Manufacturing method of printed circuit board

Abstract

The invention discloses a manufacturing method of a printed circuit board, and the method comprises the steps: providing N core boards, and preparing an expansion material at a via hole region of each core board; laminating the N core boards to form a multi-layer board; drilling holes in the positions, corresponding to the expansion materials, of the multi-layer board to form via holes; copper is deposited in the via hole, so that hole copper is formed on the inner wall of the via hole; the multilayer board is heated, and pressure is applied to the multilayer board in the extending direction of the via hole; and removing the expansion material. By adopting the method, the ideal condition of zero stub can be realized, reflection and resonance in the signal transmission process are reduced, and the integrity of signal transmission is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of printed circuit boards, and in particular, to a method for manufacturing a printed circuit board. Background Art

[0002] In related technologies, the hole copper, i.e., the stub, which has no connection and no transmission function, is drilled off by back drilling. However, due to the influence of the change in the medium thickness and the drilling depth control ability, the ideal situation of zero stub cannot be achieved by back drilling. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, an object of the present invention is to provide a method for manufacturing a printed circuit board. By using this method, the ideal situation of zero stub can be achieved, the reflection and resonance during the signal transmission can be reduced, and the integrity of the signal transmission can be improved.

[0004] To solve the above problems, an embodiment of the first aspect of the present invention provides a method for manufacturing a printed circuit board. The method includes: providing N core boards, and preparing expansion materials at the via regions on each core board; laminating the N core boards to form a multilayer board; drilling holes at positions corresponding to the expansion materials on the multilayer board to form vias; depositing copper in the vias so that a hole copper is formed on the inner wall of the vias; heating the multilayer board and applying pressure to the multilayer board along the extending direction of the vias; and removing the expansion materials.

[0005] According to the method for manufacturing a printed circuit board of the embodiment of the present invention, based on the characteristic that the expansion material expands when heated, before forming the hole copper on the inner wall of the via of the multilayer board, the expansion materials are prepared at the via regions on each core board in the multilayer board, and then by using the characteristic that the expansion material expands when heated, the hole copper at the position of the expansion material is broken, so that when the expansion material is removed, the remaining copper on the surface of the expansion material is also removed, which is convenient for subsequent removal of the hole copper between non-interconnecting layers, thereby achieving zero stub. Thus, compared with the method of removing the stub by back drilling in the prior art, in the present application, the hole copper between non-interconnecting layers is disconnected by the heat expansion of the expansion material, which is convenient for subsequent removal of the hole copper between non-interconnecting layers, thereby achieving the ideal situation of zero stub, reducing the reflection and resonance during the signal transmission, and improving the integrity of the signal transmission.

[0006] In some embodiments, laminating the N core boards to form a multilayer board includes: providing prepregs; making slots on the prepregs, wherein the positions of the slots match the positions of the expansion materials; and laminating the N core boards through the separation of the prepregs to form a multilayer board.

[0007] In some embodiments, removing the expansion materials includes: performing ultrasonic degreasing on the multilayer board to remove the expansion materials.

[0008] In some embodiments, the ultrasonic power range for ultrasonic stripping is 4 A to 5 A, and the liquid used during ultrasonic stripping is a strongly alkaline liquid.

[0009] In some embodiments, the strongly alkaline liquid is a NaOH solution, the concentration of the NaOH solution is 180 g / L to 200 g / L, and the cleaning temperature range of the NaOH solution is 75 °C to 95 °C.

[0010] In some embodiments, after removing the swelling material, the method further includes: performing flash plating on the multilayer board; performing micro-etching on the multilayer board to remove the hole copper at the prepreg; performing electroplating on the multilayer board.

[0011] In some embodiments, performing micro-etching on the multilayer board includes: performing micro-etching on the multilayer board using sulfuric acid, and the concentration of the sulfuric acid is 30 g / L to 80 g / L.

[0012] In some embodiments, the swelling material is ink or swelling resin, and the thickness range of the swelling material is 100 μm to 200 μm.

[0013] In some embodiments, drilling holes to form vias at positions on the multilayer board corresponding to the swelling material includes: drilling holes to form vias at positions on the outer surface of the multilayer board corresponding to the center position of the swelling material, wherein the diameter of the swelling material in the direction perpendicular to the via is greater than the diameter of the via.

[0014] In some embodiments, the heating temperature range during heating of the multilayer board is 250 °C to 300 °C.

[0015] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, wherein: Figure 1 is a flowchart of a method for manufacturing a printed circuit board according to an embodiment of the present invention; Figure 2 is a schematic diagram of a core board according to an embodiment of the present invention; Figure 3 is a schematic diagram of a printed circuit board process according to an embodiment of the present invention; Figure 4Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 5 Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 6 Schematic diagram of ultrasonic treatment of a multilayer board according to an embodiment of the present invention; Figure 7 Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 8 Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 9 Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 10 Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 11 Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 12 Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 13 Schematic diagram of a printed circuit board manufacturing process according to another embodiment of the present invention; Figure 14 Flow chart of a method for manufacturing a printed circuit board according to another embodiment of the present invention.

[0017] Reference numerals: Core board 1; via area 2; swelling material 3; multilayer board 4; via 5; hole copper 6; prepreg 7. Detailed description of the embodiments

[0018] The embodiments of the present invention will be described in detail below. The embodiments described with reference to the drawings are exemplary. The embodiments of the present invention will be described in detail below.

[0019] To solve the above problems, a first aspect embodiment of the present invention provides a method for manufacturing a printed circuit board. Using this method, an ideal situation of zero stubs can be achieved, reflections and resonances during signal transmission can be reduced, and the integrity of signal transmission can be improved.

[0020] The following refers to Figure 1 to describe the method for manufacturing a printed circuit board according to an embodiment of the present invention. As Figure 1 shown, the method includes: step S1 to step S6.

[0021] Step S1, provide N core boards, and prepare swelling material at the via area on each core board.

[0022] Among them, the core board 1 is as Figure 2 shown. The via area 2 is the area where vias are to be fabricated on the core board 1. The via area 2 is as Figure 3 shown. The via area 2 can be within the image area.

[0023] Specifically, provide N core boards 1, and prepare an expansion material 3 at the via area 2 on each core board 1. Preparing the expansion material 3 at the via area 2 is as Figure 4 shown.

[0024] Step S2, laminate the N core boards to form a multilayer board.

[0025] Specifically, laminate the N core boards to form a multilayer board. For example, press the N core boards together through high temperature and high pressure to form a multilayer board.

[0026] Step S3, drill holes at positions corresponding to the expansion material on the multilayer board to form vias.

[0027] Among them, the via is also called a metallized hole, which is a printed wire connecting between layers in the multilayer board. Drill a common hole at the intersection of the wires that need to be connected between layers. This common hole is the via, and the number of vias is not limited.

[0028] Step S4, deposit copper in the vias so that a hole copper is formed on the inner wall of the vias.

[0029] Exemplarily, deposit a thin layer of copper on the inner wall of the vias through chemical copper deposition so that a hole copper is formed on the inner wall of the vias.

[0030] Step S5, heat the multilayer board and apply pressure to the multilayer board along the extension direction of the vias.

[0031] Specifically, heat the multilayer board so that the expansion material expands when heated. During the expansion process of the expansion material, apply pressure to the multilayer board along the extension direction of the vias, thereby ensuring that the expansion material expands along the extension direction of the vias, that is, ensuring that the expansion material does not expand along the direction parallel to the vias, and further avoiding the quality risk of the board bulging.

[0032] Step S6, remove the expansion material.

[0033] In an embodiment, in the high-frequency range, during the signal transmission process, where the signal arrives, an instantaneous current will be generated between the signal line and the reference plane (power supply or ground plane) due to the establishment of an electric field. If the transmission line is isotropic, then as long as the signal is being transmitted, there will always be a current I. And if the output voltage of the signal is V, during the signal transmission process, the transmission line will be equivalent to a resistor with a magnitude of V / I. This equivalent resistor is called the characteristic impedance Z of the transmission line. During the signal transmission process, if the characteristic impedance on the transmission path changes, the signal will generate reflections and resonances at the nodes with impedance discontinuities.

[0034] Specifically, since not all layers need to be interconnected in the multilayer board design, and during the process of fabricating vias, there are redundant copper pillars between non-interconnected layers, that is, there are redundant copper pillars in the via copper formed on the inner wall of the via. These copper pillars are called stubs, and during the via processing, the stubs will cause impedance discontinuities, thereby generating effects such as signal reflections and resonances. As the frequency increases, the impact of the stubs on the signal transmission integrity also increases. Therefore, controlling the stub length can reduce the adverse effects of the stubs on the signal. In order to achieve zero stubs, in this application, before forming the via copper on the inner wall of the via, an expansion material is prepared at the via area on each core board, and then through the heat expansion characteristics of the expansion material, the expansion material is made to expand along the extension direction of the via, so that the via copper at the position of the expansion material breaks. Thus, while removing the expansion material, the redundant copper on the surface of the expansion material is removed to disconnect the electrical connection of the via copper at the position of the expansion material, facilitating the subsequent removal of the via copper between non-interconnected layers, thereby achieving zero stubs. Compared with the method of removing stubs by back drilling in the prior art, in this application, the via copper between non-interconnected layers is disconnected through the heat expansion characteristics of the expansion material, facilitating the subsequent removal of the via copper between non-interconnected layers, and the remaining length of the stubs can be reduced to zero, achieving the ideal situation of zero stubs, thereby reducing reflections and resonances during the signal transmission process and improving the integrity of signal transmission. In addition, the manufacturing method of the printed circuit board in this application is applicable to printed circuit board products with a transmission speed of 112G and higher.

[0035] The manufacturing method of a printed circuit board according to an embodiment of the present invention is based on the characteristic that an expansion material expands when heated. Before forming hole copper on the inner wall of a via in a multilayer board, an expansion material is prepared at the via area on each core board in the multilayer board. Then, by using the characteristic that the expansion material expands when heated, the hole copper at the position of the expansion material is broken, so as to remove the remaining copper on the surface of the expansion material while removing the expansion material, facilitating the subsequent removal of the hole copper between non-interconnecting layers, thereby achieving zero stubs. Thus, compared with the method of removing stubs by back drilling in the prior art, in this application, the hole copper between non-interconnecting layers is disconnected by the thermal expansion of the expansion material, facilitating the subsequent removal of the hole copper between non-interconnecting layers, thereby achieving the ideal situation of zero stubs, reducing reflection and resonance during signal transmission, and improving the integrity of signal transmission.

[0036] In some embodiments, laminating N core boards 1 to form a multilayer board 4 includes: as Figure 5 shown, providing a prepreg 7; making slots on the prepreg 7, wherein the positions of the slots match the positions of the expansion material 3; separating by the prepreg 7, and performing board lamination on the N core boards 1 to form a multilayer board 4, and the multilayer board 4 is formed by laminating the N core boards 1 and the prepreg 7 with each other.

[0037] In an embodiment, a gap of 0.25 mm is reserved between the left, right, and upper directions of the prepreg slots and the expansion material.

[0038] In some embodiments, removing the expansion material includes: performing ultrasonic degreasing on the multilayer board to remove the expansion material. Specifically, in this application, the ultrasonic degreasing method is used to degrease the expansion material. That is, as Figure 6 shown, when using an ultrasonic generator 8 to perform ultrasonic treatment on the multilayer board 4, the multilayer board 4 is perpendicular to the ground, that is, the via 5 is parallel to the ground, so as to better degrease the expansion material, and the ultrasonic transmitters are placed on both sides of the multilayer board 4. When the thickness of the multilayer board 4 is less than 2.4 mm, the ultrasonic treatment time for the multilayer board 4 is 1 min of unilateral ultrasonic treatment (minute), and after 1 min, the multilayer board 4 is inverted and ultrasonic treatment is continued for 1 min, so as to avoid the problem that the expansion material on one side is not degreased cleanly.

[0039] In some embodiments, the ultrasonic power range of ultrasonic degreasing is 4 A to 5 A. Among them, the ultrasonic power can be 4 A, 4.5 A, 5 A, etc., and there is no limitation in this regard. The liquid used during ultrasonic degreasing is a strongly alkaline liquid. That is, when performing ultrasonic degreasing on the multilayer board, a strongly alkaline liquid is used to dissolve the expansion material, so as to take away the hole copper at the position of the expansion material, and disconnect the connection between the circuit at this position and the circuit at the core board position. Since the strongly alkaline liquid has strong dissolution and corrosion capabilities, it can effectively dissolve the expansion material.

[0040] In some embodiments, the strongly alkaline liquid is a NaOH solution, the concentration of the NaOH solution is 180 g / L to 200 g / L, the concentration of the NaOH solution can be 180 g / L, 190 g / L, 200 g / L, etc., and there is no limitation thereto. The cleaning temperature range of the NaOH solution is 75°C to 95°C, and the cleaning temperature range can be 75°C, 80°C, 90°C, or 95°C.

[0041] In some embodiments, after removing the swelling material, the multilayer board is subjected to flash plating to thicken the thickness of the hole copper formed on the inner wall of the via, and then the multilayer board is subjected to micro-etching to remove the hole copper at the prepreg, that is, the thin copper between the positions of the swelling material is etched away, so that the disconnection distance of the hole copper at the positions of the swelling material is enlarged, so that the electrical connection between the positions of the swelling material is completely disconnected. Then, the multilayer board is subjected to electroplating to thicken the thickness of the hole copper at the core board in the multilayer board.

[0042] In addition, it should be noted that since the multilayer board is ultrasonically rinsed to disconnect the electrical connection between the circuit at the position of the swelling material and the hole copper at the core board position, during the electroplating process of the multilayer board, the hole copper at this position will not have a large thickness change and remains thin copper, while the hole copper thickness at other positions thickens during the electroplating process.

[0043] In the embodiment, according to Figures 2 - 13 the manufacturing method of the printed circuit board in the present application is described, which specifically includes the following content: First, provide Figure 2 the core board 1 shown in the figure. The core board 1 is cut and the pattern is transferred. The core board 1 after pattern transfer is as Figure 3 shown in the figure; the swelling material 3 is prepared at the via area 2 on each core board 1. The prepared swelling material 3 is as Figure 4 shown in the figure, as Figure 5 shown in the figure. Slots are made on the prepreg 7, and N core boards 1 are assembled and laminated to form a multilayer board 4. The formed multilayer board 4 is as Figure 7 shown in the figure. The positions on the multilayer board 4 corresponding to the swelling material 3, that is, Figure 7 the dotted box area, are drilled to form vias 5. The vias 5 are as Figure 8 shown in the figure; copper is deposited in the vias 5 so that hole copper 6 is formed on the inner wall of the vias 5. The multilayer board 4 is heated, and pressure is applied to the multilayer board 4 along the extending direction of the vias 5, so that the swelling material 3 expands along the extending direction of the vias 5 when heated, so as to push out and break the copper deposition layer on the surface of the swelling material 3. As Figure 9 shown in the figure, a part of the swelling material 3 is exposed. The multilayer board 4 is ultrasonically rinsed to remove the swelling material 3. As Figure 10 shown in the figure is the hole copper after removing the swelling material 3. The multilayer board 4 is subjected to flash plating, as Figure 11The figure shows a schematic diagram after the inner wall of the thickened via 5 forms the via copper 6. Then, the multi-layer board 4 is subjected to micro-etching to remove the via copper 6 at the prepreg 7. After removing the via copper 6 at the prepreg 7, as Figure 12 shown, the multi-layer board 4 is subjected to electroplating treatment. Figure 13 The figure shows a schematic diagram of thickening the via copper 6.

[0044] In some embodiments, the micro-etching of the multi-layer board includes: micro-etching the multi-layer board with sulfuric acid. That is to say, micro-etching the multi-layer board with sulfuric acid to etch away the thin copper between the positions of the swelling material, so as to expand the disconnection distance of the via copper at the positions of the swelling material, thereby completely disconnecting the electrical connection between the positions of the swelling material, while the thickness of other electroplated and thickened copper layers changes little. The concentration of sulfuric acid is 30 g / L to 80 g / L, and the concentration of sulfuric acid can be 30 g / L, 40 g / L, 50 g / L, 70 g / L or 80 g / L.

[0045] In an embodiment, vias are formed in the multi-layer board. The via includes a first hole section penetrating through N core boards, a second hole section penetrating through the solder mask, and a third hole section penetrating through the prepreg. The multi-layer board is pressurized and heated so that the solder mask expands due to heat and ejects the surface of the second hole section, so as to disconnect the connection between the via copper of the second hole section and the via copper of the second hole section and the third hole section. Then, the via copper on the inner wall of the second hole section is removed by micro-etching. Thus, the ideal situation of zero stubs is achieved.

[0046] In addition, when the multi-layer board is subjected to electroplating treatment, the thickness of the via copper in the first hole section and the third hole section increases, while the thickness of the via copper in the first hole section and the third hole section changes little during the micro-etching process.

[0047] In some embodiments, the swelling material is solder mask or swelling resin. The solder mask can be a high-temperature swelling solder mask. The solder mask is a customized solder mask, which has the characteristics of not being easy to deposit copper, and the surface copper layer is sparse and not dense after copper deposition, and it will expand when heated and is extremely easy to be washed off by a strong alkaline solution. The thickness value range of the swelling material is 100μm to 200μm, and the thickness value of the swelling material can be 100μm, 150μm, 190μm or 200μm. The thickness of the solder mask is 30 - 60μm, preferably 40μm.

[0048] In an embodiment, the solder mask process can use the spraying or screen printing method.

[0049] In some embodiments, holes are drilled at positions corresponding to the expansion material on the multilayer board to form vias, including: drilling holes at positions on the outer surface of the multilayer board corresponding to the center position of the expansion material to form vias, so as to ensure that the expansion material can expand thermally, push out and break the electroless copper layer on the surface of the expansion material, and expose a part of the expansion material, prompting the expansion material to be stripped and the electroless copper layer on the surface of the expansion material to be removed. Among them, the diameter of the expansion material in the direction perpendicular to the via is greater than the diameter of the via, so that the via is located within the expansion material.

[0050] In an embodiment, the diameter of the expansion material in the direction perpendicular to the via is equal to the diameter of the via plus 150 μm to 200 μm. That is to say, since there are deviations in the equipment during drilling, which will cause the position of the via to shift, the diameter of the expansion material in the direction perpendicular to the via needs to be greater than the diameter of the via.

[0051] In some embodiments, the heating temperature range during heating of the multilayer board is 250 °C to 300 °C, and the heating temperature can be 250 °C, 260 °C, 270 °C, 280 °C, 290 °C or 300 °C. Under this temperature treatment, the inner layer ink of the board expands when heated, pushes out and breaks the sparse electroless copper layer on the surface, exposes a part of the ink, and prompts the ink to be stripped and the electroless copper layer on the surface of the ink to be taken away.

[0052] In some embodiments, the pressure applied during pressing of the multilayer board is the same as that of the panel lamination.

[0053] The following refers to Figure 14 shown to illustrate the manufacturing method of the printed circuit board according to the embodiment of the present invention, and the specific content is as follows.

[0054] Step S7, cut the core board and perform pattern transfer.

[0055] Step S8, prepare the expansion material at the via area on the core board.

[0056] Step S9, slot the prepreg, and the position of the slot matches the position of the expansion material.

[0057] Step S10, perform panel lamination on N core boards to form a multilayer board.

[0058] Step S11, drill holes at positions on the multilayer board corresponding to the expansion material.

[0059] Step S12, deposit copper in the via so that the inner wall of the via forms hole copper.

[0060] Step S13, heat the multilayer board and apply pressure to the multilayer board along the extension direction of the via.

[0061] Step S14: ultrasonically degrease the multilayer board.

[0062] Step S15: perform flash plating on the multilayer board to thicken the thickness of the hole copper formed on the inner wall of the via.

[0063] Step S16: micro-etch the multilayer board to remove the hole copper at the prepreg.

[0064] Step S17: perform electroplating on the multilayer board to thicken the thickness of the hole copper at the core board in the multilayer board.

[0065] In summary, in the present application, by utilizing the characteristic that the expansion material expands when heated, the expansion material can expand along the extension direction of the via when heated. Then, combined with the degreasing process of the expansion material, the remaining copper at the position of the expansion material is removed, so that the electrical connection between the positions of the expansion material is completely broken, facilitating the subsequent removal of the hole copper between non-interconnecting layers, thus achieving the ideal situation of zero residual stubs, reducing reflection and resonance during signal transmission, and improving the integrity of signal transmission.

[0066] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example.

[0067] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for manufacturing a printed circuit board, characterized in that: The method comprises: Providing N core boards, and preparing expansion material at a via region on each core board; Laminating N core boards to form a multilayer board; Drilling holes at positions on the multilayer board corresponding to the expansion material to form vias; Depositing copper in the via hole so that copper is formed on the inner wall of the via hole; heating the multilayer board and applying pressure to the multilayer board along the extending direction of the via hole; The expanded material is removed.

2. The method for manufacturing a printed circuit board according to claim 1, characterized in that: N core boards are laminated to form a multilayer board, including: Provide prepreg; Making grooves on the prepreg, wherein the positions of the grooves match the positions of the expansion materials; The N core boards are separated by the prepreg sheets and laminated to form a multilayer board.

3. The method for manufacturing a printed circuit board according to claim 1, characterized in that: Removing the expansion material comprises: The multilayer board is subjected to ultrasonic stripping to remove the expansion material.

4. The method for manufacturing a printed circuit board according to claim 3, characterized in that: The ultrasonic power range of ultrasonic fading is 4A~5A, and the liquid used in ultrasonic fading is a strong alkaline liquid.

5. The method for manufacturing a printed circuit board according to claim 4, characterized in that: The strong alkaline liquid is a NaOH solution, the concentration of the NaOH solution is 180 g / L to 200 g / L, and the cleaning temperature range of the NaOH solution is 75° C. to 95° C.

6. The method for manufacturing a printed circuit board according to any one of claims 2 to 5, characterized in that: After removing the expansion material, the method further comprises: Performing flash plating on the multilayer board; Micro-etching the multilayer board to remove the hole copper at the prepreg; The multilayer board is electroplated.

7. The method for manufacturing a printed circuit board according to claim 6, characterized in that: Micro-etching the multilayer board comprises: The multilayer board is micro-etched with sulfuric acid, and the concentration of the sulfuric acid is 30 g / L to 80 g / L.

8. The method for manufacturing a printed circuit board according to claim 1, characterized in that: The expansion material is ink or expansion resin, and the thickness of the expansion material ranges from 100 μm to 200 μm.

9. The method for manufacturing a printed circuit board according to claim 1, characterized in that: Drilling holes at positions corresponding to the expansion material on the multilayer board to form vias comprises: A via hole is formed by drilling at a position on the outer surface of the multilayer board corresponding to the center position of the expansion material, wherein a diameter of the expansion material in a direction perpendicular to the via hole is larger than a diameter of the via hole.

10. The method for manufacturing a printed circuit board according to claim 1, characterized in that: The heating temperature range when heating the multilayer board is 250° C. to 300° C.

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