A PCB inner layer circuit manufacturing method based on inkjet printing technology

Abstract

The application discloses a kind of based on ink-jet printing technology's PCB inner layer circuit manufacturing method, belong to printed circuit board manufacturing technical field.The method is through the spreading characteristic parameter of calibrating ink on pretreatment copper surface and solidification shrinkage, constructs point spread function to describe the thickness distribution profile after unit ink solidification;After initial binary pixel diagram is rasterized to target circuit pattern, based on point spread function and target pattern, it is generated compensation ink gray scale diagram by inversion iterative operation, to pre-offset the pattern distortion caused by ink spreading and shrinkage;Then, this compensation gray scale diagram controls ink-jet equipment to spray conductive ink or resist ink, and forms inner layer circuit after solidification.The method eliminates traditional dry film, exposure, developing procedure, realizes high-precision, high-consistency circuit manufacturing, especially suitable for rapid proofing and multi-variety, small-batch flexible manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit board manufacturing technology, and relates to a method for fabricating PCB inner layer circuits based on inkjet printing technology. Background Technology

[0002] In the manufacturing of multilayer printed circuit boards (PCBs), the fabrication of inner layer circuit patterns is one of the core processes. Traditional subtractive processing relies on multiple steps—dry film lamination, film alignment, UV exposure, development, etching, and film removal—to transfer the design pattern onto the copper surface and form the circuitry. While this process is mature and stable, suitable for standardized mass production, it reveals significant shortcomings when facing the demands of rapid prototyping, sample production, and flexible manufacturing with diverse product types and small batches during the R&D phase. Dry film lamination and exposure equipment are expensive, and each pattern requires a dedicated film, leading to long changeover times, material waste, and high costs, making it unsuitable for rapid iteration and customized production.

[0003] In recent years, inkjet printing technology has been introduced into the PCB manufacturing field due to its advantages of non-contact, plateless, and direct digital output. The basic idea is to use inkjet printers to directly spray conductive or resist ink onto a copper surface, where it cures to form circuits or resist patterns, thus eliminating tedious processes such as dry film application, exposure, and development. However, directly printing the design pixel-by-pixel often fails to achieve the required line accuracy. This is mainly because after liquid ink is sprayed onto the copper surface, it is affected by the ink's own spreading characteristics and subsequent curing shrinkage, resulting in a significant deviation between the final line width and the target design value. Edges are blurred, and short circuits can easily occur between adjacent lines due to excessive ink spreading, or open circuits due to improper compensation. Existing compensation methods are mostly based on simple empirical rules for overall line width scaling, which cannot accurately depict the superimposed effect of ink droplet spreading and shrinkage on the contours of arbitrarily complex graphics, making it difficult to ensure high fidelity in the fabrication of high-density, fine-pitch inner layer circuits.

[0004] Therefore, how to accurately model the ink spreading and curing shrinkage behavior of inkjet printing, and invert this model into a method that can accurately compensate for any circuit pattern pixel by pixel, so as to achieve high-precision and high-consistency production of the target circuit pattern, has become an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for fabricating PCB inner layer circuits based on inkjet printing technology, thereby solving the aforementioned technical problems.

[0006] The technical solution adopted in this invention is as follows: A method for fabricating inner layer circuits of a PCB based on inkjet printing technology includes: rasterizing the target circuit pattern to be fabricated to obtain an initial binary pixel image, wherein the value of each pixel in the initial binary pixel image represents whether a circuit exists at that pixel; obtaining the spreading characteristic parameters and curing shrinkage rate of inkjet ink on a pre-treated copper surface, wherein the spreading characteristic parameters represent the spreading ability of ink on the copper surface, and the curing shrinkage rate represents the volume shrinkage ratio of ink after curing from a liquid state; and constructing a point diffusion function based on the spreading characteristic parameters and curing shrinkage rate, wherein the point diffusion function is defined as the thickness distribution profile formed by a unit volume of ink on the copper surface after spreading and curing, and the point diffusion function... Constructed as: ; in, The curing shrinkage rate is... The spreading feature radius is determined by the spreading feature parameters; based on the point spread function and the initial binary pixel image, a compensated inkjet grayscale image is generated through inversion operation, wherein the grayscale value of each pixel in the compensated inkjet grayscale image corresponds to the ink volume that the inkjet printer should spray at that pixel; the inkjet printer is controlled according to the compensated inkjet grayscale image to spray conductive ink or resist ink onto the pre-processed copper surface; the ink sprayed onto the copper surface is cured to form an inner layer circuit that conforms to the target circuit pattern.

[0007] Optionally, the step of generating a compensated inkjet grayscale image through inversion operation based on the point spread function and the initial binary pixel image includes: The initial binary pixel map is defined as the target solidification thickness distribution B(x,y); Establish a positive prediction model for ink curing: ; in, To predict the thickness distribution of the cured ink, The image to be solved is the compensated inkjet grayscale image, and * indicates a two-dimensional convolution operation. By minimizing the cost function Seeking a solution The cost function Defined as predicting thickness distribution With the target thickness distribution Degree of deviation between: ; Through iterative optimization, Minimize, at this point This serves as the compensation inkjet grayscale image.

[0008] Optionally, the iterative optimization employs the Lucy-Richardson deconvolution algorithm, whose iterative format is as follows: ; in, This is the compensated grayscale image obtained in the k-th iteration. Point spread function The function after being centrally symmetrically flipped, This represents a pixel-wise dot product operation; Iteration initial value Let the initial binary pixel image be defined. When the number of iterations reaches a preset value or The iteration stops when the value falls below a set threshold, and the final value is output. This serves as the compensation inkjet grayscale image.

[0009] Optionally, during the iteration process, for Apply a nonnegativity constraint to ensure that the grayscale value obtained in any iteration is not less than zero.

[0010] Optionally, the spreading feature parameters are obtained and the spreading feature radius is determined. The process includes: Under the same process conditions as the fabrication of the circuit, the inkjet printing equipment is controlled to spray ink onto the pretreated copper surface to form isolated ink droplet arrays or single-pixel wide lines. The ink after spraying is subjected to the curing process described above, and the spreading diameter d of a single ink droplet or the line width of a single pixel line is measured after curing. Based on the point spread function The contour characteristics are used to calculate the spreading feature radius from the spreading diameter d. The inverse calculation formula is: ; The spreading diameter d is defined as the diameter corresponding to the point where the thickness profile of the cured ink droplet decays to half of its maximum thickness.

[0011] Optionally, the grayscale values ​​in the compensated inkjet grayscale image are mapped to the number of ink droplets ejected by the inkjet printer at each pixel position or the volume of a single ink droplet, and the resolution of the initial binary pixel image is consistent with the printing resolution of the inkjet printer.

[0012] Optionally, the ink is a conductive ink containing metal nanoparticles, which directly forms a conductive circuit after curing; or, the ink is an etch-resistant ink, which leaves a circuit pattern on the copper surface after etching and film removal after curing.

[0013] Optionally, the spreading characteristic parameters and curing shrinkage rate are pre-measured by ink spraying and curing experiments on the same pre-treated copper surface as the fabricated circuit, and used as fixed parameters for the construction of the point diffusion function and the inversion calculation.

[0014] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. By constructing a point spread function characterizing the combined effects of ink spreading and curing shrinkage, and incorporating the convolution of this function into a forward prediction model, precise pixel-by-pixel compensation can be performed on any target graphic to generate an optimal inkjet grayscale image. This method eliminates the graphic distortion caused by ink spreading and shrinkage from a physical mechanism perspective, significantly improving the linewidth accuracy and edge sharpness of fine lines produced by inkjet printing, ensuring that the final cured line graphic highly matches the design target.

[0015] 2. It automatically solves the compensation grayscale image by using inversion operation (such as the Lucy-Richardson deconvolution algorithm), without relying on manual experience to repeatedly adjust printing parameters. It can adapt to any complex circuit pattern, and is especially suitable for R&D prototyping and flexible manufacturing scenarios with multiple varieties and small batches with frequent line changes. It significantly shortens the graphic data preparation time and improves production efficiency.

[0016] 3. The spreading characteristic parameters and curing shrinkage rate are pre-calibrated through standardized experiments and can be fixed for mass production. Once the calibration is completed, automated high-precision compensation can be performed on any pattern. The method has extremely high consistency and repeatability, reducing the impact of material batch fluctuations or process parameter drift on the compensation effect.

[0017] 4. It eliminates the cumbersome processes of applying dry film, exposure, and development in traditional processes, as well as the investment in related equipment and materials. Only inkjet printing equipment and curing devices are needed to complete the inner layer circuit production, which greatly reduces the prototyping cost and equipment footprint, simplifies the operation process, and improves environmental friendliness. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a flowchart illustrating the principle of a PCB inner layer circuit fabrication method based on inkjet printing technology. Figure 2 These are micrographs comparing the PCB inner layer circuit fabrication effects of the method in this embodiment with those of existing technologies. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0022] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0023] Example 1: like Figure 1 As shown in the figure, this embodiment elaborates in detail on the method principle involved in the PCB inner layer circuit fabrication method based on inkjet printing technology.

[0024] The target line graphic to be created is first rasterized to generate an initial binary pixel image. In this initial binary pixel image, each pixel has a value of either "0" or "1". A pixel with a value of "1" indicates that the target line exists at that pixel location, and a pixel with a value of "0" indicates that the target line does not exist at that pixel location. To maximize the inherent precision of the inkjet printer, the resolution of this initial binary pixel image is set to be the same as the printing resolution of the inkjet printer, so that each pixel corresponds exactly to an addressing position on the printer.

[0025] Because liquid ink spreads naturally along the pre-treated copper surface after being sprayed, and its volume shrinks during the subsequent curing process, if the ink is sprayed in equal amounts according to the initial binary pixel image, the resulting circuit pattern will be significantly wider than the design target, with blurred edges, failing to meet the requirements for fabricating fine circuits. To eliminate this systematic distortion, this technical solution constructs a point spread function. This function is used to quantitatively describe the relative thickness distribution profile of a unit volume of ink on a pretreated copper surface after spreading and curing. Considering the isotropic and locally smooth characteristics of ink droplet spreading on a flat copper surface, this technical solution constructs the point spread function as a two-dimensional Gaussian function: ; In the above formula, The curing shrinkage rate of ink is defined as the percentage decrease in volume of ink after it has cured from a liquid state. It represents the retention coefficient of the volume after curing, ensuring that the total integral value of the point diffusion function is consistent with the remaining volume after curing; The spreading feature radius is determined by the spreading feature parameters of the ink on the pretreated copper surface. Intuitively, The larger the value, the more severe the ink spreading and the wider the influence range of a single ink droplet; It directly expresses the relative ink thickness formed by a unit volume of ink at coordinate (x,y).

[0026] The processing logic for the point spread function representation above is as follows: When a drop of liquid ink is sprayed onto a pretreated copper surface, the ink undergoes two physical processes simultaneously: first, it spreads outwards along the copper surface; second, it shrinks and solidifies due to solvent evaporation or resin cross-linking. The spreading process determines the spatial extent of the droplet's influence, while the shrinking process determines the final thickness reached at the center of the droplet.

[0027] The spreading process of a droplet on a smooth, uniform surface typically exhibits a distribution pattern of being thicker at the center and thinner at the edges. This pattern can be well described mathematically by a two-dimensional Gaussian function. The exponential term of the Gaussian function... This depicts the trend of thickness decreasing with increasing distance from the center. The rate of decrease is determined by the spreading feature radius. Decide, The larger the size, the farther the ink spreads, the more even the thickness distribution, and the wider the range of influence.

[0028] Regarding the shrinkage process, the liquid ink will shrink in volume after curing. Let the shrinkage ratio be... (That is, the volume shrinks by a certain percentage after curing) Then, the actual remaining equivalent volume ratio after curing is This volume shrinkage acts evenly across the entire thickness profile of the ink droplet; therefore, in the mathematical expression describing the thickness distribution after curing, the overall amplitude needs to be factored in by 1. Scale according to the ratio.

[0029] Taking into account the combined effects of spreading and contraction, the amplitude coefficient (1) β) is combined with a two-dimensional Gaussian function and divided by a normalization factor. This makes the two-dimensional integral value of the function exactly equal to 1. β means that the point diffusion function fully describes the thickness of the cured ink contributed by each position on the copper surface after the ink is spread and shrunken, which conforms to the basic physical constraint of volume or mass conservation.

[0030] In the aforementioned two-dimensional Gaussian function, the curing shrinkage rate characterizes the proportion of volume reduction of the ink after it transitions from a liquid state to a fully cured state, and is derived from independent experimental calibration of actual inks under specific curing conditions. In this scheme, This determines the overall amplitude level of the point spread function. When Increase, 1 As the diffusion function decreases, the overall amplitude of the point spread function also decreases. This means that for the same volume of jet ink, the thickness contribution after curing becomes thinner. During subsequent inversion compensation, the control system automatically increases the grayscale value at the corresponding position in the inkjet grayscale map, i.e., increases the amount of jet ink, to compensate for the thickness reduction caused by curing shrinkage and ensure that the final cured line thickness reaches the target value.

[0031] Spread feature radius The ability of ink to spread on a pretreated copper surface is characterized by a back-calculation of the spreading diameter of isolated ink droplets after curing. In this scheme, This determines the spatial width of the influence range of the point spread function. An increase in thickness indicates more severe ink spreading, a wider influence area of ​​individual ink droplets, and a corresponding decrease in the center peak thickness. This will be addressed during subsequent inversion compensation. The larger the value, the stronger the smoothing effect of the dot spread function. The gray value of the edge pixels in the inkjet grayscale image will be reduced accordingly. That is, by reducing the amount of ink at the edge, the edge widening effect caused by excessive spreading is offset, thereby achieving precise control of line width shrinkage.

[0032] Point spread function value It is the core input for both the forward prediction model and the inversion operation. It defines the relative ink thickness after curing at position (x,y), contributed by a unit volume of ink located at the origin. In the convolution operation, it is used as the convolution kernel, determining the weight of the influence of the ink ejected from each pixel on the thickness distribution of surrounding pixels.

[0033] After constructing the point spread function described above, the initial binary pixel image is used as the desired final cured ink thickness distribution, denoted as B(x,y). Since the actual cured ink thickness distribution is the convolution result of the ink volume distribution ejected from the compensated inkjet grayscale image and the point spread function, a forward prediction model is established: ; in, This represents a compensated inkjet grayscale image, where the grayscale value of each pixel represents the volume of ink that the inkjet printer should eject at that pixel location; * indicates a two-dimensional convolution operation. This is the thickness distribution of the cured ink predicted based on the current compensated inkjet grayscale image.

[0034] The processing logic of the above-mentioned positive prediction model representation is as follows: During inkjet printing, for compensating inkjet grayscale images The ink sprayed at each pixel location does not have a curing thickness distribution on the copper surface limited to that pixel area itself, but rather spreads outward from that pixel according to a point diffusion function. The outline diffuses outwards and solidifies. This means that any point on the final copper surface... The thickness of the cured ink at a point is formed by the superposition and accumulation of the thickness contributions of ink droplets ejected from numerous surrounding pixels at that point.

[0035] Mathematically, this process, where "each location independently contributes to diffusion, and the overall result is a linear superposition of these contributions," can be precisely described by two-dimensional convolution operations. This applies to compensating inkjet grayscale images. As the input signal, the point spread function Treating them as system response functions, convolving them yields the result. This refers to the predicted distribution of cured ink thickness at each pixel location on the entire copper surface. This forward prediction model establishes a causal mapping relationship from "spray ink volume distribution" to "final cured thickness distribution," which is the basis for achieving accurate compensation in this solution.

[0036] Compensated inkjet grayscale image The core variable to be solved represents the inkjet printing device at each pixel position. The grayscale code of the ink volume to be ejected. It is one of the final outputs of this solution, directly driving the inkjet printer to eject ink. Changes will directly affect the predicted thickness distribution. The overall shape.

[0037] The point spread function H(x,y) serves as the convolution kernel, defining the spatial diffusion behavior of the ink. Its parameters... and Once calibrated, it becomes a fixed convolution kernel. Decision made The degree to which the local ink distribution is smoothed and diffused is the fundamental reason for the difference between the original design and the actual solidified graphic.

[0038] Predicted Cured Ink Thickness Distribution The output of the positive prediction model represents the current compensated grayscale image. and known point spread function Under these conditions, the expected ink thickness distribution that will ultimately solidify on the copper surface is determined. In subsequent inversion calculations, The difference between the two will be calculated and adjusted accordingly, and the comparison will be made with the target thickness distribution. .

[0039] To ensure that the final circuit pattern closely matches the target pattern, it is necessary to solve for an optimal compensated inkjet grayscale image. This makes the predicted thickness distribution possible. The difference between the target thickness distribution B(x,y) and the target thickness distribution is minimized. A cost function is defined to represent this difference. for: ; This cost function measures the overall deviation between the predicted thickness and the target thickness at all pixel locations. By minimizing the cost function... The optimal G(x,y) can be obtained by solving for it.

[0040] The ultimate goal of this approach is to make the cured ink thickness distribution approximate the target thickness distribution corresponding to the target circuit pattern as closely as possible. To quantitatively measure this approximation, a calculable error metric needs to be defined. Cost function The cost function is calculated as the sum of squares of the difference between the predicted and target thicknesses, i.e., the sum of the squares of the deviations at all pixel locations. Using a sum-of-squares form ensures two things: first, that both positive and negative deviations are effectively accumulated without canceling each other out; and second, that the cost function is smooth and differentiable, facilitating subsequent minimization using gradient-based optimization algorithms. Cost Function The smaller the value of , the higher the overall consistency between the predicted solidification result and the target graphic. When the global minimum value is obtained, the corresponding G(x,y) is the optimal compensated inkjet grayscale image.

[0041] In the formula, the target solidification thickness distribution B(x,y) is defined by the initial binary pixel image and is the ideal target value for the final line thickness distribution formed on the copper surface. In the line region, B(x,y) takes a certain expected normalized thickness value; in the non-line region, B(x,y) takes a value of zero. B(x,y) is the constraint and convergence objective of the entire optimization problem. Any prediction result that deviates from B(x,y) will be amplified by the cost function JJ and included in the overall error.

[0042] The predicted thickness distribution of the cured ink, D(x,y), is the actual possible thickness distribution output by the forward prediction model. The cost function, by calculating the deviation between D(x,y) and B(x,y), drives the optimization algorithm to continuously adjust the grayscale image G(x,y), so that D(x,y) gradually approaches B(x,y). The impact of the cost function on the output G(x,y) is indirect: minimizing the cost function drives the direction and step size of the iterative optimization process, ultimately determining the distribution shape to which G(x,y) converges.

[0043] To solve this minimization problem, this technical solution employs an iterative optimization algorithm, preferably the Lucy-Richardson deconvolution algorithm. This algorithm can robustly recover the original input G(x,y) given the point spread function H(x,y) and the target image B(x,y). Its iterative formula is as follows: ; In the above iterative formula, This is the compensated grayscale image obtained in the k-th iteration. The initial value for iteration can be directly set as the initial binary pixel image; It is the point spread function The function obtained after performing a centrosymmetric flip, this flipping operation is the adjoint kernel required by the deconvolution algorithm; symbol This represents pixel-by-pixel multiplication; the denominator contains... This represents the ratio of the solidified thickness distribution predicted positively based on the current estimate to the actual target thickness distribution. Back projection, thereby updating During the iterative optimization process, the compensated inkjet grayscale image obtained in each iteration is... Non-negativity constraints are applied to all values, forcing all grayscale values ​​less than zero to be set to zero, ensuring that the grayscale value of any pixel in the compensated inkjet grayscale image is not less than zero. When the number of iterations reaches a preset number, or the cost function... When the value drops below the preset threshold, the iteration stops, and the current G(x,y) is output as the final compensated inkjet grayscale image.

[0044] The technical solution processing logic corresponding to the above formula is as follows: The problem of finding the optimal compensated inkjet grayscale image G(x,y) can be mathematically reduced to the problem of deconvolving the original input distribution G(x,y) given the target curing thickness distribution B(x,y) and the convolution kernel H(x,y). This is a typical ill-conditioned inverse problem, and direct inversion often leads to unstable solutions and amplified noise.

[0045] The Lucy-Richardson deconvolution algorithm is a classic iterative deconvolution method, particularly suitable for image restoration problems involving Poisson noise or non-negativity constraints. Based on a Bayesian statistical inference framework, this algorithm iteratively approximates the optimal solution. The core computational logic of its iterative formula is: [The algorithm then proceeds to the next step, but the provided text is incomplete and requires further context.] First, the prediction result is obtained through forward convolution. Then the target value The ratio of the error signal to the predicted result is calculated pixel by pixel; then, the image of this ratio is convolved with the flipped point spread function H(-x,-y), and the error signal is back-projected back to each pixel; finally, this back-projection result is used as a gain factor and multiplied pixel by pixel to the current estimate. The above yields an updated estimate. This iterative mechanism can robustly recover the original input distribution given the convolution kernel and the target image, and naturally preserves the non-negativity of the solution.

[0046] The k-th iteration of the compensated grayscale image estimation This is the estimate of the final output G(x,y) for the current iteration step. After each iteration update, this estimate moves one step closer to a better solution.

[0047] The target solidification thickness distribution B(x,y) serves as the target image for deconvolution, providing a convergence basis for the iterative process. The boundary sharpness and linewidth of B(x,y) directly affect the edge gradient features of the final compensated grayscale image.

[0048] H(x,y) is used for forward prediction convolution, and H(-x,-y) is used for error backprojection convolution. Together, they complete the closed loop of prediction and correction. H(x,y)'s... The parameters determine the spatial range of smoothing and backprojection in each iteration, affecting the convergence speed and the final compensation accuracy.

[0049] Ratio Term This ratio reflects the pixel-level deviation between the target thickness and the current predicted thickness. A ratio greater than 1 indicates that the current prediction is too thin, requiring an increase in ink volume for that pixel and its surrounding area; a ratio less than 1 indicates that the prediction is too thick, requiring a decrease in ink volume. This ratio directly controls the direction and magnitude of correction in each iteration.

[0050] The final G(x,y) after iterative convergence is the desired compensated inkjet grayscale image. This output grayscale image contains precise pixel-by-pixel ink volume compensation information, so that when the inkjet printer sprays ink onto the copper surface according to this grayscale image, the final cured thickness distribution D(x,y) can approximate the target thickness distribution B(x,y) as closely as possible after the combined effects of spreading and curing shrinkage, thus achieving high-precision inner layer circuit fabrication.

[0051] Each grayscale value in the compensated inkjet grayscale image G(x,y) corresponds to the volume of ink that the inkjet printer should eject at a pixel location. In actual control, the grayscale value can be mapped to the actual number of ink droplets ejected by the inkjet printer at that pixel location, or the volume adjustment of a single ink droplet. After this mapping is completed, the inkjet printer can be driven to eject conductive ink or resist ink onto the pre-treated copper surface. Finally, the ink ejected onto the copper surface is cured to form an inner layer circuit that matches the height of the target circuit pattern.

[0052] To obtain the spreading feature radius required to construct the point spread function In addition to the curing shrinkage rate β, this embodiment also provides a parameter calibration process. Under the same process conditions as the actual fabrication of the circuit, isolated ink droplet arrays or single-pixel wide lines are formed by jetting ink onto the pre-treated copper surface and undergoing the same curing process. The spreading diameter d of a single ink droplet after curing is measured, which is defined as the diameter corresponding to the point where the thickness profile of the cured ink droplet decays to half of its maximum thickness. The spreading feature radius is calculated by using the contour line properties of the point spread function. The inverse calculation formula is: ; The curing shrinkage rate β can be obtained directly by measuring the change in ink droplet volume before and after curing, or indirectly by measuring the integral value of the thickness distribution of a known volume of ink after curing. The spreading characteristic radius obtained by the above calibration process... The curing shrinkage rate β is used as a fixed parameter and applied to the compensation calculation of subsequent arbitrary graphics.

[0053] This formula is used to calculate, from experimentally measurable macroscopic geometric quantities (spreading diameter of the cured ink droplets), characteristic parameters describing the microscopic broadening of the point diffusion function. Its mathematical derivation is based on the two-dimensional Gaussian function form used by the point spread function H(x,y).

[0054] For a two-dimensional Gaussian function, its maximum value is at the origin. When the thickness decays from the peak to half, we have... Solving for the radial distance from the origin at this point yields the answer. Since the spreading diameter d is defined as the diameter corresponding to the point where the thickness profile decays to half of its maximum thickness, the diameter is equal to twice the feature radius, i.e. By transforming the equation, the spreading characteristic radius can be obtained. Inverse calculation formula .

[0055] This formula establishes a quantitative conversion relationship between the physical quantity that can be directly measured by the microscope in the calibration experiment (diameter at half height) and the abstract parameter in the theoretical model (spreading characteristic radius).

[0056] In the parameter calibration experiment, the contour diameter of a single ink droplet at half-height of its thickness after curing was directly measured using an optical microscope, which is the method for obtaining the spreading characteristic radius. The experimental input quantity. The measurement accuracy of d directly determines The calibration accuracy. The larger the measured value of d, the more severe the ink spread on the copper surface, and the more accurate the calculated value. It will also increase accordingly.

[0057] The output parameter of this formula is the feature radius. It will be directly substituted into the point spread function H(x,y) and participate in all subsequent forward prediction convolution and inversion iteration operations. The accuracy of the values ​​taken fundamentally determines the precision of the entire compensation system: if If the calibration is too small, the compensation will be insufficient to offset the actual spreading, resulting in a final line width that is too wide; if If the calibration is too large, the edges of the compensation grayscale image will be excessively shrunk, which may result in a narrower line width or even broken lines.

[0058] In actual PCB manufacturing, the copper surface of copper-clad laminates typically undergoes pretreatment processes such as mechanical brushing or chemical micro-etching to increase surface roughness and surface energy, thereby improving ink adhesion. These treatments often impart specific directional textures to the copper surface, such as linear grooves along the brushing direction. When conductive or resist ink is sprayed onto such a copper surface, the spreading speed and extent of the ink along the texture direction may be significantly greater than that perpendicular to the texture direction, resulting in elliptical rather than ideally circular ink droplet outlines after curing. If isotropic point diffusion functions are still used for compensation, it will cause excessive thinning of lines parallel to the texture direction and insufficient compensation of lines perpendicular to the texture direction, ultimately resulting in inconsistent line widths in different directions, which can severely affect signal integrity and yield.

[0059] Therefore, in order to further improve The calibration accuracy is particularly important for cases where the directional texture of the pre-treated copper surface causes anisotropic ink spreading. This embodiment introduces direction-dependent spreading characteristic parameters when constructing the point spread function. The specific process is as follows: Under the same process conditions as fabricating the circuitry, an inkjet printer is used to spray isolated ink droplet arrays onto the pre-treated copper surface. After the same curing process, an optical microscope or profilometer is used to measure the spreading diameter *dparallel* of the cured ink droplets parallel to the copper surface texture direction and the spreading diameter *dperpendicular* of the cured ink droplets perpendicular to the copper surface texture direction. The spreading diameter is defined as described above, i.e., the diameter corresponding to the profile of the cured ink droplet thickness decreasing to half its maximum thickness.

[0060] Subsequently, based on the measured spreading diameters in the two directions, the spreading characteristic radius σ_parallel in the parallel direction and the spreading characteristic radius σ_perpendicular in the perpendicular direction are calculated respectively. The calculation formula is as follows: ; At the same time, the curing shrinkage rate β of the ink under the corresponding curing conditions is obtained, and its calibration method is the same as that described above.

[0061] Based on the aforementioned directional spreading characteristic radius, the point spread function is constructed as an elliptic Gaussian function: ; In this expression, the x-axis of the coordinate system is aligned with the direction parallel to the copper surface brush texture, and the y-axis is aligned with the direction perpendicular to the texture. When σparallel = σperpendicular, the function naturally degenerates into the isotropic circular Gaussian point diffusion function described above.

[0062] After obtaining the anisotropic point spread function, the forward prediction model, cost function, and inversion operation framework remain consistent with Example 1. The forward prediction model is still D(x,y) = G(x,y) * H(x,y), but the convolution kernel H(x,y) is now an elliptic Gaussian kernel. When iteratively solving for the compensated inkjet grayscale image G(x,y), the Lucy-Richardson deconvolution algorithm or other constrained optimization algorithms can still be used. The point spread function H(x,y) and its flip kernel H(-x,-y) in the iterative formula both use the aforementioned anisotropic kernel. Similarly, during the iteration process, the cost function is adjusted accordingly. Apply non-negative constraints. In the obtained compensated inkjet grayscale image, there will be differences in ink volume compensation for lines parallel to the copper surface texture and lines perpendicular to it. This will offset the difference in the degree of spreading in the two directions, so that the line width of the final cured lines can accurately reach the target value in all directions.

[0063] Traditional inkjet printing directly sprays ink in equal amounts according to the design. As the ink spreads naturally on the copper surface and then cures and shrinks, the actual lines become wider and the edges become blurred, making it difficult to guarantee the precision of fine lines.

[0064] like Figure 2 The image shown is a microscopic photograph comparing the fabrication effects of the PCB inner layer circuitry using the method of this embodiment with those of existing technologies. The image is divided into two regions by a vertical white dividing line. The circuit patterns shown in both regions are identical serpentine traces and groups of equally spaced parallel lines.

[0065] The left side corresponds to "Prior Technology: Direct Inkjet Printing." The lines are generally continuous and complete, without any open or short circuit defects. However, slight wavy irregularities are visible at the edges of the lines, and the line width exhibits noticeable variations in thickness in localized areas, with deviations within ±15% of the nominal line width. The spacing between adjacent lines is slightly reduced in some areas, but remains clearly separated. This side of the graphic represents the typical mass-produced board appearance achievable with conventional inkjet printing processes without the use of compensation algorithms.

[0066] The right-hand area corresponds to "Invention: Inkjet Compensation Technology". Compared with the left-hand area, the line edges are very straight and sharp, the line width and height are uniform, and the spacing between adjacent lines is equal everywhere. No identifiable line width fluctuations or spacing changes were observed, presenting a high-quality appearance of precision machining.

[0067] The comparison diagram visually demonstrates the significant improvement in line width consistency, edge straightness, and spacing uniformity achieved by the present invention through pixel-by-pixel precise compensation of ink spreading and curing shrinkage using the point diffusion function inversion compensation algorithm, while maintaining line integrity.

[0068] The core idea of ​​this scheme is a closed-loop control of "model prediction + inversion compensation". First, two key physical parameters are obtained through experimental calibration: the spreading characteristic radius σ, which characterizes the ink's spreading ability, and the curing shrinkage rate β, which characterizes volume change. Based on these parameters, a point spread function H(x,y) is constructed to accurately describe the curing thickness distribution profile of a single ink droplet on a copper surface after spreading and shrinking. Then, the point spread function is used as a convolution kernel to establish a forward prediction model from the ink jet distribution G(x,y) to the curing thickness distribution D(x,y). On this basis, with the target line pattern B(x,y) as the desired output, the optimal compensation inkjet grayscale image G(x,y) is obtained through inversion using iterative optimization algorithms such as Lucy-Richardson deconvolution, ensuring that the cost function between the predicted curing thickness and the target thickness distribution is optimized. minimize.

[0069] The essence of this inversion operation is to preemptively "counteract" the unavoidable spreading and shrinking effects in subsequent processes: automatically reducing ink volume at the edge areas of the lines to counteract spreading and widening, and automatically increasing ink volume inside the lines to compensate for shrinkage and thinning. Finally, the inkjet printer precisely controls the ink ejection volume at each pixel position based on the compensated grayscale image, and after curing, a high-precision inner layer line that matches the height of the target graphic is formed.

[0070] The entire solution transforms macroscopic process deviations into inverse problems that can be precisely solved through mathematical modeling, achieving a leap from "experience-based trial and error" to "algorithm-driven" approaches. Without increasing hardware costs, it significantly improves the linewidth consistency, edge clarity, and graphic fidelity of inkjet-printed PCB inner layer circuits.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating inner layer circuitry of a PCB based on inkjet printing technology, characterized in that, include: The target line graphic to be produced is rasterized to obtain an initial binary pixel image. The value of each pixel in the initial binary pixel image represents whether a line exists at that pixel. The spreading characteristic parameters and curing shrinkage rate of inkjet ink on a pretreated copper surface are obtained. The spreading characteristic parameters characterize the spreading ability of ink on the copper surface, and the curing shrinkage rate characterizes the volume shrinkage ratio of ink after curing from liquid state. Based on the spreading characteristic parameters and curing shrinkage rate, a point diffusion function is constructed. The point diffusion function is defined as the thickness distribution profile formed by a unit volume of ink on a copper surface after spreading and curing. Constructed as: ； in, The curing shrinkage rate is... The spreading feature radius is determined by the spreading feature parameters; Based on the point spread function and the initial binary pixel image, a compensated inkjet grayscale image is generated through inversion operation. The grayscale value of each pixel in the compensated inkjet grayscale image corresponds to the volume of ink that the inkjet printer should eject at that pixel. The inkjet printing equipment is controlled according to the compensated inkjet grayscale image to spray conductive ink or anti-corrosion ink onto the pre-treated copper surface. The ink sprayed onto the copper surface is cured to form an inner layer circuit that conforms to the target circuit pattern.

2. The method for fabricating PCB inner layer circuits based on inkjet printing technology according to claim 1, characterized in that, The process of generating a compensated inkjet grayscale image based on the point spread function and the initial binary pixel image through inversion operation includes: The initial binary pixel map is defined as the target curing thickness distribution B(x,y); Establish a positive prediction model for ink curing: ； in, To predict the thickness distribution of the cured ink, The image to be solved is the compensated inkjet grayscale image, and * indicates a two-dimensional convolution operation. By minimizing the cost function Seeking a solution The cost function Defined as predicting thickness distribution With the target thickness distribution Degree of deviation between: ； Through iterative optimization, Minimize, at this point This serves as the compensation inkjet grayscale image.

3. The method for fabricating PCB inner layer circuits based on inkjet printing technology according to claim 2, characterized in that, The iterative optimization employs the Lucy-Richardson deconvolution algorithm, whose iterative format is as follows: ； in, This is the compensated grayscale image obtained in the k-th iteration. Point spread function The function after being centrally symmetrically flipped, This represents a pixel-wise dot product operation; Iteration initial value Let the initial binary pixel image be defined. When the number of iterations reaches a preset value or The iteration stops when the value falls below a set threshold, and the final value is output. This serves as the compensation inkjet grayscale image.

4. A method for fabricating PCB inner layer circuits based on inkjet printing technology according to claim 3, characterized in that, During the iteration process, Apply a nonnegativity constraint to ensure that the grayscale value obtained in any iteration is not less than zero.

5. A method for fabricating PCB inner layer circuitry based on inkjet printing technology according to claim 1, characterized in that, Obtain the spreading feature parameters and determine the spreading feature radius. The process includes: Under the same process conditions as the fabrication of the circuit, the inkjet printing equipment is controlled to spray ink onto the pretreated copper surface to form isolated ink droplet arrays or single-pixel wide lines. The ink after spraying is subjected to the curing process described above, and the spreading diameter d of a single ink droplet or the line width of a single pixel line is measured after curing. Based on the point spread function The contour characteristics are used to calculate the spreading feature radius from the spreading diameter d. The inverse calculation formula is: ； The spreading diameter d is defined as the diameter corresponding to the point where the thickness profile of the cured ink droplet decays to half of its maximum thickness.

6. A method for fabricating PCB inner layer circuitry based on inkjet printing technology according to claim 1, characterized in that, The grayscale values ​​in the compensated inkjet grayscale image are mapped to the number of ink droplets ejected by the inkjet printer at each pixel position or the volume of a single ink droplet, and the resolution of the initial binary pixel image is consistent with the printing resolution of the inkjet printer.

7. A method for fabricating PCB inner layer circuitry based on inkjet printing technology according to claim 1, characterized in that, The ink is a conductive ink containing metal nanoparticles, which directly forms a conductive circuit after curing; or, the ink is an etch-resistant ink, which leaves a circuit pattern on the copper surface after etching and film removal after curing.

8. A method for fabricating PCB inner layer circuitry based on inkjet printing technology according to claim 1, characterized in that, The spreading characteristic parameters and curing shrinkage rate were pre-measured by ink spraying and curing experiments on the same pre-treated copper surface as the fabricated circuit, and were used as fixed parameters for the construction of the point diffusion function and the inversion calculation.

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