Blind hole cleaning method of printed circuit board
By using CF-3004 proximity nozzles in the blind hole cleaning process of printed circuit boards, the problem of incomplete removal of graphite at the bottom of blind holes in traditional processes is solved, and more efficient cleaning results are achieved, and product yield and production efficiency are improved.
Patent Information
- Application Number
- CN202510500227.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-21
- Publication Date
- 2025-06-06
AI Technical Summary
The traditional blind hole cleaning process of printed circuit boards has unstable effect on the graphite removal at the bottom of the hole, which may lead to residual graphite remaining at the bottom of the hole, affecting the binding force of the plating layer and the substrate, and leading to electrical failure.
The CF-3004 proximity nozzle is used for fixing and washing. By adjusting the pressure and distance of the nozzle, the proximity and injection pressure between the nozzle and the plate surface are increased, the buffering effect of the liquid layer pool effect is weakened, the erosion ability of the potion and water flow is improved, and the graphite at the bottom of the blind hole is completely removed.
Effectively reduce the risk of blind pore residual carbon, improve product yield, reduce production costs, ensure good combination of plating and substrate, and avoid electrical failure.
Smart Images
Figure CN120111786A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of printed circuit board cleaning, and in particular relates to a method for cleaning blind holes of a printed circuit board. Background Art
[0002] Printed circuit boards (PCB boards) are key components in electronic devices, used to support and connect electronic components. They have become an indispensable part of modern electronic equipment manufacturing due to their advantages such as high density, high reliability, designability, producibility, testability, and assemblability.
[0003] Blind vias are opened on printed circuit boards. Blind vias are an important tool in PCB design, which are used to optimize space, improve electrical performance, reduce interference, and enhance the mechanical stability of circuit boards. The processes for removing carbon residues from blind vias in the black shadow process mainly include fixing, water washing, and micro-etching. However, these traditional processes have the problem of unstable cleaning effects in actual applications, especially in the removal of graphite at the bottom of blind vias. Although the graphite around the hole mouth and the hole wall can be well cleaned, there is a risk of incomplete cleaning of the graphite at the bottom of the blind via, and a layer of graphite may remain at the bottom of the hole, which appears as a black line in the slice observation (such as Figure 7 The presence of the black line will lead to insufficient bonding between the coating and the substrate, which will increase the internal resistance of the circuit when powered on for a long time or during thermal shock tests, eventually leading to electrical failure. Summary of the invention
[0004] In view of this, the present invention provides a method for cleaning blind holes of a printed circuit board, which can effectively reduce the risk of carbon residue in the blind holes, improve the yield of the product, and reduce the production cost.
[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for cleaning blind holes of a printed circuit board, comprising the following steps: S1. After treatment, a layer of conductive graphite is attached to the hole wall and around the hole mouth of the blind hole; S2, entering the fixing area, adjusting the nozzle pressure and the distance from the blind hole, spraying liquid medicine to the blind hole through the nozzle to remove unnecessary graphite from the hole wall of the blind hole and around the hole mouth; S3, entering the water washing area, adjusting the nozzle pressure and the distance from the blind hole, and then spraying water to the blind hole through the nozzle to remove the chemical solution residue left after the fixing process and the graphite residue around the hole opening in the hole; S4, enter the micro-etching tank, use chemicals to remove the graphite on the copper foil on the board surface and the inner copper layer at the bottom of the blind hole, and provide a rough and good surface for subsequent processes.
[0006] Preferably, the specific steps of step S1 are: S11, placing the semi-finished plate in the black shadow line for PI adjustment, using chemical means to etch and roughen the pore wall medium and adjust the surface charge of the medium, so that the pore wall is conducive to the subsequent black shadow groove graphite adhesion; S12, entering the pre-micro-etching tank to clean the oxide on the copper surface; S13. Enter the black shadow area and attach a layer of conductive graphite to the hole wall, bottom and around the hole mouth.
[0007] Preferably, in step S2 and step S3, the nozzle model used is a proximity type CF-3004B nozzle.
[0008] Preferably, the distance between the nozzle and the printed circuit board is 35 mm.
[0009] Preferably, in step S3 and step S4, the number of nozzles is multiple, and the distance between two adjacent nozzles is 20 mm.
[0010] Preferably, in step S3 and step S4, the spray pressure of each nozzle is 0.6-1.4Kg / cm 2 .
[0011] Preferably, the printed circuit board is immersed in the liquid medicine while the liquid medicine is sprayed through the nozzle.
[0012] Preferably, in step S2, the printed circuit board obtained in step S1 is conveyed to a fixing area by a roller conveyor device.
[0013] Compared with the prior art, the present invention has the following beneficial effects: In the fixing area, the present invention converts the ordinary nozzle into a CF-3004 proximity nozzle, which is closer to the board surface and has a greater nozzle pressure, effectively weakening the buffering effect of the tank liquid on the board surface pool effect and strengthening the flushing effect of the nozzle. The liquid medicine corrodes the accumulated graphite layers around the orifice and inside and at the bottom of the hole, reducing the binding force between the accumulated graphite layers, making them loose, and flowing out of the surface with the water flow under the flushing effect of the new nozzle. In the water washing area, while improving the water flow flushing ability of the nozzle, the present invention has no liquid layer immersion, thereby losing the buffering and protective effect of the liquid layer pool effect on the residual carbon, greatly improving the cleaning effect of the water washing section on the residual carbon. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 A conventional common nozzle diagram provided by an embodiment of the present invention; Figure 2 A diagram of a CF-3004 proximity nozzle provided in accordance with an embodiment of the present invention; Figure 3 A schematic diagram of the stratification of the graphite layer after fixing provided by an embodiment of the present invention; Figure 4A diagram showing a blind hole after cleaning using the method of the present invention provided in one embodiment of the present invention; Figure 5 A blind hole image after cleaning using a conventional blind hole cleaning technology provided by an embodiment of the present invention; Figure 6 A cross-sectional view of a slice after cleaning a blind hole using the method of the present invention provided in one embodiment of the present invention; Figure 7 A cross-sectional view of a blind hole after cleaning using a conventional blind hole cleaning technology provided by an embodiment of the present invention; Figure 8 A schematic diagram comparing the effects of the new and old blind hole cleaning technologies provided in one embodiment of the present invention.
[0015] Note: Figure 1 In the middle, the nozzle spacing is 100mm, the spraying height is 80mm, and the spraying water curtains do not overlap; Figure 2 The distance between the nozzles is 20mm, the spraying height is 35mm, and the spraying water curtains overlap; Figure 4 In the case of blind holes, there is no graphite residue at the bottom of the blind hole; Figure 5 In the case of a blind hole, the bottom was not cleaned and graphite remained. Figure 6 In the example, the bottom of the blind hole is well bonded to the inner layer, and there is no graphite residue or delamination. DETAILED DESCRIPTION
[0016] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand the present invention more clearly.
[0017] Printed circuit boards (PCB boards) are key components in electronic devices, used to support and connect electronic components. They have become an indispensable part of modern electronic equipment manufacturing due to their advantages such as high density, high reliability, designability, producibility, testability, and assemblability.
[0018] Blind vias are opened on printed circuit boards. Blind vias are an important tool in PCB design, which are used to optimize space, improve electrical performance, reduce interference, and enhance the mechanical stability of circuit boards. The processes for removing carbon residues from blind vias in the black shadow process mainly include fixing, water washing, and micro-etching. However, these traditional processes have the problem of unstable cleaning effects in actual applications, especially in the removal of graphite at the bottom of blind vias. Although the graphite around the hole mouth and the hole wall can be well cleaned, there is a risk of incomplete cleaning of the graphite at the bottom of the blind via, and a layer of graphite may remain at the bottom of the hole, which appears as a black line in the slice observation (such as Figure 7 The presence of the black line will lead to insufficient bonding between the coating and the substrate, which will increase the internal resistance of the circuit when powered on for a long time or during thermal shock tests, eventually leading to electrical failure.
[0019] In order to solve the above problems, the attached Figure 1-8 The present invention provides a printed circuit board The blind hole cleaning method comprises the following steps: S1. After treatment, a layer of conductive graphite is attached to the hole wall and around the hole mouth of the blind hole; S2, enter the fixing area, adjust the nozzle pressure and the distance from the blind hole, and then The nozzle sprays liquid medicine to the blind hole to remove unnecessary graphite from the hole wall and around the hole mouth of the blind hole; For example, in the fixing area, the excess graphite on the surface of the PCB board and the hole wall and hole mouth is removed by the combined action of the solution and the nozzle. Fixing is to remove the unnecessary graphite layer on the surface by spraying the fixing solution or chemical solution combined with the high-pressure jet of the nozzle. The purpose of this step is to ensure that the graphite is attached only in the required areas (such as the blind hole wall and the bottom of the hole) to avoid graphite being left in places where it should not appear, thereby affecting the subsequent process or electrical performance.
[0020] S3, enter the water washing area, adjust the nozzle pressure and the distance from the blind hole, and then The nozzle sprays water to the blind hole to remove chemical solution residues left after the fixing process and graphite residues around the hole opening; For example, in the water washing area, a nozzle is used to flush and clean the board surface, hole wall and excess graphite around the hole opening of the blind hole. The purpose of water washing is to remove the chemical solution residue left after the fixing process, as well as the graphite residue around the hole opening in the hole. This step usually uses a water-based solution or deionized water to ensure that the PCB surface is clean and free of pollution, and to avoid residual chemicals or graphite affecting subsequent processes.
[0021] S4, enter the micro-etching tank, use the solution to remove the copper foil on the board surface and the inner copper on the bottom of the blind hole. Graphite, and provide a rough and good surface for subsequent processes.
[0022] Specifically, after entering the micro-etching tank, the residual graphite on the copper foil on the board surface and the inner copper layer at the bottom of the blind hole is removed with a chemical solution. Micro-etching usually uses a weak acid or micro-etching agent solution to remove the graphite residue on the copper surface or the inner copper layer at the bottom of the hole and provide a rough and good surface for subsequent processes. This process removes unnecessary substances through a slight etching effect and provides a better adhesion basis for the next plating process.
[0023] Furthermore, the specific steps of step S1 are: S11, placing the semi-finished plate in the black shadow line for PI adjustment, using chemical means to etch and roughen the pore wall medium and adjust the surface charge of the medium, so that the pore wall is conducive to the subsequent black shadow groove graphite adhesion; Specifically, in this step, the semi-finished PCB board is placed in the black shadow line for PI (Polyimide) adjustment. The main purpose of PI adjustment is to treat the hole wall medium by chemical methods to achieve roughening of the hole wall surface. This treatment process can increase the surface area of the hole wall, which is conducive to the graphite adhesion in the subsequent process.
[0024] Specifically, the PI adjustment step includes using a chemical etchant to etch the pore wall to remove irregular films or residual substances on the pore wall, and through this process, the charge characteristics of the pore wall are adjusted to make it more conducive to the adhesion of graphite. In this way, the charge properties of the pore wall are optimized, making it easier for graphite to adhere and adhere stably.
[0025] S12, entering the pre-micro-etching tank to clean the oxide on the copper surface; Specifically, the main purpose of entering the pre-etching tank is to clean the oxide on the copper surface. In PCB manufacturing, the copper surface is easily exposed to the air to form an oxide layer, which will affect the adhesion of copper plating or graphite in subsequent processes. The chemical etching solution (usually a weak acid solution) in the pre-etching tank removes the oxide layer on the copper surface to ensure that the copper surface is clean, providing good surface conditions for subsequent electroplating and graphite adhesion.
[0026] S13. Enter the black shadow area and attach a layer of conductive graphite to the hole wall, bottom and around the hole mouth.
[0027] Specifically, after entering the black shadow area, a layer of conductive graphite will adhere to the hole wall, hole bottom and around the hole mouth. At this stage, by placing the PCB board into the black shadow tank, with the help of chemical gas or liquid medium, graphite will be evenly attached to the hole wall, hole bottom and around the hole mouth of the blind hole. Graphite is a conductive material, usually used to form a conductive film, providing good electrical connection and conductive performance. The role of the black shadow area is to ensure that the conductive graphite can be evenly coated on the blind hole area of the PCB, providing a conductive path for subsequent electroplating and electrical connection.
[0028] Further, in step S2 and step S3, the nozzle model used is a proximity CF-3004B nozzle. In some embodiments, the distance between the nozzle and the printed circuit board is 35 mm. In some embodiments, in step S3 and step S4, the number of nozzles is multiple, and the distance between two adjacent nozzles is 20 mm. Further, in step S3 and step S4, the spray pressure of each nozzle is 0.6-1.4 Kg / cm 2 .
[0029] Further, while the liquid medicine is sprayed through the nozzle, the printed circuit board is immersed in the liquid medicine.
[0030] Furthermore, in step S2, the printed circuit board obtained in step S1 is conveyed to the fixing area by a roller conveyor device.
[0031] The blind hole cleaning method of a printed circuit board provided by the present invention has a CF-3004 proximity nozzle closer to the board surface and a higher working pressure of the nozzle compared with the traditional blind hole cleaning method.
[0032] In the fixing area, the conventional ordinary nozzle is far away from the plate surface, and there is a layer of soaking solution between the nozzle and the plate surface. Although the low-pressure water mist sprayed by the ordinary nozzle has a certain flushing effect on the surface and wall of the blind hole after being buffered by the liquid layer pool effect, there is a certain uncertainty in the cleaning effect on the graphite at the bottom of the hole. Although the soaking solution can bite the accumulated graphite layer and loosen it, the flushing of the ordinary nozzle cannot flush the blind hole immersed in the tank liquid because it is buffered by the tank liquid. The graphite layer in the blind hole is bitten or remains at the bottom of the hole due to gravity. Schematic diagram of the specific structure of the graphite layer (such as Figure 1 ). Graphite has a typical layered structure. The two layers are only bound together by van der Waals force, and the bonding strength is low. They are easily separated from each other under the action of chemicals. However, the graphite layer and the dielectric layer (such as PP / PI / AD) are bound to each other by electron adsorption, and the bonding force is relatively strong. Therefore, the fixing solution cannot bite the graphite on the interface. In order to remove the graphite on the copper foil, it is necessary to use micro-etching solution to bite the copper foil in the subsequent process, and clean the graphite layer on the interface by etching the copper foil.
[0033] The present invention converts an ordinary nozzle into a CF-3004 proximity nozzle, which is closer to the board surface and has a greater nozzle pressure, effectively weakening the buffering effect of the tank liquid on the board surface pool effect and strengthening the scouring effect of the nozzle. The liquid medicine corrodes the accumulated graphite layers around the hole mouth, inside the hole and at the bottom of the hole, reducing the bonding force between the accumulated graphite layers and loosening them, and flowing out of the surface together with the water flow under the scouring action of the new nozzle.
[0034] In the water washing area after fixing, the common nozzle spraying and soaking procedure of the traditional cleaning technology has poor effect of water washing and flushing due to its low nozzle pressure, long distance from the board surface, and the buffering effect of the liquid layer pool effect. It is difficult to remove the accumulated graphite adhering to the hole wall or remaining at the bottom of the hole after the fixing area is bitten. In order to solve the problems in the water washing section, we upgraded the common nozzle to CF-3004 proximity nozzle, thereby shortening the distance between the upper and lower nozzles and the board surface and increasing the nozzle pressure, and improving the original soaking and spraying mode to pure spraying mode. By shortening the distance between the nozzle and the board surface and replacing it with a high-pressure nozzle to improve the flushing ability of the nozzle, the loose graphite adhering to the hole wall and remaining at the bottom of the hole flows out of the PCB board with the water flow under the flushing of the pressure water flow. The new blind hole cleaning technology improves the flushing ability of the nozzle water flow, but there is no liquid layer immersion, thus losing the buffering and protective effect of the liquid layer pool effect on the residual carbon, which greatly improves the cleaning effect of the water washing section on the residual carbon.
[0035] Setting Example Example 1 A printed circuit board cleaning method is provided. Without changing the composition and concentration of the original cleaning agent, the nozzle design is re-optimized, the spraying distance is changed, and the optimal spraying pressure is tested to meet the product cleaning requirements.
[0036] The product number used is S42015, the blind hole diameter of the printed circuit board is 100μm, the hole depth is 70μm, and the number of blind holes per PNL is 2815. In steps S2 and S3, the nozzle model used is a proximity CF-3004B nozzle, the distance between the nozzle and the printed circuit board is 35mm, the distance between the two nozzles is 50mm, and the injection pressure of each nozzle is 0.6Kg / cm 2 .
[0037] Example 2 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those in Example 1, except that the spray pressure of each nozzle is 0.8 Kg / cm 2 .
[0038] Example 3 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those in Example 1, except that the spray pressure of each nozzle is 1.0 Kg / cm 2 .
[0039] Example 4 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those in Example 1, except that the spray pressure of each nozzle is 1.2 Kg / cm 2 .
[0040] Example 5 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those in Example 1, except that the spray pressure of each nozzle is 1.4 Kg / cm 2 .
[0041] Comparative Example 1 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those of embodiment 1, except that, in step S2, only spraying is performed without soaking.
[0042] Comparative Example 2 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those of embodiment 1, except that, in step S3, soaking is performed simultaneously with spraying.
[0043] Comparative Example 3 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those in Example 1, except that the spray pressure of each nozzle is 1.6 Kg / cm 2 . Comparative Example 4 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those in Example 1, except that the spray pressure of each nozzle is 0.6 Kg / cm 2 .
[0044] Comparative Example 5 A method for cleaning a printed circuit board is provided, wherein the steps are the same as those of embodiment 1, except that in step S2, only spraying is performed without soaking, and in step S3, soaking is performed while spraying.
[0045] Performance testing and results Table 1 shows the yield test data of Examples 1-5 and Comparative Examples 1-5.
[0046] Table 1
[0047] in conclusion: The invention improves the design of the spray nozzle without changing the composition and proportion of the cleaning agent.
[0048] 1. The nozzle spacing is changed from 100mm to 20mm to ensure that the spraying water curtains overlap and there is no blind area for cleaning; 2. The proximity long nozzle design is adopted, and the distance between the nozzle and the cleaning product is shortened from 80mm to 35mm; 3. The cleaning method of the water washing section is changed from soaking + spraying to spraying (retain soaking + spraying). Spraying can directly rinse the bottom of the blind hole of the product, improving the cleaning effect.
[0049] 4. After comparison and verification, the spray cleaning pressure is > 1.0Kg / cm 2The defective rate is reduced from 0.845% to 0.004%, which can meet the black shadow process requirements and stabilize the quality.
[0050] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. A method for cleaning blind holes of a printed circuit board, characterized in that: The following steps are involved: S1. After treatment, a layer of conductive graphite is attached to the hole wall and around the hole mouth of the blind hole; S2, entering the fixing area, adjusting the nozzle pressure and the distance from the blind hole, spraying liquid medicine to the blind hole through the nozzle to remove unnecessary graphite from the hole wall of the blind hole and around the hole mouth; S3, entering the water washing area, adjusting the nozzle pressure and the distance from the blind hole, and then spraying water to the blind hole through the nozzle to remove the chemical solution residue left after the fixing process and the graphite residue around the hole opening in the hole; S4, enter the micro-etching tank, use chemicals to remove the graphite on the copper foil on the board surface and the inner copper layer at the bottom of the blind hole, and provide a rough and good surface for subsequent processes.
2. The method according to claim 1, characterized in that The specific steps of step S1 are: S11, placing the semi-finished plate in the black shadow line for PI adjustment, using chemical means to etch and roughen the pore wall medium and adjust the surface charge of the medium, so that the pore wall is conducive to the subsequent black shadow groove graphite adhesion; S12, entering the pre-micro-etching tank to clean the oxide on the copper surface; S13. Enter the black shadow area and attach a layer of conductive graphite to the hole wall, bottom and around the hole mouth.
3. The method according to claim 1, characterized in that In step S2 and step S3, the nozzle model used is a proximity type CF-3004B nozzle.
4. The method according to claim 3, characterized in that It is characterized in that The distance between the nozzle and the printed circuit board is 35 mm.
5. The method according to claim 4, characterized in that In step S3 and step S4, the number of nozzles is multiple, and the distance between two adjacent nozzles is 20 mm.
6. The method according to claim 5, characterized in that In step S3 and step S4, the spray pressure of each nozzle is 0.6-1.4Kg / cm 2 .
7. The method according to claim 1, characterized in that In step S2, the printed circuit board is immersed in the liquid medicine while the liquid medicine is sprayed through the nozzle.
8. The method according to claim 1, characterized in that: In step S2, the printed circuit board obtained in step S1 is conveyed to a fixing area by a roller conveyor device.