A speckle device for wire bonding machine and control method thereof

Abstract

The present invention discloses a speckle device for a wire bonding machine and a control method thereof, the device comprises: a T-shaped three-way lens barrel, a beam splitter, an adjustable lens group, a laser, a digital imaging module and an image recording and processing module; the T-shaped three-way lens barrel is provided with a side-through section and a straight-through section, the straight-through section is provided with a first opening end and a second opening end, the beam splitter is located in the three-way lens barrel, and forms a 45-degree angle with the optical axis of the straight-through section, the digital imaging module records a laser speckle digital picture containing the surface features of the arc to be measured, the adjustable lens group focuses and adjusts the laser spot irradiated on the arc, the image recording and processing module receives the laser speckle digital picture in different states, performs conversion and analysis between the spatial domain and the spatial frequency domain, and obtains spatial shape and position change information and the spatial shape and position continuous change trend of the arc to be measured. The present invention can convert tiny spatial scale changes into obvious changes in the spatial frequency domain and measure them, and improves the measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of wire bonding detection, and in particular to a speckle device for a wire bonding machine and a control method thereof, which are suitable for geometric shape, position and displacement detection of micro-scale objects. Background Art

[0002] Speckle measurement technology is mainly used in the field of photomechanics for full-field deformation measurement and analysis of specimens. Generally, the main feature of the optical path of this technology is to irradiate the specimen over a large area with a divergent light beam that is expanded and can cover the specimen. The speckle pattern is recorded by a camera, and the speckle pattern of the test piece before and after loading is used for data processing to perform digital operations to obtain an interference fringe pattern containing the in-plane and out-of-plane displacement information of the beam-irradiated surface. The fringe order represents the displacement difference of the "pair point", and then the phase diagram is obtained through phase shift technology, and the displacement information is restored by "unwrapping".

[0003] Speckle shearing technology is the mainstream technology for speckle measurement in recent years. It divides the speckle light path of the test piece into two beams with different phase characteristics, and then superimposes them at the camera. The camera directly records the interference pattern after the superposition of the speckle pattern. If there are surface defects on the object, the phase line of the interference pattern after the two beams are superimposed will be distorted compared with the phase line of the defect-free area, thereby obtaining defect information.

[0004] GB / T 34886-2017 (Nondestructive Testing of Composite Materials by Laser Dislocation Speckle Detection Method) specifies the laser dislocation speckle detection method for composite materials. The characteristic of its measurement optical path is that the laser is diverged at a large angle by using a beam expander to illuminate the object to be measured, and then the speckle carrying the surface information of the object to be measured is divided into two beams, which are superimposed and received at the camera after being dislocated. What the camera actually receives is the interference pattern (shearing speckle) of the two beams of dislocation and superimposed speckle. The interference pattern has the typical "butterfly" interference pattern characteristics, and then the off-surface displacement information is obtained by "unwrapping" according to the interference pattern. This method is suitable for the detection of defects such as bulges and depressions on the surface of large plates and components such as laminates, honeycomb sandwich components, and foam boards. And because the coverage range of the beam is too large after beam expansion, the speckle of irrelevant measurement objects will interfere with the speckle of small-scale objects to be measured. Therefore, the speckle detection method with similar characteristics of beam expansion light source cannot detect small-scale objects to be measured.

[0005] Among the existing speckle measurement schemes, there are ultrafast digital speckle systems and experimental methods based on pulsed lasers, which use impact test methods to test the ultra-high strain mechanical properties of samples, thereby improving the rapid response capabilities of the lighting and imaging systems, but the scope of application is still for larger sample components, and a beam expander is explicitly used in the optical path; there are also methods, devices and equipment for speckle calibration, which are methods for identifying the 3D contour of an object using speckle. Since the surface of the object is at different angles to the optical axis of the emitted light, the phase of the reflected light beam in different surface areas changes greatly. Therefore, it is necessary to use a diffraction element to form a characteristic speckle, then irradiate it on a calibration plate, and compare the speckle pattern projected on the calibration plate with the standard pattern to obtain the curvature, lateral angle, distance, size and other data of the object surface for calibration. This method is aimed at the field of surface reconstruction of larger-sized 3D objects, not for micro-scale measurements.

[0006] Wire bonding is a technology that uses thin metal wires with a diameter of about 20 to 80 μm, and uses heat, pressure, and ultrasonic energy to weld the metal wires to the chip frame pads to achieve electrical interconnection between the chip and the frame and information exchange between chips. Wire bonding machines are special equipment used to complete the wire bonding process. At present, the method for measuring wire bonding arcs is to measure the images after microscope imaging. Because the wire wires are extremely thin, the magnification of the microscope is required to be high, which restricts the observation range accordingly. With the development of chip functions, the density of I / O ports on chips is getting larger and larger, and the lead size is getting smaller and smaller. The displacement and deformation of the bonding wire arc affect the chip reliability. In addition, the bonding package with multiple rows of leads has complex spatial positions of the leads, which makes it more difficult to focus and image using a microscope.

[0007] The existing optical microscopic measurement method is still based on the optical microscope, and the scale conversion relationship between the image space and the actual space is obtained by referring to the ruler for measurement. The total magnification of the microscope = eyepiece × objective lens magnification, the magnification is about 40 times-1600 times, and the range suitable for observation and measurement is between 200nm-2000μm. Among them, the objective lens is the main component to improve the resolution of the observed object, but the working distance of the objective lens is negatively correlated with its magnification. The working distance of the 40× objective lens is less than 1mm, which greatly restricts the magnification limit of the optical microscope. When measuring opaque objects, it is necessary to use reflected lighting, and it is necessary to reserve enough working distance for the light source to cover the object to be measured. This limitation will result in the actual magnification of the optical microscope system with reflected lighting is not high, and the measurement accuracy of the micrometer scale is much lower than that of the optical microscope system with transmitted lighting. In addition, due to the high processing accuracy requirements of the lenses in the imaging system, affected by aberrations, it is impossible to measure with the same conversion scale and conversion accuracy in the entire image space.

[0008] In summary, due to the limited space in the wire bonding machine, it is not realistic to arrange a set of microscopic imaging devices in addition to the existing operation observation microscope for wire arc measurement. Therefore, it is necessary to innovatively solve the problem of extremely fine wire movement and deformation measurement in such a small space. Summary of the invention

[0009] In order to overcome the defects and shortcomings of the prior art, the present invention provides a speckle device for a wire bonding machine and a control method thereof. The present invention can convert tiny spatial scale changes into obvious changes in the spatial frequency domain and measure them, thereby reducing the secondary impact on the light field information caused by the aperture edge diffraction of the light-transmitting element in the optical path, and can also reduce the measurement errors caused by illumination at different angles.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] The present invention provides a speckle device for a wire bonding machine, comprising: a T-shaped three-way lens barrel, a beam splitter lens, an adjustable lens group, a laser, a digital imaging module and an image recording and processing module;

[0012] The T-shaped three-way lens barrel is provided with a side section and a straight section, one end of the side section is connected to the straight section, the other end of the side section is provided with an open end, the straight section is provided with a first open end and a second open end, the first open end points to the arc to be measured, and the second open end points to the digital imaging module;

[0013] The laser is used to generate a laser beam, and the laser beam is injected into the open end of the side passage section of the T-shaped three-way lens barrel;

[0014] The beam splitter is located in the three-way lens barrel, at the connection between the straight section and the side section, and forms an angle of 45° with the optical axis of the straight section. The beam splitter is used to reflect the laser beam incident from the opening end of the side section to the first opening end of the straight section. The laser emitted from the first opening end of the straight section is reflected by the surface of the arc to be measured to form surface scattered light. The surface scattered light is collected by the first opening end of the straight section of the T-shaped three-way lens barrel and then re-enters the T-shaped three-way lens barrel. It is transmitted on the beam splitter according to the transmission direction and reaches the second opening end of the straight section of the T-shaped three-way lens barrel.

[0015] The digital imaging module is used to record a laser speckle digital image containing the surface features of the arc to be measured;

[0016] One side of the adjustable lens group is connected to the open end of the side pass section, and the other side is connected to the laser. The adjustable lens group moves in the direction of the optical axis of the side pass section of the T-shaped three-way lens barrel to adjust the focus of the laser spot irradiated on the line arc;

[0017] The image recording and processing module is connected to the digital imaging module, and is used to receive laser speckle digital images in different states, and adopt the Fourier analysis method to perform conversion and analysis between the spatial domain and the spatial frequency domain based on the inverse proportional scale transformation relationship from the spatial domain to the spatial frequency domain of the spatial light information, so as to obtain the spatial shape and position change information and the spatial shape and position continuous change trend of the line arc to be measured.

[0018] As a preferred technical solution, the adjustable lens group includes a single lens and a displacement adjustment component. The position of the single lens is adjusted by the displacement adjustment component so that the laser beam emitted from the first opening end of the straight-through section end is focused on the line arc to be measured with a smaller spot.

[0019] As a preferred technical solution, the adjustable lens group adopts a collimating lens group to focus the laser beam irradiated on the surface of the arc to be measured.

[0020] The present invention also provides a control method for a speckle device for a wire bonding machine, provided with the above-mentioned speckle device for a wire bonding machine, comprising the following steps:

[0021] The digital imaging module records the light field distribution of the speckle on a plane perpendicular to the normal of the reflecting surface. The image recording and processing module uses the angular spectrum theory of diffraction to inversely analyze the propagation characteristics of the light beam to obtain the shape characteristics of the arc to be measured.

[0022] Using the laser speckle digital image of the surface of the arc to be measured, the geometric shape and position change data of the points on the arc to be measured under different states are calculated;

[0023] The displacement of the measured arc is measured and calibrated.

[0024] As a preferred technical solution, the change data of the geometric shape and position of the points on the same measured arc under different states are calculated, and the specific steps include:

[0025] The digital imaging module records the speckle light field distribution u(x, y). When the measured arc undergoes an in-plane displacement (Δx, Δy), the speckle distribution v(x, y) is recorded, which can be expressed as:

[0026] v(x,y)=u(x-Δx,y-Δy)

[0027] U(x f ,y f )、V(x f ,y f ) functions are the Fourier transforms of u(x, y) and v(x, y), respectively. f ,y f is the spatial frequency domain coordinate, we have:

[0028]

[0029] According to the definition of the cross-correlation function and the convolution theorem, the Fourier transform of the cross-correlation function R(x f ,y f )for:

[0030]

[0031] Where V * (x f ,y f ) is V(x f ,y f ) conjugate, U * (x f ,y f ) is U(x f ,y f ), let F(x f ,y f )=U(x f ,y f ) * (x f ,y f ), using the inverse Fourier transform, we get the correlation function r:

[0032] r(x,y)=F(x,y)*δ(x-Δx,y-Δy)

[0033] δ(x, y) is the impulse function. From the autocorrelation property, we can get the coordinates (Δx, Δy) of the peak value of the above formula F(x, y), thereby obtaining the in-plane displacement of the object.

[0034] As a preferred technical solution, the displacement of the arc to be measured is measured and calibrated, and the specific steps include:

[0035] Record the original laser speckle digital image of the arc to be measured and the laser speckle digital image taken after horizontal displacement;

[0036] The cross-correlation calculation is performed on the displaced laser speckle digital image and the original laser speckle digital image one by one, and the coordinate information of the peak value of the calculated correlation function on the two-dimensional image is obtained;

[0037] The known laser beam size and imaging element working distance parameters are used to convert the displacement direction of the actual arc to be measured and the conversion relationship between the spatial displacement of the arc to be measured corresponding to each pixel;

[0038] Deviation correction is performed by setting the angular spectrum calibration coefficient, or by expanding the laser beam, or by shortening the working distance of the imaging element to correct the system error.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] (1) The present invention allows the laser speckle reflected from the surface of the lead to be measured to pass through a transmission distance much greater than the laser wavelength, and then the optical field distribution of the speckle is recorded by an optoelectronic digital imaging module (CCD or CMOS) in a plane perpendicular to the normal of the arc reflection surface to be measured; then, the Fourier analysis method is used to utilize the inverse proportional scale transformation relationship from the spatial domain to the spatial frequency domain of spatial light information to convert the tiny spatial domain size change and displacement change into a larger scale relationship in the spatial frequency domain for measurement and recording. The present invention solves the technical problems of low optical microscope measurement resolution and measurement accuracy affected by illumination angle, wavelength, etc. in the reflective lighting system, and can convert tiny spatial scale changes into obvious changes in the spatial frequency domain and measure them; at the same time, the present invention also solves the problem of too small working distance from the objective lens to the lead to be measured in the wire bonding machine, which affects the bonding process.

[0041] (2) In terms of measurement content, the present invention can also use the unique laser speckle pattern on the surface of the object to be measured to perform relevant calculations to obtain the change data of the geometric shape and position of a specific point on the same object to be measured under different states. In comparison, the measurement method of optical imaging can only identify the general contour changes of the object to be measured, and cannot accurately record the spatial movement of a specific point on the object to be measured.

[0042] (3) In terms of optical path design, since the size of the optoelectronic imaging device is very small compared to the distance between it and the sample to be measured, when the reflected signal of the sample to be measured is received, the light beam is incident in the normal direction of the reflective surface of the object to be measured. In addition, the CCD or CMOS digital imaging module can directly receive the lower-order signal (near axis) in the modulated light field formed after being scattered by the lead surface, reducing the secondary impact of the aperture edge diffraction of the light-transmitting element in the optical path on the light field information, and can also reduce the measurement error caused by illumination at different angles.

[0043] (4) Since the pattern acquisition process does not involve an optical lens, the present invention is not affected by aberrations during measurement, thereby improving measurement accuracy.

[0044] (5) In terms of operation, the laser speckle information obtained by the detection method of the present invention mainly comes from the surface of the object to be measured, and is mainly related to the number and size of effective speckles received by the digital imaging module (CCD or CMOS). The measurement results are all determined by the calculation results, avoiding errors caused by human judgment. At the same time, in order to solve the contradiction between the measurement range and the measurement accuracy, the present invention also provides a pair of adjustable lens groups for adjusting the waist position of the laser beam incident on the lead sample to be measured. Since the Gaussian beam is approximately parallel within the Rayleigh length, a larger waist radius corresponds to a longer Rayleigh length. Therefore, for the measurement objects at different distances, in order to meet the far-field diffraction conditions, it is necessary to adjust the waist of the Gaussian beam so that the laser beam incident on the sample surface maintains better collimation. By comprehensively adjusting the beam size and the working distance of the imaging element, the constraint relationship between the measurement range and the measurement accuracy of the device is solved. Compared with the optical microscopic measurement technology that switches the measurement range and accuracy by replacing the objective lens and the eyepiece, the operation is more convenient and cost-saving, and the overall space occupation is small, and the installation position is flexible. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic structural diagram of a speckle device for a wire bonding machine according to the present invention;

[0046] Figure 2 It is a schematic diagram of the working principle of the speckle device of the present invention;

[0047] Figure 3 A schematic diagram of the reflected light field obtained by irradiating a metal filament with a laser beam according to the present invention;

[0048] Figure 4 (a) is a schematic diagram of the original speckle pattern of the metal lead of the present invention;

[0049] Figure 4 (b) is a schematic diagram of the speckle pattern recorded when the lead wire is displaced 50 μm in the horizontal direction of the present invention;

[0050] Figure 4 (c) is a schematic diagram of the speckle pattern recorded when the lead wire of the present invention is displaced 100 μm in the horizontal direction;

[0051] Figure 5 A schematic diagram showing the comparison between the displacement measurement result of the present invention and the calibration line;

[0052] Among them, 1-T-type three-way lens barrel, 2-beam splitter lens, 3-adjustable lens group, 4-laser, 5-digital imaging module, 6-image recording and processing module, 11-incident laser, 22-surface scattered light, 33-line arc to be measured. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0054] Example

[0055] like Figure 1 , Figure 2 As shown, this embodiment provides a speckle device for a wire bonding machine, comprising: a T-shaped three-way lens barrel 1, a beam splitter lens 2, an adjustable lens group 3, a laser 4, a digital imaging module 5, and an image recording and processing module 6;

[0056] The T-type three-way lens barrel 1 is provided with a side-through section and a straight-through section, the opening end of the side-through section is A, and the straight-through section has two opening ends, namely, a first opening end B and a second opening end C. The beam splitter 2 is located in the three-way lens barrel, and the beam splitter is located at the connection between the straight-through section and the side-through section, and forms an angle of 45° with the optical axis of the straight-through section. The first surface of the beam splitter is used to reflect the laser beam incident from the opening end of the side-through section to the first opening end B of the straight-through section; the laser emitted from the first opening end B of the straight-through section is reflected by the surface of the arc 33 to be measured to form surface scattered light 22, and the surface scattered light 22 is collected by the first opening end B of the straight-through section of the T-type three-way lens barrel and re-enters the T-type three-way lens barrel, and is transmitted on the beam splitter 2 according to the transmission direction, and reaches the second opening end C of the T-type three-way lens barrel, and is recorded by the digital imaging module 5 as a laser speckle digital image containing the surface features of the arc to be measured.

[0057] One side of the adjustable lens group 3 is connected to the side through section opening end A, and the other side is connected to the laser 4. The through section opening end B points to the target to be measured, and the through section opening end C is connected to the digital imaging module 5. The digital imaging module 5 and the image recording and processing module 6 are electrically connected.

[0058] Combination Figure 2 As shown, the incident laser 11 emitted by the laser 4 is incident from the side end A of the T-type three-way barrel after passing through the adjustable lens group 3. Since the laser emitted by the laser is a Gaussian beam, after a certain distance of transmission, the laser beam will increase according to the law of far-field divergence angle with distance. Therefore, when using it, it is also necessary to use the adjustable lens group to move in a small range in the direction of the optical axis of the side pass section of the T-type three-way barrel to focus and adjust the laser spot irradiated on the arc. Usually, the adjustable lens group is composed of a single lens and a small displacement adjustment component, and a collimator group with better performance can also be used. For the former, by adjusting the position of the single lens through the small displacement adjustment component, the laser beam emitted from the first open end of the straight-through section can be focused on the target to be measured with a smaller spot; the collimator group is used for lasers with divergent characteristics such as fiber lasers. Regardless of which of the above means is used, the laser beam irradiated on the target to be measured is focused.

[0059] Due to the coherence of the laser and the roughness of the surface of the object to be tested in the laser wavelength range, the digital imaging module records a high-contrast particle pattern signal containing the surface features of the arc to be tested, and sends it to the image recording and processing module. The image recording and processing module calculates the particle patterns of the arc to be tested in different states, sets the parameters such as the acquisition time and image resolution of the particle patterns; converts and analyzes the particle patterns of the same object to be tested in different states in the spatial domain and the spatial frequency domain, and then extracts the operation parameters to obtain its spatial shape and position change information. Similarly, by processing the particle patterns within a time interval, the continuous change trend of the spatial shape and position of the arc to be tested can be obtained.

[0060] In this embodiment, specific implementation steps of the speckle device for a wire bonding machine include:

[0061] S1: After the laser speckle reflected from the surface of the lead to be tested has a transmission distance far greater than the laser wavelength, the light field distribution of the speckle is recorded by the digital imaging module (CCD or CMOS) on a plane perpendicular to the normal of the reflection surface. Generally speaking, when the object to be tested has a large radius of curvature at the focal point of the laser beam, its reflection surface is approximately a plane, the light intensity of the reflected light spot has a distribution symmetrical to the optical axis, and has the characteristic of equal statistical dimensions in all directions of spatial distribution on the plane parallel to the reflection surface. When the object to be tested is a filament with cylindrical features and a diameter close to the size of the incident light beam, the distance from each point on its surface to the optoelectronic digital imaging module varies in the order of the wavelength, and the angle between the tangent of each point and the optical axis decreases with the increase of the distance from the optical axis. Therefore, the reflected light spot has the characteristic of being perpendicular to the axial direction of the cylindrical object to be tested and stretched to both sides, and the smaller the filament diameter, the longer the reflected light spot is stretched. This feature can be regarded as the result of the surface profile of the cylindrical sample adjusting the reflected light beam. The propagation characteristics of the light beam are analyzed using the angular spectrum theory of diffraction, and then the shape characteristics of the object to be tested are obtained.

[0062] S2: Using the unique laser speckle pattern on the surface of the object to be measured, relevant calculations are performed to obtain the change data of the geometric shape and position of a specific point on the same object to be measured under different states, as follows:

[0063] The speckle light field distribution u(x, y) is recorded at the digital imaging module, and the speckle distribution v(x, y) is recorded when the object undergoes an in-plane displacement (Δx, Δy):

[0064] v(x,y)=u(x-Δx,y-Δy)

[0065] U(x f ,y f )、V(x f ,y f) functions are the Fourier transforms of u(x, y) and v(x, y), respectively. f ,y f is the spatial frequency domain coordinate, we have:

[0066]

[0067] According to the definition of the cross-correlation function and the convolution theorem, the Fourier transform of the cross-correlation function R(x f ,y f )for:

[0068]

[0069] Where V * (x f ,y f ) is V(x f ,y f ) conjugate, U * (x f ,y f ) is U(x f ,y f ), let F(x f ,y f )=U(x f ,y f ) * (x f ,y f ). Using the inverse Fourier transform, we get the correlation function r:

[0070] r(x,y)=F(x,y)*δ(x-Δx,y-Δy)

[0071] δ(x, y) is the impulse function. From the autocorrelation property, we can know that the in-plane displacement of the object can be obtained by obtaining the coordinates (Δx, Δy) of the peak value of the above formula F(x, y).

[0072] The present embodiment defines the "imaging element working distance" of the device as the distance between the digital imaging module and the object to be measured. A smaller irradiation beam and a farther imaging element working distance can both reduce the number of received speckles and increase their size, thereby enhancing the resolution and measurement sensitivity of the target to be measured; conversely, a larger laser beam and a closer imaging element working distance can both increase the number of received speckles and reduce their size, thereby expanding the measurement range. This adjustment solves the restrictive relationship between the measurement range and measurement accuracy of the device by comprehensively adjusting the beam size and the imaging element working distance. Compared with the optical microscopic measurement technology that switches the measurement range and accuracy by replacing the objective lens and the eyepiece, the operation is more convenient and cost-effective, and the overall space occupied is small, and the installation position is flexible.

[0073] Since the format size of the receiving device is much smaller than the "working distance of the imaging element", the reflected speckle can only be received by the imaging device when the angle between the incident light beam and the normal is zero.

[0074] In this embodiment, the spatial shape and size of the object to be measured are measured, and the specific steps include: the diffraction phenomenon of light is one of the important characteristics of the wave nature of light. When the distance between the light field distribution plane and the filament is much greater than the wavelength, the diffraction light field obtained after irradiating the filament with a laser beam can be approximately analyzed using the scalar diffraction theorem. Since the surface of the metal wire has a large reflectivity, the laser speckle reflected from its surface is modulated and contains a large amount of spatial frequency domain information that matches its characteristics. Therefore, the spatial shape and size of the thin metal wire can be measured. The process is as follows: Under the condition of satisfying Fraunhofer diffraction, a digital imaging module is used as a light screen to directly record the reflected light field on the metal filament irradiated by the laser beam, such as Figure 3 As shown in the figure, there are three significant horizontal elongated bright spots in the central area, which correspond to the reflected light field of a vertically placed metal wire. The pixel information corresponding to the shape of the bright spot is converted into the actual size according to the pixel size of 1.4μm, and then converted in combination with the working distance of the imaging element. That is, according to the angular spectrum theory of diffraction, the spatial shape and size of the thin metal wire can be inverted.

[0075] In this embodiment, the displacement of the object to be measured is measured and calibrated, and the specific steps include:

[0076] First, the original speckle pattern of the metal lead, such as Figure 4 As shown in (a), the speckle pattern photographed by the adjustment device after the horizontal displacement of each interval of 10 μm is recorded by the digital imaging module, as shown in Figure 4 (b) Figure 4 (c) shows the speckle pattern recorded after the lead wire is displaced by 50μm and 100μm in the horizontal direction. Figure 1 Cross-correlation calculations are performed one by one to obtain the coordinate information of the peak value of the calculated correlation function on the two-dimensional image; then the displacement direction of the actual object to be measured and the spatial displacement conversion relationship of each pixel corresponding to the object to be measured are obtained using known parameters such as the laser beam size and the working distance of the imaging element. Figure 5 As shown in the figure, the displacement measurement results are compared with the calibration line (y=x). It can be seen in the figure that in the small displacement range (<50μm), the measurement results are in good agreement with the calibration curve. In the larger displacement range (50-100μm), due to the larger diffraction angle and the system error of the mechanical displacement adjustment device used, a large accumulated deviation occurs. In this case, correction can be made by setting the angular spectrum calibration coefficient, or by expanding the laser beam or shortening the working distance of the imaging element (both equivalent to expanding the measurable range), so as to improve the regional measurement accuracy.

[0077] The present invention solves the technical problems that the optical microscope measurement resolution of the reflective lighting system is not high and the measurement accuracy is affected by the lighting angle, wavelength and other methods. It can convert tiny spatial scale changes into obvious changes in the spatial frequency domain and measure them; at the same time, the present invention also solves the problem that the working distance from the objective lens to the lead to be measured is too small to affect the bonding work.

[0078] The digital imaging module of this embodiment adopts a CMOS sensor with an image area of ​​6.18 mm×5.85 mm, a pixel size of 1.4 μm, and a shooting pixel of 1920×1080. The CMOS sensor is directly connected to the C port of the T-type three-way lens barrel.

[0079] The speckle device for wire bonding machine of this embodiment is mainly used in the field of semiconductor integrated circuit packaging and testing, specifically for measuring the displacement and deformation of wire bonding wire arcs, etc. It can also be used for measuring the tiny displacement and deformation of other fine targets with high reflectivity.

[0080] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A speckle device for a wire bonding machine, characterized in that: include: T-type three-way lens barrel, beam splitter, adjustable lens group, laser, digital imaging module and image recording and processing module; The T-shaped three-way lens barrel is provided with a side section and a straight section, one end of the side section is connected to the straight section, the other end of the side section is provided with an open end, the straight section is provided with a first open end and a second open end, the first open end points to the arc to be measured, and the second open end points to the digital imaging module; The laser is used to generate a laser beam, and the laser beam is injected into the open end of the side passage section of the T-shaped three-way lens barrel; The beam splitter is located in the three-way lens barrel, at the connection between the straight section and the side section, and forms an angle of 45° with the optical axis of the straight section. The beam splitter is used to reflect the laser beam incident from the opening end of the side section to the first opening end of the straight section. The laser emitted from the first opening end of the straight section is reflected by the surface of the arc to be measured to form surface scattered light. The surface scattered light is collected by the first opening end of the straight section of the T-shaped three-way lens barrel and then re-enters the T-shaped three-way lens barrel. It is transmitted on the beam splitter according to the transmission direction and reaches the second opening end of the straight section of the T-shaped three-way lens barrel. The digital imaging module is used to record a laser speckle digital image containing the surface features of the arc to be measured; One side of the adjustable lens group is connected to the open end of the side pass section, and the other side is connected to the laser. The adjustable lens group moves in the direction of the optical axis of the side pass section of the T-shaped three-way lens barrel to adjust the focus of the laser spot irradiated on the line arc; The adjustable lens group includes a single lens and a displacement adjustment component, and the position of the single lens is adjusted by the displacement adjustment component so that the laser beam emitted from the first opening end of the straight-through section end is focused on the arc to be measured with a smaller spot; The adjustable lens group uses a collimating lens group to focus the laser beam irradiated on the surface of the arc to be measured; The image recording and processing module is connected to the digital imaging module, and is used to receive laser speckle digital images in different states, and adopt the Fourier analysis method to perform conversion and analysis between the spatial domain and the spatial frequency domain based on the inverse proportional scale transformation relationship from the spatial domain to the spatial frequency domain of the spatial light information, so as to obtain the spatial shape and position change information and the spatial shape and position continuous change trend of the line arc to be measured.

2. A control method for a speckle device of a wire bonding machine, characterized in that: The speckle device for a wire bonding machine according to claim 1 comprises the following steps: The digital imaging module records the light field distribution of the speckle on a plane perpendicular to the normal of the reflecting surface. The image recording and processing module uses the angular spectrum theory of diffraction to perform inversion analysis on the propagation characteristics of the light beam to obtain the shape characteristics of the arc to be measured. Using the laser speckle digital image of the surface of the arc to be measured, the geometric shape and position change data of the points on the arc to be measured under different states are calculated; The change data of the geometric shape and position of the points on the same measured arc under different states are calculated. The specific steps include: The digital imaging module records the speckle light field distribution u(x, y). When the measured arc undergoes an in-plane displacement (Δx, Δy), the speckle distribution v(x, y) is recorded, which can be expressed as: v(x,y)=u(x-Δx,y-Δy) U(x f ,y f )、V(x f ,y f ) functions are the Fourier transforms of u(x, y) and v(x, y), respectively. f ,y f is the spatial frequency domain coordinate, we have: According to the definition of the cross-correlation function and the convolution theorem, the Fourier transform of the cross-correlation function R(x f ,y f )for: Where V * (x f ,y f ) is V(x f ,y f ) conjugate, U * (x f ,y f ) is U(x f ,y f ), let F(x f ,y f )=U(x f ,y f ) * (x f ,y f ), using the inverse Fourier transform, we get the correlation function r: r(x,y)=F(x,y)*δ(x-Δx,y-Δy) δ(x, y) is the impulse function. From the autocorrelation property, we can get the coordinates (Δx, Δy) of the peak value of the above formula F(x, y), thus obtaining the in-plane displacement of the object. The displacement of the arc to be measured is measured and calibrated.

3. The control method of the speckle device for a wire bonding machine according to claim 2, characterized in that: The specific steps of measuring and calibrating the displacement of the arc to be measured include: Record the original laser speckle digital image of the arc to be measured and the laser speckle digital image taken after horizontal displacement; The cross-correlation calculation is performed on the displaced laser speckle digital image and the original laser speckle digital image one by one, and the coordinate information of the peak value of the calculated correlation function on the two-dimensional image is obtained; The known laser beam size and imaging element working distance parameters are used to convert the displacement direction of the actual arc to be measured and the conversion relationship between the spatial displacement of the arc to be measured corresponding to each pixel; Deviation correction is performed by setting the angular spectrum calibration coefficient, or by expanding the laser beam, or by shortening the working distance of the imaging element to correct the system error.

Images