Laser drilling method

Abstract

The present application relates to the technical field of circuit board processing, and specifically provides a laser drilling method; wherein the circuit board includes an upper surface layer, an intermediate layer, and a lower surface layer stacked in sequence, the upper surface layer being provided with a first energy absorbing portion, and the lower surface layer being provided with a second energy absorbing portion, wherein the surface roughness of the first energy absorbing portion is lower than the surface roughness of the second energy absorbing portion. The present application provides a first energy absorbing portion with a lower roughness on the upper surface layer and a second energy absorbing portion with a higher roughness on the lower surface layer, so that the absorption rate of the second energy absorbing portion of the second surface layer to attenuated laser light is improved, thereby ensuring that the quality of the holes burned through the upper and lower surface layers during the laser drilling process is relatively close, with small differences in hole diameter and roundness, thereby improving the product quality of the circuit board.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board processing, and in particular to a circuit board, a circuit board pretreatment method and a laser hole opening method. Background Art

[0002] With the rapid development of the electronics industry, the production requirements of the circuit board manufacturing industry, which is the main pillar of the electronics industry, are becoming higher and higher. The number of layers of the circuit boards is increasing, and the hole density on the circuit boards is increasing while the diameter is decreasing.

[0003] Lasers are commonly used to drill holes in double-sided copper-clad PCBs or the core layer of multilayer PCBs. The laser beam conditions at the incident and exit surfaces differ significantly. The laser beam at the incident surface is well collimated, imparting a balanced energy profile to the copper surface. However, as the laser beam exits the exit surface, it partially diverges after passing through the processing medium, and its energy is attenuated accordingly. Consequently, the hole quality at the exit surface differs significantly from that at the incident surface, affecting the consistency of the hole structure at both ends and, consequently, the quality of the circuit board. Summary of the Invention

[0004] In view of this, the present application provides a circuit board to solve the problem of large quality differences between the two ends of holes produced by laser drilling of circuit boards in the prior art.

[0005] In a first aspect, the present application provides a circuit board, which includes an upper surface layer, an intermediate layer, and a lower surface layer stacked in sequence, wherein a first energy absorbing portion is provided on the upper surface layer, and a second energy absorbing portion is provided on the lower surface layer, wherein the surface roughness of the first energy absorbing portion is lower than the surface roughness of the second energy absorbing portion.

[0006] In the above scheme, a laser processing method can be used to drill holes in the circuit board, and the laser is irradiated on the circuit board from the upper surface layer to the lower surface layer. After burning through the upper surface layer and the middle layer, the laser reaches the lower surface layer. At this time, the laser is interfered with by the hole walls of the burnt holes in the upper surface layer and the middle layer, and there is a certain attenuation in the laser emission process. Therefore, the burning efficiency and burning effect on the lower surface layer are worse than those on the upper surface layer. In order to reduce the difference in the laser burning effect between the upper surface layer and the lower surface layer, this scheme provides a first energy absorbing portion with a lower roughness on the upper surface layer of the circuit board and a second energy absorbing portion with a higher roughness on its lower surface layer. This improves the absorption rate of the attenuated laser light by the second energy absorbing portion of the second surface layer, thereby reducing the difference in hole diameter and roundness between the two ends of the laser processing. In this way, the quality of the holes burned in the upper surface layer and the lower surface layer is closer, thereby improving the product quality of the circuit board.

[0007] In a possible design, the upper surface layer and the lower surface layer are metal layers, and the middle layer is an insulating layer.

[0008] In the above scheme, the metal materials involved in the upper surface layer and the lower surface layer may include but are not limited to copper materials or aluminum materials, so that the advantages of copper's good conductivity and good laser processability can be utilized to drill holes in it, and the material of the middle layer includes resin, and the good insulation and toughness of the resin can be utilized to ensure the working stability and structural strength of the circuit board.

[0009] In a possible design, the thickness of the upper surface layer is greater than the thickness of the lower surface layer.

[0010] In the above scheme, it is further limited that the thickness of the upper surface layer is greater than that of the lower surface layer. In this way, during the laser drilling process, the laser reaches the lower surface layer after burning through the upper surface layer and the middle layer. At this time, the laser is interfered by the hole walls of the burnt holes in the upper surface layer and the middle layer, and the laser has a certain attenuation. The thinner lower surface layer is more easily burned through by the laser. The thinned lower surface layer is used to balance the influence of the laser energy attenuation, further ensuring that the quality of the holes burned by the laser on the upper surface layer and the lower surface layer is relatively close, the difference in hole diameter and the difference in roundness are small.

[0011] In a possible design, the thickness of the upper surface layer is 1-2 μm greater than the thickness of the lower surface layer.

[0012] In the above scheme, the thickness difference between the upper surface layer and the lower surface layer is further limited to ensure that the thickness difference between the lower surface layer and the upper surface layer is within an appropriate range, so that the holes formed after the attenuated laser burns the lower surface layer have small differences in aperture and roundness with the holes on the upper surface, so that the hole quality of the two is relatively close.

[0013] In a possible design, the surface roughness Rz of the first energy absorbing portion is in a range of 0-2 μm, and the surface roughness Rz of the second energy absorbing portion is in a range of 3-4 μm.

[0014] In the above solution, the surface roughness Rz of the first energy absorbing portion is further limited to 0-2 μm, and the surface roughness Rz of the second energy absorbing portion is further limited to 3-4 μm. The above roughness range can ensure that the first and second energy absorbing portions can better absorb laser energy and achieve a faster processing rate.

[0015] In a possible design, the first energy absorbing portion is provided on a side of the upper surface layer close to the middle layer, and / or a side of the upper surface layer away from the middle layer.

[0016] In the above solution, when the first energy-absorbing portion is positioned on the side of the upper surface layer closest to the middle layer, its ability to absorb laser energy decreases, resulting in better adhesion between the upper surface layer and the middle layer. However, an excessively rough surface can cause attenuation and loss of relatively high-frequency transmission signals. When the first energy-absorbing portion is positioned on the side of the upper surface layer farther from the middle layer, its ability to absorb laser energy increases. In summary, the specific placement of the first energy-absorbing portion can be flexibly adjusted based on actual circumstances.

[0017] In a possible design, the second energy absorbing portion is provided on a side of the lower surface layer close to the middle layer, and / or a side of the lower surface layer away from the middle layer.

[0018] When the second energy-absorbing portion is positioned on the side of the lower surface layer closest to the middle layer, its ability to absorb laser energy decreases, resulting in better adhesion between the lower surface layer and the middle layer. However, an excessively rough surface can cause attenuation and loss of relatively high-frequency transmission signals. When the second energy-absorbing portion is positioned on the side of the lower surface layer farther from the middle layer, its ability to absorb laser energy is stronger. In summary, the specific placement of the second energy-absorbing portion can be flexibly adjusted based on actual conditions.

[0019] In a second aspect, the present application further provides a circuit board preprocessing method, the method comprising:

[0020] Provide upper surface parts, middle parts and lower surface parts;

[0021] performing a roughening process on the lower surface member so as to form a second energy absorbing portion on the lower surface member, wherein the surface roughness of the second energy absorbing portion is greater than the surface roughness of the upper surface member;

[0022] The upper surface piece, the middle piece and the lower surface piece are stacked and pressed in sequence.

[0023] In the above scheme, the lower surface part is roughened to form a relatively rough second energy absorbing part on the lower surface part, so that the surface roughness of the second energy absorbing part is greater than the surface roughness of the upper surface part. Then, the upper surface part, the middle part and the lower surface part are pressed together to form a circuit board. When the circuit board after the above pretreatment is laser processed, the laser is irradiated on the circuit board along the direction from the upper surface part to the lower surface part. After burning through the upper surface part and the middle part, the laser reaches the lower surface part. At this time, the laser is interfered by the hole walls of the burn-through holes of the upper surface part and the middle part, and the laser has a certain attenuation, so the burning efficiency and burning effect on the lower surface part are poor. In order to reduce the difference in laser burning effects on the upper surface part and the lower surface part, this solution configures different roughness for the lower surface and the upper surface. Specifically, a second energy-absorbing portion with a higher roughness is formed on the lower surface part by a roughening treatment method, so that the absorption rate of the second energy-absorbing portion of the lower surface part to the attenuated laser is improved, thereby making the difference in the diameter and roundness of the holes burned by the laser on the upper surface part and the lower surface part small, so that the consistency of the holes and the opening quality on both sides are closer, thereby improving the product quality of the circuit board.

[0024] In one possible design, the roughening treatment of the lower surface member includes:

[0025] The lower surface member is roughened by using a browning process, a blackening process, or a laser roughening process.

[0026] In the above solution, the browning process or the blackening process can efficiently and quickly roughen the lower surface member and ensure that the rough portion on the second energy absorbing part is relatively uniform.

[0027] In one possible design, before stacking and pressing the upper surface piece, the middle piece, and the lower surface piece in sequence, the pretreatment method includes:

[0028] The upper surface member is roughened to form a first energy absorbing portion on the upper surface member, wherein the surface roughness of the second energy absorbing portion is greater than the surface roughness of the first energy absorbing portion.

[0029] In the above scheme, not only the lower surface part is roughened, but the upper surface part can also be roughened, and the surface roughness of the second energy absorbing part on the upper surface part is made greater than the surface roughness of the first energy absorbing part on the lower surface part. In this way, when the laser is irradiated on the upper surface part, the first energy absorbing part can also be used to enhance the upper surface part's absorption of laser energy, thereby accelerating the speed of laser burning and perforation, and thus improving the overall process efficiency and the production quality of the circuit board.

[0030] In a third aspect, the present application also provides a laser drilling method, which includes: drilling a hole in a circuit board by laser, wherein the circuit board is the circuit board described in the above-mentioned first aspect scheme, or is a circuit board processed using the above-mentioned second aspect circuit board pretreatment method.

[0031] In the above scheme, based on the circuit board in the above-mentioned first aspect embodiment, or the circuit board pre-processed by the above-mentioned second aspect embodiment, drilling holes in the circuit board by the laser drilling method obviously also has the advantages of high drilling quality and fast drilling efficiency.

[0032] Other features and advantages of the embodiments of the present application will be described in the subsequent description, and in part will become apparent from the description, or be understood by practicing the embodiments of the present application. The purposes and other advantages of the embodiments of the present application are achieved and obtained by the structures particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 A schematic diagram of the assembly of a circuit board provided in an embodiment of the present application;

[0035] Figure 2 A schematic diagram of the press-fitting of a circuit board provided in an embodiment of the present application;

[0036] Figure 3 A schematic diagram of the structure of the circuit board provided in the embodiment of the present application (I);

[0037] Figure 4 Schematic diagram of the structure of the circuit board provided in the embodiment of the present application (II);

[0038] Figure 5 Schematic diagram of the structure of the circuit board provided in the embodiment of the present application (III);

[0039] Figure 6 Schematic diagram of the structure of the circuit board provided in the embodiment of the present application (IV);

[0040] Figure 7 This is a flowchart of a circuit board preprocessing method provided in an embodiment of the present application.

[0041] Reference numerals:

[0042] 100-circuit board;

[0043] 1-upper surface layer;

[0044] 11- first energy absorbing part;

[0045] 2-middle layer;

[0046] 3-lower surface layer;

[0047] 31-Second energy absorbing part.

[0048] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application. DETAILED DESCRIPTION

[0049] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0050] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0051] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0052] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0053] It should be noted that the directional words such as "upper", "lower", "left", and "right" described in the embodiments of the present application are described based on the angles shown in the accompanying drawings and should not be understood as limiting the embodiments of the present application. In addition, in the context, it should be understood that when it is mentioned that an element is connected to another element "on" or "under", it can not only be directly connected to the other element "on" or "under", but also be indirectly connected to the other element "on" or "under" through an intermediate element.

[0054] The existing technology uses laser processing to drill holes in double-sided copper-clad PCB circuit boards or the core layer of multi-layer PCB boards. In actual application scenarios, the inventors found that there is a significant difference in the state of the laser beam on the light-entering surface and the light-exiting surface. Specifically, the laser beam on the light-entering surface has good collimation, and the energy acting on the metal surface is balanced; when the laser is emitted from the light-exiting surface, because the beam will become partially divergent after passing through the processing medium, its energy will also be attenuated accordingly. Therefore, the hole processing quality of the light-exiting surface relative to the light-entering surface shows a large difference, which affects the consistency of the two ends of the hole structure, and thus affects the quality of the circuit board. In order to solve the above technical problems, the inventive concept of this application was conceived, which will be specifically explained through the following embodiments.

[0055] The following describes a specific embodiment of the circuit board according to the structure of the circuit board provided in the embodiment of the present application.

[0056] Existing circuit boards 100, also known as PCBs (Printed Circuit Boards), or circuit boards, are facing increasingly higher requirements, with more and more layers and a higher density of holes with decreasing diameters. A single circuit board 100 often has tens of thousands of holes, with diameters ranging from 0.05 to 3.0 mm. Generally speaking, double-sided copper-clad laminates with circuitry on both sides can achieve a high level of integration. Because there are circuit conductors on both sides, there must be an appropriate electrical connection between the two sides. This "bridge" between the circuits is called a through-hole. Existing mechanical drills for processing tiny through-holes cannot meet product requirements in terms of production capacity and quality. The high energy and collimation properties of laser drilling provide a convenient way to process tiny through-holes.

[0057] However, direct hole forming by laser will bring about its own unique quality defects. The quality of the laser-processed light entrance surface and light exit surface is inconsistent. Specifically, because the energy of the laser is more concentrated on the light entrance side, the processed holes have good roundness and processing quality. When the laser passes through the workpiece, the energy of the laser will inevitably be attenuated to a certain extent. Therefore, the roundness and processing quality of the laser-processed light exit hole are poor, and the diameter of the light exit hole is also smaller than the diameter of the light entrance hole. Under certain conditions where the laser attenuation is more serious, the hole processed by the laser is even conical, which seriously affects the normal use of the circuit board 100.

[0058] To solve the above problems, the present application provides a circuit board 100, which includes an upper surface layer 1, an intermediate layer 2 and a lower surface layer 3 stacked in sequence, a first energy absorbing portion 11 is provided on the upper surface layer 1, and a second energy absorbing portion 31 is provided on the lower surface layer 3, wherein the surface roughness of the first energy absorbing portion 11 is lower than the surface roughness of the second energy absorbing portion 31.

[0059] See also Figure 1 and Figure 2 The three-layer structure of the circuit board 100 includes a conductive upper surface layer 1 and a lower surface layer 3 and an insulating intermediate layer 2 sandwiched between the two. The upper surface layer 1, the intermediate layer 2 and the lower surface layer 3 can be bonded together using a commonly used adhesive, or the three can also be pressed into an integrated circuit board 100 structure using, for example, a lamination process; illustratively, the thickness of the upper surface layer 1 can range from 2 to 6 μm, the thickness of the intermediate layer 2 can range from 100 to 200 μm, and the thickness of the lower surface layer 3 can range from 2 to 5 μm.

[0060] The first energy absorbing portion 11 can be a smooth surface structure or a rough surface structure, and the second energy absorbing portion 31 can be a rough surface structure. Figure 4 As long as the surface roughness of the second energy absorbing portion 31 is higher than that of the first energy absorbing portion 11, it is sufficient. Surface roughness refers to the unevenness of the machined surface, characterized by small pitches and tiny peaks and valleys. The distance between two peaks or valleys (wave pitch) is very small (less than 1 mm), which is a microscopic geometric shape error. The smaller the surface roughness, the smoother the surface.

[0061] In one embodiment, for example, the first energy absorbing portion 11 of the circuit board can be configured as a smooth surface structure, while the second energy absorbing portion 31 of the circuit board can be configured as a rough surface structure. Laser processing of the smooth surface structure of the first energy absorbing portion can reduce the energy absorption efficiency of the first energy absorbing portion due to its smooth surface structure. This can also make the hole roundness of the second energy absorbing portion closer when the laser beam passes through the second energy absorbing portion, thereby improving the consistency of the holes at both ends. It should be noted that the energy absorption efficiency of the first energy absorbing portion can also be improved, and the specific configuration can be selected based on the thickness of the first energy absorbing portion.

[0062] Surface roughness can be compared using interferometry. Specifically, the principle of light wave interference is used to display the shape error of the measured surface as interference fringes. These fringes are then magnified using a high-magnification microscope and measured to determine the surface roughness. Stylus and light section methods, commonly used by those skilled in the art, can also be used for comparison and will not be detailed here.

[0063] The circuit board 100 in the embodiment of the present application can be drilled using a laser. The laser can be a green laser with a wavelength in the range of 492-577 nm. The laser is irradiated on the circuit board 100 along the direction from the upper surface layer 1 to the lower surface layer 3. Figure 1The direction of the laser is the direction of the arrow. After burning through the upper surface layer 1 and the middle layer 2, the laser reaches the lower surface layer 3. At this time, the laser is interfered with by the walls of the holes burned through the upper surface layer 1 and the middle layer 2. The laser is attenuated to a certain extent, resulting in poor burning efficiency and effect on the lower surface layer 3. In order to reduce the difference in the burning effect of the laser on the upper surface layer 1 and the lower surface layer 3, this solution provides a first energy absorbing portion 11 with a lower roughness on the upper surface layer 1 and a second energy absorbing portion 31 with a higher roughness on the lower surface layer 3. This improves the absorption rate of the attenuated laser by the second energy absorbing portion 31 of the second surface layer, thereby reducing the difference in the diameter and roundness of the holes burned through by the laser on the upper surface layer 1 and the lower surface layer 3. This results in a relatively similar quality of the holes processed at both ends, thereby improving the product quality of the circuit board 100.

[0064] In one embodiment, the upper surface layer 1 and the lower surface layer 3 can be metal layers, including but not limited to copper metal layers or aluminum metal layers, and the middle layer 2 can be an insulating layer, including but not limited to resin layers.

[0065] The materials of the upper surface layer 1 and the lower surface layer 3 both include copper. The upper surface layer 1 and the lower surface layer 3 can be pure copper or copper alloys or other types of metals. In this way, copper can be drilled by taking advantage of its good conductivity and good laser processability.

[0066] The material of intermediate layer 2 includes resin. Intermediate layer 2 can be a sheet-like material made of wood pulp paper or fiberglass cloth as a reinforcing material, impregnated with resin glue, and then heat-pressed. This arrangement utilizes the excellent insulation and toughness of resin to ensure the operational stability and structural strength of circuit board 100.

[0067] In one embodiment, the thickness of the upper surface layer 1 is greater than the thickness of the lower surface layer 3 .

[0068] It can be understood that during the laser drilling process, the energy of the laser irradiated on the material is mainly used to melt the material and thus drill a hole. The thicker the material, the slower the drilling speed and the greater the energy required to make the material reach the melting temperature.

[0069] To this end, this embodiment further limits the thickness of the upper surface layer 1 to be greater than the thickness of the lower surface layer 3. In this way, during the laser drilling process, the laser reaches the lower surface layer 3 after burning through the upper surface layer 1 and the middle layer 2. At this time, the laser is interfered by the hole walls of the burnt holes in the upper surface layer 1 and the middle layer 2, and the laser has a certain attenuation, and the thinner lower surface layer 3 is more easily burned through by the laser. The thinned lower surface layer 3 is used to balance the influence of the laser energy attenuation, further ensuring that the quality of the holes burned by the laser on the upper surface layer 1 and the lower surface layer 3 are relatively close, the difference in hole diameter and the difference in roundness are small.

[0070] In one embodiment, the thickness of the upper surface layer 1 is 1-2 μm greater than the thickness of the lower surface layer 3 .

[0071] This embodiment further limits the thickness difference between the upper surface layer 1 and the lower surface layer 3, ensuring that the thickness difference between the lower surface layer 3 and the upper surface layer 1 is within an appropriate range. Through experiments and analysis, the inventors found that when the thickness of the upper surface layer 1 is greater than that of the lower surface layer 3, and the difference between the two is less than 1 μm, the thinned lower surface layer 3 does not effectively balance the factor of laser energy attenuation, and the quality of the upper and lower holes still has a certain gap. When the thickness of the upper surface layer 1 is greater than that of the lower surface layer 3, and the difference between the two is greater than 2 μm, the thinned lower surface layer 3 will experience significant deformation even under the burning of the attenuated laser energy, which also affects the quality of the circuit board 100.

[0072] In summary, the thickness of the upper surface layer 1 is set to be 1-2 μm larger than the thickness of the lower surface layer 3, so that the holes formed after the attenuated laser burns the lower surface layer 3 have small differences in aperture and roundness with the holes on the upper surface, thereby improving the consistency of the holes opened at both ends and thus improving the quality of the holes.

[0073] In one embodiment, the surface roughness Rz of the first energy absorbing portion 11 is 0-2 μm, and the surface roughness Rz of the second energy absorbing portion 31 is 3-4 μm. The above surface roughnesses are all Rz roughnesses.

[0074] Referring to the figure, the surface roughness range Rz of the first energy absorbing portion 11 is further defined as 0-2 μm, and the surface roughness range Rz of the second energy absorbing portion 31 is 3-4 μm. This roughness range ensures that the first energy absorbing portion 11 and the second energy absorbing portion 31 effectively absorb laser energy, achieving a faster processing rate. The roughness values ​​in this embodiment can be measured using the aforementioned roughness detection method.

[0075] In one embodiment, see Figure 4 、 Figure 5 and Figure 6 The first energy absorbing portion 11 is provided on a side of the upper surface layer 1 close to the middle layer 2 and / or a side of the upper surface layer 1 away from the middle layer 2 .

[0076] When the first energy absorbing portion 11 is provided on the side of the upper surface layer 1 close to the middle layer 2, the upper surface layer 1 may be roughened before being pressed together with the middle layer 2. Because the first energy absorbing portion 11 is in contact with the middle layer 2, its ability to absorb laser energy is reduced, but this also improves the adhesion between the upper surface layer 1 and the middle layer 2. It should be noted that an excessively rough surface may cause attenuation and loss of relatively high-frequency transmission signals.

[0077] When the first energy-absorbing portion 11 is positioned on the side of the upper surface layer 1 facing away from the intermediate layer 2, the upper surface layer 1 can be roughened before laminating the upper surface layer 1 and the intermediate layer 2, or the upper surface layer 1 can be roughened after lamination. Positioning the first energy-absorbing portion 11 on the side of the upper surface layer 1 facing away from the intermediate layer 2 enhances the upper surface layer 1's ability to absorb laser energy because the laser is directly irradiated on the first energy-absorbing portion 11, effectively absorbing the laser energy.

[0078] In summary, the specific location of the first energy absorbing part 11 can be flexibly adjusted according to actual conditions.

[0079] In one embodiment, see Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 The second energy absorbing portion 31 is provided on a side of the lower surface layer 3 close to the middle layer 2 and / or a side of the lower surface layer 3 away from the middle layer 2 .

[0080] When the second energy-absorbing portion 31 is disposed on the side of the lower surface layer 3 close to the intermediate layer 2, the lower surface layer 3 can be roughened before being pressed together with the intermediate layer 2. This method reduces the ability of the lower surface layer 3 to absorb laser energy, but improves the adhesion between the lower surface layer 3 and the intermediate layer 2. However, it should be noted that an excessively rough surface will cause attenuation and loss of relatively high-frequency transmission signals.

[0081] When the second energy-absorbing portion 31 is positioned on the side of the lower surface layer 3 facing away from the intermediate layer 2, the lower surface layer 3 can be roughened before laminating the lower surface layer 3 and the intermediate layer 2, or the roughening can be performed after lamination. When the second energy-absorbing portion 31 is positioned on the side of the lower surface layer 3 facing away from the intermediate layer 2, because it is not in contact with other physical parts, its ability to absorb laser energy is enhanced. In summary, the specific placement of the second energy-absorbing portion 31 can be flexibly adjusted based on actual circumstances.

[0082] Second, see Figure 7 , the present application also provides a circuit board preprocessing method, the method comprising:

[0083] Provide upper surface parts, middle parts and lower surface parts;

[0084] performing a roughening process on the lower surface member so as to form a second energy absorbing portion on the lower surface member, wherein the surface roughness of the second energy absorbing portion is greater than the surface roughness of the upper surface member;

[0085] The upper surface piece, the middle piece and the lower surface piece are stacked and pressed together in sequence.

[0086] In this embodiment, the upper and lower surface members may comprise conductive metal materials, and the intermediate member may comprise insulating resin materials. The lower surface member is roughened, which may be achieved by chemical treatment (e.g., roughening or browning), mechanical treatment (e.g., shot peening or grinding), or laser roughening. This allows for the formation of a relatively rough second energy-absorbing portion on the lower surface member, where the surface roughness of the second energy-absorbing portion is greater than that of the upper surface member. Subsequently, the upper surface member, intermediate member, and lower surface member are pressed together to form a circuit board. During laser processing of the pre-treated circuit board, a laser beam is directed from the upper surface member toward the lower surface member. After burning through the upper and intermediate members, the laser beam reaches the lower surface member. At this point, the laser beam is interfered with by the walls of the burn-through holes in the upper and intermediate members, causing some attenuation of the laser beam, resulting in poor burning efficiency and effect on the lower surface member. In order to reduce the difference in laser burning effects on the upper surface part and the lower surface part, this solution uses a roughening method to form a second energy-absorbing part with a higher roughness on the lower surface part, so that the absorption rate of the second energy-absorbing part of the lower surface part to the attenuated laser is improved, thereby making the quality of the holes burned by the laser on the upper surface part and the lower surface part closer, with small differences in aperture and roundness, thereby improving the product quality of the circuit board.

[0087] In one embodiment, roughening the lower surface member includes:

[0088] The lower surface part is roughened using a browning process, a blackening process or a laser roughening process.

[0089] The browning process or the blackening process can efficiently and quickly roughen the lower surface part and ensure that the rough portion on the second energy absorbing part is relatively uniform.

[0090] In one embodiment, before stacking and pressing the upper surface piece, the middle piece, and the lower surface piece in sequence, the pre-processing method includes:

[0091] The upper surface member is roughened to form a first energy absorbing portion on the upper surface member, wherein the surface roughness of the second energy absorbing portion is greater than the surface roughness of the first energy absorbing portion.

[0092] In the above embodiment, not only the lower surface part is roughened, but the upper surface part is also roughened. The specific treatment method can be a chemical treatment method (such as roughening treatment, browning treatment, etc.) or a mechanical treatment method (such as shot peening, grinding, etc.), and the surface roughness of the second energy absorbing part on the upper surface part is made greater than the surface roughness of the first energy absorbing part on the lower surface part. In this way, when the laser is irradiated on the upper surface part, the first energy absorbing part can also be used to enhance the upper surface part's absorption of laser energy, thereby accelerating the speed of laser burning and perforation, and thus improving the overall process efficiency and the production quality of the circuit board.

[0093] In one embodiment, the first energy absorbing part 11 of the circuit board can be selected to be processed as a smooth surface structure, and the second energy absorbing part 31 of the circuit board can be selected to be processed as a rough surface structure, that is, only the second energy absorbing part is provided with a rough surface mechanism. The specific process can refer to the description of the first aspect embodiment above. In order to avoid redundancy, it will not be described in detail this time.

[0094] In a third aspect, the present application further provides a laser drilling method, comprising: drilling a hole in a circuit board using a laser, wherein the circuit board is any of the embodiments of the first aspect, or a circuit board processed using the circuit board pretreatment method of any of the embodiments of the second aspect. In this embodiment, the laser drilling method also has the advantages of high drilling quality and high drilling efficiency.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A laser drilling method, characterized in that: include: Use laser to open holes in the circuit board; The circuit board includes an upper surface layer, an intermediate layer, and a lower surface layer stacked in sequence, the upper surface layer is provided with a first energy absorbing portion, and the lower surface layer is provided with a second energy absorbing portion; The surface roughness of the first energy absorbing portion is lower than that of the second energy absorbing portion, so that the absorption rate of the attenuated laser by the second energy absorbing portion provided on the lower surface layer is improved, and the difference in diameter and roundness of the holes burned by the laser on the upper surface layer and the lower surface layer is small.

2. The laser drilling method according to claim 1, characterized in that: The upper surface layer and the lower surface layer are both metal layers, and the middle layer is an insulating layer.

3. The laser drilling method according to claim 1, characterized in that: The thickness of the upper surface layer is greater than the thickness of the lower surface layer.

4. The laser drilling method according to claim 1 or 3, characterized in that: The thickness of the upper surface layer is 1-2 μm greater than the thickness of the lower surface layer.

5. The laser drilling method according to claim 1, characterized in that: The surface roughness of the first energy absorbing portion is in a range of 0-2 μm, and the surface roughness of the second energy absorbing portion is in a range of 3-4 μm.

6. The laser drilling method according to claim 1, characterized in that: The first energy absorbing portion is provided on a side of the upper surface layer close to the middle layer and / or a side of the upper surface layer away from the middle layer.

7. The laser drilling method according to claim 1, characterized in that: The second energy absorbing portion is provided on a side of the lower surface layer close to the middle layer and / or a side of the lower surface layer away from the middle layer.

8. The laser drilling method according to claim 1, characterized in that: The method for manufacturing the circuit board includes: Provide upper surface parts, middle parts and lower surface parts; performing a roughening process on the lower surface member so as to form a second energy absorbing portion on the lower surface member, wherein the surface roughness of the second energy absorbing portion is greater than the surface roughness of the upper surface member; The upper surface piece, the middle piece and the lower surface piece are stacked and pressed in sequence.

9. The laser drilling method according to claim 8, characterized in that: Before stacking and pressing the upper surface member, the middle member, and the lower surface member in sequence, the method for manufacturing the circuit board further includes: The upper surface member is roughened to form a first energy absorbing portion on the upper surface member, wherein the surface roughness of the second energy absorbing portion is greater than the surface roughness of the first energy absorbing portion.

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