Surface-mounted NTC (Negative Temperature Coefficient) thermistor, preparation method and glass atomization liquid

Abstract

The invention relates to the technical field of NTC (Negative Temperature Coefficient) thermistors, in particular to an SMD (Surface Mount Device) NTC thermistor, a preparation method and glass atomized liquid. The preparation method comprises the following steps: S1, vertically fixing the SMD NTC thermistor semiconductor ceramic particles, and placing the SMD NTC thermistor semiconductor ceramic particles at a spraying station; s2, spraying the glass atomized liquid to the periphery of the side surface of the SMD NTC thermistor semiconductor ceramic particle through ultrasonic atomization equipment to obtain a semi-finished product; wherein the spraying angle between a spray head of the ultrasonic atomization equipment and the spraying station is 20-50 degrees; s3, the semi-finished product is placed in a sintering environment to be sintered, the sintering temperature curve Tmax ranges from 870 DEG C to 950 DEG C, and the peak temperature lasting time ranges from 10 min to 20 min; and S4, carrying out end sealing, electrode sintering and electroplating on the sintered semi-finished product to obtain a surface-mounted NTC thermistor finished product with a glass protection layer on the periphery of the side surface.

Description

Technical Field

[0001] The invention relates to the technical field of chip-type NTC thermistors, in particular to a chip-type NTC thermistor and a preparation method thereof, and a glass atomizing liquid. Background Art

[0002] Chip NTC thermistor (Negative Temperature Coefficient Thermistor) is made of manganese, cobalt, nickel and other metal oxides as the main materials, and is made of ceramic technology. It has the characteristic that the resistance value decreases as the temperature rises, so it has functions such as temperature detection and control, temperature compensation, surge current suppression, fluid flow testing, etc. In addition, chip NTC thermistor has the advantages of high temperature sensitivity, good reliability, strong interchangeability, easy processing into various required shapes and sizes, small size, no lead wires, and suitable for high-density surface mounting. It is widely used in home appliances, digital communications, automobiles, industry, medical and other fields.

[0003] At present, the solder used in SMD NTC thermistors is mainly tin paste or silver paste. During the silver paste soldering process, since there is no protective layer on the four sides of the SMD thermistor chip, the silver paste is easy to spread to the middle of the chip (such as Figure 1 ), resulting in a shortened effective distance of the ceramic body, drifting resistance of the chip NTC thermistor, and even the risk of short circuit. In order to improve the weldability of the chip NTC thermistor, the chip NTC thermistor soldered with solder paste needs to be electroplated with nickel and tin layers on the end electrodes to form an electroplating layer. However, the electroplating solution will corrode the ceramic body of the chip NTC thermistor, causing the resistance of the chip NTC thermistor to drift and reduce the reliability of the chip NTC thermistor. In addition, the chip NTC thermistor without a protective layer on the sides has higher requirements for the use environment. Harmful factors such as moisture, acid, alkali, and electric fields in the environment may cause the performance of the chip NTC thermistor to drift and the reliability to deteriorate. With the development trend of miniaturization of chip NTC thermistors, the size of chip NTC products is also moving towards smaller and thinner directions, which makes the above problems more prominent.

[0004] At present, in order to solve the above problems, the industry forms a protective layer (such as Figure 2 ). However, the pneumatic spraying glass protective layer process has the following problems: First, this process easily forms an inverted trapezoidal patch type NTC thermistor, and the glass liquid easily accumulates on the top of the ceramic particles. The glass protective layer becomes thinner from top to bottom, resulting in an uneven glass layer (such as Figure 3); Second: Air pressure spraying cannot be used on small or thin SMD NTC thermistors. The air pressure of air gun spraying is relatively large, and the contact area on the film is small. The SMD NTC thermistor is easy to flip over and cannot be sprayed; Third: The accuracy of air pressure spraying is relatively low, and it is difficult to accurately control the thickness of the glass protective layer of the SMD NTC thermistor. Summary of the invention

[0005] The embodiments of the present invention provide a chip-type NTC thermistor and a preparation method thereof, and a glass atomizing liquid to solve the above-mentioned technical problems.

[0006] The present invention discloses a method for preparing a patch type NTC thermistor with a glass protective layer, comprising the steps of:

[0007] S1: vertically fix the SMD NTC thermistor semiconductor ceramic particles, and place the SMD NTC thermistor semiconductor ceramic particles at the spraying station;

[0008] S2: Spraying the glass atomized liquid onto the sides of the semiconductor ceramic particles of the SMD NTC thermistor through an ultrasonic atomizing device to obtain a semi-finished product; wherein the spraying angle between the nozzle of the ultrasonic atomizing device and the spraying station is 20° to 50°;

[0009] S3: placing the semi-finished product in a sintering environment for sintering, the sintering temperature curve Tmax = 870°C ~ 950°C, and the peak temperature duration is 10 ~ 20 minutes;

[0010] S4: The sintered semi-finished product is sealed, the electrode is sintered, and electroplated to obtain a finished NTC thermistor with a glass protective layer on all sides.

[0011] Optionally, in step S2, the spraying height from the spray head to the spraying station is 30 mm to 50 mm.

[0012] Optionally, in step S2, the spraying times of the nozzle is 3 to 10 times.

[0013] Optionally, in step S2, the spraying flow rate of the nozzle is 1 ml / min to 4 ml / min.

[0014] Optionally, in step S2, the heating temperature of the semiconductor ceramic grain of the SMD NTC thermistor is 30°C to 80°C.

[0015] Optionally, step S1 specifically includes:

[0016] Use a vibration loading machine to fix the SMD NTC thermistor semiconductor ceramic particles upright on the adhesive tape.

[0017] The present invention also discloses a chip-type NTC thermistor. The surface of the chip-type NTC thermistor is covered with a glass protective layer, and the glass protective layer is prepared and formed in the preparation method of any one of claims 1 to 6.

[0018] Optionally, the thickness of the glass protection layer is 5-80 μm.

[0019] The present invention also discloses a glass atomizing liquid, which is applied to the above-mentioned preparation method and comprises 5 to 10 parts of glass powder, 0.2 to 0.5 parts of polyvinyl alcohol and 0.5 to 3 parts of polyethylene glycol in parts by weight.

[0020] Optionally, the components of the glass powder include Si:Al:Mg:K:Zn:Ca:Zr:Ba=(8.5~15.0):(0.5~2.0):(0.5~2.0):(0.5~1.5):(0.5~2.0):(0.7~2.0):(0.5~1.5):(0.2~1.0) in molar ratio.

[0021] Compared with the prior art, the method for preparing a chip NTC thermistor with a glass protective layer provided by the embodiment of the present invention has the following beneficial effects: the applicant has found that if the spraying angle α between the nozzle of the ultrasonic atomization equipment nozzle and the spraying station is too small, the glass atomized liquid will accumulate on the top of the chip NTC thermistor and be missing at the bottom, while if the angle is too large, the opposite will happen. Finally, the chip NTC thermistor is difficult to be completely and evenly covered and protected by the glass protective layer, resulting in unstable performance and reduced reliability. Therefore, in step S2, the spraying angle α between the nozzle of the ultrasonic atomization equipment and the spraying station is set to 20°~50°. Within this angle range, the spraying angle α between the nozzle and the spraying station is moderate, which can avoid the uneven phenomenon that the glass atomized liquid accumulates on the top of the chip NTC thermistor and the bottom is missing due to the spraying angle α being too small, and the uneven phenomenon that the glass atomized liquid accumulates at the bottom of the chip NTC thermistor and the top is missing due to the spraying angle α being too large. The chip NTC thermistor finally processed can be completely and evenly covered and protected by the glass protective layer, ensuring stable performance and improving reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, in which:

[0023] Figure 1 This is a solder diagram of a SMD NTC thermistor;

[0024] Figure 2 This is a schematic diagram of a chip NTC thermistor;

[0025] Figure 3This is a schematic diagram of the glass protective layer being poorly sprayed and in an inverted trapezoidal shape;

[0026] Figure 4 Schematic diagram of a nozzle spraying glass atomized liquid according to an embodiment of the present invention;

[0027] Figure 5 is a schematic diagram of a semi-finished product uniformly covered with glass powder (white part) according to an embodiment of the present invention;

[0028] Figure 6 is a schematic diagram of a semi-finished product covered with a transparent glass protective layer according to an embodiment of the present invention;

[0029] Figure 7 It is a schematic diagram of a transparent glass protective layer with uniform thickness according to an embodiment of the present invention (blue numbers indicate thickness: 8.896 μm on the upper left, 8.261 μm on the upper right, 7.307 μm on the lower left, and 6.990 μm on the lower right).

[0030] The reference numerals in the figures are:

[0031] 1. Solder; 2. Solder paste; 3. Electroplating layer; 4. SMD NTC thermistor semiconductor ceramic particles; 5. SMD NTC thermistor; 6. Nozzle; 7. Semi-finished product; 8. Glass protective layer; 9. Heating platform; 10. Glass atomizing liquid. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. Now, in conjunction with the accompanying drawings, the preferred embodiments of the present invention are described in detail.

[0033] A protective layer (such as a protective layer 8) is formed by spraying a glass protective layer 8 on the sides of the SMD NTC thermistor 5 by air pressure. Figure 2 ), the air pressure spraying glass protective layer 8 process uses the air pressure of the air gun to spray the glass liquid around the sides of the ceramic particles, and forms the glass protective layer 8 after sintering. However, the air pressure spraying glass protective layer 8 process has the following problems: First, the process is easy to form an inverted trapezoidal SMD NTC thermistor 5, and the glass liquid is easy to accumulate the glass protective layer 8 on the top of the SMD NTC thermistor semiconductor ceramic particles 4. The glass protective layer 8 becomes thinner from top to bottom, resulting in an uneven glass layer (such as Figure 3 ); Second: Air pressure spraying cannot be used on small or thin SMD NTC thermistors 5. The air pressure of the air gun spraying is relatively high, and the SMD NTC thermistor 5 is easy to fall over and cannot be sprayed. Third: The precision of air pressure spraying is relatively low, and it is difficult to accurately control the thickness of the glass protective layer 8 of the SMD NTC thermistor 5.

[0034] The embodiment of the present invention provides a method for preparing a chip-type NTC thermistor 5 having a glass protective layer 8, such as Figures 4 to 7 As shown, the method for preparing the SMD NTC thermistor 5 with the glass protective layer 8 comprises the following steps:

[0035] S1: vertically fix the SMD NTC thermistor semiconductor ceramic particles, and place the SMD NTC thermistor semiconductor ceramic particles at the spraying station;

[0036] S2: Spraying the glass atomized liquid onto the sides of the semiconductor ceramic particles of the SMD NTC thermistor through an ultrasonic atomizing device to obtain a semi-finished product; wherein the spraying angle between the nozzle of the ultrasonic atomizing device and the spraying station is 20° to 50°;

[0037] S3: placing the semi-finished product in a sintering environment for sintering, the sintering temperature curve Tmax = 870°C ~ 950°C, and the peak temperature duration is 10 ~ 20 minutes;

[0038] S4: The sintered semi-finished product is sealed, the electrode is sintered, and electroplated to obtain a finished NTC thermistor with a glass protective layer on all sides.

[0039] The preparation method of the chip NTC thermistor 5 with a glass protective layer 8 of the present invention adopts an ultrasonic atomization device, and the air pressure is extremely small and can be ignored, which solves the problem that the chip NTC thermistor 5 is easy to tip over due to the high air pressure in traditional air pressure spraying and cannot be applied to miniaturized or thin chip NTC thermistor semiconductor ceramic particles 4. At the same time, the atomized particles are small and the coating is thin, which solves the problem of uneven appearance of the glass protective layer 8, which is large on the top and small on the bottom, caused by the accumulation of spray liquid on the top of the chip NTC thermistor semiconductor ceramic particles 4 during traditional air pressure spraying. The preparation method of the present invention has simple process operation, high production efficiency, low cost, few influencing factors and easy control, and does not affect the performance of the chip NTC thermistor 5 while improving the reliability of the chip NTC thermistor 5. In addition, the process has no adverse effect on the environment and is in line with the development direction of modern green manufacturing.

[0040] More importantly, the applicant has found that if the spraying angle α between the nozzle 6 of the sonic atomization device and the spraying station is too small, the glass atomized liquid 10 will accumulate on the top of the SMD NTC thermistor 5 and be missing at the bottom, while if the angle is too large, the opposite will happen. Finally, the SMD NTC thermistor 5 is difficult to be completely and evenly covered and protected by the glass protective layer 8, resulting in unstable performance and reduced reliability. Therefore, in step S2, the spraying angle α between the nozzle 6 of the ultrasonic atomization equipment and the spraying station is set to 20°~50°. Within this angle range, the spraying angle α between the nozzle 6 and the spraying station is moderate, which can avoid the uneven phenomenon that the glass atomized liquid 10 accumulates on the top of the chip NTC thermistor 5 and is missing at the bottom due to the spraying angle α being too small, and the uneven phenomenon that the glass atomized liquid 10 accumulates at the bottom of the chip NTC thermistor 5 and is missing at the top due to the spraying angle α being too large. The chip NTC thermistor 5 finally processed can be completely and evenly covered and protected by the glass protective layer 8, ensuring stable performance and improving reliability.

[0041] Regarding the spraying angle α between the nozzle 6 and the spraying station, further combined with the following Table 1, within the range of 20° to 50°, when other spraying parameters remain unchanged, the larger the spraying angle, the thicker the glass protective layer 8 sprayed around the sides of the SMD NTC thermistor semiconductor ceramic particle 4. This is because within the range of 20° to 50°, the larger the angle α, the steeper the spray trajectory of the nozzle 6 relative to the sides of the SMD NTC thermistor semiconductor ceramic particle 4, so that more glass atomized liquid 10 can be sprayed onto the surface around the sides of the SMD NTC thermistor semiconductor ceramic particle 4. Of course, as mentioned above, when the angle α is too large or too small (exceeding 20° to 50°), the glass atomized liquid 10 will accumulate at the bottom of the SMD NTC thermistor 5, while the top is missing or the opposite is uneven.

[0042] Specifically, the spraying angle α between the nozzle 6 of the ultrasonic atomization equipment and the spraying station can be any one of 20°C, 22°C, 24°C, 26°C, 28°C, 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C, 46°C, 48°C, and 50°C.

[0043] In step S1, the semiconductor ceramic particles 4 of the SMD NTC thermistor are fixed upright, so that the sides of the semiconductor ceramic particles 4 of the SMD NTC thermistor are in a state that is easy to be sprayed. The two ends of the NTC thermistor are usually used for welding electrodes, and the sides between the electrodes are the so-called sides, and the semiconductor ceramic particles of the thermistor are the main substrate for preparing the NTC thermistor, and are prepared into the finished NTC thermistor in the subsequent process. The SMD NTC thermistor semiconductor ceramic particles 4 that have been fixed upright are placed in the spraying station and sprayed in the subsequent process.

[0044] In step S2, spraying a glass protective layer 8 around the sides of the semiconductor ceramic particle 4 of the SMD NTC thermistor can prevent the solder 1 from diffusing into the middle of the SMD NTC thermistor 5 during the welding process to affect the performance of the SMD NTC thermistor 5, and protect the ceramic body from being corroded by the plating solution during the electroplating process of the SMD NTC thermistor 5, which may cause the performance drift and reliability reduction of the SMD NTC thermistor 5. At the same time, it can also shield harmful substances in the environment, improve the ability of the SMD NTC thermistor 5 to resist mechanical stress, and thus improve the reliability of the SMD NTC thermistor 5.

[0045] In step S3, the semi-finished product 7 can be carried in a calcining bowl, and the mesh belt furnace temperature curve Tmax is set to 870℃~950℃, and the peak temperature duration is 10~20min for sintering. After sintering, the patch semi-finished product 7 protected by a 5~40μm transparent glass layer can be obtained. In the present invention, Tmax and the peak temperature time are adjusted according to the thickness of the glass protective layer 8, that is, the parameters affecting the spraying thickness are related to the sintering temperature and the peak temperature time. The thicker the sprayed glass protective layer 8, the higher the sintering temperature required for firing the transparent glass protective layer 8, or the longer the peak temperature time, otherwise the glass protective layer 8 will appear whitish and opaque.

[0046] Specifically, Tmax may be any one of 870° C., 880° C., 890° C., 900° C., 910° C., 920° C., 930° C., 940° C., and 950° C. The peak temperature duration may be any one of 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, and 20 min.

[0047] In step S4, the sintered semi-finished product 7 is capped, electrode sintered, and electroplated using conventional processes, which will not be described in detail here.

[0048] Furthermore, in step S2, the spraying height from the nozzle to the spraying station is 30 mm to 50 mm. The applicant has found that if the spraying height from the nozzle 6 to the heating platform 9 is too low, the solvent in the atomized liquid will not have time to evaporate and form droplets that agglomerate on the semiconductor ceramic particles 4 of the SMD NTC thermistor. If the height is too high, the atomized liquid will evaporate too much during the spraying process, and the semiconductor ceramic particles 4 of the SMD NTC thermistor will be attached too little or unevenly. Finally, the SMD NTC thermistor 5 is not completely protected by the glass protective layer 8, resulting in unstable performance and reduced reliability.

[0049] Further combined with the following Table 1, when the spraying height is within the range of 30 mm to 50 mm and other spraying parameters remain unchanged, the higher the spraying height, the thicker the glass protective layer 8 sprayed around the sides of the SMD NTC thermistor semiconductor ceramic particle 4. This is because within the range of 30 mm to 50 mm, the spraying height changes from low to high, and the spraying angle of the nozzle 6 relative to the SMD NTC thermistor semiconductor ceramic particle 4 will also change, so that the glass atomized liquid 10 sprayed to the surface thickness of the side of the SMD NTC thermistor semiconductor ceramic particle 4 changes from thin to thick.

[0050] Specifically, the spraying height can be any one of 30mm, 32mm, 34mm, 36mm, 38mm, 40mm, 42mm, 44mm, 46mm, 48mm, and 50mm.

[0051] Further, in step S2, the spraying times of the nozzle is 3 to 10 times. The applicant has found that if the spraying times are too few, the glass powder content attached to the semiconductor ceramic particles 4 of the SMD NTC thermistor is small, the glass protective layer 8 is not completely covered, and the protection effect is not achieved. The performance of the SMD NTC thermistor 5 is unstable and the reliability is reduced. If the spraying times are too many, the efficiency is reduced and the cost is increased. In this scheme, the spraying times of the nozzle 6 are further set to 3 to 10 times, and the spraying times are moderate, which avoids the problems of too few spraying times, the glass powder content attached to the semiconductor ceramic particles of the SMD NTC thermistor is small, the glass protective layer 8 is not completely covered, and the protection effect is not achieved. The performance of the SMD NTC thermistor 5 is unstable and the reliability is reduced, and the problem of too many spraying times, the efficiency is reduced and the cost is increased. Specifically, the spraying times of the nozzle 6 can be any of 3, 4, 5, 6, 7, 8, 9, and 10 times.

[0052] Further, in step S2, the spray flow rate of the nozzle is 1ml / min to 4ml / min. The applicant has found that too small a spray flow rate may lead to discontinuous atomization, incomplete atomization range, the glass protective layer 8 cannot play a protective role, and reduce production efficiency, unstable performance and reduced reliability of the chip NTC thermistor 5, and too large a flow rate may cause the nozzle 6 to be difficult to atomize the glass atomizing liquid 10, and spraying cannot be achieved. In this scheme, the spray flow rate of the nozzle 6 is further set to 1ml / min to 4ml / min, avoiding the problem that too small a spray flow rate may lead to discontinuous atomization, incomplete atomization range, the glass protective layer 8 cannot play a protective role, and reduce production efficiency, unstable performance and reduced reliability of the chip NTC thermistor 5, and too large a flow rate may cause the nozzle 6 to be difficult to atomize the glass atomizing liquid 10, and spraying cannot be achieved. Specifically, the spraying flow rate of the nozzle 6 can be any one of 1 ml / min, 1.5 ml / min, 2 ml / min, 2.5 ml / min, 3 ml / min, 3.5 ml / min, and 4 ml / min.

[0053] Furthermore, in step S2, the heating temperature of the chip NTC thermistor semiconductor ceramic particles 4 is 30°C to 80°C. The applicant has found that the heating temperature of the chip NTC thermistor semiconductor ceramic particles 4 is closely related to the glass atomizing liquid 10. During the spraying process of the glass atomizing liquid 10, there are two trends on the chip NTC thermistor semiconductor ceramic particles 4: volatilization and flow to the bottom of the chip NTC thermistor semiconductor ceramic particles 4. By controlling the heating temperature, the volatilization rate of the glass atomizing liquid 10 and the degree of flow to the bottom of the chip NTC thermistor semiconductor ceramic particles 4 can be controlled to achieve a balance and obtain a uniform and dense glass protective layer 8. If the heating temperature is too high, the glass atomized liquid 10 evaporates too quickly during the spraying process, which may easily lead to the glass atomized liquid 10 not adhering to the SMD NTC thermistor semiconductor ceramic particles 4, or adhering unevenly, and the glass atomized liquid 10 has no tendency to flow to the bottom of the SMD NTC thermistor semiconductor ceramic particles 4, resulting in the accumulation of atomized liquid at the top to form an inverted trapezoid, which will cause the glass protective layer 8 to be uneven, and the SMD NTC thermistor 5 is not completely covered by the glass protective layer 8, resulting in unstable performance and reduced reliability. If the temperature is too low, on the contrary, the glass atomized liquid 10 evaporates too slowly, and flows too fast to the bottom of the SMD NTC thermistor semiconductor ceramic particles 4, accumulating at the bottom of the SMD NTC thermistor semiconductor ceramic particles 4 or on a carrier such as adhesive tape, resulting in the disadvantage of glass atomized liquid 10 accumulating at the bottom. In the present scheme, the heating temperature of the semiconductor ceramic particle 4 of the SMD NTC thermistor is further set to 30°C ~ 80°C, so as to avoid the problem that the heating temperature is too high, the glass atomized liquid 10 evaporates too quickly during the spraying process, which easily leads to the problem that the glass atomized liquid 10 does not adhere to the semiconductor ceramic particle 4 of the SMD NTC thermistor, or adheres unevenly, and the glass atomized liquid 10 has no tendency to flow to the bottom of the semiconductor ceramic particle 4 of the SMD NTC thermistor. If the temperature is too low, on the contrary, the glass atomized liquid 10 evaporates too slowly, and flows too quickly to the bottom of the semiconductor ceramic particle 4 of the SMD NTC thermistor, accumulating at the bottom of the semiconductor ceramic particle 4 of the SMD NTC thermistor or on a carrier such as adhesive tape, resulting in the problem of glass atomized liquid 10 accumulating at the bottom.

[0054] Further combined with the following Table 1, since the higher the temperature, the faster the glass atomizing liquid 10 evaporates, when other spraying parameters remain unchanged, within the heating temperature range of 30°C to 80°C, the lower the heating temperature, the thicker the glass protective layer 8 obtained by spraying.

[0055] Specifically, the heating temperature of the chip NTC thermistor semiconductor ceramic particle 4 can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C.

[0056] Further, step S1 is specifically as follows: using a vibration loading machine to fix the SMD NTC thermistor semiconductor ceramic grain upright on the adhesive tape. After the SMD NTC thermistor semiconductor ceramic grain 4 is fixed on the adhesive tape, it is placed on a heating platform 9 with vacuum adsorption and heating functions as a spraying station, and the heating temperature of the heating platform 9 is 30°C to 80°C, thereby achieving the heating temperature of the SMD NTC thermistor semiconductor ceramic grain 4 at 30°C to 80°C.

[0057] Since the top and bottom (two ends) of the SMD NTC thermistor semiconductor ceramic particle 4 need to be welded with electrodes later, they cannot be covered by the glass protective layer 8. During the spraying process, the bottom of the SMD NTC thermistor semiconductor ceramic particle 4 is fixed on the adhesive tape and blocked to avoid the spraying of the glass atomized liquid 10, and the top can be blocked as necessary to avoid spraying the glass atomized liquid 10.

[0058] Specifically, in the preparation method of the present invention, the obtained glass protective layer 8 of the SMD NTC thermistor 5 is relatively thin, with a thickness of 5 to 80 μm. The thickness of the glass protective layer 8 can be controlled by spraying angle, spraying height, spraying times, spraying flow rate and heating temperature, while ensuring that the glass protective layer 8 is evenly covered, and the glass protective layer 8 has high hardness, good wear resistance and strong chemical stability. It can not only solve the problem of the resistance drift of the SMD NTC thermistor 5 caused by the diffusion of solder 1 to the center of the SMD NTC thermistor 5 and the migration of silver paste during welding, but also effectively protect the ceramic body of the SMD NTC thermistor 5 from being corroded by the electroplating solution during the electroplating process to improve the reliability of the SMD NTC thermistor 5. At the same time, it can protect the SMD NTC thermistor 5 from being affected by harmful substances in the environment during the use of the SMD NTC thermistor 5, resulting in performance drift, and improve the mechanical properties of the SMD NTC thermistor 5, thereby improving the reliability of the SMD NTC thermistor 5.

[0059] The present invention also discloses a chip NTC thermistor 5, the surface of which is covered with a glass protective layer 8, which is prepared and formed in the above-mentioned preparation method. The glass protective layer 8 of the chip NTC thermistor 5 is prepared and formed in the above-mentioned preparation method, and the chip NTC thermistor 5 has the glass protective layer 8, which also has the same technical effects as above, and will not be described in detail here.

[0060] Furthermore, the thickness of the glass protective layer 8 is 5-80 μm, and the glass protective layer 8 is relatively thin. Specifically, the thickness of the glass protective layer 8 can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, or 80 μm.

[0061] Table 1

[0062]

[0063] The present invention also discloses a glass atomizing liquid 10, which is applied to the above-mentioned preparation method and includes 5 to 10 parts of glass powder, 0.2 to 0.5 parts of polyvinyl alcohol and 0.5 to 3 parts of polyethylene glycol by weight. If the glass powder component is too small, it means that the solid content of the atomized liquid sprayed out in a single spray is very small. If the thickness of the glass protective layer 8 is to be the same, the number of spraying times required will increase by many times, which is inefficient and costly. If the glass powder component is too large, it is difficult for the nozzle 6 to atomize and cannot be atomized. In this solution, the glass powder content is moderate, which avoids the problem that the solid content of the atomized liquid sprayed out in a single spray is very small. If the thickness of the glass protective layer 8 is to be the same, the number of spraying times required will increase by many times, which is inefficient and costly, and the problem that the glass powder component is too large, it is difficult for the nozzle 6 to atomize and cannot be atomized.

[0064] Polyvinyl alcohol and polyethylene glycol both have a dispersing effect, making the glass atomized liquid 10 more uniform and preventing the glass powder from settling, and the glass protective layer 8 is also more uniform. In addition, polyvinyl alcohol and polyethylene glycol also act as a binder in this solution, which can improve the strength of the glass protective layer 8 attached to the semiconductor ceramic particles 4 of the SMD NTC thermistor, making the glass protective layer 8 less likely to be damaged or fall off. However, the amount of polyvinyl alcohol and polyethylene glycol added needs to be adjusted accordingly according to the components of the glass powder. Too much or too little amount cannot play a role in dispersing and strengthening adhesion. The glass atomized liquid 10 cannot be well dispersed, affecting the spraying and the uniformity of the glass protective layer 8, resulting in the glass protective layer 8 after sintering being bumpy, and the SMD NTC thermistor 5 cannot be fully protected.

[0065] The glass powder can be any one of 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts, 8.5 parts, 9 parts, 9.5 parts, and 10 parts, the polyvinyl alcohol can be any one of 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, and 0.5 parts, and the polyethylene glycol can be any one of 0.5 parts, 1 parts, 1.5 parts, 2 parts, 2.5 parts, and 3 parts.

[0066] Specifically, 5 to 10 parts of the glass powder prepared above, 0.2 to 0.5 parts of polyvinyl alcohol, and 0.5 to 3 parts of polyethylene glycol or other dispersants can be added to the solvent pure water and mixed uniformly by ball milling to prepare the glass atomized liquid 10. Mixing by ball milling can not only make various substances fully mixed uniformly, but also prevent the glass powder from agglomerating.

[0067] Further, according to the molar ratio, the components of the glass powder include Si: Al: Mg: K: Zn: Ca: Zr: Ba in a molar ratio of (8.5-15.0): (0.5-2.0): (0.5-2.0): (0.5-1.5): (0.5-2.0): (0.7-2.0): (0.5-1.5): (0.2-1.0). The glass powder ratio in this scheme is lead-free, which not only conforms to the development direction of green production, but also can obtain a low-melting-point glass powder with a melting point lower than the decomposition temperature of the NTC ceramic phase without causing the performance of the chip NTC thermistor 5 to be unstable. At the same time, the glass powder of this ratio has a good bonding force with the NTC ceramic after sintering, but there will be no glass penetration phenomenon that causes the problem of poor performance concentration of the chip NTC thermistor 5.

[0068] The technical solution of the present invention is further illustrated by specific embodiments below.

[0069] Step 1: Porcelain powder is batched, ball-milled, isostatically pressed, and sintered at high temperature to obtain a thermal semiconductor ingot with a resistivity of about 3.0KΩ.mm and a B value of 3900K, and then sliced ​​into pieces at 0.95mm. The above-mentioned pieces are sliced ​​and chamfered to a size of 0.5mmX0.2mm to obtain semiconductor ceramic particles.

[0070] Step 2: Weigh 40g of glass powder with a molar ratio of Si:Al:Mg:K:Zn:Ca:Zr:Ba=10.65:1.72:1.23:0.92:1.20:1.46:0.90:0.58, 15g of polyvinyl alcohol and 15g of polyethylene glycol, add them into 430g of solvent pure water, ball mill for 24h and mix evenly to prepare a glass spray liquid.

[0071] Step 3: Adjust the frequency of the vibration loading machine to 15HZ, fix the thermistor ceramic particles upright on the adhesive tape, pour the above-mentioned glass spray liquid into a beaker and suck it into the liquid pump through the straw of the ultrasonic atomization equipment. Set the spray angle to 45°, the spray height to 40mm, the number of sprays to 3 times, the spray flow rate to 3ml, and the heating temperature of the heating platform 9 to 70°C. Then put the adhesive tape with the ceramic particles on the heating platform 9 with a vacuum adsorption function and turn on the vacuum to flatten the adhesive tape. It is required to be free of bubbles. After resetting the nozzle 6 of the ultrasonic atomization equipment, press the start button to spray, and you can get a chip-type NTC thermistor semi-finished product 7 (such as Figure 5 ).

[0072] Step 4: The semi-finished product 7 is carried in a calcining pot, and the mesh belt furnace temperature is set to Tmax = 900 ° C, and the peak temperature duration is 15 minutes for sintering. After sintering, a patch semi-finished product 7 (such as Figure 5 and Figure 7 ).

[0073] Step 5: The semi-finished product 7 is subjected to end-capping, electrode sintering and electroplating to obtain a finished NTC thermistor 5 with glass protective layers 8 on four sides.

[0074] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. For those skilled in the art, the technical solutions described in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents; and all these modifications and replacements should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a chip-type NTC thermistor with a glass protective layer, characterized in that: Includes steps: S1: vertically fix the SMD NTC thermistor semiconductor ceramic particles, and place the SMD NTC thermistor semiconductor ceramic particles at the spraying station; S2: Spraying the glass atomized liquid onto the sides of the semiconductor ceramic particles of the SMD NTC thermistor through an ultrasonic atomizing device to obtain a semi-finished product; wherein the spraying angle between the nozzle of the ultrasonic atomizing device and the spraying station is 20° to 50°; S3: placing the semi-finished product in a sintering environment for sintering, the sintering temperature curve Tmax = 870°C ~ 950°C, and the peak temperature duration is 10 ~ 20 minutes; S4: The sintered semi-finished product is sealed, the electrode is sintered, and electroplated to obtain a finished NTC thermistor with a glass protective layer on all sides.

2. The preparation method according to claim 1, characterized in that: In step S2, the spraying height from the spray head to the spraying station is 30 mm to 50 mm.

3. The preparation method according to claim 2, characterized in that: In step S2, the spraying times of the nozzle is 3 to 10 times.

4. The preparation method according to claim 3, characterized in that: In step S2, the spraying flow rate of the nozzle is 1 ml / min to 4 ml / min.

5. The preparation method according to claim 4, characterized in that: In step S2, the heating temperature of the semiconductor ceramic grain of the SMD NTC thermistor is 30°C to 80°C.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The step S1 is specifically as follows: Use a vibration loading machine to fix the SMD NTC thermistor semiconductor ceramic particles upright on the adhesive tape.

7. A chip NTC thermistor, characterized in that: The surface of the chip-type NTC thermistor is covered with a glass protective layer, and the glass protective layer is prepared and formed in the preparation method according to any one of claims 1 to 6.

8. The chip NTC thermistor according to claim 7, characterized in that: The thickness of the glass protective layer is 5-80 μm.

9. A glass atomizing liquid, used in the preparation method according to any one of claims 1 to 6, characterized in that: In parts by weight, it comprises 5 to 10 parts of glass powder, 0.2 to 0.5 parts of polyvinyl alcohol and 0.5 to 3 parts of polyethylene glycol.

10. The glass atomizing liquid according to claim 9, characterized in that: According to the molar ratio, the components of the glass powder include Si:Al:Mg:K:Zn:Ca:Zr:Ba=(8.5~15.0):(0.5~2.0):(0.5~2.0):(0.5~1.5):(0.5~2.0):(0.7~2.0):(0.5~1.5):(0.2~1.0).

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