Method for improving warping of packaging substrate through laser drilling

Abstract

The invention discloses a method for improving package substrate warpage through laser drilling, and the method comprises the following steps: providing a copper-clad substrate which comprises a substrate, a front copper foil layer and a back copper foil layer, and the front copper foil layer and the back copper foil layer are arranged at the two sides of the substrate; grooving the copper-clad substrate by using a drilling machine to obtain a hole; based on finite element analysis, simulating the relationship between the drilling layout and the stress, and obtaining an area, which is easy to warp, of the substrate; cleaning the front copper foil layer and the back copper foil layer; and drilling the front copper foil layer or the back copper foil layer by using a laser drilling machine to obtain a micron-sized groove so as to reduce the overall or local volume of the copper foil. According to the method, a laser drilling method is adopted, dense drilling is carried out on the area with the high copper coverage rate in the surface of the copper foil layer, laser drilling is encrypted in the edge area of the copper foil layer, symmetric compensation design is adopted, the drilling density is increased at the corresponding positions of the sparse areas of the front and back copper foils, the overall or local copper foil size is effectively reduced, and the warping risk is effectively reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printed circuit board processing, and particularly relates to a method for improving warping of a packaging substrate by laser drilling. BACKGROUND

[0002] The description in this section merely provides background information related to the present disclosure and does not constitute the prior art.

[0003] With the rapid development of electronic products, the requirements for printed circuit boards are also increasing. Multi-layer circuit boards are widely used in mobile phones, digital cameras, notebook computers and digital products because of their high-density integration technology, which can make the terminal product design more miniaturized and meet higher standards of electronic performance and efficiency. However, in the process of manufacturing multi-layer circuit boards, the design of mechanical blind holes often leads to warping of the circuit board, affecting use and installation work. This warping problem is mainly due to the difference in thickness and thermal expansion rate of the blind hole substrate and the copper foil layer, as well as the difference in physical parameters of the blind hole substrate and the copper foil layer, resulting in asymmetry of the blind hole substrate and the copper foil layer, and thus stress asymmetry in the process of pressing.

[0004] In addition, with the thinning of the packaging thickness, the resin layer occupies more space, further exacerbating the warping risk. A PCB (Printed Circuit Board) is composed of copper foil, resin, glass cloth and other materials, and the physical and chemical properties of these materials are different. After being pressed together, thermal stress remains, leading to deformation. At the same time, in the process of PCB processing, various processes such as high temperature, mechanical cutting, wet treatment, etc. are involved. Due to the difference in physical properties, the thermal conductivity of the resin material is much lower than that of the copper foil, resulting in a difference in thermal expansion coefficient, which causes bending and warping problems. Therefore, a new technical means is needed to reduce the overall or local copper foil volume, reduce the copper foil stress, and thus reduce the warping risk.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely describing the technical solutions of the present application, and for the convenience of understanding by those skilled in the art. The above technical solutions cannot be considered as known by those skilled in the art only because they are described in the background section of the present application. SUMMARY

[0006] The present application solves the technical problem of the prior art by providing a method for improving warping of a packaging substrate by laser drilling, which directly uses laser drilling to process grooves and roughness on the copper foil layer.

[0007] The present application discloses a method for improving warping of a packaging substrate by laser drilling, comprising the following steps: A copper-clad substrate is provided, which includes a substrate and front and back copper foil layers disposed on both sides of the substrate. A slot is formed in the copper-clad substrate using a drilling machine. The surface of the copper-clad substrate is cleaned and micro-etched. Based on finite element analysis, the relationship between drilling layout and stress is simulated to obtain the area of the substrate where warping is likely to occur. The front and back copper foil layers are cleaned. A laser drilling machine is used to drill the front or back copper foil layer to obtain micron-level grooves to reduce the overall or local copper foil volume. The depth, diameter and spacing of the grooves obtained by laser drilling are tested. The front and back copper foil layers are processed. The hole wall residue is removed by cleaning and the copper-clad substrate is subjected to heat treatment. Silicon dioxide nano-coating particles are used to fill and seal the grooves.

[0008] Further, in the step of "cleaning the surface of the copper-clad substrate and micro-etching it", the cleaning of the surface of the copper-clad substrate uses 10% H2SO4+5% H2O2, the temperature is 40℃~50℃, and the soaking time is 1min~3min. The micro-etching of the copper-clad substrate uses a 5% Na2S2O8 solution, the temperature is 20℃, and the etching rate is 0.5μm / min.

[0009] Further, in the step of "using a laser drilling machine to drill the front or back copper foil layer to obtain micron-level grooves", the power of the laser drilling machine is 8W~20W, the scanning speed is 500mm / s~1200mm / s, and the frequency is 10kHz~30kHz.

[0010] Further, in the step of "using a laser drilling machine to drill the front or back copper foil layer to obtain micron-level grooves", in the continuously covered area of the front copper foil layer, the high current path or signal line is avoided, and the laser drilling machine is used for intensive drilling to obtain multiple grooves.

[0011] Further, in the method for improving the warpage of a packaging substrate by laser drilling, in the step of "drilling the front copper foil layer or the back copper foil layer by a laser drilling machine to obtain microscale grooves", when the back copper foil layer has a copper layer sparse area, laser drilling is performed on the front copper foil layer at a position corresponding to the copper layer sparse area to obtain microscale grooves to reduce the volume of the front copper foil layer.

[0012] Further, in the method for improving the warpage of a packaging substrate by laser drilling, the diameter of the grooves is 30 μm to 50 μm, and the ratio of the spacing between adjacent grooves to the diameter of the grooves is 1:2.

[0013] Further, in the method for improving the warpage of a packaging substrate by laser drilling, in the step of "drilling the front copper foil layer or the back copper foil layer by a laser drilling machine to obtain microscale grooves", intensive drilling is performed within 5 mm to 10 mm of the edge of the copper foil layer to obtain a plurality of grooves.

[0014] Further, in the method for improving the warpage of a packaging substrate by laser drilling, the depth of the grooves is determined by the following formula: Groove target depth = copper foil layer design thickness + positive tolerance + safety margin wherein the copper foil thickness is determined according to the design of the substrate; the positive tolerance is the upper limit deviation of the copper foil thickness; and the safety margin compensates for the fluctuation in laser processing.

[0015] Further, in the method for improving the warpage of a packaging substrate by laser drilling, the diameter of the grooves is 30 μm to 50 μm, and the ratio of the spacing between adjacent grooves to the diameter of the grooves is 1:1.

[0016] Further, in the method for improving the warpage of a packaging substrate by laser drilling, in the step of "cleaning to remove residue from the hole wall and performing heat treatment on the copper-clad substrate", an acid etching device with ultrasonic cleaning is used for cleaning, a solution of FeCl3 is used, the etching rate is 5 μm / min, the time is 1 min to 2 min; the ultrasonic frequency is 40 kHz to 80 kHz, the power density is 0.5 W / cm² to 1.5 W / cm², the time is 2 min to 3 min; the copper-clad substrate is laid flat in a quartz tray, a box-type atmosphere furnace is used, the proportion of nitrogen and hydrogen mixed gas in the furnace is N2:H2=95:5, a vacuum pump is started to draw to -0.08 Mpa, the oxygen content is controlled to be less than 10 ppm, the gas flow rate is 10 L / min to 15 L / min, heating to 180 °C to 200 °C, heating time 30 min to 60 min, heating rate 5 °C / min to 8 °C / min, cooling rate 1 °C / min to 2 °C / min, cooling to below 60 °C to take out the copper-clad substrate.

[0017] Further, in the step of "filling and sealing the grooves with silica nano-coated particles" of the above-mentioned method for improving the warping of a packaging substrate by laser drilling, the copper-clad substrate is placed in a silica dispersion solution, vacuumed to 10 -2 Pa 10 -3 Pa, the bubbles in the grooves are discharged, liquid penetration is promoted, complete filling is achieved through capillary force, the copper-clad substrate is removed after returning to normal pressure, the solvent is volatilized by heating in a nitrogen oven at 80°C for 5 min, and then the copper-clad substrate is heated to 150°C for 30 min for curing.

[0018] In summary, the above-mentioned method used in the embodiments of the present application has the following advantages: 1. The method for improving the warping of a packaging substrate by laser drilling disclosed in the present application uses a laser drilling method to densely drill in the area with high copper coverage on the surface of the copper foil layer, to obtain a plurality of micron-level grooves, effectively reducing the overall or local copper foil volume, significantly reducing the stress concentration of the copper foil, and effectively reducing the warping risk; the laser drilling is densified in the range of 5-10 mm from the edge of the copper foil layer, effectively improving the strength of the edge of the substrate, effectively solving the stress concentration problem caused by the traditional blind hole design, and reducing the risk of warping; a symmetric compensation design is used to increase the drilling density at the corresponding positions of the sparse areas of the copper foil on the front and back surfaces, reduce the copper foil volume, balance the stress on the front and back surfaces, and effectively solve the problem of asymmetric stress caused by material performance differences in the prior art; 2. The heating and annealing treatment after drilling reduces residual stress, and the grooves are filled with silica particles, which can optimize stress distribution and inhibit warping deformation.

[0019] In order to further understand the features and technical contents of the present application, please refer to the following detailed description and drawings of the present application. However, the drawings provided are only for reference and illustration, and are not intended to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments or the prior art described in the specification, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments described in the specification, and those skilled in the art can also obtain other drawings according to these drawings without creating any inventive labor.

[0021] Figure 1 is a step schematic diagram of the method for improving the warping of a packaging substrate by laser drilling in the embodiments of the present application; Figure 2 is a planar schematic diagram of the first copper foil layer before groove processing in the embodiments of the present application; Figure 3 is a plan view of the first copper foil layer after groove processing in an embodiment of the present application; Figure 4 is a plan view of the edge area of the copper foil layer after groove processing in an embodiment of the present application; Figure 5 and Figure 6 is a structural view of the front copper foil layer and the back copper foil layer after groove processing in an embodiment of the present application; Figure 7 is a filling view of the front copper foil layer and the silicon dioxide nano coating particles in an embodiment of the present application.

[0022] The reference numerals of the above drawings are as follows: 1, front copper foil layer; 2, groove; 3, through hole; 4, blind hole; 5, sparse area of copper layer; 6, back copper foil layer; 7, silicon dioxide nano coating particles. DETAILED DESCRIPTION

[0023] In order to make the person skilled in the art better understand the technical solutions in the specification, the technical solutions in the specification will be described clearly and completely in the specification below in conjunction with the drawings in the specification. Obviously, the described embodiments are only part of the embodiments of the specification, not all the embodiments. Based on the embodiments in the specification, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the specification.

[0024] The following is to illustrate the embodiments of the present application by specific specific embodiments, and the person skilled in the art can understand the advantages and effects of the present application from the disclosed content in the specification. The present application can be implemented or applied by other different specific embodiments, and each detail in the specification can be modified and changed in different views and applications without departing from the concept of the present application. In addition, the drawings of the present application are only simple schematic illustrations, not the depiction according to the actual size, and the prior declaration. The following embodiments will further illustrate the related technical content of the present application, but the disclosed content is not used to limit the protection scope of the present application.

[0025] It should be understood that although the terms "first", "second", "third" and the like may be used herein to describe various components or signals, these components or signals should not be limited by these terms. These terms are mainly used to distinguish one component from another component, or one signal from another signal. In addition, the term "or" used herein may include any one or more combinations of the associated listed items.

[0026] Referring to Figures 1 to 7 The embodiment of the present application discloses a method for improving the warping of a packaging substrate by laser drilling, comprising the following steps: A copper-clad substrate is provided, which includes a substrate and a front copper foil layer 1 and a back copper foil layer 6 arranged on both sides of the substrate; A slotting machine is used to slot the copper-clad substrate to obtain an opening, thereby obtaining a through hole 3 and a blind hole 4; The surface of the copper-clad substrate is cleaned and micro-etched; Based on finite element analysis, the relationship between drilling layout and stress is simulated to obtain the area of the substrate prone to warping; The front copper foil layer 1 and the back copper foil layer 6 are cleaned; A laser drilling machine is used to drill the front copper foil layer 1 or the back copper foil layer 6 to obtain micron-level grooves 2 to reduce the overall or local copper foil volume; The depth, diameter and spacing of the grooves 2 obtained by laser drilling are tested; The front copper foil layer 1 and the back copper foil layer 6 are processed, and the copper-clad substrate is processed by laser drilling, and the groove side wall angle is controlled at 70-80° to avoid subsequent coating from being unable to fill; The hole wall residues are removed by cleaning, and the copper-clad substrate is subjected to heat treatment; The grooves are filled and sealed with silicon dioxide nano coating particles 7.

[0027] Specifically, in the step of "cleaning the surface of the copper-clad substrate and micro-etching", 10% H2SO4+5% H2O2 is used to clean the surface of the copper-clad substrate at a temperature of 40-50°C for 1-3 min, and 5% Na2S2O8 solution is used to micro-etch the copper-clad substrate at a temperature of 20°C with an etching rate of 0.5 μm / min, so that the copper foil roughness Ra of the substrate surface is increased to 0.8-1.2 μm (to enhance the uniformity of laser absorption).

[0028] Specifically, in the step of "using a laser drilling machine to drill the front copper foil layer 1 or the back copper foil layer 6 to obtain micron-level grooves 2", the power of the laser drilling machine is 8-20 W, the scanning speed is 500-1200 mm / s, and the frequency is 10-30 kHz.

[0029] Specifically, in the step of "using a laser drilling machine to drill the front copper foil layer 1 or the back copper foil layer 6 to obtain micron-level grooves 2", in the continuously covered area of the front copper foil layer 1, the high current path or signal line is avoided, and the laser drilling machine is used for intensive drilling to obtain a plurality of grooves 2.

[0030] Specifically, refer to Figure 5 and Figure 6In the present embodiment, in the step of "drilling the front copper foil layer 1 or the back copper foil layer 6 with a laser drill to obtain microscale grooves 2", when the back copper foil layer 6 has a copper layer sparse area 5, laser drilling is performed at the position corresponding to the copper layer sparse area 5 of the front copper foil layer 1 to obtain microscale grooves 2 to reduce the volume of the front copper foil layer 1.

[0031] Specifically, in the present embodiment, the diameter of the grooves 2 is 30-50 μm, and the ratio of the pitch between adjacent grooves 2 to the diameter of the grooves 2 is 1:2.

[0032] Specifically, referring to Figure 4 In the present embodiment, in the step of "drilling the front copper foil layer 1 or the back copper foil layer 6 with a laser drill to obtain microscale grooves 2", intensive drilling is performed within the copper foil layer edge area 5-10 mm to obtain a plurality of grooves 2.

[0033] Specifically, in the present embodiment, the depth formula of the grooves 2 within the copper foil layer edge area 5-10 mm is: Groove target depth = copper foil layer design thickness + positive tolerance + safety margin Wherein, the copper foil thickness is determined according to the substrate design; the positive tolerance is the upper limit deviation of the thickness provided by the copper foil manufacturer, usually +2-3 μm; the safety margin is to compensate for the fluctuation of laser processing, usually +1 μm. The grooves within the copper foil layer edge area 5-10 mm can be to punch through the copper foil layer, and after penetration, the following advantages are obtained: maximum stress interruption: the copper foil on both sides of the groove is completely separated, allowing free micro-deformation; reducing local stiffness: the bending stiffness of the copper foil edge is reduced to close to the water of the substrate.

[0034] Specifically, in the present embodiment, the diameter of the grooves 2 within the copper foil layer edge area 5-10 mm is 30-50 μm, and the ratio of the pitch between adjacent grooves 2 to the diameter of the grooves 2 is 1:1.

[0035] In this embodiment, the ratio of the distance between adjacent grooves in the edge area of the copper foil layer to the diameter of the grooves is 1:1. This design has the following advantages: ① Cut off the stress transmission path: Introduce micron-level grooves in the edge of the copper foil, which essentially creates tiny, controllable "breaks" or "weak points" in the copper foil. These grooves break the continuity of the copper foil in the edge area; ② Provide stress release area: When the substrate tries to deform due to temperature change or residual stress, the copper foil at the edge of the groove can undergo small, local elastic or plastic deformation (such as micro-buckling, micro-slippage), rather than transmitting stress rigidly to the entire copper foil plane; ③ Reduce local stiffness: Grooves significantly reduce the local stiffness and bending stiffness of the copper foil in the groove area, making it easier to conform to the shrinkage or expansion of the substrate, thereby absorbing and dissipating locally concentrated stress; ④ Balance stress distribution: By introducing these controllable "weak points" at key locations (usually the edges where stress concentration is most severe), stress can be guided to release at these points, avoiding stress accumulation throughout the substrate to the extent that macroscopic warping occurs, making the stress distribution more uniform. Imagine a thin film (copper foil) tightly stretched on a substrate (resin) that will shrink. If the film is a complete piece, the film will wrinkle (warp) when the substrate shrinks. If a number of tiny, regular notches (grooves) are pre-cut in the edge of the film, when the substrate shrinks, the stress will be preferentially released at these notches, and the edge of the notches will undergo small deformation, thereby preventing the entire film from wrinkling.

[0036] In this embodiment, stress is the internal force between parts of an object when it deforms due to external factors (force, humidity, temperature field change, etc.). The internal force per unit area is called stress. Elastic modulus is a physical quantity that describes the ability of a solid material to resist deformation, defined as the ratio of stress to strain.

[0037] After processing, the acid etching equipment with ultrasonic cleaning is used for cleaning, the ultrasonic cavitation effect is used to enhance the penetration ability of the acid solution, accelerate the oxide dissolution and the debris separation: solution: FeCl3(concentration 2.5 mol / L, temperature 40℃), etching rate 5 μm / min, time 1 min~2 min; ultrasonic frequency 40 kHz~80 kHz, power density 0.5 W / cm²~1.5 W / cm², time 2 min~3 min, completely remove the residues in the hole. Specifically, in the embodiment, in the step "cleaning to remove the hole wall residues and heating treatment of the copper clad substrate", the acid etching equipment with ultrasonic cleaning is used for cleaning, the solution of FeCl3is used, the etching rate is 5 μm / min, the time is 1 min~2 min; the ultrasonic frequency is 40 kHz~80 kHz, the power density is 0.5 W / cm²~1.5 W / cm², the time is 2 min~3 min; the copper clad substrate is laid in the quartz tray, the box type atmosphere furnace is used, the proportion of nitrogen and hydrogen mixed gas in the atmosphere furnace is N2:H2=95:5, the vacuum pump is started to be pumped to-0.08 Mpa, the oxygen content is controlled to be less than 10 ppm, the gas flow rate is 10 L / min~15 L / min, heated to 180℃~200℃, the heating time is 30 min~60 min, the heating rate is 5℃ / min~8℃ / min, the cooling rate is 1℃ / min~2℃ / min, and the copper clad substrate is taken out when the temperature is cooled to below 60℃. Plasma activation: parameters: argon / oxygen mixture ratio 4:1, power 500 W, processing time 3 minutes, surface contact angle from 80° to below 10°. During the drilling process of the copper clad substrate, the copper grain rearrangement caused by the local melting-solidification process around the micro-holes will produce compression or tensile residual stress, and the interface shear stress caused by the difference of the thermal expansion coefficient of the dielectric layer, the annealing is performed by using the box type atmosphere furnace, and the stepwise heating and cooling is used to make the copper lattice reorganize by dislocation slip, recrystallization and other ways, remove the residual moisture and stress of the copper foil.

[0038] Specifically, referring to Figure 7 In the embodiment, in the step "filling and sealing the groove by using the silica nano coating particles 7", the copper clad substrate is put into the silica dispersion liquid, vacuum extraction is performed to 10 -2 Pa~10 -3Pa, the bubble in the discharge groove, promote liquid penetration, by capillary force to achieve full filling, restore normal pressure after taking the copper clad substrate, using nitrogen oven 80 ℃ hot air heating 5 min volatile solvent, and then heated to 150 ℃ baking 30 min, curing, cooling to room temperature after taking. SiO2nanodispersion preparation: select the particle size of 10-50 nm of silicon dioxide nanoparticles powder into the solvent (such as water, ethanol or ethylene glycol), concentration 10-20 wt%, adding dispersant, ratio 10-15 wt%, ultrasonic treatment (30-60 minutes) to make the particles uniformly dispersed, to avoid agglomeration.

[0039] The substrate after drilling is cleaned, and the surface is activated using plasma cleaning. Then the grooves are filled and sealed with silica nano coating particles 7, and the silica nano coating particles 7 are cured using a nitrogen oven with stepwise temperature rise. The low thermal expansion coefficient and elastic modulus of silica can optimize the stress distribution of copper foil and resin (SiO2nanoparticles can enhance the rigidity and anti-deformation ability of micropores), thereby inhibiting the warping deformation. The thermal expansion coefficient (CTE) of silica is relatively low (about 0.5×10 -6 / ℃), which is closer to the CTE of the resin substrate (10-20×10 -6 / ℃), and by filling the grooves, the thermal stress difference between the copper foil (CTE 17×10 -6 / ℃) and the substrate can be balanced, reducing the plate warping caused by temperature changes. The elastic modulus of silica nanoparticles (~70 GPa) is between copper (130 GPa) and resin (3-5 GPa), which can gradiently transition the stress distribution and reduce the interface stress concentration.

[0040] In the prior art, the temporary carrier plate is usually made of heat-deformed glue and thick copper plate, and the two coreless substrates are bonded together by using the heat adhesion of PP. These methods often have problems such as complex process, high cost, low efficiency, etc., which are difficult to meet the growing production demand. In the process of manufacturing multilayer circuit boards, the design of mechanical blind holes often leads to warping of the circuit board, affecting the use and installation work. This warping problem is mainly due to the difference in thickness and thermal expansion speed between the blind hole substrate and the copper foil layer, as well as the difference in physical parameters between the blind hole substrate and the copper foil layer, resulting in asymmetry of the blind hole substrate and the copper foil layer, and thus stress asymmetry during pressing.

[0041] Bending warpage can be offset by designing symmetrical copper layers or using grid-like copper to reduce stress concentration. The prior art does not use laser drilling to control the volume of copper. Laser drilling technology can achieve very high precision, which helps to reduce the thermal impact and mechanical stress on the circuit board material during drilling, thereby reducing the risk of board warpage. Unlike traditional mechanical drilling, laser drilling is a non-contact machining method, which means it does not exert physical pressure on the circuit board, thereby reducing the likelihood of deformation; in addition, laser drilling can accommodate different substrates, including flexible and hard boards, which allows it to maintain high processing quality when dealing with different materials.

[0042] By the above method in the embodiment, based on finite element analysis (FEA) simulation of drilling layout in stress relationship, copper foil reduction area is designed to avoid high current path or signal line, and the area where the substrate is prone to warpage (such as copper density uneven area, heat stress concentration area) is determined. The copper foil layer needs to be cleaned before processing to ensure that the oxidation layer, oil stains or residues on the surface of the substrate are removed. In the embodiment, a laser drilling machine is used to drill densely in the area with high copper coverage on the surface of the copper foil layer, obtaining a plurality of micron-level grooves 2, effectively reducing the overall or local copper foil volume, significantly reducing the stress concentration of the copper foil, effectively reducing the warpage risk, and solving the problem of low efficiency of traditional copper foil reduction method; the laser drilling process used in the embodiment has the advantages of high precision, strong controllability, flexible adjustment, etc. compared with the traditional etching process, and can be dynamically adjusted according to different product requirements and copper coverage, effectively meeting the diversified design requirements of circuit boards; the embodiment increases the density of laser drilling within the range of 5mm-10mm from the edge of the copper foil layer, effectively improving the strength of the edge of the substrate, and effectively solving the problem of stress concentration caused by traditional blind hole design, thereby reducing the risk of warpage; the embodiment uses a symmetric compensation design to increase the drilling density in the corresponding position of the sparse area of the copper foil on the front and back surfaces, reduce the volume of the copper foil, balance the stress on the front and back surfaces, and effectively solve the problem of stress asymmetry caused by material performance differences in the prior art; the embodiment uses laser drilling to obtain a plurality of grooves 2, and the depth of the grooves 2 is controlled within the thickness range of the copper foil layer, avoiding damage to the underlying insulating material and ensuring the normal use performance of the circuit board.

[0043] The micron-level grooves 2 act as local "elastic hinges" to absorb the thermal stress generated by the CTE (coefficient of thermal expansion) difference between the copper foil and the resin interface, reducing the transmission of stress to the edge. The dense grooves 2 divide the continuous copper foil layer into micro-zones, breaking the stress continuity and avoiding edge concentration release. The slight collective change of the edge of the grooves 2 can hinder crack propagation and inhibit delamination caused by warpage. The grooves 2 are designed in a directional manner, such as radial arrangement, to guide the thermal expansion along a specific direction and reduce anisotropic warpage. The groove 2 design can actively induce a small pre-deformation in a specific direction to offset the warpage trend in subsequent processes.

[0044] The above disclosure is merely the preferred embodiments of the present application, and is not intended to limit the scope of patent application of the present application. Any equivalent technical changes made according to the content of the specification and drawings of the present application shall be included in the scope of patent application of the present application.

[0045] The various embodiments in the specification are described in a progressive manner, and the same or similar parts between the various embodiments can be mutually referred to, and each embodiment focuses on the difference from other embodiments.

[0046] Although the present application is described through embodiments, those skilled in the art know that there are many modifications and changes to the present application without departing from the spirit of the present application, and it is intended that the appended embodiments include these modifications and changes without departing from the present application.

Claims

1. A method for improving warping of a packaging substrate using laser drilling, characterized in that, Includes the following steps: A copper-clad substrate is provided, the copper-clad substrate including a substrate and a front copper foil layer and a back copper foil layer disposed on both sides of the substrate; The copper-clad substrate is slotted using a drilling machine to obtain openings; Clean the surface of the copper-clad substrate and perform micro-etching on it; Based on finite element analysis, the relationship between drilling layout and stress was simulated to identify the areas of the substrate that are prone to warping. Clean the front and back copper foil layers; A laser drilling machine is used to drill holes in the front copper foil layer or the back copper foil layer to obtain micron-level grooves in order to reduce the overall or local copper foil volume. The depth, diameter, and spacing of the grooves obtained by laser drilling were tested; The front copper foil layer and the back copper foil layer are processed; Cleaning removes residue from the hole walls and heats the copper-clad substrate; The groove is filled and sealed using silica nano-coating particles.

2. The method for improving board warping of a packaging substrate by laser drilling according to claim 1, characterized in that, In the step "cleaning the surface of the copper-clad substrate and micro-etching it", the surface of the copper-clad substrate is cleaned using 10% H2SO4 + 5% H2O2 at a temperature of 40℃~50℃ for 1min~3min. The copper-clad substrate is micro-etched using 5% Na2S2O8 solution at a temperature of 20℃ and an etching rate of 0.5μm / min.

3. The method for improving board warping of a packaging substrate by laser drilling according to claim 1, characterized in that, In the step "using a laser drilling machine to drill holes in the front copper foil layer or the back copper foil layer to obtain micron-level grooves", the power of the laser drilling machine is 8W to 20W, the scanning speed is 500mm / s to 1200mm / s, and the frequency is 10kHz to 30kHz.

4. The method for improving board warping of a packaging substrate by laser drilling according to claim 1, characterized in that, In the step "Drilling the front copper foil layer or the back copper foil layer with a laser drilling machine to obtain micron-level grooves", in the area continuously covered by the front copper foil layer, avoiding high current paths or signal lines, dense drilling is performed using a laser drilling machine to obtain multiple grooves. When there are sparse copper areas in the back copper foil layer, laser drilling is performed on the front copper foil layer at the position corresponding to the sparse copper area to obtain micron-level grooves in order to reduce the copper foil volume of the front copper foil layer.

5. The method for improving board warping of a packaging substrate by laser drilling according to claim 4, characterized in that, The diameter of the groove is 30μm to 50μm, and the ratio of the spacing between adjacent grooves to the diameter of the groove is 1:

2.

6. The method for improving board warping of a packaging substrate by laser drilling according to claim 1, characterized in that, In the step "Drilling holes in the front copper foil layer or the back copper foil layer using a laser drilling machine to obtain micron-level grooves", dense drilling is performed within 5mm to 10mm of the edge area of ​​the copper foil layer to obtain multiple grooves.

7. The method for improving board warping of a packaging substrate by laser drilling according to claim 1 or 6, characterized in that, The formula for the depth of the groove is: The target depth of the groove = the design thickness of the copper foil layer + positive tolerance + safety margin; The copper foil thickness is determined based on the substrate design; the positive tolerance is the upper limit deviation of the copper foil thickness; and the safety margin is to compensate for fluctuations in laser processing.

8. The method for improving board warping of a packaging substrate by laser drilling according to claim 6, characterized in that, The diameter of the groove within 5mm to 10mm of the edge region of the copper foil layer is 30μm to 50μm, and the ratio of the spacing between adjacent grooves within 5mm to 10mm of the edge region of the copper foil layer to the diameter of the groove is 1:

1.

9. The method for improving board warping of a packaging substrate by laser drilling according to claim 1, characterized in that, In the step "cleaning to remove residue from the hole walls and heating the copper-clad substrate", an acid etching device with ultrasonic-assisted cleaning is used for cleaning, using a FeCl3 solution, with an etching rate of 5 μm / min and a time of 1 min to 2 min; the ultrasonic frequency is 40 kHz to 80 kHz, the power density is 0.5 W / cm² to 1.5 W / cm², and the time is 2 min to 3 min; the copper-clad substrate is laid flat in a quartz tray, and a box-type atmosphere furnace is used, with a nitrogen-hydrogen mixed gas ratio of N2:H2=95:

5. The vacuum pump is started to evacuate to -0.08 MPa, the oxygen content is controlled to be less than 10 ppm, the gas flow rate is 10 L / min to 15 L / min, and the temperature is heated to 180℃ to 200℃ for 30 min to 60 min, with a heating rate of 5℃ / min to 8℃ / min and a cooling rate of 1℃ / min to 2℃ / min. The copper-clad substrate is removed after cooling to below 60℃.

10. The method for improving board warping of a packaging substrate by laser drilling according to claim 1, characterized in that, In step "filling and sealing the groove with silica nano-coating particles", the copper-clad substrate is immersed in a silica dispersion and a vacuum is drawn to 10. -2 Pa~10 -3 Pa, remove air bubbles from the groove, promote liquid penetration, achieve complete filling through capillary force, remove the copper-clad substrate after restoring normal pressure, use a nitrogen oven at 80°C for 5 minutes to evaporate the solvent, then heat to 150°C for 30 minutes to cure, and remove after cooling to room temperature.

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