Method for etching circuit of support plate

Abstract

The invention discloses a carrier board circuit etching method, which comprises the following steps of: providing a production board which is subjected to hole filling, pattern electroplating and film stripping so as to form a step height difference between copper surfaces at a circuit position and a non-circuit position; spraying hydrogen peroxide on the board surface of the production board, removing the hydrogen peroxide on the circuit copper surface, and only retaining the hydrogen peroxide on the non-circuit copper surface; dilute sulphuric acid is sprayed on the plate surface of the production plate, the dilute sulphuric acid and hydrogen peroxide are mixed to form a micro-etching solution, the non-circuit copper surface is subjected to micro-etching, the dilute sulphuric acid is sprayed, standing is conducted for 5 minutes, then the production plate is cleaned, and the micro-etching step is repeated at least once till a base material on the non-circuit copper surface is exposed; spraying dilute sulphuric acid on the surface of the production board, removing the dilute sulphuric acid on the copper surface of the circuit, only retaining the exposed dilute sulphuric acid on the base material, and then roasting to concentrate the dilute sulphuric acid into concentrated sulphuric acid to etch the exposed base material so as to expose copper teeth; and etching and removing all the exposed copper teeth. According to the method, the purpose of etching the precise circuit of the carrier plate can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, and in particular to a method for etching a carrier circuit. Background Art

[0002] IC substrate is a new type of high-end PCB product that has emerged in recent years. It is called the jewel in the crown of PCB. IC substrate is developed on the basis of HDI board. It is a technological innovation that adapts to the rapid development of electronic packaging technology. It has excellent characteristics such as high density, high precision, high performance, miniaturization and lightness.

[0003] The circuits and spacing of the IC substrate are very small, reaching less than 15 microns. The circuit copper thickness is only about 15 microns, the bottom copper thickness is less than 5 microns, and the copper foil has a copper tooth depth of 2 microns.

[0004] Differential etching is a key step in the semi-additive process, which is to quickly etch away the thin copper in the non-pattern area without etching too much copper in the pattern area.

[0005] Using the traditional differential etching method, an etching amount higher than twice the copper tooth depth is required to completely etch away the copper teeth on the surface of the substrate. When the bottom copper thickness is uneven, an etching amount greater than the bottom copper thickness must be used. When the bottom copper thickness is 3±2 microns, the etching amount needs to reach 9 microns to completely etch the bottom copper on the surface of the substrate. The line spacing needs to be at least 4 microns before etching, and the maximum minimum width of the spacing after etching is 22 microns, which does not meet the requirement of less than 15 microns.

[0006] Another example is the prior public patent with application number CN202211463735: For the rapid flash etching method of the hydrogen peroxide plus sulfuric acid formula currently used for IC substrates and SLP-like substrates, the organic additives are easy to remain and wrap the copper teeth, resulting in the problem of copper tooth residue. It adopts a two-level rapid flash etching method. After the rapid flash etching of the existing hydrogen peroxide plus sulfuric acid formula, a new level of micro-etching with an additive-free formula is added to specifically etch the copper teeth of IC substrates and SLP-like substrate copper foils, and eliminate the adverse effects of organic additive residues, and then the normal contour copper foil of normal copper teeth can be used to improve the adhesion of the copper foil and ensure the quality. This method also requires an etching amount twice the depth of the copper teeth to completely etch away the bottom copper layer, and it is difficult to achieve a line width and line gap below 15 microns. Summary of the invention

[0007] In view of the above-mentioned existing technical defects, the present invention provides a method for etching the circuit of a carrier board, in which a micro-etching solution for etching the copper layer and concentrated sulfuric acid for etching the substrate are distributed in a targeted manner at the circuit gap position, and multiple micro-etching methods are used to reduce the amount of etching on the top surface of the circuit copper, and the copper teeth on the non-circuit copper surface can be effectively removed, thereby achieving the purpose of precise circuit etching of the carrier board.

[0008] In order to solve the above technical problems, the present invention provides a method for etching a substrate circuit, comprising the following steps:

[0009] S1. Provide a production board that has been subjected to hole filling and pattern electroplating and film stripping, wherein during pattern electroplating, only copper is electroplated on the production board without tin electroplating, so as to form a step height difference between the copper surfaces at the circuit and the copper surfaces at the non-circuit;

[0010] S2. Spray a layer of hydrogen peroxide on the surface of the production board, and then remove the hydrogen peroxide on the circuit copper surface, leaving only the hydrogen peroxide on the non-circuit copper surface;

[0011] S3, spray a layer of dilute sulfuric acid on the board surface of the production board, and the dilute sulfuric acid and the hydrogen peroxide on the board surface are mixed to form a micro-etching solution to micro-etch the non-circuit copper surface; spray the dilute sulfuric acid and let it stand for 5 minutes before cleaning the production board;

[0012] S4, repeating steps S2 to S3 at least once until the substrate at the non-circuit copper surface is exposed;

[0013] S5. Spray a layer of dilute sulfuric acid on the surface of the production board, and then remove the dilute sulfuric acid on the copper surface of the circuit, leaving only the dilute sulfuric acid on the exposed substrate;

[0014] S6, then the production board is baked to concentrate the dilute sulfuric acid on the board surface into concentrated sulfuric acid, and the concentrated sulfuric acid corrodes the exposed substrate to expose the copper teeth;

[0015] S7, repeat steps S2 to S3 at least once until all the exposed copper teeth are etched away.

[0016] Furthermore, in step S1, after hole filling and pattern electroplating, the copper thickness at the circuit is 12±2 microns, and the copper thickness at the non-circuit is 1-5 microns.

[0017] Furthermore, in step S1, the line gap after hole filling and pattern plating is controlled at 4 microns.

[0018] Furthermore, in step S2, the mass percentage concentration of hydrogen peroxide is 10%-15%.

[0019] Furthermore, in step S2, after spraying the hydrogen peroxide, the hydrogen peroxide on the copper surface of the circuit is removed by absorbing it with a rubber scraper or a water-absorbing roller.

[0020] Furthermore, in step S3, the mass percentage concentration of the dilute sulfuric acid is 10%-20%.

[0021] Furthermore, in step S5, after the dilute sulfuric acid is sprayed, the dilute sulfuric acid on the copper surface of the circuit is removed by suction using a rubber scraper or a water-absorbing roller.

[0022] Furthermore, in step S5, the mass percentage concentration of the dilute sulfuric acid is 20%-30%.

[0023] Furthermore, in step S6, the production board is placed in an oven at a temperature of 100-150°C for baking.

[0024] Furthermore, in step S6, the baking time is 15-30 minutes.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The components of the micro-etching liquid are decomposed into two parts (i.e., hydrogen peroxide and dilute sulfuric acid), and then the micro-etching liquid composed of hydrogen peroxide and dilute sulfuric acid is adsorbed at the line gap due to the surface tension of the liquid, and the amount of corrosion on the top surface of the line is very small. Multiple micro-etching methods are used to effectively reduce the amount of corrosion on the line copper and effectively control the width of the line and line gap.

[0027] 2. After the substrate at the non-circuit copper surface is exposed, the dilute sulfuric acid is concentrated to form concentrated sulfuric acid by baking, and the exposed part of the substrate where the copper teeth are engaged is corroded by the concentrated sulfuric acid to completely expose the copper teeth at the non-circuit copper surface. Then, the exposed copper teeth at the circuit gap are etched away in a targeted manner by spraying hydrogen peroxide and dilute sulfuric acid in batches. In this method, the amount of micro-etching on the copper side of the circuit is relatively small during the process of corroding the substrate with concentrated sulfuric acid and micro-etching the copper teeth with micro-etching liquid, so as to achieve the purpose of precise circuit etching of the substrate and meet the requirement that the circuit and line gap of the IC substrate are both below 15 microns. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of hole filling and pattern electroplating on a production board in an embodiment;

[0029] Figure 2 This is a schematic diagram of hydrogen peroxide remaining in the line gap of the production board in the embodiment;

[0030] Figure 3 This is a schematic diagram of the embodiment after the copper layer at the non-circuit copper surface is etched away on the production board;

[0031] Figure 4 This is a schematic diagram of dilute sulfuric acid remaining in the line gap of the production board in the embodiment;

[0032] Figure 5 is a schematic diagram of etching the substrate on the production board in the embodiment;

[0033] Figure 6 This is a schematic diagram of the process after the copper teeth are removed from the production board in the embodiment. DETAILED DESCRIPTION

[0034] In order to more fully understand the technical content of the present invention, the technical solution of the present invention will be further introduced and illustrated in conjunction with specific embodiments below.

[0035] Example 1

[0036] A method for etching a substrate circuit shown in this embodiment includes the following steps:

[0037] a. Paste dry film on the production board (i.e. IC carrier board), and form outer circuit pattern on the production board after exposure and development. The area outside the outer circuit pattern is covered and protected by dry film. Then fill holes (i.e. hole filling electroplating) and pattern electroplating are performed on the production board to thicken the copper thickness at the outer circuit pattern. The blind holes on the board have been filled and leveled by electroplating. During pattern electroplating, only copper is electroplated without tin. Then the film is removed to form a step height difference between the line copper surface 1 and the non-line copper surface 2. Due to the step height difference, a line gap 3 (such as Figure 1 shown).

[0038] In the above, the production board is a multi-layer board in which the inner core board and the outer copper foil are pressed together by a semi-cured sheet, and the multi-layer board has been drilled, copper plated or black shadow processed in sequence; the outer copper foil adopts VLP copper foil (ultra-low profile copper foil), and its copper teeth are about 1.5 microns, and the copper thickness of the production board (i.e., the bottom copper thickness) is 3±1μm before hole filling and pattern electroplating, and the copper thickness at the circuit after hole filling and pattern electroplating is 12±2 microns, the line width is 20 microns, and the line gap is 4 microns.

[0039] Based on this, the micro-etching amount of the non-circuit copper surface on the production board is controlled at 3 microns before the copper teeth are exposed, and the micro-etching amount is controlled at 1 micron after the copper teeth are exposed. Similarly, the side etching amount of the circuit copper before and after the copper teeth are exposed is 4 microns. That is, if the circuit copper is side-etched on both sides, the width of the entire line gap will become 8 microns wider. Combined with the initial line gap width of 4 microns, the final actual line width and line gap of the finished product are both 12 microns.

[0040] b. Spray a layer of hydrogen peroxide on the surface of the production board, and then use the step height difference between the circuit copper surface and the non-circuit copper surface to remove the hydrogen peroxide on the circuit copper surface by squeegee or water-absorbing roller, leaving only the hydrogen peroxide on the non-circuit copper surface (i.e., the concave position) 4 (such as Figure 2 shown).

[0041] In the above, the mass percentage concentration of hydrogen peroxide is 10%-15%, that is, the mass fraction of the solute in the hydrogen peroxide is 10%-15%.

[0042] c. Spray a layer of dilute sulfuric acid on the surface of the production board. The dilute sulfuric acid and the remaining hydrogen peroxide on the board surface are mixed to form a micro-etching solution, so that the non-circuit copper surface is micro-etched with the micro-etching solution, and the circuit copper side is also side-etched simultaneously. After spraying the dilute sulfuric acid and letting it stand for 5 minutes, clean the production board to remove the micro-etching solution on the production board, that is, the production board is only micro-etched for 5 minutes each time.

[0043] In the above, the mass percentage concentration of the dilute sulfuric acid is 10%-20%, that is, the mass fraction of the solute in the dilute sulfuric acid is 10%-20%.

[0044] In the above, the micro-etching solution composed of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) reacts with copper (Cu). In this reaction, hydrogen peroxide acts as an oxidant, sulfuric acid provides an acidic environment, and copper is oxidized into copper ions. The chemical reaction equation is as follows:

[0045] Cu+H2O2+H2SO4=CuSO4+2H2O

[0046] The ionic formula is:Cu+H2O2+2H + =Cu 2+ +2H2O

[0047] In this reaction, copper (Cu) is oxidized by hydrogen peroxide, increasing its valence from 0 to +2, generating copper sulfate (CuSO4); the oxygen element in hydrogen peroxide decreases from -1 to -2, generating water (H2O); sulfuric acid mainly provides hydrogen ions (H + ) participates in the reaction and promotes the entire redox process, ultimately causing micro-corrosion of copper.

[0048] d. Repeat steps b to c at least once until the substrate 5 at the non-circuit copper surface is exposed (e.g. Figure 3 As shown); according to actual production verification, taking the bottom copper 3±1μm as an example, in step d, steps b to c need to be repeated four times to expose the substrate at the non-circuit copper surface, plus the first time, that is, a total of five micro-etching processes need to be performed.

[0049] e. Spray a layer of dilute sulfuric acid on the surface of the production board, and then use the step height difference between the circuit copper surface and the non-circuit copper surface to remove the dilute sulfuric acid on the circuit copper surface by squeegee or water-absorbing roller, leaving only the dilute sulfuric acid on the exposed substrate 6 (such as Figure 4 shown).

[0050] In the above, the mass percentage concentration of the dilute sulfuric acid is 20%-30%, that is, the mass fraction of the solute in the dilute sulfuric acid is 20%-30%.

[0051] f. Then, the production board is placed in an oven at a temperature of 100-150°C and baked for 15-30 minutes. The water in the dilute sulfuric acid is evaporated and removed by baking, so that the dilute sulfuric acid remaining on the board surface is concentrated into concentrated sulfuric acid, and the concentrated sulfuric acid corrodes the exposed substrate, thereby completely exposing the copper teeth 7 (such as Figure 5 shown).

[0052] h. Repeat steps b to c at least once until all exposed copper teeth are etched away (e.g. Figure 6 As shown), fine outer layer circuits are finally produced, and the line width and line gap of the final actual finished product are controlled at 12 microns, achieving the purpose of precise circuit etching of the substrate and meeting the requirement that the circuit and line gap of the IC substrate are both less than 15 microns.

[0053] Example 2

[0054] A method for etching a substrate circuit shown in this embodiment includes the following steps:

[0055] a. Paste dry film on the production board (i.e. IC carrier board), and form outer circuit pattern on the production board after exposure and development. The area outside the outer circuit pattern is covered and protected by dry film. Then fill holes (i.e. hole filling electroplating) and pattern electroplating are performed on the production board to thicken the copper thickness at the outer circuit pattern. The blind holes on the board have been filled and leveled by electroplating. During pattern electroplating, only copper is electroplated without tin. Then the film is removed to form a step height difference between the line copper surface 1 and the non-line copper surface 2. Due to the step height difference, a line gap 3 (such as Figure 1 shown).

[0056] In the above, the production board is a multi-layer board in which the inner core board and the outer copper foil are pressed together by a semi-cured sheet, and the multi-layer board has been drilled, copper plated or black shadow processed in sequence; the outer copper foil adopts VLP copper foil (ultra-low profile copper foil), and its copper teeth 4 are about 0.5 microns, and the copper thickness of the production board (i.e., the bottom copper thickness) before filling and pattern plating is 1.5±0.5μm, and the copper thickness at the circuit after filling and pattern plating is 12±2 microns, the line width is 12 microns, and the line gap is 4 microns.

[0057] Based on this, the micro-etching amount of the non-circuit copper surface on the production board is controlled at 1.5 microns before the copper teeth are exposed, and the micro-etching amount is controlled at 0.5 microns after the copper teeth are exposed. Similarly, the side etching amount of the circuit copper before and after the copper teeth are exposed is 2 microns. That is, if the circuit copper is side-etched on both sides, the width of the entire line gap will become 4 microns wider. Combined with the initial line gap width of 4 microns, the final actual line width and line gap of the finished product are both 8 microns.

[0058] b. Spray a layer of hydrogen peroxide on the surface of the production board, and then use the step height difference between the circuit copper surface and the non-circuit copper surface to remove the hydrogen peroxide on the circuit copper surface by squeegee or water-absorbing roller, leaving only the hydrogen peroxide on the non-circuit copper surface (i.e., the concave position) 4 (such as Figure 2 shown).

[0059] In the above, the mass percentage concentration of hydrogen peroxide is 10%-15%, that is, the mass fraction of the solute in the hydrogen peroxide is 10%-15%.

[0060] c. Spray a layer of dilute sulfuric acid on the surface of the production board. The dilute sulfuric acid and the remaining hydrogen peroxide on the board surface are mixed to form a micro-etching solution, so that the non-circuit copper surface is micro-etched with the micro-etching solution, and the circuit copper side is also side-etched simultaneously. After spraying the dilute sulfuric acid and letting it stand for 5 minutes, clean the production board to remove the micro-etching solution on the production board, that is, the production board is only micro-etched for 5 minutes each time.

[0061] In the above, the mass percentage concentration of the dilute sulfuric acid is 10%-20%, that is, the mass fraction of the solute in the dilute sulfuric acid is 10%-20%.

[0062] In the above, the micro-etching solution composed of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) reacts with copper (Cu). In this reaction, hydrogen peroxide acts as an oxidant, sulfuric acid provides an acidic environment, and copper is oxidized into copper ions. The chemical reaction equation is as follows:

[0063] Cu+H2O2+H2SO4=CuSO4+2H2O

[0064] The ionic formula is:Cu+H2O2+2H + =Cu 2+ +2H2O

[0065] In this reaction, copper (Cu) is oxidized by hydrogen peroxide, increasing its valence from 0 to +2, generating copper sulfate (CuSO4); the oxygen element in hydrogen peroxide decreases from -1 to -2, generating water (H2O); sulfuric acid mainly provides hydrogen ions (H + ) participates in the reaction and promotes the entire redox process, ultimately causing micro-corrosion of copper.

[0066] d. Repeat steps b to c at least once until the substrate 5 at the non-circuit copper surface is exposed (e.g. Figure 3 As shown); according to actual production verification, taking the bottom copper 3±1μm as an example, in step d, steps b to c need to be repeated four times to expose the substrate at the non-circuit copper surface, plus the first time, that is, a total of five micro-etching processes need to be performed.

[0067] e. Spray a layer of dilute sulfuric acid on the surface of the production board, and then use the step height difference between the circuit copper surface and the non-circuit copper surface to remove the dilute sulfuric acid on the circuit copper surface by squeegee or water-absorbing roller, leaving only the dilute sulfuric acid on the exposed substrate 6 (such as Figure 4 shown).

[0068] In the above, the mass percentage concentration of the dilute sulfuric acid is 20%-30%, that is, the mass fraction of the solute in the dilute sulfuric acid is 20%-30%.

[0069] f. Then, the production board is placed in an oven at a temperature of 100-150°C and baked for 15-30 minutes. The water in the dilute sulfuric acid is evaporated and removed by baking, so that the dilute sulfuric acid remaining on the board surface is concentrated into concentrated sulfuric acid, and the concentrated sulfuric acid corrodes the exposed substrate, thereby completely exposing the copper teeth 7 (such as Figure 5 shown).

[0070] h. Repeat steps b to c at least once until all exposed copper teeth are etched away (e.g. Figure 6 As shown), fine outer layer circuits are finally produced, and the line width and line gap of the final actual finished product are controlled at 8 microns, achieving the purpose of precise circuit etching of the substrate and meeting the requirement that the circuit and line gap of the IC substrate are both less than 15 microns.

[0071] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for etching a substrate circuit, characterized in that: The following steps are involved: S1. Provide a production board that has been subjected to hole filling and pattern electroplating and film stripping, wherein during pattern electroplating, only copper is electroplated on the production board without tin electroplating, so as to form a step height difference between the copper surfaces at the circuit and the copper surfaces at the non-circuit; S2. Spray a layer of hydrogen peroxide on the surface of the production board, and then remove the hydrogen peroxide on the circuit copper surface, leaving only the hydrogen peroxide on the non-circuit copper surface; S3, spray a layer of dilute sulfuric acid on the board surface of the production board, and the dilute sulfuric acid and the hydrogen peroxide on the board surface are mixed to form a micro-etching solution to micro-etch the non-circuit copper surface; spray the dilute sulfuric acid and let it stand for 5 minutes before cleaning the production board; S4, repeating steps S2 to S3 at least once until the substrate at the non-circuit copper surface is exposed; S5. Spray a layer of dilute sulfuric acid on the surface of the production board, and then remove the dilute sulfuric acid on the copper surface of the circuit, leaving only the dilute sulfuric acid on the exposed substrate; S6, then the production board is baked to concentrate the dilute sulfuric acid on the board surface into concentrated sulfuric acid, and the concentrated sulfuric acid corrodes the exposed substrate to expose the copper teeth; S7, repeat steps S2 to S3 at least once until all the exposed copper teeth are etched away.

2. The method for etching a substrate circuit according to claim 1, characterized in that: In step S1, after hole filling and pattern electroplating, the copper thickness at the circuit is 12±2 microns, and the copper thickness at the non-circuit is 1-5 microns.

3. The method for etching a substrate circuit according to claim 1, characterized in that: In step S1, the line gap after hole filling and pattern electroplating is controlled at 4 microns.

4. The method for etching a substrate circuit according to claim 1, characterized in that: In step S2, the mass percentage concentration of hydrogen peroxide is 10%-15%.

5. The method for etching a carrier circuit according to claim 1, characterized in that: In step S2, after spraying hydrogen peroxide, the hydrogen peroxide on the copper surface of the circuit is removed by absorbing it with a rubber scraper or a water-absorbing roller.

6. The method for etching a carrier circuit according to any one of claims 1 to 5, characterized in that: In step S3, the mass percentage concentration of dilute sulfuric acid is 10%-20%.

7. The method for etching a substrate circuit according to claim 1, characterized in that: In step S5, after the dilute sulfuric acid is sprayed, the dilute sulfuric acid on the copper surface of the circuit is removed by suction using a rubber scraper or a water-absorbing roller.

8. The method for etching a substrate circuit according to claim 1, characterized in that: In step S5, the mass percentage concentration of the dilute sulfuric acid is 20%-30%.

9. The method for etching a carrier circuit according to claim 8, characterized in that: In step S6, the production board is placed in an oven at a temperature of 100-150°C for baking.

10. The method for etching a carrier circuit according to claim 9, characterized in that: In step S6, the baking time is 15-30 minutes.

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