Metal wire cleanliness evaluation device and method

Abstract

The invention relates to the technical field of metal wire cleanliness evaluation, in particular to a metal wire cleanliness evaluation device and method. The invention provides a metal wire cleanliness evaluation device. The metal wire cleanliness evaluation device comprises a charge unit and an electrostatic deflection unit which are arranged in sequence, the charge unit comprises a corona wire and a tubular cathode plate, and the corona wire is located at the axial center position of the tubular cathode plate; the electrostatic deflection unit comprises an anode plate and a cathode plate, and the anode plate and the cathode plate are oppositely arranged in parallel and are perpendicular to the ground. According to the device for evaluating the cleanliness of the metal wire, the particles adsorbed on the surface of the metal wire are charged through the charging unit, the metal wire containing the charged particles enters the electrostatic deflection unit and deflects under the action of electric field force, and the quantitative relation among the cleanliness, the charging amount, the wire quality, the deflection angle and the electric field intensity is established based on the electrostatic principle; and the cleanliness index is defined, so that quantitative evaluation on the surface cleanliness of the metal wire is realized.

Description

Technical Field

[0001] The invention relates to the technical field of metal wire cleanliness evaluation, and in particular to a metal wire cleanliness evaluation device and method. Background Art

[0002] Metal wires, such as bonding wires, are wires used for electronic packaging and connection, and are widely used in semiconductor packaging, microelectronic devices, etc. In the production process of bonding wires, multiple process steps are usually used to improve the performance of bonding wires, including drawing, annealing, and rewinding.

[0003] During the production process of bonding wires, dust particles are easily adsorbed on the surface of the bonding wires. These particles are easily embedded in the bonding wires or remain on the surface during the subsequent drawing or annealing and rewinding process, thereby deteriorating the performance of the bonding wires. The cleanliness of the bonding wire surface directly affects the quality and reliability of the final product.

[0004] At present, the main method for testing and evaluating the surface cleanliness of metal wires is macroscopic visual inspection through stereo microscopes. This method requires the inspectors to have rich experience, can only perform qualitative evaluation, and can only visually inspect the outermost layer of metal wire on the spool, resulting in a limited number of test samples and difficulty in comprehensively evaluating the overall cleanliness of the metal wire. In addition, since the test results rely on the experience and judgment of the operator, there may be large subjective errors, affecting the accuracy and consistency of the test results.

[0005] In view of this, this invention is proposed. Summary of the invention

[0006] The first object of the present invention is to provide a metal wire cleanliness evaluation device, which can realize continuous quantitative evaluation of the cleanliness of the metal wire surface.

[0007] A second object of the present invention is to provide a method for evaluating the cleanliness of a metal wire, which can accurately and quantitatively evaluate the surface cleanliness of the metal wire.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] In a first aspect, the present invention provides a metal wire cleanliness evaluation device, comprising a charging unit and an electrostatic deflection unit arranged in sequence;

[0010] The charging unit comprises a corona wire and a tubular cathode plate, wherein the corona wire is located at the axial center of the tubular cathode plate;

[0011] The electrostatic deflection unit comprises an anode plate and a cathode plate, wherein the anode plate and the cathode plate are arranged relatively parallel and perpendicular to the ground.

[0012] Furthermore, the voltage applied to the charging unit is U c ;

[0013] Where, M is the surface roughness coefficient of the corona wire; δ is the relative density of the gas; a is the radius of the corona wire, in cm; b is the inner radius of the tubular cathode plate, in cm;

[0014] Where A is the Hamaker constant between the metal wire and the particle; d p is the equivalent diameter of the particle, in m; x is the center distance between the metal wire and the corona wire, in cm; Z is the distance between the particle and the surface of the metal wire, in nm; q s is the saturated charge of the particles, in C.

[0015] Furthermore, the length of the tubular cathode plate is l c ;

[0016] Where v is the moving speed of the metal wire, in m / s; τ is the charging time constant, in s.

[0017] Furthermore, the voltage applied to the electrostatic deflection unit is U e ;

[0018] Where D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm.

[0019] Further, it includes at least one of the following features (1) to (9);

[0020] (1) The diameter of the corona wire is 0.2 to 0.3 cm;

[0021] (2) The inner radius of the tubular cathode plate is 1 to 2 cm;

[0022] (3) The length of the tubular cathode plate is 100 to 200 mm;

[0023] (4) The width of the anode plate and the cathode plate is 10 to 30 cm;

[0024] (5) The height of the anode plate and the cathode plate is 10 to 50 cm;

[0025] (6) The vertical distance between the anode plate and the cathode plate is 2 to 3 cm;

[0026] (7) In the charging unit, the center distance between the metal wire and the corona wire is 0.35 to 0.45 cm;

[0027] (8) The voltage applied to the charging unit is 14 to 31 kV;

[0028] (9) The voltage applied to the electrostatic deflection unit is 20 to 100 kV.

[0029] In a second aspect, the present invention further provides a method for evaluating the cleanliness of a metal wire, using the above-mentioned device for evaluating the cleanliness of a metal wire, comprising the following steps:

[0030] After the metal wire enters the charging unit to charge the particles on the surface of the metal wire, it enters the electrostatic deflection unit to be deflected, and the cleanliness of the metal wire is evaluated according to the parameters of the metal wire and the electrostatic deflection unit; wherein the parameters include the deflection angle of the metal wire.

[0031] Furthermore, the following relationship is satisfied:

[0032] Where U c is the DC voltage applied to the charging unit, in kV; M is the surface roughness coefficient of the corona wire; δ is the relative density of the gas; a is the radius of the corona wire, in cm; b is the inner radius of the tubular cathode plate, in cm;

[0033] Where A is the Hamaker constant between the metal wire and the particle; d p is the equivalent diameter of the particle, in m; x is the center distance between the metal wire and the corona wire, in m; Z is the distance between the particle and the surface of the metal wire, in nm; q s is the saturated charge of the particles, in C.

[0034] Furthermore, the following relationship is satisfied: In the formula, l c is the length of the tubular cathode plate, in mm; v is the moving speed of the metal wire, in m / s; τ is the charging time constant, in s.

[0035] Furthermore, the following relationship is satisfied: Where U e is the DC voltage applied between the anode plate and the cathode plate of the electrostatic deflection unit, in kV; D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm.

[0036] Furthermore, the cleanliness of the metal wire is evaluated according to the cleanliness index Cl. The larger the Cl is, the worse the cleanliness of the metal wire is.

[0037] in, In the formula, Cl is the cleanliness index, the unit is C / m 2 ;d wis the diameter of the metal wire, in μm; ρ is the density of the metal wire, in g / cm 3 ; g is the acceleration due to gravity, in m / s 2 ; D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm; α is the deflection angle of the metal wire, in degrees; U e It is the DC voltage applied between the anode and cathode plates of the electrostatic deflection unit, in kV.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The metal wire cleanliness evaluation device and method of the present invention adopts a charging unit designed based on the corona effect to saturate the particles on the surface of the metal wire with electricity, and an electrostatic deflection unit can flexibly adjust the deflection angle of the charged wire; based on the electrostatic principle, a quantitative relationship between cleanliness, charge, wire quality, deflection angle, and electric field strength is established, and a cleanliness index is defined to achieve comparison and quantitative evaluation of the surface cleanliness of wires of different materials and wire diameters; the designed charging unit and electrostatic deflection unit are compact and small in structure, and can be conveniently integrated and installed at the rear end of annealing and wire drawing equipment; in conjunction with the wire retracting and unwinding mechanism, continuous quantitative evaluation of the surface cleanliness of the metal wire can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 It is a schematic structural diagram of the metal wire cleanliness evaluation device of the present invention.

[0042] Figure 2 Schematic diagram of a charging unit of the present invention.

[0043] Figure 3 It is a schematic diagram of the deflection of the metal wire in the electrostatic deflection unit of the present invention and a force analysis diagram of the metal wire in the electrostatic deflection unit.

[0044] Figure 4 These are stereo microscope images of bonding wires in three situations in Example 1 of the present invention.

[0045] Reference numerals:

[0046] 11-corona wire; 12-tubular cathode plate; 21-anode plate; 22-cathode plate; 3-first power supply; 4-second power supply; 51-pay-off shaft; 52-tension wheel; 53-first guide wheel; 54-driving wheel; 55-second guide wheel; 56-take-up shaft; 61-camera; 62-computer; 7-metal wire. DETAILED DESCRIPTION

[0047] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0048] The following is a detailed description of a metal wire cleanliness evaluation device and method of the present invention.

[0049] See also Figure 1 , in some embodiments of the present invention, a metal wire cleanliness evaluation device is provided, comprising a charging unit and an electrostatic deflection unit arranged in sequence;

[0050] The charging unit includes a corona wire 11 and a tubular cathode plate 12, wherein the corona wire 11 is located at the axial center of the tubular cathode plate 12;

[0051] The electrostatic deflection unit includes an anode plate 21 and a cathode plate 22 . The anode plate 21 and the cathode plate 22 are arranged relatively parallel and perpendicular to the ground.

[0052] In some embodiments of the present invention, the corona wire 11 and the tubular cathode plate 12 of the charging unit are coaxial.

[0053] In some embodiments of the present invention, the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit are arranged vertically.

[0054] The metal wire cleanliness evaluation device of the present invention utilizes the corona effect to ionize local air in the charging unit to charge the particles adsorbed on the surface of the metal wire. When the metal wire containing the charged particles enters the electrostatic deflection unit and passes through the uniform electric field, the metal wire will be deflected under the action of the electric field force. The deflection angle is related to the charge of the particles on the surface of the metal wire, the electric field strength, and the quality of the metal wire in the uniform electric field area. Therefore, the cleanliness of the metal wire surface can be quantitatively evaluated through indicators related to the metal wire deflection angle.

[0055] The charging unit designed based on the corona effect makes the particles on the surface of the metal wire saturated with electricity, and the electrostatic deflection unit can flexibly adjust the deflection angle of the charged wire; based on the electrostatic principle, a quantitative relationship between cleanliness, charge and wire quality, deflection angle and electric field strength is established, and the cleanliness index is defined to achieve comparison and quantitative evaluation of the surface cleanliness of wires of different materials and wire diameters; the designed charging unit and electrostatic deflection unit are compact and small in structure, so that the device can be integrated into the back end of the wire drawing or annealing equipment, and can achieve continuous quantitative evaluation of the surface cleanliness of the metal wire.

[0056] In some embodiments of the present invention, the voltage applied to the charging unit is U c ;

[0057] Where, M is the surface roughness coefficient of the corona wire; δ is the relative density of the gas; a is the radius of the corona wire, in cm; b is the inner radius of the tubular cathode plate, in cm;

[0058] Where A is the Hamaker constant between the metal wire and the particle; d p is the equivalent diameter of the particle, in m; x is the center distance between the metal wire and the corona wire, in cm; Z is the distance between the particle and the surface of the metal wire, in nm; q s is the saturated charge of the particle, in C.

[0059] The charging unit applies voltage U c It depends on the values ​​of a, b, and x.

[0060] In some embodiments of the present invention, the length of the tubular cathode plate is l c ;

[0061] Where v is the moving speed of the metal wire, in m / s; τ is the charging time constant, in s.

[0062] The length of the tubular cathode plate must meet the requirement of saturation charging of the particles at a certain moving speed of the metal wire.

[0063] In some embodiments of the present invention, the voltage applied to the electrostatic deflection unit is U e ;

[0064] Where D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm.

[0065] Applied voltage U e It is affected by the structural parameters of the charging unit and the distance D between the deflection unit plates.

[0066] In some embodiments of the present invention, the diameter of the corona wire 11 of the charging unit is 0.2-0.3 cm; typically but not limiting, for example, the diameter of the corona wire 11 of the charging unit can be 0.2 cm, 0.25 cm, 0.3 cm or a range of any two thereof.

[0067] In some embodiments of the present invention, the length of the corona wire 11 of the charging unit is greater than or equal to the length of the tubular cathode plate 12 .

[0068] In some embodiments of the present invention, the material of the corona wire 11 of the charging unit includes stainless steel.

[0069] In some embodiments of the present invention, the cross-sectional shape of the corona wire 11 of the charging unit is circular.

[0070] In some embodiments of the present invention, the inner radius of the tubular cathode plate 12 of the charging unit is 1 to 2 cm; typically but not restrictively, for example, the inner radius of the tubular cathode plate 12 of the charging unit can be 1 cm, 1.5 cm, 2 cm or a range of any two thereof.

[0071] In some embodiments of the present invention, the length of the tubular cathode plate 12 of the charging unit is 100 to 200 mm; typically but not restrictively, for example, the length of the tubular cathode plate 12 of the charging unit can be 100 mm, 120 mm, 140 mm, 160 mm, 180 mm, 200 mm or a range of any two thereof.

[0072] In some embodiments of the present invention, the thickness of the tubular cathode plate 12 of the charging unit is 1-3 mm; typically but not limiting, for example, the thickness of the tubular cathode plate 12 can be 1 mm, 2 mm, 3 mm or a range of any two thereof.

[0073] In some embodiments of the present invention, the tubular cathode plate 12 of the charging unit is made of stainless steel or aluminum alloy.

[0074] In some embodiments of the present invention, the tubular cathode plate 12 of the charging cell is grounded.

[0075] In some embodiments of the present invention, in the electrostatic deflection unit, the width of the anode plate 21 and the cathode plate 22 is 10 to 30 cm; typically but not restrictively, for example, in the electrostatic deflection unit, the width of the anode plate 21 and the cathode plate 22 can be 10 cm, 15 cm, 20 cm, 25 cm, 30 cm or a range of any two thereof.

[0076] In some embodiments of the present invention, in the electrostatic deflection unit, the height of the anode plate 21 and the cathode plate 22 is 10 to 50 cm; typically but not restrictively, for example, in the electrostatic deflection unit, the height of the anode plate 21 and the cathode plate 22 can be 10 cm, 20 cm, 30 cm, 40 cm, 50 cm or a range of any two thereof.

[0077] In some embodiments of the present invention, in the electrostatic deflection unit, the vertical distance between the anode plate 21 and the cathode plate 22 is 2 to 3 cm; typically but not restrictively, for example, in the electrostatic deflection unit, the vertical distance between the anode plate 21 and the cathode plate 22 can be 2 cm, 2.5 cm, 3 cm or a range of any two thereof.

[0078] In some embodiments of the present invention, the thickness of the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit are independently 1 to 3 mm; typically but not restrictively, for example, the thickness of the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit can be independently 1 mm, 2 mm, 3 mm or a range of any two thereof; the thickness of the anode plate 21 and the cathode plate 22 are the same.

[0079] In some embodiments of the present invention, the material of the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit includes stainless steel.

[0080] In some embodiments of the present invention, in the charging unit, the center distance between the metal wire and the corona wire 11 is 0.35-0.45 cm; typically but not restrictively, for example, in the charging unit, the center distance between the metal wire and the corona wire 11 can be 0.35 cm, 0.4 cm, 0.45 cm or a range of any two thereof.

[0081] In some embodiments of the present invention, the voltage applied to the charging unit is 14-31 kV; typically but not limiting, for example, the voltage applied to the charging unit can be 14 kV, 20 kV, 25 kV, 31 kV or a range of any two thereof.

[0082] In some embodiments of the present invention, the voltage applied to the electrostatic deflection unit is 20-100 kV; typically but not limiting, for example, the voltage applied to the electrostatic deflection unit can be 20 kV, 40 kV, 60 kV, 80 kV, 100 kV or a range of any two thereof.

[0083] In some embodiments of the present invention, the metal wire cleanliness evaluation device further includes a first power source 3 and a second power source 4;

[0084] The corona wire 11 of the charging unit is connected to the positive electrode of the first power source 3, and the tubular cathode plate 12 of the charging unit is connected to the negative electrode of the first power source 3;

[0085] The anode plate 21 of the electrostatic deflection unit is connected to the positive electrode of the second power supply 4 , and the cathode plate 22 of the electrostatic deflection unit is connected to the negative electrode of the second power supply 4 .

[0086] In some embodiments of the present invention, the first power source 3 and the second power source 4 include a DC / DC direct current boost module.

[0087] The DC / DC direct current boost module outputs high-voltage direct current, specifically by generating low-voltage pulses through high-frequency oscillation, then boosting the voltage to a predetermined voltage value through a pulse transformer, and then obtaining high-voltage direct current through pulse rectification; the first power supply 3 and the second power supply 4 respectively power the charging unit and the electrostatic deflection unit, and are independently controlled.

[0088] In some embodiments of the present invention, the metal wire cleanliness evaluation device also includes a mobile unit; the mobile unit includes a pay-off shaft 51, a tension wheel 52, a first guide wheel 53, a driving wheel 54, a second guide wheel 55 and a take-up shaft 56 arranged in sequence; the charging unit is arranged between the first guide wheel 53 and the driving wheel 54, and the electrostatic deflection unit is arranged between the driving wheel 54 and the second guide wheel 55.

[0089] In some embodiments of the present invention, the mobile unit further includes a servo motor drive, and the pay-off shaft 51, the take-up shaft 56 and the driving wheel 54 are driven by the servo motor.

[0090] The pay-off shaft, take-up shaft and driving wheel are driven by a servo motor, and the tension wheel provides the pay-off tension; the parts of the pay-off shaft, take-up shaft, guide wheel and driving wheel that contact the surface of the metal wire are provided with an insulating coating.

[0091] In some embodiments of the present invention, the metal wire cleanliness evaluation device further includes a quantitative evaluation unit, and the quantitative evaluation unit includes a camera 61 and a computer 62 .

[0092] The camera 61 is used to take a picture of the deflection of the metal wire to obtain an image; the computer 62 is used to process the image, calculate the deflection angle of the metal wire to obtain the corresponding cleanliness.

[0093] In some embodiments of the present invention, a method for evaluating the cleanliness of a metal wire is provided, which uses the above-mentioned device for evaluating the cleanliness of a metal wire and comprises the following steps:

[0094] After the metal wire enters the charging unit to charge the particles on the surface of the metal wire, it enters the electrostatic deflection unit to be deflected, and the cleanliness of the metal wire is evaluated based on the parameters of the metal wire and the electrostatic deflection unit; wherein the parameters include the deflection angle of the metal wire.

[0095] In some embodiments of the present invention, a method for evaluating the cleanliness of a metal wire, using the above-mentioned device for evaluating the cleanliness of a metal wire, specifically comprises the following steps:

[0096] The metal wire enters the charging unit at a certain moving speed through the pay-off shaft 51, the tension wheel 52 and the first guide wheel 53 in sequence. When the metal wire passes through the charging unit, the particles on the surface of the metal wire are saturated and charged.

[0097] Then it enters the electrostatic deflection unit, and the pay-off shaft 51 and the driving wheel 54 are regulated to rotate synchronously, the take-up shaft 56 is stationary, and the second guide wheel 55 is also stationary, so that the metal wire in the electrostatic deflection unit naturally sags in a U shape, and is located in the middle position of the anode plate 21 and the cathode plate 22. The metal wire is simultaneously affected by the electric field force, gravity and support force in the uniform electric field of the electrostatic deflection unit, and deflects, so that the metal wire remains stable at a certain deflection angle;

[0098] The deflection of the metal wire in the electrostatic deflection unit is photographed by a camera 61 to obtain an image; the image is processed by a computer 62 to calculate the deflection angle of the metal wire; and the cleanliness of the metal wire is evaluated according to the deflection angle of the metal wire;

[0099] After the evaluation is finished, the second power supply 4 is turned off, the take-up shaft 56, the pay-off shaft 51 and the driving wheel 54 rotate synchronously, keep the line speed consistent, and wind the evaluated section of metal wire onto the take-up shaft 56. At this time, the new section of metal wire has been saturated and charged by the charging unit, the pay-off shaft 51 and the driving wheel 54 are regulated to rotate synchronously, the take-up shaft 56 is stationary, and the second guide wheel 55 is also stationary, so that the metal wire in the electrostatic deflection unit naturally sags in a U shape, and the second power supply 4 is turned on. The section of metal wire is in the middle position of the anode plate 21 and the cathode plate 22 and enters the uniform electric field deflection area formed by the anode and cathode plates, and deflection occurs. The section of metal wire continues to be quantitatively evaluated through the camera 61 and the computer 62. Repeating the above process can achieve continuous overall evaluation of the metal wire.

[0100] In some embodiments of the present invention, the metal wire moves in a direction parallel to the corona wire 11 and passes through the charging unit.

[0101] In some embodiments of the present invention, the metal wires include bonding wires.

[0102] In some embodiments of the present invention, the input terminals of the first power supply 3 and the second power supply 4 input a voltage of 12 to 24 V, which can ensure personnel safety.

[0103] In some embodiments of the present invention, the DC voltage U applied to the charging unit (between the corona wire 11 and the tubular cathode plate 12) is c The following relationship is satisfied:

[0104] Where U c is the DC voltage applied to the charging unit, in kV; M is the surface roughness coefficient of the corona wire; δ is the relative density of the gas; a is the radius of the corona wire, in cm; b is the inner radius of the tubular cathode plate, in cm.

[0105] The first power source applies a DC voltage U to the charging unit. c The inner radius b of the tubular cathode plate and the radius a of the corona wire should be designed to ensure that the electric field strength E generated on the surface of the corona wire a Greater than the corona initiation electric field strength E c , causing the air near the corona line to ionize, that is kV; where M is the surface roughness coefficient of the corona wire, for smooth corona wire (conductor), M=1; δ is the relative density of the gas.

[0106] For example, for a = 0.1 cm, b = 1 cm, M = 1, δ = 1, U c >13.4kV; can meet the corona discharge requirements.

[0107] See also Figure 2 , the local air near the corona wire 11 in the charging unit is ionized, and corona discharge occurs, thereby generating a large number of electrons and positive ions. The free electrons are immediately attracted by the corona wire 11 (positive electrode) and lose their charge. The positive ions move toward the tubular cathode plate 12 under the action of the electric field and fill the space between the two electrodes. When the metal wire 7 that absorbs the particles enters the charging unit at a certain moving speed, the positive ions meet the particles and attach to the particles to make the particles positively charged.

[0108] In some embodiments of the present invention, the DC voltage U applied to the charging unit (between the corona wire 11 and the tubular cathode plate 12) is c The following relationship is satisfied:

[0109] Where A is the Hamaker constant between the metal wire and the particle; d p is the equivalent diameter of the particle, in m; x is the center distance between the metal wire and the corona wire, in cm; Z is the distance between the particle and the surface of the metal wire, in nm; q s is the saturated charge of the particles, in C.

[0110] In some embodiments of the present invention, in the charging unit, the length l of the tubular cathode plate 12 is c and the moving speed v of the metal wire satisfy the following relationship:

[0111] In the formula, l cis the length of the tubular cathode plate, in mm; v is the moving speed of the metal wire, in m / s; τ is the charging time constant, in s.

[0112] The charge of a single particle in the electric field of a charging unit Among them, ε r is the relative dielectric constant of the particle, usually ranging from 2 to 8, where ε r is 5; ε0 is the dielectric constant of vacuum, ε0 is 8.85×10 -12 C 2 / N·m;d p is the particle equivalent diameter, m; U c is the DC voltage applied by the first power supply between the corona wire and the tubular cathode plate, kV; b is the inner radius of the tubular cathode plate, cm; a is the radius of the corona wire, cm; x is the center distance between the metal wire and the corona wire, cm; τ is the charging time constant, unit is s; Where N0 is the ion density, ions / m 3 ; e is the electron charge, 1.6×10 -19 C; K is the ion mobility, m 2 / s·V; under atmospheric temperature conditions, the typical distribution of N0 and K is N0=5×10 14 pcs / m 3 , K = 2.2 × 10 - 4 m 2 / (s·V), the charging time constant is τ=0.002s. When t≥10τ, the particle is saturated with charge, i.e., q p ≈q s ;q s is the saturation charge of the particles, Design the length l of the tubular cathode plate of the charging unit c , the moving speed v of the metal wire meets the saturation charge requirement of the particles, that is At the same time, the voltage U c , so that the electric field force F e No greater than the van der Waals force F v ,in, Among them, A is the Hamaker constant between the metal wire and the particle; Z is the distance between the particle and the surface of the metal wire, which usually works in the range of 0.4 to 10 nm, and Z is usually 0.4 nm; that is,

[0113] In some embodiments of the present invention, the second power supply 4 applies a DC voltage U between the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit. e The vertical distance D between the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit satisfies the following relationship:

[0114] Where U e is the DC voltage applied by the second power supply between the anode plate and the cathode plate of the electrostatic deflection unit, in kV; D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm.

[0115] The electrostatic deflection unit includes two vertically and relatively parallel electrode plates, one end of which is connected to the positive pole of the power supply, which is the anode plate, and the other end is connected to the negative pole of the power supply and grounded, which is the cathode plate; the distance between the positive and negative plates is D, and the DC voltage applied between the positive and negative plates by the second power supply is U e , resulting in a uniform electric field between the anode and cathode plates. To prevent the particles from escaping from the metal wire adsorption, the uniform electric field should be no greater than the electric field strength at the location of the metal wire in the charged unit, that is,

[0116] In some embodiments of the present invention, the cleanliness of the metal wire is evaluated according to the cleanliness index Cl, and the larger the Cl, the worse the cleanliness of the metal wire;

[0117] in, Where Cl is the cleanliness index, the unit is C / m 2 ;d w is the diameter of the metal wire, in μm; ρ is the density of the metal wire, in g / cm 3 ; g is the acceleration due to gravity, in m / s 2 , D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm; α is the deflection angle of the metal wire, in degrees; U e It is the DC voltage applied between the anode and cathode plates of the electrostatic deflection unit, in kV.

[0118] Based on the corona effect and the principle of electrostatics, the metal wire particles are charged and deflected. By defining the cleanliness index Cl and establishing the quantitative relationship between cleanliness, charge and wire quality, deflection angle and electric field strength, the quantitative evaluation of the wire surface cleanliness can be achieved. The cleanliness index Cl formula takes into account the influence of wire material, diameter and length on cleanliness, and can realize the comparison and evaluation of the cleanliness of wires of different materials, diameters and lengths.

[0119] The particles adsorbed on the surface of the metal wire in the charged unit bond are saturated and positively charged. After the surface-charged metal wire enters the electrostatic deflection area, it is deflected toward the cathode plate by the electric field force of the uniform electric field. The deflection angle is related to the electric field force and gravity acting on the metal wire in the deflection area.

[0120] See also Figure 3After the particles adsorbed on the surface of the metal wire are saturated and charged in the charging unit, they enter the electrostatic deflection unit, and the pay-off shaft and the driving wheel are regulated to rotate synchronously, while the take-up shaft is stationary, so that the metal wire in the electrostatic deflection system naturally sags in a U shape and is located in the middle of the two parallel electrode plates. e Due to the adsorption of positively charged particles, the metal wire is simultaneously subjected to an electric field force F in a uniform electric field. e , gravity and support force; the balance of these three forces will keep the metal wire stable at a certain deflection angle α. According to the force analysis diagram, F e =Gtanα, then Where G is the gravity of the sagging metal wire; d is the length of the metal wire in the deflection area; q t is the total charge of the metal wire; n is the number of particles, and the charge of the metal wire is proportional to the number of particles; d w is the diameter of the metal wire; ρ is the density of the metal wire; in the metal wire cleanliness evaluation device, the more particles adsorbed on the surface of the metal wire, the larger the particle size, and the greater the total charge. For metal wires of the same diameter and length, the greater the total charge, the worse the cleanliness; according to the charge formula, the total charge is also related to the length of the metal wire l d and diameter d w If the cleanliness of metal wires with different wire diameters and lengths is evaluated, the charge per unit surface area of ​​the metal wire can be used to express it. Among them A W =πd w l d , is the surface area of ​​the metal wire in the deflection zone; the greater the charge per unit surface area (Cl), the worse the cleanliness of the metal wire surface. Therefore, the cleanliness index can be defined by Quantitative evaluation of metal wire surface cleanliness.

[0121] The deflection area is a uniform electric field area formed by the positive and negative plates, which is used to deflect the charged metal wire. The length of the metal wire in the deflection area is l d It refers to the length of the U-shaped metal wire between the parallel anode and cathode plates. Figure 3 The length of the metal wire 7.

[0122] The operating mechanism of the electrostatic deflection unit is as follows: after the metal wire with adsorbed particles passes through the charging unit, it synchronously drives the pay-off shaft and the driving wheel to rotate with a certain tension, and keeps the take-up shaft stationary, so that the tensioned metal wire naturally droops in a U shape; then the second power supply supplies the electrostatic deflection unit with a DC high voltage U e The drooping metal wire is simultaneously subjected to electric field force, gravity, and supporting force, causing it to deflect and maintain a certain deflection angle α. The surface cleanliness of the metal wire is quantitatively evaluated by Cl.

[0123] In some embodiments of the present invention, in the charging unit:

[0124] The first power source 3 applies a DC voltage U to the charging unit. c 14~31kV;

[0125] The radius a of the corona wire 11 is 0.1 to 0.15 cm;

[0126] The length of the corona wire 11 is 120 to 240 mm, which is greater than or equal to the length of the tubular cathode plate 12;

[0127] The inner radius b of the tubular cathode plate 12 is 1 to 2 cm;

[0128] The length l of the tubular cathode plate 12 c 100~200mm;

[0129] The center distance x between the metal wire and the corona wire 11 is 0.35 to 0.45 cm;

[0130] The moving speed v of the metal wire is 0.1 to 3 m / s.

[0131] In some embodiments of the present invention, in the electrostatic deflection unit:

[0132] The second power supply applies a DC voltage U between the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit. e 20~100kV;

[0133] The width w of the anode plate 21 and the cathode plate 22 is 10 to 30 cm, preferably 10 to 20 cm;

[0134] The height h of the anode plate 21 and the cathode plate 22 is 10 to 50 cm, preferably 10 to 30 cm;

[0135] The vertical distance D between the anode plate 21 and the cathode plate 22 is 2 to 3 cm.

[0136] The charging unit applies voltage U c It is related to the values ​​of a, b, and x. When a = 0.1 cm, for b = 1 cm, x = 0.35-0.45 cm, U c The value is 14~24kV; for b=2cm, U c The value is 19~31kV; to ensure the saturation charge of the particles, the charging time t c The range of 0.02 to 0.06 s is required. Considering the convenience of equipment integration and installation, the moving speed v of the metal wire is controlled at 0.1 to 3 m / s, and the length l of the tubular cathode plate is c In the range of 100 to 200 mm; the key structural parameters of the above-mentioned charging unit can ensure dp The parallel plates in the electrostatic deflection unit are 10 to 30 cm wide, 10 to 50 cm high, 2 to 3 cm apart, and the applied voltage U e Affected by the structural parameters of the charging unit and the distance D between the deflection unit plates, it is 20 to 100 kV, thereby ensuring that the uniform electric field strength between the parallel plates in the deflection area does not exceed the electric field strength at the metal wire of the charging unit.

[0137] In some embodiments of the present invention, specific parameter settings in the metal wire cleanliness evaluation method are shown in Table 1.

[0138] Table 1

[0139]

[0140] Example 1

[0141] See also Figure 1 The bonding wire cleanliness evaluation device provided in this embodiment includes: a charging unit, an electrostatic deflection unit, a first power source 3, a second power source 4, a moving unit and a quantitative evaluation unit;

[0142] The charging unit includes a corona wire 11 and a tubular cathode plate 12, wherein the corona wire 11 is located at the axial center of the tubular cathode plate 12; the corona wire 11 is coaxial with the tubular cathode plate 12; the corona wire 11 is connected to the positive electrode of the first power source 3, and the tubular cathode plate 12 is connected to the negative electrode of the first power source 3;

[0143] The radius a of the corona wire 11 is 0.1 cm, the length is 120 mm, the material is stainless steel, and the cross-section shape is circular; the thickness of the tubular cathode plate 12 is 2 mm, the material is stainless steel, the inner radius b is 1 cm, and the length is l c 100mm;

[0144] The electrostatic deflection unit includes an anode plate 21 and a cathode plate 22, which are arranged relatively parallel and perpendicular to the ground; the anode plate 21 is connected to the positive electrode of the second power supply 4, and the cathode plate 22 is connected to the negative electrode of the second power supply 4;

[0145] The thickness of the anode plate 21 and the cathode plate 22 are both 2 mm, the width is 20 cm, the height is 20 cm, and the material is stainless steel. The vertical distance between the anode plate 21 and the cathode plate 22 is 2 cm;

[0146] The first power supply 3 and the second power supply 4 include a DC / DC direct current boost module;

[0147] The mobile unit includes a pay-off shaft 51, a tension wheel 52, a first guide wheel 53, a driving wheel 54, a second guide wheel 55 and a take-up shaft 56 which are arranged in sequence; the charging unit is arranged between the first guide wheel 53 and the driving wheel 54, and the electrostatic deflection unit is arranged between the driving wheel 54 and the second guide wheel 55;

[0148] The quantitative evaluation unit includes a camera 61 and a computer 62 .

[0149] The bonding wire cleanliness evaluation method provided in this embodiment uses the above-mentioned device and includes the following steps:

[0150] The bonding wire is passed through the pay-off shaft 51, the tension wheel 52 and the first guide wheel 53 at a speed of 1 m / s and a tension of 2 gf into the charging unit. The bonding wire moves in a direction parallel to the corona wire 11 and passes through the charging unit. In the process of passing through the charging unit, the particles on the surface of the bonding wire are saturated and charged.

[0151] The first power source 3 applies a DC voltage U to the charging unit. c This voltage is greater than the initial corona voltage of 13.4 kV when a = 0.1 cm, b = 1 cm, M = 1, and δ = 1, which is sufficient to make the electric field intensity E a Greater than the corona initiation electric field strength E c ;

[0152] In the charging unit, the bonding wire and the corona wire 11 are parallel, and the center distance between the bonding wire and the corona wire 11 is 0.35 cm; the spatial electric field intensity here is 18.6 kV / cm, which not only prevents the air gap between the bonding wire and the corona wire from being broken down and burning the bonding wire, but also ensures that the particles on the surface of the bonding wire are effectively charged;

[0153] The length l of the tubular cathode plate of the charging unit c 100mm, which can meet the saturation charge requirement of the particles for the bonding wire moving speed below 3m / s; for the particle equivalent diameter d p The bonding wire passes through a 100mm long tubular cathode plate at a speed of 1m / s. To ensure that the electric field force F e No greater than the van der Waals force F v , then it is required that U c ≤26.9V; therefore U c 15kV fully meets this requirement;

[0154] After passing through the charging unit, the bonding wire enters the electrostatic deflection unit, and the pay-off shaft 51 and the driving wheel 54 are regulated to rotate synchronously, and the take-up shaft 56 is stationary, so that the bonding wire in the electrostatic deflection unit naturally sags in a U shape and is located in the middle of the anode plate 21 and the cathode plate 22;

[0155] The second power supply applies a DC voltage U between the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit. e The voltage is 35 kV, and the vertical distance D between the anode plate 21 and the cathode plate 22 is 2 cm. The uniform electric field (17.5 kV / cm) meets the requirement that the electric field strength at the bonding wire in the charged unit is not greater than (18.6 kV / cm).

[0156] A high voltage U is applied between the anode plate 21 and the cathode plate 22. e Due to the adsorption of positively charged particles, the bonding wire is simultaneously subjected to an electric field force F in a uniform electric field. e , gravity and supporting force, the three forces balance will cause the bonding wire to deflect toward the cathode plate 22, so that the bonding wire remains stable at a certain deflection angle;

[0157] Then, the camera 61 is used to take a picture of the deflection of the bonding wire, and the computer 62 processes the image obtained by the picture to calculate the deflection angle α of the bonding wire.

[0158] The key structural parameters of the bonding wire cleanliness evaluation device are a = 0.1 cm, b = 1 cm, x = 3.5 cm, U c =15kV, U e =35kV, D=2cm.

[0159] The first case: For Pure silver bonding wire, bonding wire length in deflection zone l d The length of the bond wire is 20 cm, the deflection angle α is 12°, and the total charge of the bond wire is q t 7.84×10 -13 C, 283 d p For particles of 5 μm, Cl = 6.25 × 10 -8 C / m 2 ;

[0160] The second case: For Pure silver bonding wire, bonding wire length in deflection zone l d is 20cm, the deflection angle α is 30°, and the total charge q of this section of bonding wire is t 2.13×10 -12 C, 770 5μm particles are adsorbed on the surface of the bonding wire, Cl = 1.70×10 -7 C / m 2 ;

[0161] The third case: For Pure silver bonding wire, bonding wire length in deflection zone l d is 30cm, the deflection angle α is 10°, and the total charge q of this section of bonding wire is t 1.02×10-12 C, which is equivalent to 367 d adsorbed on the surface of the bonding wire. p For particles of 5 μm, Cl = 6.48 × 10 -8 C / m 2 ;

[0162] The cleanliness indexes Cl of the above three cases are 6.25×10 -8 C / m 2 , 1.7×10 -7 C / m 2 , 6.48×10 - 8 C / m 2 , indicating that among the bonding wire cleanliness evaluation methods, the first case has the best cleanliness, the third is second, and the second is the worst.

[0163] After the evaluation is completed, the second power supply 4 is disconnected, and the take-up shaft 56, the pay-off shaft 51 and the driving wheel 54 rotate synchronously to keep the line speed consistent. After the next section of the bonding wire enters the deflection area of ​​the electrostatic deflection unit, the section is continuously evaluated and the above process is repeated to achieve continuous overall evaluation of the bonding wire.

[0164] Evaluation effect:

[0165] Since there is currently a lack of quantitative evaluation methods for bonding wire cleanliness, the three situations in this embodiment are qualitatively verified using traditional visual methods. The results are as follows: Figure 4 As shown; Figure 4 (a) is the first case; Figure 4 (b) is the second case; Figure 4 (c) is the third case. Figure 4 The following are three images of the bonding wire surface taken with a stereo microscope. From the figure, we can see that there are bright spots on the wire surface, which are caused by the adsorbed surface particles making the wire surface uneven. Figure 4 (a) has relatively few bright spots, indicating that there are fewer adsorbed particles and the cleanliness is relatively the best. Figure 4 (b) has the most bright spots, indicating the most adsorbed particles and the worst cleanliness. The above qualitative analysis results are consistent with the quantitative evaluation results in this example, indicating the effectiveness and correctness of this method.

[0166] Example 2

[0167] See also Figure 1 The bonding wire cleanliness evaluation device provided in this embodiment includes: a charging unit, an electrostatic deflection unit, a first power source 3, a second power source 4, a moving unit and a quantitative evaluation unit;

[0168] The charging unit includes a corona wire 11 and a tubular cathode plate 12, wherein the corona wire 11 is located at the axial center of the tubular cathode plate 12; the corona wire 11 is coaxial with the tubular cathode plate 12; the corona wire 11 is connected to the positive electrode of the first power source 3, and the tubular cathode plate 12 is connected to the negative electrode of the first power source 3;

[0169] The radius a of the corona wire 11 is 0.1 cm, the length is 120 mm, the material is stainless steel, and the cross-sectional shape is circular; the thickness of the tubular cathode plate 12 is 2 mm, the material is stainless steel, the inner radius b is 2 cm, and the length is l c 100mm;

[0170] The electrostatic deflection unit includes an anode plate 21 and a cathode plate 22, which are arranged relatively parallel and perpendicular to the ground; the anode plate 21 is connected to the positive electrode of the second power supply 4, and the cathode plate 22 is connected to the negative electrode of the second power supply 4;

[0171] The thickness of the anode plate 21 and the cathode plate 22 are both 2 mm, the width is 20 cm, the height is 30 cm, and the material is stainless steel. The vertical distance between the anode plate 21 and the cathode plate 22 is 2 cm;

[0172] The first power supply 3 and the second power supply 4 include a DC / DC direct current boost module;

[0173] The mobile unit includes a pay-off shaft 51, a tension wheel 52, a first guide wheel 53, a driving wheel 54, a second guide wheel 55 and a take-up shaft 56 which are arranged in sequence; the charging unit is arranged between the first guide wheel 53 and the driving wheel 54, and the electrostatic deflection unit is arranged between the driving wheel 54 and the second guide wheel 55;

[0174] The quantitative evaluation unit includes a camera 61 and a computer 62 .

[0175] The bonding wire cleanliness evaluation method provided in this embodiment uses the above-mentioned device and includes the following steps:

[0176] The bonding wire is passed through the pay-off shaft 51, the tension wheel 52 and the first guide wheel 53 at a speed of 0.5 m / s and a tension of 2 gf into the charging unit. The bonding wire moves in a direction parallel to the corona wire 11 and passes through the charging unit. In the process of passing through the charging unit, the particles on the surface of the bonding wire are saturated and charged.

[0177] The first power source 3 applies a DC voltage U to the charging unit. c 30kV; this voltage is greater than the initial corona voltage of 17.5kV when a = 0.1cm, b = 2cm, M = 1, δ = 1, which is enough to make the electric field intensity E a Greater than the corona initiation electric field strength E c ;

[0178] In the charging unit, the bonding wire and the corona wire 11 are parallel, and the center distance between the bonding wire and the corona wire 11 is 0.4 cm; the spatial electric field intensity here is 25.0 kV / cm, which not only prevents the air gap between the bonding wire and the corona wire from being broken down and burning the bonding wire, but also ensures that the particles on the surface of the bonding wire are effectively charged;

[0179] The length l of the tubular cathode plate of the charging unit c 100mm, which can meet the saturation charge requirement of the particles for the bonding wire moving speed below 3m / s; for the particle equivalent diameter d p The bonding wire passes through a 100mm long tubular cathode plate at a speed of 0.5m / s. To ensure that the electric field force F e No greater than the van der Waals force F v , then it is required that U c ≤40.0kV; therefore U c 30kV fully meets this requirement;

[0180] After passing through the charging unit, the bonding wire enters the electrostatic deflection unit, and the pay-off shaft 51 and the driving wheel 54 are regulated to rotate synchronously, and the take-up shaft 56 is stationary, so that the bonding wire in the electrostatic deflection unit naturally sags in a U shape and is located in the middle of the anode plate 21 and the cathode plate 22;

[0181] The second power supply applies a DC voltage U between the anode plate 21 and the cathode plate 22 of the electrostatic deflection unit. e The voltage is 40 kV, and the vertical distance D between the anode plate 21 and the cathode plate 22 is 2 cm. The uniform electric field (20 kV / cm) meets the requirement that the electric field strength at the bonding wire in the charged unit is not greater than (25.0 kV / cm).

[0182] A high voltage U is applied between the anode plate 21 and the cathode plate 22. e Due to the adsorption of positively charged particles, the bonding wire is simultaneously subjected to an electric field force F in a uniform electric field. e , gravity and supporting force, the three forces balance will cause the bonding wire to deflect toward the cathode plate 22, so that the bonding wire remains stable at a certain deflection angle;

[0183] Then, the camera 61 is used to take a picture of the deflection of the bonding wire, and the computer 62 processes the image obtained by the picture to calculate the deflection angle α of the bonding wire.

[0184] The key structural parameters of the bonding wire cleanliness evaluation device are a = 0.1 cm, b = 2 cm, x = 4.0 cm, U c =30kV, U e =40kV, D=2cm.

[0185] The first case: For Pure silver bonding wire, bonding wire length in deflection zone ld The length of the bond wire is 25 cm, the deflection angle α is 15°, and the total charge of the bond wire is q t 1.69×10 -12 C, 397 d p For particles of 5 μm, Cl = 8.62 × 10 -8 C / m 2 ;

[0186] The second case: For Pure silver bonding wire, bonding wire length in deflection zone l d The length of the bond wire is 25 cm, the deflection angle α is 18°, and the total charge of the bond wire is q t 1.31×10 -12 C, 308 5μm particles are adsorbed on the surface of the bonding wire, Cl = 8.36×10 -8 C / m 2 ;

[0187] The third case: For Pure silver bonding wire, bonding wire length in deflection zone l d is 30cm, the deflection angle α is 15°, and the total charge q of this section of bonding wire is t 1.05×10 -12 C, which is equivalent to 247 d adsorbed on the surface of the bonding wire. p For particles of 5 μm, Cl = 9.31 × 10 -8 C / m 2 ;

[0188] The cleanliness indexes Cl of the above three cases are 8.62×10 -8 C / m 2 ,8.36×10 -8 C / m 2 ,9.31×10 - 8 C / m 2 , indicating that in this bonding wire cleanliness evaluation method, the second case has the best cleanliness, the first case is second, and the third case has the worst cleanliness.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A metal wire cleanliness evaluation device, characterized in that: It includes a charging unit and an electrostatic deflection unit which are arranged in sequence; The charging unit comprises a corona wire and a tubular cathode plate, wherein the corona wire is located at the axial center of the tubular cathode plate; The electrostatic deflection unit comprises an anode plate and a cathode plate, wherein the anode plate and the cathode plate are arranged in parallel with each other and perpendicular to the ground.

2. The metal wire cleanliness evaluation device according to claim 1, characterized in that: The voltage applied to the charging unit is U c ; Where, M is the surface roughness coefficient of the corona wire; δ is the relative density of the gas; a is the radius of the corona wire, in cm; b is the inner radius of the tubular cathode plate, in cm; Where A is the Hamaker constant between the metal wire and the particle; d p is the equivalent diameter of the particle, in m; x is the center distance between the metal wire and the corona wire, in cm; Z is the distance between the particle and the surface of the metal wire, in nm; q s is the saturated charge of the particle, in C.

3. The metal wire cleanliness evaluation device according to claim 1, characterized in that: The length of the tubular cathode plate is l c ; Where v is the moving speed of the metal wire, in m / s; τ is the charging time constant, in s.

4. The metal wire cleanliness evaluation device according to claim 2, characterized in that: The voltage applied to the electrostatic deflection unit is U e ; Where D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm.

5. The metal wire cleanliness evaluation device according to claim 1, characterized in that: The method comprises at least one of the following features (1) to (9); (1) The diameter of the corona wire is 0.2 to 0.3 cm; (2) The inner radius of the tubular cathode plate is 1 to 2 cm; (3) The length of the tubular cathode plate is 100 to 200 mm; (4) The width of the anode plate and the cathode plate is 10 to 30 cm; (5) The height of the anode plate and the cathode plate is 10 to 50 cm; (6) The vertical distance between the anode plate and the cathode plate is 2 to 3 cm; (7) In the charging unit, the center distance between the metal wire and the corona wire is 0.35 to 0.45 cm; (8) The voltage applied to the charging unit is 14 to 31 kV; (9) The voltage applied to the electrostatic deflection unit is 20 to 100 kV.

6. A method for evaluating the cleanliness of a metal wire, characterized in that: The metal wire cleanliness evaluation device according to any one of claims 1 to 5 comprises the following steps: After the metal wire enters the charging unit to charge the particles on the surface of the metal wire, it enters the electrostatic deflection unit to be deflected, and the cleanliness of the metal wire is evaluated according to the parameters of the metal wire and the electrostatic deflection unit; wherein the parameters include the deflection angle of the metal wire.

7. The method for evaluating the cleanliness of a metal wire according to claim 6, characterized in that: The following relationship is satisfied: Where U c is the DC voltage applied to the charging unit, in kV; M is the surface roughness coefficient of the corona wire; δ is the relative density of the gas; a is the radius of the corona wire, in cm; b is the inner radius of the tubular cathode plate, in cm; Where A is the Hamaker constant between the metal wire and the particle; d p is the equivalent diameter of the particle, in m; x is the center distance between the metal wire and the corona wire, in cm; Z is the distance between the particle and the surface of the metal wire, in nm; q s is the saturated charge of the particles, in C.

8. The method for evaluating the cleanliness of a metal wire according to claim 7, characterized in that: The following relationship is satisfied: In the formula, l c is the length of the tubular cathode plate, in mm; v is the moving speed of the metal wire, in m / s; τ is the charging time constant, in s.

9. The method for evaluating the cleanliness of a metal wire according to claim 7, characterized in that: The following relationship is satisfied: Where U e is the DC voltage applied between the anode plate and the cathode plate of the electrostatic deflection unit, in kV; D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm.

10. The method for evaluating the cleanliness of a metal wire according to claim 6, characterized in that: The cleanliness of the metal wire is evaluated according to the cleanliness index Cl. The larger the Cl, the worse the cleanliness of the metal wire. in, Where Cl is the cleanliness index, the unit is C / m 2 ;d w is the diameter of the metal wire, in μm; ρ is the density of the metal wire, in g / cm 3 ; g is the acceleration due to gravity, in m / s 2 ; D is the vertical distance between the anode plate and the cathode plate of the electrostatic deflection unit, in cm; α is the deflection angle of the metal wire, in degrees; U e It is the DC voltage applied between the anode and cathode plates of the electrostatic deflection unit, in kV.

Images