Technological method based on PCB hard board drilling

Abstract

The invention discloses a PCB (printed circuit board) hard board drilling process method, which is characterized in that two lasers with different wavelengths are used for processing a PCB hard board blind hole, one light source adopts picosecond ultraviolet laser, and the other light source adopts CO2 laser; according to the method, by means of the characteristics that picosecond ultraviolet laser has high absorptivity and small focusing light spots on metal materials such as bright copper, high-precision, high-quality and low-heat-influence windowing operation is carried out on the surface of the bright copper, and small blind holes smaller than micrometers are formed; by utilizing the characteristics that CO2 laser has high absorptivity and large focusing light spots on non-metallic materials such as glass fibers, high-efficiency, high-reliability and no-damage bottom copper degumming operation is carried out in a round window after windowing, and a deep blind hole with the depth larger than 0.5 mm is realized.

Description

Technical Field

[0001] The invention relates to the field of laser drilling, and in particular to a process method for drilling holes in a PCB hard board using a dual-light source laser drilling technology. Background Art

[0002] PCB (Printed Circuit Board) is a printed circuit board, which is the carrier and connection platform of electronic components. The holes on the PCB are used to achieve electrical connections between different layers or install components. The holes on the PCB can be divided into through holes, blind holes and buried holes. Through holes are holes that run through the entire PCB, blind holes are holes from the outer layer to the inner layer but not through the entire PCB, and buried holes are holes between the inner layers but not connected to the outer layer.

[0003] The drilling process on PCB is one of the most critical and time-consuming processes in the PCB manufacturing process. The quality of the drilling process directly affects the performance and reliability of the PCB. At present, there are two mainstream PCB drilling processes: mechanical drilling and laser drilling. Mechanical drilling is to use a mechanical drill to make holes on the PCB, and laser drilling is to use a laser beam to ablate or evaporate materials on the PCB to form holes.

[0004] Mechanical drilling and laser drilling each have their own advantages and disadvantages. Mechanical drilling is low-cost, fast, and suitable for mass production, but it is difficult to achieve small-diameter, high-precision, and high-density drilling, and it is easy to cause problems such as drill wear, chip blockage, and plate deformation. Laser drilling can achieve small-diameter, high-precision, and high-density drilling without contacting the plate, reducing mechanical damage and pollution, but it is high-cost, slow, and suitable for small-batch production. It is easy to cause problems such as heat-affected zones and increased difficulty in metallized vias.

[0005] At present, there are two commonly used laser drilling processes: CO2 laser drilling and UV laser drilling. CO2 laser drilling uses an infrared laser with a wavelength of 10.6 microns for drilling, and UV laser drilling uses an ultraviolet laser with a wavelength of 355 nanometers or 266 nanometers for drilling. CO2 laser drilling and UV laser drilling also have their own advantages and disadvantages. CO2 laser drilling can effectively cut non-metallic materials such as glass fiber, and there is no need to pre-treat the surface of the plate, but the absorption rate of metal materials such as bright copper is low, and it is difficult to achieve small blind holes less than 50 microns, and the focused spot is large, resulting in uneven thickness of the via wall. UV laser drilling can effectively cut metal materials such as bright copper, and the focused spot is small, which can achieve small blind holes less than 30 microns, and the heat-affected zone is small, but the absorption rate of non-metallic materials such as glass fiber is low, and it is difficult to achieve deep blind holes with a depth greater than 0.5 mm, and the surface of the plate needs to be pre-treated, such as browning or blackening, to increase the absorption rate of the laser.

[0006] In order to solve the above technical problems and meet user needs, the present invention proposes a process method based on PCB hard board drilling. The method adopts dual-light source laser drilling technology, that is, using picosecond ultraviolet laser and CO2 laser with two different wavelengths for drilling, so as to achieve high-efficiency, high-quality, low-cost and low-pollution PCB hard board drilling. Summary of the invention

[0007] The purpose of the present invention is to provide a process method for drilling holes in a PCB hard board, which adopts a dual-light source laser drilling technology, that is, using picosecond ultraviolet laser and CO2 laser with two different wavelengths for drilling, to solve the following technical problems in the prior art:

[0008] PCB boards no longer need to be browned or blackened before processing, reducing environmental and industrial pollution caused by chemical reactions;

[0009] The problem of large focusing spot of CO2 laser itself, which makes it difficult to process holes of 50 microns or less, has been solved.

[0010] The present invention meets the following user needs:

[0011] The same device can process holes with a diameter of more than 50 microns as well as holes with a diameter of less than 50 microns, which improves the applicability and flexibility of the device.

[0012] Reduce excessive environmental and industrial pollution caused by browning or blackening processes, and enhance environmental awareness and social responsibility;

[0013] It reduces related cost expenditure and improves economic benefits.

[0014] In order to achieve the above object, the present invention provides a process method based on PCB hard board drilling, which comprises the following steps:

[0015] Use picosecond UV laser to perform window opening operation at the preset drilling position on the PCB board, that is, cut a circular window with the same or slightly larger size as the preset drilling hole on the bright copper surface;

[0016] Use CO2 laser to remove glue inside the circular window after opening, that is, cut a circular blind hole with the same or slightly smaller depth than the preset drilling depth on non-metallic materials such as fiberglass;

[0017] Through-hole metallization is performed on the PCB board to achieve electrical connection between different layers.

[0018] The present invention uses two lasers with different wavelengths to process blind holes in PCB hard boards, one of which uses a picosecond ultraviolet laser and the other uses a CO2 laser. The purpose is:

[0019] Taking advantage of the high absorption rate and small focused spot of picosecond UV laser on bright copper and other metal materials, high-precision, high-quality, and low-heat-affected window opening operations are performed on the bright copper surface to achieve small blind holes less than 50 microns.

[0020] Taking advantage of the high absorption rate and large focused spot of CO2 laser for non-metallic materials such as glass fiber, high-efficiency, high-reliability and damage-free bottom copper degumming operations are performed inside the circular window after the window is opened, achieving deep blind holes with a depth greater than 0.5 mm.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This method combines the advantages of picosecond UV laser and CO2 laser with two different wavelengths to achieve high-efficiency, high-quality, low-cost and low-pollution PCB hard board drilling.

[0023] This method does not require pretreatment of PCB boards, reducing environmental and industrial pollution caused by chemical reactions;

[0024] This method can realize small blind holes less than 50 microns and deep blind holes with a depth greater than 0.5 mm, meeting the drilling requirements of different sizes and depths;

[0025] This method uses a flying optical path and a 4-axis linkage system for window processing, which improves processing efficiency and accuracy;

[0026] The method uses an aspheric beam shaper to obtain flat-top light for debonding, thereby improving the debonding quality and reliability.

[0027] This method is applicable to PCB hard boards of different types and specifications and is extensive and flexible. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process method of drilling holes in a PCB hard board according to the present invention;

[0029] Figure 2 is a schematic diagram of the present invention using picosecond ultraviolet laser to perform window opening operation;

[0030] Figure 3 Schematic diagram of two modes of window opening operation using picosecond ultraviolet laser in the present invention, namely, point-line cutting mode and IDMode mode;

[0031] Figure 4 It is a schematic diagram of the present invention using CO2 laser to perform glue removal operation;

[0032] Figure 5-1 It is a schematic diagram of a method of using CO2 laser to perform adhesive removal operation in the present invention, namely, the Cycle Mode method;

[0033] Figure 5-2 It is a schematic diagram of a method of using CO2 laser to perform adhesive removal operation in the present invention, namely, the Burst Mode method;

[0034] Figure 6 It is a schematic diagram of the present invention using a flying optical path and a 4-axis linkage system to perform window processing;

[0035] Figure 7 This is a simplified diagram of the optical path design of the CO2 laser end used in the present invention;

[0036] Figure 8 It is a principle diagram of obtaining flat-top light by using an aspheric beam shaper according to the present invention.

[0037] In the figure: 1. Picosecond UV laser; 2. CO2 laser; 3. PCB board; 4. Preset drilling position; 5. Bright copper surface; 6. Round window; 7. Round blind hole; 9. Metal layer; 10. Bottom copper surface; 11. Plane reflector; 12. Aspheric beam shaper; 13. Aperture; 14. Galvanometer; 15. Field mirror. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The process method based on PCB hard board drilling first requires a machine equipped with two light sources, one is a picosecond ultraviolet laser 1, and the other is a CO2 laser 2. The picosecond ultraviolet laser 1 can use a laser in the 355nm band, the laser frequency range is 150Khz-600Khz, and the power is 20W.

[0040] CO2 laser 2 can use a laser in the 9.3um-10.6um band with a power of 100W. Based on this drilling equipment, in order to consider the speed of drilling efficiency, the UV end uses a flying optical path and a 4-axis linkage system for window opening processing, while the CO2 end uses a fixed axis system for glue removal processing. The specific implementation method is as follows:

[0041] like Figure 2 As shown, a window opening operation is performed at a preset drilling position 4 on a PCB board 3 using a picosecond ultraviolet laser 1. The picosecond ultraviolet laser 1 is controlled by a flying optical path and a 4-axis linkage system to cut a circular window 6 on a bright copper surface 5. The diameter of the circular window 6 is the same as or slightly larger than the preset drilling size, and the depth of the circular window 6 is the same as or slightly smaller than the thickness of the bright copper surface 5.

[0042] Picosecond UV laser 1 can adopt two different window opening methods, namely point-line cutting method and ID Mode method; when the aperture of the window opening is in the range of 30um-100um, the processing method adopts the point-line cutting method, and when the aperture of the window opening is in the range of 100um-200um, the processing method adopts the ID Mode method.

[0043] like Figure 3 As shown, the figure above is a schematic diagram of the point-line cutting method. The point-line cutting method is to calculate the number of light spots emitted by the laser when the galvanometer 14 moves the arc length when processing a circular pattern according to the focused spot size and arc length formula, and force the laser to emit fewer light spots, thereby improving the window opening efficiency. Under normal circumstances, when we laser process a circular pattern, the laser emits a continuous light spot, that is to say, this light emission method does not consider the size of the light spot and the problem of light spot overlap. When we consider the size of the light spot and the problem of light spot overlap, we can force the laser to emit fewer light spots when processing a circular pattern. When we set the appropriate light spot value, we will further improve the efficiency of window opening in the processing method; for example: if you need to open a 100um window hole on a 10um thick copper surface, assuming that my focused spot size is 10-25um, the conventional processing method uses a continuous light emission method when processing this 100um circle, that is, the laser is always emitting light when the galvanometer 14 moves a 100um arc. When the point-line cutting method is used to process this 100um circle, the number of light spots emitted by the laser when the galvanometer 14 moves a 100um arc length is calculated according to the light spot size and arc length formula.

[0044] like Figure 3 As shown in the figure below, the schematic diagram of the ID Mode method; the implementation principle of ID Mode is: first, a light spot is excited at the center of the processing hole, and then the light spots required for processing the periphery of the processing hole are calculated according to the size of the light spot and the size of the hole to be processed, so that the center distance of the central light spot to the center of the peripheral light spot can be obtained, and the center position of this distance is used as the radius to excite the internal light spot. Under normal circumstances, a 200um hole requires two inner and outer circles to be processed. The IDMode processing method is a processing method that evolved from point-line cutting and is specifically designed for processing holes with larger apertures. Of course, this processing method also has a certain aperture threshold, and it is impossible to process a certain hole in an unlimited range. Its processing range is about 200um.

[0045] A CO2 laser 2 is used to remove glue inside the circular window 6 after the window is opened, that is, a circular blind hole 7 with the same or slightly smaller depth than the preset drilling depth is cut on the non-metallic material such as fiberglass. Figure 4As shown, the CO2 laser 2 is controlled by the fixed axis system to cut a circular blind hole 7 inside the circular window 6 after the window is opened. The diameter of the circular blind hole 7 is the same as or slightly smaller than the diameter of the circular window 6, and the depth of the circular blind hole 7 is the same as or slightly smaller than the preset drilling depth.

[0046] CO2 laser 2 can use two different glue removal methods, namely Cycle Mode and Burst Mode.

[0047] like Figure 5-1 As shown, the Cycle Mode is a processing method that excites a light spot once for each hole in the same scanning area, that is, after exciting a light spot at the opening of a hole, it continues to excite with a light spot until the last hole is processed, and then returns to the initially processed hole and repeats the processing with the set number of light spots.

[0048] Specifically, Cycle Mode is a processing method that excites a light spot once for each hole in the same Scan Area. In this way, in the same Scan Area, after a light spot is excited for opening a hole, it is continuously excited with a light spot until the last hole is processed, and then returns to the initially processed hole, and the processing is repeated with the set number of light spots. The Pulse interval is not processed with the set Pulse cycle, but is determined by the Galvano swing speed. Compared with Burst Mode, the processing time is longer. On the other hand, the time interval between the light spots for processing each hole is getting longer and longer, and the adverse effects of heat energy accumulation can also be reduced. It can reduce Figure 5-1 This phenomenon can be achieved by using long pulse width processing, and the taper rate can also be improved. It is a processing method that emphasizes processing quality.

[0049] like Figure 5-2 As shown, the Burst Mode method is a processing method that requires continuous pulse excitation when processing a hole, that is, when processing a hole, multiple pulses are continuously emitted according to the set pulse period.

[0050] Specifically, Burst Mode is a processing method that requires continuous pulse excitation when processing a hole. The interval between pulses in this mode is determined by the set pulse cycle. Its processing advantage is that the shorter the pulse cycle setting, the shorter the processing time, which is a method that emphasizes processing speed.

[0051] like Figure 1As shown, the hole wall metallization treatment is performed on the PCB board 3 to achieve electrical connection between different layers. After the hole wall metallization treatment is performed on the PCB board 3, the wall of the drilled hole is covered with a metal layer 9, and the metal layer 9 is connected to the bright copper surface 5 and the bottom copper surface 10, thereby achieving electrical connection between different layers.

[0052] like Figure 6 As shown, the principle of the present invention using the flying optical path and the 4-axis linkage system for window processing is as follows: the flying optical path refers to adding a plane reflector 11 between the laser output end and the incident end of the galvanometer 14, and making it move with the processing platform, so as to ensure that the laser beam is always perpendicular to the galvanometer 14. The 4-axis linkage system means that the X / Y axis of the platform, the X axis and the Z axis of the galvanometer 14 can be interpolated and controlled at the same time, that is, the four axes can be controlled in simultaneous linkage. The movement speed during this simultaneous linkage is a synthetic speed, not the individual motion control. It is a point in space that moves through the four axes at the same time to reach another point in the space, moves simultaneously from the starting point, and stops at the end point at the same time. The movement speed of each intermediate axis is the speed of each axis synthesized internally according to the programming speed through the motion interpolation algorithm of the controller. When this synthetic speed is used in actual production and processing, it can effectively avoid a series of delay problems such as waiting delay, acceleration and deceleration delay, and processing area splicing delay caused by non-linkage, thereby improving processing efficiency.

[0053] like Figure 7 and Figure 8 As shown, the optical path design of the CO2 laser end of the present invention is as follows: the CO2 laser 2 output end introduces the laser beam into the aspheric beam shaper 12 through a group of reflectors. The aspheric beam shaper 12 diverges the stronger energy in the center of the Gaussian beam through the central concave surface, and the surrounding convex surfaces gather the weaker energy around the Gaussian beam, so as to obtain a uniform energy distribution on the working surface, that is, flat top light. The flat top light passes through a group of apertures 13 to select a suitable spot size, and then passes through a group of galvanometers 14 and field lenses 15 for scanning and focusing, and finally performs debonding processing on the PCB board 3.

[0054] The principle of using the aspheric beam shaper 12 to obtain the flat top light in the present invention is as follows: the aspheric beam shaper 12 is an optical element that uses the concave and convex changes of the aspheric mirror to change the energy distribution of the Gaussian beam. The first step of the aspheric mirror is to focus and constrain the beam of the single-mode laser contacting the convex part of the mirror surface, and the second step is to expand the beam of the single-mode laser contacting the concave part of the mirror surface. After expansion and contraction, a cylindrical flat top light is finally obtained.

[0055] Specifically, the principle of the aspheric beam shaper 12 to obtain a flat-top light is to diverge the stronger energy in the center of the Gaussian beam through the central concave surface, and to gather the weaker energy around the Gaussian beam through the surrounding convex surfaces, so as to obtain a uniform energy distribution on the working surface. The first step of the aspheric mirror is to focus and constrain the beam of the single-mode laser contacting the convex part of the mirror surface, and the second step is to expand the beam of the single-mode laser contacting the concave part of the mirror surface. After expansion and contraction, a cylindrical flat-top light is finally obtained. The function of the aperture 13 is mainly to filter the stray light at the edge of the beam in the optical path and change the energy density of the beams passing through it. In use, apertures 13 of different sizes in the range of 2.6mm-8mm are selected according to the size of the window opening at the ultraviolet end. The actual number required varies slightly according to different designs. In this patent design, a total of 18 apertures 13 of different sizes in the range of 2.6-8mm are required to meet the processing technology of CO2 end degumming.

[0056] The laser wavelength used for debonding at the 2nd end of CO2 laser is 9.3um-10.6um. In the actual processing, different wavelengths within the available range will be selected for processing according to the different materials of the internal glue layer of PCB board 3. The shaping scheme adopts an aspheric optical shaping system. This shaping scheme is different from the diffraction optical shaping DOE and the refractive optical shaping π-shaper. It can better achieve the homogenization effect of the large spot CO2 beam from Gauss to flat top, and can ensure that the beam has high uniformity not only on one plane, but also within a certain range from the exit surface.

[0057] The above is a specific implementation method of the process method based on PCB hard board drilling of the present invention, which can effectively solve the technical problems and user needs existing in the prior art.

[0058] The present invention can also be modified appropriately according to actual needs, for example:

[0059] The present invention can adjust the power, frequency, pulse width, scanning speed, scanning times and other parameters of picosecond ultraviolet laser and CO2 laser according to different drilling sizes and depths to optimize the drilling effect;

[0060] The present invention can select picosecond ultraviolet lasers and CO2 lasers of different wavelengths according to different PCB board materials and thicknesses to adapt to different absorption rates and thermal effects;

[0061] The present invention can select different metal layer materials and thicknesses according to different via wall metallization methods to meet different electrical connection requirements.

[0062] These modifications all fall within the protection scope of the present invention.

[0063] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A process method based on PCB hard board drilling, characterized in that: The method comprises the following steps: Use picosecond UV laser to perform window opening operation at the preset drilling position on the PCB board, that is, cut a circular window with the same or slightly larger size as the preset drilling hole on the bright copper surface; Use CO2 laser to remove glue inside the circular window after opening, that is, cut a circular blind hole with the same or slightly smaller depth than the preset drilling depth on non-metallic materials such as fiberglass; Through-hole metallization is performed on the PCB board to achieve electrical connection between different layers.

2. A process method based on PCB hard board drilling according to claim 1, characterized in that: The picosecond ultraviolet laser adopts a flying optical path and a 4-axis linkage system for window opening processing. The flying optical path refers to adding a plane reflector between the laser output end and the galvanometer incident end, and making it move with the processing platform, so as to ensure that the laser beam always enters the galvanometer vertically; the 4-axis linkage system means that the X / Y axis of the platform, the X axis and the Z axis of the galvanometer can be interpolated and controlled at the same time, that is, the four axes can be controlled in simultaneous linkage.

3. The process method for drilling holes in a PCB hard board according to claim 1, characterized in that: The CO2 laser uses a fixed axis system for glue removal processing. The fixed axis system means that the Z axis of the fixed galvanometer will not move during the processing, and only the X / Y axis of the platform and the X axis of the galvanometer are controlled in motion.

4. The process method for drilling holes in a PCB hard board according to claim 1, characterized in that: The picosecond ultraviolet laser can adopt two different window opening methods, namely the point-line cutting method and the ID Mode method; when the aperture of the window is in the range of 30um-100um, the processing method adopts the point-line cutting method, and when the aperture of the window is in the range of 100um-200um, the processing method adopts the ID Mode method.

5. The process method for drilling holes in a PCB hard board according to claim 1, characterized in that: The CO2 laser can adopt two different glue removal methods, namely the Cycle Mode method and the Burst Mode method; the Cycle Mode method is a processing method in which a light spot is excited once for each hole in the same scanning area, that is, after exciting a light spot at the opening of the hole, it is continuously excited with a light spot until the last hole is processed, and then returns to the initially processed hole and repeats the processing with a set number of light spots; the Burst Mode method is a processing method that requires continuous pulse excitation when processing a hole, that is, when processing a hole, multiple pulses are continuously emitted according to the set pulse period.

6. The process method for drilling holes in a PCB hard board according to claim 1, characterized in that: The CO2 laser end uses an aspheric beam shaper to convert a Gaussian beam into a flat-top light, and selects a suitable flat-top spot size through a set of apertures; the aspheric beam shaper is an optical element that uses the concave and convex changes of an aspheric mirror to change the energy distribution of a Gaussian beam; the first step of the aspheric mirror is to focus and constrain the beam of the single-mode laser contacting the convex part of the mirror surface, and the second step is to expand the beam of the single-mode laser contacting the concave part of the mirror surface, and finally obtain a cylindrical flat-top light after expansion and contraction.

7. A device for implementing the process method for drilling holes in a PCB hard board according to claims 1 to 6, characterized in that: The equipment includes: A picosecond UV laser, used to emit picosecond UV laser; A CO2 laser for emitting CO2 laser; a flying optical path for introducing picosecond UV laser into the galvanometer; A 4-axis linkage system to control the X / Y axis of the platform, the X and Z axis of the galvanometer; A fixed axis system to control the scanning and focusing of the CO2 laser; An aspheric beam shaper to convert CO2 laser light into a flat-top beam; A set of reflectors for introducing picosecond UV laser and CO2 laser into the flying optical path and aspheric beam shaper respectively; A set of apertures to select the appropriate flat-top spot size; A processing platform for fixing PCB boards.

Images