Method and device for welding micro-fluidic chip by laser

Abstract

The invention relates to the technical field of laser welding of micro-fluidic chips, in particular to a method and device for laser welding of a micro-fluidic chip. The method for laser welding of the micro-fluidic chip comprises the following steps: positioning the micro-fluidic chip, acquiring a local picture of the micro-fluidic chip through a visual detection module, controlling two end parts to automatically adjust positions on a space coordinate axis, and ensuring that a cover plate is tightly attached to the micro-fluidic chip; and the target heating light spot is aligned with the molten pool part, so that the matching degree of a real-time crystal phase image formed on the molten pool part and a target crystal phase image is larger than a set value, the welding procedure is completed in an automatic control and detection mode, and finally annealing is conducted to complete welding. The welding method is high in automation degree, laser welding is conducted through the laser welding head module, heating is fast, efficiency is high, and accurate and automatic welding is achieved by judging a crystal phase image.

Description

Technical Field

[0001] The invention relates to the technical field of laser welding, in particular to a method and a device for laser welding a microfluidic chip. Background Art

[0002] Microfluidic chip technology is widely used in biomedicine, chemical analysis, environmental monitoring and other fields. Microfluidic chips are usually made of multiple layers of transparent materials, including polycarbonate (PC), polymethyl methacrylate (PMMA), glass, etc. In these materials, the construction of microchannels is usually completed by etching or molding. Since the size of microfluidic chips is very small, usually between a few microns and a few millimeters, precise welding technology becomes particularly important.

[0003] The welding of microfluidic chips usually requires bonding different layers or components together to form a complete chip that is sealed and can withstand various experimental conditions. The sealing methods of microfluidic chips mainly include ion bonding, film bonding, ultrasonic welding and hot pressing. These traditional sealing methods can realize the assembly and connection of microfluidic chips, but they have certain limitations in welding accuracy, thermal damage, sealing and adaptability to different materials. Especially when dealing with transparent materials, tiny structures and high precision requirements, it is difficult to provide ideal welding effects.

[0004] Laser welding technology has become an important direction for solving the welding problem of microfluidic chips in recent years due to its advantages such as high precision, low heat input and high adaptability. However, as microfluidic chips become smaller and smaller, the precision requirements for microfluidic chip processing will become higher and higher. This requires the integration of laser welding and optical detection related technologies to detect and ensure the quality of welding in real time during welding. Summary of the invention

[0005] The technical problem to be solved by the present invention is: to provide an improved method for solving the problems existing in the prior art in the above-mentioned background technology.

[0006] The technical solution adopted by the present invention to solve the technical problem is: in order to solve the problems existing in the prior art in the above-mentioned background technology, a method for laser welding a microfluidic chip is provided.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a method for laser welding a microfluidic chip, comprising the following steps: S1, clean the microfluidic chip and cover sheet, and fix the microfluidic chip with a pneumatic clamp; S2. Setting the target crystal phase image according to the material and specifications of the cover sheet, and setting the motion path of the motion control module according to the different channel shapes of the microfluidic chip; S3, the laser welding head module emits a laser, and aims at the target heating spot of the molten pool composed of the two ends of the microfluidic chip and the cover sheet and the limited space around them, so that the matching degree between the real-time crystal phase image formed on the molten pool and the target crystal phase image is greater than the set value, and the images of the two ends are collected by the CCD camera and the illumination light source, and the positions of the microfluidic chip and the cover sheet are detected in real time, and the heating spot is moved according to the set movement path, and laser heating welding is performed; S4. After welding, a short-duration pulsed laser is used for annealing. The narrow area close to the surface is heated, while the back is kept at room temperature and then cooled to room temperature after the furnace cools.

[0008] Furthermore, in step S1, the grease on the surface of the microfluidic chip and the cover sheet is dissolved, and the oxide film and oil stains on the microfluidic chip and the cover sheet are removed.

[0009] Furthermore, the setting of the target crystal phase image in step S2 is specifically as follows: a cover plate of a material and specification is selected, the target heating spot of the laser welding head module is aimed at the cover plate, the balance between the vapor pressure and the surface tension and gravity of the liquid metal is achieved in this local area, and the heating is completed along the radial direction, and then the crystal phase image is acquired.

[0010] Furthermore, in step S3, the laser welding head module uses an ultraviolet laser, and the laser wavelength emitted is 365nm, which is focused into a light spot with a diameter of 1μm through the welding head.

[0011] Furthermore, it is focused into a light spot with a diameter of 1 μm. Specifically, the laser with a wavelength of 365 nm emitted by the ultraviolet laser is first filtered out by a filter to remove other stray light except the ultraviolet laser, coupled to the receiving optical fiber through a fiber coupler, and then the laser beam is parallelized by a fiber collimator. The collimated laser beam passes through a long-distance objective lens, and the light path is guided to the objective lens for focusing, thereby obtaining a light spot with a focused diameter of 1 μm.

[0012] Furthermore, when laser heating welding is performed in step S3, the focusing depth of the laser needs to be adjusted. , the calculation formula is as follows: (1), In formula (1), d is the thickness of the cover sheet; During laser welding, the power of the laser P The welding time t There is a nonlinear relationship between the power of the laser P and temperature μ The relationship between them is: (2), In formula (2), μrepresents the temperature of the laser, m and n is a constant; The temperature μ With time t The relationship satisfies the heat conduction equation, which is as follows: (3), In formula (3), k is the thermal diffusivity, which depends on the thermal conductivity, density and heat capacity of the material. is a time variable t With spatial variables ( x , y , z ), is the temperature of a point in space μ About Time t The rate of change, , and Respectively represent the temperature on the spatial coordinate axis x axis, y Axis and z Second derivative of axis; Then calculate the thermal equilibrium value of temperature T(t) , the calculation formula is as follows: (4), In formula (4), is room temperature, T max is the maximum temperature, τ is the time constant, indicating that the temperature reaches the maximum value T max The time scale required, e, is the base of the natural exponential, a special mathematical constant.

[0013] A device for laser welding a microfluidic chip is also mentioned, comprising: A laser welding head module, comprising an ultraviolet laser and a welding head, wherein the ultraviolet laser emits ultraviolet laser light, and the welding head focuses the laser beam into a light spot; Visual inspection module, which includes a CCD camera and an illumination source, for real-time inspection of the welding process; The clamping and positioning module includes a pneumatic clamp and a three-dimensional motion platform, which is used for fixing the microfluidic chip and aligning it during welding; The control module includes an industrial computer and a motion execution system. The industrial computer controls the laser welding head module, the visual inspection module, the clamping and positioning module and the motion execution system. The motion execution system drives the welding head to move.

[0014] Furthermore, the laser welding head module also includes a fiber coupler and a fiber collimator. The fiber coupler is used to couple the light emitted by the ultraviolet laser into the receiving optical fiber, and the fiber collimator is used to convert the laser beam into a parallel one.

[0015] Furthermore, the laser welding head module also includes an infrared thermal imager, and the infrared thermal imager and the visual detection module are both installed on the outside of the welding head.

[0016] Furthermore, the infrared thermal imager and the CCD camera are provided with a clock signal generator.

[0017] Beneficial effects of the present invention: The present invention positions the microfluidic chip, collects a local image of the microfluidic chip through a visual detection module, controls the two ends to automatically adjust positions on the spatial coordinate axis, and ensures that the cover sheet and the microfluidic chip are closely fitted; and aligns the molten pool portion with a target heating light spot, so that the matching degree between the real-time crystal phase image formed on the molten pool portion and the target crystal phase image is greater than a set value, and completes the welding process through automatic control and detection, and finally anneals to complete the welding; The laser welding method of the present invention has a high degree of automation, and uses a laser welding head module for laser welding. The laser beam can be concentrated in a very small area to ensure the accuracy and precision of welding. The ultraviolet laser performs welding at a temperature of <200°C, and the heat-affected zone generated is very small. During the welding process, the light beam directly interacts with the workpiece without direct contact, which can avoid mechanical damage to the microfluidic chip. The high-quality weld has fewer pores and inclusions, fast heating, and high efficiency. By judging the crystal phase image, accurate automatic welding can be achieved. The visual inspection module of the present invention collects the situation of the welding surface in real time, that is, whether the local area has reached a balance between the steam pressure and the surface tension and gravity of the liquid metal, and automatically adjusts the angle of the welding head according to the surface conditions to ensure the accuracy of the welding; The laser welding device of the present invention installs both the infrared thermal imager and the visual detection module on the outside of the welding head to form an automatic focusing system, which can quickly adjust the positions of the infrared thermal imager and the visual detection module according to the distance and angle that change in real time during the welding process, thereby obtaining the best image and temperature data; In the present invention, a clock signal generator is set on the infrared thermal imager and the CCD camera to ensure that the thermal image data and the image data can be synchronously collected and processed at the millisecond level. This high-precision time synchronization mechanism will make the thermal image data and the image data highly consistent in time, thereby ensuring the reliability and accuracy of the data. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0019] Figure 1 It is a structural schematic diagram of the device of the present invention.

[0020] Figure 2 It is a schematic diagram of the device of the present invention.

[0021] Figure 3 A control block diagram of the device of the present invention.

[0022] Figure 4 is a flow chart of the method of the present invention.

[0023] Figure 5 It is a schematic diagram of welding of the method of the present invention.

[0024] Figure 6 It is the annealing flow chart of the method of the present invention.

[0025] Figure 7 It is a schematic diagram of the relationship between time and temperature during the annealing process in the method of the present invention.

[0026] Figure 8 It is a schematic diagram of the carbon strips on the glass slide photographed by a CCD camera in the method of the present invention.

[0027] Fig. 9 is a SEM image of a carbon ribbon fused on an Al plate in the method of the present invention.

[0028] Fig.10 yes Fig. 9 Magnified view of the middle edge.

[0029] In the figure: 1. UV laser; 2. Welding head; 3. CCD camera; 4. Illumination light source; 5. Pneumatic clamp; 6. Three-dimensional motion platform; 7. Industrial computer; 8. Motion execution system; 9. Fiber optic coupler; 10. Fiber optic collimator; 11. Infrared thermal imager. DETAILED DESCRIPTION

[0030] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0031] like Figure 1 to Figure 3As shown, a device for laser welding microfluidic chips includes a laser welding head module, a visual inspection module, a clamping and positioning module and a control module. The laser welding joint module includes an ultraviolet laser 1 and a welding head 2. The ultraviolet laser 1 emits ultraviolet laser, and the welding head 2 focuses the laser beam into a light spot; the visual inspection module includes a CCD camera 3 and an illumination light source 4, which are used for real-time detection of the welding process; the clamping and positioning module includes a pneumatic clamp 5 and a three-dimensional motion platform 6, which are used for fixing the microfluidic chip and aligning it during the welding process; the control module includes an industrial computer 7 and a motion execution system 8, the industrial computer 7 controls the laser welding head module, the visual inspection module, the clamping and positioning module and the motion execution system, and the motion execution system 8 drives the welding head 2 to move.

[0032] The laser welding head module also includes a fiber coupler 9 and a fiber collimator 10. The fiber coupler 9 is used to couple the light emitted by the ultraviolet laser into the receiving fiber, and the fiber collimator 10 is used to convert the laser beam into a parallel beam. The laser welding head module also includes an infrared thermal imager 11. The infrared thermal imager 11 and the visual detection module are both installed on the outside of the welding head 2 to form an automatic focusing system. The positions of the infrared thermal imager 11 and the visual detection module can be quickly adjusted according to the distance and angle that change in real time during the welding process, so as to obtain the best image and temperature data; the infrared thermal imager 11 and the CCD camera 3 are provided with a clock signal generator to ensure that the thermal image data and the image data can be synchronously collected and processed at the millisecond level. This high-precision time synchronization mechanism will make the thermal image data and the image data highly consistent in time, thereby ensuring the reliability and accuracy of the data.

[0033] The visual inspection module is the primary factor that determines the welding accuracy. It is preferred to use a fiber optic spectrometer to measure the real-time reflectance spectrum of the material. It has a built-in near-infrared camera CCD and a thermal imaging camera, which can detect the unevenness of the material surface in real time and automatically adjust the light receiving angle of the light spectrometer according to the surface shape to ensure the accuracy of the spectral data. The infrared camera CCD and thermal imaging camera are connected to the PC, record the image and send it to the image processing program on the PC. Its function is to collect the image of the weldment, identify the position of the weldment and align it; the function of the motion execution system is to drive the welding head to move; the laser of the laser welding head module emits a laser to melt the weldment and complete the welding.

[0034] like Figure 4 As shown, the method for laser welding a microfluidic chip comprises the following steps: Start the above-mentioned laser welding device for microfluidic chips, and prepare first: use an external cleaning mechanism to dissolve the grease on the surface of the microfluidic chip and the cover sheet by spraying alcohol, remove the oxide film and oil stains of the microfluidic chip and the cover sheet, and prevent pores and slag inclusions during welding. Secondly, use a pneumatic clamp 5 to fix the microfluidic chip to ensure the fit. The pneumatic clamp 5 adjusts the clamping force through gas pressure and can evenly distribute the clamping pressure. The pneumatic system responds quickly and can adjust the pressure. It is suitable for the precise fixation of small structures such as microfluidic chips to ensure that they do not move during the processing process.

[0035] Set welding parameters: Set the target crystal phase image according to the material and specifications of the cover sheet, specifically: select a cover sheet of a certain material and specification, aim the target heating spot of the laser welding head module at the cover sheet, achieve a balance between the vapor pressure and the surface tension and gravity of the liquid metal in this part, and complete heating along the radial direction, and then collect the crystal phase image; set the motion path of the motion control module according to the different channel shapes of the microfluidic chip. Among them, the balance between the vapor pressure and the surface tension and gravity of the liquid metal depends on the melting point of the material, so it can be achieved only by monitoring the temperature.

[0036] Welding: The laser welding head module emits a laser and aims at the target heating spot of the molten pool composed of the two ends of the microfluidic chip and the cover sheet (both are rectangular parallelepipeds, and the two ends are the two long sides of the rectangular parallelepiped) and the limited space around them, so that the matching degree between the real-time crystal phase image formed on the molten pool and the target crystal phase image is greater than the set value, and the images of the two ends are collected by the CCD camera 3 and the illumination light source 4, and the positions of the microfluidic chip and the cover sheet are detected in real time. The heating spot is moved according to the set motion path, and laser heating welding is performed. Specifically, the welding device is controlled by the industrial computer 7, including the switch of the ultraviolet laser 1, the display of the image collected by the CCD camera 3, the brightness adjustment of the illumination light source 4, and the movement of the three-dimensional motion platform 6, so as to realize the automatic welding of the welding device, such as Figure 5 shown.

[0037] Among them, the laser welding head module adopts an ultraviolet laser with a laser wavelength of 365nm, which is focused into a light spot with a diameter of 1μm through the welding head. Specifically, the laser with a wavelength of 365nm emitted by the ultraviolet laser is first filtered out by a filter to remove other stray light except the ultraviolet laser, and then coupled to the receiving optical fiber through a fiber coupler, and then the laser beam is parallelized by a fiber collimator. The collimated laser beam passes through a long-distance objective lens, and the light path is guided to the objective lens for focusing to obtain a light spot with a focusing diameter of 1μm. At this time, the energy density of the laser reaches the highest at the light spot, so that the microfluidic chip can be effectively processed.

[0038] Compared with green light and infrared, ultraviolet laser has a smaller thermal effect. As the laser wavelength becomes shorter, various materials have a higher absorption rate, so ultraviolet laser is also called "cold light" and its processing materials are also called "cold processing". The cover material on the microfluidic chip is PMMA, PC and other polymer materials, which have a low melting point, generally <200℃, and absorb ultraviolet laser well. This welding uses ultraviolet laser at a relatively low temperature.

[0039] When performing laser heating welding, it is necessary to adjust the laser focus depth , the calculation formula is as follows: (1), In formula (1), d is the thickness of the cover sheet; Since the thickness of the cover plate is about 1 mm, during the welding process, the focusing position of the laser cannot be simply focused on the surface of the cover plate, but should be focused at a depth of 0.5 mm±0.1 mm under the cover plate to ensure that the weld has a high quality.

[0040] During laser welding, the power of the laser P The welding time t There is no nonlinear relationship between them, but it is affected by a variety of physical and process parameters. The power of the laser P and temperature μ The relationship between them is: (2), In formula (2), μ represents the temperature of the laser, m and n is a constant; The temperature μ With time t The relationship satisfies the heat conduction equation (which describes how heat is transferred in the material and how the temperature changes over time in laser welding), which is as follows: (3), In formula (3), k is the thermal diffusivity, which is determined by the thermal conductivity, density and heat capacity of the material; is a time variable t With spatial variables ( x , y , z ), is the temperature of a point in space μ About Time t The rate of change, , and Respectively represent the temperature on the spatial coordinate axisx axis, y Axis and z The solution of the heat equation has the property of smoothing the initial temperature, which means that heat propagates from high temperature to low temperature. In general, many different initial states will tend to the same steady state (thermal equilibrium). So calculate the thermal equilibrium value of temperature T(t) , the calculation formula is as follows: (4), In formula (4), e is the base of the natural exponent, which is a special mathematical constant approximately equal to 2.718281828459045; is room temperature, but in some cases, such as during preheating, the initial temperature may be higher than room temperature; T max is the maximum temperature, which depends on the properties of the material and the power of the laser; τ is the time constant, indicating that the temperature reaches the maximum value T max The required time scale, which represents the influence of laser power, material properties and welding area geometry, needs to be determined experimentally to generate a standard database. The smaller the value of τ, the faster the temperature rises and the shorter the time it takes to reach the required welding temperature.

[0041] Post-welding treatment: Figure 6 As shown, the laser is an ultraviolet laser 1, and the optical system is: the laser wavelength of 365nm emitted by the ultraviolet laser is first filtered out by a filter to remove other stray light except the ultraviolet laser, and then coupled to the receiving optical fiber through a fiber coupler, and then the laser beam is parallelized by a fiber collimator. The collimated laser beam does not need to be focused and passes through an optical switch. The opening and closing time of the optical switch is precisely controlled to adjust the repetition frequency and pulse width of the pulse laser to generate a pulsed laser. After welding, a short-time pulsed ultraviolet laser 1 is used for annealing. Pulsed laser means that the laser is emitted in the form of short pulses rather than continuous beams; due to the short nature of the pulses, the heating and cooling of the material are completed in a very short time, so a very high heating rate can be achieved. In pulsed laser annealing, the laser is directed to a sample that can be moved underneath. Due to the short pulse time of tens of nanoseconds, only a narrow area close to the surface is heated, while the back is kept at room temperature, and then slowly cooled (generally furnace cooling) and then cooled to room temperature, the annealing temperature is precisely controlled, such as Figure 7 As shown, ensure that the annealing process is carried out within the appropriate temperature range. At the same time, the image recorded by the CCD camera 3 is sent to the image processing program on the PC to check and accept the quality of welding. Finally, the laser welding device of the microfluidic chip is turned off.

[0042] like Figure 8As shown in the figure, the carbon strip on the glass slide (as a mask to cover the part that does not need to be welded, ensuring that the laser only irradiates the area that needs to be welded) is taken by a near-infrared CCD camera before welding. Fig. 9 and Fig.10 Shown are SEM images of carbon ribbon fused on Al plate for the entire view (magnification: 100) and edge view (magnification: 400), from which it can be seen that the welding quality is very smooth and defect-free.

[0043] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for laser welding a microfluidic chip, characterized in that: The steps include: S1, clean the microfluidic chip and cover sheet, and fix the microfluidic chip with a pneumatic clamp; S2. Setting the target crystal phase image according to the material and specifications of the cover sheet, and setting the motion path of the motion control module according to the different channel shapes of the microfluidic chip; S3, the laser welding head module emits a laser, and aims at the target heating spot of the molten pool composed of the two ends of the microfluidic chip and the cover sheet and the limited space around them, so that the matching degree between the real-time crystal phase image formed on the molten pool and the target crystal phase image is greater than the set value, and the images of the two ends are collected by the CCD camera and the illumination light source, and the positions of the microfluidic chip and the cover sheet are detected in real time, and the heating spot is moved according to the set movement path, and laser heating welding is performed; S4. After welding, a short-duration pulsed laser is used for annealing. The narrow area close to the surface is heated, while the back is kept at room temperature and then cooled to room temperature after the furnace cools.

2. The method for laser welding a microfluidic chip according to claim 1, characterized in that: In step S1, the grease on the surface of the microfluidic chip and the cover sheet is dissolved, and the oxide film and oil stains on the microfluidic chip and the cover sheet are removed.

3. The method for laser welding a microfluidic chip according to claim 1, characterized in that: The setting of the target crystal phase image in step S2 is specifically as follows: select a cover plate of a material and specification, align the target heating spot of the laser welding head module with the cover plate, achieve a balance between the steam pressure and the surface tension and gravity of the liquid metal in this local area, and complete heating along the radial direction, and then collect the crystal phase image.

4. The method for laser welding a microfluidic chip according to claim 1, characterized in that: In step S3, the laser welding head module uses an ultraviolet laser, and the laser wavelength emitted is 365nm, which is focused into a light spot with a diameter of 1μm through the welding head.

5. The method for laser welding a microfluidic chip according to claim 4, characterized in that: Focused into a light spot with a diameter of 1μm, specifically: the laser with a wavelength of 365nm emitted by the ultraviolet laser is first filtered out by a filter to remove other stray light except the ultraviolet laser, coupled to the receiving optical fiber through a fiber coupler, and then parallelized by a fiber collimator. The collimated laser beam passes through a long-distance objective lens, and the light path is guided to the objective lens for focusing to obtain a light spot with a focused diameter of 1μm.

6. The method for laser welding a microfluidic chip according to claim 1, characterized in that: When laser heating welding is performed in step S3, the laser focus depth needs to be adjusted. , the calculation formula is as follows: （1）， In formula (1), d is the thickness of the cover sheet; During laser welding, the power of the laser P The welding time t There is a nonlinear relationship between the power of the laser P and temperature μ The relationship between them is: （2）， In formula (2), μ represents the temperature of the laser, m and n is a constant; The temperature μ With time t The relationship satisfies the heat conduction equation, which is as follows: （3）， In formula (3), k is the thermal diffusivity, which depends on the thermal conductivity, density and heat capacity of the material. is a time variable t With spatial variables ( x , y , z ), is the temperature of a point in space μ About Time t The rate of change, , and Respectively represent the temperature on the spatial coordinate axis x axis, y Axis and z Second derivative of axis; Then calculate the thermal equilibrium value of temperature T(t) , the calculation formula is as follows: （4）， In formula (4), is room temperature, T max is the maximum temperature, τ is the time constant, indicating that the temperature reaches the maximum value T max The time scale required, e, is the base of the natural exponential, a special mathematical constant.

7. A device for laser welding a microfluidic chip, characterized in that: include: A laser welding head module, comprising an ultraviolet laser and a welding head, wherein the ultraviolet laser emits ultraviolet laser light, and the welding head focuses the laser beam into a light spot; Visual inspection module, which includes a CCD camera and an illumination source, for real-time inspection of the welding process; The clamping and positioning module includes a pneumatic clamp and a three-dimensional motion platform, which is used for fixing the microfluidic chip and aligning it during welding; The control module includes an industrial computer and a motion execution system. The industrial computer controls the laser welding head module, the visual inspection module, the clamping and positioning module and the motion execution system. The motion execution system drives the welding head to move.

8. The device for laser welding a microfluidic chip according to claim 7, characterized in that: The laser welding head module also includes a fiber coupler and a fiber collimator. The fiber coupler is used to couple the light emitted by the ultraviolet laser into the receiving optical fiber, and the fiber collimator is used to convert the laser beam into a parallel beam.

9. The device for laser welding a microfluidic chip according to claim 7, characterized in that: The laser welding head module also includes an infrared thermal imager, and the infrared thermal imager and the visual detection module are both installed on the outside of the welding head.

10. The device for laser welding a microfluidic chip according to claim 9, characterized in that: The infrared thermal imager and the CCD camera are provided with a clock signal generator.

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