WO2025200182A1 - Laser pre-drilling and mechanical drilling machining method - Google Patents

Abstract

A laser pre-drilling and mechanical drilling machining method. The method comprises: performing laser pre-drilling on a board to be machined (S110); and on the basis of the pre-drilled hole, performing secondary drilling by means of a drill tool to form a target hole (S120), the depth h of the pre-drilled hole meeting h≥D/2tan(a/2), wherein a is a drill tip angle, h is the depth of the pre-drilled hole, and D is the diameter of a drill bit during the secondary drilling. According to the method, the relation between the depth of the pre-drilled hole and the depth of the target hole is specified; and by defining the depth of the pre-drilled hole, a drill tip for the secondary drilling can be ensured to be completely wrapped by the pre-drilled hole, thereby exerting the function of the pre-drilled hole for guiding the secondary drilling.

Description

Laser pre-guiding and mechanical drilling processing methods

This application claims priority to the Chinese patent application filed with the China Patent Office on March 27, 2024, with application number 202410353636.8, the entire contents of which are incorporated by reference into this application.

Technical Field

The present application relates to the field of drilling technology, for example, to a laser pre-guiding and mechanical drilling method.

Background Art

With the development of multilayer printed circuit board (PCB) technology, the demand for high-aspect-ratio holes has increased dramatically, posing challenges to processing costs and efficiency. High-aspect-ratio holes refer to holes with an aspect ratio greater than 15:1.

Due to the large depth of the large aspect ratio hole, the pre-drilling-step drilling process is used to achieve the drilling. However, the pre-drilling-secondary drilling process has the following problems: deviation of the hole, tool breakage, and low processing efficiency.

1. The poor repeatability of pre-drilling and secondary drilling results in offset holes.

The machining of high-aspect-ratio microvias (board thickness ≥3.2mm, drill diameter ≤0.3mm, aspect ratio greater than 15:1) within PCBs presents issues with hole position accuracy due to factors such as equipment errors, system jitter, and clamping and positioning. Currently, drilling machines have an XY platform error of ±10μm, spindle runout of ±20μm, and a minimum total hole machining error of ±30μm. Using a pre-drilling-through-hole process, repeated positioning errors can lead to offset holes at the hole entrance after completion.

2. The mismatch between the pre-hole diameter and the through hole leads to problems of offset holes and broken needles.

If the pre-drilling diameter is too large, the through-hole diameter cannot cover the error of the pre-drilling process, resulting in large deviation in the position of the finished hole and poor hole shape (such as a gourd hole). If the pre-drilling diameter is too small, the pre-drilling hole will not significantly center the drill bit, resulting in skewed holes. At the same time, the axial force of the drill bit cannot be reduced. In severe cases, the drill bit may break, as shown in Figure 1.

3. The pre-hole depth does not match the drill bit and plate thickness, resulting in broken needles.

The depth of the pre-hole is too small, and the pre-hole has no guiding effect on the drill bit. The large impact of the drill bit when drilling during through-hole processing causes the problem of skew hole, as shown in Figure 2; the depth of the pre-hole is too large, and the drilling force is unstable after the drill bit drills in. The axial force on the drill bit fluctuates, and the drill bit cannot stably cut the material in the deep hole, resulting in the drill bit breaking.

4. The mismatch between the number of segments and the plate thickness leads to difficulty in chip removal and low processing efficiency.

If the drill bit drills too deep in the PCB at one time, the chips in the spiral groove cannot be discharged in time, resulting in The drill's spiral grooves clog, and the drill bit breaks due to excessive chip-blocking torque, as shown in Figure 3. Chip evacuation speed is related to the number of segments; a higher number of segments improves chip evacuation efficiency. However, an inappropriate number of segments can lead to extremely low production efficiency. Therefore, research is needed to determine how to optimally set the number of segments to resolve the conflict between poor chip evacuation and production efficiency.

Pre-drilling-mechanical through-hole drilling includes mechanical segmented drilling, mechanical pre-drilling-mechanical through-hole drilling, laser-mechanical composite processing, and laser pre-machining-mechanical finishing. The following applications have been filed in the industry:

Application CN202011477150.3 uses a three-stage segmented drilling method for processing high-aspect ratio PCBs. The first drilling depth is 2/5 of the PCB thickness, the second drilling depth is 3/10 of the PCB thickness, and the third drilling depth is 3/10 of the PCB thickness. The drill bit length is greater than 1 to 1.5 mm of the board thickness.

Application 201910410847.X controls the total copper layer drilled through each drilling segment to less than 10oz, and enables segmented drilling through PCBs with a thickness of less than or equal to 1.2mm.

The above application is based on a mechanical segmented drilling method, which limits the limit of each segmented drilling. However, the greater the effective blade length of the drill bit, the more likely the drill bit will deviate from the hole during the first drilling process. The above application fails to solve the problems of drill deviation and tool breakage caused by the deviated hole in the first segment of drilling with a large depth-to-diameter ratio in subsequent segmented drilling.

Application No. 201910326937.0 was used to process the fifth generation mobile communication technology (5th Generation, 5G) antenna polytetrafluoroethylene (PTFE) based PCB using a diamond drill to pre-drill to a depth of 8mm, control the depth and stay for 10 seconds before drilling down to 8mm to obtain a hole with a wall roughness of 0 to 25μm.

Application No. 201910312292.5 pre-drills a small hole smaller than the target aperture and then uses a drill bit with the target aperture to process PTFE-based PCBs. This method can solve the problems of tool chip removal, tool winding, and reduce burrs on the hole wall.

The above applications all provide pre-drilling and through-drilling by using a tool. However, as the number of pre-drilled holes increases, the tool wear becomes more severe, and the problem of reduced pre-drilling quality due to increased pre-drilling tool wear is not solved.

Application No. 201711173692.X provides a method for combined laser and mechanical processing of PCBs. This method uses the same positioning hole to perform sequential laser drilling or mechanical drilling on different machine tools. The method specifies that when the target aperture is less than 0.1mm, the aperture produced by laser processing should be 60% to 90% of the target aperture. When the target aperture is greater than 0.1mm, the aperture produced by laser processing should be 50% to 90% of the target aperture. This method only provides a range within which the pre-drilled aperture is smaller than the target aperture. It does not clarify the relationship between the shape and size of the laser-drilled hole and the mechanically drilled hole, and fails to address the problem of differentiated hole processing for different board thicknesses and aspect ratios.

Application 201110065069.9 provides a method for high-quality through-hole machining of hard and brittle materials. Laser machining creates a through hole in the blank, providing a path for the grinding wire to finely machine the blank's hole wall, resulting in high-quality micro-through holes (<100μm). The purpose of laser pre-machining in this application is to provide a channel for subsequent processing of the material. It does not mention how to ensure the verticality of the drill bit during mechanical machining of the through hole by using the proportional relationship between the pre-drilled hole diameter and depth and the through hole machining diameter and depth. Table 1 shows the drilling methods and their corresponding defects in related technologies.

Table 1 Drilling methods and corresponding defects in related technologies

Summary of the Invention

The present application provides a laser pre-guiding and mechanical drilling processing method, which clarifies the relationship between the pre-drilling depth and the target hole depth. By limiting the pre-drilling depth, it can ensure that the drill tip of the secondary drilling is completely wrapped by the pre-drilling hole, thereby playing a guiding role of the pre-drilling on the secondary drilling.

The present application provides a laser pre-guiding and mechanical drilling method, comprising:

Laser pre-drilling of the processed plate;

On the basis of pre-drilling, secondary drilling is performed by a drill to form a target hole; the depth h of the pre-drilling hole satisfies: h≥D/2tan(a/2); where a is the drill point angle, h is the depth of the pre-drilling hole, and D is the diameter of the drill bit during secondary drilling.

In one or more embodiments, the depth h of the pre-drilled hole satisfies: A×T≥h, where T is the depth of the pre-drilled hole. The thickness of the workboard, A is the depth coefficient.

In one or more embodiments, the depth factor is determined according to the wavelength of the selected laser.

In one or more embodiments, the aperture d of the pre-drilled hole satisfies: 0.9×K1×K2≥d/D≥0.5×K1×K2; wherein K1 is the plate correction coefficient; and K2 is the plate size coefficient.

In one or more embodiments, the hole depth ratio of the target hole is greater than 15.

In one or more embodiments, during the secondary drilling, a segmented drilling method is used to form the target hole.

In one or more embodiments, during segmented drilling, the depth of each drilling is less than or equal to the maximum drilling depth of the drill bit, and the maximum drilling depth of the drill bit is ≤ the blade length of the drill bit - the thickness of the protective cover plate - 0.7 mm. The protective cover plate refers to the protective plate covering the plate to be drilled during the mechanical drilling process.

In one or more embodiments, before the laser pre-drilling of the processed plate, the process further includes: pre-processing the processed plate, wherein the pre-processing includes measuring and correcting the warping of the processed plate after lamination.

In one or more embodiments, when the warpage of the processed plate is greater than 0.75%, the processed plate is subjected to stress release treatment until the warpage of the processed plate is less than or equal to 0.75%.

In one or more embodiments, a reference point is provided in the plate to be processed, and the reference point is used to define the axis center line of the laser optical axis and the axis center line of the mechanical drill bit, so that the axis center lines of the drill bit coincide during the two drilling processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a structure in which a tool is broken due to a biased hole in the related art;

FIG2 is a schematic diagram of the structure of a partial hole in the related art;

FIG3 is a schematic diagram of a tool breakage caused by excessive drilling depth in the related art;

FIG4 is a schematic diagram of the structure of the pre-drilled hole in this application;

FIG5 is a schematic diagram of a target hole formed by secondary drilling in the present application;

FIG6 is a schematic diagram of the drill point angle of the present application;

FIG7 is a flow chart of the laser pre-guiding and mechanical drilling method provided in this application.

DETAILED DESCRIPTION

The following will describe an optional embodiment of the present application with reference to the accompanying drawings. The present application may be implemented in various forms and should not be limited to the embodiments set forth herein.

The terms used in this application are for the purpose of describing particular embodiments only and are not intended to limit this application. As used in this application and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term "and/or" refers to and encompasses any and all possible combinations of one or more of the associated listed items.

Although the terms "first", "second", "third", etc. may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "plurality" means two or more, unless otherwise specified.

Example 1

The present application provides a laser pre-guiding and mechanical drilling method, which includes the following steps, as shown in FIG7 .

S110, pre-drilling the processed plate with laser. In the present application, laser can be used to drill the processed plate to obtain pre-drilled holes.

S120. Perform secondary drilling on the basis of the pre-drilled hole to form a target hole; the depth h of the pre-drilled hole satisfies: h≥D/2tan(a/2); where a is the drill point angle, h is the depth of the pre-drilled hole, and D is the diameter of the drill bit during secondary drilling.

In this application, pre-drilling is performed by laser drilling, and secondary drilling is performed by mechanical drilling.

During secondary drilling, the depth of the pre-drilled hole must completely enclose the drill tip. As shown in Figure 6, the drill tip angle is a, and the diameter of the drill bit during secondary drilling is D. The minimum depth required to completely enclose the drill tip is D/2tan(a/2). Therefore, this application limits the minimum depth of the pre-drilled hole to D/2tan(a/2); at this point, the drill tip of the secondary drill is completely enclosed by the pre-drilled hole, and the pre-drilled hole can serve as a guide for secondary drilling.

As shown in FIG6 , the drill tip in this application refers to the portion of the front end of the drill bit that includes the chisel edge; that is, when secondary drilling is performed, the chisel edge portion of the drill tip needs to be completely covered by the pre-drilled hole.

The pre-drilled hole in this application may also be referred to as a pre-hole, that is, a hole formed by pre-drilling before performing target hole diameter processing.

In one or more embodiments, the hole depth ratio of the target hole is greater than or equal to 15.

In one or more embodiments, during the secondary drilling, a segmented drilling method is used to form the target hole.

The present application sets the minimum depth of the pre-drilled hole to D/2tan(a/2) because: if the axis of the drill cutter coincides with the axis of the pre-drilled hole at the moment the secondary drilling cutter contacts the workpiece, the drill tip is completely wrapped by the pre-drilled hole, which can ensure that the axis of the secondary drilling hole and the pre-drilled hole completely coincide, avoiding the drilling position or size deviation caused by the center offset of the secondary drilling hole and the pre-drilled hole. If the axis of the drill cutter deviates from the axis of the pre-drilled hole at the moment the secondary drilling cutter contacts the workpiece, when the mechanical drill cutter falls within the width of the pre-drilled hole and drills downward, the side wall of the pre-drilled hole has a large resistance to the mechanical drill cutter, and the axis of the mechanical drill cutter will be corrected toward the axis of the pre-drilled hole. If the hole depth is too small, the mechanical drill cutter cannot be offset to the center position. The minimum value specified in the present application can ensure that the axis of the mechanical drill cutter can slide from the offset position to the position of the axis of the pre-drilled hole, achieving a guiding effect.

Example 2

The present application provides a laser pre-guiding and mechanical drilling method, comprising:

Laser pre-drilling of the processed plate;

A secondary drilling is performed based on the pre-drilled hole to form a target hole. The depth h of the pre-drilled hole satisfies the following: A×T ≥ h ≥ D/2tan(a/2). Where a is the drill point angle, h is the depth of the pre-drilled hole, and D is the diameter of the drill bit used in the secondary drilling. T is the thickness of the plate being processed, and A is the depth coefficient, which is determined by the type of laser selected during the pre-drilling process. In one or more embodiments, the depth coefficient is determined by the wavelength of the selected laser.

The maximum value of h in this application should not be too large. If the value of h is too large, it will increase the pre-drilling time, which is not conducive to improving the efficiency of drilling processing. At the same time, in the process of pre-drilling with laser, there is a certain restrictive relationship between the diameter and depth of the pre-drilled hole. The greater the depth of the pre-drilled hole, the diameter will increase accordingly, and the laser heat generated will also increase. Excessive laser heat can easily cause the processed plate to be deformed by heat, etc. When setting the pre-drilling depth in this application, it is necessary to ensure the processing quality of the laser pre-drilling (aperture, heat-affected zone), and at the same time meet the sufficient axial guidance effect during mechanical secondary drilling. On this basis, the maximum laser processing depth obtained in this application is A×T, and the minimum processing depth is D/2tan(a/2).

Laser pre-drilling processes include infrared laser processing with a wavelength of 1064nm-9.4μm, ultraviolet laser processing with a wavelength of 248nm-355nm, and green laser processing with a wavelength of 532nm. Experimental data for the extreme processing of laser pre-drilling processes are shown in Table 2. The depth coefficient, and thus the maximum pre-drilling depth, is determined by the laser wavelength. This fully accounts for the thermal effects of the laser energy in the pre-drilled hole, ensuring the accuracy and quality of the laser pre-drilling process.

Table 2 Depth coefficients corresponding to different lasers

Example 3

The present application provides a laser pre-guiding and mechanical drilling method, comprising:

Laser pre-drilling of the processed plate;

Secondary drilling is performed on the basis of pre-drilling to form a target hole; the depth h of the pre-drilling hole satisfies: h≥D/2tan(a/2); where a is the drill point angle, h is the depth of the pre-drilling hole, and D is the diameter of the drill bit during secondary drilling.

In addition to specifying the minimum depth of the pre-drilled hole, this application also needs to consider the pre-drilled hole diameter. In this application, the pre-drilled hole diameter range is 0.9 × K1 × K2 ≥ d/D ≥ 0.5 × K1 × K2. The pre-drilled hole diameter d satisfies the following: 0.9 × K1 × K2 ≥ d/D ≥ 0.5 × K1 × K2. K1 is the plate correction factor, and K2 is the plate size factor.

If the diameter of the pre-drilled hole is too small, due to the positioning error during the two drilling processes, the starting point of the secondary drilling may fall outside the pre-drilled hole, resulting in the pre-drilled hole and the secondary drilling hole not coinciding; only when the starting point of the secondary drilling hole falls inside the pre-drilled hole, during the secondary drilling process, the side wall of the pre-drilled hole has a greater resistance to the mechanical drill bit, and the mechanical drill bit will deviate toward the center of the pre-drilled hole until the mechanical drill bit coincides with the center of the pre-drilled hole, achieving the effect of centering the pre-drilled hole.

If the pre-drilled hole diameter is too large, the mechanical drilling process will easily cause the hole diameter to exceed the preset target value. At the same time, a pre-drilled hole diameter that is too large will also increase the pre-drilled hole depth, increasing the required laser heat and posing the risk of thermal deformation of the processed board. Furthermore, a pre-drilled hole diameter that is too large will increase the pre-drilling time, which is not conducive to improving drilling efficiency.

Due to equipment accuracy limitations, in one embodiment, the machining error for mechanical drilling is ±25 μm, and the machining error for laser drilling is ±15 μm. The pre-drilled hole diameter range set in this application can cover positioning errors within 50 microns, avoiding the problem of misalignment caused by positioning accuracy during the two drilling processes.

The minimum value of the ratio of the pre-drilled hole to the target hole diameter is set to 0.5×K1×K2 in this application. This is based on the minimum positioning deviation in the two drilling processes to ensure the positioning of the drill bit in the secondary drilling process. The minimum consideration for pre-drilling required for the centering effect. In addition, the plate warpage is related to the plate correction coefficient and the plate size coefficient. The plate warpage affects the range of the laser pre-drilling diameter. The plate correction coefficient K1 and the plate size coefficient K2 are used to correct the minimum laser pre-drilling diameter to avoid the drill tip not being fully covered due to the pre-drilling being too small during secondary drilling.

This application sets the maximum value of the ratio of the pre-drilled hole to the target aperture to 0.9×K1×K2, which is based on the consideration of processing efficiency and the necessity of secondary drilling target diameter processing. When the ratio of the pre-drilled hole diameter to the target aperture exceeds 0.9×K1×K2, the overall combined processing efficiency is not significantly improved compared with the efficiency of traditional technology, and due to the problem of repeated positioning deviation in the two processing, it is very easy to cause the center of the secondary drilling hole to not coincide with the pre-drilled hole, resulting in defects such as gourd holes. When the ratio of the pre-drilled hole diameter to the target aperture is less than or equal to 0.9×K1×K2, the overall combined processing efficiency is improved by 20% compared with the traditional technology, and when there is a positioning deviation between the two processing, it can also ensure that the secondary drilling covers the pre-drilled hole, ensuring the hole position accuracy of the overall drilling.

In this application, the plate correction coefficient K1 is determined by the material of the plate being processed. The plate correction coefficient K1 decreases as the coefficient of expansion of the plate being processed increases. When the plates being processed are stacked in the XY plane, the plate correction coefficient K1 decreases as the asymmetric residual copper rate in the Z-axis direction increases. In other words, when the plate material has a high coefficient of expansion, or when the stacking is in the XY plane with an asymmetric residual copper rate in the Z-axis direction, the corresponding plate correction coefficient value is low. Conversely, a lower plate correction coefficient K1 corresponds to a larger value.

When multiple PCB cores (or one or more types) are pressed together (using high-temperature, high-pressure, or friction-fusion processes) to form a semi-finished PCB, the thickness and flatness of various regions within the semi-finished product vary. These differences in thickness and flatness are collectively referred to as PCB flatness. Therefore, the sheet correction factor, K1, comprehensively evaluates PCB flatness by combining thickness differences and warpage.

The plate size coefficient K2 is determined by the size of the plate being processed. The plate size coefficient K2 decreases as the size of the plate being processed increases. For example, when the size of the plate being processed is large, the corresponding plate size coefficient value is low.

This is because considering the processing efficiency of laser pre-hole, the smaller the size of the PCB, the smaller the expansion and contraction coefficient of the board edge area, and vice versa.

In this application, maintaining the diameter of the pre-drilled hole within an appropriate range can serve as a centering tool for the secondary drilling. When the diameter of the pre-drilled hole is maintained within the range of 0.9×K1×K2≥d/D≥0.5×K1×K2, it can ensure that the drill tip falls within the diameter of the pre-drilled hole during the secondary drilling. At the same time, when the axis lines of the two drillings are offset, the mechanical drill will deviate toward the center of the pre-drilled hole due to the greater resistance of the pre-drilled hole sidewall to the mechanical drill bit until the mechanical drill bit and the center of the pre-drilled hole coincide with each other, achieving the effect of centering the pre-drilled hole.

Example 4

The present application provides a laser pre-guiding and mechanical drilling method, comprising:

S1: Pre-processing of PCB.

Determine the board size factor based on the size of the PCB, and determine the board correction factor based on the material of the PCB.

Before the laser pre-drilling is performed on the processed plate, the method further includes: pre-processing the processed plate, wherein the pre-processing includes measuring and correcting the warping of the processed plate after pressing.

When the warping degree of the processed plate is greater than 0.75%, the processed plate is subjected to stress release treatment until the warping degree of the processed plate is less than or equal to 0.75%.

After the daughterboard or motherboard is pressed together, the PCB thickness is measured and sorted. The sorted and stacked boards are then passed through a board straightening machine, with the board warpage less than or equal to 0.75%. Excessive board warpage can affect the effectiveness of straight-line drilling. If the board warpage exceeds 0.75%, the board needs to be straightened to release stress. If the board warpage exceeds 0.75%, stress relief treatment is required. Treatment methods include cooling and stabilization, gravity straightening, high-temperature pressure relief, and high-temperature straightening. When the board warpage is less than or equal to 0.75%, drilling accuracy can be ensured by correcting the board size factor and the board correction factor.

Based on the target hole depth and diameter, the drill bit size and model for secondary drilling, as well as the laser wavelength selected for pre-drilling, are determined, and the pre-drilled hole diameter and depth are calculated. In one or more embodiments, the thickness of the plate being processed is determined. A thicker plate requires a greater pre-drilling depth. The corresponding laser type is selected based on the maximum achievable processing depths of lasers of different wavelengths as shown in Table 2.

The depth h of the pre-drilling hole satisfies: A×T≥h≥D/2tan(a/2); wherein a is the drill point angle, h is the depth of the pre-drilling hole, and D is the diameter of the drill bit during secondary drilling; T is the thickness of the processed plate, and A is the depth coefficient, which is determined by the laser type selected during the pre-drilling process.

The pre-drilled hole diameter d satisfies the following equation: 0.9 × K1 × K2 ≥ d/D ≥ 0.5 × K1 × K2, where K1 is the plate correction factor, K2 is the plate size factor, and D is the diameter of the drill bit used for secondary drilling.

The pre-drilling depth set in this application can ensure the quality of laser pre-drilling processing (aperture, heat-affected zone), and at the same time provide sufficient axial guidance during mechanical secondary drilling.

The pre-drilled hole diameter set in this application can play a centering role for the secondary drilling. When the diameter of the pre-drilled hole is kept in the range of 0.9×K1×K2≥d/D≥0.5×K1×K2, it can ensure that the drill tip falls within the pre-drilled hole diameter during the secondary drilling. At the same time, when the axis line of the two drillings is offset, due to the greater resistance of the side wall of the pre-drilled hole to the mechanical drill bit, the mechanical drill bit will deviate towards the center of the pre-drilled hole until the mechanical drill bit coincides with the center of the pre-drilled hole, achieving the effect of centering the pre-drilled hole.

S2: Laser pre-drilling the processed plate using a laser drilling method.

When using ultraviolet laser and green laser to process pre-holes, the hole shape of the laser pre-hole is controlled by setting industrial-grade processing parameters such as average power, repetition frequency, pulse width, number of pulses, galvanometer scanning speed, and galvanometer scanning path.

When using infrared band to process pre-holes, the hole shape of the laser pre-hole is controlled by setting industrial-grade processing parameters such as pulse energy, pulse width, pulse number, aperture diameter, and collimator type.

During the pre-drilling process, after part of the material is removed by laser processing, the material on the hole wall near the laser action area softens or melts and then re-cools and solidifies. The macrostructure of this part of the re-solidified material is relatively loose, which can play a certain buffering role for the secondary drilling tool and is easily removed by the drill in the secondary drilling process, forming smaller crushed chips that are discharged smoothly, avoiding chip blockage of the drill.

The drilling process can cover a certain depth processing range based on the focal depth of the laser processing system. When the depth of the hole required for pre-drilling exceeds the focal depth range of the laser processing system, the laser focal length needs to be adjusted. In one or more embodiments, for every 1 micron increase in the depth of the pre-drilled hole, the laser focal length is adjusted downward by 1 micron along the axis of the pre-drilled hole. The focusing function of this application is divided into progressive and inching types. The progressive type is used for laser beam processing with a small focal depth, and the inching type is used for laser beam processing with a large focal depth. For example, when the focal depth is 20 to 40 μm, a small pulse energy laser beam can be used for progressive processing with a speed of 200 to 400 μm/s; when the focal depth is 40 to 200 μm, a large pulse energy laser beam can be used for inching processing with a step distance of 40 to 200 μm. The axial focus position can be adjusted in the following ways:

(1) Axial mechanical movement mechanism focusing

During the laser processing process, as the depth of the laser pre-drilling increases, the axial mechanical moving mechanism drives the optical path downward, and the light spot acting on the surface of the material begins to move into the material, increasing the depth of the pre-drilling.

(2) 3D galvanometer focusing

During the laser processing process, the three-dimensional galvanometer realizes zoom processing through the preset three-dimensional processing model, and forms a laser pre-hole with a three-dimensional structure inside the material. The shape of the pre-hole corresponds to the three-dimensional processing model.

The laser machine tool table is equipped with a fixed component, and one or more laser optical axes are located above the table, configured to simultaneously process multiple locations on the PCB. The fixed component can adsorb the pressed PCB to the table to prevent positional deviation during the pre-drilling process. The fixed component includes flattening methods such as a vacuum adsorption platform and a pin-fixing platform. Based on the pre-drilled hole depth and hole diameter determined in step S1, pre-drilling programming is performed in the laser machine tool. The laser machine tool can complete pre-drilling of the specified depth and hole diameter according to the pre-set program.

S3: Based on the pre-drilled hole, a mechanical drill is used to perform secondary drilling to form the target hole.

The present application can set a reference point on the PCB. There can be multiple reference points. The reference points are used to define the position of the laser axis centerline and the mechanical drill axis centerline to ensure that the positions of the two are consistent with the reference points. The distance is constant, which can ensure that the axis of the laser optical axis and the axis of the mechanical drill bit coincide with each other, thereby improving the accuracy of the two drillings.

The secondary drilling process of this application can be carried out in the form of multiple drillings. The number of segments of mechanical drilling can be determined according to the thickness of the plate and the maximum drilling depth of the drill bit; a reasonable number of segments can ensure smooth chip removal during the secondary drilling process, and can also ensure that the drilling efficiency is basically unaffected, wherein the maximum drilling depth of the drill bit is ≤ the blade length of the drill bit - the thickness of the protective cover plate - 0.7mm, and the protective cover plate refers to the protective plate covering the top of the plate to be drilled during the mechanical drilling process. During segmented drilling, the depth of each drilling is less than or equal to the maximum drilling depth of the drill bit. The relationship between the number of segments of this application is as follows:

(Plate thickness - pre-drilling depth) / drilling depth of each segment, plate thickness < drill bit blade length, and each segment drilling depth is less than or equal to the maximum drilling depth of the drill bit.

This embodiment has the following beneficial effects:

1. The proportional relationship between the pre-drilling depth and hole diameter and the mechanical drilling depth and hole diameter is proposed to provide sufficient guidance and centering for mechanical drilling and solve the problem of skewed holes in the drilling process of holes with large depth-to-diameter ratios.

2. Laser processing of pre-pilot holes is used to solve the problem of decreased pre-drilling quality due to increased wear of pre-drilling tools in mechanical pre-drilling, as well as the problem of decreased repeat positioning accuracy caused by the positioning error of ±30μm between two mechanical drillings.

3. Establish the relationship between pre-guide hole depth, step-by-step drilling depth and multi-layer printed circuit board stacking to solve the problem of differentiated hole processing with different board thicknesses and different aspect ratios.

The present application provides a laser pre-drilling and mechanical drilling processing method, comprising: laser pre-drilling a plate to be processed; performing secondary drilling on the basis of the pre-drilling by a drill to form a target hole; the depth h of the pre-drilling satisfies: h≥D/2tan(a/2); wherein a is the drill tip angle, h is the depth of the pre-drilling, and D is the diameter of the drill bit during secondary drilling. During secondary drilling, the depth of the pre-drilling needs to completely cover the drill tip. The drill tip angle of the drill bit is a, and the diameter of the drill bit during secondary drilling is D. The minimum depth that completely covers the drill tip is D/2tan(a/2). When the axis of the drill bit coincides with the axis of the pre-drilled hole at the moment the drill bit of the secondary drilling contacts the material to be processed, the drill tip is completely wrapped by the pre-drilled hole, which can ensure that the axis of the secondary drilling hole completely coincides with the axis of the pre-drilled hole, thereby avoiding deviations in drilling position or size due to center offset between the secondary drilling hole and the pre-drilled hole. If the secondary drilling tool's axis deviates from the pre-drilled hole's axis at the moment it contacts the material being processed, the mechanical drill will experience significant resistance from the pre-drilled hole's sidewalls as it drills downward within the pre-drilled hole's width. This will cause the tool's axis to shift toward the pre-drilled hole's axis, potentially preventing it from shifting to the center if the hole depth is too small. The minimum pre-drilled hole depth specified in this application ensures the tool's axis can slide from the offset position to the pre-drilled hole's axis, achieving a guiding effect.

Unless otherwise specified, the relative arrangement, numbers, and Word expressions and numerical values do not limit the scope of this application. At the same time, for ease of description, the sizes of the multiple parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific values should be interpreted as merely exemplary and not as limitations. Therefore, other examples of the exemplary embodiments may have different values. Similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be discussed in subsequent figures.

In the description of this application, the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of this application; the directional words "inside and outside" refer to the inside and outside relative to the outlines of the multiple components themselves.

For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be subsequently positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" may include both "above" and "below". The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used herein are interpreted accordingly.

In addition, the use of words such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above words have no special meaning and therefore cannot be understood as limiting the scope of protection of this application.

Claims (10)

A laser pre-guiding and mechanical drilling method, comprising: Laser pre-drilling of the processed plate; On the basis of the pre-drilling, secondary drilling is performed by a drill to form a target hole; wherein the depth h of the pre-drilling hole satisfies: h≥D/2tan(a/2); wherein a is the drill point angle, h is the depth of the pre-drilling hole, and D is the diameter of the drill bit in the case of the secondary drilling. The method according to claim 1, wherein the depth h of the pre-drilled hole further satisfies: A×T≥h, T is the thickness of the processed plate, and A is the depth coefficient. The method according to claim 2, wherein the depth factor is determined according to the wavelength of the selected laser. The method according to claim 1, wherein the aperture d of the pre-drilled hole satisfies: 0.9×K1×K2≥d/D≥0.5×K1×K2; wherein K1 is the plate correction coefficient; and K2 is the plate size coefficient. The method according to claim 1, wherein the hole depth ratio of the target hole is greater than or equal to 15. The method according to claim 1, wherein, in the case of the secondary drilling, the target hole is formed by a segmented drilling method. The method according to claim 6, wherein, in the case of segmented drilling, the depth of each drilling is less than or equal to the maximum drilling depth of the drill bit, and the maximum drilling depth of the drill bit is ≤ the blade length of the drill bit - the thickness of the protective cover plate - 0.7 mm, and the protective cover plate is a protective plate covering the top of the processed plate during the mechanical drilling process. The method according to claim 1, wherein, before laser pre-drilling the processed plate, it further comprises: pre-processing the processed plate, wherein the pre-processing comprises measuring and correcting the warpage of the processed plate after pressing. The method according to claim 8, wherein, when the warping of the processed plate is greater than 0.75%, the processed plate is subjected to stress release treatment until the warping of the processed plate is less than or equal to 0.75%. The method according to claim 8, wherein a reference point is provided on the plate to be processed, and the reference point is used to define the laser optical axis and the axis center line of the mechanical drill bit so that the axis center lines in the two drilling processes coincide.