A rigid-flex printed circuit board and a via filling process thereof

Abstract

The application discloses a soft and hard combined plate and a hole filling process thereof. The hole filling process of the soft and hard combined plate comprises the following steps: adopting forward current and reverse current to alternately pulse electroplate copper in a hole structure, so as to form a solid copper column capable of filling the hole structure; compared with a traditional resin plug hole process, the forward current is used for depositing copper material, and the reverse current is used for electrolyzing excess copper on a surface layer, so that an end surface of the solid copper column is flush with a plate surface of the soft and hard combined plate, and it is not necessary to perform plate grinding after hole filling, thus eliminating the risk of damaging copper at a hole bottom in a plate grinding process; the reverse current can strip off impurities, loose copper crystals and other substances attached to a hole wall surface in an electrolytic manner, so as to avoid structural defects such as "black lines" on the hole wall; the hole is filled by using forward and reverse current pulses, so that a newly added thickness of the plate surface of the soft and hard combined plate is very small, and it is not necessary to set steps such as copper reduction, resin plug hole, ceramic plate grinding and cap electroplating in a traditional process, so that a process flow is simplified.

Description

Technical Field

[0001] This application relates to the field of printed circuit board technology, and in particular to a rigid-flex board and its via filling process. Background Technology

[0002] The application of rigid-flex PCBs in high-current transmission scenarios is becoming increasingly widespread. To ensure the reliability of high-current micro-orifices, traditional processes often use resin plugging, which involves first electroplating the hole walls and then filling the micro-orifices with resin to enhance the structural strength of the holes.

[0003] However, traditional resin plugging processes have the following significant drawbacks: 1. The thickness of the flexible and rigid areas of the rigid-flex PCB is different. During the ceramic grinding process after resin plugging, the grinding brush cannot evenly contact the surfaces of the flexible and rigid areas, making it easy for the copper at the bottom of the hole in the rigid area to be over-ground, leading to serious problems such as open circuits in the hole copper; 2. Black lines are easily formed on the hole wall during the electroplating process before resin plugging. These black lines are prone to local overheating under high current conditions; 3. Traditional resin plugging processes are long and inefficient. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a rigid-flex PCB and its via filling process, which can simplify the process flow and improve the via filling quality.

[0005] According to the via filling process of the rigid-flex PCB according to the first aspect of this application, the rigid-flex PCB includes a flexible board and a rigid board, and is provided with a via structure, wherein the via structure is a through hole or a blind hole; the via filling process of the rigid-flex PCB includes: Prepare the flexible circuit board and process the first hole in the flexible circuit board; The flexible board and the rigid board are laminated to form a rigid-flex board, and a second hole connected to the first hole is processed on the rigid board. The first hole and the second hole together form the hole structure. Copper is pulse-plated in the hole structure using alternating forward and reverse currents to form a solid copper pillar capable of filling the hole structure. The surface of the rigid-soft bonded board is cleaned with a cleaning solution.

[0006] According to some embodiments of this application, the method of alternating forward and reverse current pulse electroplating of copper within the hole structure to form a solid copper pillar capable of filling the hole structure includes: The positive current is used to electroplate copper material onto the hole wall of the hole structure; The copper material electroplated on the hole wall of the hole structure is electrolyzed using the reverse current to remove structural defects on the copper material.

[0007] According to some embodiments of this application, the method of alternating forward and reverse current pulse electroplating of copper within the hole structure to form a solid copper pillar capable of filling the hole structure includes: The current density of the forward current is greater than the current density of the reverse current, so that the strength of the copper material electroplated by the forward current is greater than the strength of the copper material electrolyzed by the reverse current. The duration of the forward current is longer than the duration of the reverse current, so as to deposit copper material layer by layer in the hole structure.

[0008] According to some embodiments of this application, the current density of the forward current is greater than the current density of the reverse current, including: The current density of the forward current is set to 1.0 ASD-2.5 ASD, and the current density of the reverse current is set to 0.2 ASD-0.8 ASD. The duration of the forward current is greater than the duration of the reverse current, including: The duration of the forward current is set to 10ms-60ms, and the duration of the reverse current is set to 1ms-10ms.

[0009] According to some embodiments of this application, the method of alternating forward and reverse current pulsed copper plating within the hole structure includes: The duty cycle of the forward current and the reverse current is set to 80%-95%.

[0010] According to some embodiments of this application, the method of alternating forward and reverse current pulsed copper plating within the hole structure includes: The electroplating solution is prepared using 50g / L-80g / L of copper ions, 100g / L-180g / L of sulfuric acid, 40ppm-80ppm of chloride ions, 0.5ml / L-2.5ml / L of accelerator, 5ml / L-15ml / L of inhibitor, and 5ml / L-15ml / L of leveling agent. The forward current and the reverse current are obtained by pulse electroplating copper using the electroplating solution.

[0011] According to some embodiments of this application, the method of alternating forward and reverse current pulsed copper plating within the hole structure includes: The current density of the forward current and the reverse current increases linearly in the boundary region where the rigid board and the flexible board meet and remains at a preset threshold.

[0012] According to some embodiments of this application, before the step of alternately pulse-plating copper with forward and reverse current within the hole structure to form a solid copper pillar capable of filling the hole structure, the method further includes: The catalyst is attached to the pore walls of the pore structure; A chemical copper plating solution, combined with a catalyst, is used to deposit copper onto the pore walls of the pore structure.

[0013] According to a second aspect embodiment of this application, a rigid-flex PCB is manufactured using the above-described rigid-flex PCB filling process, the rigid-flex PCB comprising: A flexible circuit board, the flexible circuit board including a first region and a second region, the first region having a first hole; A rigid board, which is laminated on opposite sides of the flexible board in the first region, and the rigid board is provided with a second hole communicating with the first hole; The first hole and the second hole form the hole structure.

[0014] According to some embodiments of this application, the interior of the hole structure is provided with a solid copper pillar, which is formed by forward and reverse current pulse electroplating deposition.

[0015] According to some embodiments of this application, the end face of the solid copper pillar is flush with the surface of the rigid-flexible bonded plate.

[0016] According to some embodiments of this application, a reinforcing plate is laid on the surface of the rigid plate, and the reinforcing plate can cover the opening of the hole structure.

[0017] The rigid-flex PCB and its via-filling process according to the embodiments of this application have at least the following beneficial effects: First, a first hole is drilled on the flexible PCB, and a rigid PCB is laminated onto the flexible PCB. After lamination, a second hole is drilled on the rigid PCB, so that the first hole and the second hole form a hole structure. This application uses a via-filling process of positive and negative current pulse electroplating copper instead of the traditional resin plugging process. Compared with the traditional resin plugging process, the positive current in this application is used for the deposition of copper material, so that a solid copper pillar is formed in the hole structure, while the negative current is used for electrolytic electrolysis of excess copper on the surface, so that the end face of the solid copper pillar is flush with the surface of the rigid-flex PCB, eliminating the need for... By performing grinding after filling the holes, the risk of damaging the copper at the bottom of the holes during the grinding process is eliminated at the source. At the same time, the reverse current of this application can electrolytically remove impurities and loose copper crystals attached to the surface of the hole wall, thereby avoiding structural defects such as "black lines" on the hole wall. In addition, due to the use of positive and negative current pulse filling, the filling process of this application results in a very small increase in the thickness of the rigid-flex board. Furthermore, the solid copper pillars formed in the hole structure have good conductivity, eliminating the need for copper reduction, resin plugging, ceramic grinding, and cap electroplating steps in traditional processes, thus simplifying the process flow.

[0018] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0019] The present application will be further illustrated below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments illustrated in the following drawings are exemplary and are only used to explain the present application, and should not be construed as limiting the present application.

[0020] Figure 1 This is a flowchart of the hole-filling process for the rigid-flex PCB according to an embodiment of this application; Figure 2 This is a schematic diagram of the rigid-flex PCB structure according to an embodiment of this application; Figure 3 This is a top view of the rigid-flex PCB according to an embodiment of this application; Figure 4 This is a schematic diagram of the blind hole type hole structure in the rigid-flex PCB of this application embodiment; Figure 5 This is a schematic diagram of the through-hole structure in the rigid-flex plate of this application embodiment; Figure 6 This is a schematic diagram of the structure after a reinforcing plate is installed on the rigid-flex PCB according to an embodiment of this application.

[0021] Figure label: 100. Rigid-flex PCB; 101. Flexible PCB; 102. Rigid PCB; 103. Hole structure; 104. Reinforcing PCB. Detailed Implementation

[0022] The embodiments of this application are described in detail below with reference to the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0023] In the description of this application, it should be understood that the terms "center", "middle", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0024] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0025] In the description of this application, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0026] In the description of this application, the use of terms such as "one embodiment," "some embodiments," "an example," "some instances," "some embodiments," "illustrative embodiment," "example," "specific example," and "some examples" indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0027] The rigid-flex board 100 involved in this application includes a flexible board 101 and a rigid board 102. The flexible board 101 is flexible relative to the rigid board 102, while the rigid board 102 is rigid relative to the flexible board 101. Furthermore, the surface area of ​​the rigid board 102 is smaller than that of the flexible board 101. When the rigid board 102 is laminated onto the flexible board 101 to form the rigid-flex board 100, a portion of the structure of the flexible board 101 is exposed outside the rigid board 102, which facilitates the deformation of the rigid-flex board 100 in this portion to adapt to specific application scenarios.

[0028] The rigid-flex board 100 has a hole structure 103, and the finished rigid-flex board 100 needs to be filled with the hole structure 103. The traditional process uses resin to fill the hole structure 103. The resin plugging process includes steps such as copper reduction, copper plating, copper immersion, resin plugging, board grinding, and cap electroplating.

[0029] Compared to the traditional resin plugging process, this application adopts a pulse filling process. In this process, the pulse filling process modifies the traditional DC electroplating to a pulse electroplating filling technology formed by alternating positive and negative currents. During this process, the hole structure 103 is directly filled and leveled, eliminating the need for copper reduction, resin plugging, grinding, capping electroplating, and other processes.

[0030] like Figure 4 and Figure 5 As shown, the hole structure 103 in this application is a through hole or a blind hole. When the hole structure 103 is formed as a through hole, the drilling process needs to penetrate through the rigid-flex plate 100. However, when the hole structure 103 is formed as a blind hole, the drilling process only penetrates the L1 and L2 layers of the rigid-flex plate 100, or only penetrates the L1, L2 and L3 layers of the rigid-flex plate 100.

[0031] like Figure 1 As shown, Figure 1 This is a flowchart of a via filling process for a rigid-flex board 100 according to an embodiment of this application. The via filling process for the rigid-flex board 100 includes, but is not limited to, the following steps: Prepare a flexible circuit board 101, and machine the first hole on the flexible circuit board 101; Flexible board 101 and rigid board 102 are laminated to form a flexible-rigid bonded board 100, and a second hole connected to the first hole is processed on the rigid board 102. The first hole and the second hole together form a hole structure 103. Copper is pulsed in the hole structure 103 by alternating forward and reverse currents to form a solid copper pillar that can fill the hole structure 103. The surface of the rigid-soft bonded board 100 is cleaned with cleaning solution.

[0032] In some embodiments, a flexible board 101 is first prepared, and a first hole is formed on the flexible board 101 using a specific process. Specifically, the first hole is formed by laser drilling. On this basis, a rigid board 102 is laminated onto the flexible board 101 to form a rigid-flex board 100.

[0033] In order to form the hole structure 103 on the rigid-flex board 100, a second hole also needs to be made on the rigid board 102 of the rigid-flex board 100 using a specific process. Specifically, the method of processing the second hole also includes laser drilling.

[0034] It is understandable that the positions of the first hole and the second hole correspond to each other, so that the first hole and the second hole are connected to each other and together form the hole structure 103.

[0035] Furthermore, to fill the hole structure 103, this application adopts a pulse filling process instead of the traditional resin plugging process, that is, to use alternating forward and reverse current to pulse electroplating copper in the hole structure 103, thereby forming a solid copper pillar with good conductivity in the hole structure 103.

[0036] It is worth noting that the pulse via filling process of this application eliminates the need for a grinding process, thereby eliminating the risk of damage to the copper at the via opening caused by the height difference between the rigid and flexible boards. Specifically, after adopting the pulse via filling process, only metallic copper exists within the via structure 103 on the rigid-flex board 100, without resin or other foreign matter. Simultaneously, the forward current in the pulse via filling process electroplats copper preferentially to deposit at the bottom of the via structure 103, filling the via structure 103 with solid copper pillars from bottom to top. The reverse current preferentially electrolyzes excess copper on the surface at the via opening and board surface, achieving a smoothing effect on the copper material. Therefore, the flatness tolerance of the board surface after pulse via filling can be controlled within ±10μm, directly meeting the requirements for outer layer circuit fabrication without the need for an additional grinding process.

[0037] Furthermore, the pulse via filling process of this application does not require a pre-set copper reduction step. In traditional resin via filling processes, due to the tip effect of DC electroplating, the copper deposition rate at the board surface and via openings is much faster than that on the via walls, resulting in a thicker copper layer after electroplating. If the original surface copper is not thinned, the excessive copper thickness after the additional electroplating can easily lead to severe side etching of fine outer layer circuits in later stages, making it difficult to create fine lines. However, the reverse current in the process of this application has an electrochemical polishing effect. Since the via openings and board surface are at the tip of the electric field, the reverse current preferentially electrolyzes away the excess copper at these locations, while the copper plating in the low-current region inside the via structure 103 is retained. This achieves the technical effect of copper accumulation inside the via structure 103 while the copper thickness on the board surface is almost minimal. In actual operation, the internal space of the via structure 103 is filled with solid copper pillars, while the newly added plating layer on the board surface is very thin, making the overall copper thickness just suitable for the etching of the outer layer circuits, eliminating the need for an additional copper reduction step.

[0038] The pulse-filling process of this application eliminates the need for a capping electroplating step after filling. Traditional resin-filling processes require a second capping electroplating because the DC electroplating process only creates a hollow copper cylinder on the inner wall of the hole structure 103, into which resin is then poured. Since the resin exposed outside the hole opening is non-conductive, a second copper plating layer must be applied to cover the opening to ensure circuit continuity. In contrast, the process of this application fills the hole structure 103 with a solid copper pillar. The solid copper pillar is integral with the outer copper layer of the board, and the hole opening is already metallic copper, eliminating the need for an additional capping electroplating step.

[0039] As can be seen, compared with the traditional resin plugging process, the pulse filling process of this application eliminates the steps of copper reduction, resin plugging, plate grinding, and cap electroplating, effectively simplifying the process flow and improving processing efficiency.

[0040] Additionally, refer to Figure 1 The steps include: using alternating forward and reverse currents to pulse-plate copper within the hole structure 103 to form a solid copper pillar capable of filling the hole structure 103, which may include, but is not limited to, the following steps: Copper material is electroplated on the hole wall of hole structure 103 using a forward current; Copper material formed by electroplating the hole walls of the reverse current electrolytic hole structure 103 is used to remove structural defects on the copper material.

[0041] In some embodiments, the forward current is used to electroplate copper onto the hole walls of the hole structure 103, while the reverse current is used to electrolyze the electroplated copper material. The alternating action of the forward and reverse currents in pulse electroplating can continuously "refresh" the hole wall surface during the electroplating process, which can improve the adhesion of the plating layer on the one hand, and eliminate structural defects such as "black lines" on the hole walls that are easily generated by traditional DC electroplating on the other hand.

[0042] Firstly, pulsed through-hole filling improves the adhesion of the plating layer. Forward current electroplating tends to cause copper ions to accumulate at the hole opening, resulting in coarse and loose surface grains that are prone to internal stress. In contrast, reverse current electrolysis dissolves the loose and burr-like copper particles on the surface, exposing a dense copper substrate. This facilitates subsequent copper growth on a clean and dense substrate, ensuring fine grains and improving the adhesion of the plating layer to both flexible board 101 and rigid board 102 substrates.

[0043] Secondly, the pulsed via-filling process eliminates structural defects. The essence of structural defects such as "black lines" lies in the rough grains, pinholes, interlayer impurities, and gaps or plating breaks formed by hydrogen retention in the inner wall coating of the via structure 103. The reverse current in the pulsed via-filling process can electrolytically remove hydrogen bubbles, impurities, and loose copper crystals adsorbed on the via walls, ensuring fine, layer-by-layer growth of the plating, resulting in dense and compact grains, avoiding bubble gaps and delamination gaps, and fundamentally preventing structural defects such as "black lines."

[0044] Additionally, refer to Figure 1 The steps include: using alternating forward and reverse currents to pulse-plate copper within the hole structure 103 to form a solid copper pillar capable of filling the hole structure 103, which may include, but is not limited to, the following steps: The current density of the forward current is greater than that of the reverse current, so that the strength of the copper material plated by the forward current is greater than that of the copper material electrolyzed by the reverse current. The duration of the forward current is longer than the duration of the reverse current, so as to deposit copper material layer by layer in the hole structure 103.

[0045] In some embodiments, to ensure that a copper plating layer can grow layer by layer inside the hole structure 103, the electroplating effect of the forward current must be greater than the electrolytic effect of the reverse current. This can be achieved by the following technical means: first, the current density of the forward current is greater than the current density of the reverse current; second, the duration of the forward current is greater than the duration of the reverse current. Specifically, both of these technical means are employed simultaneously in some embodiments of this application.

[0046] It is understandable that a forward current density greater than a reverse current density results in a greater strength for copper plating material when plated with a forward current than when electrolyzed with a reverse current, facilitating the layer-by-layer growth of the copper plating. Furthermore, a forward current duration greater than a reverse current duration allows for a longer time for copper plating material to be plated than for electrolytic copper material, also facilitating the layer-by-layer growth of the copper plating.

[0047] Additionally, refer to Figure 1 The steps involve the forward current density being greater than the reverse current density, and may include, but are not limited to, the following steps: Set the forward current density to 1.0ASD-2.5ASD and the reverse current density to 0.2ASD-0.8ASD.

[0048] Steps: The duration of the forward current is longer than the duration of the reverse current, and may include, but is not limited to, the following steps: Set the duration of the forward current to 10ms-60ms and the duration of the reverse current to 1ms-10ms.

[0049] In some embodiments, the current density of the forward current is set to 1.0 ASD-2.5 ASD, preferably 1.5 ASD-2.0 ASD; the current density of the reverse current is set to 0.2 ASD-0.8 ASD, preferably 0.3 ASD-0.5 ASD.

[0050] Furthermore, the duration of the forward current is set to 10ms-60ms, preferably 20ms-40ms; the duration of the reverse current is set to 1ms-10ms, preferably 2ms-5ms.

[0051] Additionally, the step of pulse electroplating copper within the hole structure 103 using alternating forward and reverse currents may include, but is not limited to, the following steps: Set the duty cycle of the forward and reverse currents to 80%-95%.

[0052] In some embodiments, the duty cycle of the forward current and the reverse current is set to 80%-95%, preferably, the duty cycle of the forward current and the reverse current is set to 85%-90%.

[0053] The duty cycle is the percentage of the energized time within one pulse cycle out of the total cycle. When the forward and reverse currents use a low duty cycle of 10%-30%, the power-off time during the via filling process is relatively long, and the copper ions consumed in the via structure 103 have sufficient time to diffuse and replenish, but the copper deposition rate is slow and the production capacity is extremely low.

[0054] Furthermore, when the forward and reverse currents adopt a high duty cycle of over 70%, the power-off time during the hole-filling process is very short, which can ensure that copper is deposited inside the hole structure 103 at a high speed, which is beneficial to improving production capacity and can meet the processing requirements of the rigid-flex board 100 of this application.

[0055] Additionally, the step of pulse electroplating copper within the hole structure 103 using alternating forward and reverse currents may include, but is not limited to, the following steps: The electroplating solution is prepared using 50g / L-80g / L of copper ions, 100g / L-180g / L of sulfuric acid, 40ppm-80ppm of chloride ions, 0.5ml / L-2.5ml / L of accelerator, 5ml / L-15ml / L of inhibitor, and 5ml / L-15ml / L of leveling agent. Forward and reverse currents are achieved by pulse electroplating of copper using an electroplating solution.

[0056] Additionally, the step of pulse electroplating copper within the hole structure 103 using alternating forward and reverse currents may include, but is not limited to, the following steps: The current density of forward and reverse current increases linearly in the boundary region between rigid board 102 and flexible board 101 and remains at a preset threshold.

[0057] In some embodiments, the current density of the forward and reverse currents during normal operation is first set according to actual needs, i.e., a preset threshold.

[0058] Furthermore, this application employs a "soft-start" mode to control the forward and reverse currents in the bonding boundary area between the flexible board 101 and the rigid board 102, that is, the current linearly rises to the set value within 3 to 5 minutes, thereby avoiding stress concentration in the coating caused by material differences.

[0059] Additionally, before the step of pulse electroplating copper in the hole structure 103 using alternating forward and reverse currents to form a solid copper pillar capable of filling the hole structure 103, the following steps may be included but are not limited to: The catalyst is attached to the pore walls of the porous structure 103; Copper was deposited on the pore walls of the pore structure 103 using a chemical copper plating solution and a catalyst.

[0060] In some embodiments, a copper plating process is required before the pulsed via filling process. Since the inner wall of the via structure 103 is primarily made of an insulating material and is non-conductive, it is difficult to directly electroplate copper using forward current. Therefore, a copper plating process is necessary before copper plating.

[0061] The catalyst for the copper plating process can be palladium. First, the soft and hard bonding plate 100 is soaked in an activation solution containing palladium ions, so that the pore walls of the porous structure 103 adsorb a layer of fine palladium metal particles.

[0062] Furthermore, a solution containing divalent copper ions, formaldehyde reducing agent, complexing agent, and pH stabilizer is used to undergo an autocatalytic reaction under the catalysis of palladium particles, resulting in the precipitation of the first thin copper layer; the newly generated copper itself also has catalytic ability, which facilitates the continuous autonomous growth of the copper layer.

[0063] like Figure 2 and Figure 3 As shown in the figure, this application embodiment provides a rigid-flex board 100, which includes a flexible board 101 and a rigid board 102. The flexible board 101 includes a first region and a second region, and a first hole is disposed in the first region. The rigid board 102 is laminated on the flexible board 101 in the first region. When the rigid board 102 is laminated on the flexible board 101, the second hole on the rigid board 102 communicates with the first hole, so that the first hole and the second hole together form a hole structure 103.

[0064] Specifically, one flexible board 101 is provided, and four rigid boards 102 are provided. Two first regions are provided on the flexible board 101, and a second region is located between the two first regions. Each first region is equipped with two rigid boards 102, and the two rigid boards 102 are laminated on opposite sides of the flexible board 101 in the first region.

[0065] like Figure 6 As shown, in some embodiments, the surface of the rigid plate 102 is covered with a reinforcing plate 104, which is made of a rigid material.

[0066] Understandably, after the rigid plate 102 and the flexible plate 101 are laminated to form the rigid-flex plate 100, the rigid plate 102 is located on the surface of the rigid-flex plate 100, while the flexible plate 101 is located in the inner layer of the rigid-flex plate 100. As the lamination process proceeds, the first hole and the second hole mate with each other, thereby forming the hole structure 103.

[0067] To ensure the strength of the hole structure 103 on the rigid-flex plate 100, a reinforcing plate 104 is provided on the rigid-flex plate 100. Since the reinforcing plate 104 needs to cover the surface of the rigid-flex plate 100, the reinforcing plate 104 is laid on the surface of the rigid plate 102.

[0068] Furthermore, the reinforcing plate 104 can cover the opening of the hole structure 103, thereby preventing the hole structure 103 from opening to the outside.

[0069] It is worth noting that when the rigid-flex plate 100 is equipped with a reinforcing plate 104, the hole structure 103 does not require a hole-filling process. The hollow hole structure 103 covers the bottom of the reinforcing plate 104. In this case, the reinforcing bonding force of the rigid-flex plate 100 is less than 0.8 kg / cm². 2 If the rigid-flex plate 100 is in an excessively high temperature environment, such as an ambient temperature of 200℃-260℃, air bubbles are likely to appear at the opening position of the hole structure 103.

[0070] Correspondingly, when the rigid-flex PVC board 100 adopts the hole-filling process of this application, the surface of the rigid-flex PVC board 100 is free of holes, and the reinforcing bonding force of the rigid-flex PVC board 100 is greater than 1.2 kg / cm². 2 Even when the rigid-flex plate 100 is in an excessively high temperature environment, air bubbles are not likely to appear at the opening position of the hole structure 103.

[0071] In some embodiments, the interior of the hole structure 103 is provided with solid copper pillars, which are solid copper pillars deposited by the pulsed via filling process.

[0072] Furthermore, since the solid copper pillar is made by pulse filling process, the end face of the solid copper pillar is flush with the surface of the rigid-flexible bonding board 100, eliminating the need for an additional grinding process.

[0073] In actual implementation, the rigid-flex PCB formed by the hole filling process of this application can achieve zero copper breaks in the hole structure, zero black lines on the hole wall, and can increase production efficiency by 10% to 20%.

[0074] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application. Furthermore, unless otherwise specified, the embodiments and features described in the embodiments of this application can be combined with each other.

Claims

1. A process for filling holes in a rigid-flex PCB, characterized in that, The rigid-flex PCB includes a flexible board and a rigid board, and has a hole structure, wherein the hole structure is a through hole or a blind hole; the hole filling process of the rigid-flex PCB includes: Prepare the flexible circuit board and process the first hole in the flexible circuit board; The flexible board and the rigid board are laminated to form a rigid-flex board, and a second hole connected to the first hole is processed on the rigid board. The first hole and the second hole together form the hole structure. Copper is pulse-plated in the hole structure using alternating forward and reverse currents to form a solid copper pillar capable of filling the hole structure. The surface of the rigid-soft bonded board is cleaned with a cleaning solution.

2. The rigid-flex PCB filling process according to claim 1, characterized in that, The method of pulse electroplating copper within the hole structure using alternating forward and reverse currents to form a solid copper pillar capable of filling the hole structure includes: The positive current is used to electroplate copper material onto the hole wall of the hole structure; The copper material electroplated on the hole wall of the hole structure is electrolyzed using the reverse current to remove structural defects on the copper material.

3. The rigid-flex PCB filling process according to claim 2, characterized in that, The method of pulse electroplating copper within the hole structure using alternating forward and reverse currents to form a solid copper pillar capable of filling the hole structure includes: The current density of the forward current is greater than the current density of the reverse current, so that the strength of the copper material electroplated by the forward current is greater than the strength of the copper material electrolyzed by the reverse current. The duration of the forward current is longer than the duration of the reverse current, so as to deposit copper material layer by layer in the hole structure.

4. The rigid-flex PCB filling process according to claim 3, characterized in that: The current density of the forward current is greater than the current density of the reverse current, including: The current density of the forward current is set to 1.0 ASD-2.5 ASD, and the current density of the reverse current is set to 0.2 ASD-0.8 ASD. The duration of the forward current is greater than the duration of the reverse current, including: The duration of the forward current is set to 10ms-60ms, and the duration of the reverse current is set to 1ms-10ms.

5. The rigid-flex PCB filling process according to claim 1, characterized in that, The method of pulse electroplating copper within the hole structure using alternating forward and reverse currents includes: The duty cycle of the forward current and the reverse current is set to 80%-95%.

6. The rigid-flex PCB filling process according to claim 1, characterized in that, The method of pulse electroplating copper within the hole structure using alternating forward and reverse currents includes: The current density of the forward current and the reverse current increases linearly in the boundary region where the rigid board and the flexible board meet and remains at a preset threshold.

7. The rigid-flex PCB filling process according to claim 1, characterized in that, Before employing alternating forward and reverse current pulse electroplating within the hole structure to form a solid copper pillar capable of filling the hole structure, the method further includes: The catalyst is attached to the pore walls of the pore structure; A chemical copper plating solution, combined with a catalyst, is used to deposit copper onto the pore walls of the pore structure.

8. A rigid-flex PCB, characterized in that, The rigid-flex PCB is manufactured using the via-filling process described in any one of claims 1-7, wherein the rigid-flex PCB comprises: A flexible circuit board, the flexible circuit board including a first region and a second region, the first region having a first hole; A rigid board, which is laminated on opposite sides of the flexible board in the first region, and the rigid board is provided with a second hole communicating with the first hole; The first hole and the second hole form the hole structure.

9. The rigid-flex PCB according to claim 8, characterized in that, The hole structure contains a solid copper pillar, which is formed by electroplating deposition using forward and reverse current pulses.

10. The rigid-flex PCB according to claim 8, characterized in that, The surface of the rigid plate is covered with a reinforcing plate, which can cover the opening of the hole structure.

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