Preparation method of miniaturized encapsulated PTC (Positive Temperature Coefficient) thermosensitive resistor for temperature compensation

Abstract

The invention discloses a preparation method of a miniaturized encapsulated PTC (Positive Temperature Coefficient) thermistor for temperature compensation, and belongs to the technical field of production of PTC thermistors. Comprising the following steps: burdening: uniformly mixing barium titanyl oxalate, strontium titanyl oxalate, barium carbonate, tin dioxide, yttrium oxide, titanium dioxide and silicon dioxide, granulating, and pre-sintering to form a PTC ceramic powder raw material; manufacturing a ceramic green body; sintering to obtain a resistor blank; preparing a nickel electrode; preparing a silver electrode; scribing to obtain a resistor chip; welding a leading-out wire; and packaging to form a double-layer packaging structure, so as to obtain the miniaturized packaging type PTC thermosensitive resistor for temperature compensation. The miniaturized encapsulated PTC thermistor for temperature compensation, which is prepared by the preparation method disclosed by the invention, has a relatively wide resistance value range, a relatively wide working temperature range, a relatively wide temperature coefficient range, relatively high resistance value precision and a relatively small volume, and the application requirements of the encapsulated PTC thermistor for temperature compensation are better met.

Description

Technical Field

[0001] This invention belongs to the field of PTC thermistor manufacturing technology, specifically relating to a method for preparing a miniaturized encapsulated temperature compensation PTC thermistor. Background Technology

[0002] Thermistors, due to their resistance changing with temperature, can be used to compensate for temperature drift in electronic circuits, resulting in more stable circuit operation. As electronic circuits continue to miniaturize, the requirements for miniaturization of temperature compensation components are also increasing.

[0003] Traditional temperature compensation thermistors include PTC thermistors (positive temperature coefficient thermistors) and NTC thermistors (negative temperature coefficient thermistors). However, due to the differences in the temperature change characteristics of semiconductor ceramic resistors, slowly changing PTC thermistors are more suitable for temperature compensation over a wider temperature range than abruptly changing PTC and NTC thermistors.

[0004] Traditional temperature-compensating PTC thermistors come in two types: encapsulated (also known as solder-encapsulated) and surface-mount (SMD) PTC thermistors. While SMD PTC thermistors are relatively small, they have no leads and are only suitable for surface mounting, not through-hole mounting. Figure 1 As shown, the traditional encapsulated temperature compensation PTC thermistor 1 has two leads 2, which are suitable for insertion. However, in order to meet the basic requirements of resistivity, operating temperature, temperature coefficient and other parameters, its size is relatively large (its maximum head size is 7mm×5mm), which cannot meet the needs of miniaturization. At the same time, it also has the defects of narrow resistance range (100Ω~10kΩ), low resistance accuracy (maximum ±10%), narrow operating temperature range (-55℃~100℃) and narrow temperature coefficient range (1% / ℃~8% / ℃). Summary of the Invention

[0005] The purpose of this invention is to provide a method for manufacturing a miniaturized encapsulated temperature-compensated PTC thermistor that has a small size, a wide resistance range, a wide operating temperature range, a wide temperature coefficient range, and high resistance accuracy in order to solve the above-mentioned problems.

[0006] The present invention achieves the above objectives through the following technical solutions: A method for fabricating a miniaturized encapsulated temperature-compensated PTC thermistor includes the following steps: Step 1, Ingredients: Mix barium titanium oxalate, strontium titanium oxalate, barium carbonate, tin dioxide, yttrium oxide, titanium dioxide, and silicon dioxide evenly, then granulate and pre-fire to form PTC ceramic powder raw material; Step 2: Using mechanical pressing, the PTC ceramic powder raw material is pressed into round ceramic green bodies, with the weight of a single ceramic green body controlled between 0.1g and 0.15g. Step 3: Sinter the ceramic green body at a high temperature of 1300℃~1450℃ for 25 min~35 min, and after cooling, obtain a disc-shaped resistance blank. Step 4: Prepare a layer of nickel electrodes on the upper and lower surfaces of the resistor blank by chemical nickel plating to obtain a resistor with PTC characteristics; Step 5: Using screen printing, a layer of silver paste is printed on the outer surface of the nickel electrodes on the upper and lower surfaces of the resistor. After high-temperature firing at 450℃~550℃, a uniform silver electrode is formed on the surface of the nickel electrode, forming a dual-electrode structure together with the nickel electrode. Step 6: Using a dicing process, the resistor body is diced into multiple resistor chips with smaller electrode areas. The resistor chips with the target resistance value are screened in an oil bath at a temperature of 25℃±0.05℃. False resistor chips are eliminated by electric shock with a voltage of 15V. The resistor chips are then heat-treated at 250℃±5℃ for 48 h±2h to obtain stable and reliable resistor chips. Step 7: Using silver-containing high-temperature solder, the lead wires are connected to the resistor chip by brazing to form an effective electrical connection. Step 8: First, encapsulate the resistor chip after soldering the lead wires with silicone resin, and then encapsulate it with red epoxy resin to form a double-layer encapsulation structure. Then, heat-treat it at 150℃±5℃ for 100 h±4 h to obtain a miniaturized encapsulated temperature compensation PTC thermistor.

[0007] Preferably, to achieve better product performance, in step 1, the mass ratio of barium titanium oxalate, strontium titanium oxalate, barium carbonate, tin dioxide, yttrium oxide, titanium dioxide, and silicon dioxide is 60:31:11:11:0.3:2.5:3.7; in step 2, the PTC ceramic powder raw material is pressed into a ceramic green body with a diameter of 6.5±0.2mm and a thickness of 1.2±0.2mm using a mold with a diameter of 6.5mm; in step 3, the ceramic green body is sintered at a high temperature of 1370℃ for 30 minutes, and after furnace cooling, a resistance blank with a diameter of 5.5±0.5mm is obtained. In step 5, a layer of 5080 silver paste is printed on the outer surface of the nickel electrodes on the upper and lower surfaces of the resistor, and then burned into the surface of the nickel electrodes at a high temperature of 500°C. In step 6, the area of ​​the resistor chip is 1mm×1mm. The resistor chip is electrically charged with 15V to eliminate dummy resistor chips, and then heat-treated at 250°C for 48 hours to obtain a stable and reliable resistor chip. In step 8, after heat-treatment at 150°C for 100 hours, a miniaturized encapsulated temperature compensation PTC thermistor is obtained. The head size of the miniaturized encapsulated temperature compensation PTC thermistor is 3mm×3mm.

[0008] The beneficial effects of this invention are as follows: This invention utilizes barium titanium oxalate, strontium titanium oxalate, barium carbonate, tin dioxide, yttrium oxide, titanium dioxide, and silicon dioxide as raw materials. The maximum sintering temperature is set to 1300~1450℃, and furnace cooling is employed. This results in a finished product with a wide resistance range (200Ω~100kΩ), a wide operating temperature range (-55℃~125℃), a wide temperature coefficient range (1% / ℃~12% / ℃), and high resistance accuracy (maximum ±5%). Simultaneously, it achieves a smaller size (maximum head size 3mm×3.5mm), better meeting the application requirements of encapsulated temperature-compensated PTC thermistors for small size, wide range, and high precision. Furthermore, by setting double-layer electrodes, dicing, and heat treatment, [further details are needed to complete the translation]. The resulting resistor chip exhibits excellent microstructure uniformity and structural uniformity, resulting in higher reliability, precision, and better performance consistency across batches. By employing silver-containing high-temperature solder with a softening point above 280℃, the solder is prevented from remelting during high-temperature use. The silver content also reduces the risk of silver erosion during soldering, improving the strength and durability of the solder joints and reducing defects such as cold soldering or cracking. Simultaneously, the encapsulation material employs a two-layer structure. The inner layer is a relatively dense and transparent silicone resin, which acts as a barrier, forming a basic isolation between the PTC ceramic body and the external environment, enhancing the environmental adaptability of the ceramic body. The outer layer is a high-temperature resistant red epoxy encapsulation material, which enhances the product's mechanical strength and environmental adaptability, ensuring product reliability. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the main structure of a traditional encapsulated PTC thermistor for temperature compensation. Figure 2 This is a partial cross-sectional main view of the miniaturized encapsulated temperature compensation PTC thermistor described in this invention; Figure 3 This is the resistance-temperature curve of a miniaturized encapsulated temperature-compensated PTC thermistor obtained in an embodiment of the present invention. Detailed Implementation

[0010] The present invention will be further described below with reference to embodiments and accompanying drawings: Example

[0011] A miniaturized encapsulated temperature-compensated PTC thermistor is prepared using the following steps: Step 1, Ingredients: Mix barium titanium oxalate, strontium titanium oxalate, barium carbonate, tin dioxide, yttrium oxide, titanium dioxide, and silicon dioxide in a mass ratio of 60:31:11:11:0.3:2.5:3.7 until homogeneous, then granulate and pre-fire to form PTC ceramic powder raw material; Step 2: Using mechanical pressing, the PTC ceramic powder raw material is pressed into a ceramic green body with a diameter of 6.5 ± 0.2 mm and a thickness of 1.2 ± 0.2 mm using a mold with a diameter of 6.5 mm. The weight of a single ceramic green body is controlled between 0.1 g and 0.15 g. Step 3: Place the ceramic green body in a high temperature of 1300℃~1450℃ for sintering for 25 min~35 min, and cool it in the furnace to obtain a circular resistance blank with a diameter of 5.5±0.5mm; the preferred sintering temperature is 1370℃, and the preferred sintering time is 30 min. Step 4: Prepare a layer of nickel electrodes on the upper and lower surfaces of the resistor blank by chemical nickel plating to obtain a resistor with PTC characteristics; Step 5: Using screen printing, a layer of 5080 silver paste is printed on the outer surface of the nickel electrodes on the upper and lower surfaces of the resistor. After high-temperature burning at 450℃~550℃, a uniform silver electrode is formed on the surface of the nickel electrode, forming a double electrode structure together with the nickel electrode; the preferred high-temperature burning temperature is 500℃. Step 6: Using a precision dicing process, the resistor body is diced into multiple resistor chips with smaller electrode areas. The resistor chips with the target resistance value are screened in an oil bath at a temperature of 25℃±0.05℃. False resistor chips are eliminated by electric shock with a 15V voltage. The resistor chips are then heat-treated at 250℃±5℃ (preferably 250℃±5℃) for 48 h±2 h (preferably 48 h) to obtain stable and reliable resistor chips. Step 7: Using silver-containing high-temperature solder, the lead wires are connected to the resistor chip by brazing to form an effective electrical connection. Step 8: First, encapsulate the resistor chip after soldering the leads with silicone resin, then encapsulate it with red epoxy resin to form a double-layer encapsulation structure. Subsequently, heat-treat the chip at 150℃±5℃ (preferably 150℃) for 100 h±4 h (preferably 100 h) to obtain the desired result. Figure 2 The miniaturized encapsulated temperature-compensated PTC thermistor 3 shown has the following resistance-temperature curve: Figure 3 As shown, the resistor chip 6 inside is encapsulated with silicone resin 4 and red epoxy resin 5 in sequence. The resistor chip 6 is soldered to two leads 7, and its head size is 3mm×3mm. The performance of the miniaturized encapsulated temperature-compensated PTC thermistor 3 prepared according to the present invention was tested through the following experiments, and the results are as follows: 1) Temperature surge: After 5 temperature surge tests at -55℃ to 125℃ with a conversion time of ≤1min, the resistance change rate of the product before and after the test is between -0.25% and 0.41%, and the required value is ≤10%.

[0012] 2) Load life: The resistance change rate before and after 250h, 500h, 750h and 1000h tests with rated power applied to the product is shown in the table below, indicating good long-term reliability.

[0013] 3) High temperature exposure: In an environment of 125℃, the resistance change rate of the product after 100h and 1000h is 0.08%~-2.38% and 0.73%~-1.09% respectively, indicating good long-term reliability.

[0014] The performance comparison between the miniaturized encapsulated temperature compensation PTC thermistor 3 prepared by this invention and the conventional encapsulated temperature compensation PTC thermistor is shown in the table below: The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the technical solutions of the present invention. Any technical solution that can be implemented based on the above embodiments without creative effort should be considered to fall within the scope of protection of the patent of the present invention.

Claims

1. A method for fabricating a miniaturized encapsulated temperature-compensated PTC thermistor, characterized in that: Includes the following steps: Step 1, Ingredients: Mix barium titanium oxalate, strontium titanium oxalate, barium carbonate, tin dioxide, yttrium oxide, titanium dioxide, and silicon dioxide evenly, then granulate and pre-fire to form PTC ceramic powder raw material; Step 2: Using mechanical pressing, the PTC ceramic powder raw material is pressed into round ceramic green bodies, with the weight of a single ceramic green body controlled between 0.1g and 0.15g. Step 3: Sinter the ceramic green body at a high temperature of 1300℃~1450℃ for 25 min~35 min, and after cooling, obtain a disc-shaped resistance blank. Step 4: Prepare a layer of nickel electrodes on the upper and lower surfaces of the resistor blank by chemical nickel plating to obtain a resistor with PTC characteristics; Step 5: Using screen printing, a layer of silver paste is printed on the outer surface of the nickel electrodes on the upper and lower surfaces of the resistor. After high-temperature firing at 450℃~550℃, a uniform silver electrode is formed on the surface of the nickel electrode, forming a dual-electrode structure together with the nickel electrode. Step 6: Using a dicing process, the resistor body is diced into multiple resistor chips with smaller electrode areas. The resistor chips with the target resistance value are screened in an oil bath at a temperature of 25℃±0.05℃. False resistor chips are eliminated by electric shock with a voltage of 15V. The resistor chips are then heat-treated at 250℃±5℃ for 48 h±2h to obtain stable and reliable resistor chips. Step 7: Using silver-containing high-temperature solder, the lead wires are connected to the resistor chip by brazing to form an effective electrical connection. Step 8: First, encapsulate the resistor chip after soldering the lead wires with silicone resin, and then encapsulate it with red epoxy resin to form a double-layer encapsulation structure. Then, heat-treat it at 150℃±5℃ for 100 h±4 h to obtain a miniaturized encapsulated temperature compensation PTC thermistor.

2. The method for preparing a miniaturized encapsulated temperature-compensated PTC thermistor according to claim 1, characterized in that: In step 1, the mass ratio of barium titanium oxalate, strontium titanium oxalate, barium carbonate, tin dioxide, yttrium oxide, titanium dioxide, and silicon dioxide is 60:31:11:11:0.3:2.5:3.7; in step 2, the PTC ceramic powder raw material is pressed into a ceramic green body with a diameter of 6.5±0.2mm and a thickness of 1.2±0.2mm using a mold with a diameter of 6.5mm; in step 3, the ceramic green body is sintered at a high temperature of 1370℃ for 30min, and after furnace cooling, a resistance blank with a diameter of 5.5±0.5mm is obtained; in step 5, ... A layer of 5080 silver paste is printed on the outer surface of the nickel electrodes on the upper and lower surfaces of the resistor, and then burned into the surface of the nickel electrodes at a high temperature of 500℃. In step 6, the area of ​​the resistor chip is 1mm×1mm. The resistor chip is electrically charged with 15V to eliminate dummy resistor chips, and then heat-treated at 250℃ for 48h to obtain a stable and reliable resistor chip. In step 8, after heat-treatment at 150℃ for 100h, a miniaturized encapsulated temperature compensation PTC thermistor is obtained. The head size of the miniaturized encapsulated temperature compensation PTC thermistor is 3mm×3mm.

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