JPH04329616A - Laminated type electronic component - Google Patents

Abstract

PURPOSE:To improve permeation of a plating liquid by coating an external electrode made of silver or silver palladium with a conductive resin which is not permeable to water before the final plating step. CONSTITUTION:A rectangular-parallelopiped ceramic base 2 of 5.5mm length, 5.0mm width, and 2.0mm thickness with 50 layers of inner electrodes 1 is baked at high temperature. Then, end faces of a rectangular parallelopiped where end faces of an inner electrodes 1 are exposed are coated by dipping with a paste made of silver powder, glass frit, ethylenecellulose, and terpineol. After drying, this workpiece is baked in an electric furnace to form an external electrode 3. It is dip-coated with an epoxy-baked conductive adhesive containing silver powder so that the external electrode 3 layer is covered. Through s plating technique, a solder plating liquid is used to form a solder film 5 by electric plating.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the external electrode structure of multilayer electronic components, and particularly to improving the mounting reliability of electronic components such as chip-type multilayer capacitors and multilayer varistors that are surface-mounted on a substrate.

0002

2. Description of the Related Art Multilayer electronic components, such as multilayer ceramic capacitors, are used in large quantities because they can be directly surface-mounted on a substrate and can be easily soldered and mounted in a short time.

As shown in FIG. 2, these have one layer of internal electrodes embedded inside the ceramic body 2, and the lead terminals are made of silver or silver and palladium powder, glass frit, and a resin vehicle. The external electrodes 3 are manufactured by applying a paste and firing at a high temperature, usually 600° C. or higher. To solder and mount such a chip-shaped electronic component on a printed wiring board, first print and coat cream solder on the pattern part of the board, place the three external electrodes of the chip component on top of it, and heat it. By heating to the melting temperature of the solder in a furnace, the external electrode 3 portion and the pattern portion of the substrate are joined by soldering. This method is called reflow soldering, but as a method that is more suitable for mass production and can be mounted on both sides of the board in a short time, it is possible to bond the chip components to the board with an adhesive and immerse them in a jet of molten solder. There is a flow mounting method in which the external electrode 3 and the pattern portion of the board are soldered. However, in the above-mentioned structure of the external electrode 3, since the external electrode 3 comes into direct contact with the molten solder, the silver in the external electrode 3 diffuses into the solder and a part of the external electrode 3 disappears, which is called a solder trap. Due to this phenomenon, flow implementation is not possible. To implement the flow,
The external electrode structure must be such that nickel 6 and solder 5 made of tin and lead are sequentially formed on the surface of the external electrode 3 by electroplating. However, in the electroplating process, the plating solution permeates through the external electrode 3 and into the slight voids in the ceramic body 2 that normally do not cause problems, resulting in a decrease in electrical performance such as loss coefficient, etc. There were drawbacks such as loss of long-term reliability. This is because in the conventional technology, the fine structure of the external electrode cannot be made into a dense structure that does not allow liquid to penetrate by the above manufacturing method.

For the above reasons, electronic components such as large chip capacitors (approximately 4 mm square or larger), which are relatively prone to forming voids, are usually not plated with nickel or solder, and therefore are mounted on boards using the reflow method. The disadvantage was that it was limited to. In addition, small electronic parts are plated with nickel and solder for flow use, but for the reasons mentioned above, parts that require high reliability are not plated and therefore cannot be used with the flow method. there were.

[0005]

[Problems to be Solved by the Invention] As mentioned above, in the prior art, when nickel plating and solder plating are performed in order to solder electronic components such as chip-type multilayer ceramic capacitors to a board by the flow method, the plating During the process, the plating solution penetrates into the inside of the component through the external electrode portion, particularly into the gap between the internal electrode layer and the ceramic layer, resulting in a disadvantage in that the electrical performance and long-term reliability are degraded.

[0006] In order to solve the problems of the prior art described above, the present invention improves the structure of the external electrode layer that serves as the base before plating, thereby preventing penetration of the plating solution during the plating process and improving electrical conductivity. Our objective is to provide multilayer electronic components such as multilayer ceramic capacitors and multilayer varistors that can be plated without deteriorating performance or long-term reliability, and therefore can be mounted on boards using the industrially advantageous flow soldering method. This is the purpose.

[0007]

[Means for Solving the Problems] The present invention provides an internal electrode layer, an external electrode made of silver or silver and palladium formed at the end of the internal electrode layer, and a conductive resin formed to cover the external electrode. and a laminated electronic component comprising a solder film made of tin and lead formed by electroplating on the surface of the conductive resin, the conductive resin having a thermosetting resin as a base material. , silver, nickel, aluminum, and zinc, and has a volume resistivity of 1×10 −3 Ωcm or less.

[0008]

[Function] In the laminated electronic component constructed according to the present invention, the external electrodes made of silver or silver palladium are coated with a conductive resin that does not allow water to penetrate before the final plating process. This prevents the plating solution from penetrating into the exposed end surface of the internal electrode, thus reducing the electrical performance and long-term reliability caused by the plating solution penetrating through the gap between the internal electrode layer and the ceramic layer. can be completely prevented from decreasing.

[0009]

[Embodiment] A multilayer ceramic capacitor will be described as an example. As shown in FIG. 1, according to a known manufacturing method, one layer of internal electrodes has 50 layers, a length of 5.5 mm, a width of 5.0 mm,
After firing a rectangular ceramic body 2 with a thickness of 2.0 mm at a high temperature, 80 parts of silver powder, 10 parts of glass frit, 5 parts of ethyl cellulose resin, and tar are applied to the end face of the rectangular parallelepiped where the end face of the internal electrode 1 is exposed. A paste consisting of 5 parts of Pineol was applied by dipping, dried and fired in an electric furnace at 800°C to form three layers of external electrodes. Next, a commercially available epoxy conductive adhesive containing 80 parts of silver powder was applied by dip coating to cover the three external electrode layers, and was cured by heating at 200° C. for 30 minutes to form a conductive layer 4. The volume resistivity of this material after curing was 1×10 −4 Ωcm. Next, using a known plating technique, electroplating was performed to a thickness of 5 μm using a solder plating solution consisting of 90% tin and 10% lead.
A solder film 5 was formed.

[0010] A capacitor manufactured by the above method is used as an example, and for comparison, a sample formed up to the electrode layer under the same conditions as this example was coated with a nickel plating layer and a nickel plating layer of 90% tin and 10% lead according to a known technique. solder layers were sequentially electroplated, each with a thickness of 5 μm.

[0011] Each of the methods of the above embodiment and the conventional example
00 samples were prepared, and the capacitance, dielectric loss tangent, insulation resistance, and withstand voltage of these samples were determined according to JIS C 64.
Table 1 shows the results of 100% inspection according to the standards specified in 23.

0012

[Table 1] As is clear from Table 1, the defect rate of the electrical characteristics of the example is clearly lower than that of the conventional example. This is the result of preventing it from penetrating into the body 2.

[0013] Next, after the above inspection, 100 samples each were sampled from the samples of the example and the conventional example, and a high temperature load test was conducted in which a DC voltage of 100V was applied for 2000 hours at a temperature of 125°C. While no failure was observed in the conventional example, there was a 3% insulation resistance failure (10 MΩ or less), indicating that the example was clearly more reliable. The reason for this is also the same as above.

Furthermore, when the sample according to the example was immersed in molten solder at 270° C. for 10 seconds and the surface of the external electrode 3 was observed, no solder curling phenomenon was observed, indicating that the entire surface of the external electrode 3 was covered with new solder. Therefore, we confirmed that board mounting using flow soldering is possible.

[0015] As a result of prototyping capacitors using various conductive adhesives having different volume resistivities after curing in the same manner as in the above example and measuring their electrical characteristics, it was found that If a capacitor with a coefficient exceeding 1 x 10-3 Ωcm is used, the dielectric loss tangent of the capacitor shall be JIS C
The result was that the dielectric loss tangent value specified in 6423 was not satisfied. From this result, it was found that the volume resistivity of the conductive adhesive used in the present invention must be 1×10 −3 Ωcm or less.

[0016]

[Effects of the Invention] As described above, the laminated electronic component of the present invention shows no deterioration in electrical characteristics and reliability even after the intended plating, and has high solder heat resistance. Since it is possible to use a flow soldering method using molten solder, it is possible to provide a laminated electronic component of great industrial value.

[Brief explanation of drawings]

FIG. 1 is a front cross-sectional view showing a multilayer ceramic capacitor that is an embodiment of the present invention.

FIG. 2 is a front cross-sectional view showing a conventional multilayer ceramic capacitor.

[Explanation of symbols]

1 Internal electrode 2 Ceramic body 3 External electrode 4 Conductive layer 5 Solder film

Claims (2)

[Claims] 1. At least two or more internal electrode layers embedded inside a ceramic body, external electrodes formed on the end faces of the ceramic body from which the ends of the internal electrode layers are alternately exposed, and A laminated electronic component comprising: a conductive layer made of metal powder and resin formed to cover an external electrode; and a solderable metal film made of tin and lead alloy on the surface of the conductive layer. 2. The conductive layer contains powder of at least one of silver, nickel, aluminum, and zinc in a base material made of a thermosetting resin, and has a volume resistivity of 1×10 after curing.
2. The laminated electronic component according to claim 1, which has a resistance of -3 Ωcm or less.