Hole metallization method for high-frequency high-speed multilayer flexible circuit board

Abstract

The invention relates to the technical field of hole metallization of circuit boards, and discloses a hole metallization method of a high-frequency high-speed multilayer flexible circuit board, which comprises the following steps of: 1, performing preset treatment; step 2, hole finishing and roughening treatment; step 3, pre-processing; step 4, carrying out metallization treatment on the black shadow holes; step 5, electro-coppering treatment; and step 6, quality inspection and test processing. According to the hole metallization method for the high-frequency and high-speed multilayer flexible circuit board, through the high-frequency and high-speed multilayer flexible circuit board made of special materials and designed, the transmission speed of signals on the circuit board is higher, signal delay and distortion are reduced, meanwhile, the hole metallization process is optimized, it can be ensured that the metallization layer has good conductivity, and the hole metallization performance is improved. The efficiency and stability of signal transmission are further improved, and signal loss is an important problem in high-frequency and high-speed application.

Description

Technical Field

[0001] The invention relates to the technical field of hole metallization of circuit boards, and in particular to a hole metallization method of a high-frequency and high-speed multi-layer flexible circuit board. Background Art

[0002] A flexible printed circuit board is an electronic component that uses a flexible insulating material as a substrate, prints or etches a conductive material (such as copper, silver, etc.) on the insulating material, and connects electronic components through circuit connections. Flexible printed circuit boards use thin insulating and conductive materials, making the entire circuit board light, thin, and compact, making it easy to carry and use. Flexible printed circuit boards have good flexibility and crease resistance, can be bent and folded at any angle, and can adapt to various complex application scenarios. Flexible printed circuit boards use high-quality insulating and conductive materials, and undergo strict production process control to improve the stability and reliability of the circuit board. Flexible printed circuit boards can use a variety of processing technologies such as printing, etching, and cutting to facilitate customization and mass production.

[0003] Hole metallization of flexible circuit boards is a key process that enables electrical connection between different layers on the flexible circuit board through metallized holes. The main purpose of hole metallization is to deposit a layer of conductive metal on the hole wall of the flexible circuit board to achieve electrical connection between layers.

[0004] The current hole metallization method of flexible circuit boards may not fully meet the needs of high-frequency and high-speed signal transmission in terms of design and material selection, which may easily lead to signal delay and distortion. During the high-frequency signal transmission process, due to the limitations of its material properties, interlayer connection structure and hole metallization process, the current existing hole metallization method of flexible circuit boards may cause flexible circuit boards to face greater signal loss problems. Summary of the invention

[0005] In view of the above-mentioned existing hole metallization method of flexible circuit boards, the design and material selection may not fully meet the needs of high-frequency and high-speed signal transmission, which may easily lead to signal delay and distortion. In the process of high-frequency signal transmission, due to the limitations of its material properties, interlayer connection structure and hole metallization process, the existing hole metallization method of flexible circuit boards may cause the flexible circuit boards to face greater signal loss problems, and the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to provide a method for hole metallization of a high-frequency, high-speed, multi-layer flexible circuit board, the purpose of which is: by adopting special materials and designs, the signal transmission speed on the circuit board is faster, the signal delay and distortion are reduced, and at the same time, the hole metallization process is optimized to ensure that the metallization layer has good conductivity, further improving the efficiency and stability of signal transmission.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for hole metallization of a high-frequency and high-speed multi-layer flexible circuit board, comprising step one, preset processing;

[0008] S1, firstly, drilling via holes of different densities and diameters on the printed circuit board using a drilling device;

[0009] S2, after drilling, the copper-clad board will have some small burrs at the hole opening. The burrs are removed by grinding equipment to ensure that the hole opening is smooth;

[0010] S3, then the multi-layer PCB is cleaned by a cleaning device to remove drilling contamination and hole micro-etching;

[0011] Step 2: hole filling and roughening treatment;

[0012] S1, remove grease, impurities and other pollutants on the hole wall again with a cleaning agent to ensure that the hole wall surface is clean;

[0013] S2, then through chemical treatment, a uniform negative charge layer is formed on the surface of the pore wall;

[0014] S3, then use chemical reagents to corrode the hole wall to form tiny unevenness on the surface, thereby increasing the surface area and roughness;

[0015] Step 3: Pre-processing;

[0016] S1, preparing a solution: using analytically pure tetrahydrofuran as a solvent, dissolving the B-stage epoxy resin in the prepreg (PREPREG) at a ratio of 5-30%;

[0017] S2, soaking in solution: immerse the drilled circuit board to be metallized in the solution prepared in step 3 S1 for more than 15 minutes, then remove it and shake off the liquid on the board surface and in the hole;

[0018] S3, baking and curing: put the circuit board into a 160℃ oven and bake for 1-2 hours;

[0019] Step 4: metallization treatment of black shadow holes;

[0020] S1, performing conventional degumming operation on the circuit board after baking in step 3 S3;

[0021] S2, first prepare the shadow potion, and then put the shadow potion into the shadow tank;

[0022] S3, immersing the circuit board in a black shadow tank for black shadow treatment;

[0023] S4, after the black shadow treatment, a fixing treatment is required to fix the conductive layer on the hole wall;

[0024] S5, then, micro-etching the circuit board using a micro-etching agent;

[0025] Step 5: electroplating copper;

[0026] S1, then put the circuit board into the electroplating tank, and make sure that the circuit board and the electroplating tank are in good contact, then add the electroplating solution into the electroplating tank, and then turn on the power to electroplate the circuit board. The copper ions in the electroplating solution are reduced to metallic copper under the action of the current and deposited on the hole wall and board surface of the circuit board. As the electroplating time increases, the thickness of the copper layer gradually increases;

[0027] S2, then use distilled water to clean the circuit board to remove the residual plating solution and impurities after electroplating, then put the cleaned circuit board into an oven for drying to remove moisture and residual solvent, and finally perform anti-oxidation treatment on the circuit board;

[0028] Step 6: Quality inspection and testing process;

[0029] S1, firstly, perform an appearance inspection on the hole wall after metallization to ensure that the surface is flat, free of cracks, bubbles and other defects;

[0030] S2, finally, the metallized high-frequency and high-speed multi-layer flexible circuit board is subjected to performance testing, including electrical performance testing and mechanical performance testing, to ensure that it meets the design requirements and usage requirements.

[0031] As a preferred solution of the hole metallization method of the high-frequency and high-speed multi-layer flexible circuit board of the present invention, wherein: the cleaning treatment in step 1 S3 usually uses an alkaline potassium permanganate treatment method.

[0032] As a preferred solution of the hole metallization method of the high-frequency, high-speed, multi-layer flexible circuit board of the present invention, wherein: the chemical treatment in step 2 S2 is to immerse or spray the hole wall with a specific chemical solution.

[0033] As a preferred scheme of the hole metallization method of the high-frequency, high-speed, multi-layer flexible circuit board of the present invention, wherein: the concentration of the chemical reagent in step 2 S3 is 25-35%, and the temperature of the chemical reagent is between 30-45°, the flexible circuit board is immersed in the chemical reagent for 20-40 seconds, taken out, and the liquid on the board surface and in the hole is shaken off.

[0034] As a preferred scheme of the hole metallization method of the high-frequency, high-speed, multi-layer flexible circuit board described in the present invention, wherein: the black shadow solution in the step four S2 includes, by mass percentage, 2-12% graphite, 1-8% polyethylene glycol, 0.5-6% glycerol, 0.1-0.5% n-butanol, 0.2-1% methyl cellulose, 0.2-0.6% carboxymethyl cellulose, 0.1-0.4% sodium carboxymethyl cellulose, 5-15% carbonate system buffer solution (adjusting the pH of the hole metallization solution to 6-18), and 10-45% water.

[0035] As a preferred solution of the hole metallization method of the high-frequency and high-speed multi-layer flexible circuit board of the present invention, the main components of the micro-etching agent in step 4 S5 are sodium persulfate and sulfuric acid.

[0036] As a preferred solution of the hole metallization method of the high-frequency and high-speed multi-layer flexible circuit board of the present invention, wherein: the electroplating solution in step five S1 is composed of copper sulfate, sulfuric acid and additives.

[0037] The beneficial effects of the present invention are as follows: by adopting a high-frequency, high-speed, multi-layer flexible circuit board made of special materials and designs, the signal transmission speed on the circuit board is made faster, and the signal delay and distortion are reduced. At the same time, the hole metallization process is optimized to ensure that the metallization layer has good conductivity, further improving the efficiency and stability of signal transmission. In high-frequency and high-speed applications, signal loss is an important issue. The multi-layer flexible circuit board can reduce the signal loss during transmission through a fine hole metallization process, improve the integrity and quality of the signal, and finally, the optimized hole metallization method can also reduce the thermal resistance between the metal layer and the substrate, further improving the heat dissipation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0039] Figure 1 The figure is a schematic diagram of the overall process of the hole metallization method of the high-frequency and high-speed multi-layer flexible circuit board of the present invention. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0041] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0042] Example 1

[0043] Reference Figure 1 , as an embodiment of the present invention, provides a method for metallizing holes in a high-frequency, high-speed, multi-layer flexible circuit board, and the method for metallizing holes in a high-frequency, high-speed, multi-layer flexible circuit board comprises:

[0044] Step 1: preset processing;

[0045] S1, first use drilling equipment to drill through holes of different densities and diameters on the printed circuit board. This is the first step to achieve electrical connection and the basis for subsequent metallization process;

[0046] S2, after drilling, the copper clad board will have some small burrs at the hole mouth, which can be removed by grinding equipment.

[0047] Make sure the orifice is smooth;

[0048] S3, then use cleaning equipment to clean the entire hole of the multi-layer PCB to remove drilling stains and hole micro-etching. Any grease, impurities or oxides may affect the adhesion and conductivity of the subsequent metallization layer;

[0049] Step 2: hole filling and roughening treatment;

[0050] S1, remove grease, impurities and other pollutants on the hole wall again with a cleaning agent to ensure that the hole wall surface is clean;

[0051] S2, then through chemical treatment, a uniform negative charge layer is formed on the surface of the pore wall, which is conducive to the subsequent adsorption and deposition of metal ions;

[0052] S3, then use chemical reagents to corrode the hole wall to form tiny unevenness on the surface, thereby increasing the surface area and roughness;

[0053] Step 3: Pre-processing;

[0054] S1, preparing a solution: using analytically pure tetrahydrofuran as a solvent, dissolving the B-stage epoxy resin in the prepreg (PREPREG) at a ratio of 5-30%;

[0055] S2, soaking in solution: immerse the drilled circuit board to be metallized in the solution prepared in step 3 S1 for more than 15 minutes, then remove it and shake off the liquid on the board surface and in the hole;

[0056] S3, baking and curing: put the circuit board into a 160℃ oven and bake for 1-2 hours;

[0057] Step 4: metallization treatment of black shadow holes;

[0058] S1, performing conventional degumming operation on the circuit board after baking in step 3 S3;

[0059] S2, first prepare the shadow potion, and then put the shadow potion into the shadow tank;

[0060] S3, immersing the circuit board in a black shadow tank for black shadow treatment. The black shadow agent in the black shadow tank contains unique additives and conductive colloid substances, which can form a conductive layer on the hole wall. The black shadow agent is also a slightly alkaline liquid. Through its unique composition, it can evenly deposit a layer of conductive material on the hole wall, providing a basis for the subsequent metallization process;

[0061] S4, after the black shadow treatment, a fixing treatment is required to fix the conductive layer on the hole wall. The fixing agent can effectively remove the excess black shadow agent on the hole wall, so that the conductive layer is more evenly and stably distributed on the hole wall;

[0062] S5, then, the circuit board is micro-etched by a micro-etching agent. Through the side etching effect, the shadow agent residue on the copper surface can be removed, and the copper surface is roughened at the same time, and the bonding force between the subsequent metal layer and the substrate is enhanced. However, it should be noted that since the resin and glass fiber are inert, the micro-etching agent cannot remove the shadow agent on the board;

[0063] Step 5: electroplating copper;

[0064] S1, then put the circuit board into the electroplating tank, and make sure that the circuit board and the electroplating tank are in good contact, then add the electroplating solution into the electroplating tank, and then turn on the power to electroplate the circuit board. The copper ions in the electroplating solution are reduced to metallic copper under the action of the current and deposited on the hole wall and board surface of the circuit board. As the electroplating time increases, the thickness of the copper layer gradually increases;

[0065] S2, then use distilled water to clean the circuit board to remove the residual plating solution and impurities after electroplating, then put the cleaned circuit board into an oven for drying to remove moisture and residual solvent, and finally perform anti-oxidation treatment on the circuit board to improve the surface quality and electrical performance of the metallization layer;

[0066] Step 6: Quality inspection and testing process;

[0067] S1, firstly, perform an appearance inspection on the hole wall after metallization to ensure that the surface is flat, free of cracks, bubbles and other defects;

[0068] S2, finally, the metallized high-frequency and high-speed multi-layer flexible circuit board is subjected to performance testing, including electrical performance testing and mechanical performance testing, to ensure that it meets the design requirements and usage requirements.

[0069] The cleaning process in step 1 S3 is usually carried out using an alkaline potassium permanganate treatment method.

[0070] The chemical treatment in step 2 S2 is to immerse or spray the hole wall with a specific chemical solution.

[0071] In step 2 S3, the concentration of the chemical reagent is 25-35%, and the temperature of the chemical reagent is between 30-45°. The flexible circuit board is immersed in the chemical reagent for 20-40 seconds, then taken out, and the liquid on the board surface and in the hole is shaken off.

[0072] In step 4 S2, the black shadow solution comprises, by mass percentage, 2% graphite, 1.2% polyethylene glycol, 0.5% glycerol, 0.1% n-butanol, 0.2% methyl cellulose, 0.2% carboxymethyl cellulose, 0.2% sodium carboxymethyl cellulose, 5% carbonate system buffer solution (to adjust the pH of the porous metallization solution to 6), and 10% water;

[0073] First, a plasma generator is used to form low-temperature oxygen plasma, and graphite is sent into a plasma cracking chamber through nitrogen. The temperature is controlled at 600° C., and the graphite surface is oxidized (6 seconds) to obtain highly dispersed graphite; then the highly dispersed graphite is added to water, and polyethylene glycol, glycerol, n-butanol, methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose and a carbonate system buffer solution are added under stirring, and ultrasonic stirring is performed to obtain the porous metallization solution.

[0074] The main components of the micro-etching agent in step 4 S5 are sodium persulfate and sulfuric acid.

[0075] The electroplating solution in step five S1 is composed of copper sulfate, sulfuric acid and additives.

[0076] Example 2

[0077] The black shadow solution in step 4 S2 includes, by mass percentage, 4% graphite, 3% polyethylene glycol, 1.5% glycerol, 0.2% n-butanol, 0.4% methyl cellulose, 0.3% carboxymethyl cellulose, 0.2% sodium carboxymethyl cellulose, 7% carbonate system buffer solution (to adjust the pH of the porous metallization solution to 8), and 15% water.

[0078] Example 3

[0079] The black shadow solution in step 4 S2 includes, by mass percentage, 7% graphite, 3% polyethylene glycol, 4% glycerol, 0.3% n-butanol, 0.5% methyl cellulose, 0.3% carboxymethyl cellulose, 0.25% sodium carboxymethyl cellulose, 10% carbonate system buffer solution (to adjust the pH of the porous metallization solution to 12), and 27% water.

[0080] Example 4

[0081] The black shadow solution in step 4 S2 includes, by mass percentage, 10% graphite, 6% polyethylene glycol, 4% glycerol, 0.4% n-butanol, 0.8% methyl cellulose, 0.5% carboxymethyl cellulose, 0.3% sodium carboxymethyl cellulose, 12% carbonate system buffer solution (to adjust the pH of the porous metallization solution to 15), and 35% water.

[0082] Example 5

[0083] The black shadow solution in step 4 S2 includes, by mass percentage, 12% graphite, 8% polyethylene glycol, 6% glycerol, 0.5% n-butanol, 1% methyl cellulose, 0.6% carboxymethyl cellulose, 0.4% sodium carboxymethyl cellulose, 15% carbonate system buffer solution (to adjust the pH of the porous metallization solution to 18), and 45% water.

[0084] By using special materials and designs for high-frequency, high-speed, multi-layer flexible circuit boards, the signal transmission speed on the circuit board is faster, reducing signal delay and distortion. At the same time, the hole metallization process is optimized to ensure that the metallization layer has good conductivity, further improving the efficiency and stability of signal transmission. In high-frequency and high-speed applications, signal loss is an important issue. The multi-layer flexible circuit board can reduce the loss of signals during transmission and improve the integrity and quality of signals through the fine hole metallization process. Finally, the optimized hole metallization method can also reduce the thermal resistance between the metal layer and the substrate, further improving the heat dissipation performance.

[0085] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for hole metallization of a high-frequency, high-speed, multi-layer flexible circuit board, characterized in that: include: Step 1: preset processing; S1, firstly, drilling via holes of different densities and diameters on the printed circuit board using a drilling device; S2, after drilling, the copper-clad board will have some small burrs at the hole opening. The burrs are removed by grinding equipment to ensure that the hole opening is smooth; S3, then the multi-layer PCB is cleaned by a cleaning device to remove drilling contamination and hole micro-etching; Step 2: hole filling and roughening treatment; S1, remove grease, impurities and other pollutants on the hole wall again with a cleaning agent to ensure that the hole wall surface is clean; S2, then through chemical treatment, a uniform negative charge layer is formed on the surface of the pore wall; S3, then use chemical reagents to corrode the hole wall to form tiny unevenness on the surface, thereby increasing the surface area and roughness; Step 3: Pre-processing; S1, preparing a solution: using analytically pure tetrahydrofuran as a solvent, dissolving the B-stage epoxy resin in the prepreg (PREPREG) at a ratio of 5-30%; S2, soaking in solution: immerse the drilled circuit board to be metallized in the solution prepared in step 3 S1 for more than 15 minutes, then remove it and shake off the liquid on the board surface and in the hole; S3, baking and curing: put the circuit board into a 160℃ oven and bake for 1-2 hours; Step 4: metallization treatment of black shadow holes; S1, performing conventional degumming operation on the circuit board after baking in step 3 S3; S2, first prepare the shadow potion, and then put the shadow potion into the shadow tank; S3, immersing the circuit board in a black shadow tank for black shadow treatment; S4, after the black shadow treatment, a fixing treatment is required to fix the conductive layer on the hole wall; S5, then, micro-etching the circuit board using a micro-etching agent; Step 5: electroplating copper; S1, then put the circuit board into the electroplating tank, and make sure that the circuit board and the electroplating tank are in good contact, then add the electroplating solution into the electroplating tank, and then turn on the power to electroplate the circuit board. The copper ions in the electroplating solution are reduced to metallic copper under the action of the current and deposited on the hole wall and board surface of the circuit board. As the electroplating time increases, the thickness of the copper layer gradually increases; S2, then use distilled water to clean the circuit board to remove the residual plating solution and impurities after electroplating, then put the cleaned circuit board into an oven for drying to remove moisture and residual solvent, and finally perform anti-oxidation treatment on the circuit board; Step 6: Quality inspection and testing process; S1, firstly, perform an appearance inspection on the hole wall after metallization to ensure that the surface is flat, free of cracks, bubbles and other defects; S2, finally, the metallized high-frequency and high-speed multi-layer flexible circuit board is subjected to performance testing, including electrical performance testing and mechanical performance testing, to ensure that it meets the design requirements and usage requirements.

2. The method for hole metallization of a high-frequency, high-speed, multi-layer flexible circuit board according to claim 1, characterized in that: The cleaning treatment in step 1 S3 usually uses an alkaline potassium permanganate treatment method.

3. The method for hole metallization of a high-frequency, high-speed, multi-layer flexible circuit board according to claim 1, characterized in that: The chemical treatment in step 2 S2 is to immerse or spray the hole wall with a specific chemical solution.

4. The method for hole metallization of a high-frequency, high-speed, multi-layer flexible circuit board according to claim 3, characterized in that: In step 2 S3, the concentration of the chemical reagent is 25-35%, and the temperature of the chemical reagent is between 30-45°. The flexible circuit board is immersed in the chemical reagent for 20-40 seconds, then taken out, and the liquid on the board surface and in the hole is shaken off.

5. The method for hole metallization of a high-frequency, high-speed, multi-layer flexible circuit board according to claim 1, characterized in that: The black shadow potion in step 4 S2 includes, by mass percentage, 2-12% graphite, 1-8% polyethylene glycol, 0.5-6% glycerol, 0.1-0.5% n-butanol, 0.2-1% methyl cellulose, 0.2-0.6% carboxymethyl cellulose, 0.1-0.4% sodium carboxymethyl cellulose, 5-15% carbonate system buffer solution (to adjust the pH of the porous metallization solution to 6-18), and 10-45% water.

6. The method for hole metallization of a high-frequency, high-speed, multi-layer flexible circuit board according to claim 1, characterized in that: The main components of the micro-etching agent in step 4 S5 are sodium persulfate and sulfuric acid.

7. The method for hole metallization of a high-frequency, high-speed, multi-layer flexible circuit board according to claim 1, characterized in that: The electroplating solution in step five S1 is composed of copper sulfate, sulfuric acid and additives.

Images