JP2009170706A - Multilayer electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the decrease of the capacitance of a multilayer electronic component caused by the breakage of joints of an external electrode and internal electrodes by relaxing stress caused by a difference between a wiring substrate and an electronic component base body. <P>SOLUTION: A multilayer ceramic capacitor 1 has a structure having the electronic component base body 2 in which the internal electrodes 4 are alternately stacked through ceramic dielectrics 3 composed mainly of barium titanate, and the external electrode 5 formed on the surface of the base body where leading terminals 4a of the internal electrodes 4 are exposed. The external electrode 5 has an underlying metal layer 5a which closely contacts with the base body 2 and electrically connected with the leading terminals 4a, a first plated metal layer 5b to protect the underlying metal layer, and a second plated metal layer 5c to improve solder wettability with the first plated metal layer to protect the underlying metal layer 5a. Grooves 6 which extend vertically against the internal electrodes 4 and contact with the internal electrodes 4 are formed in the vicinity of the leading terminals 4a of the base body 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer electronic component such as a multilayer ceramic capacitor, a multilayer capacitor array, or a multilayer LCR composite component, and more particularly to a multilayer electronic component having good resistance to stress.

  A multilayer ceramic electronic component such as a multilayer ceramic capacitor has a substantially rectangular parallelepiped-shaped electronic component element body and an internal electrode that is embedded in the electronic component element body and exposed at the surface of the electronic component element body. And at least a pair of external electrodes formed on the exposed surface of the electronic component element body and electrically connected to the internal electrodes, and the external electrodes are connected to the internal electrodes. In addition to the underlying metal layer to be formed, it is composed of a plurality of conductive layers such as a plated metal layer for protecting the underlying metal layer and improving solder wettability.

  Such a laminated electronic component is mounted on a wiring board by soldering to constitute an electronic circuit. A laminated electronic component mounted on a wiring board is subjected to various stresses. For example, during soldering, thermal stress due to heat from a reflow furnace or the like is applied to the laminated electronic component. Further, after mounting the laminated electronic component on the wiring board, mechanical stress due to the deflection of the wiring board is applied. Since such stress is applied particularly to the external electrode, the connection between the external electrode and the internal electrode may be broken. Therefore, the capacitance of the laminated electronic component may be reduced.

As one means for solving such a problem, there is a means disclosed in Japanese Patent Application Laid-Open No. 2002-203737. In this method, by providing a dense first electrode layer having a high glass content and a porous second electrode layer having a low glass content, the durability against mechanical stress due to the deflection of the wiring board is improved. It is.

JP 2002-203737 A

However, with the means of the above-mentioned Patent Document 1, it is difficult to improve durability against thermal stress. Since the mechanical stress due to the deflection of the wiring board is mainly the stress applied to the external electrode, the above means for providing the external electrode with a structure for relaxing the stress is effective. However, since the thermal stress is the stress generated by the difference in thermal expansion between the wiring board and the electronic component body, it is necessary to reduce the difference in thermal expansion between the wiring board and the electronic component body in order to reduce the thermal stress. There is. The means of Patent Document 1 does not disclose means for reducing the difference in thermal expansion between the wiring board and the electronic component element body.

The present invention relieves the stress due to the difference in thermal expansion between the wiring board and the electronic component body, and prevents a decrease in the capacitance of the laminated electronic component due to the disconnection between the external electrode and the internal electrode. is there.

In the present invention, a substantially rectangular parallelepiped-shaped electronic component element, an internal electrode embedded in the electronic component element and having a lead-out end exposed on the surface of the electronic component element, and the electronic component element In the laminated electronic component having an external electrode formed on the surface where the leading end is exposed and electrically connected to the internal electrode, the external electrode includes a base metal layer containing a conductive metal and a glass component. A groove extending in a direction perpendicular to the internal electrode and in contact with the internal electrode is formed in the vicinity of the leading end portion of the electronic component element body, and the glass component is formed in the groove. Proposed multilayer electronic components are filled.

  Since the Young's modulus of the glass component is lower than the Young's modulus of barium titanate used for the electronic component element body, the wiring board and the electronic component element body are formed by the groove filled with the glass component if the above-described solution structure is used. The stress due to the difference in thermal expansion can be relaxed.

  According to the present invention, the stress due to the difference in thermal expansion between the wiring board and the electronic component body is relieved, and the capacitance of the laminated electronic component is prevented from being lowered due to the disconnection between the external electrode and the internal electrode. be able to.

An embodiment of a multilayer electronic component according to the present invention will be described by taking a multilayer ceramic capacitor as an example. The present invention is applicable to multilayer composite electronic components such as multilayer capacitor arrays and multilayer LC filters in addition to multilayer ceramic capacitors.

  FIG. 1 is a schematic longitudinal sectional view showing a multilayer ceramic capacitor according to the present invention. The multilayer ceramic capacitor 1 has an electronic component body 2 in which internal electrodes 4 are alternately stacked via a ceramic dielectric 3 mainly composed of barium titanate, and a lead end portion of the internal electrode 4 The external electrode 5 is formed on the surface where the 4a is exposed. The external electrode 5 has a solder metal wettability with a base metal layer 5a that is in close contact with the electronic component body 2 and is electrically connected to the lead end 4a, and a first plated metal layer 5b that protects the base metal layer 5a. A second plated metal layer 5c to be improved. Further, a groove 6 extending in a direction perpendicular to the internal electrode 4 and in contact with the internal electrode 4 is formed in the vicinity of the leading end 4 a of the electronic component body 2.

The base metal layer 5 a has a role of being electrically connected to the lead end 4 a of the internal electrode 4. The underlying conductive layer 5a is formed by a method in which a conductive paste is applied and baked on the electronic component body 2 after baking. The conductive paste used for the base metal layer 5a includes a conductive metal serving as a conductive material and a glass component serving as a binding aid for closely contacting the electronic component body 2. Examples of the conductive material include Ni, Cu, and Ag. As the glass component, Li—Si glass, B—Si glass, or the like is used.

The first plated metal layer 5b covers the entire base metal layer 5a and serves to protect the base metal layer 5a. Examples of the metal used for the first plated metal layer 5b include Ni and Cu. The second plated metal layer 5c covers the entire first plated metal layer 5b and has a role of improving solder wettability. Examples of the metal used for the second plated metal layer 5c include Sn or Sn alloy.

The internal electrodes 4 are embedded in the electronic component body 2, and the internal electrodes 4 facing each other through the ceramic dielectric 3 are exposed at different ends of the electronic component body 2 at one end of each. . This exposed portion becomes the extraction end 4a. Examples of the metal constituting the internal electrode 4 include base metals such as Ni and Cu, and noble metals such as Ag and Pd. In recent years, since the number of internal electrodes has increased due to the increase in capacity, base metals such as Ni and Cu are often used from the viewpoint of cost.

  The combination of the metal of the internal electrode 4 and the metal of the base metal layer 5a is determined by the material of the ceramic dielectric 3, etc., but it is particularly preferable that the internal electrode 4 is Ni and the base metal layer 5a is Cu. In this combination, solid phase diffusion occurs between Ni of the internal electrode 4 and Cu of the underlying metal layer 5a, and a Ni—Cu alloy can be generated to obtain a good bonded state.

  The groove 6 extends in the direction perpendicular to the internal electrode 4 in the vicinity of the lead-out end portion 4 a of the electronic component element body 2, and is further formed in contact with the internal electrode 4. The groove 6 is filled with a glass component. The glass component filled in the groove 6 is substantially the same as the glass component contained in the conductive paste for forming the base metal layer 5a. Further, in addition to the glass component, a part of the metal of the internal electrode 4 may enter the groove 6.

  The groove 6 is in a state of being wedged extending from the internal electrode 4 and biting into the electronic component body 2. Further, since the glass component filled in the groove 6 is diffused from the conductive paste constituting the base metal layer 5a, the base metal layer 5a and the electronic component body 2 are firmly bonded. The glass component filled in the groove 6 is, for example, zinc borosilicate glass having a Young's modulus of about 6 to 8 GPa and lower than the Young's modulus of 40 GPa of barium titanate used for the electronic component body. Thereby, when the multilayer ceramic capacitor 1 is mounted on the wiring board, even if stress is generated due to a difference in thermal expansion between the wiring board and the electronic component body, the stress is relieved by the glass component having a low Young's modulus. . Due to this stress relaxation action, durability against thermal stress can be improved.

  Here, the vicinity of the extraction end corresponds to the depth D from the surface where the extraction end 4a is exposed to the groove 6 as shown in FIG. Although there is no restriction | limiting in particular about this depth D, if it is 8 micrometers or more, joining of the internal electrode 4 and the base metal layer 5a will become more favorable.

  Next, the manufacturing method of the multilayer ceramic capacitor of this invention is demonstrated. First, the baked electronic component body 2 is prepared before the base conductive layer 5a is formed.

  This electronic component body 2 is obtained as follows. First, a reduction-resistant ceramic powder mainly composed of barium titanate is kneaded with an organic binder to form a slurry, which is formed into a sheet with a doctor blade or the like to obtain a ceramic green sheet. An Ni conductive paste is applied in a predetermined pattern to the ceramic green sheet by screen printing to form an internal electrode pattern. The ceramic green sheets on which the internal electrode patterns are formed are punched into a predetermined shape, and a predetermined number of the punched ceramic green sheets are stacked and thermocompression bonded to form a laminate. This laminate is cut and divided into a predetermined individual chip size (for example, 4.0 mm × 2.0 mm) to obtain an unfired body of the electronic component body 2. The green body is fired in a nitrogen-hydrogen atmosphere at 1100 to 1300 ° C. to obtain the electronic component body 2 having a predetermined size (for example, 3.2 mm × 1.6 mm size).

  Subsequently, a conductive paste is applied by dipping on the surface of the obtained electronic component element body 2 where the leading end 4a is exposed. This conductive paste contains Cu as a conductive metal and zinc borosilicate glass as a glass component. The electronic component body 2 coated with the conductive paste is heated in a nitrogen atmosphere to form the base metal layer 5a. The heating temperature at this time is set to a temperature higher than the softening point of the glass component of the conductive paste to be used. For example, when the normal baking temperature of zinc borosilicate glass is 100 to 300 ° C. higher than the softening point of about 600 ° C., baking is performed at a temperature 20 to 60 ° C. higher. As a result, the glass component in the conductive paste diffuses into the electronic component body 2.

  When the glass component diffuses into the electronic component body 2, the groove 6 is formed at the boundary between the portion where the glass is diffused and the portion where the glass is not diffused. Although the mechanism is unknown, the depth at which the groove 6 is formed is determined by the depth at which the glass component diffuses. Note that the diffusion depth of the glass can be adjusted by the material of the ceramic dielectric 3 and the type of conductive metal of the conductive paste, in addition to the baking temperature of the conductive paste. The formed groove 6 is filled with a part of the diffused glass component.

  Subsequently, a plated metal layer is formed on the base metal layer 5a by an electrolytic plating method. The plated metal layer may be a single layer, but the first plated metal layer 5b made of Cu, Ni or the like for the purpose of protecting the base and the second made of Sn or the like for improving solder wettability. A plurality of plated metal layers of the plated metal layer 5c may be formed.

  Next, a heat cycle test is performed on the multilayer ceramic capacitor 1 thus obtained to verify the effect of the present invention. 100 samples each having a baking temperature of 0 μm (comparative example), 3 μm, and 8 μm were prepared by changing the baking temperature. Each sample was soldered to a glass-epoxy resin substrate, and the initial capacitance was measured. Next, each sample was put into a heat cycle test with a temperature change of −55 ° C. to + 125 ° C. taken as one cycle in one hour. The capacitance that was 10% or less of the initial capacitance was defined as the capacitance NG, and the number thereof was defined as the occurrence rate. In addition, the depth D of the groove 6 is extracted from each of the five samples, polished from the side surface, and from the boundary between the base metal layer 5a and the electronic component body 2 to the contact portion between the groove 6 and the internal electrode 4. The distance was measured and obtained from an average value of a total of 25 points at 5 points per piece. The result is shown in the graph of FIG.

  As shown in FIG. 2, in the comparative example in which the groove 6 is not formed, that is, 0 μm, a capacitance NG of 40% or more is generated in 100 cycles. However, in the case where the groove 6 is formed, it is 20% or less even at 500 cycles, and in particular, when the depth D is 8 μm, the capacitance NG is not generated even at 500 cycles.

  From the above results, according to the present invention, the capacitance of the multilayer electronic component due to the fact that the stress due to the difference in thermal expansion between the wiring board and the electronic component element body is alleviated and the connection between the external electrode and the internal electrode is broken. Can be prevented.

It is a fragmentary sectional view showing typically the multilayer ceramic capacitor of the present invention. It is a graph which shows the result of a heat cycle test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic capacitor 2 Electronic component body 3 Ceramic dielectric 4 Internal electrode 4a Lead-out end 5 External electrode 5a Underlying conductive layer 5b First plating metal layer 5c Second plating metal layer 6 Groove

Claims (1)

An electronic component element body having a substantially rectangular parallelepiped shape, an internal electrode embedded in the electronic component element body and having an extraction end exposed on the surface of the electronic component element element, and the extraction end part of the electronic component element body In a laminated electronic component having an external electrode formed on the exposed surface and electrically connected to the internal electrode,
The external electrode has a base metal layer containing a conductive metal and a glass component,
A groove extending in a direction perpendicular to the internal electrode and in contact with the internal electrode is formed in the vicinity of the leading end of the electronic component body,
A laminated electronic component, wherein the groove is filled with a glass component.

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