A method for manufacturing a PCB with a PTH slot and back drilling holes

Abstract

The present invention discloses a method for manufacturing a PCB with a PTH slot and a backdrilled hole, comprising the following steps: backdrilling at a position corresponding to the PTH slot in a production board to form a backdrilled hole; then controlling the depth of a blind slot at a position corresponding to the PTH slot on the production board, wherein the size of the blind slot is larger than the size of the backdrilled hole; metalizing the backdrilled hole and the blind slot through copper deposition and full-board electroplating to form a PTH slot through the blind slot; applying a film to the production board, and sequentially exposing and developing to form an outer layer circuit pattern on the production board, wherein the film corresponding to the backdrilled hole position is exposed during exposure, while positions in the PTH slot other than the backdrilled hole are not exposed; pattern electroplating the production board, and then stripping the film; applying a film to the production board, and forming a cover hole pattern at both the backdrilled hole and the PTH slot after exposure and development, and sequentially etching, stripping the film, and stripping the tin to produce an outer layer circuit on the production board. The method of the present invention solves the defect of poor tin plating and tin stripping when the aspect ratio of the backdrilled hole is too large, thereby improving production quality.

Description

Technical Field

[0001] The present invention relates to the technical field of printed circuit board manufacturing, and in particular to a manufacturing method of a PCB having a PTH groove and a back drill hole. Background Art

[0002] As the pace of global digital transformation continues to accelerate, the proportion of fast communication technology in the communications industry is gradually increasing. Some technologically advanced companies are increasingly focusing on research on signal integrity transmission. PTH metallized holes can achieve electrical connections between conductive patterns on the inner and outer layers of a PCB, or between inner and outer layers. With the development of diverse electronic products, the form of component patch and plug-in components has also changed. According to the installation requirements of some components, after the PTH slot is drilled, a through hole connecting to the PTH slot needs to be drilled on the back of the PTH slot to serve as the back-drilled hole of the PTH slot. After metallization, this through hole is used to connect to the pins on the component later, thereby improving the reliability of the electrical connection.

[0003] The basic process of making PTH slots by conventional back drilling is as follows: front process → outer layer drilling → back drilling (slot hole) → milling PTH slot → copper deposition → electroplating → film lamination → exposure → pattern electroplating → film stripping → etching → tin stripping → outer layer AOI → back process.

[0004] When conventional back-drilling is used to produce PTH trenches, due to their large size, the dry film cannot cover the PTH trench when the outer layer pattern is produced using a negative film process, resulting in the etching away of the copper in the trench hole. Therefore, only a positive film process can be used for production. Tin has higher rigidity and can cover the PTH trench. However, when the aspect ratio of the back-drilled hole in the trench is large (when the back-drilled hole is very deep and small), the solution cannot flow in the hole, making it difficult to fully cover it with tin. The outer layer etching can easily cause the copper in the back-drilled hole to be etched away, resulting in poor connection after the components are installed later. In addition, the aspect ratio of the back-drilled hole is too large, and the tin layer on the inner wall of the hole is difficult to be removed during the tin stripping process, resulting in poor tin stripping. Summary of the Invention

[0005] In response to the above-mentioned existing technical defects, the present invention provides a method for manufacturing a PCB with a PTH groove and back-drilled holes, which solves the defects of poor tin plating and tin stripping caused by an excessively large aspect ratio of the back-drilled holes, thereby improving production quality.

[0006] In order to solve the above technical problems, the present invention provides a method for manufacturing a PCB having a PTH groove and a back-drilled hole, comprising the following steps:

[0007] S1. Back-drill at the position corresponding to the PTH slot in the production board to form a back-drilled hole;

[0008] S2, then control the depth of milling a blind groove at the position corresponding to the PTH groove on the production board, and the size of the blind groove is larger than the size of the back drilled hole;

[0009] S3, sequentially performing copper deposition and full-board electroplating to metallize the back-drilled holes and blind slots, so that the blind slots become PTH slots;

[0010] S4. Laminating the film on the production board, and forming the outer circuit pattern on the production board after sequential exposure and development. During exposure, the film corresponding to the back-drilled hole position is exposed together, while the positions in the PTH slot other than the back-drilled hole are not exposed; then pattern electroplating is performed on the production board to sequentially add a copper layer and a tin layer on the outer circuit pattern, and then the film is stripped;

[0011] S5. Paste the film on the production board, and form cover hole patterns at the back drill holes and PTH grooves after exposure and development. Then, etch, strip the film and remove the tin in sequence to obtain the outer layer circuit on the production board.

[0012] Furthermore, in step S1 , the thickness-to-diameter ratio of the back-drilled hole is ≥10:1.

[0013] Furthermore, in step S1, after the back-drilled holes are drilled, the production board is rinsed twice using high-pressure water washing.

[0014] Furthermore, in step S1, back drilling is performed at the center position of the production board corresponding to the PTH groove to form a back drilled hole.

[0015] Furthermore, in step S1, during back drilling, a cut is made on the back side of the PTH slot and a back drill hole is drilled.

[0016] Furthermore, in step S4, the film attached to the production board is a dry film with a thickness of 50 μm.

[0017] Furthermore, in step S4, the film corresponding to the back-drilled hole position is also exposed during exposure to form a cover hole pattern, and the outer diameter of the cover hole pattern is 0.1 mm larger than the back-drilled hole diameter.

[0018] Furthermore, in step S5, the outer diameter of the cover hole pattern on one side of the back-drilled hole is 0.15 mm larger than the diameter of the back-drilled hole, and the single side of the cover hole pattern on one side of the PTH groove is 0.15 mm larger than the PTH groove.

[0019] Furthermore, the production board is a multi-layer board in which an inner core board and an outer copper foil are pressed together by a prepreg.

[0020] Furthermore, the production board undergoes an outer layer drilling step before back drilling.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] In the present invention, when forming the outer layer circuit pattern, the film corresponding to the back-drilled hole position is exposed at the same time, that is, the back-drilled hole is covered by the film after development, while the position other than the back-drilled hole in the PTH groove is not exposed. In this way, when the pattern is electroplated, the back-drilled hole is not electroplated, that is, no tin is plated, which can avoid the problem of poor tin stripping caused by the tin layer on the inner wall of the hole being difficult to remove during the tin stripping process. On the other hand, the tin layer will be plated on the wall of the PTH groove to protect the copper layer in the PTH groove. In combination with the hole-covering pattern formed during the secondary film lamination, the problem of copper being etched out of the back-drilled hole and the PTH groove during the outer layer etching can be avoided. DETAILED DESCRIPTION

[0023] In order to more fully understand the technical content of the present invention, the technical solution of the present invention will be further introduced and illustrated in conjunction with specific embodiments below.

[0024] Example

[0025] This embodiment shows a method for manufacturing a PCB, which includes a process for solder masking with a variegated ink, and includes the following processing steps in sequence:

[0026] (1) Cutting: Cut the core board according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm, and the thickness of the copper layer on both surfaces of the core board is 0.5oz.

[0027] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, use a vertical coating machine to coat the photosensitive film, the film thickness of the photosensitive film is controlled at 8μm, and a fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler). After development, the inner layer circuit pattern is formed; inner layer etching, the exposed and developed core board is etched to etch the inner layer circuit, and the inner layer line width is measured to be 3mil; inner layer AOI, then check the inner layer circuit for defects such as open and short circuits, circuit gaps, and circuit pinholes. Defective products will be scrapped, and products without defects will be sent to the next process.

[0028] (3) Lamination: The browning speed is based on the browning thickness of the bottom copper. The core board, prepreg, and outer copper foil are laminated in sequence as required. Then, appropriate lamination conditions are selected according to the Tg of the sheet material to press the laminated board to form a production board.

[0029] (4) Drilling: Based on existing drilling technology, drilling is performed on the production board according to design requirements.

[0030] (5) Back drilling: Back drilling is performed at the center position of the PTH slot in the production board to form a back drilled hole.

[0031] In one embodiment, during back drilling, the back of the PTH slot is cut and a back-drilled hole is drilled, which can reduce the burr generation at the hole opening. The hole opening burr on one side of the PTH slot can be removed during the subsequent drilling.

[0032] In one embodiment, the back-drilled via has a thickness-to-diameter ratio of ≥10:1.

[0033] (6) Water washing: Use high-pressure water washing to rinse the production board twice to remove drilling stains.

[0034] (7) Milling slot: mill a blind slot at the position corresponding to the PTH slot on the production board. The size of the blind slot is larger than the size of the back drilled hole, and the back drilled hole is in the center of the blind slot.

[0035] (8) Copper plating: A thin layer of copper is deposited on the board surface, hole wall and groove wall by using the chemical copper plating method. The backlight test is level 10, and the thickness of the copper plating in the hole is 0.5μm.

[0036] (9) Full board electroplating: The production board is electroplated for the entire board 1, and the thickness of the hole copper and the board surface copper layer is thickened to metallize the back drilled holes and blind slots to form metallized holes and PTH slots.

[0037] (10) Making the outer layer circuit (positive film process): including the following steps:

[0038] a. Transfer of outer layer pattern - first, apply a 50μm thick dry film to the surface of the production board, and then use a fully automatic exposure machine and positive circuit film to complete the outer layer circuit exposure with a 5-7 grid exposure ruler (21 grid exposure ruler). After development, the outer layer circuit pattern is formed on the production board. During exposure, the film corresponding to the back-drilled hole position is exposed together, while the positions in the PTH slot other than the back-drilled hole are not exposed to form a cover hole pattern. The outer diameter of the cover hole pattern is 0.1mm larger than the back-drilled hole diameter so that the back-drilled hole is covered and protected by the dry film;

[0039] b. Electroplating of outer pattern - Then copper and tin are plated on the production board respectively. The electroplating parameters are set according to the required copper thickness. Copper plating is performed at a current density of 1.8ASD for 60 minutes on the entire board. Tin plating is performed at a current density of 1.2ASD for 10 minutes. The tin thickness is 3-5μm. Copper and tin layers are added on the outer circuit pattern and PTH slot in sequence. Then the film is stripped.

[0040] c. Transferring the cover hole pattern: Apply dry film to the surface of the production board again. After exposure and development, cover hole patterns are formed on both the back-drilled hole and the PTH groove. Preferably, the outer diameter of the cover hole pattern on the back-drilled hole side is 0.15mm larger than the back-drilled hole diameter, and the cover hole pattern on the PTH groove side is 0.15mm larger than the PTH groove on one side to ensure that the copper layer inside the hole and the copper layer on the groove wall are protected.

[0041] d. Outer layer etching - then etching, film stripping and tin stripping are carried out in sequence to etch the outer layer circuit on the production board;

[0042] e. Outer layer AOI - Use the automatic optical inspection system to detect whether the outer layer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc. by comparing with the CAM data.

[0043] (11) Solder mask and silk screen characters: After silk screen printing solder mask ink on the surface of the production board, it is sequentially processed through pre-curing, exposure, development and heat curing to solidify the solder mask ink into a solder mask layer; specifically, the solder mask ink and the characters on the TOP surface are added with "UL mark", so that a layer is coated on the circuits and substrates that do not need to be soldered to prevent bridging between circuits during soldering, provide a permanent electrical environment and chemical corrosion resistance, and at the same time beautify the appearance.

[0044] (12) Surface treatment (nickel-gold deposition): The copper surface of the pad at the solder mask window position is chemically deposited with a nickel layer and a gold layer of a certain required thickness. The nickel layer thickness is 3-5μm; the gold layer thickness is 0.05-0.1μm.

[0045] (13) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0046] (14) Molding: According to the existing technology and the design requirements, the PCB is manufactured with a shape tolerance of + / -0.05mm.

[0047] (15) FQC: Inspect the appearance of the PCB according to the customer's acceptance standards and our inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

[0048] (16) FQA: Re-test the PCB appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. to see if they meet customer requirements.

[0049] (17) Packaging: According to the packaging method and packaging quantity required by the customer, the PCB is sealed and packed, and desiccant and humidity card are placed before shipment.

[0050] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for manufacturing a PCB with a PTH slot and back drilling holes, characterized in that: The following steps are involved: S1. Back-drill at the position corresponding to the PTH groove in the production board to form a back-drilled hole. The thickness-to-diameter ratio of the back-drilled hole is ≥10:

1. S2, then control the depth of milling a blind groove at the position corresponding to the PTH groove on the production board, and the size of the blind groove is larger than the size of the back drilled hole; S3, sequentially performing copper deposition and full-board electroplating to metallize the back-drilled holes and blind slots, so that the blind slots become PTH slots; S4. Laminating the film on the production board, and forming the outer circuit pattern on the production board after sequential exposure and development. During exposure, the film corresponding to the back-drilled hole position is exposed together, while the positions in the PTH slot other than the back-drilled hole are not exposed; then pattern electroplating is performed on the production board to sequentially add a copper layer and a tin layer on the outer circuit pattern, and then the film is stripped; S5. Paste the film on the production board, and form cover hole patterns at the back drill holes and PTH grooves after exposure and development. Then, etch, strip the film and remove the tin in sequence to obtain the outer layer circuit on the production board.

2. The method for manufacturing a PCB having a PTH groove and back drilling holes according to claim 1, characterized in that: In step S1 , after the back-drilled holes are drilled, the production board is rinsed twice using high-pressure water washing.

3. The method for manufacturing a PCB having a PTH groove and back drilling holes according to claim 1, characterized in that: In step S1, back drilling is performed at the center position of the PTH groove in the production board to form a back drilled hole.

4. The method for manufacturing a PCB having a PTH groove and back-drilled holes according to any one of claims 1 to 3, characterized in that: In step S1 , during back drilling, a cut is made on the back side of the PTH slot and a back drill hole is drilled.

5. The method for manufacturing a PCB having a PTH groove and back drilling holes according to claim 1, characterized in that: In step S4, the film attached to the production board is a dry film with a thickness of 50 μm.

6. The method for manufacturing a PCB having a PTH groove and back drilling holes according to claim 1, characterized in that: In step S4, the film corresponding to the back-drilled hole position is exposed together to form a cover hole pattern, and the outer diameter of the cover hole pattern is 0.1 mm larger than the back-drilled hole diameter.

7. The method for manufacturing a PCB having a PTH groove and back drilling holes according to claim 1, characterized in that: In step S5, the outer diameter of the cover hole pattern on one side of the back-drilled hole is 0.15 mm larger than the back-drilled hole diameter, and the single side of the cover hole pattern on one side of the PTH groove is 0.15 mm larger than the PTH groove.

8. The method for manufacturing a PCB having a PTH groove and back drilling holes according to claim 1, characterized in that: The production board is a multi-layer board in which an inner core board and an outer copper foil are pressed together by a prepreg.

9. The method for manufacturing a PCB having a PTH groove and back drilling holes according to claim 1, characterized in that: Production boards undergo an outer layer drilling step before back drilling.