TECHNICAL FIELD

The present invention relates to a ceramic electronic device formed with an external electrode.

BACKGROUND

Many electronic devices such as ceramic electronic devices are mounted inside an electronic apparatus.

Conventionally, in order to mount these electronic devices, a lead-free solder of Sn—Ag—Cu based, and a conductive adhesive agent added with conductive fine particles such as a metal filler and the like to a heat curable resin such as an epoxy resin and the like are used as a bonding material. The bonding material is selected mainly depending on environment to be used.

In recent years, the environment in which an inverter circuits using SiC power semiconductor is used is expected to become higher than 150° C. Thus, for such circuit substrate, mounting technology capable of maintaining a stable bonding force (that is, high mounting reliability) is demanded even when thermal stress is applied. In response to such demands, as a bonding material, a high temperature solder such as Au—Ge, Au—Sn, and the like, a conductive adhesive agent with improved heat resistance, and the like are developed. Note that, in order to ensure the mounting reliability, the electronic components which is the object to be bonded needs to be optimized in addition to the optimization of the bonding material.

As the external electrode of the ceramic electronic device corresponding to the conductive adhesive agent, Patent Document 1 discloses technology of forming an intermediate electrode layer made of Ni plating and an upper electrode layer made of Pd or Pd—Ni alloy on a base electrode layer. Further, Patent Document 1 discloses that by regulating a thickness of Ni as the intermediate electrode layer by a predetermined condition, Ag is prevented from migrating, and the conductive adhesive agent is suppressed from oozing out and also suppressed from causing short circuit between the external electrodes during mounting. Thereby, Patent Document 1 describes that a heat shock resistance against the heat stress of 150° C. or so can be satisfied.

However, the technology disclosed in Patent Document 1 had a possibility that the heat shock resistance and a highly accelerated lifetime cannot be satisfied when harsh heat stress such as 200° C. or so is applied.

[Patent Document 1] JP Patent Application Laid Open No. 2015-29050

SUMMARY

The present invention is achieved in view of such circumstances, and the object is to provide a ceramic electronic device capable of ensuring a mounting reliability even when heat stress is applied.

In order to attain the above object, a multilayer electronic component according to the first aspect of the present invention includes

a ceramic body having ceramic layers and internal electrode layers stacked in alternating manner and

a terminal electrode formed at an end face of the ceramic body;

wherein

the terminal electrode includes

a base electrode layer formed so to electrically connect with the internal electrode layers,

an intermediate electrode layer formed at an outer side of the base electrode layer, and

an upper electrode layer formed at an outer side of the intermediate electrode layer;

the base electrode layer includes a metal component and a glass component;

the intermediate electrode layer includes Ni;

the upper electrode layer includes Pd or Au; and

a surface roughness Ra1 of the base electrode layer in the terminal electrode is 5.0 μm or less.

In the terminal electrode having a multilayer structure as mentioned in above, by regulating the surface roughness Ra1 of the base electrode layer to 5.0 μm or less, defect such as pinhole and the like at the intermediate electrode layer can be reduced, thus a smooth intermediate electrode layer is easily obtained. As a result, in the ceramic electronic device according to the first aspect of the present invention, even when the ceramic electronic device is exposed under high temperature condition such as 200° C. or so for a long period of time after mounting using the bonding material, an insulation resistance scarcely decreases. That is, the ceramic electronic device according to the first aspect of the present invention can improve a highly accelerated lifetime than the conventional technology and the mounting reliability is improved.

Also, in order to attain the above object, a ceramic electronic device according to the second aspect of the present invention includes

a ceramic body having ceramic layers and internal electrode layers stacked in alternating manner and

a terminal electrode formed at an end face of the ceramic body;

wherein

the terminal electrode comprises

a base electrode layer formed so to electrically connect with the internal electrode layers,

an intermediate electrode layer formed at an outer side of the base electrode layer, and

an upper electrode layer formed at an outer side of the intermediate electrode layer;

the base electrode layer includes a metal component and a glass component;

the intermediate electrode layer includes Ni;

the upper electrode layer includes Pd or Au; and

the surface roughness Ra1 of the base electrode layer, a surface roughness Ra2 of the intermediate electrode layer, and a surface roughness Ra3 of the upper electrode layer satisfy a relationship of Ra1>Ra3≥Ra2

In the terminal electrode having the multilayer structure as mentioned in above, by roughening the surface of the upper electrode layer to provide a surface roughness of each layer to satisfy the relationship of Ra1>Ra3≥Ra2, tensile stress acting on the upper electrode layer from the intermediate electrode layer can be reduced. As a result, the ceramic electronic device according to the second aspect of the present invention can suppress a crack to the upper electrode layer even when a plurality of times of heat shocks of −55° C. to 200° C. is applied after mounted using the bonding material. Also, even if a crack is formed, the crack is suppressed from progressing. That is, the ceramic electronic device according to the second aspect of the present invention can improve the heat shock resistance compared to the conventional technology and can improve the mounting reliability.

Also, when the ceramic electronic device includes both of the first and second aspects of the present invention, that is the surface roughness Ra1 of the base electrode layer is 5.0 μm or less and a surface roughness of each layer satisfies a relationship of Ra1>Ra3≥Ra2, then a good highly accelerated lifetime and a good heat shock resistance can be both attained, and the mounting reliability further improves.

Note that, preferably the thickness of the upper electrode layer is 1.0 μm or less. In the present invention, by making the thickness of the upper electrode layer to 1.0 μm or less, a cost for raw materials can be reduced and the mounting reliability can be further improved.

As the glass component included in the base electrode layer, zinc oxide (ZnO), boron oxide (B2O3), silicon oxide (SiO2), and aluminum oxide (Al2O3) can be included. By including these glass compounds, a dense base electrode layer can be easily obtained.

Also, in case of including the above-mentioned glass compounds, a ratio of content of zinc oxide with respect to a sum of contents of boron oxide, silicon oxide, and aluminum oxide (ZnO/(B2O3+SiO2+Al2O3)) is preferably 0.25 to 0.32 when the glass component as a whole is 100 mol. In addition, a ratio of content of boron oxide with respect to a sum of contents of silicon oxide and aluminum oxide ((B2O3/(SiO2+Al2O3)) is preferably 0.60 to 0.70 when the glass component as a whole is 100 mol.

As mentioned in above, by including a predetermined compound by a predetermined content ratio as the glass component in the base electrode layer, smoother surface of the intermediate electrode layer can be attained. As a result, the highly accelerated lifetime and the heat shock resistance can be enhanced even more, and the mounting reliability can be improved even more.

Also, preferably, in the surface of the upper electrode layer, the content ratio of Ni is 5.0 wt % or less. As such, when exposure of Ni is little around the surface of the upper electrode layer, decrease of the bonding strength caused by oxidation of Ni component can be suppressed. As a result, the highly accelerated lifetime and the heat shock resistance can be enhanced even more, and the mounting reliability can be improved even more.

