Patent Description:
As a general resin sealing method for a power module, transfer molding using a molding resin such as epoxy resin is performed. In conventional transfer molding, inside a mold, a void due to air entrapment by flow of the molding resin or gas generated from the molding resin, can occur.

In addition, a void can also occur in an insulation adhesion member having high thermal conductivity, provided between a heatsink and a heat dissipation portion of a semiconductor device. In the case of using a sheet-like insulation adhesion member, a void occurs between the insulation adhesion member and a lead frame by air entrapment at the time of pasting. In the case where a liquid insulation adhesion member is cured and used, a void occurs due to gas of a solvent separated from an adhesive agent during a curing process. In any of the cases, the presence of a void leads to reduction in electric insulation property, moisture-proof property, heat dissipation property, and adhesion property, so that the function of the semiconductor device is lowered.

As conventional technology for inhibiting occurrence of a void at the time of resin sealing, a configuration in which a mold is provided with an air vent for discharging a void, is known. For example, in a resin sealing molding apparatus for an electronic component disclosed in <CIT>, a gate is provided at one end of a cavity formed inside an upper die and a lower die, a resin reservoir part is provided near the other end of the cavity on the opposite side from the gate, and the resin reservoir part and the outside communicate with each other through an air vent.

Other example of the prior art can be seen in documents <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

However, in the method of providing the air vent in the mold, it is necessary to provide the air vent in advance at a part where a void is expected to occur, and if a void occurs at an unexpected part, it is necessary to work the mold again. Thus, there is a problem that time and cost are required for working the mold.

The present disclosure has been made to solve the above problem, and an object of the present disclosure is to provide a semiconductor device that inhibits occurrence of a void in a molding resin or an insulation adhesion member and has a high function and high reliability, at low cost.

A semiconductor device according to the present disclosure includes the technical features of claim <NUM>.

The semiconductor device according to the present disclosure has the scale-like portion provided over both sides across the resin boundary portion on the lead frame, whereby air present inside the resin can be discharged to the outside of the mold during a resin sealing process, thus providing a void inhibition effect. Therefore, it is not necessary to work an air vent in the mold and a semiconductor device having a high function and high reliability can be obtained at low cost.

Objects, features, aspects, and effects of the present disclosure other than the above will become more apparent from the following detailed description with reference to the drawings.

Hereinafter, a semiconductor device according to embodiment <NUM> will be described with reference to the drawings. <FIG> is a sectional view showing the semiconductor device according to embodiment <NUM>, and <FIG> is a sectional view showing a transfer molding process for the semiconductor device according to embodiment <NUM>. A semiconductor device <NUM> according to embodiment <NUM> includes a semiconductor element <NUM>, a lead frame <NUM>, a wire <NUM> and an inner lead <NUM> which are wiring members, an external terminal <NUM>, a molding resin <NUM>, and the like. In the drawings, the same or corresponding parts are denoted by the same reference characters.

The semiconductor element <NUM> is, for example, an insulated-gate bipolar transistor (IGBT), a metal-oxide-semiconductor field-effect transistor (MOSFET), an IC chip, an LSI chip, or the like, and is mounted on a mounting portion of the lead frame <NUM> via a joining member <NUM> such as solder or silver. It is noted that a component (not shown) other than the semiconductor element <NUM> is also mounted on the mounting portion of the lead frame <NUM>.

The lead frame <NUM> is made from a copper plate or a copper alloy plate. For the purpose of improving corrosion resistance and heat resistance, the surface of the lead frame <NUM> may be coated with a metal plating 2a such as gold, silver, nickel, or tin, and among these, nickel is often employed. The lead frame <NUM> has a scale-like portion <NUM> where scale-shaped projections are formed consecutively. The scale-like portion <NUM> is provided over both sides across a resin boundary portion 2b which is the boundary between the inside and the outside of an area sealed by the molding resin <NUM> on the lead frame <NUM>. The scale-like portion <NUM> will be described later in detail.

An electrode pad of the semiconductor element <NUM> is connected to the external terminal <NUM> via the wire <NUM> connected by wire bonding or the inner lead <NUM> made from a copper plate or a copper alloy plate. The wire <NUM> and the inner lead <NUM> may be replaced with each other. The wire <NUM> is made from gold, silver, aluminum, copper, or the like, and has a wire diameter of about <NUM> to <NUM>.

Of the lead frame <NUM>, at least a surface on which the semiconductor element <NUM> is mounted is sealed by the molding resin <NUM> which is a thermosetting resin such as epoxy resin. In the semiconductor device <NUM> according to embodiment <NUM>, surfaces on both sides of the lead frame <NUM> are sealed by one type of molding resin <NUM>. The molding resin <NUM> formed in an approximately rectangular parallelepiped shape has a gate breaking trace 8b at a part of a side surface 8a thereof, and the scale-like portion <NUM> is provided at the resin boundary portion 2b on the side opposite to the side surface 8a having the gate breaking trace 8b.

The transfer molding process for the semiconductor device <NUM> according to embodiment <NUM> will be described with reference to <FIG>. Inside a mold <NUM>, the lead frame <NUM> on which the semiconductor element <NUM> and the like are mounted is placed, and a melted molding resin is injected into a cavity <NUM> of the mold <NUM> through a gate <NUM>. The clearance between the external terminal <NUM> and the mold <NUM> is made extremely narrow so that a large amount of the molding resin <NUM> will not leak from the mold <NUM>.

In the transfer molding process, a part to which the straight distance from the gate breaking trace 8b is longest in the semiconductor device <NUM> (in the case of a rectangular module, a side opposite to the gate breaking trace 8b) is the last part to be filled with the molding resin. The molding resin <NUM> flows into the last filled part, in a state of being high in viscosity and low in wettability. Therefore, a void due to air entrapment is likely to occur at the last filled part.

Therefore, as means for inhibiting a void in the molding resin <NUM>, the semiconductor device <NUM> has the scale-like portion <NUM> provided across the resin boundary portion 2b on the lead frame <NUM>. The scale-like portion <NUM> reaches abutting surfaces <NUM> of the upper die and the lower die of the mold <NUM>. The molding resin flowing on the scale-like portion <NUM> forms a discharge path for air owing to recesses/projections on the scale-like portion <NUM>, whereby air is discharged through the abutting surfaces <NUM> of the mold <NUM>. The discharge path for air formed in the molding resin disappears when the molding resin is completely cured. Owing to such an action, the scale-like portion <NUM> exhibits the same void inhibiting effect as with an air vent, without providing an air vent in the mold <NUM>.

The molding resin remaining in the gate <NUM> is called a runner 8c. After transfer molding, the semiconductor device <NUM> is taken out from the mold <NUM>, and immediately after this, gate breaking is performed to separate the runner 8c and the semiconductor device <NUM> from each other. The gate breaking trace 8b remains at the side surface 8a of the molding resin <NUM> after the gate breaking.

Next, the structure of the scale-like portion <NUM> will be described in detail. <FIG> is an enlarged top view of a part of the scale-like portion, <FIG> is a sectional view cut at a part indicated by A-A in <FIG> is a sectional view cut at a part indicated by B-B in <FIG>. <FIG> are scanning electron microscope photographs showing the structure of the scale-like portion. The scale-like portion <NUM> is obtained by deforming the surface of the lead frame <NUM> into a scaly shape by consecutively applying a laser beam as a spot on the lead frame <NUM>, and is formed in a given straight line with a predetermined width W as shown in <FIG>. In <FIG>, an arrow denoted by L represents the longitudinal direction of the scale-like portion <NUM>.

The scale-like portion <NUM> includes a scale portion <NUM> on which scale-shaped projections are consecutively provided, and ridge portions <NUM> provided on both sides of the scale portion <NUM> in parallel to the longitudinal direction L of the scale-like portion <NUM>. As shown in <FIG>, the ridge portions <NUM> are raised to be higher than the scale portion <NUM> and an area between the two ridge portions <NUM> has a groove shape. The width W and the height of the scale-like portion <NUM> can be adjusted using laser output, scan speed, and the like. The width W of the scale-like portion <NUM> is set to about <NUM> to <NUM>, for example. The greater the width W of the scale-like portion <NUM> is, the higher the void inhibition effect is.

Since the scale-like portion <NUM> is formed through laser application, the scale-like portion <NUM> can be easily formed at any location on the lead frame <NUM>, and the flatness of the lead frame <NUM> is not lost during the working. It is also easy to selectively process only a part where the scale-like portion <NUM> is to be provided while avoiding a part where the scale-like portion <NUM> is not to be provided, e.g., a wire connection portion or the like. In addition, the scale-like portion <NUM> may be provided in a curved line. Further, if the scale-like portion <NUM> is formed by a unicursal processing pattern, the takt time can be shortened and productivity is improved.

In the case where it has been found that a void is likely to occur at an unexpected part of the semiconductor device <NUM> through investigation using an ultrasonic imaging device or the like, a long manufacturing period and great cost are required for modifying the mold or newly creating a mold. The scale-like portion <NUM> is very effective for such a situation, and the scale-like portion <NUM> only has to be provided at a part where it has been found that a void is likely to occur. Thus, working for the mold is not needed and a void can be coped with at low cost.

Arrangement examples of the scale-like portion <NUM> and the effects thereof will be described with reference to <FIG>. In <FIG>, and <FIG>, the scale-like portions <NUM> are arranged such that the longitudinal direction L of the scale-like portions <NUM> is perpendicular to the resin boundary portion 2b. In <FIG> and <FIG>, the scale-like portions <NUM> are arranged such that the longitudinal direction L of the scale-like portions <NUM> is parallel to the resin boundary portion 2b. As shown in <FIG> and <FIG>, in the case where the scale-like portions <NUM> are arranged such that the longitudinal direction L of the scale-like portions <NUM> is parallel to the resin boundary portion 2b, considering positional deviation (about <NUM> at maximum) during laser processing, the width W of each scale-like portion <NUM> is set to be great (for example, about <NUM>) so as to ensure that the scale-like portion <NUM> is formed across the resin boundary portion 2b.

In the example shown in <FIG>, a plurality of (here, four) scale-like portions <NUM> are provided across the resin boundary portion 2b at a part to which the straight distance from the gate breaking trace 8b is longest on the lead frame <NUM>. In the examples shown in <FIG> and <FIG>, a plurality of scale-like portions <NUM> are provided at intervals on the resin boundary portion 2b on the side opposite to the side surface having the gate breaking trace 8b. Using the configurations as shown in <FIG> can inhibit a void near the last part to be filled with the molding resin.

In the examples shown in <FIG> and <FIG>, a plurality of scale-like portions <NUM> are provided at intervals over the entire areas of the resin boundary portions 2b on the four sides of the rectangular module. It is noted that, although the scale-like portions <NUM> are arranged at equal intervals in <FIG>, the scale-like portions <NUM> do not necessarily need to be arranged at equal intervals, and may be closely arranged at a part where a void is likely to occur. Using the configurations as shown in <FIG> and <FIG> can cope with voids at every part inside the molding resin <NUM>.

Next, the function of the scale-like portion <NUM> in the semiconductor device <NUM> will be described with reference to <FIG>. <FIG> is an enlarged top view of a part of the semiconductor device in the case where the longitudinal direction of the scale-like portion is perpendicular to the resin boundary portion, and <FIG> is a sectional view cut at a part indicated by C-C in <FIG>. <FIG> is an enlarged top view of a part of the semiconductor device in the case where the longitudinal direction of the scale-like portion is parallel to the resin boundary portion, and <FIG> is a sectional view cut at a part indicated by D-D in <FIG>.

In the examples shown in <FIG>, the surface of the lead frame <NUM> is coated with the metal plating 2a, and the scale-like portion <NUM> is formed on the metal plating 2a. Copper which is the material of the lead frame <NUM> is readily oxidized, and cost is required for management of the oxidation degree if the lead frame <NUM> is in an exposed state. Therefore, if the scale-like portion <NUM> is formed with the metal plating 2a remaining on the surface of the lead frame <NUM>, copper oxidation degree management becomes easy. In addition, laser working is easier for the metal plating 2a such as nickel, as compared to copper which has a high reflectance for a laser beam.

In the case of forming the scale-like portion <NUM> on the lead frame <NUM> coated with the metal plating 2a, the scale-like portion <NUM> may be formed at both of the metal plating 2a and the lead frame <NUM> under the metal plating 2a. That is, the lead frame <NUM> may be exposed or deformed at the scale-like portion <NUM>. In any case, a void inhibition effect can be obtained in accordance with the dimensions in width W, height, and longitudinal direction L of the scale-like portion <NUM>.

In the transfer molding process, normally, sealing is made at the abutting surfaces <NUM> of the upper die and the lower die of the mold <NUM> (see <FIG>) so that resin will not leak. At this time, if the sealing is loose, resin leakage occurs and unnecessary resin burr is formed. The unnecessary resin burr adversely affects tie bar cutting, lead forming, and the like in the subsequent processes, and it becomes necessary to add a process of removing the resin burr, and therefore this is undesirable.

On the other hand, as shown in <FIG>, at the scale-like portion <NUM> provided for discharging a void, resin leakage 8d (area represented by dots in the drawings) occurs within the range of the scale-like portion <NUM>. Therefore, the scale-like portion <NUM> is provided at such a location that any functional problem does not arise even when the resin leakage 8d occurs. The resin leakage amount at the scale-like portion <NUM> varies depending on the molding pressure, the shape of the scale-like portion <NUM>, or the like. However, the resin leakage 8d occurring at the scale-like portion <NUM> is accumulated in the scale-like portion <NUM> and does not spread to a part other than the scale-like portion <NUM>. Therefore, the adverse effect as described above is unlikely to occur.

As shown in <FIG> and <FIG>, in the case where the longitudinal direction L of the scale-like portion <NUM> is perpendicular to the resin boundary portion 2b, the resin leakage 8d in the longitudinal direction L is inhibited by the scale portion <NUM>, and the resin leakage 8d in the direction (transverse direction in <FIG>) perpendicular to the longitudinal direction L is inhibited by the ridge portions <NUM>. Thus, the width of the resin leakage 8d can be kept within a narrow range equal to the width W of the scale-like portion.

As shown in <FIG>, in the case where the longitudinal direction L of the scale-like portion <NUM> is parallel to the resin boundary portion 2b, the resin leakage 8d in the direction (vertical direction in <FIG>) perpendicular to the longitudinal direction L is inhibited by the ridge portion <NUM>. Thus, the range of the resin leakage 8d can be kept within a short distance from the resin boundary portion 2b to the ridge portion <NUM>. As described above, since the range of the resin leakage 8d varies depending on the arrangement relationship between the longitudinal direction L of the scale-like portion <NUM> and the resin boundary portion 2b, the arrangement relationship is appropriately selected in accordance with the condition around the part where the scale-like portion <NUM> is provided.

In embodiment <NUM>, transfer molding is used for the resin sealing process. However, the manufacturing method for the semiconductor device <NUM> is not limited thereto. For example, injection molding may be used, which can contribute to cost reduction for resin.

As described above, according to embodiment <NUM>, the scale-like portion <NUM> is provided over both sides across the resin boundary portion 2b on the lead frame <NUM>, whereby air present inside the molding resin can be discharged to the outside of the mold <NUM> in the resin sealing process, thus providing a void inhibition effect. Since the scale-like portion <NUM> is formed by applying a laser beam to the lead frame <NUM>, it is possible to easily provide the scale-like portion <NUM> at a part where a void is likely to occur, and flatness of the lead frame <NUM> is not lost during working. Further, working for providing an air vent in the mold is not needed, and a void can be coped with at low cost. Thus, according to embodiment <NUM>, the semiconductor device <NUM> having a high function and high reliability can be obtained at low cost.

<FIG> is a sectional view showing a semiconductor device according to embodiment <NUM>, <FIG> is a sectional view showing a first-time transfer molding process for the semiconductor device according to embodiment <NUM>, and <FIG> is a sectional view showing a second-time transfer molding process for the semiconductor device according to embodiment <NUM>. A semiconductor device <NUM> according to embodiment <NUM> includes a first resin (hereinafter, molding resin <NUM>) and a second resin (hereinafter, second molding resin <NUM>).

The lead frame <NUM> of the semiconductor device <NUM> has a mounting portion 2A on which the semiconductor element <NUM> is mounted, and a heat dissipation portion 2B opposite to the mounting portion 2A. The mounting portion 2A is sealed by the molding resin <NUM>, and the heat dissipation portion 2B is sealed by the second molding resin <NUM>. A scale-like portion 3b is provided over both sides across a resin boundary portion 2c of an area sealed by the second molding resin <NUM> on the heat dissipation portion 2B. On the heat dissipation portion 2B of the lead frame <NUM>, a thin molding portion 9d having a thickness of about <NUM> to <NUM> is formed. The thin molding portion 9d is joined to a heatsink made of copper or aluminum, via a heat dissipation member such as grease.

The molding resin <NUM> and the second molding resin <NUM> are both made from thermosetting epoxy resin or the like. It is noted that, for the second molding resin <NUM> on the heat dissipation portion 2B side, a high-heat-dissipation resin having a higher thermal conductivity than the molding resin <NUM> is used. The thermal conductivity of the second molding resin <NUM> is <NUM> W/m·K to <NUM> W/m-K. For the molding resin <NUM> on the mounting portion 2A side, a low-stress resin which is a molding resin for a general integrated circuit is used.

The transfer molding process for the semiconductor device <NUM> according to embodiment <NUM> will be described with reference to <FIG> and <FIG>. Manufacturing of the semiconductor device <NUM> includes two times of transfer molding processes. As shown in <FIG>, in the first-time transfer molding process, the lead frame <NUM> on which the semiconductor element <NUM> and the like are mounted is placed inside a first mold 20A, and the cavity <NUM> is present on the mounting portion 2A side of the lead frame <NUM>. A melted molding resin is injected into the cavity <NUM> of the first mold 20A through an upper gate 22A.

The molding resin flows on the mounting portion side of the lead frame <NUM> to fill the cavity <NUM>. After the first-time transfer molding process, the molded product is taken out from the first mold 20A, and immediately after this, a gate breaking process for separating a runner 8c from the molded product is performed. After the gate breaking, the gate breaking trace 8b (see <FIG>) remains at the side surface 8a of the molding resin <NUM>.

Subsequently, the second-time transfer molding process is performed. For the purpose of enhancing the adhesion property between the molding resin <NUM> and the second molding resin <NUM>, a UV treatment or a plasma treatment may be performed on the molding resin <NUM> after the first-time transfer molding process. As shown in <FIG>, inside a second mold 20B used in the second-time transfer molding process, the lead frame <NUM> of which the mounting portion 2A side has been sealed through the first-time transfer molding process is placed, and the cavity <NUM> is present on the heat dissipation portion 2B side of the lead frame <NUM>.

The melted second molding resin is injected into the cavity <NUM> through a lower gate 22B. The second molding resin flows into the cavity <NUM> to form the thin molding portion 9d and flows to the scale-like portion 3b. The second molding resin flowing on the scale-like portion 3b forms a discharge path for air owing to recesses/projections on the scale-like portion 3b, whereby air is discharged through the abutting surfaces <NUM> of the second mold 20B. After the second-time transfer molding process, the molded product is taken out from the second mold 20B, and immediately after this, a gate breaking process of separating a runner 9c from the molded product is performed. After the gate breaking, a gate breaking trace 9b (see <FIG>) remains at a side surface 9a of the second molding resin <NUM>.

The thin molding portion 9d covering the heat dissipation portion 2B of the lead frame <NUM> is a thin high-heat-dissipation resin which is excellent in heat dissipation property, but has a high flow resistance during molding and thus is poor in fluidity, so that a void due to air entrapment is likely to occur. According to embodiment <NUM>, a void can be effectively inhibited by providing the scale-like portion 3b on the heat dissipation portion 2B side, whereby the semiconductor device <NUM> which is excellent in heat dissipation property and has a high function and high reliability can be obtained at low cost. It is noted that, in embodiment <NUM>, as in a semiconductor device 101A shown in <FIG>, a scale-like portion 3a may be provided at the resin boundary portion 2b of the area sealed by the molding resin <NUM> on the mounting portion 2A, whereby the same effects as in the above embodiment <NUM> can be obtained.

In embodiment <NUM>, a semiconductor device having an insulation adhesion member on the heat dissipation portion 2B side of the lead frame <NUM> will be described with reference to <FIG>. In a semiconductor device <NUM> shown in <FIG>, the mounting portion 2A of the lead frame <NUM> is sealed by the molding resin <NUM>, and an insulation adhesion member <NUM> is provided on the heat dissipation portion 2B. In a semiconductor device <NUM> shown in <FIG>, a heatsink <NUM> is provided on the heat dissipation portion 2B of the lead frame <NUM> with an insulation adhesion member <NUM> interposed therebetween.

The insulation adhesion member <NUM> is made of mainly epoxy resin, ceramic, silicone, or the like, and is a high-thermal-conductivity member having a thermal conductivity of <NUM> W/m·K to <NUM> W/m·K. As the insulation adhesion member <NUM>, a sheet-like member may be used or a liquid insulation adhesion member may be cured and used. In the case of the sheet-like insulation adhesion member <NUM>, a void can occur at a pasted surface of the insulation adhesion member <NUM> due to air entrapment at the time of pasting. In the case of curing the liquid insulation adhesion member <NUM> to be used, a void due to gas of a solvent or the like separated from the adhesive agent during the curing process can occur inside the insulation adhesion member <NUM>. Both of the above cases can cause reduction in electric insulation property, moisture-proof property, heat dissipation property, and adhesion property. Therefore, a void needs to be inhibited and it is effective to provide the scale-like portion 3b.

In the examples shown in <FIG>, the scale-like portion 3a is provided over both sides across the resin boundary portion 2b on the mounting portion 2A of the lead frame <NUM>. The function of the scale-like portion 3a is the same as in the above embodiment <NUM> and therefore description thereof is omitted. Further, the scale-like portion 3b is provided over both sides across an insulation adhesion member boundary portion 2d which is the boundary between the inside and the outside of an area covered by the insulation adhesion member <NUM> on the heat dissipation portion 2B of the lead frame <NUM>. Thus, air entrapped when the sheet-like insulation adhesion member <NUM> is pasted or gas of a solvent separated during the curing process of the liquid insulation adhesion member <NUM> is discharged through the scale-like portion 3b, whereby a void is inhibited.

In a semiconductor device <NUM> shown in <FIG>, the thickness of the lead frame <NUM> differs between the part where the semiconductor element <NUM> is mounted and the part having the external terminal <NUM>. Therefore, around the heat dissipation portion 2B of the lead frame <NUM>, the molding resin <NUM> is flush with the heat dissipation portion 2B. Further, the insulation adhesion member <NUM> is provided on the heat dissipation portion 2B and the molding resin <NUM> being flush with the heat dissipation portion 2B. In this case, merely providing the scale-like portion on the heat dissipation portion 2B side of the lead frame <NUM> cannot obtain a void inhibition effect.

Accordingly, in the semiconductor device <NUM>, a scale-like portion 3c is formed continuously to the end of the molding resin <NUM>, i.e., the side surface 8a from the heat dissipation portion 2B of the lead frame <NUM> covered by the insulation adhesion member <NUM>. Thus, air inside the insulation adhesion member <NUM> or at the pasted surface thereof can be discharged, whereby a void inhibition effect is obtained. It is noted that the scale-like portion 3c can be formed by one-time processing without changing the laser application condition between the heat dissipation portion 2B of the lead frame <NUM> and the molding resin <NUM>. Alternatively, it is also possible to perform processing with different application conditions for the heat dissipation portion 2B and the molding resin <NUM> by switching an application program during one-time processing.

Further, the heatsink <NUM> (see <FIG>) may be provided on the heat dissipation portion 2B of the semiconductor device <NUM> shown in <FIG>, with the insulation adhesion member <NUM> interposed therebetween. Providing the heatsink <NUM> obtains a semiconductor device having a small interfacial thermal resistance and excellent heat dissipation property. It is noted that a glass epoxy substrate or the like may be provided on the heat dissipation portion 2B of the lead frame <NUM> with the insulation adhesion member <NUM> interposed therebetween.

Claim 1:
A semiconductor device comprising:
a lead frame (<NUM>) on which a semiconductor element (<NUM>) is mounted and which is made of metal; and
a resin (<NUM>, <NUM>) sealing, of the lead frame (<NUM>), at least a surface on which the semiconductor element (<NUM>) is mounted, wherein
the lead frame (<NUM>) has a scale-like portion (<NUM>, 3a, 3b) on which scale-shaped projections are consecutively formed,
wherein the scale-like portion (<NUM>, 3a, 3b) is provided over both sides across a resin boundary portion (2b, 2c) which is a boundary between inside and outside of an area sealed by the resin (<NUM>, <NUM>) on the lead frame (<NUM>);
characterized in that
the scale-like portion (<NUM>) includes a scale portion (<NUM>) on which the scale-shaped projections are consecutively provided, and ridge portions (<NUM>) provided on both sides of the scale portion (<NUM>).