A method for preparing BME MLCCs with bleeder resistors at high temperature

Abstract

A method for fabricating a BME MLCC with a bleed resistor at high temperature is disclosed. The BME MLCC includes a ceramic core, two end electrodes disposed opposite each other on both sides of the ceramic core, a resistive layer disposed on the surface of the ceramic core between the two end electrodes, and two overlapping electrodes respectively connected between the end of the resistive layer and the opposite end electrodes. This application, by defining the structure of the BME ceramic capacitor and using a step-by-step sintering process, sets overlapping electrodes between the copper end electrodes and the resistive layer. While achieving a conductive connection between the copper end electrodes and the resistive layer, it avoids the risk of a sintering reaction between the copper end electrodes and the ruthenium oxide-based resistive layer at high temperature, so that the fabricated BME MLCC meets the required design requirements.

Description

Technical Field

[0001] This invention belongs to the field of BME MLCC fabrication, specifically relating to a method for fabricating BME MLCCs containing bleeder resistors at high temperatures. Background Technology

[0002] High-voltage multilayer ceramic capacitors consist of three parts: internal electrodes, external electrodes, and ceramic material. In electronic circuits, especially high-power circuits, the voltage at the output of a high-voltage capacitor can rise to its peak value due to no-load conditions after power is applied, easily causing the capacitor to break down. A charged capacitor can also pose an electric shock risk. Therefore, a bleeder resistor needs to be connected in parallel with the capacitor to protect the circuit from voltage surges and overvoltages. This resistor quickly releases the energy stored in the capacitor when the power is off or a circuit malfunctions, preventing sudden voltage spikes that could damage other sensitive components. However, this additional resistor will occupy space on the PCB (printed circuit board).

[0003] To address the aforementioned issues, Chinese patent CN105070504B discloses a resistor-capacitor hybrid device. This device utilizes a third and fourth electrode disposed on a dielectric substrate, with a resistive layer positioned between them, forming a surface-mount resistor structure. This patent achieves both resistance and capacitance on a single surface-mount device, reducing PCB layout space and shortening PCB traces. This structure is suitable for manufacturing PME MLCCs (Precious Metal Electrode Multi-Layer Ceramic Capacitors, typically using precious metals such as silver, palladium, or platinum as electrode materials), as precious metal systems can be sintered with ceramics in air. However, precious metals are expensive and their prices fluctuate greatly, resulting in extremely high and volatile manufacturing costs. However, its application to BME MLCCs (Base Metal Electrode Multi-Layer Ceramic Capacitors) is less problematic. Ceramic capacitors (MLCCs) refer to multilayer ceramic capacitors that use base metals, typically nickel and copper, as electrode materials. During their fabrication, nickel and copper readily react with resistors made from ruthenium-based resistive pastes during high-temperature sintering (nickel and copper have higher metal activity than ruthenium and readily undergo redox reactions with ruthenium oxide at high temperatures). This degrades the resistive performance of the prepared BME capacitors, failing to meet design requirements. Lowering the sintering temperature affects the formation of the terminal electrodes; maintaining the sintering temperature makes it impossible to obtain the desired performance of BME MLCCs, significantly limiting their application and requiring further improvement. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing BMEMLCC containing a bleeder resistor at high temperature.

[0005] The present invention adopts the following technical solution:

[0006] A method for preparing a BME MLCC with a bleed resistor at high temperature, wherein the BME MLCC includes a ceramic core, two end electrodes disposed opposite to each other on both sides of the ceramic core, a resistive layer disposed on the surface of the ceramic core between the two end electrodes, and two overlapping electrodes respectively connected between the end of the resistive layer and the opposite end electrode.

[0007] Its preparation method includes the following steps:

[0008] Step 1: Sequentially sintering overlapping electrodes and a resistance layer onto the surface of the fired ceramic core, or sequentially sintering a resistance layer and overlapping electrodes. When sintering overlapping electrodes, overlapping electrode paste is printed on the surface of the fired ceramic core, and then sintered at 600-900℃ for 5-45 minutes to form overlapping electrodes on the surface of the ceramic core. When sintering the resistance layer, resistance paste is printed on the surface of the fired ceramic core, which is then placed in a kiln and sintered at 600-900℃ for 5-45 minutes to form a resistance layer between the two overlapping electrodes.

[0009] Step 2: Apply copper paste to both ends of the ceramic core, and then sinter at 600-900℃ for 5-45 minutes to form end electrodes, thereby obtaining the BME MLCC with bleed resistor.

[0010] Furthermore, the BME MLCC also includes a protective layer covering the surface of the resistive layer and two electroplated layers respectively covering the outer surfaces of the two end electrodes. The two ends of the protective layer are respectively disposed on the surfaces of the two overlapping electrodes, and the upper end of the electroplated layer is disposed on the surface of the overlapping electrodes adjacent to the end of the protective layer.

[0011] Furthermore, the process includes step three, coating a protective layer onto the surface of the sintered ceramic core with end electrodes to cover the formed resistive layer, and then curing it at 150-300°C to form a protective layer on the surface of the ceramic core, thereby obtaining the BME MLCC containing the discharge resistor.

[0012] Furthermore, step one also includes: coating a protective layer on the surface of the ceramic core with the sintered resistance layer to cover the formed resistance layer, and then sintering it at a temperature of 600-900℃ for 5-45 minutes to form the protective layer.

[0013] Furthermore, the thickness of the protective layer is 1-100 μm.

[0014] Furthermore, the electrode paste used for bonding is one or more of conductive silver paste, conductive silver-palladium paste, and conductive silver-platinum paste.

[0015] Furthermore, the resistive paste is a ruthenium oxide-based resistive paste.

[0016] As can be seen from the above description of the present invention, compared with the prior art, the beneficial effects of the present invention are: by defining the structure of the BME ceramic capacitor and using a step-by-step sintering process, the present application sets an overlap electrode between the terminal electrode copper and the resistive layer, thereby avoiding the risk of sintering reaction between the terminal electrode copper and the ruthenium oxide resistive layer at high temperature while achieving a conductive connection between the terminal electrode copper and the resistive layer, so that the prepared BME MLCC meets the required design requirements. Attached Figure Description

[0017] Figure 1 This is a structural cross-sectional view of the first embodiment of BME MLCC;

[0018] Figure 2 This is a structural cross-sectional view of the second embodiment of BME MLCC;

[0019] Figure 3 This is a schematic diagram of the product in Example 1;

[0020] Figure 4 This is a schematic diagram of the product in Example 2;

[0021] Figure 5 This is a schematic diagram of the product in Example 3;

[0022] In the figure, 1-ceramic core, 2-end electrode, 3-resistive layer, 4-overlapping electrode, 5-protective layer, 6-electroplating layer. Detailed Implementation

[0023] The present invention will be further described below through specific embodiments.

[0024] A BME MLCC with a discharge resistor includes a ceramic core 1, two electrodes 2 disposed opposite to each other on both sides of the ceramic core 1, a resistive layer 3 disposed on the surface of the ceramic core 1 between the two electrodes 2, two overlapping electrodes 4 respectively connected between the end of the resistive layer 3 and the opposite end electrode 2, a protective layer 5 covering the surface of the resistive layer 3, and two electroplated layers 6 respectively covering the outer surface of the two electrodes 2. Specifically, the two ends of the protective layer 5 are respectively disposed on the surface of the two overlapping electrodes 4, and the upper end of the electroplated layer 6 is disposed on the surface of the overlapping electrodes 4 adjacent to the end of the protective layer 5. Further, the thickness of the protective layer 5 is 1-100 μm. During preparation, a suitable polymer slurry can be selected as the protective layer 5 according to the application requirements. The specific selection will not be further elaborated here.

[0025] Among them, the lap electrode 4 is sintered from the lap electrode paste, and the lap electrode paste is one or more of conductive silver paste, conductive silver palladium paste, and conductive silver platinum paste; the lap electrode paste selected for the preparation of BME MLCC in this application is a sintered conductive silver paste. This sintered conductive silver paste uses low melting point glass powder as a binder phase and can generally be sintered into a film at temperatures above 500°C. The sintering process of silver paste begins with the softening of glass powder at high temperature to form molten glass. This molten glass then impregnates the silver powder and the terminal electrodes and discharge resistors on both sides. On one hand, this causes the silver powder particles to rearrange and coalesce, forming a conductive network upon cooling and shrinkage. On the other hand, as the molten glass impregnates the ceramic capacitor substrate, some silver powder is dispersed onto the terminal electrodes and discharge resistors, creating a connection between them. However, the sintering temperature of the conductive silver paste affects its adhesion. Excessively high sintering temperatures or excessively long holding times can lead to uneven distribution of the glass phase, causing the molten glass to accumulate on the silver film surface, forming a glassy layer that affects adhesion and increases the resistance of the discharge resistor. After numerous trials, the sintering temperature was determined to be 600℃-900℃. At this temperature, the lower the viscosity of the molten glass in the silver paste, the better its fluidity, resulting in better impregnation of the silver powder and substrate and better rearrangement of the silver powder, leading to stable resistance.

[0026] Resistive layer 3 is formed by sintering a resistive paste, specifically a ruthenium oxide-based resistive paste, which features a wide resistance range, good resistance stability, and excellent repeatability. BME high-voltage multilayer ceramic capacitors operate at high voltages, typically >1000V, requiring the integrated resistors to withstand high voltage and high power loads. According to the film resistance formula, obtaining a high-resistance resistive film requires the largest possible sheet resistance (SDR). Given the limited surface area of ​​the ceramic capacitor substrate, a feasible and effective method is to use a resistive material with high SDR, such as a ruthenium oxide-based resistive material. Therefore, ruthenium oxide-based resistive pastes are currently widely chosen as the resistive paste.

[0027] There are four main methods for preparing BME MLCCs in this application, as detailed below:

[0028] First method

[0029] Reference Figure 1 A method for preparing BME MLCCs containing bleeder resistors at high temperature includes the following steps:

[0030] Step 1: Print the lap electrode paste on the surface of the fired ceramic core, and then sinter it at 600-900℃ for 5-45 minutes to form the lap electrode on the surface of the ceramic core.

[0031] Step 2: Print resistance paste between the two overlapping electrodes, and send it into a kiln to sinter at a temperature of 600-900℃ for 5-45 minutes to form a resistance layer between the two overlapping electrodes.

[0032] Step 3: Apply copper paste to both ends of the ceramic core, and then sinter it at 600-900℃ in a nitrogen atmosphere for 5-45 minutes to form end electrodes.

[0033] Step 4: A protective layer is coated on the surface of the sintered ceramic core with end electrodes to cover the formed resistive layer. Then, it is cured at 150-300℃ for 30-120 minutes to form a protective layer on the surface of the ceramic core. Then, an electroplating layer is formed on the outer periphery of the formed end electrodes to obtain the BME MLCC containing the discharge resistor.

[0034] Second method

[0035] Reference Figure 2 A method for preparing BME MLCCs containing bleeder resistors at high temperature includes the following steps:

[0036] Step 1: Print the resistive paste on the surface of the fired ceramic core, and send it into the kiln to sinter at a temperature of 600-900℃ for 5-45 minutes to form a resistive layer on the surface of the ceramic core.

[0037] Step 2: Print the lap electrode paste on the surface of the ceramic core with the sintered resistance layer, and then sinter it at 600-900℃ for 5-45 minutes to form the lap electrode on the surface of the ceramic core.

[0038] Step 3: Apply copper paste to both ends of the ceramic core, and then sinter it at 600-900℃ in a nitrogen atmosphere for 5-45 minutes to form end electrodes.

[0039] Step 4: A protective layer is coated on the surface of the sintered ceramic core with end electrodes to cover the formed resistive layer. Then, it is cured at 150-300℃ for 30-120 minutes to form a protective layer on the surface of the ceramic core. Then, an electroplating layer is formed on the outer periphery of the formed end electrodes to obtain the BME MLCC containing the discharge resistor.

[0040] Third method

[0041] Reference Figure 1 A method for preparing BME MLCCs containing bleeder resistors at high temperature includes the following steps:

[0042] Step 1: Print the lap electrode paste on the surface of the fired ceramic core, and then sinter it at 600-900℃ for 5-45 minutes to form the lap electrode on the surface of the ceramic core.

[0043] Step 2: Print resistance paste between the two overlapping electrodes, and send it into a kiln to sinter at a temperature of 600-900℃ for 5-45 minutes to form a resistance layer between the two overlapping electrodes.

[0044] Step 3: Coat the surface of the ceramic core with the sintered resistance layer with a protective layer to cover the formed resistance layer, and then sinter at 600-900℃ for 5-45 minutes to form a protective layer on the surface of the ceramic core.

[0045] Step 4: Apply copper paste to both ends of the ceramic core, and then sinter it at 600-900℃ in a nitrogen atmosphere for 5-45 minutes to form end electrodes; then electroplate an electroplating layer on the outer periphery of the formed end electrodes to obtain the BME MLCC containing the bleeder resistor.

[0046] Fourth method

[0047] Reference Figure 2 A method for preparing BME MLCCs containing bleeder resistors at high temperature includes the following steps:

[0048] Step 1: Print the resistive paste on the surface of the fired ceramic core, and send it into the kiln to sinter at a temperature of 600-900℃ for 5-45 minutes to form a resistive layer on the surface of the ceramic core.

[0049] Step 2: Print the lap electrode paste on the surface of the fired ceramic core, and then sinter it at 600-900℃ for 5-45 minutes to form lap electrodes on the surface of the ceramic core.

[0050] Step 3: Coat the surface of the ceramic core with the sintered resistance layer with a protective layer to cover the formed resistance layer, and then sinter at 600-900℃ for 5-45 minutes to form a protective layer on the surface of the ceramic core.

[0051] Step 4: Apply copper paste to both ends of the ceramic core, and then sinter it at 600-900℃ in a nitrogen atmosphere for 5-45 minutes to form end electrodes; then electroplate an electroplating layer on the outer periphery of the formed end electrodes to obtain the BME MLCC containing the bleeder resistor.

[0052] Process testing

[0053] The specific design requirements for the BME MLCC prepared in this application are as follows: capacitance of (200±20)nF, and loss tangent DF < 15×10⁻⁶. -4 The discharge resistor is (500±100)MΩ.

[0054] Example 1

[0055] A method for preparing BME MLCCs with bleed resistors at high temperature includes the following steps:

[0056] Step 1: Print the lap electrode paste on the surface of the fired ceramic core, and then sinter it at 600℃ for 45 minutes to form the lap electrode on the surface of the ceramic core.

[0057] Step 2: Print the resistive paste between the two overlapping electrodes, and send it into the kiln to sinter at 600°C for 45 minutes to form a resistive layer between the two overlapping electrodes.

[0058] Step 3: Apply copper paste to both ends of the ceramic core, and then sinter at 600°C under a nitrogen atmosphere for 45 minutes to form end electrodes.

[0059] Step 4: A protective layer is coated on the surface of the sintered ceramic core with end electrodes to cover the formed resistive layer. Then, it is cured at 220°C for 75 minutes to form a protective layer on the surface of the ceramic core. Then, an electroplating layer is formed on the outer periphery of the formed end electrodes to obtain the BME MLCC containing the discharge resistor.

[0060] Example 2

[0061] A method for preparing BME MLCCs with bleed resistors at high temperature includes the following steps:

[0062] Step 1: Print the lap electrode paste on the surface of the fired ceramic core, and then sinter it at 750°C for 10 minutes to form the lap electrode on the surface of the ceramic core.

[0063] Step 2: Print the resistive paste between the two overlapping electrodes, and send it into the kiln to sinter at 850°C for 15 minutes to form a resistive layer between the two overlapping electrodes.

[0064] Step 3: A protective layer is coated onto the surface of the sintered ceramic core with end electrodes to cover the formed resistive layer, and then sintered at 750℃ for 10 minutes to form a protective layer on the surface of the ceramic core.

[0065] Step 4: Copper paste is applied to both ends of the ceramic core, and then sintered at 850°C in a nitrogen atmosphere for 15 minutes to form end electrodes; then an electroplating layer is formed on the outer periphery of the formed end electrodes to obtain the BMEMLCC containing the bleeder resistor.

[0066] Example 3

[0067] A method for preparing BME MLCCs with bleed resistors at high temperature includes the following steps:

[0068] Step 1: Print the lap electrode paste on the surface of the fired ceramic core, and then sinter it at 900℃ for 5 minutes to form the lap electrode on the surface of the ceramic core.

[0069] Step 2: Print the resistive paste between the two overlapping electrodes, and send it into the kiln to sinter at 900℃ for 5 minutes to form a resistive layer between the two overlapping electrodes.

[0070] Step 3: Apply copper paste to both ends of the ceramic core, and then sinter at 900°C under a nitrogen atmosphere for 5 minutes to form end electrodes.

[0071] Step 4: A protective layer is coated on the surface of the sintered ceramic core with end electrodes to cover the formed resistive layer, and then cured at 220°C for 75 minutes to form a protective layer on the surface of the ceramic core. Then, an electroplating layer is formed on the outer periphery of the formed end electrodes to obtain the BME MLCC containing the discharge resistor.

[0072] Example 4

[0073] A method for preparing BME MLCCs with bleed resistors at high temperature includes the following steps:

[0074] Step 1: Print the resistive paste on the surface of the fired ceramic core, and send it into the kiln to sinter at 850°C for 15 minutes to form a resistive layer on the surface of the ceramic core.

[0075] Step 2: Print the lap electrode paste on the surface of the ceramic core with the sintered resistance layer, and then sinter it at 750°C for 10 minutes to form the lap electrode on the surface of the ceramic core.

[0076] Step 3: A protective layer is coated onto the surface of the sintered ceramic core with end electrodes to cover the formed resistive layer, and then sintered at 750℃ for 10 minutes to form a protective layer on the surface of the ceramic core.

[0077] Step 4: Copper paste is applied to both ends of the ceramic core, and then sintered at 850°C in a nitrogen atmosphere for 15 minutes to form end electrodes; then an electroplating layer is formed on the outer periphery of the formed end electrodes to obtain the BMEMLCC containing the bleeder resistor.

[0078] Comparative Example 1

[0079] Its BME MLCC structure is basically the same as that of Example 1, except that: no lap electrode is set, the resistive layer is directly connected to the end electrode, and correspondingly, step one is not set in the preparation method.

[0080] Comparative Example 2

[0081] Its BME MLCC structure is basically the same as that of Example 2, except that: no lap electrode is set, the resistive layer is directly connected to the end electrode, and correspondingly, step one is not set in the preparation method.

[0082] Comparative Example 3

[0083] Its BME MLCC structure is basically the same as that of Example 3, except that: no lap electrode is set, the resistive layer is directly connected to the end electrode, and correspondingly, step one is not set in the preparation method.

[0084] Comparative Example 4

[0085] Commercially available BME MLCCs do not have a resistive layer.

[0086] Comparative Example 5

[0087] Its BME MLCC structure is basically the same as that of Example 2, except that the overlapping electrode paste uses a copper-nickel resistive paste.

[0088] Comparative Example 6

[0089] Its BME MLCC structure is basically the same as that of Example 2, except that the lap electrode paste uses lanthanum boron resistive paste.

[0090] Comparative Example 7

[0091] Its BME MLCC structure is basically the same as that of Example 2, except that the overlapping electrode paste uses palladium-silver resistive paste.

[0092] The BME MLCCs obtained in Examples 1-4 and Comparative Examples 1-7 were tested, and the following data were obtained:

[0093]

[0094] The technical solution defined in this application, as shown in the table above, can achieve the required design requirements. Specifically, by defining the structure of the BME ceramic capacitor and using a step-by-step sintering process, an overlap electrode is set between the terminal copper electrode and the resistive layer. This achieves a conductive connection between the terminal copper electrode and the resistive layer while avoiding the risk of a sintering reaction between the terminal copper electrode and the ruthenium oxide resistive layer at high temperatures.

[0095] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing BME MLCCs containing bleeder resistors at high temperature, characterized in that: The BME MLCC includes a ceramic core, two electrodes disposed opposite to each other on both sides of the ceramic core, a resistive layer disposed on the surface of the ceramic core between the two electrodes, two overlapping electrodes respectively connected between the end of the resistive layer and the opposite end electrode, a protective layer covering the surface of the resistive layer, and two electroplated layers respectively covering the outer surfaces of the two electrodes; the two ends of the protective layer are respectively disposed on the surface of the two overlapping electrodes, and the upper end of the electroplated layer is disposed on the surface of the overlapping electrodes adjacent to the end of the protective layer; Its preparation method includes the following steps: Step 1: Print the resistive paste on the surface of the fired ceramic core, and send it into the kiln to sinter at a temperature of 600-900℃ for 5-45 minutes to form a resistive layer on the surface of the ceramic core. Step 2: Print the lap electrode paste on the surface of the ceramic core with the sintered resistance layer, and then sinter it at 600-900℃ for 5-45 minutes to form the lap electrode on the surface of the ceramic core. Step 3: Apply copper paste to both ends of the ceramic core, and then sinter it at 600-900℃ in a nitrogen atmosphere for 5-45 minutes to form end electrodes. Step 4: A protective layer is coated on the surface of the sintered ceramic core with end electrodes to cover the formed resistive layer. Then, it is cured at 150-300℃ for 30-120 minutes to form a protective layer on the surface of the ceramic core. Then, an electroplating layer is formed on the outer periphery of the formed end electrodes to obtain the BME MLCC containing the discharge resistor. The resistive paste is a ruthenium oxide-based resistive paste; the overlapping electrode paste is one or more of conductive silver paste, conductive silver-palladium paste, and conductive silver-platinum paste.

2. The method for preparing BME MLCCs with bleeder resistors at high temperature according to claim 1, characterized in that: The thickness of the protective layer is 1-100 μm.

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