JPH0234449B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for insulating laminated ceramic electronic components.

Multilayer ceramic electronic components have been put to practical use in many types, including multilayer ceramic capacitors, multilayer ceramic varistors, multilayer ceramic substrates, multilayer ceramic inductors, multilayer ceramic electrostrictive elements, multilayer ceramic piezoelectric elements, and multilayer ceramic sensors.

Since these laminated ceramic electronic components are all small, the distance between the terminal electrodes for taking out the electrodes to the outside is small, making it difficult to ensure insulation and reliability between the terminal electrodes. In laminated ceramic parts, silver or gold-palladium alloys have generally been baked as terminal electrodes due to technical and cost considerations. However, since silver undergoes migration in the presence of water, its reliability, especially in humidity load tests, has been significantly reduced.

To solve this problem, silver-palladium alloys with high palladium content are used, silver electrodes are coated with base metals such as solder, nickel, copper, etc. by plating, or terminal electrodes are used. Research and development is being carried out to attach copper or nickel using methods such as electroless plating.

However, all of these methods have problems such as ineffectiveness, complicated manufacturing processes, and restrictions on the ceramic materials that can be used, and high costs, which prevent them from being put into practical use. .

Therefore, for multilayer ceramic electronic components with leads, hermetic seals have been put into practical use as an external insulation method to ensure reliability against environmental changes, and are an extremely excellent insulation method. However, since this increases the size and significantly increases the cost, it has to be used only in areas where reliability is particularly required.

Therefore, insulation using organic resins such as epoxy is used as an alternative method for external insulation and packaging of electronic components with leads, but since organic resins allow almost 100% of water vapor to pass through, they are difficult to prevent migration. However, no preventive effect could be obtained at all, and the reliability of moisture resistance load was significantly lowered.

In addition, methods for insulating the conductor parts of electronic components with inorganic materials include the screen printing method and dip method using insulating paste containing inorganic insulating materials used in HIC, etc., and the spray method using insulating material powder. Although screen printing methods can print uniformly, it is difficult to align them, and in addition, in the case of individual small parts, it is not possible to process large quantities, resulting in high costs. was. In addition, it was necessary to prepare a screen for each circuit, which caused many problems in terms of process control. The dip method and spray method have the advantage of being able to produce large quantities at low cost, but they have problems with the quality of the insulating layer, such as the positioning of the insulating layer being inaccurate, the thickness being uneven, and pinholes easily occurring. Due to its drawbacks, it was only used in limited areas.

As described above, various methods have been tried to ensure reliability by examining materials for terminal electrodes and packaging methods, but no significant improvements have been seen. Because it is difficult to ensure insulation reliability at the component level, attempts have been made to ensure insulation reliability by covering the entire circuit in which the components are mounted with organic resin, etc. However, there are problems such as increased cost and increased size, and there is little improvement in reliability.

On the other hand, applying powder to a conductor by electrophoresis is a technique that has been put into practical use in the fields of metal painting, enamel, etc., but in all cases it is a technique for applying to large objects. Also, for electronic parts, Electrochemistry Vol. 40, No. 7 page 478 and Special Publication No. 48-6299
As described in , it is being researched as a connectivity for silicon devices. However, all of these techniques cover the entire surface with organic, inorganic, or a mixture thereof, and as in the present invention, the surface of a very fine conductor part is selectively covered and the adjacent ceramic material part is also covered. It did not include anything that would form an insulator.

As described above, it has been extremely difficult to reliably insulate the externally exposed electrode portions of laminated ceramic electronic components, and in reality, they are either not insulated at all or are insulated using insufficient insulation methods. As a result, the reliability of these electronic components has been significantly reduced.

The present invention proposes a new external insulation method that solves all of these problems, and has the feature that even small shapes can be insulated reliably and at low cost.

The present invention utilizes an electrophoresis method using a metal conductor of a laminated ceramic electronic component as one electrode.
This method involves applying inorganic powder onto a metal conductor. By this method, the inorganic powder is applied not only to the metal conductor part but also to the adjacent ceramic body part, and then by baking it, it becomes an electronic component. It was discovered that it can be used as external insulation for

According to the method of the present invention, it is possible to selectively and easily form a uniform insulating layer on the electrode portions exposed to the outside of laminated ceramic electronic components, and it is also possible to process small components in large quantities. It is also possible to reduce costs.

The present invention will be explained in detail below using examples.

Example 1 Manufactured by a commonly used method
Silver paste was applied using the dip method, which is commonly used for BaTiO ₃ multilayer ceramic chip capacitors with dimensions of 1 mm x 2 mm x 1 mm and a capacitance of 0.1 μF, and external electrodes were baked on both ends of the chip.

The external electrodes were made of 100% silver and baked at 900°C.

This chip capacitor is fixed using a device as shown in Fig. 1, placed in a tank 5 containing slurry 4 for electrophoresis, and a DC voltage 6 is applied to apply an insulating layer. I went. The composition of the slurry for electrophoresis was as shown below, and these components were sufficiently uniformly dispersed using a homogenizer to prepare the slurry for electrophoresis.

Ethyl alcohol 400ml Lead borosilicate glass powder 50g Polyvinyl butyral 4g Water 8ml Tank 5 containing slurry 4 was stirred uniformly using stirrer 7, and 50V DC was applied between sample 3 and counter electrode 2. The voltage was applied for 5 minutes.

As a result, a uniform glass powder layer with a thickness of about 300 μm was formed on the surface of the electrode.

This multilayer capacitor was heat treated at 800℃ for 10 minutes,
Baked the insulation layer.

Lead wires were soldered to the electrodes, and capacitance, dielectric loss, and insulation resistance were measured.

As a result, no change was observed in the electrical properties compared to those before forming the insulating layer.

Next, this sample was subjected to a test in which a DC voltage of 50 V was applied in a constant temperature bath at 85° C. and a relative humidity of 90 to 95%.

As a result, the samples without an insulating layer and the samples covered with organic resin reached the shute state within 300 hours, but the samples insulated according to the manufacturing method of the present invention remained in a shudder state even after 500 hours. No change was observed in the electrical properties.

Example 2 A conductive circuit was formed on an alumina substrate by a thick film method using silver-palladium paste according to a commonly used method.

This conductor circuit was immersed in a slurry for electrophoresis, and a DC voltage was applied so that the cathode and counter electrode became the anode.

The composition of the slurry and the voltage application conditions were the same as in Example 1.

As a result, only on and near the surface conductor layer
A 300 μm inorganic powder layer was formed. This board
The insulating layer was baked by heat treatment at 830°C for 10 minutes.

The insulating layer formed by this method was uniform and free of pinholes.

Example 3 External electrodes were baked at 800° C. on a PZT-based laminated ceramic piezoelectric element obtained by laminating green sheets and sintering them.

In order to form an insulating layer by electrophoresis in the same manner as described in Example 1, the sample was placed in a slurry bath and a DC voltage was applied.

The following slurry composition was used for electrophoresis.

Isopropia alcohol 400ml Lead borosilicate crystallized glass 50g Iodine 3g A direct current of 150V was applied for 3 minutes between the sample and the counter electrode.

As a result, a glass powder layer with a thickness of 200 μm was formed on the external electrode.

This sample was heat-treated at 800℃ for 10 minutes,
Baked the insulation layer.

After the laminated ceramic piezoelectric element with the insulating layer formed in this manner was polarized, an AC voltage of 300V was applied to it and it was vibrated, and it showed good vibration characteristics.

Furthermore, this sample was vibrated by applying a voltage at a humidity of 90 to 95% and a temperature of 40°C, but no abnormality occurred even after continuous operation for 500 hours.

As shown in the examples above, according to the present invention,
The insulating layer can be selectively and uniformly formed near the external electrode exposed part of a laminated ceramic electronic component, and the insulating layer can be formed across both the ceramic part and the electrode part, and moreover, by baking. ,
It becomes a dense glass or ceramic layer, making it possible to form chip-shaped laminated ceramic electronic components with excellent moisture resistance and insulation resistance.

Furthermore, since the electrophoresis method allows large quantities to be processed, mass production is possible and manufacturing costs can be reduced.

In the embodiments of the present invention, a multilayer ceramic capacitor, a multilayer ceramic substrate, and a piezoelectric element are shown.
It is clear that the method of the present invention can be applied to all other laminated ceramic electronic components such as laminated varistors, laminated inductors, and laminated sensors.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the electrophoresis method of the present invention. The numbers in the diagram are 1: anode, 2: cathode, 3: chip sample,
4; Slurry, 5; Constant temperature bath, 6; DC power supply, 7;
A stirrer is shown.

Claims (1)

[Claims] 1. Part or all of one or more terminal electrodes or wiring exposed to the outside of a ceramic electronic component is used as one electrode, and a separately prepared electrode plate is used as a counter electrode in a suspension in which inorganic powder is dispersed. A method for insulating ceramic electronic parts, comprising the steps of applying the inorganic powder to the exposed terminal electrode or the exposed wiring by electrophoresis by applying a DC voltage between both electrodes, and then baking it.