Millimeter wave radar circuit board preparation method based on pulse electroplating

Abstract

The invention relates to the technical field of radar circuit board preparation, in particular to a millimeter wave radar circuit board preparation method based on pulse electroplating, which comprises the following steps: carrying out pulse electroplating copper plating on a semi-finished printed circuit board, and determining whether the change trend of bubble density is consistent according to a second number proportion of bubble density curves in a plurality of areas, and determining a judgment mode for qualification of the copper plating process according to a judgment result. Acquiring the rate matching degree of the copper plating process to determine the qualification of the copper plating process, or acquiring the retention duration mean value of the bubbles for the plurality of bubble distribution areas to determine the qualification of the copper plating process; adjusting the axis included angle between the nozzle axis of the electrolyte and the axis of the blind hole or the nozzle pressure of the electrolyte according to the pulsation speed; and determining the copper distribution deviation in the blind hole, and optimizing the second preset proportion or optimizing the preset pulsation speed based on the copper distribution deviation. According to the invention, the copper plating quality in the blind hole is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of radar circuit boards, and particularly to a method for preparing a millimeter-wave radar circuit board based on pulse electroplating. Background Art

[0002] As a core sensor for autonomous driving and intelligent transportation systems, the high-frequency signal transmission performance of millimeter-wave radars poses stringent requirements on the dielectric properties, signal integrity, and thermal reliability of PCBs. The traditional direct current electroplating process faces multiple challenges in the manufacturing of millimeter-wave radar circuit boards: when filling blind vias with copper, it is easy to produce depressions and copper powder contamination, resulting in a decrease in the etching accuracy of antennas; the laminated structure of high-frequency boards and FR-4 due to the mismatch of thermal expansion coefficients is prone to warping, affecting the stability of the antenna pattern; in addition, the surface roughness of the traditional electroplated copper layer will exacerbate signal scattering, resulting in excessive phase accuracy deviation in the millimeter-wave band and unable to meet the requirements of 4D imaging radars for millimeter-level detection accuracy. Therefore, it is urgent to develop a process based on pulse electroplating to suppress concentration polarization by dynamically regulating the current density, reduce the fluctuation of copper ion concentration gradient, and at the same time combine low-roughness copper foil with ceramic-filled substrates to achieve high-precision filling of blind vias and low-loss transmission of high-frequency signals.

[0003] Chinese Patent Application Publication No.: CN111491466A discloses a method for preparing a 77GHz millimeter-wave radar circuit board, including the following steps: separately manufacturing L1-L2 laminates, L3-L4 laminates, and L5-L6 laminates; sequentially laminating the three laminates to obtain a combined board; subjecting the combined board to operations such as routing, first copper reduction and brownification, first outer dry film, acidic etching, laser blind vias, second outer dry film, and pattern electroplating, and performing subsequent processes according to the conventional circuit board processing flow; the laser blind via step sequentially includes: first drilling, first copper deposition on the copper-clad plate, second copper reduction and brownification, resin plugging of vias, second drilling, and second copper deposition on the copper-clad plate and other processing steps. The invention adopts the laser blind via processing steps of first drilling, first copper deposition on the copper-clad plate, second copper reduction and brownification, resin plugging of vias, second drilling, and second copper deposition on the copper-clad plate, and adopts the method of window laser to reduce the difficulty of copper reduction, improve the copper reduction accuracy, thereby improving the quality and reducing the generation of defects.

[0004] There are also the following problems in the prior art: during the preparation process of millimeter-wave radar circuit boards in the prior art, due to the too large aspect ratio of the blind vias, it is easy to cause the formation of a laminar flow stagnation zone of the electrolyte in the blind vias, leading to an imbalance in the copper ion concentration gradient, and further resulting in thin copper at the bottom of the holes, resulting in low copper plating quality in the blind vias. Summary of the Invention

[0005] Therefore, the present invention provides a method for preparing a millimeter-wave radar circuit board based on pulse electroplating to overcome the problem of low copper plating quality in blind vias caused by the too large aspect ratio of the blind vias in the prior art.

[0006] To achieve the above object, the present invention provides a method for preparing a millimeter-wave radar circuit board based on pulse electroplating, including: Performing pulse electroplating copper plating on a semi-finished printed circuit board, and determining whether the change trends of the bubble density curves in several cathode regions during the copper deposition stage are consistent by obtaining the ratio of the number of bubble density curves with consistent change trends in the total number of cathode regions; Obtaining the copper thickness growth rate during the copper deposition stage and the copper thickness reduction rate during the copper dissolution stage to determine the rate matching degree, and determining the qualification of the copper plating process according to the rate matching degree, or, for several bubble distribution regions, obtaining the average residence time of the bubbles to determine the qualification of the copper plating process; Determining the pulsation speed of the electrolyte in the blind hole under the condition that the copper plating process is qualified to adjust the axis angle between the nozzle axis of the electrolyte and the axis of the blind hole or the nozzle pressure of the electrolyte; Determining the quality inspection period of the finished printed circuit board according to the recovery time of the copper ion concentration in the electrolyte, determining the copper distribution deviation in the blind hole based on the random sampling test results of several inspection periods, and optimizing the determination criterion of the change trend of the bubble density or optimizing the comparison criterion of the pulsation speed based on the copper distribution deviation.

[0007] Further, during the copper deposition stage, the process of judging the consistency of the change trends of the bubble density of the cathode bubbles in several regions includes: Obtaining several frames of images for a single region to establish a bubble density curve according to the bubble density of a single frame of image; Dividing a single bubble density curve into several curve segments based on the coordinate nodes of the horizontal axis; Comparing several bubble density curves respectively based on the curve segments; Determining that the curve segments with the same slope have the same change trend, and determining that several bubble density curves have the same change trend based on the comparison result that the first quantity ratio is greater than or equal to the first preset ratio; Determining that the change trends of the bubble density of the cathode bubbles are consistent based on the comparison result that the second quantity ratio is greater than or equal to the second preset ratio; Determining that the change trends of the bubble density of the cathode bubbles are inconsistent based on the comparison result that the second quantity ratio is less than the second preset ratio; Wherein, the first quantity ratio is the ratio of the number of curve segments with the same change trend to the total number of curve segments of the corresponding bubble density curve, and the second quantity ratio is the ratio of the number of bubble density curves with the same change trend to the total number of bubble density curves.

[0008] Further, under the condition that the change trend of the bubble density is determined to be consistent, the process of determining the qualification of the copper plating process based on the rate matching degree includes: Determine the ratio of the copper thickness growth rate in the copper deposition stage to the copper thickness reduction rate in the copper dissolution stage of the copper plating process as the rate matching degree; Compare the rate matching degree with a preset matching degree respectively; Determine that the copper plating process is qualified based on the comparison result that the rate matching degree is less than or equal to the first preset matching degree and greater than or equal to the second preset matching degree.

[0009] Further, under the condition that the change trend of the bubble density is determined to be inconsistent, the process of determining the qualification of the copper plating process according to the average residence time of the bubbles includes: Obtain several frames of images for a single area to determine the average residence time of the bubbles; Compare the average residence time with a preset time; Determine that the average residence time of the bubbles in a single area is qualified based on the comparison result that the average residence time is less than or equal to the preset time; Determine the proportion of the third quantity of the area where the average residence time is qualified and compare it with a third preset proportion; Determine that the copper plating process is qualified based on the comparison result that the third quantity proportion is greater than or equal to the third preset proportion.

[0010] Further, under the condition that the copper plating process is determined to be qualified, the process of determining the adjustment axis angle according to the pulsation velocity of the electrolyte in the blind hole includes: Compare the pulsation velocity with a preset pulsation velocity respectively; Determine to reduce the axis angle based on the comparison result that the pulsation velocity is greater than the first preset pulsation velocity; Wherein, the axis angle is the angle between the nozzle axis and the blind hole axis, subtract the pulsation velocity from the first preset pulsation velocity to obtain a first velocity difference, and set several angle adjustment coefficients corresponding to the first velocity difference to reduce the axis angle according to the angle adjustment coefficients.

[0011] Further, under the condition that the copper plating process is determined to be qualified, the process of determining the nozzle pressure of the electrolyte according to the pulsation velocity of the electrolyte in the blind hole includes: Compare the pulsation velocity with a preset pulsation velocity respectively; Determine to increase the nozzle pressure based on the comparison result that the pulsation velocity is less than the second preset pulsation velocity; Among them, the difference between the second preset pulsating speed and the pulsating speed is obtained to acquire a second speed difference, and a number of pressure adjustment coefficients corresponding to the second speed difference are set to increase the nozzle pressure according to the pressure adjustment coefficients.

[0012] Further, the determination process of the recovery duration of the copper ion concentration includes: Real-time monitor the copper ion concentration of the electrolyte and establish an ion concentration curve; On the ion concentration curve, a horizontal line is established with a preset ion concentration as the ordinate, parallel to the horizontal axis; Determine the average value of the time differences of several intersections of the horizontal line and the ion concentration curve, and determine the average time difference as the recovery duration.

[0013] Further, according to the recovery duration, the quality inspection period of the finished printed circuit board is determined. For a single inspection period, the determination process of the copper distribution deviation in the blind hole includes: For a single blind hole, determine the first area ratio where the copper thickness is greater than the first preset copper thickness and the second area ratio where the copper thickness is less than the second preset copper thickness; Determine the absolute area difference between the first area ratio and the second area ratio; For a single inspection, determine the standard deviation of several absolute area differences, and determine the standard deviation as the copper distribution deviation. Further, the process of determining to optimize the second preset ratio according to the copper distribution deviation includes: Compare the copper distribution deviation with a preset deviation; Based on the comparison result that the copper distribution deviation is greater than the preset deviation, determine to optimize the second preset ratio; Determine the first deviation value between the copper distribution deviation and the preset deviation; Set a number of ratio optimization coefficients corresponding to the first deviation value to increase the second preset ratio according to the ratio optimization coefficients.

[0014] Further, the process of determining to optimize the preset pulsating speed according to the copper distribution deviation includes: Compare the copper distribution deviation with a preset deviation; Based on the comparison result that the copper distribution deviation is less than or equal to the preset deviation, determine to optimize the preset pulsating speed; Determine the second deviation value between the preset deviation and the copper distribution deviation; Set a number of speed optimization coefficients corresponding to the second deviation value to respectively decrease the first preset pulsating speed and increase the second preset pulsating speed according to the speed optimization coefficients.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows. The present invention divides the semi-finished printed circuit board into several regions, and determines the qualification of the copper plating process according to the consistency of the change trend of the bubble density. In the copper plating process, the consistency of the change trend of the bubble density is the core index for evaluating the stability of the copper plating process and the quality of the coating. The change of the bubble density reflects the dynamic balance between the electrochemical reaction rate in the plating solution and the gas evolution. If the change trend of the bubble density in each region shows a sudden change, it indicates that at least one copper plating parameter deviates from the set value and needs to be adjusted; the determination method for the qualification of the copper plating process is determined according to the determination result of the trend consistency of the bubble density. For the case of qualified consistency, the overall copper thickness is determined. For the case of unqualified consistency, the qualification of the copper plating process is determined according to the determination results of each region, so as to improve the determination efficiency while ensuring the determination accuracy; according to the determination result of the qualification of the overall copper plating process, the state of the electrolyte in the blind hole is determined, and the copper plating quality in the blind hole is further determined, and the unqualified situation is accurately adjusted, so as to further improve the copper plating quality of the printed circuit board; the quality inspection period is determined according to the recovery time of the copper ion concentration. Too long or too short recovery time of the copper ion concentration will reduce the copper plating quality. In this case, the detection period is shortened, and the determination criterion for the change trend of the bubble density or the determination criterion for the copper plating quality in the blind hole is improved according to the periodic detection results, so as to further improve the copper plating quality in the blind hole of the printed circuit board.

[0016] Furthermore, the present invention determines the change trend of the bubble density by comparing the bubble density curves in segments during the copper deposition stage. During the copper plating process, the bubble density will show a regular change with the increase of the copper plating time. The change rules of several regions are compared with each other to determine whether the change trend of the bubble density is consistent, thereby improving the determination criterion for the overall copper plating process and further improving the copper plating quality in the blind hole of the printed circuit board.

[0017] Furthermore, the present invention determines the qualification of the copper plating process according to the rate matching degree. During the copper plating process of the printed circuit board, the forward current density and the reverse current density are alternated. The forward current density increases the copper thickness, and the reverse current density decreases the copper thickness. If the increase rate of the copper thickness and the decrease rate of the copper thickness do not match, it will lead to unqualified thickness of the overall coating or unqualified roughness of the coating. The overall copper plating quality is determined according to the rate matching degree, improving the determination accuracy of the overall quality, and thus further improving the copper plating quality in the blind hole of the printed circuit board.

[0018] Furthermore, the present invention determines the qualification of the copper plating quality in the area based on the average residence time of the bubbles. If the residence time of the bubbles is too long, defects such as pitting will appear on the copper plating surface. The copper plating quality of the local area is determined according to the average residence time of the bubbles, and the qualification of the copper plating process is determined according to the statistical results of the area copper plating quality, thereby improving the determination accuracy of the copper plating quality and further improving the copper plating quality in the blind holes of the printed circuit board.

[0019] Furthermore, the present invention determines the copper plating quality in the blind hole by the pulsation speed of the electrolyte in the blind hole. An appropriate pulsation speed can enhance the exchange rate of copper ions inside and outside the blind hole and relieve concentration polarization. An excessively high pulsation speed will destroy the steady state of the plating solution in the blind hole, resulting in local supersaturation of copper ions and triggering reverse current to break through the coating, forming protrusions or voids. An excessively low pulsation speed will cause inhibitors to accumulate at the hole mouth, inhibiting deposition on the hole wall and forming depressions. By monitoring the pulsation speed and adjusting it specifically for the situation of too high or too low pulsation speed, the copper plating quality in the blind holes of the printed circuit board is further improved.

[0020] Furthermore, the present invention raises the determination criterion for the change trend of the bubble density under the condition of large copper distribution deviation, and raises the determination criterion for the copper plating quality in the blind hole under the condition of small copper distribution deviation. The determination of the qualification of the copper plating process or the determination of the copper plating quality in the blind hole is essentially the determination of the fluidity of the electrolyte. When the change trends of the bubble density are inconsistent, it indicates that the overall flow of the electrolyte is uneven, there are stagnant areas, leading to an imbalance in the copper ion concentration gradient, and it is more likely to cause low copper plating quality in the blind hole; under the condition that the overall flow uniformity of the electrolyte is qualified, the determination criterion for the pulsation speed of the electrolyte in the blind hole is raised, and the determination criterion for the copper plating quality in the blind hole is raised more specifically, thereby further improving the copper plating quality in the blind holes of the printed circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flowchart of the preparation method of the millimeter-wave radar circuit board based on pulse electroplating according to the embodiment of the present invention; Figure 2 It is a flowchart of determining the consistency of the change trend of the bubble density of the cathode bubbles according to the embodiment of the present invention; Figure 3 It is a flowchart of determining the qualification of the copper plating process based on the rate matching degree according to the embodiment of the present invention; Figure 4 It is a flowchart of determining the qualification of the copper plating process according to the average residence time of the bubbles according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] To make the objectives and advantages of the present invention more clear and understandable, the present invention will be further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and do not limit the protection scope of the present invention.

[0024] Please refer to Figures 1 - 4 as shown Figure 1 which is a flowchart of a method for preparing a millimeter-wave radar circuit board based on pulse electroplating according to an embodiment of the present invention; Figure 2 which is a flowchart of determining the consistency of the change trend of the bubble density of cathode bubbles according to an embodiment of the present invention; Figure 3 which is a flowchart of determining the qualification of the copper plating process based on the rate matching degree according to an embodiment of the present invention; Figure 4 which is a flowchart of determining the qualification of the copper plating process according to the average residence time of bubbles according to an embodiment of the present invention.

[0025] An embodiment of the present invention provides a method for preparing a millimeter-wave radar circuit board based on pulse electroplating, including: Step S1, after the substrate is surface-cleaned, inner layer pattern processing, multi-layer board lamination, drilling, electroless copper plating, and outer layer image transfer processing are sequentially performed to obtain a semi-finished printed circuit board; Step S2, perform pulse electroplating copper plating on the semi-finished printed circuit board, and determine whether the change trend of the bubble density is consistent by obtaining the ratio of the number of bubble density curves with consistent change trends in several cathode regions during the copper deposition stage to the total number; Step S3, obtain the copper thickness growth rate during the copper deposition stage and the copper thickness reduction rate during the copper dissolution stage to determine the rate matching degree, and determine the qualification of the copper plating process according to the rate matching degree, or, for several bubble distribution regions, obtain the average residence time of bubbles to determine the qualification of the copper plating process; Step S4, determine the pulsation speed of the electrolyte in the blind hole based on the determination result of the qualification of the copper plating process, and adjust the axis angle between the axis of the electrolyte spray head and the axis of the blind hole or the spray pressure of the electrolyte according to the comparison result between the pulsation speed and the preset pulsation speed; Step S5, determine the quality inspection period of the finished printed circuit board according to the recovery time of the copper ion concentration in the electrolyte, determine the copper distribution deviation in the blind hole based on the random sampling test results of several inspection periods, and optimize the second preset ratio or the preset speed based on the copper distribution deviation.

[0026] Specifically, the processes of surface cleaning of the substrate, inner layer pattern processing, multilayer board lamination, drilling, electroless copper plating, and outer layer image transfer are all prior arts and will not be elaborated here.

[0027] Specifically, the regional division criterion for the surface of the printed circuit board can be based on the distribution density of holes. For example, taking the distribution density of holes as 10 holes / cm 2 as the basis for regional division, and there is no specific limitation.

[0028] Specifically, in the copper deposition stage, the process of judging the consistency of the change trend of the bubble density of cathode bubbles in several regions includes: Obtaining several frames of images for a single region to establish a bubble density curve based on the bubble density of a single frame of image; Dividing a single said bubble density curve into several curve segments based on the coordinate nodes of the horizontal axis; Comparing several said bubble density curves respectively based on the curve segments; Determining that the curve segments with consistent slopes have a consistent change trend, and determining that several said bubble density curves have a consistent change trend based on the comparison result that the first quantity ratio is greater than or equal to the first preset ratio; Determining that the change trend of the bubble density of the cathode bubbles is consistent based on the comparison result that the second quantity ratio is greater than or equal to the second preset ratio; Determining that the change trend of the bubble density of the cathode bubbles is inconsistent based on the comparison result that the second quantity ratio is less than the second preset ratio; Wherein, the first quantity ratio is the ratio of the number of curve segments with a consistent change trend to the total number of curve segments of the corresponding bubble density curve, and the second quantity ratio is the ratio of the number of said bubble density curves with a consistent change trend to the total number of the bubble density curves.

[0029] Specifically, the first preset ratio and the second preset ratio are determined according to the historical copper plating process. The value range of the first preset ratio is set to [60%, 80%], and 70% is preferably selected in the embodiments of the present invention; the value range of the first preset ratio is set to [70%, 90%], and 80% is preferably selected in the embodiments of the present invention.

[0030] Specifically, under the condition of determining that the change trend of the bubble density is consistent, the process of determining the qualification of the copper plating process based on the rate matching degree includes: Determining the ratio of the copper thickness growth rate in the copper deposition stage to the copper thickness reduction rate in the copper dissolution stage of the copper plating process as the rate matching degree; Comparing the rate matching degree with the preset matching degree respectively; Determine that the copper plating process is qualified based on the comparison result that the rate matching degree is less than or equal to the first preset matching degree and greater than or equal to the second preset matching degree; Determine that the copper plating process is unqualified based on the comparison result that the rate matching degree is greater than the first preset matching degree or less than the second preset matching degree.

[0031] Specifically, the value of the preset matching degree is the value corresponding to the mode of the rate matching degree of the qualified copper plating process in the historical copper plating process, and the specific value range is set to [2.5, 5], and the preferred value in the embodiment of the present invention is 3.

[0032] It can be understood that during the copper plating process, the forward current and the reverse current alternate. A large rate matching degree means that the copper deposition rate caused by the forward current is too fast or the copper ablation rate caused by the reverse current is too slow. An overly fast copper deposition rate will lead to insufficient replenishment of copper ions in the holes, resulting in an overly thin or even copper-free copper layer at the bottom of the holes. An overly slow copper ablation rate cannot effectively defoam and dissolve the oxides at the hole openings, leading to an increase in the surface roughness of the copper deposition and a decrease in the uniformity of the copper deposition thickness.

[0033] Under the condition that it is determined that the change trends of the bubble densities are inconsistent, the process of determining the qualification of the copper plating process according to the average residence time of the bubbles includes: Obtain several frames of images for a single region to determine the average residence time of the bubbles; Compare the average residence time with a preset time; Determine that the average residence time of the bubbles in a single region is qualified based on the comparison result that the average residence time is less than or equal to the preset time; Determine that the average residence time of the bubbles in a single region is unqualified based on the comparison result that the average residence time is greater than the preset time; Determine the proportion of the third quantity of the regions where the average residence time is qualified and compare it with a third preset proportion; Determine that the copper plating process is qualified based on the comparison result that the third quantity proportion is greater than or equal to the third preset proportion; Determine that the copper plating process is unqualified based on the comparison result that the third quantity proportion is less than the third preset proportion.

[0034] Specifically, the preset time is determined based on the benchmark that the residence time of the bubbles does not affect the copper plating quality, and the specific value range is set to [2s, 5s], and the preferred value in the embodiment of the present invention is 3s.

[0035] Specifically, the value of the third preset proportion is determined according to the process of qualified historical copper plating quality, and the specific value range is set to [80%, 95%], and the preferred value in the embodiment of the present invention is 90%.

[0036] Specifically, under the condition that the copper plating process is determined to be unqualified, the process of determining the vacuum-assisted duration before copper plating according to the bubble density of the cathode includes: Comparing the bubble density with a preset density; Based on the comparison result that the bubble density is greater than the preset density, it is determined to increase the vacuum-assisted duration; Subtracting the bubble density from the preset density to obtain a density difference; A number of duration adjustment coefficients corresponding to the density difference are set to increase the vacuum-assisted duration according to the duration adjustment coefficients.

[0037] Specifically, the value of the preset density is the average bubble density of the cathode qualified in the historical copper plating process, and the specific value range is set to [10 bubbles / cm 2 , 100 bubbles / cm 2 , and preferably 50 bubbles / cm in the embodiments of the present invention 2 .

[0038] Specifically, comparing the first density difference with a preset density difference; Based on the comparison result that the first density difference is greater than the preset density difference, it is determined to increase the vacuum-assisted duration with a first duration adjustment coefficient; Based on the comparison result that the first density difference is less than or equal to the preset density difference, it is determined to increase the vacuum-assisted duration with a second duration adjustment coefficient.

[0039] Specifically, the value range of the preset density difference is set to [5 bubbles / cm 2 , 20 bubbles / cm 2 , and preferably 10 bubbles / cm in the embodiments of the present invention 2 ; the value range of the first duration adjustment coefficient is set to [1.5, 2], and preferably 1.8 in the embodiments of the present invention; the value range of the second duration adjustment coefficient is set to [1.1, 4], and preferably 1.3 in the embodiments of the present invention.

[0040] Specifically, under the condition that the copper plating process is determined to be qualified, the process of determining the adjustment of the axis angle according to the pulsation speed of the electrolyte in the blind hole includes: Comparing the pulsation speed with a preset pulsation speed respectively; Based on the comparison result that the pulsation speed is greater than the first preset pulsation speed, it is determined to reduce the axis angle; Wherein, the axis angle is the angle between the nozzle axis and the blind hole axis, subtracting the pulsation speed from the first preset pulsation speed to obtain a first speed difference, and setting a number of angle adjustment coefficients corresponding to the first speed difference to reduce the axis angle according to the angle adjustment coefficients.

[0041] It is understandable that the pulsating velocity is the random fluctuation component of the instantaneous velocity, that is, the deviation between the instantaneous velocity and the average velocity.

[0042] Specifically, under the condition that the copper plating process is determined to be qualified, the process of determining the spray head pressure of the electrolyte according to the pulsating velocity of the electrolyte in the blind hole includes: Comparing the pulsating velocity with a preset pulsating velocity respectively; Determining to increase the spray head pressure based on the comparison result that the pulsating velocity is less than the second preset pulsating velocity; Wherein, subtracting the second preset pulsating velocity from the pulsating velocity to obtain a second velocity difference, and setting a number of pressure adjustment coefficients corresponding to the second velocity difference to increase the spray head pressure according to the pressure adjustment coefficients.

[0043] Specifically, the values of the first preset pulsating velocity and the second preset pulsating velocity are determined according to the historical copper plating process with qualified copper plating quality. The value range of the first preset pulsating velocity is set to [5 cm / s, 8 cm / s], and preferably 7 cm / s in the embodiment of the present invention; the value range of the second preset pulsating velocity is set to [2 cm / s, 4 cm / s], and preferably 3 cm / s in the embodiment of the present invention.

[0044] It is understandable that when the pulsating velocity is too large, it is necessary to reduce the axis angle. When the angle between the spray head axis and the blind hole axis decreases, the jet direction is closer to perpendicular, which can reduce the lateral impact force and the turbulence intensity in the blind hole, and the pulsating velocity will decrease as the turbulence intensity decreases; when the pulsating velocity is too small, it is necessary to increase the spray head pressure to increase the pulsating velocity.

[0045] Specifically, comparing the first velocity difference with a preset difference; Determining to reduce the axis angle with a first angle adjustment coefficient based on the comparison result that the first velocity difference is greater than or equal to the preset difference; Determining to reduce the axis angle with a second angle adjustment coefficient based on the comparison result that the first velocity difference is less than the preset difference.

[0046] Specifically, the value range of the preset difference is set to [0.5 cm / s, 1.5 cm / s], and preferably 0.8 cm / s in the embodiment of the present invention; the value range of the first angle adjustment coefficient is set to [0.6, 0.8], and preferably 0.75 in the embodiment of the present invention; the value range of the second angle adjustment coefficient is set to [0.81, 0.92], and preferably 0.85 in the embodiment of the present invention.

[0047] Specifically, comparing the second velocity difference with the preset difference; Determine to increase the pressure of the nozzle with a first pressure adjustment coefficient based on the comparison result that the second speed difference is greater than or equal to the preset difference; Determine to increase the pressure of the nozzle with a second pressure adjustment coefficient based on the comparison result that the second speed difference is less than the preset difference.

[0048] Specifically, the value range of the first pressure adjustment coefficient is set to [1.3, 1.5], and 1.4 is preferred in the embodiments of the present invention; the value range of the second pressure adjustment coefficient is set to [1.1, 1.29], and 1.2 is preferred in the embodiments of the present invention.

[0049] Specifically, the determination process of the recovery duration of the copper ion concentration includes: Monitor the copper ion concentration of the electrolyte in real time and establish an ion concentration curve; On the ion concentration curve, establish a horizontal line parallel to the horizontal axis with a preset ion concentration as the ordinate; Determine the average value of the time differences of several intersections of the horizontal line and the ion concentration curve, and determine the average value of the time differences as the recovery duration.

[0050] It can be understood that during the copper plating process of the printed circuit board, as the forward current density continues, the copper ions in the electrolyte will undergo a reduction reaction and adhere to the surface of the board, and the concentration gradually decreases. At the same time, the anode is constantly supplying copper ions, so the copper ion concentration will fluctuate with time. When the electrolyte circulation or replenishment is insufficient, it will lead to too long a recovery time of the copper ion concentration. When the recovery duration is too short and the copper ions are not consumed in time, it will lead to the copper ion reduction rate exceeding the surface atom migration rate, forming dendritic crystals and reducing the bonding force of the coating.

[0051] Specifically, determine the quality inspection period of the finished printed circuit board according to the recovery duration. For a single inspection period, the determination process of the copper distribution deviation in the blind hole includes: For a single blind hole, determine the first area ratio where the copper thickness is greater than the first preset copper thickness and the second area ratio where the copper thickness is less than the second preset copper thickness; Determine the absolute area difference between the first area ratio and the second area ratio; For a single inspection, determine the standard deviation of several absolute area differences and determine the standard deviation as the copper distribution deviation.

[0052] Specifically, the quality inspection period of the printed circuit board is negatively correlated with the recovery duration, and the specific inspection period is determined according to the required accuracy of the copper plating of the circuit board.

[0053] Specifically, the value range of the first preset copper thickness is set to [22 μm, 25 μm], and 23 μm is preferred in the embodiments of the present invention; the value range of the second preset copper thickness is set to [18 μm, 20 μm], and 18 μm is preferred in the embodiments of the present invention.

[0054] Specifically, the process of optimizing the second preset ratio according to the copper distribution deviation includes: Comparing the copper distribution deviation with a preset deviation; Determining to optimize the second preset ratio based on the comparison result that the copper distribution deviation is greater than the preset deviation; Determining a first deviation value between the copper distribution deviation and the preset deviation; Setting a number of ratio optimization coefficients corresponding to the first deviation value to optimize the second preset ratio according to the ratio optimization coefficients.

[0055] Specifically, the process of optimizing the preset pulsation speed according to the copper distribution deviation includes: Comparing the copper distribution deviation with a preset deviation; Determining to reduce the preset pulsation speed based on the comparison result that the copper distribution deviation is less than or equal to the preset deviation; Determining a second deviation value between the preset deviation and the copper distribution deviation; Setting a number of speed optimization coefficients corresponding to the second deviation value to respectively reduce the first preset pulsation speed and increase the second preset pulsation speed according to the speed optimization coefficients.

[0056] Specifically, comparing the first deviation value with a preset deviation value; Determining to increase the second preset ratio with a first ratio optimization coefficient based on the comparison result that the first deviation value is greater than or equal to the preset deviation value; Determining to increase the second preset ratio with a second ratio optimization coefficient based on the comparison result that the first deviation value is less than the preset deviation value.

[0057] Specifically, comparing the second deviation value with a preset deviation value; Determining to reduce the first preset pulsation speed with a first speed optimization coefficient and increase the second preset pulsation speed with a second speed optimization coefficient based on the comparison result that the second deviation value is greater than or equal to the preset deviation value; Determining to reduce the first preset pulsation speed with a third speed optimization coefficient and increase the second preset pulsation speed with a fourth speed optimization coefficient based on the comparison result that the second deviation value is less than the preset deviation value.

[0058] Specifically, the value range of the preset deviation is set to [0.5, 1.2], and 0.8 is preferred in the embodiments of the present invention; the value range of the preset deviation value is set to [0.1, 0.4], and 0.2 is preferred in the embodiments of the present invention.

[0059] Specifically, the value range of the first proportion optimization coefficient is set to [1.1, 1.2], and 1.15 is preferred in the embodiments of the present invention; the value range of the second proportion optimization coefficient is set to [1.01, 1.09], and 1.05 is preferred in the embodiments of the present invention; the value range of the first speed optimization coefficient is set to [0.91, 0.93], and 0.92 is preferred in the embodiments of the present invention; the value range of the second speed optimization coefficient is set to [1.04, 1.07], and 1.06 is preferred in the embodiments of the present invention; the value range of the third speed optimization coefficient is set to [0.94, 0.98], and 0.95 is preferred in the embodiments of the present invention; the value range of the fourth speed optimization coefficient is set to [1.02, 1.03], and 1.02 is preferred in the embodiments of the present invention.

[0060] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for preparing a millimeter wave radar circuit board based on pulse electroplating, characterized in that: include: Pulse electroplating copper is performed on the semi-finished printed circuit board, and the number of bubble density curves with the same change trend in several cathode regions in the copper deposition stage is obtained, and the second number ratio of the total number is used to determine whether the change trend of the bubble density is consistent; Obtaining the copper thickness growth rate in the copper deposition stage and the copper thickness reduction rate in the copper dissolution stage to determine the rate matching degree, and determining the eligibility of the copper plating process according to the rate matching degree, or, for several bubble distribution areas, obtaining the average residence time of the bubbles to determine the eligibility of the copper plating process; Under the condition that the copper plating process is qualified, the pulsation speed of the electrolyte in the blind hole is determined to adjust the angle between the axis of the electrolyte nozzle and the axis of the blind hole or the nozzle pressure of the electrolyte; The quality inspection cycle of the finished printed circuit board is determined according to the recovery time of the copper ion concentration in the electrolyte, the copper distribution deviation in the blind hole is determined based on the random sampling inspection results of several inspection cycles, and the judgment basis of the change trend of the bubble density or the comparison basis of the pulsation speed is optimized based on the copper distribution deviation.

2. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 1, characterized in that: During the copper deposition stage, the process of judging the consistency of the changing trend of the bubble density of the cathode bubbles in several regions includes: Acquire a plurality of frame images for a single region to establish a bubble density curve according to the bubble density of the single frame image; Dividing the single bubble density curve into a plurality of curve segments based on the coordinate nodes of the abscissa axis; Comparing the plurality of bubble density curves respectively based on the curve segment; Determine a curve segment with a consistent slope as having a consistent change trend, and determine a plurality of bubble density curves as having a consistent change trend based on a comparison result that the first quantity ratio is greater than or equal to a first preset ratio; Determining that the change trend of the bubble density of the cathode bubbles is consistent based on a comparison result that the second number ratio is greater than or equal to the second preset ratio; Determining that the change trend of the bubble density of the cathode bubbles is inconsistent based on a comparison result that the second number proportion is less than the second preset proportion; Among them, the first number proportion is the ratio of the number of curve segments with consistent change trends to the total number of curve segments of the corresponding bubble density curve, and the second number proportion is the ratio of the number of bubble density curves with consistent change trends to the total number of bubble density curves.

3. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 2, characterized in that: Under the condition that the change trend of the bubble density is determined to be consistent, the process of determining the eligibility of the copper plating process based on the rate matching degree includes: The ratio of the copper thickness growth rate in the copper deposition stage of the copper plating process to the copper thickness reduction rate in the copper dissolution stage is determined as the rate matching degree; Comparing the rate matching degree with the preset matching degree respectively; The copper plating process is determined to be qualified based on a comparison result that the rate matching degree is less than or equal to the first preset matching degree and greater than or equal to the second preset matching degree.

4. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 2, characterized in that: Under the condition that the change trend of bubble density is inconsistent, the process of determining the eligibility of the copper plating process according to the mean value of the bubble residence time includes: Acquire several frames of images for a single area to determine the average residence time of the bubble; Comparing the mean stay duration with a preset duration; Determining that the average residence time of the bubbles in a single area is qualified based on a comparison result that the average residence time is less than or equal to the preset time; Determine a third quantity ratio of the areas having a qualified average length of stay and compare it with a third preset ratio; The copper plating process is determined to be qualified based on the comparison result that the third quantity proportion is greater than or equal to the third preset proportion.

5. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 4, characterized in that: Under the condition that the copper plating process is qualified, the process of determining the adjustment axis angle according to the pulsation speed of the electrolyte in the blind hole includes: comparing the pulsation speed with the preset pulsation speed respectively; Determining to reduce the axis angle based on a comparison result that the pulsation speed is greater than a first preset pulsation speed; Among them, the axis angle is the angle between the nozzle axis and the blind hole axis, the pulsating speed is subtracted from the first preset pulsating speed to obtain a first speed difference, and several angle adjustment coefficients corresponding to the first speed difference are set to reduce the axis angle according to the angle adjustment coefficient.

6. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 4, characterized in that: Under the condition that the copper plating process is qualified, the process of determining and adjusting the nozzle pressure of the electrolyte according to the pulsation speed of the electrolyte in the blind hole includes: comparing the pulsation speed with the preset pulsation speed respectively; Determining to increase the nozzle pressure based on a comparison result that the pulsation speed is less than a second preset pulsation speed; The second preset pulsation speed is subtracted from the pulsation speed to obtain a second speed difference, and a plurality of pressure adjustment coefficients corresponding to the second speed difference are set to increase the nozzle pressure according to the pressure adjustment coefficients.

7. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 6, characterized in that: The process of determining the recovery time of the copper ion concentration includes: Monitor the copper ion concentration of the electrolyte in real time and establish an ion concentration curve; On the ion concentration curve, a horizontal line is established parallel to the abscissa axis with the preset ion concentration as the ordinate; The average time difference between a plurality of intersection points of the horizontal line and the ion concentration curve is determined, and the average time difference is determined as the recovery duration.

8. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 7, characterized in that: The quality inspection cycle of the finished printed circuit board is determined according to the recovery time. For a single inspection cycle, the process of determining the copper distribution deviation in the blind hole includes: Determine, for a single blind hole, a first area ratio where the copper thickness is greater than a first preset copper thickness and a second area ratio where the copper thickness is less than a second preset copper thickness; Determine an absolute difference in area between the first area ratio and the second area ratio; The standard deviation of several of the absolute differences in area is determined for a single test, and the standard deviation is determined as the copper distribution deviation.

9. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 8, characterized in that: The process of determining and optimizing the second preset proportion according to the copper distribution deviation includes: comparing the copper distribution deviation with a preset deviation; Determine to optimize the second preset proportion based on the comparison result that the copper distribution deviation is greater than the preset deviation; Determining a first deviation value between the copper distribution deviation and the preset deviation; A plurality of proportion optimization coefficients corresponding to the first deviation value are set to increase the second preset proportion according to the proportion optimization coefficients.

10. The method for preparing a millimeter wave radar circuit board based on pulse electroplating according to claim 9, characterized in that: The process of determining and optimizing the preset pulsation speed according to the copper distribution deviation includes: comparing the copper distribution deviation with a preset deviation; Determining to optimize the preset pulsation speed based on a comparison result that the copper distribution deviation is less than or equal to the preset deviation; Determining a second deviation value between the preset deviation and the copper distribution deviation; A plurality of speed optimization coefficients corresponding to the second deviation value are set to respectively reduce the first preset pulsation speed and increase the second preset pulsation speed according to the speed optimization coefficients.

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