JP2000299242A - Ceramic electronic component and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic electronic component which is so structured as not to generate whiskers in an Sn plating layer, even in an environment such as a temperature change test where a thermal cycling between low temperature and high temperature is repeatedly. SOLUTION: Outer electrodes 3 are formed on the edge faces of an ceramic element 2 for the formation of a ceramic electronic component, where the outer electrode 3 is composed of a thick-film electrode 4 formed on the edge face of the ceramic element 2, an Ni plating layer 5 formed on the thick-film electrode 4, a whisker restraining layer 6 formed on the Ni plating layer 5, and an Sn plating layer 7 formed coming into contact with the whisker restraining layer 6 and serving as the outermost layer of the outer electrode 3. The whisker restraining layer 6 contains a metallic material, which is substantially larger in linear expansion coefficient than the outermost Sn plating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure of an external electrode of a ceramic electronic component.

[0002]

2. Description of the Related Art For example, in a ceramic electronic component such as a chip-type multilayer ceramic capacitor, it is common practice to mount an external electrode formed outside a chip body on a printed wiring board or the like by soldering. I have. In this case, a configuration in which the outermost layer of the external electrode is formed of a Sn or Sn alloy film is generally used in order to improve the solderability at a relatively low cost. Sn and S
The n-alloy film has an advantage that solder wettability is much better than that of Ni or Cu, and that mounting defects are less likely to occur when electronic components are mounted by processing such as reflow or flow. Because.

[0003] Fig. 2 shows an example of a ceramic electronic component in which Sn or a Sn alloy conventionally used is provided on the outermost layer. FIG. 2 is a cross-sectional view showing a chip-type multilayer ceramic capacitor 11, which is mainly composed of a ceramic body 12 and external electrodes 13 formed at both ends of the ceramic body 12 in a U-shape. External electrode 13
Is a thick film electrode 1 formed in contact with the ceramic body 12.
4. Ni plating layer 15 formed on thick film electrode 14, N
Sn plating layer or Sn formed on i-plating layer 15
Alloy plating layer (hereinafter simply referred to as “Sn plating layer”) 1
6 of three layers. Here, the thick film electrode 14 is formed by baking a metal paste such as Ag or Cu, and the Ni plating layer 15 is formed by Ni electric field plating.
The n plating layers 16 are formed by Sn electroplating.

[0004]

By the way, when the ceramic electronic component having the above-mentioned structure is subjected to a temperature change test, which is a kind of environmental test, the Sn plating layer 16 corresponding to the outermost layer of the external electrode 13 having a three-layer structure is formed. It has recently become clear that whiskers (whisker-like Sn projections) may occur. At this time, the detailed mechanism of whisker generation has not been clarified. However, if whiskers are generated at external electrodes of electronic components mounted on a circuit board, there is a risk of short-circuiting with adjacent components or wiring patterns. Until now, the reason that these problems did not occur in the conventional external electrode was that the size of the whisker generated was sufficiently small as compared with the interval between adjacent components or wiring patterns. Conceivable. In the future, as the mounting density of the circuit components increases, the intervals between the components and the wiring patterns become narrower, so that it is expected that the risk of the short-circuit failure caused by the whiskers will increase.

[0005] In order to solve this problem, a material which is less likely to generate whiskers and has high solder wettability, for example, Au or Pd
A method of providing such a film on the outermost layer of the external electrode has been studied as a countermeasure. However, since these materials are all precious metals, the cost of materials is high, and as a result, there is a new problem that the price of products increases. As long as the generation of whiskers can be suppressed, Sn is the most suitable material as an electrode material provided in the outermost layer of the terminal electrode,
There is a need for a method that can suppress the generation of whiskers while using Sn.

Accordingly, an object of the present invention is to provide a ceramic electronic component having a structure that does not generate whiskers in a Sn plating layer even in an environment where low and high temperature cycles are repeated, such as a temperature change test, and a method of manufacturing the same. To provide.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the occurrence of whiskers generated in the Sn plating layer depends on the type of metal material formed immediately below the Sn plating layer. I found that. More specifically, whisker suppression comprising a metal material having a linear expansion coefficient substantially larger than the linear expansion coefficient of the Sn plating layer, for example, a metal material such as Zn, Al, or Pb, immediately below the Sn plating layer The inventors have found that whiskers generated in the Sn plating layer can be suppressed by forming the layer, and have completed the present invention.

As described above, at this time, the details of the mechanism of whiskers generated by the temperature change test are unknown. In this regard, the present inventors believe that the stress generated at the interface between the Sn plating layer and the underlying layer in contact therewith is one factor in the driving force for the generation / elongation of whiskers. It is considered that this stress is generated due to a difference in linear expansion coefficient between the Sn plating layer and the underlying layer in contact with the Sn plating layer. More specifically, from the point that whiskers are generated from the inside of the Sn plating layer, the generation of whiskers gradually increases as compressive stress is repeatedly applied to the Sn plating layer.
It is believed that elongation occurs.

The reason why compressive stress is applied to the Sn plating layer is that when the Sn plating layer is formed on a base layer having a smaller linear expansion coefficient than the Sn plating layer, when the temperature rises, the Sn plating The case where the Sn plating layer is formed on the base layer having a larger linear expansion coefficient than the layer is the case where the temperature is lowered. However,
For example, as is clear from the experimental examples shown in Table 3 below,
Sn on the underlayer having a higher linear expansion coefficient than the Sn plating layer
It has been confirmed that when the plating layer is formed and the temperature is lowered, a whisker does not occur although a compressive stress is applied to the Sn plating layer.

[0010] Considering these points, it is considered that the whisker generation condition is that a compressive stress is applied to the Sn plating layer when the temperature rises. Therefore, in order to suppress the generation of whiskers, the configuration of the external electrode should be changed when the temperature rises.
What is necessary is just to adopt a configuration in which a compressive stress is not applied to the n-plated layer, that is, a configuration in which an underlayer made of a metal material having a larger linear expansion coefficient than the Sn-plated layer is further provided as a whisker suppression layer immediately below the Sn-plated layer. (Note that the Ni plating layer formed immediately below the Sn plating layer in the external electrode of the conventional structure is a metal material having a smaller linear expansion coefficient than the Sn plating layer.)

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the ceramic electronic component of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing a chip-type multilayer ceramic capacitor 1, which is mainly composed of a ceramic body 2 and external electrodes 3 formed at both ends of the ceramic body 2 in a U-shape. The external electrode 3 includes a thick film electrode 4 formed in contact with the ceramic body 2, a Ni plating layer 5 formed on the thick film electrode 4, a whisker suppression layer 6 formed on the Ni plating layer 5, and a whisker suppression. And an Sn plating layer 7 formed in contact with the layer 6 and located at the outermost layer of the external electrode 3. Here, the thick film electrode 4 is made of Ag.
By baking the paste, the Ni plating layer 5 is formed by electrolytic plating of Ni, the whisker suppressing layer 6 is formed by electrolytic plating of Al, and the Sn plating layer 7 is formed by electrolytic plating of Sn. The thick film electrode 4 may use a Cu paste other than the Ag paste, and the whisker suppressing layer 6 may be formed by electrolytic plating of Zn, Ag, or Pb other than Al.

Here, Al and Zn used as the whisker suppressing layer 6 are metal materials having a larger linear expansion coefficient than the Sn plating layer 7. Note that Ag can also be used as the whisker suppression layer 6 in the present invention. In this regard,
The actual linear expansion coefficient of Ag is slightly smaller than that of the Sn plating layer 7. However, the difference between the linear expansion coefficients of the two is small, and as is clear from the experimental results shown in Tables 2 and 3 below, almost no whiskers are generated even when Ag is used as the whisker suppressing layer 6. The whiskers generated are of a size that does not pose a problem in practical use. Therefore, Ag is not a substitute for being a base layer that can suppress the situation that “whiskers are generated by the stress caused by the difference in linear expansion coefficient”, and is one kind of the metal material that realizes the purpose of the present invention. It can be evaluated that there is no change.

First, a temperature change test was performed on the ceramic electronic component having the above-described configuration under the conditions shown in Table 1 below to confirm whether or not whiskers were generated. Table 2 shows the results of the temperature change test. In addition, in Table 2, in addition to the test result of the electronic component having the structure of the present embodiment, the test result of the temperature change test of the electronic component having the structure of the conventional example is also shown for comparison.

[0015]

[Table 1]

[0016]

[Table 2]

As is clear from the results shown in Table 2, a remarkable effect of suppressing the generation of whiskers can be confirmed in the ceramic electronic component employing the structure of this embodiment.

Next, it was confirmed how the generation of whiskers generated by the temperature change test changes depending on the material of the underlayer (whisker suppression layer) formed immediately below the Sn plating layer. The results of this experiment are shown in Table 3 below. In the experiment, after forming an Sn plating layer on various metal thin plates by electrolytic plating, the sample was subjected to the test described in Table 1 above.
A temperature change test was performed under the same conditions as shown in FIG.

[0019]

[Table 3]

Further, Sn formed on various metal thin plates
The whisker suppression effect was also confirmed when the plating layer was made of various Sn alloy plating instead of Sn simple plating. The experimental results are shown in Tables 4, 5, 6, and 7 below.
Shown in

[0021]

[Table 4]

[0022]

[Table 5]

[0023]

[Table 6]

[0024]

[Table 7]

As is clear from the results of the above experiments,
By forming a whisker suppressing layer made of a metal material having a substantially higher linear expansion coefficient than the Sn plating layer directly below the Sn plating layer (including both Sn simple plating and Sn alloy plating), the temperature change test results. It can be confirmed that whiskers generated on the surface of the Sn plating layer can be effectively suppressed.

Conventionally, as a test for confirming the generation of whiskers, a constant temperature test (a test for observing the occurrence of whiskers after standing at a constant temperature for a certain period of time) has been conducted. When a thermostatic test was performed on each sample shown in Table 7, no whiskers were observed as observed after the temperature change test for both the external electrode having the configuration of the present invention and the external electrode having the conventional structure. .

[0027]

As is apparent from the above description, a metal material having a linear expansion coefficient substantially larger than the linear expansion coefficient of the Sn plating layer immediately below the Sn plating layer located at the outermost layer of the external electrode. By forming the whisker suppressing layer containing whiskers, it is possible to effectively suppress the generation of whiskers generated on the surface of the Sn plating layer due to a temperature change. This makes it possible to mount components with higher mounting density when mounting components on a substrate.

Here, as a metal material suitable as a whisker suppressing layer, Al, Zn, Pb, which have a larger linear expansion coefficient than Sn, and a slightly smaller linear expansion coefficient than Sn, but also a metal material of the present invention. Ag or the like having an effect can be used as the metal material used in the present invention.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a ceramic electronic component of the present invention.

FIG. 2 is a cross-sectional view illustrating a conventional ceramic electronic component.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Chip-type multilayer ceramic capacitor 2 ... Ceramic body 3 ... External electrode 4 ... Thick film electrode 5 ... Ni plating layer 6 ... Whisker suppression layer 7 ... Sn plating layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K044 AA13 AB10 BA06 BA10 BB02 BC11 BC14 CA18 5E001 AB03 AF00 AF06 AH01 AH07 AJ03

Claims (7)

[Claims] 1. A ceramic electronic component having an external electrode formed on a ceramic body, wherein the external electrode is formed on a thick film electrode formed on the surface of the ceramic body and on the thick film electrode. Ni plating layer and Ni
A whisker suppressing layer formed on the plating layer, and a Sn plating layer formed in contact with the whisker suppressing layer and positioned at the outermost layer of the external electrode, wherein the whisker suppressing layer is an outermost layer A ceramic electronic component comprising a metal material having a linear expansion coefficient substantially larger than a linear expansion coefficient of the Sn plating layer. 2. A metal material having a linear expansion coefficient substantially larger than a linear expansion coefficient of the Sn plating layer,
The ceramic electronic component according to claim 1, wherein at least one of n, Al, and Pb is used. 3. A ceramic electronic component in which an external electrode is formed on a ceramic body, wherein the external electrode is formed on a thick-film electrode formed on the surface of the ceramic body and on the thick-film electrode. Ni plating layer and Ni
A ceramic electronic component comprising: an Ag plating layer formed on a plating layer; and a Sn plating layer formed in contact with the Ag plating layer and located at an outermost layer of the external electrode. 4. A method for manufacturing a ceramic electronic component, comprising forming an external electrode on a ceramic body, wherein the external electrode comprises: a step of forming a thick film electrode on the surface of the ceramic body; Forming a Ni plating layer on the Ni plating layer, forming a whisker suppressing layer on the Ni plating layer, and forming a Sn plating layer as an outermost layer in contact with the whisker suppressing layer. The method of manufacturing a ceramic electronic component, wherein the suppression layer is formed to include a metal material having a linear expansion coefficient substantially larger than a linear expansion coefficient of the outermost Sn plating layer. 5. A metal material having a linear expansion coefficient substantially larger than a linear expansion coefficient of the Sn plating layer,
The method for manufacturing a ceramic electronic component according to claim 4, wherein the method is formed to include at least one of n, Al, and Pb. 6. A method for manufacturing a ceramic electronic component, comprising forming an external electrode on a ceramic body, wherein the external electrode comprises: a step of forming a thick-film electrode on the surface of the ceramic body; Forming a Ni plating layer on the Ni plating layer, and forming an Ag plating layer on the Ni plating layer,
Forming a Sn plating layer as an outermost layer in contact with the Ag plating layer. 7. The ceramic electronic component according to claim 1, wherein said Sn plating layer is a Sn alloy plating layer.