SMD (Surface Mount Device) zinc oxide varistor and production method thereof

Abstract

The invention discloses a surface-mounted zinc oxide varistor and a production method, the varistor comprises a voltage-sensitive ceramic chip, surface electrodes and side electrodes positioned on the upper and lower sides or the lower side of the surface electrodes are arranged on bosses at the two ends of the voltage-sensitive ceramic chip along the length direction, and the side electrodes are used for adhering and positioning solder paste during reflow soldering and can be horizontally laid on a PCB (Printed Circuit Board) to prevent rolling. The bosses at the two ends of the voltage-sensitive ceramic chip increase the distance between the side electrode and different side surface electrodes so as to exceed the shortest distance between the two surface electrodes, and the problems that the distance is short and the voltage-sensitive voltage is reduced due to the side electrode are solved; the pressure-sensitive ceramic chip is provided with a boss height interval when being welded on the PCB so as to prevent solder paste from polluting the porcelain body at the lower side edge; in the process of the production method, the distance between the electrodes is increased by selecting low-voltage gradient powder and manufacturing a high-voltage product, flashover and side flash between the electrodes can be avoided, and the energy tolerance of the product and low-current high-voltage continuous multiple pulses can be effectively improved by adopting the low-voltage gradient powder.

Description

Technical Field

[0001] The present invention relates to the technical field of varistor, and more particularly to a chip zinc oxide varistor and a production method thereof. Background Art

[0002] Currently, most lighting devices use LED lamp beads, which have relatively poor tolerance to surge impacts in the circuit and require surge protection. Due to the conductivity of the heat-dissipating aluminum substrate, it is not suitable for plug-in components. The surge protection varistors currently in use are all packaged in surface mount form to facilitate the mass production of LED lamp heads.

[0003] However, in the prior art, such as Chinese patents CN202211338129.4, CN201610472205.9, CN201510955379.6 and CN201010580937.2 disclose multilayer varistors and methods for manufacturing the same, which use a multilayer ceramic capacitor process, using a tape casting machine for casting, printing internal electrodes, isostatic pressing, stacking and cutting, pre-binding, atmosphere sintering, electrode connection, nickel plating and tin plating and other processes. On the one hand, the investment in production equipment is large and the equipment requirements are high. On the other hand, due to the thickness limit between layers, it is suitable for rated voltage 5V-100V voltage protection. Finally, during surge impact, due to the multilayer structure, the heat is unbalanced and cracks are easily caused to fail.

[0004] For example, Chinese patent CN202010966184.2 discloses a solution that uses traditional plug-in assembly, coating flattening, and horizontal mounting; Chinese patent CN201820356800.0 discloses a matrix varistor patch packaging solution, and Chinese patent CN201711165632.3 discloses an embedded varistor flat-mount packaging solution, both of which use traditional varistor chips, and after lead or frame welding, the surface electrodes are parallel to the PCB board, flattened packaging, and SMD patching is realized, but the structure is relatively complex, the lead processing size consistency is poor, and production control is difficult, and the chip is packaged horizontally and horizontally, with superimposed leads and packaging layers, which occupies a large area of ​​the PCB board;

[0005] For example, Chinese patent CN201822145675.1 discloses a series structure varistor patch solution, which uses two varistors in series. However, the distance between the two varistor electrodes is small, which is easily penetrated by air, resulting in limited product application.

[0006] Therefore, providing a chip zinc oxide varistor and a production method is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0007] In view of this, the present invention provides a chip zinc oxide varistor and a production method, which has a simple structure, a small size, good heat dissipation, good lightning pulse resistance and low production cost.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A chip zinc oxide varistor comprises a varistor ceramic sheet. Both end bosses of the varistor ceramic sheet along the length direction are provided with surface electrodes and side electrodes located on the upper and lower sides or the lower side of the surface electrodes.

[0010] By adopting the above technical solution, the beneficial effects of the present invention are:

[0011] 1) The bosses at both ends of the varistor ceramic increase the distance between the side electrode and the different side surface electrodes to exceed the shortest distance between the two surface electrodes, avoiding the problem of short distance and drop in varistor voltage caused by the side electrode;

[0012] 2) When the varistor is soldered on the PCB, there is a height gap between the bosses to prevent solder paste from contaminating the lower side of the ceramic body;

[0013] 3) The side electrode is used for solder paste adhesion and positioning during reflow soldering, and can lie flat on the PCB to prevent rolling.

[0014] Furthermore, the surface electrode and the side electrode are both arranged on the boss by printing, rolling or pad printing.

[0015] Furthermore, the length of the varistor ceramic sheet is 3-8 mm.

[0016] The beneficial effect of adopting the above further technical solution is that the fixed length facilitates the layout of the solder joints on the PCB board.

[0017] Furthermore, the boss is provided with a metal sheet, a metal sleeve or a metal ring.

[0018] The beneficial effects of adopting the above further technical solution are that the current during surge impact can be balanced, the elasticity of the solder joint connection can be increased, and it is suitable for high temperature difference environment.

[0019] Furthermore, an insulating layer is coated on the varistor ceramic body.

[0020] The production method of the above-mentioned chip zinc oxide varistor comprises the following steps:

[0021] 1) Prepare powder: prepare low-gradient zinc oxide powder;

[0022] 2) Pressing the green body: using a mold with a prefabricated boss to press a rectangular green body sheet;

[0023] 3) Debinding and firing: The green sheet is pre-debinded and then fired to form a pressure-sensitive ceramic sheet;

[0024] 4) Making surface electrodes, printing, rolling or pad printing conductive electrodes on the boss bodies at both ends of the varistor along the length direction to form surface electrodes;

[0025] 5) Make side electrodes, print, roll or transfer conductive electrodes on the R corner sides of the bosses at both ends of the varistor along the length direction to form side electrodes; or in step 4), the conductive electrodes are diffused to the sides or lower sides around the bosses, thereby forming surface electrodes and side electrodes at the same time.

[0026] By adopting the above technical solution, the beneficial effects of the present invention are:

[0027] 1) By selecting powder with lower voltage gradient to produce high voltage products, the distance between electrodes can be increased to avoid sparking and side flash between electrodes;

[0028] 2) The use of lower gradient powder can effectively improve the product's energy tolerance and continuous multiple pulses of small current and high voltage.

[0029] Furthermore, in step 1), 40-100 low gradient powder or 100-180 low gradient powder is selected.

[0030] Furthermore, the height of the prefabricated boss in step 2) is 0.1-1 mm.

[0031] Furthermore, in step 3), the green sheet is pre-debinded and then trial-fired, and different voltage gradients are obtained by adjusting the temperature. Then, the varistor voltage is measured and the firing temperature is confirmed.

[0032] The beneficial effect of adopting the above further technical solution is that different voltage gradients can be controlled by adjusting the material formula and the firing temperature to achieve different varistor voltages at a fixed thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0034] Figure 1 The accompanying drawing is a front view of a chip zinc oxide varistor in Example 1;

[0035] Figure 2 The accompanying drawing is a top view of a chip zinc oxide varistor in Example 1;

[0036] Figure 3 The accompanying drawing is a side view of a chip zinc oxide varistor in Example 1;

[0037] Figure 4 The accompanying drawing is a front view of a chip zinc oxide varistor in Example 2;

[0038] Figure 5 The accompanying drawing is a top view of a chip zinc oxide varistor in Example 2;

[0039] Figure 6 The accompanying drawing is a side view of a chip zinc oxide varistor in Example 2;

[0040] Figure 7 The accompanying drawing is a front view of a chip zinc oxide varistor in Example 3;

[0041] Figure 8 The accompanying drawing is a top view of a chip zinc oxide varistor in Example 3;

[0042] Fig. 9 The accompanying drawing is a side view of a chip zinc oxide varistor in Example 3. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Embodiment 1:

[0045] like Figure 1-3 As shown, the embodiment of the present invention discloses a chip zinc oxide varistor, including a varistor ceramic 1. The varistor ceramic 1 is generally in a rectangular shape, which is convenient for suction by a nozzle and prevents rolling during patching. The length of the varistor ceramic 1 is 3-8 mm, and the fixed length is convenient for the layout of solder joints on the PCB board 2. In this embodiment, the spacing between the protection circuit pins of the PCB board 2 is usually 3 mm and 5 mm. Considering the size of the printed tin dots, the length of the varistor ceramic 1 exceeds the center distance of the solder joints and can be set to 3.5 and 5.5 mm to facilitate the adhesion of the solder paste dots. The varistor ceramic 1 is provided with surface electrodes 3 and side electrodes 4 located on the upper and lower sides of the surface electrodes 3 on the bosses at both ends along the length direction. In this embodiment, the cross section of the boss is similar to an isosceles trapezoid shape, the outer side of the boss is chamfered, and the minimum surface projection area of ​​the surface electrode 3 is between 1.5 and 30 mm. 2The side electrode 4 is used for solder paste adhesion and positioning during reflow soldering, and can lie flat on the PCB board 2 to prevent rolling. The bosses at both ends of the varistor ceramic sheet 1 of the present invention increase the distance between the side electrode 4 and the different side surface electrodes 3 to exceed the shortest distance between the two surface electrodes 3, avoiding the problem of short distance and varistor voltage drop caused by the side electrode 4, and the varistor ceramic sheet 1 has a boss height interval when soldered on the PCB board 2 to avoid solder paste contamination of the lower side ceramic body.

[0046] In order to further optimize the technical solution of the present invention, a metal sheet, a metal sleeve or a metal ring is provided on the boss, which can balance the current during surge impact, increase the elasticity of the solder joint connection, and is suitable for high temperature difference environment.

[0047] The embodiment of the present invention also discloses a method for producing the above-mentioned SMD zinc oxide varistor, comprising the following steps:

[0048] 1) Powder preparation: low-gradient zinc oxide powder is prepared; in this embodiment, the gradient G=140V / mm powder is prepared; ZnO, Bi 2 O 3 、Co 3 O 4 , Sb 2 O 3 、MnCO 3 、N i 2 O 3 , B 2 O 3 , CuO, Al 2 O 3 Powder, the molar percentage of each component is: 90-95.5%: 4-5.8%: 0.2-0.3%: 0.2-0.4%: 0.2-0.4%: 0.35-0.45%: 0.05-0.2%: 0.010-0.03%: 0.005%-0.01%; Bi 2 O 3 、Co 3 O 4 , Sb 2 O 3 、MnCO 3 、N i 2 O 3 , B 2 O 3 , CuO, Al 2 O 3 The powders are mixed and ground, and the ground mixture is mixed with ZnO and then ground, and then the mixture is spray-dried after adding glue to obtain zinc oxide pressure-sensitive ceramic powder;

[0049] 2) Pressing green pieces: Using a mold with a prefabricated boss to press a rectangular green piece; in this embodiment, the size of the mold with the prefabricated boss is 4.2×2.9, R0.1mm, the thickness of the pressed green piece is 2.9mm, and the tablet density E is 3.4g / cm 3 ;

[0050] 3) Debinding and firing: the green sheet is pre-debinded and then fired to form a varistor ceramic sheet 1; in this embodiment, the pre-debinding is carried out at a temperature of 560° for 3 hours in a muffle furnace, and then fired at a temperature of 1185° for 4.5 hours to obtain a varistor ceramic sheet 1 with a size of 2.5×2.5×3.5 mm;

[0051] 4) Making the surface electrode 3 and the side electrode 4: Take 80% silver paste and transfer print 2.0×2.5 electrodes on the outer surfaces of the two bosses of the varistor 1 to form a surface electrode 3 with a length and width of 2.0×2.0 and a side electrode 4 with a length and width of 2.0×0.25; after drying, burn the silver in a silver furnace to form the surface electrode 3 on the boss body and the side electrode 4 on the R corner side of the boss.

[0052] In order to further optimize the technical solution of the present invention, in step 3), the green sheet is pre-debinded and then trial-fired. Different voltage gradients are obtained by adjusting the temperature. Then, the varistor voltage is measured and the firing temperature is confirmed. The principle of this process is: during the sintering process, Bi 2 O 3 Segregation at the grain boundary forms a bismuth-rich thin layer, which produces a surface state and thus forms a grain boundary barrier. At a lower temperature, Bi with a low melting point 2 O 3 The bismuth-rich phase is a liquid phase that wets the ZnO grain boundary. As the sintering temperature increases, the degree of wetting of the bismuth-rich phase increases, accelerating the migration of the grain boundary, thereby promoting the continuous fusion and growth of the ZnO grains. Under a unit volume, the number of ZnO grains decreases, and the bismuth-rich grain boundary that forms a high potential barrier also decreases synchronously, thereby reducing the voltage gradient. Different voltage gradients can be obtained at different sintering temperatures, that is, different varistor voltages at fixed thicknesses. By adjusting the material formula, such as Bi 2 O 3 、Co 3 O 4 , Sb 2 O 3 、MnCO 3 By adding the same amount of zinc oxide and controlling the number of zinc oxide grains per unit thickness through the firing temperature, different voltage gradients can be achieved, thus realizing different varistor voltages at a fixed thickness.

[0053] The three parameters of the measured samples before and after the surge impact are as shown in the following table:

[0054] 4.7 ohms in series, surge pulse 1KV / 500A+AC220V, 0, 90, 180, 270° 4 phases, ±5 times each.

[0055]

[0056] Embodiment 2:

[0057] like Figure 4-6 As shown, the embodiment of the present invention discloses a chip zinc oxide varistor, which is different from the embodiment 1 in that an insulating layer 5 is coated on the main body of the varistor ceramic chip 1 .

[0058] The embodiment of the present invention also discloses a production method of a surface-mount zinc oxide varistor as described above, which differs from Embodiment 1 in that: during debinding and firing in step 3), the debinding is performed in a muffle furnace at 560° for 3 hours, and then fired at 1125° for 4.5 hours; after step 4), the product is positioned on a rocking plate, coated with epoxy resin, and cured to form an insulating layer 5.

[0059] Measure the three parameters of the sample before and after impact, as shown in the following table:

[0060] 4.7 ohms in series, surge pulse 1KV / 500A+AC220V, 0, 90, 180, 270° 4 phases, ±5 times each.

[0061]

[0062] Embodiment 3:

[0063] like Figure 7-9 As shown, the embodiment of the present invention discloses a chip zinc oxide varistor and a production method, which differs from Example 1 in that: the varistor ceramic piece 1 is provided with a surface electrode 3 and a side electrode 4 located at the lower side of the surface electrode 3 on the bosses at both ends along the length direction, that is, the top plane of the varistor ceramic piece 1 is flat, and only has a trapezoidal groove on the bottom plane, and the cross-section of the boss is similar to an isosceles trapezoid.

[0064] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0065] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A chip zinc oxide varistor, comprising a varistor ceramic, characterized in that: The varistor ceramic sheet is provided with surface electrodes and side electrodes located on the upper and lower sides or the lower side of the surface electrodes on the bosses at both ends along the length direction.

2. A chip zinc oxide varistor according to claim 1, characterized in that: The surface electrode and the side electrode are both arranged on the boss by printing, rolling or pad printing.

3. A chip zinc oxide varistor according to claim 1 or 2, characterized in that: The length of the varistor is 3-8 mm.

4. A chip zinc oxide varistor according to claim 1, characterized in that: The boss is provided with a metal sheet, a metal sleeve or a metal ring.

5. A chip zinc oxide varistor according to claim 1, characterized in that: The varistor ceramic sheet body is coated with an insulating layer.

6. A method for producing a chip zinc oxide varistor according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) Prepare powder: prepare low-gradient zinc oxide powder; 2) Pressing the green body: using a mold with a prefabricated boss to press a rectangular green body sheet; 3) Debinding and firing: The green sheet is pre-debinded and then fired to form a pressure-sensitive ceramic sheet; 4) Making surface electrodes, printing, rolling or pad printing conductive electrodes on the boss bodies at both ends of the varistor along the length direction to form surface electrodes; 5) Make side electrodes, print, roll or transfer conductive electrodes on the R corner sides of the bosses at both ends of the varistor along the length direction to form side electrodes; or in step 4), the conductive electrodes are diffused to the sides or lower sides around the bosses, thereby forming surface electrodes and side electrodes at the same time.

7. A production method according to claim 6, characterized in that: In step 1), 40-100 low gradient powder or 100-180 low gradient powder is selected.

8. A production method according to claim 6, characterized in that: The height of the prefabricated boss in step 2) is 0.1-1 mm.

9. A production method according to claim 6, characterized in that: In step 3), the green sheet is pre-debinded and then trial-fired. Different voltage gradients are obtained by adjusting the temperature. Then, the varistor voltage is measured and the firing temperature is confirmed.

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