CN101429655B - Method for making good ohmic contact electrode by local electroless plating on the surface of thermistor - Google Patents

Abstract

The invention discloses a method for manufacturing a good ohmic contact electrode by local electroless plating on the surface of a thermistor, which includes cleaning, drying, preparing and printing activation slurry, high temperature activation, nickel plating, copper plating, water washing, Dehydration, drying, tin immersion, testing and other steps; the present invention deposits a layer of nickel-copper composite electrode with good ohmic contact on the part of the thermistor's local metallization, the electrode has high bonding force, is easy to weld, and the electrical performance indicators all meet Technical requirements; increase labor productivity by more than 2 times, raw material cost is only 25% of the original, especially suitable for the manufacture of welded PTC and NTC thermistor electrodes.

Description

Method for making good ohmic contact electrode by local electroless plating on the surface of thermistor

technical field

The invention relates to a method for manufacturing a good ohmic contact electrode by local electroless plating on the surface of a semiconductor ceramic thermistor, in particular to a method for manufacturing a good ohmic contact electrode by local electroless plating on the surface of a sheet or columnar _BaTiO3 series semiconductor thermistor.

Background technique

BaTiO ₃ ceramics is a typical ferroelectric ceramic. By doping trace amounts of rare earth elements such as Y, Nb, etc., the resistivity at room temperature can be reduced to below 10 ² , and at the same time, it exhibits the PTC (Positive Temperature Coefficient) effect. That is, when the temperature exceeds the Curie temperature of the tile, the resistance value of the tile rises sharply with the rise of the temperature. This kind of ceramic thermistor with positive temperature coefficient is widely used in heating elements, overcurrent protection components, degaussing components, motor starting, temperature probes and other aspects. With the development of my country's home appliances, communications, and automobile industries, the application of PTC thermistors is becoming more and more common. As an electronic component, BaTiO ₃ -based semiconductor ceramics need to be coated with baked metal electrodes on its surface. For example, traditional baked silver electrodes have the problem of contact between semiconductor materials and metals, which cannot form a good ohmic contact electrode. Usually ceramic PTC resistance and metal contact resistance are larger. If a PTC thermistor ohmic contact electrode suitable for industrial production can be prepared under a stable process condition, it will bring great economic and social benefits to our country. There are many ways to prepare such electrodes, such as electroless nickel plating, infiltration of Ag-Zn, Al slurry, and Ag electrodes. Because Ag has strong electrical conductivity and good oxidation resistance, metal can be directly welded on the surface of Ag, so general electronic ceramics usually use silver paste to prepare electrodes. However, since Ag cannot form ohmic contact with semiconducting ceramic components, the electrode of PTC thermistor cannot be prepared directly with silver paste. It is necessary to introduce highly reducing metals into the silver paste, such as Zn, Fe, Al, Ni, etc., which can make the depletion layer on the surface of the semiconductor ceramic disappear and reduce the contact resistance. Chen Yi and others carried out "Study on the paste of silver-aluminum-tin ohmic contact easy-to-solder electrodes"("Electronic Components and Materials" 1997, 16(6): 37-40), and found that aluminum electrodes exhibited low contact resistance. However, Zhan Yizeng et al. ("Modern Technical Ceramics" 2003, 97(3): 12-15) found that the infiltration aluminum electrode has low impact current resistance, poor aging resistance and humidity characteristics, narrow infiltration temperature, and poor storage capacity of finished products. Fired aluminized electrodes cannot be used in demanding products. Professor Zhou Dongxiang et al reported (Sensors and Actuators A 101(2002): 123) Ni-P alloy formed by electroless nickel plating (after heat treatment) forms good ohmic contact electrodes with PTC semiconductor ceramics. It is said to have good stability and is widely used as an ohmic contact electrode for PTC semiconductor ceramics (Electroplating and Finishing, 2004, 23(1): 28). Its metal deposition adopts the traditional sensitization-activation method, and then deposits a layer of 0.5-0.7μm Ni-P alloy in the electroless nickel plating pool, and then grinds the surrounding nickel layer with a hollow grinder, under the condition of 300 ° C ( Nitrogen protection) heat treatment for 90 minutes, and finally a layer (2 μm) of silver electrode is formed on the top layer of the nickel-plated electrode by silver infiltration method. Although this method can meet the problem of forming a good ohmic contact between the metal electrode and the PTC semiconductor ceramic. However, the operation process is cumbersome, and the precious metal silver is required to increase the production cost. Recently, a Chinese patent (CN 1624816A) has reported a manufacturing method of a chip thermistor, the process is complicated, and the formation process of the electrode still needs noble metal silver. Then nickel and tin are electroplated, and the cost is still high.

The manufacturing process of the above-mentioned thermistor electrode still cannot get rid of the use of noble metal silver as the electrode material. And the traditional electroless nickel plating technology still needs to grind the edge. It is not suitable for cylindrical PTC thermistors with very small cross-sectional area (<3mm). After more than a year of exploration, we have developed a method for locally forming metal electrodes on PTC semiconductor ceramics, and the metal coating can form a good ohmic contact with the ceramic substrate. The local electroless copper plating process can completely replace the cumbersome and expensive silver infiltration process.

Contents of the invention

The object of the present invention is to provide a method for preparing a metal electrode with low cost, simple process and satisfactory electrical performance index through the application of semiconductor ceramic metallization activation slurry and local electroless copper plating. In this way, it can replace the expensive and energy-intensive traditional coating process, further reduce the production cost of semiconductor thermistors, and improve economic benefits.

The present invention is achieved through the following technical solutions:

The method for making good ohmic contact electrodes by local chemical plating on the surface of the above-mentioned semiconductor ceramic thermistor has the following steps:

(1) Clean and dry the front ceramic body of the semiconductor thermistor;

(2) prepare the local electroless plating activation slurry on the surface of the thermistor, the raw material components of the activation slurry are metal activator, wetting agent, thickener and toner;

(3) Print the activated paste to the parts to be metallized, dry and activate at high temperature, and cool to room temperature naturally;

(4) Place the front ceramic body of the thermistor activated by high temperature in step (3) in the electroless nickel plating solution, and deposit a Ni-P alloy transition layer less than 1 μm under the condition of 40-60 ° C, and the electroless nickel plating solution Among them, nickel acetate is selected as the nickel salt, and its weight percentage is 0.1% to 3%, sodium hypophosphite is the reducing agent, and the weight percentage is 0.5 to 10.0%, and the others are auxiliary reagents;

(6) Rinse the thermistor element deposited with a layer of metal copper electrode with tap water or deionized water, and dry it rapidly at 80° C. after dehydration with acetone;

(5) Quickly transfer the thermistor in step (4) to the electroless copper plating solution, and form a layer of bright, dense and complete metal on the part to be metallized on the surface of the thermistor under the condition of 40-70°C Copper electrodes;

(6) Rinse the thermistor element deposited with a layer of metal copper electrode with tap water or deionized water, and dry it rapidly at 80° C. after dehydration with acetone;

(7) The thermistor element is subjected to immersion tin and encapsulation treatment, and an electrical performance test is performed.

The cleaning and drying in the step (1) are under ultrasonic conditions, using a surfactant with strong cleaning ability or directly using tap water to clean, and then rinsing and drying.

The step (3) uses a 200-250-mesh screen printing machine, evaporates and removes the solvent at 180-250°C, and the activation temperature is 550-800°C.

In the electroless copper plating process of the step (5), the contact between the cylinder and the porcelain body is a point contact, thereby reducing the contact area between the plated piece and the cylinder, in order to avoid the spread of the coating.

The drying method of the step (6) includes infrared drying, oven drying or vacuum low-temperature drying.

The raw material components of the activated slurry in the step (2) include a metal activator, a wetting agent, a thickener, and a toner.

In the step (2), the wetting agent is N-methylpyrrolidone, ethylene glycol butyl ether, ethylene glycol methyl ether, acetophenone, methylcyclohexanone, and one or more of them are mixed and poured into In the above-mentioned metal activator solution, its raw material weight percentage is 60-95%.

Thickener is cellulose acetate or ethyl cellulose in described step (2), and described toner is superfine carbon powder or 200-250 purpose carbon black, adds cellulose acetate or ethyl cellulose at last, it The weight percentage of raw materials is 3.0-20%, and superfine carbon powder or 200-250 mesh carbon black is added, and the weight percentage of raw materials is 1-15%; it is slowly dissolved under the condition of 50-60 ° C, and according to the appropriate screen printing It is required to adjust the viscosity and volatility of the slurry.

The beneficial effect of the present invention is that it provides a method for preparing a metal electrode with low cost, simple process, and its electrical performance index meets the requirements. The silver process improves the labor productivity by more than 2 times, and its raw material cost is only 25% of the original.

Description of drawings

Figure 1 is an atomic force microscope (AFM) characterization of the distribution of metal particles after high temperature activation.

Detailed ways

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

Preparation _of local metallization activation slurry on the surface of thermistor, using HCl or _H2S04 as solvent, N-methylpyrrolidone, ethylene glycol methyl ether, ethylene glycol butyl ether, acetophenone, methylcyclohexanone As wetting agent, cellulose acetate and ethyl cellulose as thickener, superfine carbon powder or carbon black as precision and chromaticity regulator.

Dissolve one or more of PdCl ₂ , RuCl ₃ and RhCl ₃ with 1:2 HCl to be in ionic state. Then use ethylene glycol butyl ether, ethylene glycol methyl ether, N-methylpyrrolidone, acetophenone, methyl cyclohexanone, one or more of them are mixed and poured into hydrochloric acid dissolved in metal salts, and then added Cellulose acetate or ethyl cellulose and microfine toner or carbon black. And adjust the viscosity and volatility of the slurry according to the requirements of suitable screen printing. The addition of a thickener can improve the viscosity and printing accuracy of the activated slurry and prevent dripping. The addition of carbon powder is beneficial to distinguish the interface of the printing paste, which is convenient for observation and adjustment, and can prevent the deep oxidation of the activated metal during the firing process. After the activated slurry is prepared, it can be stored for a long time at room temperature and under airtight conditions.

The specific example of preparing the metallization activation slurry is as follows.

Activation slurry embodiment 1

Weigh 1.200g of palladium dichloride, dissolve palladium dichloride with 25mL of hydrochloric acid (HCl:H ₂ 0=1:2) to form an ion distribution state, then add 200mL of ethylene glycol methyl ether, 260mL of N-methylpyrrolidone, benzene Acetone 300mL is made into varnish and transferred into chemical reagent bottle. Add 20 mL of ethylene glycol butyl ether and 120 g of cellulose acetate. Dissolve slowly in a constant temperature water bath at 60°C. Finally, add 100g of 250 mesh superfine carbon powder and stir to mix evenly. That is, the activated slurry 1# for screen printing was obtained.

Activation slurry embodiment 2

Weigh 0.500g of palladium dichloride and 6.000g of ruthenium trichloride, dissolve the palladium dichloride and ruthenium trichloride with 50mL (HCl:H ₂ 0=1:2) of the above-mentioned hydrochloric acid to form an ion distribution state, then add ethylene dichloride 500mL of alcohol butyl ether, 200mL of N-methylpyrrolidone, and 80mL of methylcyclohexanone were made into a varnish, and transferred into a chemical reagent bottle. Add 10 mL of acetophenone and 150 g of ethylcellulose. Dissolve in a constant temperature water bath at 50°C. Finally, add 40g of 200 mesh carbon black and stir to mix evenly. Namely obtain the activated slurry 2# of screen printing.

Activation slurry embodiment 3

Weigh 0.200g of palladium dichloride, 0.500g of ruthenium trichloride and 1.000g of rhodium trichloride, and dissolve the three chlorides with 40mL (H ₂ SO ₄ :H ₂ O=1:2) of the above sulfuric acid to form an ion distribution state , and then add 450mL of ethylene glycol methyl ether, 320mL of N-methylpyrrolidone, and 120mL of acetophenone to make a varnish, and transfer it into a chemical reagent bottle. Add 20 mL of ethylene glycol butyl ether and 35 g of cellulose acetate (3.5% by weight). Dissolve slowly in a constant temperature water bath at 50°C. Finally, add 21g of 250 mesh superfine carbon powder and stir to mix evenly. Promptly obtain the activated slurry 3# of screen printing.

The invention uses the metallization activation slurry to manufacture the semiconductor ceramic metal electrode method, which can perform screen printing on the surface of the semiconductor ceramic thermistor in a line and plane manner according to the designated area. Then after drying and high temperature activation, it can be directly electroless copper plating locally, that is to form a layer of copper electrodes that are easy to weld and have good ohmic contact. After welding (dipping) the two metal electrodes, the preparation process of the positive temperature coefficient thermistor element is completed.

Before printing the activation paste, the front ceramic body of the semiconductor thermistor should be cleaned. According to the degree of oil pollution on the ceramic body in front of the thermistor, the cleaning method can be a surfactant solution with strong decontamination ability or direct ultrasonic cleaning with tap water. Then dry it at 80°C. Then use a 200-250-mesh screen printing machine to print the black activation paste on both ends of the columnar thermistor to be metallized. The solvent was evaporated at 180-250°C.

The above-mentioned ceramic thermistor containing the activation slurry is naturally cooled to room temperature after being activated at high temperature (550-800° C.). The activated semiconductor thermistor ceramic body, its solvent, thickener and carbon powder are burned to remove. A layer of highly active metal particles is uniformly distributed on the part to be metallized on the surface of the thermistor ceramic body. The particle size of the active component is about 10-30nm, and it is the activation center of the chemical deposition metal process (Figure 1).

In order to form a low-resistance ohmic contact between semiconductor ceramics and metals, further improve the rate of copper plating and the quality of copper plating, that is, before electroless copper plating, a layer of Ni-P non-Ni-P must be deposited in the electroless nickel plating solution. Crystalline alloy (<1 μm), so that the metallization of the thermistor ceramic surface has a transition metal alloy layer that can form a good ohmic contact electrode. The high temperature activated thermistor front ceramic body is placed in an electroless nickel plating solution, and a Ni-P alloy layer less than 1 μm is deposited under the condition of 40-60°C. In the electroless nickel plating solution, in order to avoid the migration of ^Cl- or SO ₄ ^2- ions, nickel acetate is selected as the nickel salt, and its weight percentage is 0.1% to 3%, and sodium hypophosphite is the reducing agent, and its weight percentage is 0.5 to 10.0% , others are auxiliary reagents. This process does not require heat treatment at 250-300°C (N ₂ gas protection), and can directly electroless copper plating to form copper electrodes that are easy to weld. Then quickly transfer the thermistor to the electroless copper plating solution. Under the condition of 40-70°C, a layer of bright, dense and complete metal copper electrodes will be formed on the part of the thermistor surface that needs to be metallized. The interface is clear, Easy to solder.

The thermistor element deposited with a layer of metal copper electrodes can be directly rinsed with tap water or deionized water, dehydrated with acetone, and quickly dried at 80°C. Drying conditions include infrared drying, oven drying or vacuum low temperature drying. Finally, the thermistor element is subjected to immersion tin and encapsulation treatment, and the electrical performance test is carried out.

Particular electroless plating on the surface of semi-conductor ceramic thermistor makes the specific embodiment of good ohmic contact electrode method as follows:

Example 1

The MZ41-05B3K15N800/75HV type thermistor front ceramic body (φ5×3mm) produced by Anshan Zhongpu Electronic Equipment Co., Ltd. is selected. Its standard resistance value is 100-200Ω, and its withstand voltage standard is 800V _ac . Clean under ultrasonic conditions for 5 minutes, rinse with tap water, and dry. Then use a screen printing machine to print the activation paste 1# to the position where the front ceramic body needs to be metallized. A margin of about 0.2 mm is left around it, and the thickness is less than 1 μm. Then dry (remove solvent) at 200-250°C. Before the electroless plating, the semiconductor thermistor after printing the activation paste was activated in a muffle furnace at 600° C. for 12 minutes. Then remove and cool to room temperature. Before electroless copper plating, deposit a layer of Ni-P alloy coating (<1μm) in the electroless nickel plating solution (60°C), and then transfer the plated part (thermistor porcelain body) to the electroless plating solution at 47°C immediately Plated in medium for 30 minutes and removed. Its electroless copper plating solution adopts the traditional technical formula:

Copper sulfate (CuSO ₄ 5H ₂ O) (AR) 8-14g/L

Sodium Potassium Tartrate (A.R.) 5-16g/L

EDTA(A.R.) 20-30g/L

Sodium hydroxide (A.R.) 12-14g/L

α,α-bipyridine (A.R.) 10-200mg/L

Potassium ferrous hydride (A.R.) 10-30mg/L

Formaldehyde (37%) (A.R.) 9-14ml/L

Ethanol (A.R.) 1.0-10ml/L

After rinsing with tap water and dehydrating with acetone, they were quickly dried at 80°C. The physical properties of the completed MZ41-05B3K15N800/75HV thermistor element were measured after tin immersion (without heat treatment). The results are shown in Table 1.

The electrical property (not heat-treated) of MZ41-05B3K15N800/75HV type thermistor in table 1. embodiment 1

sample number 1 2 3 4 5 6 7 8 9 10 Before soldering R₂₅/KΩ 5.37 5.76 10.16 12.3 7.76 12.26 9.61 12.12 9.01 9.51 R₂₅/Ω after soldering 155 151 199 160 176 173 175 136 171 159 Tensile test √ √ √ √ √ √ √ √ √ √ R₂₅/Ω before withstand voltage test 161 157 232 166 184 181 194 140 175 165 Maximum withstand voltage / V, V_max＝800V_ac √ √ √ √ √ √ 750 √ √ √ After 12h R₂₅/Ω 157 275 215 162 178 187 — 138 170 159

Note:

1. All resistance values are measured with a UT803 desktop automatic range digital multimeter at 25°C for 30 minutes;

2. The tensile test is to place the porcelain body vertically after welding, and hang a 1Kg weight for about 10 seconds, subject to the fact that the coating does not peel off from the porcelain body;

3. The withstand voltage test is that the AC voltage is continuously applied for 35 seconds, and the porcelain body is not damaged. The initial voltage of the sample is 500V _ac , and the voltage is 50V each time, and the end is 800V _ac . The instrument is a self-made withstand voltage tester.

It can be seen from the results in Table 1 that the highest withstand voltage and tensile tests of the welded thermistor can meet the production requirements.

Example 2

The front ceramic body of the MZ41-05B3K15N800/75HV thermistor produced by Anshan Zhongpu Electronic Equipment Co., Ltd. is selected. Except that the cleaning of the ceramic part is directly rinsed with tap water naturally, the other is carried out electroless copper plating to the thermistor according to the identical conditions of embodiment 1 to form a layer of bright copper electrodes. After drying, it was kept at 150° C. for 15 minutes under the protection of nitrogen, and then the temperature was lowered to room temperature and taken out. After immersion tin, carry out physical performance test. The results are shown in Table 2:

Table 2. The electrical properties of embodiment 2MZ41-05B3K15N800/75HV type thermistor (heat treated)

sample number 1 2 3 4 5 6 7 8 9 10 R₂₅/Ω before welding 268 250 236 151 178 214 208 216 255 203 R₂₅/Ω after soldering 174 154 149 127 159 173 191 165 198 171 Tensile test √ √ √ √ √ √ √ √ √ √ R₂₅/Ω before withstand voltage test 180 158 159 132 166 179 198 171 207 177 Maximum withstand voltage/VV_max＝800V_ac √ √ √ √ √ √ 500 √ √ √ After 12h R₂₅/Ω 166 150 151 127 161 173 — 164 199 171

Note: "√" in the table means the test passed, and "—" the withstand voltage test failed.

The results in Table 2 show that the resistance value of the thermistor decreases significantly after heat treatment. Basically meet the requirements of the standard resistance value. The R ₂₅ resistance after welding has little change with the R ₂₅ resistance before welding. This is because the nascent hydrogen generated in electroless copper or nickel plating is desorbed during heat treatment. At the same time, the Ni-P amorphous alloy is crystallized to form a Ni ₃ P structure, that is, a good ohmic contact is formed between the coating and the ceramic body of the semiconductor thermistor, so the resistance value is significantly reduced. However, the purpose of heat treatment can still be achieved in the immersion tin process at 242 ° C, so the heat treatment process can be exempted in the actual production process.

Example 3

Select the MZ41-08B3K25M800/85L type thermistor front ceramic body produced by Anshan Zhongpu Electronic Equipment Co., Ltd. (standard resistance value is 200-300Ω, withstand voltage standard is 800V, shape is φ7×2.5mm) according to the same implementation plan 1 Methods Ultrasonic cleaning was performed on the front ceramic body of the above-mentioned semiconductor thermistor, the activation paste 2# was screen-printed and a layer of metal copper electrode was directly deposited. After drying and tin dipping, the electrical properties were measured directly: the results are shown in Table 3.

The electrical performance of MZ41-08B3K25M800/85L type thermistor in table 3. embodiment 3

sample number 1 2 3 4 5 6 7 8 9 10 R₂₅/Ω before welding 719 289 641 649 506 1026 424 498 646 959 R₂₅/Ω after soldering 198 164 170 183 181 218 193 200 201 247 Tensile test √ √ √ √ √ √ √ √ x √ Before withstand voltage test: R₂₅/Ω 200 165 169 185 182 220 194 200 — 250 Maximum withstand voltage /V_max＝800V_ac √ √ √ √ √ √ √ √ — √ 12h R₂₅/Ω 200 163 167 180 185 220 234 201 — 245

From the analysis of the results in Table 3, it can be seen that although the R ₂₅ resistance value of the MZ41-08B3K25M800/85L type thermistor is relatively high before welding, after welding, its R ₂₅ resistance value, tensile test and maximum withstand voltage test indicators can all meet Production requirements.

Example 4

3×3mm。按照实施方案1对上述热敏电阻瓷体进行超声清洗10分钟。干燥后，用手工方法将活化浆料3#被覆到热敏电阻瓷体需金属化的部位。经650℃条件下高温活化。然后在化学镀镍池中沉积低于1μm的Ni-P合金镀层。接着迅速转移到55℃化学镀铜液中，施镀20分钟取出，经自来水漂洗和丙酮脱水后，迅速在烘箱中干燥20分钟。经浸锡后直接进行电性能测定。其测定结果见表4。The front ceramic body of MZ41-03B3K40N600/75S type thermistor (produced by Anshan Zhongpu Electronic Equipment Co., Ltd.) is selected. The standard resistance value is 300-500Ω, the withstand voltage standard is 600V _ac , and the shape is

3×3mm. According to Embodiment 1, the ceramic body of the thermistor was ultrasonically cleaned for 10 minutes. After drying, manually apply activation slurry 3# to the part of the thermistor ceramic body to be metallized. It is activated by high temperature at 650°C. Then a Ni-P alloy coating below 1 μm is deposited in an electroless nickel bath. Then quickly transfer to 55°C electroless copper plating solution, take out after plating for 20 minutes, rinse with tap water and dehydrate with acetone, and dry in oven for 20 minutes quickly. The electrical properties were measured directly after tin immersion. The measurement results are shown in Table 4.

Table 4. Performance of MZ41-03B3K40N600/75S thermistor in embodiment 4 (without heat treatment)

sample number 1 2 3 4 5 6 7 8 9 10 R₂₅/Ω before welding 576 990 789 448 455 406 1016 640 369 840 R₂₅/Ω after soldering 290 286 328 284 263 283 304 361 268 290 Tensile test √ √ √ √ √ √ √ √ √ √ R₂₅/Ω before withstand voltage test 310 314 358 309 287 309 329 277 281 309 Maximum withstand voltage / V_max＝600V_ac √ √ √ √ √ √ √ 500 √ √ After 12h R₂₅/Ω 310 322 367 314 293 312 3.88 — 269 311

If the plating layer is found to be thin and has defects after electroless copper plating, it can be washed with tap water, and then placed in the electroless copper plating solution for 10 minutes of plating. And rinse and dry according to the same method as in Example 4. The electrical properties of the MZ41-03B3K40N600/75S thermistor after secondary copper plating were tested after immersion tin, and the results are shown in Table 5.

Table 5. Performance of MZ41-03B3K40N600/75S thermistor after secondary copper plating (without heat treatment)

sample number 1 2 3 4 5 6 7 8 9 10 R₂₅/Ω before welding 469 664 769 886 522 676 615 616 743 665 R₂₅/Ω after soldering 265 325 392 364 353 314 290 336 365 322 Tensile test √ √ √ √ √ √ √ √ √ √ R₂₅/Ω before withstand voltage test 284 353 423 394 384 349 314 370 398 355 Maximum withstand voltage/VV_max＝600V_ac 550 √ √ √ √ √ 500 — √ √ After 12h R₂₅/Ω — 362 428 397 375 363 — — 398 354

It can be seen from Table 5 that the electrical performance index of the thermistor after secondary copper plating can still meet the production requirements.

According to the electrical performance analysis of the above thermistor, it is found that less than 10% of the thermistor samples cannot meet the highest withstand voltage requirement. It may be due to the migration of ions in the plating solution into the ceramic body. Resulting in a slight decrease in withstand voltage performance. Therefore, the MZ41-03B3K40N600/75S pre-ceramic body was ultrasonically cleaned according to the same method as in Example 1 until it was activated at a high temperature of 800° C. for 5 minutes. Then immerse in alcohol and cyclohexanol with 4-6 carbon atoms for 1 h, then carry out electroless nickel plating and electroless copper plating according to the same method as in Example 1 to form copper electrodes. After rinsing, dehydration, drying and immersion in tin, the withstand voltage test is carried out directly. Among its 28 samples, 2 exceed 750V, and the rest are above 600V. This result shows that after the above-mentioned treatment, the withstand voltage performance of the copper electrode formed by the electroless copper plating process is significantly higher than that of the thermistor formed by coating the aluminum paste and the silver paste to form the silver electrode.

The partial metallization process of the present invention can increase the labor productivity more than 2 times, and its raw material cost is only 25% of the original.

Claims (8)

1. semiconductive ceramic manufacturing good ohm contact electrode by thermistor surface local chemical plating method has following steps:

(1) to porcelain body before the semiconductor thermistor clean, drying;

(2) preparation thermistor surface local chemical plating actived slurry, the feed composition of described actived slurry is metal activation agent, wetting agent, thickening material and toning agent;

(3) actived slurry is printed onto the metallized position of need, drying and high-temperature activation naturally cool to room temperature;

(4) with step (3) porcelain body before the thermistor of high-temperature activation, place chemical nickel-plating liquid, be lower than the Ni-P alloy transition layer of 1 μ m 40～60 ℃ of condition deposit, in the chemical nickel-plating liquid, the selection nickel acetate is a nickel salt, and its weight percent is 0.1%～3%, and inferior sodium phosphate is a reductive agent, weight percent is 0.5～10.0%, and other are auxiliary reagent;

(5) thermistor of step (4) is transferred to rapidly in the chemical bronze plating liquid, under 40～70 ℃ condition, needed metallized position to form one deck light, densification, complete metallic copper electrode at thermistor surface;

(6) it is clean with tap water or rinsed with deionized water to deposit the thermistor element of layer of metal copper electrode, after the acetone dehydration, dry under 80 ℃ condition rapidly;

(7) thermistor element is carried out wicking and seal processing, and carry out electric performance test.

2. according to the manufacturing good ohm contact electrode by thermistor surface local chemical plating method of claim 1, it is characterized in that, cleaning, the drying of described step (1) is under the ultrasonic wave condition, with the strong tensio-active agent of cleansing power or directly clean rinsing drying then with tap water.

3. according to the manufacturing good ohm contact electrode by thermistor surface local chemical plating method of claim 1, it is characterized in that, described step (3) adopts 200～250 purpose screen processes press, removes 180～250 ℃ of condition evaporations and desolvates, and activation temperature is 550～800 ℃.

4. according to the manufacturing good ohm contact electrode by thermistor surface local chemical plating method of claim 1, it is characterized in that, the chemical-copper-plating process of described step (5), cylinder is the point type contact with contacting of porcelain body, and then reduce the contact area of plating piece and cylinder, for avoiding spreading of coating.

5. according to the manufacturing good ohm contact electrode by thermistor surface local chemical plating method of claim 1, it is characterized in that the drying mode of described step (6) comprises ultra red ray drying, oven drying or vacuum dehydrating at lower temperature.

6. according to the manufacturing good ohm contact electrode by thermistor surface local chemical plating method of claim 1, it is characterized in that, the metal activation agent is one or more in Er Lvization Palladium, ruthenium trichloride, the Trichlororhodium in the described step (2), and its raw material weight per-cent is 0.05-10%; It is dissolved in hydrochloric acid or the sulfuric acid, and presents the ion distribution state, described hydrochloric acid or vitriolic raw material weight per-cent are 0.1-10%.

7. according to the manufacturing good ohm contact electrode by thermistor surface local chemical plating method of claim 1, it is characterized in that, wetting agent is N-Methyl pyrrolidone, butyl glycol ether, ethylene glycol monomethyl ether, methyl phenyl ketone, methylcyclohexanone in the described step (2), one or more mixing are wherein poured in the above-mentioned metal activation agent solution, and its raw material weight per-cent is 60-95%.

8. according to the manufacturing good ohm contact electrode by thermistor surface local chemical plating method of claim 1, it is characterized in that, thickening material is cellulose acetate or ethyl cellulose in the described step (2), toning agent is ultra-fine carbon dust or 200-250 purpose carbon black in the described step (2), add cellulose acetate or ethyl cellulose at last, its raw material weight per-cent is 3.0-20%, and adds ultra-fine carbon dust or 200-250 purpose carbon black, and its raw material weight per-cent is 1-15%; Under 50-60 ℃ condition, slowly dissolve, and require the viscosity and the volatility of adjusting slurry according to suitable silk screen printing.

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