Method for preventing and improving edge cracking of PCB (Printed Circuit Board) molding routing board

Abstract

The invention discloses a method for preventing and improving edge cracking of a PCB (Printed Circuit Board) molded routing board, which comprises the following steps: in a molding process, when the appearance of an SET board or a unit board is routed on a production board by adopting a routing knife, the size of the single edge of the SET board or the unit board is pre-increased by 0.2 mm on the basis of design; and performing fine trimming on the SET plate or the unit plate by adopting a trimming cutter or a dense tooth cutter so as to remove the pre-enlarged part in the SET plate or the unit plate. According to the method, under the condition that the normal board milling efficiency is not affected, the problem of edge cracking of the milled board can be solved, and the board milling quality can be guaranteed.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing technology, specifically to a method for preventing and improving edge bursting on PCB molding circuit boards. Background Technology

[0002] With the development of PCB processing technology, PCB routing technology has emerged, and PCB routing is an important processing step in PCB manufacturing. PCB routing refers to the cutting of the PCB board by a routing cutter according to a preset trajectory or pattern. During the cutting process of the high-speed rotating routing cutter, resin inevitably falls off on both sides of the cutting path. This is because the board is impacted by the mechanical force of the routing cutter during the routing process, resulting in small cracks around the PP glass fiber of the PCB board edge after routing. Sometimes, the design around the PCB routing groove and forming line has graphic PADs or open windows without solder mask ink. In such boards, because there is no ink protection around the forming line during the routing process, the resin falls off and produces a halo white edge (also known as edge bursting). Edge bursting not only affects the accuracy of routing, but may also affect the effective insulation distance between the board edge and the nearest conductor, and may even lead to PCB damage and failure. The depth of this edge bursting is generally between 0.2-0.3mm, while the design IPC standard stipulates that the depth of edge bursting should not exceed 0.1mm.

[0003] In current PCB stack-up structures, the PP (polypropylene) type between the outer copper foil and the second outermost layer is typically a combination of 7628*2+2116+7628*2. This means the PP in contact with the outer copper foil is 7628, and the warp and weft yarn node width of the 7628 PP is 0.2±0.02mm. However, when the distance between the PAD or gold finger on the board and the forming line is designed to be within 0.3mm, such as 0.25mm, this distance is close to the width of the warp and weft yarn node. During the forming process, this pulls on the glass fiber, causing it to break. The breakage depth is generally the width of the warp and weft yarn, which greatly increases the probability that the depth of the white edge at the glass fiber breakage location exceeds the IPC standard during forming and forming.

[0004] In the industry, to reduce the depth of edge bursting, one approach is to control it by reducing the overall travel and rotation speed of the router cutter. However, the lower the travel and rotation speed of the router cutter, the worse the processing efficiency. Another approach is to reduce the number of PCB stacks during routerging, reduce router cutter wear, and add interlayer paper to fill the gaps between boards during processing, thereby increasing interboard pressure and reducing the size of the halo (i.e., edge bursting). However, this also affects routerging efficiency and processing results. Summary of the Invention

[0005] In view of the above-mentioned technical defects, the present invention provides a method for preventing and improving the edge breakage of PCB forming routers, which can ensure the quality of routers without affecting the normal router efficiency.

[0006] To address the aforementioned technical problems, this invention provides a method for preventing and improving edge bursting in PCB molding circuit boards, comprising the following steps: S1. In the molding process, when using a milling cutter to mill the shape of the SET board or unit board on the production board, the size of the SET board or unit board is pre-larged by 0.2mm on one side based on the design. S2. Use a trimming knife or fine-tooth knife to finely trim the SET board or unit board to remove the pre-larged part of the SET board or unit board to obtain the SET board or unit board of the designed size.

[0007] Furthermore, in step S1, the diameter of the gong cutter is ≤1.6mm.

[0008] Furthermore, in step S1, when the PAD or gold finger inside the SET board or unit board is ≤0.30mm away from the forming line on its outer perimeter and a solder mask opening design is implemented, the non-solder mask position at the forming line on the outer side of the PAD or gold finger is a high-risk position for the router board edge to burst; when the router passes through the high-risk position, the router's cutting speed is controlled to be reduced by 20% or more on the original basis.

[0009] Furthermore, in step S1, the cutting speed of the milling cutter when it is milling the plate at a position other than the high-risk position is 18 mm / s, while the cutting speed of the milling cutter when it passes through the high-risk position is reduced to 14 mm / s.

[0010] Furthermore, in step S2, when the PAD or gold finger inside the SET board or unit board is ≤0.30mm away from the forming line on its outer perimeter and a solder mask opening design is implemented, the non-solder mask position at the forming line on the outer side of the PAD or gold finger is a high-risk position for the edge of the router; when the trimming knife passes through the high-risk position, the cutting speed of the trimming knife is reduced by 20% or more on the original basis.

[0011] Furthermore, in step S2, the cutting speed of the trimming cutter when it is cutting the plate at a position other than the high-risk position is 50 mm / s, while the cutting speed of the cutting cutter when it passes through the high-risk position is reduced to 40 mm / s.

[0012] Furthermore, when using a milling machine to shape the production board, the chuck of the milling machine in use needs to be cleaned regularly every day.

[0013] Furthermore, the production board is a multilayer board made of PP to press the inner core board and the outer copper foil into one piece, and the multilayer board has successively undergone drilling, copper plating, full board electroplating and outer layer circuit fabrication processes.

[0014] Furthermore, in the multilayer board stacking structure, the PP material adjacent to the outer copper foil is of type 2116.

[0015] Furthermore, in the stacked structure of the multilayer board, the outer copper foil and the next outermost circuit are stacked sequentially from the outside in, with one first PP, four second PPs and one first PP, wherein the first PP is of type 2116 and the second PP is of type 7628.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In this invention, when milling the production board, the outer dimensions of the milling board are pre-sized by 0.2mm beyond the design. Since the edge breakage depth caused by milling is generally 0.2-0.3mm, the edge breakage (i.e., white edge) is mainly located at the pre-sized portion of the outer perimeter. Then, a sharper trimming knife or fine-toothed knife is used to perform a small-scale fine trimming on the outer perimeter after milling, reducing the pulling during the cutting process and effectively reducing the formation of edge breakage halos. During the fine trimming, the pre-sized portion from the previous milling is removed, thereby removing the edge breakage located at the pre-sized portion. After the fine trimming, the edge breakage depth of the board edge can be reduced to 0-0.1mm, which meets the design IPC standard requirements. This method can ensure the quality of milling without affecting the normal milling efficiency. The fine trimming here must also ensure the milling allowance size, so it cannot be increased indefinitely. Therefore, when using a milling knife for the first milling, only 0.2mm can be added on one side, otherwise it will affect the efficiency and quality of the fine trimming.

[0017] Secondly, when the router and trimmer pass through high-risk areas (i.e., forming lines ≤ 0.30mm from the PAD or gold finger on the board), the cutting speed of both the router and trimmer is reduced by 20% or more from the original speed. This reduces the pulling force of the tools on the high-risk areas, further reducing the size of the chipped edges. Moreover, the cutting speed is only reduced at high-risk areas, while the cutting speed remains unchanged at other locations, so the impact on the router efficiency is minimal, thus avoiding the problem of affecting processing efficiency due to reduced cutting speed.

[0018] In addition, in the stacking structure of the production board, the stacking structure of the outer PP layer is changed. The PP model adjacent to the outer copper foil is changed from the original 7628 to 2116. The warp and weft yarn node width of the PP model 2116 is 0.1mm, and the width of the PAD or gold finger in the board from the forming line is designed to be within 0.3mm. For example, when it is 0.25mm, this distance is much larger than the width of the warp and weft yarn node. As a result, the depth of the halo white edge generated when forming the plate in this method is much smaller than the depth of the halo white edge when using 7628 in the existing method, which further improves and reduces the depth of edge bursting. Detailed Implementation

[0019] To better understand the technical content of this invention, the technical solution of this invention will be further introduced and explained below in conjunction with specific embodiments.

[0020] Example The method for manufacturing a circuit board shown in this embodiment includes the following processing steps in sequence: (1) Cutting: Cut the core board according to the panel size of 520mm×620mm. The core board is 0.5mm thick and the copper layer thickness on both surfaces of the core board is 0.5oz. Multiple SET boards or unit boards are provided on the core board according to the preset rules. The SET board is composed of multiple unit boards spliced ​​together.

[0021] (2) Inner layer circuit fabrication (negative film process): Inner layer pattern transfer, photosensitive film is coated using a vertical coating machine, and the film thickness of the photosensitive film is controlled at 8μm. The inner layer circuit is exposed using a fully automatic exposure machine with 5-6 exposure rulers (21 exposure rulers). After development, the inner layer circuit pattern is formed; Inner layer etching, the inner layer circuit is etched out on the core board after exposure and development. The inner layer line width is measured to be 3mil; Inner layer AOI, and then the inner layer circuit is inspected for defects such as open circuits, short circuits, line gaps, and line pinholes. Defective products are scrapped, and defect-free products are sent to the next process.

[0022] (3) Lamination: The browning speed is based on the thickness of the bottom copper. The core board, PP and outer copper foil are stacked in sequence as required. Then, according to the Tg of the board material, appropriate lamination conditions are selected to press the laminated board to form a multi-layer production board.

[0023] In the aforementioned laminated plate structure, one first PP, four second PPs, and one first PP are stacked sequentially from the outside to the inside between the outer copper foil and the second outer circuit. That is, a total of six PPs are stacked between the outer copper foil and the second outer circuit. The first PP is model 2116, and the second PP is model 7628. This changes the PP model adjacent to the outer copper foil from 7628 to 2116. The warp and weft yarn node width of the PP with model 2116 is 0.1mm, and the width of the distance between the PAD or gold finger in the board and the forming line is designed to be within 0.3mm. For example, when it is 0.25mm, this distance is much larger than the width of the warp and weft yarn node. As a result, the depth of the halo and white edge generated during the later forming and winding process is much smaller than the depth of the halo and white edge generated when using 7628 in the existing process, thus improving and reducing the depth of edge bursting.

[0024] (4) Drilling: Drilling is performed on the production board according to the design requirements based on the existing drilling technology.

[0025] (5) Copper plating: A thin layer of copper is deposited on the board surface and hole walls using chemical copper plating. The backlight test is level 10, and the copper plating thickness in the hole is 0.5μm.

[0026] (6) Full-board electroplating: The production board is electroplated according to the design requirements to increase the thickness of the copper in the holes and the copper layer on the board surface.

[0027] (7) Fabrication of outer layer circuits (positive film process): outer layer pattern transfer, using a fully automatic exposure machine and positive film circuit film, the outer layer circuit is exposed with an exposure ruler of 5 to 7 divisions (21 divisions exposure ruler), and after development, the outer layer circuit pattern is formed on the multilayer board; outer layer pattern electroplating, and then copper and tin plating are performed on the multilayer board respectively. The electroplating parameters are set according to the required copper thickness. Copper plating is performed with a current density of 1.8 ASD for 60 minutes, and tin plating is performed with a current density of 1.2 ASD for 10 minutes, with a tin thickness of 3 to 5 μm; then the film is removed, etched and tin is removed in sequence, and the outer layer circuit is etched on the multilayer board; outer layer AOI, using an automatic optical inspection system, by comparing with CAM data, to detect whether there are defects such as open circuits, gaps, incomplete etching, and short circuits in the outer layer circuit.

[0028] In the process of manufacturing the outer layer circuitry, PADs or gold fingers with a distance of ≤0.30mm from the outer perimeter are also fabricated within the SET board or unit board.

[0029] Solder resist and silkscreen printing: After silkscreen printing solder resist ink on the surface of the multilayer board, it undergoes pre-curing, exposure, development and heat curing treatments in sequence to cure the solder resist ink into a solder resist layer; specifically, the solder resist ink on the TOP side and the TOP side characters are added with the "UL mark", thereby coating a layer on the lines and substrate that do not need to be soldered to prevent bridging between lines during soldering, provide a permanent electrical environment and chemical corrosion resistance, and at the same time improve the appearance.

[0030] In the above, when making solder mask, the PAD or gold finger ≤ 0.30mm away from the forming line is designed with solder mask opening, that is, no solder mask layer is made on the PAD or gold finger, that is, the forming line position on the outside of the PAD or gold finger is not protected by solder mask layer. Therefore, the solder mask-free position on the forming line outside the PAD or gold finger is a high-risk position for router edge explosion. When making router tape data, the cutting speed of the router cutter when passing through the high-risk position is reduced by 20% or more on the original basis. That is, the cutting speed of the router cutter when passing through the high-risk position is 20% or more lower than the cutting speed of the router cutter when passing through other non-high-risk positions.

[0031] (9) Surface treatment (immersion nickel and gold): The copper surface of the solder pads at the solder mask opening position is uniformly deposited with a nickel layer and a gold layer of a certain required thickness through chemical principle. The thickness of the nickel layer is 3-5μm; the thickness of the gold layer is 0.05-0.1μm.

[0032] (10) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0033] (11) Molding: Specifically includes the following steps: a. First, perform rough milling on the production board, that is, use a milling cutter to mill the shape of the SET board or unit board on the production board. When rough milling the shape of the SET board or unit board, first make the size of the SET board or unit board 0.2mm larger on one side than the design, that is, expand the size of the SET board or unit board by 0.2mm on the design, leaving enough margin for subsequent fine finishing.

[0034] Because the edge bursting depth caused by the grooving plate is generally 0.2-0.3mm, and the edge bursting (i.e. white edge) caused by the grooving plate is also basically in the outer periphery of the pre-parts, and in the previous stacked plate structure, the edge bursting depth caused by the grooving plate can also be controlled within 0.1-0.2mm by taking advantage of the small width of the warp and weft yarns of 2116PP. That is, when the glass fiber is stretched during the grooving process, the breaking depth is generally the width of the warp and weft yarn node of 2116PP, and the maximum generally does not exceed twice the width of the warp and weft yarn node.

[0035] In the above, the diameter of the milling cutter is ≤1.6mm, preferably 1.4mm. Preferably, when using a 1.6mm router tool for routerging, the router tool travels at a speed of 18mm / s when routerging in locations other than high-risk areas, and the router tool travels at a speed of 14mm / s when passing through high-risk areas without solder mask.

[0036] b. Use a trimming knife or fine-tooth knife to finely trim the SET board or unit board to remove the pre-large portion of the SET board or unit board, obtaining the SET board or unit board (i.e., the shipping unit) of the designed size; that is, use a sharper trimming knife to finely trim a small amount of material on the outer perimeter after the board is cut, reducing the pulling during the cutting process, which can effectively reduce the generation of edge bursting and halo. During the fine trimming, the pre-large portion of the board is removed, and the edge bursting at the pre-large portion is also removed. After the fine trimming, the edge bursting depth of the board can be reduced to 0-0.1mm, which meets the design IPC standard requirements. This method can ensure the quality of the board without affecting the normal board cutting efficiency.

[0037] The fine-toothed knife mentioned above is a corn-shaped knife, characterized by bidirectional slotting of the blade teeth and a higher tooth density than the anti-burr knife. It can effectively suppress burrs on the board edge and is suitable for fine finishing processes with high requirements for edge bursting.

[0038] In the above, the preferred trimming knife is a single right-handed blade, which is characterized by unidirectional grooving of the blade teeth, sharp blade teeth, and is suitable for fine trimming of small allowances, resulting in a significant cutting effect on fiberglass sheets.

[0039] Preferably, the cutting speed of the trimmer is 50 mm / s when it is routering at locations other than high-risk areas, while the cutting speed of the router is reduced to 40 mm / s when it passes through high-risk areas without solder resist.

[0040] As mentioned above, when using a milling machine to form the production board, the chuck of the milling machine in use needs to be cleaned regularly every day to prevent dust and other debris from affecting its torque and to ensure that the milling machine has sufficient torque (the torque requirement when milling the board is generally ≥110N*cm). That is, the milling machine must be operated under the premise that there are no abnormalities. Regular cleaning of the chuck will usually increase the torque by 10%-20%.

[0041] (12) FQC: In accordance with the customer's acceptance standards and the applicant's inspection standards, inspect the appearance of the shipment unit, and repair any defects in a timely manner to ensure excellent quality control for the customer.

[0042] (13) FQA: Re-test the appearance, hole copper thickness, dielectric layer thickness, green solder mask thickness, inner layer copper thickness, etc. of the shipped units to see if they meet the customer's requirements.

[0043] (14) Packaging: Seal the shipping unit according to the packaging method and quantity required by the customer, and put in desiccant and humidity card before shipping.

[0044] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preventing and improving edge bursting on PCB molding boards, characterized in that, Includes the following steps: S1. In the molding process, when using a milling cutter to mill the shape of the SET board or unit board on the production board, the size of the SET board or unit board is pre-larged by 0.2mm on one side based on the design. S2. Use a trimming knife or fine-tooth knife to finely trim the SET board or unit board to remove the pre-larged parts of the SET board or unit board.

2. The method for preventing and improving edge bursting of PCB molding boards according to claim 1, characterized in that, In step S1, the diameter of the gong cutter is ≤1.6mm.

3. The method for preventing and improving edge bursting of PCB molding boards according to claim 1, characterized in that, In step S1, when the PAD or gold finger inside the SET board or unit board is ≤0.30mm away from the forming line on its outer perimeter and a solder mask opening design is implemented, the non-solder mask position at the forming line on the outer side of the PAD or gold finger is a high-risk position for the router board to burst; when the router passes through the high-risk position, the router's cutting speed is controlled to be reduced by 20% or more on the original basis.

4. The method for preventing and improving edge bursting of PCB molding boards according to claim 3, characterized in that, In step S1, the cutting speed of the milling cutter is 18 mm / s when it is milling the plate at a position other than the high-risk position, while the cutting speed of the milling cutter is reduced to 14 mm / s when it passes through the high-risk position.

5. The method for preventing and improving edge bursting of PCB molding boards according to claim 1, characterized in that, In step S2, when the PAD or gold finger inside the SET board or unit board is ≤0.30mm away from the forming line on its outer perimeter and a solder mask opening design is implemented, the non-solder mask position at the forming line on the outer side of the PAD or gold finger is a high-risk position for the router edge to burst; when the trimming knife passes through the high-risk position, the cutting speed of the trimming knife is reduced by 20% or more on the original basis.

6. The method for preventing and improving edge bursting of PCB molding boards according to claim 5, characterized in that, In step S2, the cutting speed of the trimming cutter when it is cutting the plate at a location other than the high-risk position is 50 mm / s, while the cutting speed of the cutting cutter when it passes through the high-risk position is reduced to 40 mm / s.

7. The method for preventing and improving edge bursting of PCB molding boards according to claim 1, characterized in that, When using a milling machine to shape production boards, the chucks of the milling machine need to be cleaned regularly every day.

8. The method for preventing and improving edge bursting of PCB molding boards according to any one of claims 1-7, characterized in that, The production board is a multilayer board made of PP to press the inner core board and the outer copper foil into one piece, and the multilayer board has successively undergone drilling, copper plating, full board electroplating and outer circuit fabrication processes.

9. The method for preventing and improving edge bursting of PCB molding boards according to claim 8, characterized in that, In the multilayer board stacked structure, the PP material adjacent to the outer copper foil is of type 2116.

10. The method for preventing and improving edge bursting of PCB molding boards according to claim 9, characterized in that, In the stacked structure of the multilayer board, the outer copper foil and the next outermost circuit are stacked sequentially from the outside in, with one first PP, four second PPs and one first PP. The first PP is of model 2116 and the second PP is of model 7628.