Method for manufacturing a printed circuit board

Abstract

The application provides a printed circuit board preparation method and relates to the technical field of printed circuit boards. The preparation method comprises the following steps: forming an initial circuit board, the initial circuit board containing an initial via hole penetrating through the initial circuit board and an initial hole metal layer located on the inner wall of the initial via hole, and the initial via hole comprising a first via hole; bonding a temporary bonding film on the surface of the initial circuit board, the second via hole in the temporary bonding film corresponding to the first via hole one by one and exposing the aperture of the first via hole; depositing a thickened metal layer on the surface of the initial hole metal layer, the thickened metal layer extending to the inner wall of the second via hole; forming a patterned barrier layer on the surface of the thickened metal layer, and exposing the thickened metal layer located on the inner wall of the second via hole; removing the thickened metal layer on the inner wall of the second via hole by taking the barrier layer as a mask; removing the barrier layer; and debonding the temporary bonding film. The preparation method can increase the thickness of the hole metal layer, fundamentally avoid the formation of aperture bumps, and improve the yield of the printed circuit board.

Description

Technical Field

[0001] This application relates to the field of printed circuit board technology, and specifically to a method for preparing a printed circuit board. Background Technology

[0002] With the rapid development of artificial intelligence technology, the computing power demand for large-scale training and inference is growing exponentially, leading to a significant increase in the requirements for chip computing speed, data bandwidth, and power consumption. This places higher demands on the power supply capabilities of chip power supply systems. Currently, the industry generally adopts vertical power supply technology to cope with the power supply requirements under high power consumption. This involves shortening the horizontal current path from the power supply module to the chip to reduce resistance loss and improve power supply efficiency. However, the vertical current path from the power supply module through the printed circuit board (PCB) to the chip is limited by the design and processing technology of the current vias in the PCB. To meet the high current demand, related technologies mainly increase the number of vias in the current-carrying area to expand the conductive area. However, due to the physical characteristics and reliability requirements of the PCB, there is a physical limit to increasing the number of vias, and simply increasing the number of vias cannot meet the ever-increasing power supply demand. Therefore, related technologies propose increasing the thickness of the copper in the vias to adapt to the power supply requirements. Currently, the common method is to use button plating to increase the copper thickness, which involves a second plating after the copper thickness meets the normal requirements. This method results in electroplated bumps at the orifice, which need to be removed by grinding. However, the continuous force applied to the printed circuit board during grinding may cause the copper foil on the printed circuit board to lift. The lifted copper foil may bend inward and block the orifice, causing the first through-hole to overheat and burn, thus affecting the quality and yield of the printed circuit board. Summary of the Invention

[0003] This application provides a method for manufacturing a printed circuit board to reduce the adverse effects of bumps on the quality of the printed circuit board.

[0004] This application provides a method for fabricating a printed circuit board, comprising: forming an initial circuit board, the initial circuit board having an initial through-hole penetrating the initial circuit board and an initial hole metal layer located on the inner wall of the initial through-hole, the initial through-hole including a first through-hole; attaching a temporary bonding film to two opposing surfaces of the initial circuit board, the second through-hole in the temporary bonding film corresponding one-to-one with the first through-hole and exposing the opening of the first through-hole; depositing a thickened metal layer on the surface of the initial hole metal layer, the thickened metal layer extending to the inner wall of the second through-hole; forming a patterned barrier layer on the surface of the thickened metal layer, exposing the thickened metal layer located on the inner wall of the second through-hole; using the barrier layer as a mask, wet-removing the thickened metal layer on the inner wall of the second through-hole; removing the barrier layer; and debonding the temporary bonding film.

[0005] In the aforementioned method for fabricating a printed circuit board, a temporary bonding film is used to define the deposition area of ​​the thickened metal layer, ensuring that the thickened metal layer is primarily deposited on the surface of the initial hole metal layer within the first via, while the area covered by the temporary bonding film is not deposited with the thickened metal layer. The temporary bonding film, together with a barrier layer, also defines the removal area of ​​the thickened metal layer, removing only the thickened metal layer on the inner wall of the second via, i.e., only removing the thickened metal layer extending beyond the opening of the first via, thus preventing wet removal of the thickened metal layer within the first via and the area covered by the temporary bonding film. The thickened metal layer within the first via and the initial hole metal layer together constitute the hole metal layer, achieving a thickened hole metal layer that allows the first via to function as a current-carrying via to handle high-power current. Simultaneously, by removing the thickened metal layer extending beyond the opening of the first via, the formation of bumps at the hole opening can be fundamentally avoided, thereby reducing the adverse effects of bumps on the quality of the printed circuit board and improving its yield. Attached Figure Description

[0006] To more clearly illustrate the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0007] Figure 1 This is a process flow diagram of a method for manufacturing a printed circuit board according to an embodiment of this application; Figure 2 This is a schematic diagram of the structure of the initial circuit board according to the embodiments of this application; Figure 3 This is a cross-sectional view of the initial circuit board according to an embodiment of this application; Figure 4 This is a schematic diagram of the structure of attaching a temporary bonding film to the surface of the initial circuit board according to the embodiments of this application; Figure 5 This is a cross-sectional view of a temporary bonding film being laminated onto the surface of an initial circuit board according to an embodiment of this application; Figure 6 This is a cross-sectional view of a thickened metal layer and an initial barrier layer sequentially deposited on the surface of the initial hole metal layer according to an embodiment of this application; Figure 7 This is a cross-sectional view of the barrier layer formed according to an embodiment of this application; Figure 8 This is a cross-sectional view of the thickened metal layer removed from the inner wall of the second through hole according to an embodiment of this application; Figure 9 This is a cross-sectional view of the barrier layer removed according to an embodiment of this application; Figure 10This is a cross-sectional view of the re-deposited thickened metal layer according to the embodiments of this application; Figure 11 This is a cross-sectional view of the temporary bonding film with secondary opening according to the embodiments of this application; Figure 12 This is a cross-sectional view of filling the third and fourth through holes with liquid plugging resin according to the embodiments of this application; Figure 13 This is a cross-sectional view of the temporary bonded film being debonded according to the embodiments of this application; Figure 14 This is a cross-sectional view of the solid resin being removed from the fourth through hole by grinding according to an embodiment of this application; Figure 15 This is a schematic diagram of a temporary bonding film being applied to the surface of an initial circuit board according to an embodiment of this application.

[0008] Explanation of reference numerals in the attached figures: 1-Initial circuit board; 11-Initial hole metal layer; 12-First through hole; 13-Outer base copper foil; 14-Initial surface metal layer; 15-First positioning hole; 16-Third through hole; 17-Fifth through hole; 2-Temporary bonding film; 21-Second through hole; 22-Second positioning hole; 23-Fourth through hole; 31-Thickened metal layer; 32-Second thickened metal layer; 4-Barrier layer; 41-Initial barrier layer; 5-Solid resin. Detailed Implementation

[0009] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0010] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0011] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, in this specification, the term “and / or” includes any and all combinations of the associated listed items.

[0012] Firstly, reference Figure 1 This application provides a method for manufacturing a printed circuit board, comprising: Step S1, Reference Figures 2-3 An initial circuit board 1 is formed, the initial circuit board 1 includes an initial through hole penetrating the initial circuit board 1 and an initial hole metal layer 11 located on the inner wall of the initial through hole, the initial through hole including a first through hole 12. Step S2, Reference Figures 4-5 Temporary bonding films 2 are attached to two surfaces of the initial circuit board 1 that are opposite to each other. The second through hole 21 in the temporary bonding film 2 corresponds one-to-one with the first through hole 12 and exposes the opening of the first through hole 12. Step S3, Reference Figure 6 A thickened metal layer 31 is deposited on the surface of the initial hole metal layer 11, and the thickened metal layer 31 extends to the inner wall of the second through hole 21; Step S4, Reference Figure 7 A patterned barrier layer 4 is formed on the surface of the thickened metal layer 31, exposing the thickened metal layer 31 located on the inner wall of the second through hole 21. Step S5, Reference Figure 8 Using the barrier layer 4 as a mask, the thickened metal layer 31 on the inner wall of the second through hole 21 is removed by wet process. Step S6, Reference Figure 9 Remove the blocking layer 4; Step S7: Debond the temporary bonded membrane 2.

[0013] In the above-described method for manufacturing printed circuit boards, the temporary bonding film 2 is used to define the deposition area of ​​the thickened metal layer 31, so that the thickened metal layer 31 is mainly deposited on the surface of the initial hole metal layer 11 in the first via 12, while the area covered by the temporary bonding film 2 will not be deposited with the thickened metal layer 31; the temporary bonding film 2 and the barrier layer 4 together define the removal area of ​​the thickened metal layer 31, removing only the thickened metal layer 31 on the inner wall of the second via 21, that is, removing only the thickened metal layer 31 extending beyond the opening of the first via 12, avoiding wet removal of the thickened metal layer 31 in the first via 12 and the area covered by the temporary bonding film 2. The thickened metal layer 31 inside the first through hole 12 and the initial hole metal layer 11 together constitute the hole metal layer, thereby thickening the hole metal layer and enabling the first through hole 12 to carry high-power current as a current-carrying hole. At the same time, by removing the thickened metal layer 31 extending beyond the opening of the first through hole 12, the formation of hole bumps can be fundamentally avoided, thereby reducing the adverse effects of bumps on the quality of the printed circuit board and improving the yield of the printed circuit board.

[0014] Further reference Figure 3The initial circuit board 1 also includes an outer base copper foil 13 on the surface and an initial surface metal layer 14 covering the outer base copper foil 13. The outer base copper foil 13 and the initial surface metal layer 14 are used for subsequent fabrication of the outer circuit layers. (Reference) Figure 5 The temporary bonding film 2 is attached to the surface of the initial surface metal layer 14. It can not only protect the outer base copper foil 13 and the initial surface metal layer 14 during wet etching, but also prevent the deposition of a thickened metal layer 31 on the surface of the initial surface metal layer 14. This makes the outer base copper foil 13 and the initial surface metal layer 14 have a thinner thickness, which is beneficial for the fine fabrication of the outer circuit layer.

[0015] The following is a complete description of the fabrication method of the printed circuit board described above.

[0016] Step S1, Reference Figures 2-3 An initial circuit board 1 is formed, the initial circuit board 1 includes an initial through hole penetrating the initial circuit board 1 and an initial hole metal layer 11 located on the inner wall of the initial through hole, the initial through hole including a first through hole 12.

[0017] Specifically, the steps for forming the initial circuit board 1 may include the following steps performed sequentially: Inner layer image transfer: A copper-clad laminate is provided, and a photosensitive dry film is coated on the surface of the copper-clad laminate. The photosensitive dry film is exposed and developed to form a preset pattern corresponding to the inner layer circuit. The copper foil on the surface of the copper-clad laminate is etched using the photosensitive dry film as a mask. The photosensitive dry film is removed, and the copper-clad laminate forms a core board with an inner layer circuit layer on its surface.

[0018] Pressing: Multiple core boards, multiple prepregs and two outer copper foils 13 are stacked in sequence and pressed together to form a composite board blank.

[0019] Drilling: At least one initial through hole is formed in the composite board using mechanical drilling or laser drilling technology. The initial through hole cuts through the outer base copper foil 13, exposing the side of the inner circuit layer. The hole wall of the initial through hole is roughened by removing adhesive residue.

[0020] Chemical copper plating: Chemical copper plating is performed on the composite slab blank after drilling to form a seed layer on the hole wall of the initial through hole for subsequent electroplating.

[0021] One-time electroplating: The composite slab is electroplated across the entire board, meaning that metal layers are deposited simultaneously on the surface of the seed layer and the surface of the outer base copper foil 13. The seed layer located on the wall of the initial through-hole and the metal layer on the surface of the seed layer together constitute the initial hole metal layer 11. The metal layer on the surface of the outer base copper foil 13 constitutes the initial surface metal layer 14. The initial through-hole containing the initial hole metal layer 11 is the one-time electroplated through-hole. The thickness of the initial hole metal layer 11 meets the thickness requirements of the normal hole metal layer, meaning that the one-time electroplated through-hole can meet the normal current and power requirements.

[0022] In some alternative implementations, the borehole diameter can be determined during the drilling process based on the target thickness of the borehole metal layer, the finished borehole diameter, the penetration capability coefficient, and the factory's finished borehole diameter processing capability.

[0023] Specifically, the finished hole size, through-hole capability coefficient, drilled hole diameter, and target thickness of the hole metal layer satisfy the following formula: FHS=DHS-TT / TP×2; where FHS refers to the finished hole size, that is, the final measured diameter of the through hole after all the manufacturing processes of the printed circuit board are completed; DHS refers to the drilled hole size, that is, the initial bare hole diameter obtained by drilling; TT refers to the target thickness of the hole metal layer; and TP refers to the through-hole capability coefficient, which is used to represent the uniformity of the electroplated metal layer.

[0024] When selecting the drill hole diameter (DHS), it is necessary to ensure that the corresponding finished hole diameter (FHS) is greater than the minimum finished hole diameter (D) that the factory can process to accommodate the factory's processing capabilities. Simultaneously, other PCB designs should be considered, and the largest possible drill hole diameter (DHS) should be selected without conflicting with other designs. This method of determining the drill hole diameter allows the PCB to meet high power supply requirements while also satisfying the minimum processing capabilities for subsequent via plugging or electrical connections.

[0025] For example, Tables 1 and 2 show the finished hole diameter (FHS) for different drill hole diameters (DHS) and different target thicknesses (TT) of the hole metal layer when the hole penetration capability factor (TP) is 85% and 75%, respectively.

[0026] Table 1: Finished hole diameters corresponding to different borehole diameters and target metal layer thicknesses with a perforation capability coefficient of 85%.

[0027] Table 2: Finished hole diameters corresponding to different borehole diameters and target metal layer thicknesses with a penetration capability coefficient of 75%.

[0028] If the minimum finished hole diameter (D) that the factory can process is 0.1 mm and the hole penetration capability coefficient (TP) is 85%, referring to Table 1, we can see that: when the target thickness (TT) of the hole metal layer is 40 μm, the minimum drill hole diameter (DHS) can be selected as 0.2 mm; when the target thickness (TT) of the hole metal layer is 50 μm, the minimum drill hole diameter (DHS) can be selected as 0.25 mm; when the target thickness (TT) of the hole metal layer is 75 μm, the minimum drill hole diameter (DHS) can be selected as 0.30 mm.

[0029] If the minimum finished hole diameter (D) that the factory can process is 0.1 mm and the hole penetration capability coefficient (TP) is 75%, referring to Table 2, it can be seen that when the target thickness (TT) of the hole metal layer is 40 μm to 50 μm, the minimum drill hole diameter (DHS) can be selected as 0.25 mm; when the target thickness (TT) of the hole metal layer is 75 μm, the minimum drill hole diameter (DHS) can be selected as 0.35 mm.

[0030] Step S2, Reference Figures 4-5 Temporary bonding films 2 are attached to two surfaces of the initial circuit board 1 that are opposite to each other. The second through hole 21 in the temporary bonding film 2 corresponds one-to-one with the first through hole 12 in the initial circuit board 1 and exposes the opening of the first through hole 12.

[0031] In one alternative embodiment, the diameter of the second through hole 21 is larger than that of the first through hole 12 to improve the alignment between the second through hole 21 in the temporary bonding film 2 and the first through hole 12 in the initial circuit board 1.

[0032] Specifically, the difference between the diameter of the second through-hole 21 and the diameter of the first through-hole 12 can be less than or equal to 5 mil. If this difference is too large, the diameter of the second through-hole 21 may be relatively too large, which is not conducive to improving the density of the initial through-holes in the printed circuit board. By limiting the difference to the above range, it is possible to effectively improve the alignment between the second through-hole 21 in the temporary bonding film 2 and the first through-hole 12 in the initial circuit board 1 while achieving a high density of the initial through-holes in the printed circuit board.

[0033] In one alternative implementation, refer to Figure 15 The process involves attaching temporary bonding films 2 to two opposing surfaces of an initial circuit board 1, including the following steps: The initial through-holes in the initial circuit board 1 also include a first positioning hole 15; the temporary bonding films 2 are perforated to obtain spaced-apart second positioning holes 22 and second through-holes 21; the temporary bonding films 2 and the initial circuit board 1 are pressed together, controlling the alignment of the first positioning holes 15 and the second positioning holes 22 during the pressing process, so that the first through-holes 12 and the second through-holes 21 correspond one-to-one and expose the opening of the first through-hole 12. This method of first perforating the temporary bonding films 2 and then pressing them together with the initial circuit board 1 allows the perforation and pressing steps of different temporary bonding films 2 to be performed simultaneously, which is beneficial for improving the fabrication efficiency of printed circuit boards. Specifically, mechanical drilling or laser perforation processes can be used to perforate the temporary bonding films 2, and the difference between the diameter of the second through-hole 21 and the diameter of the first through-hole 12 can be 3mil-5mil.

[0034] In one alternative implementation, refer to Figure 4The process involves bonding a temporary bonding film 2 to two opposing surfaces of an initial circuit board 1, including the following steps: pressing the temporary bonding film 2 and the initial circuit board 1 together; then, based on the position of the first through-hole 12 in the initial circuit board 1, making an initial opening in the temporary bonding film 2 to obtain a second through-hole 21. This method of first pressing the temporary bonding film 2 and the initial circuit board 1 together, and then making an opening in the temporary bonding film 2, can further improve the alignment between the second through-hole 21 in the temporary bonding film 2 and the first through-hole 12 in the initial circuit board 1. Specifically, laser drilling or image transfer can be used to make the opening in the temporary bonding film 2, and the difference between the diameter of the second through-hole 21 and the diameter of the first through-hole 12 can be less than or equal to 2 mil.

[0035] In one alternative embodiment, the temporary bonding film 2 may contain an alkali-resistant polymer base film (not shown). After the temporary bonding film 2 is bonded to the two opposing surfaces of the initial circuit board 1, the alkali-resistant polymer base film is located on the outside to facilitate the subsequent formation of the barrier layer 4 and to facilitate the subsequent debonding of the temporary bonding film 2.

[0036] Furthermore, the temporary bonding film 2 also contains an adhesive layer (not shown) located on the surface of the acid and alkali resistant polymer base film. The adhesive layer has an adhesive state and a debonded state. The temperature of the debonded state can be higher than the temperature of the adhesive state. In the adhesive state, the adhesive layer can be used to bond the alkali resistant polymer base film and the initial circuit board 1. The temperature at which the temporary bonding film 2 and the initial circuit board 1 are pressed together can be determined based on the temperature of the adhesive state, and it is preferred to press together at room temperature.

[0037] Furthermore, the surface of the alkali-resistant polymer base film facing away from the adhesive layer is smooth, which reduces the degree to which the alkali-resistant polymer base film adsorbs impurities in the environment, avoids the introduction of external impurities into the printed circuit board and their adverse effects on the performance of the printed circuit board, and helps to improve the yield of the printed circuit board.

[0038] For example, the temporary bonding membrane 2 can be a resin plugging protective membrane, such as the J31 resin plugging protective membrane from Zhuhai Yixin Materials Technology Co., Ltd.

[0039] Step S3, Reference Figure 6 A thickened metal layer 31 is deposited on the surface of the initial hole metal layer 11, and the thickened metal layer 31 extends to the inner wall of the second through hole 21.

[0040] Specifically, an electroplating process can be used to deposit a thickened metal layer 31. During the electroplating process, the current preferentially concentrates at the corner of the opening of the second through hole 21, so that the metal deposition rate at the opening of the second through hole 21 is higher than the metal deposition rate inside the hole, thus forming a protrusion extending to the inner wall of the second through hole 21. Electroplating can be stopped when the height of the protrusion exceeds the thickness of the temporary bonding film 2.

[0041] In some alternative implementations, refer to Figure 5 The diameter of the second through-hole 21 is larger than that of the first through-hole 12, at which point a portion of the surface of the initial surface metal layer 14 is exposed outside the temporary bonding film 2; Reference Figure 6 During the electroplating process, a thickened metal layer 31 is deposited on the surface of the initial through-hole metal layer 11. Simultaneously, the thickened metal layer 31 is deposited on the surface of the initial surface metal layer 14 exposed outside the temporary bonding film 2, forming a thickened surface metal layer located on a local surface of the initial surface metal layer 14. This thickened surface metal layer is the thickened metal layer 31 located on the inner wall of the second through-hole 21. The initial surface metal layer 14 exposed outside the temporary bonding film 2 can disperse the current at the opening of the first through-hole 12 during the electroplating process, thereby improving the electroplating uniformity in the opening area of ​​the first through-hole 12. At the same time, since the lateral dimension of the thickened surface metal layer on the surface of the initial surface metal layer 14 is larger than the lateral dimension of the aforementioned protrusion, the deposition process of the thickened surface metal layer on the surface of the initial surface metal layer 14 is easier to control compared to the protrusion.

[0042] Because the through-hole capability is different inside the first via 12 and on the surface of the initial circuit board 1, the thickness of the thickened metal layer 31 inside the first via 12 obtained by simultaneous deposition is different from that of the thickened surface metal layer on the surface of the initial circuit board 1. It should be noted that the thickness direction of the thickened metal layer 31 inside the first via 12, the thickness direction of the initial via metal layer 11, and the target thickness direction of the via metal layer are all parallel to the extension direction of the temporary bonding film 2; the thickness direction of the initial surface metal layer 14 and the thickness direction of the thickened surface metal layer are both perpendicular to the extension direction of the temporary bonding film 2.

[0043] Step S4, Reference Figure 7 A patterned barrier layer 4 is formed on the surface of the thickened metal layer 31, exposing the thickened metal layer 31 located on the inner wall of the second through hole 21, that is, exposing one side surface of the thickened surface metal layer.

[0044] In one alternative implementation, refer to Figure 6 The thickness of the thickened metal layer 31 located on the inner wall of the second through-hole 21 is greater than or equal to the thickness of the temporary bonding film 2, so that the outer surface of the thickened metal layer 31 (protrusion or thickened surface metal layer) located on the inner wall of the second through-hole 21 is flush with or extends beyond the outer surface of the temporary bonding film 2; forming a patterned barrier layer 4 on the surface of the thickened metal layer 31 may include: (continued reference) Figure 6 An initial barrier layer 41 is deposited on the surface of the thickened metal layer 31, such that the initial barrier layer 41 on the surface of the thickened metal layer 31 located on the inner wall of the second via 21 extends beyond the outer surface of the temporary bonding film 2; Reference Figure 7The initial circuit board 1 with the initial barrier layer 41 is ground to remove the portion of the overall structure consisting of the thickened metal layer 31 and the initial barrier layer 41 that extends beyond the outer surface of the temporary bonding film 2, thereby exposing the thickened metal layer 31 located on the inner wall of the second through hole 21.

[0045] If the thickness of the thickened metal layer 31 located on the inner wall of the second via 21 is less than the thickness of the temporary bonding film 2, then the initial barrier layer 41 on the surface of the thickened metal layer 31 located on the inner wall of the second via 21 cannot exceed, or cannot fully exceed, the thickness of the temporary bonding film 2. This results in the thickened metal layer 31 located on the inner wall of the second via 21 not being exposed after grinding, and thus the barrier layer 4 cannot be obtained. It can be seen that the thickness of the temporary bonding film 2 directly affects the minimum thickness of the thickened metal layer 31 located on the inner wall of the second via 21, thereby affecting the minimum thickness of the thickened metal layer 31 located in the first via 12. That is, the thickness of the temporary bonding film 2 affects the degree of thickening of the hole metal layer by the thickened metal layer 31 in a single deposition process.

[0046] In one optional embodiment, the thickness of the temporary bonding film 2 can be 1 mil to 2 mil. This thickness range corresponds to the total thickness of the acid- and alkali-resistant polymer base film and the adhesive layer. If the thickness of the temporary bonding film 2 is too large, the thickness of the thickened metal layer 31 located on the inner wall of the second via 21 obtained by a single deposition will be correspondingly too large, resulting in an excessively large thickness of the thickened metal layer 31 within the first via 12 obtained by a single deposition, which is detrimental to controlling the thickness uniformity of the thickened metal layer 31 within the first via 12. If the thickness of the temporary bonding film 2 is too small, it will be difficult for the temporary bonding film 2 to have high strength, and it is prone to damage during the grinding of the initial barrier layer 41 to form the barrier layer 4, affecting its protective function for the initial circuit board 1. By limiting the thickness of the temporary bonding film 2 within the above range, it is easier to ensure the strength of the temporary bonding film 2 and to improve the thickness uniformity of the thickened metal layer 31 within the first via 12.

[0047] In one optional embodiment, both the initial hole metal layer 11 and the thickened metal layer 31 are made of copper, and the barrier layer 4 can be made of tin or a tin-lead alloy. The initial circuit board 1 with the initial barrier layer 41 formed can be polished using non-woven fabric, and the initial barrier layer 41 can be deposited on the surface of the thickened metal layer 31 using an electroplating process. Correspondingly, the acid and alkali resistant polymer base film needs to have high strength to avoid damage during polishing. The initial hole metal layer 11 is the initial hole copper, the initial surface metal layer 14 is the initial surface copper, the thickened surface metal layer located on a local surface of the initial surface metal layer 14 is the thickened surface copper, and the thickened metal layer 31 located within the first through hole 12 is the thickened hole copper.

[0048] Step S5, Reference Figure 8Using the barrier layer 4 as a mask, the thickened metal layer 31 on the inner wall of the second through hole 21 is removed by wet process, that is, the protrusion or thickened surface metal layer is removed.

[0049] Specifically, since the temporary bonding film 2 contains an alkali-resistant polymer base film, an alkaline etching solution can be used to wet remove the thickened metal layer 31 on the inner wall of the second through hole 21, so as to avoid damage to the temporary bonding film 2 during the wet removal process and to provide stable protection for the initial circuit board 1 below the temporary bonding film 2.

[0050] Step S6, Reference Figure 9 Remove the blocking layer 4.

[0051] The barrier layer 4 can be selectively removed using a wet etching process.

[0052] Step S7: Debond the temporary bonded membrane 2.

[0053] Specifically, since the temperature of the adhesive layer in the temporary bonding film 2 in its debonded state is higher than that in its bonded state, the adhesive force of the adhesive layer in the temporary bonding film 2 decreases when the temperature is higher than the pressing temperature. Accordingly, debonding the temporary bonding film 2 can include heating the entire assembly of the temporary bonding film 2 and the initial circuit board 1 to make the adhesive layer debonded, and then peeling off the temporary bonding film 2. By using the aforementioned temporary bonding film 2, debonding can be achieved simply by heating, making the debonding method straightforward.

[0054] After the temporary bonding film 2 is debonded, the initial surface metal layer 14 is exposed, and the composite film layer consisting of the outer base copper foil 13 and the initial surface metal layer 14 can be etched to form an outer circuit layer that is at least connected to the hole metal layer in the first via 12.

[0055] If the target thickness of the via metal layer is large, the difference between the target thickness and the initial thickness of the via metal layer 11 will be significant. This requires a larger thickness for the thickened metal layer 31, which may result in a single deposition of the thickened metal layer 31 failing to achieve the target thickness of the via metal layer. Therefore, in an optional embodiment, the steps of depositing the thickened metal layer, forming a patterned barrier layer on the surface of the thickened metal layer, wet-removing the thickened metal layer from the inner wall of the second via, and removing the barrier layer can be repeated. Steps S3-S6 are used as repeating units until the via metal layer on the inner wall of the initial via reaches the target thickness. Multiple depositions can meet higher target thickness requirements for the via metal layer, offering greater flexibility. The thicknesses of the thickened metal layers deposited multiple times can be the same or different.

[0056] In some alternative implementations, in order for the metal layer on the inner wall of the initial via to reach the target thickness, the thickness of the thickened metal layer on the sidewall of the second via 21 obtained in the last deposition process needs to be greater than the thickness of the temporary bonding film 2. In this case, the above repeating unit can be completely executed.

[0057] In some alternative embodiments, the thickness of the thickened metal layer on the sidewall of the second via 21 obtained in the final deposition process does not need to be greater than the thickness of the temporary bonding film 2 to achieve the target thickness of the hole metal layer on the inner wall of the initial via. Therefore, it is not necessary to completely execute the aforementioned repeating unit. That is, referring to... Figure 10 In response to the last deposited thickened metal layer, the thickness of the thickened metal layer located on the inner wall of the second via 21 is less than or equal to the thickness of the temporary bonding film 2, and the initial barrier layer 41 is no longer formed. Figure 10 A cross-sectional view of the secondary thickened metal layer 32 obtained by secondary deposition is shown. After debonding the temporary bonding film 2, the initial circuit board 1 containing the thickened metal layer is ground to remove the thickened metal layer that exceeds the initial surface metal layer 14, giving the initial circuit board 1 a flat surface. It should be noted that although the last deposited thickened metal layer protrudes from the surface of the initial circuit board 1 after debonding the temporary bonding film 2, the thickness of the last deposited thickened metal layer on the sidewall of the second via 21 does not exceed that of the temporary bonding film 2, and the thickness of the temporary bonding film 2 is relatively small. Therefore, the degree of protrusion of the thickened metal layer is much smaller than that of the bumps obtained by conventional via copper plating. Thus, the grinding degree of the protruding thickened metal layer is much smaller than that of the bumps obtained by conventional via copper plating. During the grinding process, the printed circuit board does not need to be subjected to continuous force for a long time, thus effectively reducing the probability of copper lifting and via blockage on the printed circuit board. At the same time, the back drill misalignment caused by the low degree of protrusion of the thickened metal layer is also very small and can be ignored. That is, although the thickened metal layer deposited in the last step protrudes from the surface of the initial circuit board 1, the low degree of protrusion of the thickened metal layer can still reduce the adverse effects of the presence of bumps on the quality of the printed circuit board, thereby improving the yield of the printed circuit board.

[0058] In an optional embodiment, the ratio of the thickness of the thickened metal layer located on the sidewall of the second via 21 to the thickness of the temporary bonding film 2 in the thickened metal layer obtained in a single deposition process can be 1.2-1.7. By limiting the ratio of the thickness of the thickened metal layer located on the sidewall of the second via 21 to the thickness of the temporary bonding film 2 obtained in a single deposition to the above range, not only can the single deposition thickness of the thickened metal layer located on the inner wall of the second via 21 be greater than the thickness of the temporary bonding film 2, thereby obtaining the barrier layer 4 through grinding, but it can also avoid the single deposition thickness of the thickened metal layer in the first via 12 being too large, resulting in poor thickness uniformity of the thickened metal layer in the first via 12, which is beneficial to improving the thickness uniformity of the thickened metal layer in the first via 12. The above ratio can be the same or different in multiple deposition processes.

[0059] In one optional embodiment, the number of depositions of the thickened metal layer can be determined as follows: Number of depositions of the thickened metal layer = (Target thickness of the hole metal layer - Initial thickness of the hole metal layer) / (Through-hole capability coefficient × Coefficient × Single deposition thickness of the thickened metal layer located on the sidewall of the second via), where the number of depositions of the thickened metal layer is rounded up. The above coefficient is mainly determined based on the current efficiency and uniformity of the electroplating production line to correct the actual electroplating process. The specific coefficient can be determined based on the electroplating production line. For example, the target thickness of the hole metal layer is 2 mil, the initial thickness of the hole metal layer is 0.7 mil, the through-hole capability coefficient is 75%, the coefficient is 80%, the thickness of the temporary bonding film is 1 mil, the ratio of the single deposition thickness of the thickened metal layer located on the sidewall of the second via to the thickness of the temporary bonding film is 1.5, and the number of depositions of the thickened metal layer = (2 - 0.7) / (75% × 80% × 1 × 1.5) = 1.44 ≈ 2.

[0060] In one alternative implementation, refer to Figures 2-3 The initial through-hole also includes a third through-hole 16; Reference Figure 5 After temporary bonding films 2 are attached to the two opposing surfaces of the initial circuit board 1, the temporary bonding films 2 cover the opening of the third through hole 16; the method for fabricating the printed circuit board also includes: referring to Figure 11 After the metal layer on the inner wall of the initial through-hole reaches the target thickness, the temporary bonding film 2 is opened a second time to obtain the fourth through-hole 23 corresponding to the third through-hole 16; Reference Figure 12 Liquid plugging resin is filled into the third through hole 16 and the fourth through hole 23, and the liquid plugging resin is cured to obtain solid resin 5; Reference Figure 13 Debonding of temporary bonded membrane 2; Reference Figure 14 The surface of the initial circuit board 1 is ground to remove the solid resin 5 in the fourth through hole 23, so that the initial circuit board 1 has a flat surface to form a cap electroplating hole at the third through hole 16.

[0061] The above-described fabrication method requires only one drilling operation to simultaneously form multiple types of initial vias, such as the first via 12 and the third via 16, in the initial circuit board 1, without the need for a secondary drilling operation for the third via 16. This reduces the process flow and improves the fabrication efficiency of the printed circuit board. Furthermore, this method effectively reduces the spacing between initial vias; the spacing between the third via 16 (which requires resin plugging) and other initial vias (which do not require plugging) can reach 5 mil-10 mil, effectively increasing the vertical wiring density and processing capability of the printed circuit board. In addition, because this method reduces the adverse effects of bumps on the quality of the printed circuit board and allows for precise control of the thickness of the surface metal layer (including the outer base copper foil 13 and the initial surface metal layer 14), the resin plugging process becomes more stable, improving resin plugging yield and thus increasing the overall yield of the printed circuit board.

[0062] The presence of the temporary bonding film 2 enables selective thickening of the hole metal layer. Since the openings of other initial vias (such as the third via 16) in the initial circuit board 1, except for the first via 12, are covered by the temporary bonding film 2, the thickened metal layer 31 will not be deposited in these initial vias and will remain at a normal thickness. Only the hole metal layer in the first via 12, which is not covered by the temporary bonding film 2 and requires high current carrying capacity, is controllably thickened. The above method can meet the high power supply requirements and avoid the cost waste caused by thickening the metal layer of the entire printed circuit board.

[0063] Specifically, liquid plugging resin can be injected and leveled sequentially to fill the third through hole 16 and the fourth through hole 23 with liquid plugging resin, so that the height of the liquid plugging resin does not exceed the temporary bonding film 2; the liquid plugging resin can be cured by baking.

[0064] It should be noted that the reference Figure 5 The initial through hole may also include a fifth through hole 17, which is used to form other structures besides the flow through hole and the cap electroplating hole.

[0065] The preparation method of this application has a simple process flow and is easy to implement. In addition, this application utilizes conventional electroplating, etching and grinding equipment, which does not require high equipment investment and is easy to promote and implement on existing production lines.

[0066] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0067] In the description of this specification, references to terms such as "some embodiments" and "optional implementations" indicate that a 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 descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0068] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for manufacturing a printed circuit board, characterized in that, include: An initial circuit board is formed, the initial circuit board having an initial through hole penetrating the initial circuit board and an initial hole metal layer located on the inner wall of the initial through hole, the initial through hole including a first through hole; Temporary bonding films are attached to two surfaces of the initial circuit board that are opposite to each other. The second through-holes in the temporary bonding films correspond one-to-one with the first through-holes and expose the openings of the first through-holes. A thickened metal layer is deposited on the surface of the initial hole metal layer, and the thickened metal layer extends to the inner wall of the second through hole; A patterned barrier layer is formed on the surface of the thickened metal layer, exposing the thickened metal layer located on the inner wall of the second through hole; Using the barrier layer as a mask, the thickened metal layer on the inner wall of the second through hole is removed by wet process; Remove the barrier layer; The temporary bonded membrane is then debonded.

2. The preparation method according to claim 1, characterized in that, The formation of a patterned barrier layer on the surface of the thickened metal layer includes: The thickness of the thickened metal layer located on the inner wall of the second through hole is greater than or equal to the thickness of the temporary bonding film, and an initial barrier layer is deposited on the surface of the thickened metal layer; The initial circuit board with the initial barrier layer is ground to remove the portion of the overall structure consisting of the thickened metal layer and the initial barrier layer that extends beyond the temporary bonding film.

3. The preparation method according to claim 2, characterized in that, The barrier layer is made of tin or a tin-lead alloy, and the initial hole metal layer and the thickened metal layer are both made of copper. An initial barrier layer is deposited on the surface of the thickened metal layer using an electroplating process; and / or, the barrier layer is selectively removed using a wet etching process.

4. The preparation method according to claim 1, characterized in that, The temporary bonding film contains an alkali-resistant polymer base film, and after the temporary bonding film is attached to the two surfaces opposite to each other on the initial circuit board, the alkali-resistant polymer base film is located on the outer side. The thickened metal layer on the inner wall of the second through hole is removed by a wet etching solution using an alkaline etching solution.

5. The preparation method according to claim 4, characterized in that, The temporary bonding film also contains an adhesive layer on the surface of the acid and alkali resistant polymer base film. The adhesive layer has an adhesive state and a debonded state. The temperature of the debonded state is higher than the temperature of the adhesive state. In the adhesive state, the adhesive layer bonds the alkali resistant polymer base film and the initial circuit board. The step of debonding the temporary bonding film includes: heating the entire assembly of the temporary bonding film and the initial circuit board to make the adhesive layer detach, and peeling off the temporary bonding film.

6. The preparation method according to claim 1, characterized in that, The diameter of the second through hole is larger than the diameter of the first through hole.

7. The preparation method according to claim 1, characterized in that, The temporary bonding film is attached to the two surfaces opposite each other on the initial circuit board, including: The initial through-hole further includes a first positioning hole; the temporary bonding film is perforated to obtain a second positioning hole and a second through-hole; the temporary bonding film and the initial circuit board are pressed together to align the first positioning hole and the second positioning hole; Alternatively, the temporary bonding film and the initial circuit board are pressed together, and then the temporary bonding film is first opened based on the position of the first through hole to obtain the second through hole.

8. The preparation method according to claim 1, characterized in that, Repeat the steps of depositing a thickened metal layer, forming a patterned barrier layer on the surface of the thickened metal layer, wet-removing the thickened metal layer from the inner wall of the second via, and removing the barrier layer, until the total thickness of the hole metal layer on the inner wall of the initial via reaches the target thickness.

9. The preparation method according to claim 8, characterized in that, The deposition number of the thickened metal layer = (target thickness of the hole metal layer - initial thickness of the hole metal layer) / (penetration capability coefficient × coefficient × thickness of the thickened metal layer located on the sidewall of the second through hole in the thickened metal layer obtained in a single deposition process), and the deposition number of the thickened metal layer is taken in decimal rounding manner; And / or, in the thickened metal layer obtained by the single deposition process, the ratio of the thickness of the thickened metal layer located on the sidewall of the second via to the thickness of the temporary bonding film is 1.2-1.

7.

10. The preparation method according to any one of claims 1 to 9, characterized in that, The initial through-hole further includes a third through-hole; after a temporary bonding film is attached to the two opposing surfaces of the initial circuit board, the temporary bonding film covers the opening of the third through-hole; the preparation method further includes: After the total thickness of the metal layer in the inner wall of the initial through hole reaches the target thickness, the temporary bonding film is opened a second time to obtain a fourth through hole corresponding to the third through hole; Liquid plugging resin is filled into the third and fourth through holes, and the liquid plugging resin is cured to obtain a solid resin; After the temporary bonding film is debonded, the surface of the initial circuit board is ground to remove the solid resin from the fourth through hole.

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