JP2009088344A - Chip resistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chip resistor having an excellent heat dissipating capacity in which plating defects of a heat dissipating electrode can be easily avoided. <P>SOLUTION: The chip resistor 1 includes: a rectangular solid shaped ceramic board 2; a pair of terminal electrodes 3 disposed at both ends of longitudinal direction of the ceramic board 2; a resistor 4 bridging the pair of terminal electrodes 3 on the one face of the ceramic board 2; an insulating protective layer 5, 6 disposed in the area covering the resistor 4; a heat dissipating electrode 7 which is disposed on the other face (or on the surface of protective layer 6) of the ceramic board 2, and is electrically isolated from the pair of the terminal electrodes 3; and a plating layer 8 coating the heat dissipating electrode 7 and the terminal electrodes 3, wherein the terminal electrodes 3 and the heat dissipating electrode 7 are configured so as to be soldered to a plurality of mutually separated lands 51, 52 on a print board 50. This chip resistor 1 is designed so that the planar shape of the heat dissipating electrode 7 is almost an elliptic shape without angularity in the periphery. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a chip resistor in which a resistor is provided on one side of a rectangular parallelepiped ceramic substrate, and in particular, a chip provided with a heat radiation electrode to release heat generated by the resistor when power is applied. Related to resistors.

  A conventional general rectangular chip resistor is provided with a resistor and an insulating protective layer covering the resistor on one side of a rectangular parallelepiped ceramic substrate, and a Ni plating layer, a Sn plating layer, or the like. A pair of attached terminal electrodes are provided at both ends in the longitudinal direction of the ceramic substrate, and the pair of terminal electrodes are bridged by a resistor. This type of chip resistor is usually surface-mounted on a mounting board such as a printed circuit board with the resistor side facing up, and each terminal electrode is soldered to a land disposed on the mounting board. However, if miniaturization of chip resistors is promoted, problems such as resistance changes due to the heat generated by the resistors when power is applied and solder joints are likely to melt. Become.

Therefore, conventionally, a heat radiation electrode having a rectangular shape in plan view, which is electrically isolated between a pair of terminal electrodes, is provided on the surface of the ceramic substrate opposite to the side where the resistor exists (surface facing the mounting substrate). By soldering this heat dissipation electrode to an electrically isolated land on the mounting board, heat generated by the resistor is released through the mounting board when power is applied, thereby improving heat dissipation and increasing the temperature. A chip resistor capable of suppressing the rise is known (for example, see Patent Document 1). In such a conventional chip resistor, it is possible to efficiently dissipate heat by connecting the land for the heat dissipation electrode to a thermal via, a heat sink or the like, and for the heat dissipation electrode separately from the land for the terminal electrode on the mounting substrate. Therefore, the mounting strength of the chip resistor to the mounting substrate is also improved.
JP-A-2-309602

  By the way, in the case where a rectangular heat radiation electrode is provided on one surface of the ceramic substrate as in the conventional chip resistor described above, a plating layer such as Ni or Sn is coated on the heat radiation electrode as well as the terminal electrode. Although it is necessary to deposit, it is not easy to deposit a plating layer having a uniform thickness on the heat dissipation electrode during barrel plating, which is generally performed at the final stage of the manufacturing process of the chip resistor. In other words, since the heat dissipation electrode that is electrically isolated on one surface of the ceramic substrate has a small amount of energization during barrel plating, the plating layer of the heat dissipation electrode is naturally thinner than the plating layer of the terminal electrode. However, at the time of barrel plating, the terminal electrode is often energized while the radiation electrode is not energized.Therefore, charges are concentrated at the four corners of the radiation electrode that is rectangular in plan view, that is, positive charges opposite to the terminal electrode are present. It concentrates and the plating layers at the four corners are easily eluted. In particular, since the elution of the Sn plating layer is remarkable, the underlying Ni plating layer is exposed at the four corners of the heat dissipation electrode after the plating process, and the Ni plating layer is oxidized in the heat dissipation electrode having such poor plating, so that the solder There has been a problem that a chip resistor that is prone to attachment failure is produced.

  The present invention has been made in view of the actual situation of the prior art, and an object of the present invention is to provide a chip resistor that has good heat dissipation and can easily avoid defective plating of the heat dissipation electrode.

  In order to achieve the above object, the present invention provides a rectangular parallelepiped ceramic substrate, a pair of terminal electrodes provided at both ends in the longitudinal direction of the ceramic substrate, and the both terminals provided on one surface of the ceramic substrate. A resistor for bridging the electrodes, an insulating protective layer provided in a region covering the resistor, and an electric circuit between the two terminal electrodes provided on the surface of the protective layer or the other surface of the ceramic substrate. A heat dissipating electrode and a plating layer deposited on the heat dissipating electrode and the terminal electrode, and the heat dissipating electrode and the terminal electrode are soldered to a plurality of lands separated from each other on the mounting substrate. The chip resistor has a configuration in which the planar shape of the heat dissipation electrode is set to an approximately elliptical shape having no corners on the outer periphery.

  In the chip resistor configured in this way, since the heat radiation electrode that is electrically isolated between the pair of terminal electrodes is formed in a substantially elliptical shape in plan view, barrel plating performed at the final stage of the manufacturing process Sometimes, the phenomenon that the positive charge concentrates on a specific portion of the heat dissipation electrode and the plating layer is eluted is less likely to occur. Further, since the heat dissipation electrode having a substantially elliptical shape in plan view can be formed relatively large between the pair of terminal electrodes, a heat dissipation effect substantially the same as that of the heat dissipation electrode having a rectangular shape in plan view can be expected.

  When a heat dissipation electrode is provided on the surface of the insulating protective layer covering the resistor, the chip resistor is face-down on the mounting substrate on which the terminal electrode land and the heat dissipation electrode land are arranged. Since it is surface-mounted, the heat generated by the resistor when power is applied can be efficiently transmitted to the heat radiation electrode or the heat radiation electrode land of the mounting substrate, and the heat dissipation can be greatly improved. In addition, even when a heat dissipation electrode is provided on the surface of the ceramic substrate opposite to the side where the resistor exists, the heat of the resistor is transferred to the heat dissipation electrode via the ceramic substrate. The heat dissipation can be improved by soldering to the land.

  According to the chip resistor of the present invention, the heat dissipating electrode that is electrically isolated between the pair of terminal electrodes is formed in a substantially elliptical shape in a plan view having no corners on the outer peripheral portion. In this barrel plating process, the phenomenon that the positive charge concentrates on a specific portion of the heat dissipation electrode and the plating layer is eluted is less likely to occur, and thus the soldering failure of the heat dissipation electrode due to the plating failure can be avoided. Further, since a relatively large heat dissipation electrode can be provided between the pair of terminal electrodes, it is possible to significantly suppress the temperature rise of the chip resistor.

  BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing a mounted state of a chip resistor according to a first embodiment of the present invention, and FIG. 2 is a plan view of the lower surface of the chip resistor. It is explanatory drawing which abbreviate | omits a layer and shows.

  The chip resistor 1 shown in these drawings includes a rectangular parallelepiped ceramic substrate 2, a pair of terminal electrodes 3 provided at both ends in the longitudinal direction of the ceramic substrate 2, and a pair of terminal electrodes 3 provided on the upper surface of the ceramic substrate 2. A resistor 4 bridging the terminal electrode 3, an insulating first protective layer 5 and a second protective layer 6 provided in a region covering the resistor 4, and a pair of terminals provided on the lower surface of the ceramic substrate 2 The heat radiation electrode 7 is electrically isolated between the electrodes 3 and the two-layered plating layer 8 attached to the heat radiation electrode 7 and the terminal electrode 3 is mainly configured. As shown in FIG. 1, this chip resistor 1 is mounted on a printed circuit board 50, which is a mounting board, and surface-mounted by soldering the terminal electrode 3 and the heat radiation electrode 7 to the corresponding lands 51 and 52, respectively. . That is, on the printed circuit board 50, a pair of lands 51 for soldering the pair of terminal electrodes 3 and a land 52 for soldering the heat dissipation electrode 7 are disposed at positions separated from each other. The land 52 for the heat radiation electrode 7 is designed so that heat can be efficiently transmitted to the heat sink 55 via the thermal via 53 and the heat radiation silicon 54. In addition, the code | symbol 40 in FIG. 1 has shown the solder.

  The ceramic substrate 2 is an alumina substrate, which is obtained by dividing a large substrate (not shown) vertically and horizontally. Each terminal electrode 3 includes a surface electrode 31 formed on the upper surface of the ceramic substrate 2 and a back electrode 32 formed on the lower surface of the ceramic substrate 2 via an end surface electrode 33 formed on the side end surface of the ceramic substrate 2. The front surface electrode 31 and the back surface electrode 32 are made of Ag / Pd, and the end surface electrode 33 is made of nickel chromium (Ni / Cr). The resistor 4 is made of ruthenium oxide or the like, and both ends in the longitudinal direction of the resistor 4 are connected to a pair of surface electrodes 31. The resistor 4 has a trimming groove (not shown) for adjusting the resistance value. The first protective layer 5 is a pre-glass coat that covers the resistor 4, and the second protective layer 6 is an overcoat made of resin or glass that covers the first protective layer 5. The heat radiation electrode 7 is made of Ag, and the planar shape of the heat radiation electrode 7 is an oval shape as shown in FIG. The plating layer 8 having a two-layer structure is for preventing electrode cracking and improving the reliability of soldering. The underlying Ni plating layer 9 and the Sn plating deposited on the Ni plating layer 9 are used. Layer 10.

  When manufacturing the chip resistor 1 configured as described above, first, a large substrate having a grid-like dividing groove formed so as to divide each chip region is prepared, and each chip resistor 1 is formed on the large substrate. A large number of front surface electrodes 31 and back surface electrodes 32 corresponding to the above are printed and formed, and the resistor 4 is printed between adjacent front surface electrodes 31. Then, after printing and forming a first protective layer (pre-glass coat) 5 on each resistor 4 of the large substrate, laser trimming or the like is performed on each resistor 4 to form a trimming groove for adjusting a resistance value. Then, a second protective layer (overcoat) 6 is formed by printing so as to cover the first protective layer 5 together with the trimming grooves. Thereafter, the heat radiation electrode 7 having a substantially elliptical shape (oval shape) in plan view, which is located away from the back electrode 32, is printed on the surface of the large substrate where the back electrode 32 is formed. Next, after dividing the large substrate along one dividing groove (primary division) to obtain a large number of strip-shaped segment pieces, sputtering or the like is applied to the segmented surfaces of the strip-shaped segment pieces to form the end face electrodes 33. Form. And after dividing each strip-shaped division | segmentation piece into the chip-sized piece along the other division | segmentation groove | channel (secondary division), these metal pieces are barrel-plated and the Ni plating layer 9 and the Sn plating layer 10 are sequentially carried out. Form. That is, first, electrolytic plating is performed in a Ni plating barrel, and then electrolytic plating is performed in a Sn plating barrel, thereby depositing a plating layer 8 having a two-layer structure on the surfaces of the terminal electrode 3 and the heat dissipation electrode 7. Thus, a large number of chip resistors 1 as shown in FIG.

  As described above, in the chip resistor 1 according to this embodiment, the electrically isolated heat radiation electrode 7 is provided between the pair of terminal electrodes 3, and the plurality of lands 51 and 52 on the printed circuit board 50 are respectively provided. Surface mounting is performed by soldering the terminal electrode 3 and the heat radiation electrode 7, and heat generated in the resistor 4 when power is applied is transferred from the heat radiation electrode 7 to the heat sink 55 via the land 52, the thermal via 53, and the like. Since it can be transmitted and efficiently dissipated, the heat dissipation is excellent and the mounting strength to the printed circuit board 50 is also high. Further, since the heat radiation electrode 7 of the chip resistor 1 is formed in a substantially oval shape (oval shape) having no corners on the outer peripheral portion, it is added to a specific part of the heat radiation electrode 7 in the barrel plating process at the manufacturing stage. The phenomenon that the electric charge concentrates and the plating layer of Sn or the like elutes hardly occurs. That is, since there is no corner portion that promotes elution of the plating layer during barrel plating in the outer peripheral portion of the heat dissipation electrode 7, the two-layered plating layer 8 (Ni plating layer 9 and Sn plating layer 10) is used as the heat dissipation electrode 7. It can be deposited stably and uniformly, and the soldering failure of the heat radiation electrode 7 due to the plating failure can be avoided.

  In addition, as shown in FIG. 2, if the heat radiation electrode 7 is set to an oval shape in which four corners of a rectangle are chamfered in an arc shape, a relatively large heat radiation electrode 7 is provided between the pair of terminal electrodes 3. Therefore, it is easy to effectively dissipate heat through the heat radiating electrode 7, and there is no possibility that the energization amount of the heat radiating electrode 7 becomes extremely short during barrel plating.

  FIG. 3 is a sectional view showing a mounted state of the chip resistor according to the second embodiment of the present invention, and FIG. 4 is an explanatory view showing the shape of the lower surface of the chip resistor with the plating layer omitted. 2 and the parts corresponding to those in FIG.

  The chip resistor 20 shown in FIG. 3 and FIG. 4 is provided with the heat radiation electrode 7 on the surface of the second protective layer 6 covering the resistor 4 and is surface-mounted on the printed board 50 face down. This is significantly different from the first embodiment described above. Therefore, in the case of this chip resistor 20, the heat generated by the resistor 4 when power is applied can be efficiently transmitted to the heat radiation electrode 7 and the land 52 of the printed circuit board 50, and the heat dissipation is greatly improved. In the second embodiment, the heat radiation electrode 7 is formed in an elliptical shape. However, the heat radiation electrode 7 may have an oval shape as in the first embodiment, or the heat radiation electrode 7 is a perfect circle. An elliptical shape close to

It is sectional drawing which shows the mounting state of the chip resistor which concerns on the example of 1st Embodiment of this invention. It is explanatory drawing which abbreviate | omits a plating layer and shows the lower surface shape of the chip resistor which concerns on the example of 1st Embodiment. It is sectional drawing which shows the mounting state of the chip resistor which concerns on the example of 2nd Embodiment of this invention. It is explanatory drawing which abbreviate | omits a plating layer and shows the lower surface shape of the chip resistor which concerns on the example of 2nd Embodiment.

Explanation of symbols

1,20 Chip resistor 2 Ceramic substrate 3 Terminal electrode 4 Resistor 5 First protective layer (pre-glass coating)
6 Second protective layer (overcoat)
7 Heat Dissipation Electrode 8 Plating Layer 9 Ni Plating Layer 10 Sn Plating Layer 50 Printed Circuit Board (Mounting Board)
51 Land (for terminal electrode) 52 Land (for heat radiation electrode) 53 Thermal via 55 Heat sink

Claims (1)

  A rectangular parallelepiped ceramic substrate, a pair of terminal electrodes provided at both ends in the longitudinal direction of the ceramic substrate, a resistor provided on one side of the ceramic substrate to bridge the terminal electrodes, and the resistor An insulating protective layer provided in a region covering the heat sink, a heat dissipating electrode provided on the surface of the protective layer or the other surface of the ceramic substrate and electrically isolated between the two terminal electrodes, and the heat dissipation In a chip resistor comprising an electrode and a plating layer deposited on the terminal electrode, wherein the heat dissipation electrode and the terminal electrode are soldered to a plurality of lands separated from each other on a mounting substrate, the planar shape of the heat dissipation electrode Is set to be a substantially oval shape having no corners on the outer periphery.

Images