A method of forming a via in a printed circuit board and a printed circuit board

Abstract

The application relates to the technical field of semiconductors, and provides a printed circuit board via hole forming method and a printed circuit board. The method comprises the following steps: providing a substrate provided with a via hole to be filled; forming a magnetic response layer on the surface of the substrate, covering one side surface of the substrate and covering the opening of the via hole; filling the via hole with a filler containing conductive particles; placing the substrate in an adjustable magnetic field in three orthogonal directions, driving the conductive particles in the filler to gather and magnetize through the magnetic field, forming chain-shaped aggregates, and gradually forming a particle column parallel to the axial direction of the via hole; solidifying the filler by using laser sintering to further tightly connect the conductive particles; further solidifying the filler by using hot air heating; stripping and removing the magnetic response layer on the surface of the substrate by using a stripping liquid; and polishing the surface of the substrate to make the surface of the via hole and the surface of the substrate flat. The application can effectively solve the problem of pad depression on the via hole, and can improve the conductive efficiency of the printed circuit board.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, and in particular to a forming method of a printed circuit board via and a printed circuit board. BACKGROUND

[0002] A printed circuit board (PCB) is a semiconductor connecting substrate with a circuit pattern printed on one or both sides. The printed circuit board is provided with pads for connecting semiconductor components. Meanwhile, the printed circuit board is also provided with conductive vias that penetrate the substrate of the printed circuit board in thickness and connect the two sides of the substrate. In the prior art, some vias are filled with a filler containing conductive particles to improve the conductivity. However, the random distribution of conductive particles in the via can cause the conductive path to bend, and the improvement of the conductivity is not ideal. Meanwhile, the high porosity after filling requires high-energy sintering, which not only increases energy consumption but also easily causes the substrate to deform due to local overheating, resulting in large contact resistance and insufficient reliability. Therefore, a solution is needed to solve the problem of unsatisfactory improvement of the conductivity of the via filled with the filler containing conductive particles and the large contact resistance and insufficient reliability caused by the process.

[0003] In addition, some pads are arranged at the positions of the vias and are connected to the vias by welding. During the welding process and the via forming process, due to uneven flow of the solder or conductive filler or improper welding process control, there are small depressions on the surface of the via, and the solder cannot completely fill the connection area between the via and the pad, thereby forming local depressions on the surface of the pad. Such depressions not only affect the appearance quality of the solder joint, but also can reduce the electrical connection reliability and mechanical strength of the semiconductor component, thereby affecting the performance and service life of the entire circuit board. Therefore, a solution is needed to solve the problem of reduction of the electrical connection reliability and mechanical strength of the semiconductor component caused by the depression of the pad, thereby affecting the performance and service life of the entire circuit board.

[0004] Therefore, a solution is needed to solve the problem of unsatisfactory improvement of the conductivity of the via filled with the filler containing conductive particles and the low component connection reliability caused by the depression of the pad, thereby affecting the overall circuit life. SUMMARY

[0005] Therefore, the present application provides a forming method of a printed circuit board via and a printed circuit board to solve the problem of unsatisfactory improvement of the conductivity of the via filled with the filler containing conductive particles and the low component connection reliability caused by the depression of the pad, thereby affecting the overall circuit life.

[0006] In a first aspect, the present application provides a forming method of a printed circuit board via, comprising the following steps:

[0007] providing a substrate; the substrate is provided with a via to be filled;

[0008] forming a magnetic response layer on the surface of the substrate; the magnetic response layer covers one side surface of the substrate and covers the opening of the via hole;

[0009] filling the via hole from the opening of the side of the substrate on which the magnetic response layer is not formed using a filler containing conductive particles;

[0010] placing the substrate in an adjustable magnetic field in three orthogonal directions, and driving the conductive particles in the filler to aggregate and magnetize by magnetic field regulation to form chain-like aggregates and gradually form particle columns parallel to the axial direction of the via hole;

[0011] solidifying the filler using laser sintering to further tightly connect the conductive particles;

[0012] further solidifying the filler using hot air heating;

[0013] removing the magnetic response layer on the surface of the substrate using a stripping solution;

[0014] polishing the surface of the substrate to make the surface of the via hole and the surface of the substrate flat.

[0015] The method for forming a via hole of a printed circuit board provided in the present application uses a filler containing conductive particles to fill the via hole, providing the via hole with conductive particles and improving the conductive performance. By driving the conductive particles in the filler through magnetic field regulation, the conductive particles in the filler can be adjusted from randomly distributed and free to particle columns parallel to the axial direction of the via hole, so that the conductive path provided by the via hole is unique and collimated, which can solve the problem that the conductive efficiency is not ideal due to the random deviation of the conductive path caused by the free distribution of the conductive particles when the via hole is filled with a filler containing conductive particles. Furthermore, a clear spatial reference is defined for subsequent processing, i.e., the final target positions of all particles are consistent, which ensures that subsequent operations will not fail due to the disorder of the initial structure. The directional arrangement ensures the linearity of the conductive particles along the depth direction of the via hole, which fundamentally reduces the bending loss of the conductive path and makes the improvement of the conductive capacity more ideal. In addition, the process operation is simple and easy to implement, and provides a basis for subsequent other processing processes, which can ensure the consistency of products in large-scale production. Moreover, the conductive column obtained by magnetic field regulation has a neat overall structure, and the carrier solvent wrapped around it is also correspondingly flat and less likely to have local depressions. Therefore, a flat via hole surface can be obtained, and the probability of depression during subsequent solder pad welding is greatly reduced, thereby solving the problem of via hole pad depression.

[0016] In another aspect of the present application, the present application also provides a printed circuit board comprising a via hole formed using the method for forming a via hole of a printed circuit board provided in the present application;

[0017] The via hole contains conductive filler, the conductive filler contains conductive particles, and the conductive particles are arranged in a particle column parallel to the axial direction of the via hole.

[0018] The printed circuit board provided by the application comprises a via formed by the via forming method of the printed circuit board provided by the application. The via is filled with a filler comprising conductive particles to provide the via with the conductive particles and improve the conductive performance. By driving the conductive particles in the filler through a magnetic field, the conductive particles in the filler can be changed from randomly distributed free particles to particles arranged in parallel with the axial direction of the via, so that the conductive path provided by the via is unique and collimated. The problem of random deviation of the conductive path caused by the free distribution of the conductive particles when the via is filled with the filler comprising the conductive particles can be solved. The straightness of the conductive particles along the depth direction of the via is ensured by the directional arrangement, which fundamentally reduces the bending loss of the conductive path and makes the improvement of the conductive capacity more ideal. In addition, the process operation is simple and easy to implement, which can ensure the product consistency in large-scale production. Moreover, the conductive column obtained by the magnetic field regulation has a neat overall structure, and the carrier solvent wrapped therearound is also correspondingly flat and less likely to have local depressions. Therefore, a flat via surface can be obtained, and the probability of depression during subsequent soldering of the pad is greatly reduced, thereby solving the problem of depression of the via pad. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the specific embodiments or the related art, the drawings needed to be used in the specific embodiments or the related art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings without creative labor based on these drawings.

[0020] Figure 1 It is a structural schematic diagram of a prior art printed circuit board.

[0021] Figure 2 It is a flowchart of the via forming method of the printed circuit board according to an embodiment of the present application.

[0022] Figure 3 It is a schematic diagram of forming a magnetic response layer on the surface of the substrate in the via forming method of the printed circuit board according to an embodiment of the present application.

[0023] Figure 4 It is a schematic diagram of filling the via with a filler comprising conductive particles in the via forming method of the printed circuit board according to an embodiment of the present application.

[0024] Figure 5 It is a schematic diagram of magnetic field regulation in the via forming method of the printed circuit board according to an embodiment of the present application.

[0025] Figure 6This is a schematic diagram illustrating the vibration process using a vibration platform in a method for forming through-holes on a printed circuit board according to an embodiment of this application.

[0026] Figure 7 This is a schematic diagram illustrating laser curing using a laser in a method for forming through-holes on a printed circuit board according to an embodiment of this application.

[0027] Figure 8 This is a schematic diagram illustrating the hot air curing process in a method for forming through-holes on a printed circuit board according to an embodiment of this application.

[0028] Figure 9 This is a schematic diagram illustrating the removal of the magnetic response layer on the substrate surface in a method for forming a through-hole in a printed circuit board according to an embodiment of this application.

[0029] Figure 10 This is a schematic diagram of polishing and grinding the protruding portion of the through hole in a method for forming a through hole on a printed circuit board according to an embodiment of this application.

[0030] Figure label:

[0031] 100 - Substrate; 110 - Magnetic response layer; 120 - Through-hole filling layer; 200 - Pad; 300 - Vibration platform. Detailed Implementation

[0032] like Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of a prior art printed circuit board, including a substrate 100 and a via filling layer 120 filled with conductive filler, and solder pads 200 are provided on the via filling layer 120.

[0033] As described in the background section, the via-hole filling layer 120 is formed using filler containing conductive particles. The conductive particles in the filler are randomly arranged within the vias, resulting in a tortuous conductive path and an unsatisfactory improvement in conductivity. Furthermore, the high porosity of the filler after filling requires high-energy sintering, increasing energy consumption and easily causing substrate deformation due to localized overheating. Therefore, it is difficult to solve these problems simply by adjusting the reflow soldering temperature profile. In addition, due to various technical reasons during the processing, localized depressions may exist on surface A of the via-hole filling layer 120. This will further cause depressions on surface B of the pads 200 disposed thereon. This phenomenon is particularly prevalent in some printed circuit boards where the via-hole filling layer 120 is formed using filler containing conductive particles. This results in poor reliability and mechanical strength in the connection with semiconductor components.

[0034] In view of this, this application provides a method for forming through-holes in a printed circuit board and a printed circuit board to solve the problems that filling through-holes with filler containing conductive particles does not improve conductivity as well as the low reliability of component connections caused by pad depressions, which affects the overall circuit life.

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0036] It should be noted that, in the description of the present application, the terms "comprise", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. The terms "first", "second" and the like in the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence.

[0037] In order to enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0038] Embodiment 1

[0039] The present embodiment provides a method for forming a through hole of a printed circuit board, referring to Figure 2 , and Figures 3-10 , comprising the following steps:

[0040] Referring to Figure 3 , a substrate 100 is provided; the substrate 100 is provided with a through hole C to be filled; the substrate may be selected as a FR-4 substrate of 0.5mm-1.6mm, for example;

[0041] Continuing to refer to Figure 3 , a magnetic response layer 110 is formed on the surface of the substrate 100; the magnetic response layer 110 covers one side surface of the substrate 100, and covers the opening of the through hole C on the side;

[0042] Referring to Figure 4 , a filler containing conductive particles is injected from the opening on the side of the substrate 100 where the magnetic response layer 110 is not formed to fill the through hole C, and a through hole filling layer 120 is formed;

[0043] Referring to Figure 5 , the substrate 100 is placed in an adjustable magnetic field M in three orthogonal directions, and the conductive particles in the filler are driven to aggregate and magnetize by the magnetic field control to form chain aggregates, and gradually form particle columns parallel to the axial direction of the through hole C;

[0044] Referring to Figure 7, using the laser L to sinter the filler to further tightly connect the conductive particles;

[0045] Referring to Figure 8 , using the hot air H to heat to further solidify the filler;

[0046] Referring to Figure 9 , using a stripping liquid to strip and remove the magnetic response layer 110 on the surface of the substrate 100;

[0047] Referring to Figure 10 , polishing the surface of the substrate 100 to make the surface of the via (i.e., the surface of the via filling layer 120) and the surface of the substrate 100 flat and flush.

[0048] The method for forming a via of a printed circuit board provided by the embodiment uses a filler containing conductive particles to fill the via C to form a via filling layer 120, so as to provide the conductive particles in the via filling layer 120 in the via C and improve the conductive performance. By driving the conductive particles in the filler through a magnetic field, the conductive particles in the filler can be adjusted from a dispersed free random distribution to a particle column parallel to the axial direction of the via C, so that the conductive path provided by the via C is unique and collimated, and the problem that the conductive efficiency is not ideal due to the random deviation of the conductive path caused by the free distribution of the conductive particles when the via is filled with the filler containing the conductive particles can be solved. Further, a clear spatial reference is defined for subsequent processing, i.e., the final target positions of all the particles are consistent in height, so as to ensure that subsequent operations will not fail due to disordered initial structure. The straightness of the conductive particles in the depth direction of the via is ensured through directional arrangement, so as to fundamentally reduce the bending loss of the conductive path; the operation is simple and easy to implement, and provides a basis for subsequent other processing processes, so as to provide a guarantee for the consistency of products in large-scale production.

[0049] Further, referring to Figure 3 In some embodiments of the present application, the step of forming the magnetic response layer 110 includes:

[0050] The magnetic response matrix is uniformly coated on the surface of the substrate 100 by a spin coating process, avoiding the opening of the via C;

[0051] The substrate 100 coated with the magnetic response matrix is placed in an oven for solidification to form the magnetic response layer 110.

[0052] In one embodiment, the coating liquid is uniformly coated on the surface of the substrate 100 by a spin coating process, the spin coating speed is controlled at 1500 r / min, and the coating thickness is adjusted to 5 μm~8 μm through the spin coating time. Then the substrate is placed in an oven for solidification, the heating rate is 5 ℃ / min, the solidification temperature is 120 ℃, and the holding time is 60 min.

[0053] The magnetic response matrix is prepared by mixing the ferriferrous oxide nanoparticles and the epoxy resin in a mass ratio of 1:4, adding 3% of the silane coupling agent as a dispersant, and stirring to mix uniformly.

[0054] In one embodiment, the process of obtaining the magnetic response matrix is as follows: ferriferrous oxide nanoparticles with a particle size of 20 nm are mixed with the epoxy resin in a mass ratio of 1:4, 3% of the silane coupling agent is added as a dispersant, and a high-speed stirrer is used to stir at a speed of 3000 r / min for 30 min to uniformity.

[0055] In some embodiments of the present application, before the magnetic response layer is formed, the following steps are further included:

[0056] The surface of the substrate 100 is bombarded by plasma to form a micro concave-convex structure on the surface of the substrate 100, and the surface of the substrate 100 is roughened; the depth / height of the micro concave-convex structure is not more than 0.5 μm.

[0057] The micro concave-convex structure is filled after the magnetic response layer 110 is formed.

[0058] The micro concave-convex structure is formed on the surface of the substrate by plasma bombardment, and then the magnetic response layer 110 is formed to cover the micro concave-convex structure, so that the contact area between the magnetic response layer 110 and the surface of the substrate 100 is increased, the bonding degree is higher, and the magnetic response layer 110 is not easy to fall off.

[0059] In one embodiment, the plasma power is 80 W, and the processing time is 90 s, so that the surface of the substrate forms a micro concave-convex structure with a depth of about 0.5 μm.

[0060] In addition, in some embodiments, before the roughening treatment of the substrate surface is performed, a first cleaning treatment of the substrate is further included to remove dust and organic contamination on the surface of the substrate 100.

[0061] In one embodiment, the first cleaning treatment includes: using a solution mixed by deionized water and anhydrous ethanol in a ratio of 3:1 for surface cleaning, and setting the frequency of the ultrasonic cleaner to 40 kHz and the cleaning time to 10 min.

[0062] Further, in some embodiments of the present application, with reference to Figure 4 , in the step of filling the through hole C to form the through hole filling layer 20,

[0063] The filler containing conductive particles is prepared by mixing copper-coated ferriferrous oxide conductive particles with a mass fraction of 65%, silicon oil carrier with a mass fraction of 30%, and thixotropic agent with a mass fraction of 5%; the particle size of the copper-coated ferriferrous oxide particles may be, for example, 5 μm~10 μm.

[0064] The through hole is filled with the above-mentioned filler containing conductive particles by dispensing machine; the filler overflows the surface of the substrate by 0.1 mm~0.2 mm.

[0065] In one embodiment, the dispensing machine pressure is 0.2 mPa, and the dispensing rate is 0.1 mL / s. The needle diameter matches the through-hole diameter (usually 80% of the through-hole diameter). When operating, keep the needle perpendicular to the substrate surface at a distance of 1 mm, inject the filling paste along the through-hole array row by row, and ensure that the paste completely fills the through-hole recess and overflows the substrate surface by about 0.1 mm to 0.2 mm.

[0066] In addition, in some embodiments, after the injection is completed, the substrate surface is scanned using an optical detector to confirm that there are no obvious bubbles or unfilled areas on the surface of all through-holes. At this time, the filling paste is in a semi-flowing state, and the viscosity is about 5000 mPa·s (millipascal·second), which provides a flow basis for subsequent magnetron self-assembly.

[0067] Further, in some embodiments of the present application, referring to Figure 5 In the step of driving the conductive particles in the filler by magnetic field regulation,

[0068] The adjustable magnetic field M in three orthogonal directions is provided by an array of electromagnetic coils in three orthogonal directions (for simplicity, only the magnetic field M in the Z-axis direction and the X-axis direction is shown in the figure), including a base magnetic field with a magnetic field strength of 0.1 T to 0.5 T in the Z-axis direction and a correction magnetic field with a magnetic field strength of 5 mT to 15 mT in the plane of the X-axis and Y-axis.

[0069] The core purpose of the three-dimensional gradient magnetic field design is to form a directional driving force through the spatial difference of the magnetic field strength. The strong magnetic field in the Z-axis (vertical) direction ensures that the conductive particles obtain the driving force to migrate upward, while the weak magnetic field in the plane is used to correct the lateral deviation of the conductive particles, so that all magnetic particles eventually converge at the axis of the through-hole filling layer 120.

[0070] With stable output of the magnetic field, the Fe3O4 modified conductive particles originally dispersed and suspended in the magnetorheological paste begin to respond: particles with a diameter of about 5 μm to 10 μm are magnetized and move directionally along the magnetic induction line direction of the composite magnetic field (since the Z-axis magnetic field strength is much greater than the X-axis and Y-axis, it is mainly the Z-axis magnetic field direction). During this process, the particles gradually form chain-like aggregates due to magnetic dipole interaction, and the extension direction of the chain is completely consistent with the magnetic induction line. By controlling the incremental rate of the magnetic field strength (for example, about 0.05 T / s), the particle migration speed can be accurately adjusted to avoid chain structure breakage due to too fast movement. Usually within 30 s to 60 s, all magnetic particles will complete the reconstruction process from the dispersed state to the vertical arrangement along the through-hole axis direction in the carrier, and finally form a conductive particle column highly coinciding with the through-hole axis, laying a structural foundation for subsequent steps.

[0071] Further, in some embodiments of the present application, referring to Figure 6, the step of driving the conductive particles in the filler by the magnetic field further comprises:

[0072] After the first regulation time, the substrate 100 is vibrated using the vibration platform 300, and the conductive particles in the filler are driven by the magnetic field for a second regulation time;

[0073] The vibration frequency of the vibration treatment is 18-22 kHz, and the amplitude is 3-5 μm;

[0074] The first regulation time is 30-60 s, and the second regulation time is 2-3 min.

[0075] When the vibration frequency is highly matched with the natural frequency (about 18-22 kHz) of the ferroferric oxide modified conductive particles, the resonance effect of the conductive particles can be excited, so that the particles which are closely arranged but still have nanoscale gaps produce regular micro-displacement. After the vibration platform 300 is started, the substrate 100 vibrates synchronously with the table, driving the filler and the magnetized conductive particles in the filler to oscillate as a whole. At this time, the viscosity of the filler is reduced due to vibration, further promoting the release of the activity space between the particles.

[0076] During the vibration process, the aforementioned three-dimensional gradient magnetic field is continuously output. The basic magnetic field (0.1-0.5 T) in the Z-axis (vertical) direction maintains the tendency of vertical arrangement of the magnetized conductive particles, and the weak gradient magnetic field (5-15 mT / mm) in the horizontal direction restrains the displacement range of the particles in the horizontal direction, preventing structural deviation caused by vibration. As the vibration continues (usually for 2-3 min), the chain-like particle aggregates formed due to magnetic dipole interaction gradually loosen, and individual particles are rearranged in the vertical direction under the driving of vibration energy: smaller particles fill the gaps between larger particles, and particles that are tilted or misaligned are corrected by vibration to a more compact stacking state. Finally, the porosity in the filling body is reduced from 8-12% to 2-4%, providing a more compact microstructure basis for subsequent steps, while the continuous action of the magnetic field ensures that the particle column remains in a stable state of high coincidence with the axis of the through hole throughout the vibration process.

[0077] Further, in some embodiments of the present application, with reference to Figure 7 , in the step of solidifying the filler using laser,

[0078] The laser head 400 is perpendicular to the substrate 100, and the center of the laser spot of the laser L coincides with the axis of the through hole;

[0079] The laser is a laser with a wavelength of 1064 nm, a power of 8-12 W, a spot diameter of 20-30 μm, and a duration of 15-20 s;

[0080] The above laser conditions are verified by experiments, which can melt the copper plating layer on the surface of the microparticles (melting point about 1085°C) without causing deformation of the PCB substrate (FR-4 material, heat resistance about 130°C) due to overheating.

[0081] During the laser solidification process, the copper plating layer on the surface of the microparticles is locally melted under the action of laser heat, and the molten metal flows into the nanoscale gap between adjacent microparticles under the driving of surface tension, forming a metallurgical bond. Since the aforementioned step has reduced the porosity of the microparticles to 2%-4%, the laser energy originally needed to penetrate a large number of inter-particle gaps is reduced due to the filling of the gaps by other small particles, reducing the required laser power.

[0082] Thereafter, further comprising:

[0083] After laser sintering, nitrogen is introduced for cooling, and the temperature is reduced to room temperature; the cooling rate is 9°C / s-11°C / s.

[0084] Through rapid cooling, the molten metal is prevented from being oxidized and the stability of the grain boundary is promoted.

[0085] Finally, the column originally formed by mechanically stacking magnetic particles is converted into a continuous copper-based conductive structure, and the electrical conductivity of the column can reach 85%-90% of that of pure copper, and the bonding strength with the PCB substrate can reach 12 N / mm 2 ~15 N / mm 2 , fully meeting the interconnection reliability requirements of high-frequency electronic devices.

[0086] In addition, in some embodiments, a second cleaning process is further included to remove excess sintering residues and fillers that do not participate in sintering.

[0087] In one embodiment, a high-precision scraper device is used for scraping treatment of the surface of the substrate, the scraper material is polytetrafluoroethylene, the blade angle with the surface of the substrate is set to 45°, and the scraping speed is controlled at 10 mm / s. During the scraping process, the pressure of the scraper on the substrate is kept constant (about 0.5 N / cm), and the excess sintering residues and fillers that do not participate in sintering on the surface of the through hole are removed by one-way scraping. After scraping, a vacuum suction device is used to clean the surface of the substrate, the vacuum degree is maintained at-0.08 MPa (mega pascal), the suction time is 30 s, and the diameter of the residual particles on the surface is ensured to be not more than 2 μm. The flatness of the final substrate surface is detected by a laser thickness gauge, and the height difference between adjacent through holes is not more than 5 μm, providing uniform surface conditions for subsequent solidification treatment.

[0088] Further, in some embodiments of the present application, with reference to Figure 8 , in the step of using hot air to further solidify the filler,

[0089] The substrate 100 was placed in a hot air circulating oven. The initial temperature of the oven was 22℃~28℃, and the temperature was increased to 75℃~85℃ at a rate of 3℃ / min, held for 30 minutes to allow the solvent remaining from the cleaning step to evaporate fully. Subsequently, the temperature was increased to 140℃~150℃ at a rate of 2℃ / min and held for 80 minutes~100 minutes to complete the cross-linking and curing of the epoxy resin. During the curing process, the air circulation rate inside the oven was controlled at 0.2 m / s. 3 / min~0.8m 3 The temperature was maintained at a constant rate of 100°C / min to ensure uniformity throughout the oven, with a temperature difference of ±2°C. The oven was then allowed to cool to room temperature (approximately 2 hours). At this point, the hardness of the magnetic response layer increased from Shore A50 before curing to Shore D75, and the bonding strength with the substrate reached grade 5B (no peeling) in the cross-cut test, providing stable substrate support for subsequent magnetic layer peeling.

[0090] Furthermore, in some embodiments of this application, reference is made to... Figure 9 In the step of stripping the response layer,

[0091] The substrate is placed in a solution bath containing a stripping solution. The stripping solution is a mixture of 5% hydrochloric acid solution with a mass concentration of 36% and 95% deionized water. The temperature of the stripping solution is 40°C. During the stripping process, a stirring device is used to stir the substrate at a speed of 50 r / min. The processing time for the stripping process is 15 min to 20 min. The substrate is removed after the magnetic response layer on the substrate surface is observed to have completely peeled off (the surface changes from dark gray to the original substrate color).

[0092] After being removed from the stripping fluid, it also includes,

[0093] Rinse with deionized water for 2-4 minutes at a flow rate of 0.3-0.7 L / min. Rinsing with deionized water removes residual stripping solution and detached iron oxide particles. The final residual iron content on the substrate surface, as determined by X-ray fluorescence spectroscopy, is less than 0.1%, meeting the requirements for subsequent electrical performance testing.

[0094] Furthermore, in some embodiments of this application, reference is made to... Figure 10 In the step of polishing the surface of substrate 100,

[0095] Use 800-grit silicon carbide sandpaper for polishing, with a polishing pressure of 0.5 N / cm. 2 ~2 N / cm 2 The surface roughness was reduced from Ra1.2μm to Ra0.3μm until polishing was completed. After polishing, a four-probe tester was used to test the electrical performance of the through-hole interconnect structure. The test current was set to 1mA, and the resistance value at both ends of the through hole was measured. The resistance of a single hole was required to be no more than 50 milliohms, and the resistance value deviation in the array was required to be no more than ±5%.

[0096] Finally, appearance inspection is performed, and the surface of the via is observed using a 50x optical microscope, and no cracks, no residual particles, and no burrs on the edges are required. After all the tests are passed, the substrate enters the packaging process, and the whole process of preparing the magnetically self-assembled via interconnection structure is completed. Subsequent soldering with the pads can be performed. Due to the foregoing processing, local depression is less likely to occur after the pads are soldered. Moreover, the conductive particles in the filler are driven by the magnetic field, and the current path provided by the conductive particles is improved, and the conductive efficiency of the printed circuit board is improved.

[0097] Embodiment 2

[0098] The present embodiment provides a printed circuit board comprising a via formed using the via forming method for a printed circuit board provided in the foregoing embodiment 1.

[0099] The via comprises a conductive filler, and the conductive filler comprises conductive particles arranged in a columnar shape parallel to the axial direction of the via.

[0100] The printed circuit board provided in the present embodiment comprises a via formed using the via forming method for a printed circuit board provided in the present application. The via is filled with a filler comprising conductive particles to provide the via with the conductive particles and improve the conductive performance. The conductive particles in the filler are driven by the magnetic field to be adjusted from a dispersed free random distribution to a columnar shape parallel to the axial direction of the via, so that the conductive path provided by the via is unique and collimated. The problem of random deviation of the conductive path caused by the free distribution of the conductive particles in the filler filled in the via and the poor conductive efficiency can be solved. The linear property of the conductive particles along the depth direction of the via is ensured by the directional arrangement, which fundamentally reduces the bending loss of the conductive path. The process is simple and easy to implement, which can ensure the product consistency in large-scale production. Moreover, the conductive column obtained by the magnetic field regulation has a neat overall structure, and the carrier solvent wrapped therearound is also correspondingly flat and less likely to have local depression. Therefore, a flat via surface can be obtained, and the probability of depression during subsequent soldering of the pads is greatly reduced, thereby solving the problem of depression of the via pads.

[0101] The above merely describes the preferred embodiments of the present application and the technical principles applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described above, and those skilled in the art can make various obvious changes, re-adjustments, mutual combinations, and replacements without departing from the protection scope of the present application. Therefore, although the present application has been described in detail through the above embodiments, the present application is not limited to the above embodiments, and more other equivalent embodiments can be included without departing from the concept of the present application, and the protection scope of the present application is determined by the appended claims.

Claims

1. A method of forming a via in a printed circuit board, characterized by, The method comprises the following steps: providing a substrate; the substrate is provided with a via to be filled; forming a magnetic response layer on the surface of the substrate; the magnetic response layer covers one side surface of the substrate and covers the opening of the via; filling the via from the opening of the side of the substrate where the magnetic response layer is not formed by using a filler containing conductive particles; placing the substrate in an adjustable magnetic field in three orthogonal directions to drive the conductive particles in the filler to aggregate and magnetize by magnetic field regulation, form chain-like aggregates, and gradually form a particle column parallel to the axis direction of the via; solidifying the filler using laser sintering to further tightly connect the conductive particles; further solidifying the filler by using hot air to heat up; removing the magnetic response layer on the surface of the substrate by using a stripping liquid; polishing the surface of the substrate to make the surface of the via and the surface of the substrate flat.

2. The method for forming a printed circuit board via according to claim 1, wherein the step of forming the magnetic response layer comprises: uniformly coating a magnetic response matrix on the surface of the substrate, avoiding the opening of the via, by using a spin coating process; placing the substrate coated with the magnetic response matrix in an oven to solidify and form the magnetic response layer; the magnetic response matrix is prepared by mixing Fe3O4 nanoparticles and epoxy resin at a mass ratio of 1:4, adding 3% of silane coupling agent as a dispersant, and stirring uniformly; before forming the magnetic response layer, further comprising: using plasma to bombard the surface of the substrate to form a micro concave-convex structure on the surface of the substrate, and roughen the surface of the substrate; the depth / height of the micro concave-convex structure is not more than 0.5 μm; the magnetic response layer fills the micro concave-convex structure.

3. The method for forming a printed circuit board via according to claim 1, wherein in the step of filling the via, the filler containing conductive particles is prepared by 65% of copper-coated Fe3O4 conductive particles, 30% of silicone oil carrier, and 5% of thixotropic agent by mass; the via is filled with the filler by dispensing the filler into the via by a dispensing machine; the filler overflows the surface of the substrate by 0.1 mm~0.2 mm.

4. The method for forming a printed circuit board via according to claim 1, wherein in the step of driving the conductive particles in the filler by magnetic field regulation, the adjustable magnetic field in three orthogonal directions is provided by an array of electromagnetic coils in three orthogonal directions, including a basic magnetic field with a magnetic field strength of 0.1 T~0.5 T in the Z-axis direction and a correction magnetic field with a magnetic field strength of 5 mT~15 mT in the plane of the X-axis and Y-axis.

5. The method for forming a printed circuit board via according to claim 1, wherein in the step of driving the conductive particles in the filler by magnetic field regulation, further comprising: after a first regulation time, using a vibration platform to vibrate the substrate while performing a second regulation time of magnetic field regulation to drive the conductive particles in the filler; the vibration frequency of the vibration treatment is 18 kHz~22 kHz, and the amplitude is 3 μm~5 μm. ​ ​ ​ ​ The first regulation time is 30s-60s, and the second regulation time is 2min-3min. 6.The method of claim 1, wherein, In the step of solidifying the filler using a laser, The laser head is perpendicular to the substrate, and the center of the light spot coincides with the axis of the via; The laser is a laser with a wavelength of 1064nm, a power of 8W-12W, a spot diameter of 20μm-30μm, and a duration of 15s-20s; After that, further comprising: After the laser sintering is completed, nitrogen is introduced for cooling, and the temperature is reduced to room temperature; the cooling rate is 9℃ / s-11℃ / s. 7.The method of claim 1, wherein, In the step of further solidifying the filler using hot air, The substrate is placed in a hot air circulating oven, the initial temperature of the oven is 22℃-28℃, the temperature is raised to 75℃-85℃ at a rate of 3℃ / min, and maintained for 30min; then the temperature is raised to 140℃-160℃ at a rate of 2℃ / min, and maintained for 80min-100min; and then cooled to room temperature; The air circulation rate in the oven during the process was 0.2 m 3 / min ~ 0.8 m 3 / min, with a temperature difference of ± 2°C throughout the oven. 8.The method of claim 1, wherein, In the step of peeling the response layer, The substrate is placed in a solution tank containing a peeling solution; the peeling solution is a mixed solution of 5% mass concentration of 36% hydrochloric acid solution and 95% deionized water; the temperature of the peeling solution is 40℃, and a stirring device is used for stirring during the peeling process at a stirring speed of 50r / min; the processing time of the peeling process is 15min-20min; After being taken out from the peeling solution, further comprising, Rinsing with deionized water for 2min-4min at a flow rate of 0.3L / min-0.7L / min. 9.The method of claim 1, wherein, In the step of polishing the surface of the substrate, Polishing was performed using a silicon carbide abrasive paper with a force of 800, and the polishing pressure was 0.5 N / cm 2 ~2 N / cm 2 , until the surface roughness was reduced to Ra 0.3 μm.

10. A printed circuit board, characterized by The via includes a conductive filler, and the conductive filler includes conductive particles arranged in a columnar shape parallel to the axial direction of the via. ​

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