1. Field of the Invention
The present invention relates to monolithic ceramic electronic components and methods of manufacturing the monolithic ceramic electronic components. The present invention particularly relates to a monolithic ceramic electronic component including external electrodes formed by plating and a method of manufacturing the monolithic ceramic electronic component.
2. Description of the Related Art
Conventional monolithic ceramic capacitors, which are typical monolithic ceramic electronic components, each include a laminate including a plurality of stacked dielectric ceramic layers and a plurality of laminar internal electrodes extending therebetween and also include a plurality of external electrodes. The internal electrodes are partly exposed at surfaces of the laminate and are electrically connected to each other with the external electrodes. FIG. 4 shows an exemplary conventional monolithic ceramic capacitor.
With reference to FIG. 4, a plurality of internal electrodes 104 and internal electrodes 105 are partly exposed at a first surface and a second surface, respectively, of a laminate 102. External electrodes are each disposed on the first or second surface of the laminate 102 such that the internal electrodes 104 and 105 are electrically connected to each other. A common method of forming the external electrodes is as described below. A metal paste containing a metal component and a glass component is applied onto the first and second surfaces of the laminate 102 and then baked, whereby paste electrode layers 106 and 107 are formed.
First plating layers 108 and 109 made of nickel are formed on the paste electrode layers 106 and 107, respectively. Second plating layers 110 and 111 made of tin are formed on the first plating layers 108 and 109, respectively. Therefore, the external electrodes each has a three-layer structure consisting of one of the paste electrode layers 106 and 107, one of the first plating layers 108 and 109, and one of the second plating layers 110 and 111.
Since the monolithic ceramic capacitor is soldered to a circuit board, the external electrodes need to have high wettability to solder. Furthermore, the external electrodes need to electrically connect the internal electrodes 104 and 105, which are electrically insulated from each other, to each other. The second plating layers 110 and 111, which are made of tin, have wettability to solder. The paste electrode layers 106 and 107 electrically connect the internal electrodes 104 and 105 to each other. The first plating layers 108 and 109 serve as bases for protecting the second plating layers 110 and 111 from solder erosion during soldering.
The paste electrode layers 106 and 107 have a large thickness of several ten to several hundred micrometers. Therefore, in order to adjust the size of the monolithic ceramic capacitor to a standard size, the effective volume of the monolithic ceramic capacitor that correlates with its capacitance needs to be reduced because the volume of the paste electrode layers 106 and 107 needs to be ensured. Since the first plating layers 108 and 109 and the second plating layers 110 and 111 have a small thickness of several micrometers, the monolithic ceramic capacitor can have an increased effective volume if the external electrodes include the first plating layers 108 and 109 and the second plating layers 110 and 111 only.
For example, Japanese Unexamined Patent Application Publication No. 63-169014 discloses a method in which conductive metal layers are deposited over side surfaces of a laminate by electroless plating such that internal electrodes which are arranged in the laminate and which are exposed at the side surfaces thereof are connected to each other.
According to the method disclosed in Japanese Unexamined Patent Application Publication No. 63-169014, external electrodes include plating layers only. Therefore, moisture may permeate the laminate through end portions of the plating layers. This results in the deterioration of lifetime properties of the laminate, the lifetime properties being evaluated by a high-temperature load test and a humidity load test.