Method for processing blind hole on flexible circuit board

Abstract

The invention provides a method for processing a blind hole in a flexible circuit board. The method comprises the following steps: providing a circuit board for processing; drawing a pre-trepanning pattern on the circuit board; performing blind hole processing on the circuit board corresponding to the position of the pre-trepanning pattern; cleaning the blind hole for the first time through plasma; cleaning the blind hole for the second time through the cleaning liquid; carrying out visual inspection on the electroplated blind hole, and carrying out electroplating filling on the blind hole; wherein the blind hole is formed in a linear filling mode, the cross section of the blind hole is square, the square blind hole is manufactured in the linear filling mode, the area of a grounding PAD can be increased, the problem of poor low resistance can be solved, and the square blind hole can remarkably improve the effect of the electroplating filling process.

Description

Technical Field

[0001] The present application belongs to the technical field of circuit boards, and in particular relates to a method for processing blind holes in flexible circuit boards. Background Art

[0002] In existing technology, blind slots in FCBs are typically circular. However, during processing and use, copper plating on circular blind holes can cause low resistance in the grounding pad. Furthermore, circular blind holes can lead to high electrical test failures, which cannot be completely resolved.

[0003] To address the above issues, no effective solutions have been proposed so far.

[0004] It should be noted that the above technical background is merely provided to provide a clear and complete description of the technical solutions of the present invention and to facilitate understanding by those skilled in the art. Simply because these solutions are described in the technical background section of the present invention, it should not be assumed that the above technical solutions are well known to those skilled in the art. Summary of the Invention

[0005] The purpose of the present application is to provide a method for processing blind holes on a flexible circuit board to solve the problem of low resistance of the grounding PAD after copper plating of the circular blind hole.

[0006] The present application provides a method for processing blind holes on a flexible circuit board, comprising:

[0007] Provide circuit boards for processing;

[0008] Drawing a pre-opening pattern on the circuit board;

[0009] Processing blind holes on the circuit board corresponding to the positions of the pre-opening patterns;

[0010] Performing a first cleaning of the blind hole by plasma;

[0011] Cleaning the blind hole a second time with a cleaning fluid;

[0012] Performing a visual inspection on the blind holes that have been electroplated, and filling the blind holes with electroplating;

[0013] The blind hole is formed by linear filling, and the cross section of the blind hole is square.

[0014] Preferably, the outer side depression deviation of the blind hole after electroplating filling is less than 3 μm.

[0015] Preferably, in the process of "electroplating and filling the blind hole", black shadow liquid is added into the blind hole.

[0016] Preferably, the cleaning solution comprises an acidic cleaning solution, and the acidic cleaning solution comprises dilute sulfuric acid (H2SO4) and hydrogen peroxide (H2O2).

[0017] Preferably, the blind hole has two opposite long sides and two opposite short sides, and the short sides are configured as arcs.

[0018] Preferably, the distance between two opposite long sides of the blind hole is 30 μm.

[0019] Preferably, the distance between two opposite short sides of the blind hole is 800 μm, 900 μm or 1000 μm.

[0020] Preferably, in the step of "processing blind holes in the circuit board", the processing is performed by UV laser.

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

[0022] 1. The present invention adopts a linear filling method to produce square blind holes, which can increase the grounding PAD area, thereby solving the problem of poor low resistance. The square blind holes can significantly improve the effect of the electroplating filling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0024] Figure 1 This is an overall flow chart of a method for processing blind holes on a flexible circuit board provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0026] In the description of the present invention, it should be noted that the terms "upper", "middle", "lower", "inside", "outside", "front", "back" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention. The terms "first", "second" and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The following describes an implementation method of the present invention based on its overall structure.

[0027] Reference Figure 1 As shown, the embodiment of the present application provides a method for processing blind holes on a flexible circuit board, comprising:

[0028] Provide circuit boards for processing;

[0029] Draw a pre-opening pattern on the circuit board;

[0030] Process blind holes on the circuit board corresponding to the location of the pre-opening pattern;

[0031] The blind holes are cleaned for the first time by plasma;

[0032] The blind hole is cleaned for the second time by using cleaning fluid;

[0033] Conduct visual inspection on the blind holes that have been electroplated and fill them with electroplating;

[0034] The blind hole is formed by linear filling, and the cross section of the blind hole is square.

[0035] According to the above process, those skilled in the art can process blind holes on the circuit board. Specifically, before processing the blind holes, those skilled in the art can draw a blind hole pattern on the circuit board, so that the blind holes can be processed according to the drawn pattern.

[0036] After the blind holes are initially processed on the circuit board, those skilled in the art continue to clean the blind holes. During the cleaning process, it can be set to a first cleaning and a second cleaning.

[0037] During the first cleaning process, plasma cleaning can be used. Those skilled in the art can use a plasma cleaning machine to perform the first cleaning.

[0038] Specifically, the specific steps for the first cleaning are as follows:

[0039] The object to be cleaned is placed in a vacuum chamber. First, ensure that there are no obvious large particles of contaminants on the object's surface. Then, the chamber is closed and the vacuum pump is activated to reduce the pressure inside the chamber to a low state. Based on the cleaning requirements, the appropriate gas is introduced into the vacuum chamber. A high-frequency power supply is applied to ionize the gas to form a plasma. The high-energy ions, electrons, and free radicals in the plasma react with the surface contaminants, breaking them down into volatile gases that are then extracted by the vacuum pump.

[0040] In the above steps, those skilled in the art may arrange to use mechanical or chemical pre-cleaning when removing large particle pollutants. When the pressure in the chamber is reduced to a low pressure state, the pressure in the vacuum chamber may be set to 0.1-10Pa. When introducing corresponding gases into the vacuum chamber, oxygen, argon, hydrogen or a mixed gas may be introduced, wherein oxygen (O2): is used to remove organic pollutants (oxidation reaction), and argon (Ar): is used to remove inorganic pollutants by physical sputtering. In the process of applying high-frequency power, radio frequency 13.56MHz or microwave 2.45GHz may be applied. When the pollutants are decomposed into volatile gases, the volatile gases include carbon dioxide (CO2), water vapor (H2O), and the like.

[0041] According to the above steps, those skilled in the art can stably perform the first cleaning, thereby removing obvious pollutants and decomposable pollutants on the circuit board.

[0042] During the second cleaning process, those skilled in the art may perform chemical cleaning, specifically by adding a cleaning liquid into the blind hole, and reacting the cleaning liquid with the processed waste in the blind hole, thereby thoroughly cleaning the waste in the blind hole.

[0043] After the blind hole is cleaned, the technicians will continue to perform visual inspection and electroplating filling. Specifically, during the visual inspection process, the residues in and around the blind hole after cleaning, the hole wall quality, and potential defects are monitored.

[0044] Specifically, during the visual inspection and electroplating filling process, monitoring of residues includes:

[0045] Test for chemical residues, specifically, check whether there are any residual cleaning agents, etching solutions or other chemicals (such as white crystals or discoloration marks) in the blind hole; test for particle contamination, specifically, check whether foreign matter such as metal debris, dust, fiber, etc. remains in the hole or at the hole mouth; test for desmear residue, specifically, check for resin or glass fiber residue caused by incomplete removal of desmear after drilling.

[0046] During the hole wall quality inspection process, hole wall roughness and hole wall damage can be detected. Specifically, hole wall roughness inspection includes observing whether the hole wall is smooth and whether there is excessive roughness or burrs. Excessive roughness or burrs may affect electroplating or signal integrity. Hole wall damage inspection includes cracks, delamination, and hole wall tears.

[0047] Furthermore, hole shape and size can be inspected. This includes checking the consistency of the hole diameter, specifically confirming whether the blind hole diameter meets the design specifications, such as the diameter deviation of laser drilling. Hole shape and size inspection also includes checking the shape of the hole opening, specifically checking whether the hole opening is round and has no deformation, depressions, or protrusions, such as the "nail head" phenomenon.

[0048] Furthermore, the surface condition can be inspected. Specifically, oxidation or discoloration can be detected, that is, whether there is any abnormality such as oxidation blackening or discoloration inside or around the hole. The integrity of the copper foil can also be inspected, that is, whether the copper foil around the hole is scratched, wrinkled, or peeled.

[0049] Among them, in the above-mentioned detection, those skilled in the art may also monitor new contamination introduced during transportation or storage, such as fingerprints, oil stains, etc.

[0050] It is understood that the blind holes can be set to square shape during the above-mentioned processing. That is, during the process of drawing the graphics, the blind holes are designed to be square. During the processing, those skilled in the art can make the square blind holes by using a linear filling method.

[0051] In summary, the use of linear filling to produce square blind vias can increase the ground pad area, thereby solving the problem of poor low resistance. Furthermore, in the above-mentioned processing, the square blind vias can significantly improve the effect of the electroplating filling process.

[0052] In an optional embodiment, preferably, the outer recess deviation of the blind hole after electroplating filling is less than 3 μm, thereby improving interconnection reliability and high density interconnection (HDI) performance.

[0053] Specifically, improving interconnect reliability involves reducing signal transmission loss. Excessive concave deviation can lead to poor connections between blind vias and inner-layer circuits, such as uneven copper thickness or fractures. Reducing deviation ensures the integrity of electrical connections and reduces the risk of impedance mismatch. Improving interconnect reliability also involves avoiding microcracks. Precisely controlling the depth of blind vias can reduce drilling stress concentration and lower the probability of cracks during subsequent thermal cycles.

[0054] Improvements in high-density interconnect (HDI) performance include supporting finer line designs. Specifically, reduced recess deviation allows for precise alignment of blind vias with fine lines, meeting high-density wiring requirements. Improvements in HDI performance also include increased interlayer alignment accuracy. Specifically, for stacked blind vias or staggered via designs, reducing deviation avoids interlayer misalignment and improves multilayer board yield.

[0055] Preferably, during the process of "electroplating and filling the blind holes," a black shadow liquid is added to the blind holes. The black shadow liquid includes an oxidant, an acid or base, a corrosion inhibitor, a surfactant, and a stabilizer. The black shadow liquid can react with the copper foil to form a rough black oxide on the surface of the copper foil, thereby increasing the surface area. Furthermore, the resulting black oxide layer forms a porous structure, which can enhance the mechanical and chemical bonding with the resin (PP sheet). Furthermore, the corrosion inhibitor, by adsorbing on the copper surface, inhibits excessive corrosion and ensures a uniform thickness of the oxide layer.

[0056] Preferably, the cleaning solution comprises an acidic cleaning solution, wherein the acidic cleaning solution comprises dilute sulfuric acid (H2SO4) and hydrogen peroxide (H2O2). The acidic cleaning solution can remove the oxide layer and metal ion contamination.

[0057] Preferably, the blind via has two opposing long sides and two opposing short sides, with the short sides being curved. This avoids plating blind spots, reduces current density concentration, lowers stress concentration, and enhances mechanical strength. Furthermore, it can optimize signal integrity and improve process yield and consistency in high-frequency applications.

[0058] In a specific configuration, preferably, the distance between two opposite long sides of the blind hole is 30 μm. Preferably, the distance between two opposite short sides of the blind hole is 800 μm, 900 μm, or 1000 μm.

[0059] In an optional embodiment, preferably, in the step of "processing blind holes in the circuit board", processing is performed by UV laser.

[0060] Although different specific embodiments are mentioned in this application, this application is not limited to the situations described in industry standards or embodiments. Some industry standards or slightly modified implementations based on customized methods or implementations described in the embodiments can also achieve the same, equivalent, or similar implementation effects as the above embodiments, or predictable implementation effects after modification. Examples that apply these modified or modified data acquisition, processing, output, judgment methods, etc. can still fall within the scope of optional implementation schemes of this application.

[0061] Although the present application has been described through embodiments, those skilled in the art will appreciate that there are many modifications and variations to the present application without departing from the spirit of the present application. It is intended that the appended embodiments include these modifications and variations without departing from the present application.

Claims

1. A method for processing blind holes on a flexible circuit board, characterized in that: include: Provide circuit boards for processing; Drawing a pre-opening pattern on the circuit board; Processing blind holes on the circuit board corresponding to the positions of the pre-opening patterns; Performing a first cleaning of the blind hole by plasma; Cleaning the blind hole a second time with a cleaning fluid; Performing a visual inspection on the blind holes that have been electroplated, and filling the blind holes with electroplating; The blind hole is formed by linear filling, and the cross section of the blind hole is square.

2. The method for processing blind holes on a flexible circuit board according to claim 1, characterized in that: The outer side depression deviation of the blind hole after electroplating filling is less than 3 μm.

3. The method for processing blind holes on a flexible circuit board according to claim 1, characterized in that: In the process of "electroplating and filling the blind hole", black shadow liquid is added into the blind hole.

4. The method for processing blind holes on a flexible circuit board according to claim 1, characterized in that: The cleaning solution includes an acidic cleaning solution, and the components of the acidic cleaning solution include dilute sulfuric acid (HzSO4) and hydrogen peroxide (H2O2).

5. The method for processing blind holes on a flexible circuit board according to claim 1, characterized in that: The blind hole has two opposite long sides and two opposite short sides, and the short sides are configured as arcs.

6. The method for processing blind holes on a flexible circuit board according to claim 5, characterized in that: The distance between two opposite long sides of the blind hole is 30 μm.

7. The method for processing blind holes on a flexible circuit board according to claim 5, characterized in that: The distance between two opposite short sides of the blind hole is 800 μm, 900 μm or 1000 μm.

8. The method for processing blind holes on a flexible circuit board according to claim 1, characterized in that: In the step of "processing blind holes in the circuit board", processing is performed by UV laser.

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