Method for manufacturing circuit board of multi-layer board
By punching blind holes on the multi-layer board and electroplating copper, combining vacuum film and metallization process, the problems of height difference and step are solved, and high-quality production of fine lines is achieved.
Patent Information
- Application Number
- CN202411182167.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-27
- Publication Date
- 2024-12-20
AI Technical Summary
In the prior art, when making fine lines, the height difference and step problems lead to imperfect film or bubbles, and the high analytical dry film thickness cannot meet the requirements of fine lines.
By punching blind holes of preset depths on the front and back of the multilayer board, and electroplating copper at the blind holes, forming steps, then removing the dry film of the first thickness, and then applying the dry film of the second thickness in vacuum, Optimize the filming method and process parameters of dry film, use a vacuum film sticker to cover the dry film, and metallize after removing residual colloids in the blind holes.
The height difference of steps is reduced, the thickness of the dry film is reduced, the film is not solid or bubbled, and the production quality of fine lines is ensured.
Smart Images
Figure CN119172930A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of circuit board printing technology, and in particular to a method for manufacturing a multilayer circuit board. Background Art
[0002] In the printed circuit board industry, the most commonly used method for making graphic circuits is the subtractive method. The subtractive method (also known as the DES process or the Tenting process in the industry) is generally used for circuits with a line width and spacing of 40 / 40um and above. However, as consumer electronic terminals continue to develop towards being lighter, thinner, shorter, and smaller, the internal space layout of the terminals is becoming increasingly stringent, and the requirements for precision circuits are also becoming higher and higher. Therefore, subtractive process innovation technology is needed to explore the production methods of more sophisticated circuits and produce graphic circuits with a line width and spacing of 35 / 35um, 30 / 30um or more sophisticated. In order to obtain good ductility and bending properties, multi-layer soft boards or soft-rigid boards often use rolled copper or high-ductility rolled copper as the base copper.
[0003] Under the existing technology, a rolled copper substrate is used in combination with a hole copper electroplating process. The circuits of the multilayer board need to overcome the height difference of the inner layer graphics after lamination (generally between 4 and 14um), as well as the steps at the blind holes and through holes after hole copper electroplating (usually more than 25um). Because high-resolution dry films must be used to make fine circuits, and high-resolution dry films are usually 15-25um thick. After the film is applied at the height difference position, poor adhesion and bubbles are likely to occur, and open circuits or broken wires will be formed after etching. At the same time, in order to meet the height difference filling situation, thicker dry films are often selected, but the resolution ability of thick dry films is insufficient and cannot meet the production requirements of fine circuits. Summary of the invention
[0004] The present application provides a method for manufacturing a circuit board of a multilayer board, which can reduce the height difference of steps and overcome the problem of inaccurate film pasting or film bubbles caused by the height difference of steps.
[0005] The present application provides a method for manufacturing a multilayer circuit board, comprising:
[0006] Provide a multi-layer board; punch blind holes of preset depth on the front and back sides of the multi-layer board;
[0007] A dry film of the first thickness is plated on the front and back sides of the multilayer board respectively;
[0008] The dry film of the first thickness does not cover the blind hole and a preset area outside the blind hole;
[0009] Electroplating copper at the locations of two blind holes in the multilayer board to form a step; and removing the dry film of the first thickness;
[0010] The sum of the bottom area of the blind hole and the preset area is taken as the exposed area; the ratio of the exposed area to the single-side surface area of the multilayer board is equal to 17%, and the thickness of the step above the board surface of the multilayer board is less than 15 microns;
[0011] Vacuum laminating a dry film of the second thickness on the front and back sides of the multilayer board respectively;
[0012] Circuit patterns are formed on the front and back sides of the multilayer board respectively, and the dry film of the second thickness is removed.
[0013] Furthermore, the method also includes:
[0014] After the blind hole is drilled, the residual colloid in the blind hole is removed by plasma cleaning.
[0015] Furthermore, the preset depth is the depth of the three-layer board; the positions of the blind holes on the front side and the blind holes on the back side do not correspond.
[0016] Furthermore, the above-mentioned method of punching blind holes of preset depths on the front and back sides of the multilayer board includes:
[0017] UV laser ablation is used to create blind holes of a preset depth.
[0018] Further, the electroplating line of the copper electroplating is a vertical electroplating line;
[0019] The current density was between 0.8-1.2 ASD and the plating time was 45 minutes.
[0020] Furthermore, the method also includes:
[0021] Before vacuum laminating the dry film of the second thickness, chemical solutions are used to remove copper surface oxides and oil stains from the front and back sides of the multilayer board, and to roughen the copper surface of the multilayer board.
[0022] Furthermore, the above-mentioned vacuum laminating a dry film of the second thickness on the front and back surfaces of the multilayer board respectively comprises:
[0023] Using a vacuum laminating machine to cover the front and back sides of the multilayer board with a dry film of the second thickness;
[0024] Among them, the laminating pressure of the vacuum laminating machine is 0.4-0.8MPa, the upper plate temperature is 55-75℃, the lower plate temperature is 55-75℃, the vacuum time is 20-40 seconds, the pressurization time is 20-50 seconds, and the vacuum degree is 2-4HPa.
[0025] Furthermore, the method also includes:
[0026] After removing the residual colloid in the blind hole by plasma cleaning, the blind hole is metallized.
[0027] Furthermore, the above-mentioned step of metallizing the blind hole includes:
[0028] The black shadow process is used to adsorb graphite on the hole wall of the blind hole to form a conductive layer.
[0029] Furthermore, the first thickness is 30 micrometers, and the second thickness is 25 micrometers.
[0030] In summary, compared with the prior art, the technical solution provided in the embodiment of the present application has at least the following beneficial effects:
[0031] The embodiment of the present application provides a method for manufacturing a circuit board of a multilayer board. Firstly, the copper plating area is improved, and the plating ratio is reduced to 17%, thereby reducing the step height difference, so that the step after copper plating is reduced from more than 25um to less than 15um, thereby reducing the second thickness of the dry film that needs to be laminated before circuit pattern production; secondly, the film lamination method and process parameters of the dry film of the second thickness are optimized. The use of a vacuum film lamination method can overcome the problem of false film lamination or film bubbles caused by the step height difference, thereby providing a guarantee for the last step of manufacturing fine circuits of multilayer boards. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 A flowchart of a method for manufacturing a multilayer circuit board is provided for an exemplary embodiment of the present application.
[0033] Figure 2 A schematic cross-sectional view of a multilayer board provided as an exemplary embodiment of the present application.
[0034] Figure 3 A cross-sectional view of a multilayer board after blind holes are drilled, provided as an exemplary embodiment of the present application.
[0035] Figure 4 A cross-sectional view of a multilayer board after hole plating with a dry film of a first thickness is provided for an exemplary embodiment of the present application.
[0036] Figure 5 A cross-sectional view of a multi-layer board after copper electroplating is provided for an exemplary embodiment of the present application.
[0037] Figure 6 A cross-sectional view of a multilayer board after removing a dry film of a first thickness is provided for an exemplary embodiment of the present application.
[0038] Figure 7 A cross-sectional view of a multilayer board after vacuum lamination of a dry film of a second thickness is provided according to an exemplary embodiment of the present application.
[0039] Figure 8 A cross-sectional view of a multilayer board after circuit patterning is provided for an exemplary embodiment of the present application. DETAILED DESCRIPTION
[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.
[0041] Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of this application.
[0042] See also Figure 1 The present application embodiment provides a method for manufacturing a multilayer circuit board, comprising:
[0043] Step S1, providing a multilayer board; and punching blind holes of preset depths on the front and back sides of the multilayer board respectively.
[0044] See also Figure 2 The multilayer board of the present application is composed of multiple copper foils, PI layers (Polyimide) and pure glue layers stacked on each other, with an inner layer depression on the front and back sides; specifically, the production process of the multilayer board includes: 1) cutting, cutting the roll-shaped flexible copper-clad board into a sheet-shaped base copper board of fixed length; 2) inner layer production, through drilling, electroplating, graphic production and other processes, to produce the upper and lower conductive inner layer light boards; 3) board arrangement and pressing, through the board arrangement and pressing method, on the basis of the aforementioned inner layer light board, a layer of single-sided board + pure glue is placed on the upper and lower sides, and a four-layer board is formed by stacking and pressing two single-sided boards and a double-sided board.
[0045] See also Figure 3 In the specific implementation process, the preset depth of the blind hole can be the depth of the three-layer board; the positions of the blind holes on the front and the back do not correspond; specifically, the present application can use ultraviolet laser ablation to laser out blind holes of a preset depth to provide a channel for the outer layer and the inner layer of the multilayer board to achieve conduction.
[0046] Step S2, a dry film having a first thickness is plated on the front and back surfaces of the multilayer board respectively.
[0047] The dry film of the first thickness does not cover the blind hole and a preset area outside the blind hole.
[0048] See also Figure 4 The present application can form a dry film of the first thickness on the base copper plate through processes such as hole plating dry film, hole plating exposure, and hole plating development, while retaining exposed blind holes and areas to be electroplated.
[0049] Step S3, electroplating copper at the locations of the two blind holes of the multilayer board to form steps; and removing the dry film of the first thickness.
[0050] See also Figure 5 and Figure 6 , wherein the sum of the bottom area of the blind hole and the preset area is taken as the exposed area; the ratio of the exposed area to the single-sided board area of the multilayer board is equal to 17%, and the thickness of the step above the board surface of the multilayer board is less than 15 microns.
[0051] Among them, the production dimensions and electroplating parameters of the multilayer board of this application can be seen in the following table:
[0052]
[0053] Specifically, the present application utilizes direct current to transfer the copper ions with full charge in the solution to the substrate at the cathode and the blind hole. The thickness of the copper ions deposited on the cathode substrate is proportional to the copper overcharge. Preferably, the present application adopts the method of hole filling electroplating. In order to ensure that the step copper thickness of the blind hole is less than 15um, the electroplating line uses VCP (vertical electroplating line) point hole filling electroplating. The product circuit area (the area covered by the dry film of the first thickness) is not copper plated, and only the blind hole position is plated. The current size determines the surface copper plating thickness and the hole filling effect. The current density of the present application is between 0.8-1.2ASD, and the electroplating time is 45 minutes.
[0054] When the production size of a multilayer board is 500mm*420mm, the area of a single-sided board is 500*420 square millimeters.
[0055] When removing the dry film, a strong alkali or a special film stripping liquid can be used to chemically react with the polymerized dry film, thereby removing the dry film on the surface of the substrate and exposing the copper foil of the substrate; the same is true when removing the second thickness of the dry film.
[0056] Step S4, vacuum laminating a dry film of the second thickness on the front and back surfaces of the multilayer board respectively.
[0057] The second thickness is smaller than the first thickness, the first thickness may be 30 micrometers, and the second thickness may be 25 micrometers.
[0058] Specifically, see Figure 7 The conventional operation is to use a laminator to press a photosensitive dry film on the copper surface as a carrier for transferring circuit pattern data. However, in order to solve the steps after blind hole electroplating and the height difference after the multi-layer board is pressed, the present application preferentially uses a vacuum laminator to cover the front and back of the multi-layer board with a second thickness of dry film respectively.
[0059] Among them, the laminating pressure of the vacuum laminating machine is 0.4-0.8MPa, the upper plate temperature is 55-75℃, the lower plate temperature is 55-75℃, the exhaust time is 20-40 seconds, the pressurization time is 20-50 seconds, and the vacuum degree is 2-4HPa. Through the above process flow, the thick dry film with a thickness of more than 50 microns commonly used in the prior art can be reduced to 25 microns.
[0060] Step S5, forming circuit patterns on the front and back surfaces of the multilayer board respectively, and removing the dry film of the second thickness.
[0061] Specifically, see Figure 8 The production of circuit patterns refers to the process of film pasting, exposure, development, acid etching, film stripping (removing the second thickness of the dry film), and finally etching a specific circuit pattern on the copper surface.
[0062] The above embodiment provides a method for manufacturing a multilayer circuit board. Firstly, the copper plating area is improved, and the plating ratio is reduced to 17%, thereby reducing the step height difference, so that the step after copper plating is reduced from more than 25um to less than 15um, thereby reducing the second thickness of the dry film that needs to be laminated before circuit pattern production; secondly, the film lamination method and process parameters of the dry film of the second thickness are optimized. The use of a vacuum film lamination method can overcome the problem of false film lamination or film bubbles caused by the step height difference, thereby providing a guarantee for the final step of manufacturing fine circuits of multilayer boards.
[0063] In some embodiments, the method further comprises:
[0064] After the blind hole is drilled, the residual colloid in the blind hole is removed by plasma cleaning. Specifically, the present application uses plasma to clean the foreign matter remaining at the bottom of the blind hole so that the wall of the blind hole has a clean surface and can be prepared for subsequent hole metallization.
[0065] Furthermore, the method also includes:
[0066] After removing the residual colloid in the blind hole by plasma cleaning, the blind hole is metallized.
[0067] Specifically, a black shadow, black hole or copper deposition process is usually used to perform metallization operations on the blind vias.
[0068] This application gives priority to the use of the black shadow process, the purpose of which is to use colloidal technology to adsorb graphite on the hole wall of the blind hole that has not yet been connected to form a conductive layer for subsequent hole copper electroplating. This is because the chemical composition used in the black shadow process is relatively simple, does not contain harmful substances such as formaldehyde, etc., the sewage treatment is simple, the water consumption is about 1 / 10 of the copper deposition process, and the cost is low; and the black shadow process is relatively short and efficient, which can significantly improve production efficiency and shorten the production cycle. In addition, the black shadow process uses graphite as a conductive material, and the conductivity of graphite is higher than that of the carbon black used in the black hole process because graphite has more free electrons.
[0069] In some embodiments, the method further includes: before vacuum laminating the dry film of the second thickness, using chemical solution to remove copper surface oxides and oil stains from the front and back surfaces of the multilayer board respectively, and roughening the copper surface of the multilayer board.
[0070] The roughened copper surfaces include the copper surfaces on the front and back sides of the multilayer board; roughening and cleaning the copper surfaces are beneficial to provide bonding strength for subsequent vacuum lamination and circuit pattern production.
[0071] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0072] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.
Claims
1. A method for manufacturing a multilayer circuit board, characterized in that: include: Provide multi-layer boards; Drilling blind holes of preset depths on the front and back sides of the multilayer board respectively; Plate a dry film of a first thickness on the front and back sides of the multilayer board respectively; Wherein, the dry film of the first thickness does not cover the blind hole and a preset area outside the blind hole; Electroplating copper at the positions of the two blind holes in the multilayer board to form a step; and removing the dry film of the first thickness; The sum of the bottom area of the blind hole and the preset area is taken as the exposed area; the ratio of the exposed area to the single-side surface area of the multilayer board is equal to 17%, and the thickness of the step above the board surface of the multilayer board is less than 15 microns; Vacuum laminating a dry film of a second thickness on the front and back surfaces of the multilayer board respectively; Circuit patterns are formed on the front and back surfaces of the multilayer board respectively, and the dry film of the second thickness is removed.
2. The method for manufacturing a multilayer circuit board according to claim 1, characterized in that: Also includes: After the blind hole is drilled, the residual colloid in the blind hole is removed by plasma cleaning.
3. The method for manufacturing a multilayer circuit board according to claim 1, characterized in that: The preset depth is the depth of the three-layer board; the positions of the blind holes on the front side and the blind holes on the back side do not correspond.
4. The method for manufacturing a multilayer circuit board according to claim 1, characterized in that: The method of punching blind holes of preset depths on the front and back surfaces of the multilayer board comprises: The blind hole of a preset depth is punched by ultraviolet laser ablation.
5. The method for manufacturing a multilayer circuit board according to claim 1, characterized in that: The electroplating line for copper electroplating is a vertical electroplating line; the current density is between 0.8-1.2ASD, and the electroplating time is 45 minutes.
6. The method for manufacturing a multilayer circuit board according to claim 1, characterized in that: Also includes: Before vacuum laminating the dry film of the second thickness, chemical solutions are used to remove copper surface oxides and oil stains from the front and back surfaces of the multilayer board, and to roughen the copper surface of the multilayer board.
7. The method for manufacturing a multilayer circuit board according to claim 1, characterized in that: The step of vacuum laminating a dry film of a second thickness on the front and back surfaces of the multilayer board comprises: Using a vacuum laminating machine to cover the front and back surfaces of the multilayer board with the dry film of the second thickness respectively; Among them, the laminating pressure of the vacuum laminating machine is 0.4-0.8MPa, the upper plate temperature is 55-75℃, the lower plate temperature is 55-75℃, the vacuum time is 20-40 seconds, the pressurization time is 20-50 seconds, and the vacuum degree is 2-4HPa.
8. The method for manufacturing a multilayer circuit board according to claim 1, characterized in that: Also includes: After the residual colloid in the blind hole is removed by plasma cleaning, the blind hole is metallized.
9. The method for manufacturing a multilayer circuit board according to claim 8, characterized in that: The step of metallizing the blind hole includes: using a black shadow process to adsorb graphite on the hole wall of the blind hole to form a conductive layer.
10. The method for manufacturing a multilayer circuit board according to claim 1, characterized in that: The first thickness is 30 micrometers, and the second thickness is 25 micrometers.