Micro-hole processing method based on ultrafast laser

Abstract

The present invention discloses a micro-hole processing method based on ultrafast laser, comprising the steps of: fixing a workpiece to a processing position; setting position parameters and processing parameters of the micro-hole to be processed; controlling the laser to process the workpiece with a first processing path, so that a circular micro-hole is formed on the workpiece; and controlling the laser to process the circular micro-hole with a second processing path, so that the circular micro-hole is corrected to a square micro-hole. The present invention can process the workpiece with an ultrafast laser, so that a circular micro-hole is first formed on the workpiece, and then the required square micro-hole is formed. In the entire processing process, not only the processing accuracy is high, but also the processing efficiency is relatively high.

Description

Technical Field

[0001] The invention relates to the technical field of laser precision machining, and in particular to a micro-hole machining method based on ultrafast laser. Background Art

[0002] Probe cards are used to perform functional tests on bare crystals before large-scale semiconductor integrated circuits are packaged, to screen out defective products, and then proceed to the subsequent packaging process to improve the yield rate. The guide plate is a core component in the probe card, which is composed of thousands of micro-through holes to ensure the accurate position of each probe.

[0003] At present, the semiconductor integrated circuit industry is developing rapidly, and the requirements for semiconductor chip production, testing and packaging are constantly increasing. Chips and circuits are developing in the direction of high pin count, high density and more compact structure. Probe cards are also developing in the direction of high pin count, ultra-fine pitch, miniaturization of guide holes, etc., which brings huge challenges to the processing of micro-holes in the guide plate. When processing high-density micro-holes through CNC machinery, there are problems such as low processing efficiency and large processing hole diameter. In addition, the contact processing tool life is low and the loss is large, which increases the production cost. Therefore, traditional mechanical processing can no longer meet the processing needs of probe cards. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a micro-hole processing method based on ultrafast laser, which can improve the processing accuracy and meet the requirements of high density, ultra-fine spacing and miniaturization of micro-holes on the workpiece.

[0005] This embodiment adopts the following technical solutions:

[0006] A micro-hole processing method based on ultrafast laser comprises the following steps:

[0007] Fix the workpiece to the processing position;

[0008] Set the position parameters and processing parameters of the micro-holes to be processed;

[0009] Controlling the laser to process the workpiece in a first processing path so as to form a circular micro-hole on the workpiece;

[0010] The laser is controlled to process the circular micro-hole in a second processing path, so that the circular micro-hole is corrected into a square micro-hole.

[0011] Furthermore, in the ultrafast laser-based micro-hole processing method, the step of controlling the laser to process the workpiece in a first processing path to form a circular micro-hole on the workpiece includes:

[0012] The laser is controlled to process the workpiece layer by layer from top to bottom in a spiral processing trajectory to form circular microholes on the workpiece.

[0013] Furthermore, in the ultrafast laser-based micro-hole processing method, the step of controlling the laser to process the circular micro-hole in a second processing path to correct the circular micro-hole into a square micro-hole includes:

[0014] The processing inclination angle and phase angle of the laser are adjusted in sequence in a preset manner, and the laser is controlled to process the circular microhole in a spiral processing trajectory, so that the circular microhole is corrected into a square microhole.

[0015] Furthermore, in the ultrafast laser-based micro-hole processing method, the step of fixing the workpiece to the processing position includes:

[0016] Fix the workpiece on the jig;

[0017] The workpiece is photographed and positioned by the visual system, and the position and direction of the workpiece are corrected by the turntable;

[0018] The laser is driven to move by the motion platform so that the laser head of the laser is aimed at the workpiece.

[0019] Furthermore, in the ultrafast laser-based micro-hole processing method, before the step of controlling the laser to process the workpiece in a first processing path to form a circular micro-hole on the workpiece, the method further includes the following steps:

[0020] Start the laser, and test and adjust the laser focus position to ensure that the laser focus is on the processing reference plane.

[0021] Furthermore, in the ultrafast laser-based micro-hole processing method, in the step of controlling the laser to process the workpiece in a first processing path to form a circular micro-hole on the workpiece, and in the step of controlling the laser to process the circular micro-hole in a second processing path to correct the circular micro-hole to a square micro-hole, the steps are also included:

[0022] Use high-pressure gas coaxial with the laser head to blow the processing part of the workpiece.

[0023] Furthermore, in the ultrafast laser-based micro-hole processing method, after the step of controlling the laser to process the circular micro-hole in the second processing path to correct the circular micro-hole into a square micro-hole, the method further includes the following steps:

[0024] The steps of processing the circular micro-holes and the square micro-holes are repeated to form a square micro-hole array on the workpiece.

[0025] Furthermore, in the ultrafast laser-based micro-hole processing method, after the step of controlling the laser to process the circular micro-hole in the second processing path to correct the circular micro-hole into a square micro-hole, the method further includes the following steps:

[0026] The workpiece is ultrasonically cleaned and blown dry with high-pressure gas.

[0027] Furthermore, in the ultrafast laser-based micro-hole processing method, before the step of fixing the workpiece to the processing position, the following steps are further included:

[0028] The protective liquid is evenly applied to the surface of the workpiece and then dried.

[0029] Furthermore, in the ultrafast laser-based micro-hole processing method, the protective liquid is a water-soluble protective liquid.

[0030] Compared with the prior art, the present invention provides a micro-hole processing method based on ultrafast laser, which can process the workpiece by ultrafast laser, so that a circular micro-hole is first formed on the workpiece, and then the required square micro-hole is formed. During the whole processing process, not only the processing accuracy is high, but also the processing efficiency is relatively high. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of a specific embodiment of the ultrafast laser-based micro-hole processing method provided by the present invention.

[0032] Figure 2 for Figure 1 FIG. 4 is a flow chart of step S100 in the ultrafast laser-based micro-hole processing method.

[0033] Figure 3 for Figure 1 Schematic diagram of the changing trend of phase angle and spot morphology in the ultrafast laser-based micro-hole processing method. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Without further description, the elements, structures and features in one embodiment can also be beneficially combined with other embodiments.

[0035] In the description of the present invention, it should be noted that the terms "upper", "lower", "bottom", "inner", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] See also Figure 1 , which is a flow chart of a specific embodiment of a micro-hole processing method based on ultrafast laser provided by the present invention, comprising the steps of:

[0038] S100, fixing the workpiece to a processing position;

[0039] S200, setting the position parameters and processing parameters of the micro-hole to be processed;

[0040] S300, controlling the laser to process the workpiece in a first processing path, so as to form a circular micro-hole on the workpiece;

[0041] S400, controlling the laser to process the circular micro-hole using a second processing path, so that the circular micro-hole is corrected into a square micro-hole.

[0042] The purpose of processing the workpiece through the above steps is to form square micro-holes with good quality, accurate size and no burrs on the workpiece. The workpiece can be a guide plate in a probe card, which needs to process thousands of micro-through holes; the laser can be an ultrafast laser, and the laser it emits is an ultrafast laser.

[0043] In industry, lasers can be divided into four categories according to the emission time: continuous wave, quasi-continuous wave, short pulse, and ultrashort pulse. Ultrafast laser refers to a pulse laser with a pulse width of picoseconds or less than picoseconds. When the laser energy is concentrated in such a short time, a huge single pulse energy and extremely high peak power can be obtained. When processing materials, the phenomenon of material melting and continuous evaporation caused by long pulse width and low intensity laser can be avoided to a large extent. Therefore, when ultrafast laser is used to process the guide plate, the interaction time between the laser and the guide plate is extremely short, and no thermal effect will be generated, which can greatly improve the processing quality.

[0044] The following example illustrates the above steps. First, in step S100, refer to Figure 2 , which specifically include:

[0045] S110, fixing the workpiece on the fixture;

[0046] S120, photographing and positioning the workpiece through a visual system, and correcting the position and direction of the workpiece by a turntable;

[0047] S130, driving the laser to move by the motion platform so that the laser head of the laser is aligned with the workpiece.

[0048] Among them, the fixture can be set on an electric turntable, and the electric turntable first rotates the fixture and the workpiece on the fixture to the processing station, and then the workpiece is photographed by the visual system to determine the position of the workpiece. Then, the workpiece can be fine-tuned by the electric turntable to correct the position of the workpiece so that the workpiece and the laser motion platform are consistent in both horizontal and vertical directions. The laser motion platform can adopt a two-dimensional linear motion platform, such as a two-dimensional linear motor. After correcting the position of the workpiece, the laser head of the laser can be driven by the motion platform to align with the workpiece, and then the microhole to be processed can be processed.

[0049] The workpiece is fixed on the fixture by vacuum adsorption, and the processing area of ​​the workpiece on the fixture is hollowed out. There are two positioning holes on the workpiece. The visual system determines whether the position of the workpiece needs to be corrected by capturing the positions of the two positioning holes. If correction is required, the visual system cooperates with the electric turntable to adjust the horizontal and vertical positions of the workpiece so that the workpiece and the laser motion platform are consistent in both horizontal and vertical directions. The visual system can capture photos by using a high-pixel CCD camera. For example, a CCD camera with more than 500,000 pixels is used, and the field of view size is set to 5*5mm, so that the position accuracy of the workpiece can be met to 0.03mm, ensuring the processing quality.

[0050] Also, please continue reading Figure 1 , before step S100, further comprising the steps of:

[0051] S50, evenly coating the surface of the workpiece with protective liquid and drying it.

[0052] In the specific implementation, the protective liquid is evenly coated on both sides of the probe card guide plate, and the thickness of the protective liquid is greater than 20um to ensure that the protective liquid can play a good protective effect. Then the probe card guide plate coated with the protective liquid is placed in an insulated box and baked for about 1 hour to completely dry the protective liquid. During the laser processing, slag and other impurities and dust will appear in the processing area of ​​the probe card guide plate. The protective liquid can prevent other areas of the probe card guide plate from being damaged by these impurities and dust, thereby improving the quality of the probe card guide plate after processing. In addition, the protective liquid can be selected as a water-soluble protective liquid, such as organic compounds such as polyvinyl alcohol. After the processing is completed. It is easy to remove the protective liquid adsorbed with impurities and dust on the probe card guide plate by washing with water.

[0053] To ensure a good processing effect, before step S300 and step S400 are performed, the following steps are also included:

[0054] S250, start the laser, and test and adjust the laser focus position to ensure that the laser focus is on the processing reference plane.

[0055] The laser focus position has a great influence on the processing effect of the square micro-hole to be processed, especially in terms of hole shape and size. Therefore, the distance from the laser head to the workpiece can be measured in combination with a height measurement sensor, and the laser focus position can be adjusted to ensure that the laser focus is located on the processing reference plane. In this embodiment, the square micro-hole aperture tolerance is ±0.0015mm, and the height sensor measurement accuracy is ±0.005mm.

[0056] In step S200, the position parameters of the micro-holes to be processed include the center coordinates of each micro-hole. Before processing, relevant processing drawings, such as CAD processing drawings, can be imported into the processing system to directly obtain the number of micro-holes, the center coordinates of each micro-hole, the micro-hole diameter and other parameters on the CAD processing drawings. Then, the processing parameters of the micro-holes to be processed are set to include parameters such as processing speed, processing frequency, processing power and the pressure of the high-pressure gas injection. The specific numerical selection can refer to the following Table 1.

[0057] Processing speed (Hz) Frequency (KHz) Power(W) Air pressure (bar) 50-200 100 / 200 4-8 2-6

[0058] Table 1. Example of laser processing parameters for micro-holes to be processed

[0059] Furthermore, the step S300 specifically includes:

[0060] The laser is controlled to process the workpiece layer by layer from top to bottom in a spiral processing trajectory to form circular microholes on the workpiece.

[0061] During processing, the laser is selected as an ultrafast laser with a pulse width of ≤800fs and a wavelength of 1064nm. Ultrafast lasers under these parameters have high peak energy and extremely narrow pulse width, almost no thermal shock and heat-affected zone, and have extremely high processing accuracy and quality. The laser can be driven by a two-dimensional linear motor to align the processing position of the microhole to be processed, and in order to ensure the accuracy of the processing position, the motion accuracy of the two-dimensional linear motor must reach ±0.002mm.

[0062] The laser used is based on a multi-axis composite scanning system and adopts a high-precision, high-speed multi-axis galvanometer with a repeatability accuracy of ±1um. It can not only control the movement path of the laser in the three directions of XYZ, but also change the processing inclination angle and phase angle of the laser to process microholes of different tapers and shapes to meet the requirements of the probe card guide plate.

[0063] Furthermore, the step S400 specifically includes:

[0064] The processing inclination angle and phase angle of the laser are adjusted in sequence in a preset manner, and the laser is controlled to process the circular microhole in a spiral processing trajectory, so that the circular microhole is corrected into a square microhole.

[0065] The processing inclination angle is the angle between the laser axis and the normal line of the workpiece surface. By changing the processing inclination angle of the laser, the taper of the entrance and exit light surfaces of the circular microhole can be adjusted.

[0066] The phase angle is the angle between sin and cos when the laser scanning galvanometer rotates. By changing the phase angle, the shape of the laser spot can be adjusted. Figure 3 In one embodiment, when the phase angle is 0°, the laser spot is a circular spot; when the phase angle is 45°, the laser spot is an elliptical spot; when the phase angle is 90°, the laser spot is a linear spot; when the phase angle increases from 90° to 180°, the laser spot gradually returns from a linear spot to a circular spot; when the phase angle increases from 180° to 360°, the laser spot repeats the process of the phase angle increasing from 0° to 180°, but the direction of the laser spot is opposite at this time.

[0067] In order to achieve the above-mentioned function of changing the laser processing inclination angle and phase angle, the laser scanning galvanometer used in the multi-axis composite scanning system can select the PRECESSION ELEPHANT 2 series scanning head, or select other laser scanning heads with the same or similar functions. In addition, the specific implementation method of changing the laser processing inclination angle and phase angle can refer to the relevant technical data, and the present invention will not elaborate on this.

[0068] During specific processing, please refer to Table 2, set the actual processing inclination angle of the laser scanning head to -9° to 9°, and debug at -100% to 100% during debugging. First, control the laser to process 300 circles of circular microholes with a phase angle of 0° and a processing inclination angle of -30%; then control the laser to process 100 circles of circular microholes with a phase angle of 90° and a processing inclination angle of -12.5%; then control the laser to process 100 circles of circular microholes with a phase angle of 180° and a processing inclination angle of -30%; then control the laser to process 100 circles of circular microholes with a phase angle of 270° and a processing inclination angle of -12.5%; finally, control the laser to process 100 circles of circular microholes with a phase angle of 360° and a processing inclination angle of -30%, so as to realize the correction of the outer side of the circular microhole and obtain a square microhole circumscribed with the circular microhole.

[0069] Serial number Number of spiral turns Radius / um Phase angle / ° Processing inclination angle / % Z-axis height change / % 1 300 12.5 0 -30 0 2 100 12.5 90 -12.5 0 3 100 12.5 180 -30 0 4 100 12.5 270 -12.5 0 5 100 12.5 360 -30 0

[0070] Table 2. Example table of trajectory parameters for the second machining path

[0071] After step S400 is completed, step S300 and step S400 may be repeated, that is, the steps of processing circular microholes and square microholes may be repeated to form a square microhole array on the workpiece.

[0072] Since the maximum size of the spot at the focus of the ultrafast laser is 20um, the pulse width is narrow, and the aperture of the smallest square microhole processed is 30*30um, its heat-affected zone is less than or equal to 1um. Therefore, the square microhole array after processing can meet the requirements of high pin count, ultra-fine pitch and miniaturization of guide holes in probe cards.

[0073] Furthermore, in step S300 and step S400, the following steps are also included:

[0074] S400X uses high-pressure gas coaxial with the laser head to blow the processing part of the workpiece.

[0075] By spraying the processing part of the workpiece with high-pressure gas coaxial with the laser head, it is beneficial to discharge the formed slag, thereby improving the processing efficiency of microholes. The presence of impurities such as oxygen, water, and hydrocarbons in the high-pressure gas will cause the loss of laser output power and cause the instability of laser emission. Therefore, the high-pressure gas can be selected as high-purity nitrogen or inert gas, and its purity needs to be greater than or equal to 99.99%.

[0076] In addition, after the square micro-hole array is formed on the workpiece, the steps are further included:

[0077] S500, ultrasonically clean the workpiece and blow dry it with high-pressure gas.

[0078] The purpose of ultrasonic cleaning is to remove the protective liquid and dust impurities on the surface of the workpiece. Therefore, the ultrasonic cleaning time can be greater than or equal to 5 minutes to ensure that the dust on the surface of the workpiece is cleaned, and then the liquid on the surface of the workpiece is blown dry with high-pressure gas. Of course, other cleaning methods and drying methods can also be used for the workpiece, and the present invention does not limit this.

[0079] In summary, the ultrafast laser-based micro-hole processing method provided by the present invention reduces the use of tools and coolants compared to traditional CNC machine tool processing technology, has faster processing efficiency, higher economic benefits, and is more environmentally friendly. At the same time, the present invention can process square micro-holes that meet the requirements of the probe card guide plate by adjusting the processing inclination angle and phase angle of the laser, and because the ultrafast laser has a small thermal impact, it can also meet the requirements of the probe card for high pin count, ultra-fine pitch, and miniaturization of the guide hole.

[0080] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. A micro-hole processing method based on ultrafast laser, It is characterized in that Includes steps: Fix the workpiece to the processing position; Set the position parameters and processing parameters of the micro-holes to be processed; Controlling the laser to process the workpiece in a first processing path so as to form a circular micro-hole on the workpiece; Controlling the laser to follow the second processing path, and adjusting the processing inclination angle and phase angle of the laser in a preset manner, changing the shape of the laser spot, processing the circular microhole, and correcting the circular microhole to a square microhole; The method of adjusting the processing inclination angle and phase angle of the laser in a preset manner, changing the shape of the laser spot, and processing the circular microhole includes: setting the actual processing inclination angle of the laser scanning head to -9° to 9°, and debugging at -100% to 100% during debugging, first controlling the laser to spirally process the circular microhole for 300 turns at a phase angle of 0° and a processing inclination angle of -30%; then controlling the laser to spirally process the circular microhole for 100 turns at a phase angle of 90° and a processing inclination angle of -12.5%; then controlling the laser to spirally process the circular microhole for 100 turns at a phase angle of 180° and a processing inclination angle of -30%; then controlling the laser to spirally process the circular microhole for 100 turns at a phase angle of 270° and a processing inclination angle of -12.5%; and finally controlling the laser to spirally process the circular microhole for 100 turns at a phase angle of 360° and a processing inclination angle of -30%.

2. The micro-hole processing method based on ultrafast laser according to claim 1, It is characterized in that The step of controlling the laser to process the workpiece in a first processing path to form a circular micro-hole on the workpiece includes: The laser is controlled to process the workpiece layer by layer from top to bottom in a spiral processing trajectory to form circular microholes on the workpiece.

3. The micro-hole processing method based on ultrafast laser according to claim 1, It is characterized in that The step of fixing the workpiece to the processing position comprises: Fix the workpiece on the jig; The workpiece is photographed and positioned by the visual system, and the position and direction of the workpiece are corrected by the turntable; The laser is driven to move by the motion platform so that the laser head of the laser is aimed at the workpiece.

4. The micro-hole processing method based on ultrafast laser according to claim 1, It is characterized in that Before the step of controlling the laser to process the workpiece in the first processing path to form a circular micro-hole on the workpiece, the step further includes: Start the laser, test and adjust the laser focus position to ensure that the laser focus is on the processing reference plane.

5. The ultrafast laser-based micro-hole processing method according to claim 1, It is characterized in that In the step of controlling the laser to process the workpiece in the first processing path to form a circular microhole on the workpiece, and in the step of controlling the laser to process the workpiece in the second processing path and adjusting the processing inclination angle and phase angle of the laser in a preset manner to change the shape of the laser spot to process the circular microhole so that the circular microhole is corrected to a square microhole, the following steps are also included: Use high-pressure gas coaxial with the laser head to blow the processing part of the workpiece.

6. The ultrafast laser-based micro-hole processing method according to claim 1, It is characterized in that After the step of controlling the laser to follow the second processing path and adjusting the processing inclination angle and phase angle of the laser in a preset manner to change the shape of the laser spot and process the circular microhole to correct the circular microhole into a square microhole, the step further includes: The steps of processing the circular micro-holes and the square micro-holes are repeated to form a square micro-hole array on the workpiece.

7. The ultrafast laser-based micro-hole processing method according to claim 1, It is characterized in that After the step of controlling the laser to follow the second processing path and adjusting the processing inclination angle and phase angle of the laser in a preset manner to change the shape of the laser spot and process the circular microhole to correct the circular microhole into a square microhole, the step further includes: The workpiece is ultrasonically cleaned and blown dry with high-pressure gas.

8. The ultrafast laser-based micro-hole processing method according to claim 1, It is characterized in that Before the step of fixing the workpiece to the processing position, the method further includes the following steps: The protective liquid is evenly applied to the surface of the workpiece and then dried.

9. The ultrafast laser-based micro-hole processing method according to claim 8, It is characterized in that The protective liquid is a water-soluble protective liquid.

Images