1. Field of the Invention
The present invention relates to multilayer electronic components and methods for producing multilayer electronic components, and particularly, to a multilayer electronic component in which external terminal electrodes that are connected to internal conductors are directly formed on surfaces of a ceramic body by plating and a method for producing the multilayer electronic component.
2. Description of the Related Art
Recently, the market for compact portable electronic devices has been expanding, including cellular phones, notebook PCs, digital cameras, and digital audio equipment. Such portable electronic devices are becoming smaller while having higher capabilities. Accordingly, smaller sizes and higher capabilities have also been demanded for numerous multilayer ceramic electronic components mounted on the portable electronic devices. For example, there has been a demand for monolithic ceramic capacitors having smaller sizes and higher capacitances.
One effective approach to provide monolithic ceramic capacitors having smaller sizes and higher capacitances is to reduce the thickness of ceramic layers. Recently, capacitors including ceramic layers having a thickness of about 3 μm or less have been produced. Although a further reduction in the thickness of the ceramic layers has been attempted, it has been difficult to ensure quality because a reduced layer thickness increases the risk of a short circuit between internal electrodes.
Another approach is to increase the effective area of the internal electrodes. However, mass production of monolithic ceramic capacitors requires side margins between the internal electrodes and side surfaces of a ceramic body and end margins between the internal electrodes and end surfaces of the ceramic body to allow for misalignment during lamination and cutting of ceramic green sheets. Therefore, to increase the effective area of the internal electrodes, the area of the ceramic layers must be increased to accommodate predetermined margins. However, there is a limitation on increasing the area of the ceramic layers within predetermined dimensional specifications of the products, and the thickness of external terminal electrodes is a hindrance to increasing the area of the ceramic layers.
Typically, external terminal electrodes of monolithic ceramic capacitors are formed by applying a conductive paste to the ends of a ceramic body and firing the paste. A common method for applying the conductive paste is to dip the ends of the ceramic body into a paste bath and to remove the ends therefrom. However, in this method, the conductive paste tends to be thickly applied at the central portions of the end surfaces of the ceramic body due to the viscosity of the conductive paste. Thus, the external terminal electrodes are partially thick (specifically, more than about 30 μm thick), and the area of the ceramic layers must be decreased accordingly.
In response to this problem, a method in which external terminal electrodes are directly formed by plating has been proposed.
In this method, plating films precipitate on exposed portions of internal electrodes at end surfaces of a ceramic body, and as the plating films grow, the exposed portions of the adjacent internal electrodes are connected together. This method enables the formation of thinner and flatter electrode films than the method using a conductive paste (see International Publication No. WO 2007/049456).
However, if the external terminal electrodes are directly formed on the surfaces of the ceramic body by plating, the following problem occurs.
If the external terminal electrodes are directly formed by plating, plating growth proceeds in two stages: a primary growth stage in which plating films grow from the exposed portions of the individual internal electrodes primarily in a spreading direction, and a secondary growth stage in which the plating films grown at the primary growth stage combine together in the spreading direction and a plating film grows from the continuous plating film primarily in a thickness direction. However, a problem arises in that it takes a significant amount of time for the separate plating films to grow and combine together in the spreading direction at the primary growth stage because the exposed portions of the internal electrodes are independent and isolated from each other. This increases the time required to form a plating film with a predetermined thickness, thus causing low productivity.