Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2003-10-29
2004-11-02
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S303000, C029S025410
Reexamination Certificate
active
06813137
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chip shaped electronic device, such as a multilayer chip varistor, not requiring glass coating or other insulative protective layers, being tolerant of temperature changes, capable of maintaining high resistance of an element surface even in reflow soldering, being highly reliable, and can be easily produced, and a method of producing the same.
2. Description of the Related Art
In recent years, along with electronic devices becoming more compact and furthermore highly performing, chip shaped electronic devices have become essential. A chip shaped electronic device is normally arranged on a circuit substrate and subjected to heat treatment together with printed solder to form a circuit. This heat treatment is called reflow soldering processing. At this time, a flux having a strong reducing power is included in the solder, and a surface of the chip device is corroded thereby to end up declining insulative resistance in some cases.
A multilayer varistor is not exceptional as a chip shaped electronic device, and an element surface of the multilayer chip varistor is reduced by reflow soldering to bring disadvantages of declining insulative resistance and declining reliability.
To solve the disadvantages, a glass is coated on the element surface of a multilayer chip varistor for improving reliability (for example, refer to the patent article 1).
However, to cover the element surface by uniformly coating a glass takes much trouble. Also, since thermal expansion coefficients of a ceramic material and a glass material are different, the boundary is liable to be damaged by a temperature cycle, etc. Therefore, cracks may arise in a glass layer, and insulation of ceramic composing the element may be damaged.
Note that a method of diffusing Li or Na on the element surface to make the surface highly resistant has been proposed (refer to the patent article 2). In the invention described in this patent article, the ratio of SIMS ion intensity M1 of Li or Na on the element surface and SIMS ion intensity M2 of Li or Na of a portion at a depth of 10 &mgr;m from the surface is made to be 10≦(M1/M2)≦50000.
In this method, however, it was found that although imperfect appearance at the time of electric plating could be improved, it was not sufficient for reducing from a flux in the reflow soldering. Namely, since a reducing power of an activated flux at the time of reflow soldering was much larger than that of electric soldering, a thickness of 10 &mgr;m or so of a range dispersed with Li or Na was not sufficient for reflow soldering.
Note that further compact electronic devices are demanded recently, and micro size chip shaped electronic devices having a size of, for example, 0.6 mm or less×0.3 mm or less×a thickness of 0.3 mm or less have been under development.
Patent Article 1: Japanese Unexamined Patent Publication No. 6-96907
Patent Article 2: Japanese Unexamined Patent Publication No. 9-246017
SUMMARY OF THE INVENTION
An object of the present invention is to provide a chip shaped electronic device, such as a multilayer chip varistor, not requiring glass coating or other insulative protective layers, being tolerant of temperature changes, capable of maintaining high resistance of an element surface even in reflow soldering, being highly reliable, and can be easily produced, and a method of producing the same.
Also, another object of the present invention is to provide a micro chip shaped electronic device (for example, having a size of 0.6 mm or less×0.3 mm or less×a thickness of 0.3 mm or less) having the above characteristics and a method of producing the same.
Chip Shaped Electronic Device
To attain the above objects, according to a first aspect of the present invention, there is provided
a chip shaped electronic device comprising an element body including zinc oxide material layers and internal electrode layers, wherein
when assuming a minimum distance from an outermost side of the internal electrode layer in the stacking direction to a surface of the element body is 1 and measuring an ion intensity ratio of an alkali metal (A) and zinc (Zn), (A/Zn), in a range from the surface of the element body to a depth of (0.9×1) by a secondary ion mass spectrometry (SIMS), 0.001≦(A/Zn)≦500.
In the first aspect, configurations of respective aspects described below are preferably applied.
According to the second aspect, there is provided
a chip shaped electronic device comprising an element body including zinc oxide material layers and internal electrode layers, wherein
when assuming a minimum distance from an outermost side of the internal electrode layer in the stacking direction to a surface of the element body is 1 and measuring an ion intensity ratio of Li and Zn, (Li/Zn), in a range from the surface of the element body to a depth of (0.9×1) by a secondary ion mass spectrometry, 0.001≦(Li/Zn)≦500.
According to the third aspect, there is provided
a chip shaped electronic device comprising an element body including zinc oxide material layers and internal electrode layers, wherein
when assuming a minimum distance from an outermost side of the internal electrode layer in the stacking direction to a surface of the element body is 1 and measuring an ion intensity ratio of Na and Zn, (Na/Zn), in a range from the surface of the element body to a depth of (0.9×1) by a secondary ion mass spectrometry, 0.001≦(Na/Zn)≦100.
According to a fourth aspect, there is provided
a chip shaped electronic device comprising an element body including zinc oxide material layers and internal electrode layers, wherein
when assuming a minimum distance from an outermost side of the internal electrode layer in the stacking direction to a surface of the element body is 1 and measuring an ion intensity ratio of K and Zn, (K/Zn), in a range from the surface of the element body to a depth of (0.9×1) by a secondary ion mass spectrometry, 0.001≦(K/Zn)≦100.
According to a fifth aspect, there is provided
a chip shaped electronic device comprising an element body including zinc oxide material layers and internal electrode layers, wherein
when assuming a minimum distance from an outermost side of the internal electrode layer in the stacking direction to a surface of the element body is 1 and measuring an ion intensity ratio of Rb and Zn, (Rb/Zn), in a range from the surface of the element body to a depth of (0.9×1) by a secondary ion mass spectrometry, 0.001≦(Rb/Zn)≦100.
According to a sixth aspect, there is provided
a chip shaped electronic device comprising an element body including zinc oxide material layers and internal electrode layers, wherein
when assuming a minimum distance from an outermost side of the internal electrode layer in the stacking direction to a surface of the element body is 1 and measuring an ion intensity ratio of Cs and Zn, (Cs/Zn), in a range from the surface of the element body to a depth of (0.9×1) by a secondary ion mass spectrometry, 0.001≦(Cs/Zn)≦100.
In the first aspect, configurations of respective aspects described below are preferably applied.
According to a seventh aspect, there is provided
a chip shaped electronic device comprising an element body including zinc oxide material layers and internal electrode layers, wherein
when measuring an ion intensity ratio of Li and Zn, (Li/Zn), in a range from the surface of the element body to a depth of 100 &mgr;m by a secondary ion mass spectrometry, it is 0.001≦(Li/Zn)≦500.
According to an eighth aspect, there is provided
a chip shaped electronic device comprising an element body including zinc oxide material layers and internal electrode layers, wherein
when measuring an ion intensity ratio of Na and Zn, (Na/Zn), in a range from the surface of the element body to a depth of 100 &mgr;m by a secondary ion mass spectrometry, it is 0.001≦(Na/Zn)≦100.
According to a ninth aspect, there is provided
a chip shaped electronic device comprising an element body includi
Kitamura Hidetaka
Matsuoka Dai
Ogasawara Tadashi
Dinkins Anthony
Oliff & Berridg,e PLC
TDK Corporation
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