUM> and the electrode plates <NUM>. Alternatively, when using the thermally conductive resin paste for the thermally conductive layer <NUM>, the thermally conductive layer <NUM> may be applied to the surfaces of the resistive body <NUM> and the electrode plates <NUM> entirely. As described above, the manufacturing step may be simplified by forming the thermally conductive layer <NUM> not only on the surface of the resistive body <NUM> but also on the surfaces of the electrode plates <NUM>.

Then the uncured thermally conductive layer <NUM> is heated into a semi-cured state. The term "semi-cured" refers to the cured state intermediately between the "uncured" state and the "completely cured" state. Determination as to whether or not the layer is in the semi-cured state may be made in accordance with the cure degree, viscosity, thermal processing conditions or the like. It is possible to use the cure degree to be calculated from the calorific value derived from the measurement utilizing the differential scanning calorimeter, for example. The semi-cured state represents the transition from the previous state (in the uncured state, or in the state before the heating process for semi-curing) to further cured state, leaving the scope for still further curing. Upon determination of the state in accordance with the cure degree, if the cure degree becomes higher than the one in the previous state, the state may be regarded as the semi-cured state. Although there is no limitation, for example, if the cure degree is in the range from <NUM>% to <NUM>%, or it is in the generally called stage B, the state may be regarded as the semi-cured state. Determination as to whether or not the layer is in the completely cured state may be made in accordance with the cure degree, the thermal processing condition or the like. It is possible to use the cure degree to be calculated from the calorific value derived from the measurement utilizing the differential scanning calorimeter. Complete curing refers to the condition where the cure degree is equal to or higher than <NUM>%, or refers to the condition generally called stage C.

As the uncured thermally conductive layer <NUM> is brought into the semi-cured state as described above, the fluidity of the thermally conductive layer <NUM> may be lowered.

Although the thermal processing condition for bringing the thermally conductive layer <NUM> into the semi-cured state is not limited in the embodiment, it is preferable to apply the process to the thermally conductive layer <NUM> at the application temperature ranging from approximately <NUM> to <NUM> for approximately <NUM> to <NUM> minutes. For example, the application temperature of the complete curing condition is kept unchanged, but the application time is set to the value approximately <NUM>% to <NUM>% of the one set for complete curing. The application temperature and the application time required for curing vary depending on the material for forming the thermally conductive layer <NUM>. Therefore, if the thermally conductive layer <NUM> is the purchased product, the thermal processing may be executed in accordance with the application temperature and the application time as prescribed by the manufacturer.

A resistor intermediate <NUM> is cut from the bonded body <NUM> having the semi-cured thermally conductive layer <NUM> as shown in <FIG> is a perspective view of the cut-out resistor intermediate <NUM>.

As the belt-like bonded body <NUM> as shown in <FIG> is longitudinally fed, the plurality of resistor intermediates <NUM> may be continuously cut by a press machine along the longitudinal direction. This makes it possible to mass-produce the resistor intermediates <NUM> in a short period of time.

The resistor intermediate <NUM> is constituted by the resistive body <NUM> having a rectangular outer shape, and the electrode plates <NUM> each having a rectangular outer shape provided at the respective sides of the resistive body <NUM>. The outer shape of the resistor intermediate <NUM> as shown in <FIG> is a mere example. It is therefore possible to form the resistor intermediate <NUM> to have the outer shape other than the one as shown in <FIG>.

As <FIG> shows, a plurality of cut portions <NUM> are formed in the resistive body <NUM> so that a meander pattern is formed for adjusting the resistance. Each length, each position, and the number of the cut portions <NUM> may be appropriately adjusted so that the resistive body <NUM> has a predetermined resistance value. The step as shown in <FIG> may be executed as needed.

As <FIG> shows, the electrode plates <NUM> are bent toward the side of the resistive body <NUM>, on which the thermally conductive layer <NUM> is laminated. Referring to <FIG>, as the thermally conductive layer <NUM> is formed on the lower surface side of the resistive body <NUM>, the electrode plates <NUM> are bent toward the lower side. Each of <FIG> shows a cross section of the resistor <NUM> as shown in <FIG>. The cut portions <NUM> expected to appear in the resistive body <NUM> as shown in <FIG> are not shown. The dimension ratio of the thickness and the length of the resistive body <NUM>, the electrode plate <NUM> and the thermally conductive layer <NUM> as shown in <FIG> is different from the one as shown in <FIG>. However, those exaggeratingly illustrated structures in the drawings are the same from a physical viewpoint.

As <FIG> show, the bent electrode plates <NUM> confront the lower side of the resistive body <NUM> via the thermally conductive layer <NUM>. <FIG> shows the structure constituted by using the resistor intermediate <NUM> that has the thermally conductive layer <NUM> on the surface of the resistive body <NUM> as shown in <FIG>, and bending the electrode plates <NUM>. The thermally conductive layer <NUM> as the single layer intervenes between the resistive body <NUM> and the bent electrode plates <NUM>.

Meanwhile, <FIG> shows the structure constituted by using the resistor intermediate <NUM> that has the thermally conductive layer <NUM> covering the surfaces from the resistive body <NUM> to the electrode plates <NUM>, and bending the electrode plates <NUM> as shown in <FIG>. Therefore, the thermally conductive layers <NUM> as double layers intervene between the resistive body <NUM> and the bent electrode plates <NUM>. Referring to <FIG>, the thermally conductive layer <NUM> as the single layer is formed at the center part of the resistive body <NUM> to which the electrode plates <NUM> do not confront.

The thermally conductive layer <NUM> in the semi-cured state is heated to be completely cured. The term "complete curing" refers to the explanation that has been already described as above.

Although the thermal processing condition for completely curing the thermally conductive layer <NUM> is not limited herein, it is preferable to apply the process to the thermally conductive layer <NUM> at the application temperature from approximately <NUM> to <NUM> for approximately <NUM> to <NUM> hours. The temperature and the time required for curing vary depending on the material for forming the thermally conductive layer <NUM>. The curing condition for the thermally conductive layer <NUM> as the purchased product is specified in accordance with the temperature and the time as prescribed by the manufacturer. For example, the application temperature to the resin for the experiment to be described later is set to be in the range from approximately <NUM> to <NUM>, and the application time is set to be in the range from approximately <NUM> minutes to <NUM> minutes (the lower the application temperature becomes, the longer the application time is set) for appropriate adjustment.

In the embodiment, it is preferable to completely cure the thermally conductive layer <NUM> while pressing the bent electrode plates <NUM> toward the resistive body <NUM>. That is, referring to <FIG>, the thermally conductive layer <NUM> is heated under the pressure while being in contact with the bent electrode plates <NUM> for curing. Referring to <FIG>, the thermally conductive layer <NUM> positioned at the inner sides of the bent electrode plates <NUM> is laminated on the thermally conductive layer <NUM> on the lower surface of the resistive body <NUM>. In the above-described state, the thermally conductive layers <NUM> are heated under pressure for completely curing. This makes it possible to adhesively fix the resistive body <NUM> to the electrode plates <NUM> securely via the thermally conductive layer <NUM>.

Then in the step as shown in <FIG>, a protective layer <NUM> is mold-formed onto the surface of the resistive body <NUM>. Preferably, the protective layer <NUM> is formed of a material with excellent heat resisting and electrically insulating properties. Although it is not intended to limit the material for forming the protective layer <NUM>, the mold-forming of the protective layer <NUM> may be executed using the resin, glass, inorganic material and the like. As <FIG> show, the protective layer <NUM> includes a surface protective layer 7a for covering the surface of the resistive body <NUM>, and a bottom surface protective layer 7b for filling the space between the bent electrode plates <NUM> at the lower surface side of the resistive body <NUM>. As <FIG> show, the bottom surface protective layer 7b and the electrode plates <NUM> constitute substantially the flush bottom surface. <FIG> shows the step subsequent to the one as shown in <FIG>, and <FIG> shows the step subsequent to the one as shown in <FIG>.

It is possible to affix a seal on the surface of the surface protective layer 7a.

As <FIG> show, plating is applied to surfaces of the electrode plates <NUM>. Although the material for forming a plating layer <NUM> is not limited, the plating layer <NUM> may be constituted by a Cu plating layer and an Ni plating layer, for example. The plating layer <NUM> serves to expand the contact area to the substrate surface on which the resistor <NUM> is disposed, and suppress the soldering erosion of the electrode plate <NUM> upon soldering of the resistor <NUM> to the substrate surface. <FIG> represents the step subsequent to the one as shown in <FIG>. <FIG> represents the step subsequent to the one as shown in <FIG>. The plating process is carried out as needed.

The resistor <NUM> manufactured through the above-described manufacturing steps includes the resistive body <NUM>, the electrode plates <NUM> disposed at both sides of the resistive body <NUM>, respectively while being bent at the lower surface side of the resistive body <NUM>, and the cured thermally conductive layers <NUM> intervening between the resistive body <NUM> and the electrode plates <NUM> as shown in <FIG>.

The thermally conductive layer <NUM> intervening between the resistive body <NUM> and the electrode plates <NUM> has the thickness (in <FIG>, the total thickness of the double layers) ranging from approximately <NUM> to <NUM>. By adjusting the thickness of the thermally conductive layer <NUM> in this manner, it is possible to improve the heat dissipation property from the resistive body <NUM> to the electrode plates <NUM> via the thermally conductive layer <NUM> appropriately. By adjusting the thickness of the thermally conductive layer <NUM> to be in the above-described range, it is possible to improve tightness of contact between the resistive body <NUM> and the electrode plates <NUM>. This makes it possible to appropriately suppress occurrence of the failure such as peeling of the electrode plate <NUM> from the thermally conductive layer <NUM>, and crack generated in the thermally conductive layer <NUM>.

The method of manufacturing the resistor <NUM> according to the embodiment is characterized by the manufacturing process for bringing the thermally conductive layer <NUM> into the semi-cured state, and further into the cured state after bending the electrode plates <NUM>.

Execution of the above-described manufacturing process allows suppression of variation in the thickness of the thermally conductive layer <NUM> between the resistive body <NUM> and the electrode plates <NUM> in comparison with the generally employed process. That is, upon execution of the heating process by bending the electrode plates <NUM>, the thermally conductive layer <NUM> is in the semi-cured state, that is, it is not uncured, but not completely cured. It is therefore possible to reduce the thickness variation in the thermally conductive layer <NUM> owing to fluidity thereof to be less than the case where the entire thermally conductive layer between the resistive body <NUM> and the electrode plates <NUM> is in the uncured state.

As described above, in the embodiment, it is possible to suppress variation in the thickness of the thermally conductive layer <NUM> between the resistive body <NUM> and the electrode plates <NUM>. This makes it possible to make the thickness between the resistive body <NUM> and the electrode plates <NUM> further uniform, and to suppress variation in the heat dissipation property, thus manufacturing the resistor <NUM> with excellent heat dissipation property. The further uniform thickness between the resistive body <NUM> and the electrode plates <NUM> may suppress generation of a gap or the like between the resistive body <NUM> and the electrode plates <NUM>, resulting in improved adhesive strength.

The uncured and solidified material, specifically, the thermally conductive resin film may be preferably used for forming the thermally conductive layer <NUM>.

When using the uncured and unsolidified material, specifically, the thermally conductive resin paste for forming the thermally conductive layer <NUM>, the thickness of the thermally conductive layer in the applied state is likely to vary. The use of the thermally conductive resin film in the uncured and solidified state for forming the thermally conductive layer <NUM> allows adjustment of the thickness between the resistive body <NUM> and the electrode plates <NUM> into more uniform state.

In the steps as shown in <FIG>, it is preferable to cure the thermally conductive layer <NUM> while pressing the bent electrode plates <NUM>. This makes it possible to securely adhere the electrode plates <NUM>.

The present invention will be described in more detail based on an example implemented to exhibit the advantageous effect of the present invention. However, the present invention is not limited to the example as described below.

In an experiment, the following resin was used, and the thermal analysis was carried out using a differential scanning calorimeter (DSC).

The DSC curve and the DDSC curve were obtained at the temperature elevation rate of <NUM>/min in the experiment.

As <FIG> shows, the curing start temperature was <NUM>, and the curing end temperature was <NUM>. At the timing when the temperature becomes <NUM> onward, transition of the phase to the combustion reaction was observed.

In accordance with the experimental result, the applied temperature was measured to be in the range from <NUM> to <NUM>.

The temperature was fixed to <NUM> to obtain the curing start temperature and the curing end temperature from the DSC curve in accordance with the holding time. The obtained experimental results are shown in <FIG>.

<FIG> shows that the curing started after a lapse of about <NUM> minutes, and the curing ended after a lapse of about <NUM> minutes.

The above-described experimental result has clarified that the resin to be used as specified above was cured under the condition at <NUM> for approximately <NUM> minutes. The curing condition coincided with the curing condition recommended by the resin manufacturer.

As the curing condition is established at <NUM> for <NUM> minutes, the curing condition in the temperature range as shown in <FIG> may be established at <NUM> for <NUM> minutes, <NUM> for <NUM> minutes, <NUM> for <NUM> minutes, <NUM> for <NUM> minutes, and <NUM> for <NUM> minutes approximately.

It is considered that the semi-curing condition is established by setting the application time to be in the range from approximately <NUM>% to <NUM>% of the above described condition while keeping the temperature unchanged. At the application temperature of <NUM>, the application time may be set to approximately <NUM> to <NUM> minutes.

The resistor according to the present invention with excellent heat dissipation property allows reduction in its height. The resistor may be surface mounted so as to be mounted to various types of circuit boards.

Claim 1:
A resistor manufacturing method comprising:
a step of adhering a thermally conductive resin film onto a surface of a resistive body (<NUM>), the thermally conductive resin film being an electrically-insulating thermal conductive layer (<NUM>) that is in an uncured and solidified state;
a step of bringing the thermally conductive resin film (<NUM>) into a semi-cured state; and
a step of bending electrode plates (<NUM>) respectively disposed at both sides of the resistive body (<NUM>), further curing the thermally conductive resin film (<NUM>) in a state where the electrode plates (<NUM>) contact the thermally conductive resin film, and performing adhesion between the resistive body (<NUM>) and the electrode plates (<NUM>) via the thermally conductive resin film.