JPH08288174A - Multilayer ceramic capacitor for high frequency power - Google Patents

Abstract

PURPOSE: To provide a multilayer ceramic capacitor for high frequency power which is small in a deterioration for a repetitive thermal stress and high in reliability. CONSTITUTION: A plurality of ceramic capacitors 12 are arranged in parallel between two electrode plates 11 and 11 and respective external electrodes 13, 13 of this capacitor 12 are fixed to the corresponding electrode plates 11, 11 using conductive adhesives 14, 14 under conditions that they are electrically connected. As the conductive adhesives 14, 14 of a thickness 500μm or less are used, a deterioration for a repetitive thermal stress is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency power monolithic ceramic capacitor having a large power capacity, a large electrostatic capacity and a large current capacity.

[0002]

2. Description of the Related Art At present, an induction heating apparatus used for quenching and welding metal is changing from a vacuum tube system to a semiconductor element system. In the semiconductor element system, a withstand voltage of about 1 kV is applied to a resonance circuit capacitor. A large power capacity, a large electrostatic capacity, and a large current capacity are required.

As the resonance circuit capacitor, a film capacitor, a mica capacitor, a module obtained by blocking a laminated ceramic capacitor, or the like is used.

FIG. 3 shows a module in which a conventional monolithic ceramic capacitor is formed into a block, and two electrode plates 1,
A plurality of monolithic ceramic capacitors 2 are arranged in parallel between the two, and the external electrodes of the capacitors 2 are fixed to the corresponding electrode plates 1, 1 by soldering 3, 3 in an electrically connected state. It has a structure in which the outside of the group of capacitors 2 is covered with an exterior resin 4.

[0005]

By the way, since a large amount of electric power is applied to the monolithic ceramic capacitor, a large amount of heat is generated and the module is used in a water-cooled state. Actually, even with water cooling, the temperature is higher than the ambient temperature by about 20 to 30 ° C,
Moreover, since it generates heat only during operation, it is repeatedly exposed to high and low temperatures.

In the conventional monolithic ceramic capacitor module for resonance circuit, the monolithic capacitor is fixedly held on the metal electrode plate by soldering. Thermal stress is applied, so repeated stress is applied to the soldered part, cracks are likely to occur due to heat shock, conductive failure occurs, and eventually it breaks and the electrode plate and the laminated ceramic capacitor come off. There's a problem.

Therefore, an object of the present invention is to provide a highly reliable high frequency power multilayer ceramic capacitor which is less likely to be deteriorated even if thermal stress is repeatedly applied to a fixed portion of the multilayer ceramic capacitor and the electrode plate. .

[0008]

In order to solve the above-mentioned problems, the present invention arranges a plurality of laminated ceramic capacitors in parallel between two electrode plates, and makes the external electrodes of the capacitors correspond to each other. In order to fix it in a state of being electrically connected to the electrode plate to be used, a structure using a conductive adhesive having a thickness of 500 μm or less is adopted.

In the present invention, the conductive adhesive is a mixture of any one of epoxy resin, phenol resin, polyimide resin and the like, and at least one of silver, copper and aluminum particles. Any thing can be used.

[0010]

[Operation] For fixing the electrode plate and the monolithic ceramic capacitor,
By using a conductive adhesive, the initial tensile stress is slightly lower than that of soldering, but there is little deterioration even when repeated thermal stress is applied, and the silver erosion phenomenon due to solder disappears,
By improving the reliability of connection, by using metal particles with high conductivity contained in the conductive adhesive,
Compared with solder, it has the same conductivity.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. 1 and 2 of the accompanying drawings.

As shown in the figure, the monolithic ceramic capacitor for high frequency power of the present invention has a plurality of monolithic ceramic capacitors 12 arranged in parallel between two electrode plates 11 and 11 and external electrodes 13 of each of the capacitors 12. , 13
To the corresponding electrode plates 11, 11 with conductive adhesives 14, 14
Fixed in an electrically connected state using a capacitor 1
The outside of the second group is covered with the exterior resin 15.

The conductive adhesive 14 is any one of epoxy resin, phenol resin, polyimide resin and the like, and at least one of silver, copper and aluminum particles as a conductive filler. Is a thermosetting adhesive that is mixed and used so that its thickness is 500 μm or less.

As the resin contained in this conductive adhesive,
Epoxy resins and phenol resins can be used continuously at 100 ° C., and when polyimide resins are used, the effect is even higher.

Further, by using the metal particles having high conductivity exemplified as the above-mentioned conductive filler, the conductivity of the adhesive is increased and the loss becomes high at high frequency, and the conductivity is equivalent to that of the solder. Becomes

The thickness of the conductive adhesive layer 14 is 500.
If it is thicker than μm, cracks will grow from the inside of the adhesive layer at the time of breakage and the adhesive strength will decrease. Further, the thermal conductivity is also lowered, the heat dissipation of the capacitor is hindered, and the temperature rise of the capacitor becomes remarkable.

Example 1 Next, the results of comparing the heat generation temperature and the tensile strength of a capacitor module prepared by soldering with a capacitor module having a different thickness using a conductive adhesive will be described. The manufacturing method is as follows.

Capacitance of 6.8 per module
A capacitor module having an electrostatic capacity of 200 nF was manufactured by using 30 nF multilayer ceramic capacitors.

The size of the monolithic ceramic capacitor is 5.7 mm in length × 5.0 mm in width × 2.0 mm in thickness,
The distance between the external electrodes of the monolithic ceramic capacitor is 5.7 m.
m.

In the assembling step, first, as shown in FIG. 2, the monolithic ceramic capacitors were placed in close contact with each other, adhered with a silicone resin adhesive, and dried at room temperature to produce an integrated block.

In order to bond the monolithic ceramic capacitors to each other, in addition to the silicone resin adhesive, an epoxy resin adhesive,
Any insulative adhesive such as an inorganic adhesive can be used.

Next, as shown in FIG. 1, two electrode plates made of a copper plate having a width of 30 mm, a length of 70 mm and a thickness of 1 mm are sandwiched between the blocks by a conductive adhesive composed of silver particles and an epoxy resin. Were adhered in a corresponding manner, and were held at 150 ° C. for 1 hour to cure the conductive adhesive. Finally, the work was set in a mold, the exterior resin made of epoxy resin was cast, and the exterior resin was cured by holding it at 150 ° C. for 2 hours to complete the capacitor module.

In addition to copper, any of high frequency low resistance conductors such as silver, aluminum, copper alloys and aluminum alloys can be used for the electrode plate.

As the exterior resin, in addition to epoxy resin, any silicone resin, urethane resin, phenol resin, etc. having insulation properties, excellent adhesion, and heat resistance up to 100 ° C. can be used. It is possible.

Table 1 shows the results of the comparison between solder and a conductive adhesive and the heat generation and tensile strength of the sample due to the difference in the thickness of the adhesive layer in the module using the copper plate as the electrode plate. Load is frequency 300kHz, apparent power 25kVA
The sample is water-cooled. The heat generation temperature in Table 1 is the difference between the surface temperature of the built-in multilayer capacitor and the ambient temperature.

With respect to the exothermic temperature, when the thickness of the adhesive layer was 500 μm or less, the exothermic temperature was the same when the conductive adhesive and the solder were used, and there was no difference in heat dissipation.

When the adhesive layer thickness is 500 μm or less, the tensile strength is higher when the conductive adhesive and the solder are used, but the conductive adhesive is sufficiently effective. .

When an adhesive is used and the thickness of the adhesive layer exceeds 500 μm, the tensile strength is lowered and the exothermic temperature is increased, which is not suitable for use.

[0029]

[Table 1]

Next, the results of the heat cycle test are shown in Table 2. The test conditions are a temperature range of −30 ° C. to 85 ° C. and 3 hours per cycle. The tensile strength was measured when the opposing electrode plates were pulled in the opposite direction.

Although the initial tensile strength of solder is higher,
It decreases in a small number of cycles, and in the long term, the conductive adhesive has higher strength.

[0032]

[Table 2]

Example 2 Epoxy resin, phenol resin, polyimide resin as a resin for the conductive adhesive and silver, copper, as a conductive filler,
Each combination is made using aluminum,
A capacitor module was produced in the same manner as in Example 1 using copper for the electrode plate.

The results of the exothermic test and the heat cycle test of the sample are shown in Table 3 together.

The load of the heat generation test was a frequency of 300 kHz and an apparent power of 25 kVA, and the sample was water-cooled. The heat generation temperature is the difference between the surface temperature of the built-in multilayer capacitor and the ambient temperature.

The heat cycle test condition is temperature range -30.
C-85 C, 3 hours per cycle. The tensile strength was measured when the opposing electrode plates were pulled in the opposite direction.

The heat generated by any conductive adhesive is 20d.
It was less than eg and was suitable for use. Also, the tensile strength after 5000 heat cycles was higher than that of solder and effective.

[0038]

[Table 3]

[0039]

As described above, according to the present invention, a conductive adhesive is used instead of solder for fixing the electrode plate and the external electrode of the monolithic ceramic capacitor. A monolithic ceramic capacitor for electric power can be provided.

Further, by using a conductive adhesive instead of solder, the phenomenon of silver erosion of the external electrode due to solder, which was a problem when soldering the external electrode of the monolithic ceramic capacitor, is eliminated, and the connection is prevented. Reliability is also improved.

Furthermore, post-cleaning as in the case of soldering is not necessary, and adverse effects on the environment such as the use of no lead element are reduced.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view of a high frequency power multilayer ceramic capacitor module according to the present invention.

FIG. 2 is an explanatory view showing an assembling process of the same.

FIG. 3 is a partially cutaway front view showing a conventional high frequency power multilayer ceramic capacitor module.

[Explanation of symbols]

 11 Electrode Plate 12 Multilayer Ceramic Capacitor 13 External Electrode 14 Conductive Adhesive 15 Exterior Resin

Claims (2)

[Claims] 1. A plurality of monolithic ceramic capacitors are arranged in parallel between two electrode plates, and each external electrode of the capacitors is fixed in a state of being electrically connected to a corresponding electrode plate. A multilayer ceramic capacitor for high-frequency power, characterized by using a conductive adhesive having a thickness of 500 μm or less. 2. The conductive adhesive is any one of an epoxy resin, a phenol resin, and a polyimide resin,
The monolithic ceramic capacitor for high frequency power according to claim 1, which is a mixture of at least one of particles of silver, copper and aluminum.