Laser system and method for processing flexible circuit board

Abstract

The present invention provides a laser system and a method for processing a flexible circuit board. The key points of the technical solution are: comprising a laser for generating a parallel laser beam, a beam expander for changing the diameter of the laser beam provided at the output end of the laser, an acousto-optic modulator for focusing the diffused parallel laser beam provided at the output end of the beam expander, a galvanometer scanning system for scanning and locating the plane position of a sample and a focusing lens for converging the laser beam provided in sequence at the output end of the acousto-optic modulator; when the system is used to process blind holes in a flexible circuit board, the drilling is continuous, and after drilling with a laser in a zero-defocus state, the drilling is quickly switched to a laser in a negative-defocus state to continue drilling; compared with the prior art method of drilling all holes with a laser in a zero-defocus state and then processing again with a laser in a negative-defocus state, the present invention has the advantages of fast switching of laser states, shortening the processing path, and improving work efficiency.

Description

Technical field

[0002] The invention relates to a laser system and a method for processing a flexible circuit board thereof. [Background Technology]

[0004] Due to the rapid development of microelectronics technology and the widespread application of large-scale and ultra-large-scale integrated circuits in recent years, the manufacture of printed circuit boards has developed towards multi-layer and multi-functionality, and the production requirements of circuit boards have become more and more sophisticated.

[0005] As printed circuit board traces become increasingly finer, the number of vias required is also shrinking, making drilling increasingly challenging. Blind via processing is a crucial process in circuit board manufacturing. Common drilling methods include mechanical drilling and laser drilling. However, mechanical drilling technology no longer meets the requirements of high-end circuit boards. Laser drilling is the technology that can handle microvia production. Laser drilling offers the advantage of producing relatively small microvias and blind vias, with diameters ranging from 50µm to 200µm. Furthermore, its cost advantage is significantly lower than other methods.

[0006] Multilayer circuit boards are typically constructed by alternating layers of copper and insulating material (substrate), with both the top and bottom layers being copper. For example, when processing blind vias in flexible circuit boards, which consist of double-sided copper foil and a substrate positioned between them, the top copper foil and substrate must be removed, leaving the bottom copper foil. Therefore, processing blind vias in flexible circuit boards requires a two-step process: first, using a focused laser to process the surface copper layer, and then using a defocused laser to process the inner layers.

[0007] In existing laser equipment, the switching speed between focused laser and defocused laser is slow. Generally, the surface copper on all holes is processed with focused laser first, and then the flexible circuit board is moved back to its original position and the inner layer board of all holes is processed again with defocused laser. This method of processing one blind hole twice has a long processing path and low efficiency. [Summary of the invention]

[0009] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a laser system that can quickly switch between focused and defocused lasers and a method for processing flexible circuit boards, which can improve processing efficiency.

[0010] The present invention is achieved through the following technical solutions: a laser system, characterized in that it includes a laser for generating a parallel laser beam, a beam expander for changing the diameter of the parallel laser beam is provided at the output end of the laser, an acousto-optic modulator for focusing the diffused parallel laser beam is provided at the output end of the beam expander, and a galvanometer scanning system for scanning and locating the plane position of a sample and a focusing lens for converging the laser beam are sequentially provided at the output end of the acousto-optic modulator.

[0011] The laser system as described above is characterized in that the acousto-optic modulator includes an acousto-optic lens capable of inputting acoustic waves to generate gradient refractive index changes and a piezoelectric driver for generating periodic oscillating acoustic waves.

[0012] The laser system as described above is characterized in that: there are two acousto-optic modulators, the acousto-optic lens has refractive layers with different refractive indices, and the boundaries of the refractive layers of the two acousto-optic lenses are perpendicular to each other and the refractive indices match each other.

[0013] The laser system as described above is characterized in that the piezoelectric driver is made of piezoelectric ceramics, and the vibration directions of the periodic oscillation sound waves generated by the piezoelectric driver are perpendicular to each other.

[0014] The laser system as described above is characterized in that the beam expander is a fixed-magnification beam expander or an electrically variable-magnification beam expander.

[0015] The laser system as described above is characterized in that an optical shutter for controlling the laser switch is provided on the laser.

[0016] The laser system as described above is characterized in that the galvanometer scanning system includes a reflector for changing the direction of the light beam and a rotary motor for fine-tuning and swinging the reflector. There are two reflectors and two corresponding rotary motors.

[0017] The laser system as described above is characterized in that the focusing lens is an f-θ focusing lens that can form a focused light spot of uniform size in the entire sample plane.

[0018] A method for processing flexible circuit boards using the above-mentioned laser system is characterized in that: when the optical shutter is opened, the laser emits a parallel laser beam, and after passing through the beam expander, the diameter of the laser beam increases, and then the laser beam is injected into the acousto-optic modulator to fine-tune the laser beam; when passing through the acousto-optic modulator, the piezoelectric driver emits different periodic oscillating sound waves to the acousto-optic lens, the refractive index of the acousto-optic lens changes, and at the same time, the direction of the laser beam changes to diverge outward or contract inward, thereby changing the position of the laser beam focus; when the laser beam diverges outward, the focus moves backward, and when the laser beam contracts inward, the focus moves forward, and the range of focus movement is within 400 microns; then, the galvanometer scanning system reflects the finely tuned laser beam downward and scans and positions the sample plane, and after reflection by the reflector, the forward and backward movement of the laser beam focus is converted into up and down movement; finally, the laser beam is focused by the focusing lens and emitted, and the emitted laser beam can produce different depths at any point on the sample plane when processing the sample. hole; since the acousto-optic modulator can change the relative position of the focus (focal plane) of the laser beam and the sample to be processed, and the faster the sound wave frequency changes, the faster its relative position changes, the laser beam can be quickly switched between positive defocus, zero defocus and negative defocus; when the laser emitted by the focusing lens is in a positive defocus state, that is, the focus is above the sample to be processed, the laser does not process the sample at this time; when the laser emitted by the focusing lens is in a zero defocus state, that is, the focus is on the upper surface of the sample to be processed, the laser processes the surface copper of the sample; when the laser emitted by the focusing lens is in a negative defocus state, that is, the focus is inside the sample to be processed, the laser processes the inner layer board of the sample; when processing the sample, the laser switches to a zero defocus state and processes a first hole on the hole position to be processed on the flexible circuit board; after the first hole is processed, the laser quickly switches to a negative defocus state and further processes the first hole into a second hole, that is, the required blind hole; after processing the hole position, the flexible circuit board is moved to continue processing the next hole position until all the hole positions are processed.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The laser system of the present invention is equipped with an acousto-optic modulator that can quickly switch the state of the laser (positive defocus, zero defocus and negative defocus).

[0021] 2. In the method for processing a flexible circuit board of the present invention, when processing blind holes in a flexible circuit board, the two drillings are continuous. After drilling with a laser in a zero-defocus state, the laser is quickly switched to a laser in a negative-defocus state to continue drilling. Compared with the prior art, which uses a laser in a zero-defocus state to drill all holes and then processes them again with a laser in a negative-defocus state, the continuous drilling method of the present invention can shorten the processing path, thereby improving processing efficiency.

Brief Description of the Drawings

[0023] FIG1 is a block diagram of the optical path of the present invention;

[0024] FIG2 is a schematic diagram of the refractive index distribution of the acousto-optic lens of the present invention;

[0025] FIG3 is a schematic diagram of the galvanometer scanning system of the present invention;

[0026] FIG4 is a schematic diagram of punching holes on a flexible printed circuit board according to the present invention, wherein Cu and PI in the figure represent the materials of the layer respectively.

[0027] In the figure: 1 is a laser; 2 is a beam expander; 3 is an acousto-optic modulator; 4 is a galvanometer scanning system; 5 is a focusing lens; 6 is an optical shutter; 7 is an acousto-optic lens; 8 is a piezoelectric driver; 9 is a reflector; 10 is a rotating motor; 11 is a first hole; 12 is a second hole. [Specific implementation method] The technical features of the present invention are further described in detail below with reference to the accompanying drawings so that those skilled in the art can understand them.

[0029] A laser system, such as Figure 1 As shown in FIG4 , a laser 1 for generating a parallel laser beam is provided. A beam expander 2 for changing the diameter of the parallel laser beam is provided at the output end of the laser 1. An acousto-optic modulator 3 for focusing the diffused parallel laser beam is provided at the output end of the beam expander 2. A galvanometer scanning system 4 for scanning and locating the plane position of the sample and a focusing lens 5 for converging the laser beam are provided at the output end of the acousto-optic modulator 3 in sequence.

[0030] The acousto-optic modulator 3 includes an acousto-optic lens 7 capable of inputting sound waves to generate a gradient refractive index change, and a piezoelectric driver 8 for generating periodic oscillating sound waves. The acousto-optic modulator 3, abbreviated as AOD in English, is a device made based on the principle of acousto-optic deflection. The acousto-optic modulator 3 can change the angle of the laser beam based on the acousto-optic interaction mechanism. The acousto-optic modulator 3 is provided with two acousto-optic lenses 7, each having a refractive layer with different refractive indices. The boundaries of the refractive layers of the two acousto-optic lenses 7 are perpendicular to each other and the refractive indices are matched.

[0031] The material of the piezoelectric driver 8 is piezoelectric ceramic, and the vibration directions of the periodic oscillation sound waves generated by the piezoelectric driver 8 are perpendicular to each other; piezoelectric ceramics are a type of electronic ceramic material with piezoelectric properties. Through the control of electronic circuits, they can generate vibrations of different frequencies, thereby emitting various sound waves.

[0032] The beam expander 2 is a fixed-magnification beam expander or an electrically variable-magnification beam expander. The beam expander 2 is a lens component capable of changing the diameter and divergence angle of the laser beam. Using the beam expander 2 can obtain a smaller focused light spot.

[0033] The laser 1 is provided with an optical shutter 6 for controlling the laser switch. The optical shutter 6 is not necessary, and the laser 1 can also be electrically controlled to emit light.

[0034] The galvanometer scanning system 4 includes a reflector 9 for changing the direction of the light beam and a rotary motor 10 for fine-tuning the swing of the reflector 9. There are two reflectors 9 and two corresponding rotary motors 10. One of the reflectors is used to locate the X-axis coordinate of the laser beam focus, and the other reflector is used to locate the Y-axis coordinate of the laser beam focus.

[0035] The focusing lens 5 is an f-θ focusing lens that can form a focused light spot of uniform size across the entire sample plane. Generally speaking, in an optical system, a laser beam will experience off-axis deflection after passing through a focusing lens system. This will result in an abnormal image or distortion relative to an ideal plane. The f-θ focusing lens, also known as a flat-field focusing lens or field lens, is a specialized lens system designed to form a focused light spot of uniform size across the entire plane. In the absence of distortion, the position of the focal point depends on the focal length of the lens and the tangent of the deflection angle.

[0036] This patent also claims protection for a method of processing a flexible circuit board using the above laser system, such as Figure 4As shown, the flexible circuit board is a multi-layer circuit board, the surface layer and the bottom layer are both copper layers, and the inner layer is alternately set as PI layer and copper layer. The Chinese name of PI is polyimide; the method is specifically as follows: when the optical shutter 6 is opened, the laser 1 emits a parallel laser beam, and the diameter of the laser beam becomes larger after passing through the beam expander 2, and then enters the acousto-optic modulator 3 to fine-tune the laser beam; when passing through the acousto-optic modulator 3, the piezoelectric driver 8 emits different periodic oscillation sound waves to the acousto-optic lens 7, and the refractive index of the acousto-optic lens 7 changes. At the same time, the direction of the laser beam changes to diverge outward or contract inward, thereby changing the position of the laser beam focus; when the laser beam diverges outward, the focus moves backward, and when the laser beam contracts inward, the focus moves forward, and the range of focus movement is within 400 microns; then, the galvanometer scanning system 4 reflects the finely adjusted laser beam downward and scans and positions the sample plane. After reflection by the reflector 9, the forward and backward movement of the laser beam focus is converted into up and down movement; finally, the laser beam passes through the focusing lens 5 After focusing, the laser beam can produce holes of different depths at any point on the sample plane when processing the sample; The laser beam can change the relative position between the focus (focal plane) of the laser beam and the sample being processed, and the faster the sound wave frequency changes, the faster the relative position changes, so the laser beam can quickly switch between positive defocus, zero defocus, and negative defocus. When the laser emitted by the focusing lens 5 is in a positive defocus state, that is, the focus is above the sample being processed, the laser does not process the sample. When the laser emitted by the focusing lens 5 is in a zero defocus state, that is, the focus is on the upper surface of the sample being processed, the laser processes the surface copper of the sample. When the laser emitted by the focusing lens 5 is in a negative defocus state, that is, the focus is inside the sample being processed, the laser processes the inner layer of the sample. When processing the sample, the laser switches to the zero defocus state and processes a first hole 11 on the hole position to be processed on the flexible circuit board. After the first hole 11 is processed, the laser quickly switches to the negative defocus state and further processes the first hole 11 into a second hole 12, which is the required blind hole. After processing the hole position, the flexible circuit board is moved to continue processing the next hole position until all the holes are processed.

[0037] The embodiments described in the present invention are merely descriptions of the preferred implementation methods of the present invention and are not intended to limit the concept and scope of the invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should fall within the scope of protection of the present invention.

Claims

1. A laser system, characterized in that: The invention comprises a laser (1) for generating a parallel laser beam, a beam expander (2) for changing the diameter of the parallel laser beam is provided at the output end of the laser (1), an acousto-optic modulator (3) for focusing the diffused parallel laser beam is provided at the output end of the beam expander (2), a galvanometer scanning system (4) for scanning and positioning the sample plane position and a focusing lens (5) for converging the laser beam are provided at the output end of the acousto-optic modulator (3), the acousto-optic modulator (3) comprises an acousto-optic lens (7) capable of inputting an acoustic wave to generate a gradient refractive index change and a piezoelectric driver (8) for generating a periodic oscillation acoustic wave, the acousto-optic modulator (3) is provided with two, The acousto-optic lens (7) has refractive layers with different refractive indices, and the boundaries of the refractive layers of the two acousto-optic lenses (7) are perpendicular to each other. The material of the piezoelectric driver (8) is piezoelectric ceramic, and the vibration directions of the periodic oscillation sound waves generated by the piezoelectric driver (8) are perpendicular to each other. The beam expander (2) is a fixed-magnification beam expander or an electric variable-magnification beam expander. A light gate (6) for controlling the laser switch is provided on the laser (1). The galvanometer scanning system (4) includes a reflector (9) for changing the direction of the light beam and a rotary motor (10) for fine-tuning the swing of the reflector (9). Two reflectors (9) are provided, and two corresponding rotary motors (10) are also provided.

2. The laser system according to claim 1, wherein: The focusing lens (5) is an f-θ focusing lens capable of forming a focused light spot of uniform size in the entire sample plane.

3. A method for processing a flexible circuit board using the laser system according to claim 1 or 2, characterized in that: When the optical gate (6) is opened, the laser (1) emits a parallel laser beam, which becomes larger in diameter after passing through the beam expander (2), and then enters the acousto-optic modulator (3) to fine-tune the laser beam; when passing through the acousto-optic modulator (3), the piezoelectric driver (8) emits different periodic oscillating sound waves to the acousto-optic lens (7), and the refractive index of the acousto-optic lens (7) changes. At the same time, the direction of the laser beam diverges outward or contracts inward, thereby changing the position of the laser beam focus; when When the laser beam diverges outward, the focus moves backward, and when the laser beam contracts inward, the focus moves forward. The range of focus movement is within 400 microns. Then, the galvanometer scanning system (4) reflects the finely adjusted laser beam downward and scans and positions the sample plane. The sample is a flexible circuit board. After being reflected by the reflector (9), the forward and backward movement of the laser beam focus is converted into an upward and downward movement. Finally, the laser beam is focused by the focusing lens (5) and then emitted. When processing the sample, the emitted laser beam can make holes of different depths at any point on the sample plane. Since the acousto-optic modulator (3) can change the focus of the laser beam and the relative position of the focal plane and the processed sample, and the faster the sound wave frequency changes, the faster the relative position changes, the laser beam can be quickly switched between positive defocus, zero defocus and negative defocus; when the laser emitted by the focusing lens (5) is in a positive defocus state, that is, the focus is above the processed sample, the laser does not process the sample at this time; when the laser emitted by the focusing lens (5) is in a zero defocus state, that is, the focus is on the upper surface of the processed sample, the laser does not process the surface of the sample at this time. Copper is processed; when the laser emitted by the focusing lens (5) is in a negative defocus state, that is, the focus is inside the sample to be processed, the laser processes the inner layer of the sample; when processing the sample, the laser switches to a zero defocus state, and processes a first hole (11) on the hole position to be processed of the sample; after the first hole (11) is processed, the laser quickly switches to a negative defocus state, and further processes the first hole (11) into a second hole (12), which is the required blind hole; after processing the hole position, the sample is moved and the next hole position is processed until all the hole positions are processed.

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