Etching method for reducing etching at tail end of copper circuit of flexible circuit board

Abstract

The invention belongs to the technical field of flexible circuit boards, and particularly relates to an etching method for reducing etching at the tail end of a copper circuit of a flexible circuit board. A miniature photoresist pattern with a specific distance S and a specific length L is arranged in an open area at the tail end of a copper circuit in an Inner Lead area. The pattern can create a local'small spacing 'etching environment at the tail end of the circuit in the etching stage, and the etching rate at the position is effectively reduced, so that the downward etching of the tail end of the circuit and the formation of'bow' defects are remarkably inhibited; meanwhile, the micro pattern falls off due to the fact that the copper surface below the micro pattern is rapidly etched through, and no residue is left. According to the invention, the integrity of the circuit structure is effectively improved, and the problem of circuit collapse during chip binding is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flexible circuit board, and particularly relates to an etching method for reducing under-etching of copper circuit ends of a flexible circuit board. BACKGROUND

[0002] The production process flow of a flexible circuit board generally comprises the steps of coating photoresist, exposure, development, etching and the like. The copper surface covered by the photoresist forms a circuit, and the exposed copper surface is etched by an etching liquid to form a circuit spacing. However, in the prior art, the copper circuit ends of the Inner Lead area often cause the etching liquid to be enriched due to low circuit density and spacious area, and the etching speed is too fast. The circuit ends will still have serious lateral under-etching even if they are protected by the photoresist, forming a commonly known "bow" structure. The structure is prone to cause the collapse of the inner lead circuit in the subsequent chip bonding process, resulting in bonding failure and affecting product yield.

[0003] Therefore, there is an urgent need for an etching method which can effectively control the etching morphology of the circuit ends of the Inner Lead area and reduce under-etching, thereby improving product yield and reliability. SUMMARY

[0004] The application aims to provide an etching method for reducing under-etching of copper circuit ends of a flexible circuit board, and aims to solve the problem of serious under-etching of the copper circuit ends of the Inner Lead area of a flexible circuit board due to too fast etching in the prior art, avoid the formation of a "bow" structure, and improve the yield of chip bonding.

[0005] In order to achieve the above-mentioned purpose, the application provides the following technical scheme: An etching method for reducing under-etching of copper circuit ends of a flexible circuit board, comprising the following steps: S1, coating: uniformly coating a layer of positive photoresist on a copper-clad substrate of a flexible circuit board; S2, exposure and development: exposing and developing the photoresist; S3, etching: performing an etching process; S4, post-processing: performing a film stripping and cleaning process to remove all residual photoresist.

[0006] Preferably, in the step S1, the thickness of the photoresist is 1-2 microns.

[0007] Preferably, the photoresist can be a conventional photoresist in the art; further preferably, it is a positive photoresist.

[0008] In some preferred embodiments, the photoresist is from MCS, model FR1000.

[0009] Preferably, in step S2, a second light-shielding pattern is added while retaining the first light-shielding pattern in the empty area at the end of the Inner Lead area on the upper surface of the quartz glass. The quartz glass and the light-shielding pattern together form a photomask.

[0010] The process of adding the light-shielding pattern to the quartz glass surface is described in [link to documentation]. Figure 1 .

[0011] Preferably, the distance between the second light-shielding pattern and the end of the Inner Lead area line is S, and the length is L.

[0012] Preferably, S = 9~10μm and L = 3~5μm.

[0013] Preferably, in step S2, the specific exposure steps are as follows: using a projection exposure machine, the exposure illuminance is 55mw / cm². 2 ~100mw / cm 2 The exposure level is 70mj~80mj.

[0014] Preferably, in step S2, the specific development step is as follows: using a tank-type immersion developer, the exposed flexible circuit board passes through the developing solution at a rate of 2~6 m / min to complete the photoresist development.

[0015] In actual production, the space between copper lines in densely packed areas is small, resulting in less etchant and less lateral etching after etching. This concept is applied to the technical solution of this invention to create small-pitch etching conditions at the ends, reducing the amount of etched material at the ends of lines in the Inner Lead region. An auxiliary light-shielding pattern is set in the open area corresponding to the end of each copper line in the Inner Lead region. After exposure and development, a micro-photoresist pattern composed of unexposed photoresist is formed on the outer side of each copper line end. The spacing S between the micro-photoresist pattern and the copper line end, and the length L along the line direction, are adjusted. Spacing S is used to precisely construct an ideal confined etching space. If S is too large, the effect of simulating a "small-pitch" environment is weakened, and the effect of suppressing etch is not significant; if S is too small, it may affect the pattern accuracy of the main circuit. Length L is a key balancing parameter. If L is too small, the accuracy of the exposure equipment may not be sufficient, and the photoresist pattern cannot be developed; if L is too large, copper layer residue will form, which does not meet product design requirements. 3μm to 5μm is the optimal range.

[0016] See the product state diagram after the photoresist has been exposed and developed. Figure 3 .

[0017] Preferably, step S3 uses an etching solution for the etching process.

[0018] Preferably, the etching process is a conventional process in the art.

[0019] Preferably, the specific steps of the etching process are as follows: using wet etching, the etching liquid etches the copper surface without photoresist, and through breaking copper, rough etching, lower etching and fine etching, the copper circuit is finally formed.

[0020] Further preferably, the specific steps of the etching process are as follows: the cleaned product belt is subjected to the etching machine, the etching machine has four spray discs, each spray disc sprays Cu 2+ The copper is etched, and the product belt sequentially passes through the four spray discs in the etching machine, and through breaking copper, rough etching, lower etching and fine etching, the circuit is finally formed.

[0021] Preferably, the spray disc is located directly above the product belt with a spacing of 50 mm.

[0022] Preferably, the main components of the etching liquid are CuCl2, H2O2, HCl and H2O.

[0023] In some preferred embodiments, the etching liquid is from Meike, model EXE-6105.

[0024] By constructing a small-interval etching condition at the end of the copper circuit, the etching result of the end of the copper circuit is consistent with that of the dense circuit area, thereby reducing the lower etching of the end of the copper circuit. The photoresist pattern added outside the end of the copper circuit is completely etched and the photoresist falls off due to the control of the interval S and the length L, the fast etching speed under the condition of low circuit density and spaciousness, and the large amount of lower etching of the copper under the photoresist.

[0025] The left view of the product before etching is shown in Figure 4 ; and the state diagram of the product after etching is shown in Figure 5 .

[0026] The present application provides a mask prepared by the etching method for reducing the lower etching of the end of the copper circuit of the flexible circuit board.

[0027] Compared with the prior art, the present application has the following advantages and beneficial effects: 1. The present application provides an etching method for reducing the lower etching of the end of the copper circuit of the flexible circuit board, by constructing a small-interval etching condition at the end of the copper circuit, the etching result of the end of the copper circuit is consistent with that of the dense circuit area, thereby effectively inhibiting the lower etching of the end of the copper circuit in the Inner Lead area, eliminating the "bow" defect and ensuring the reliability of subsequent chip binding.

[0028] 2. The present application constructs a small-interval etching condition, so that the etching result of the end of the circuit is consistent with that of the dense circuit area, and the overall etching uniformity of the product is improved.

[0029] 3. The micro light blocking pattern added in the application has a small length L, and the etching speed in the empty area is fast, so that the copper layer below the micro light blocking pattern is etched completely, and the photoresist is naturally dropped, so that no extra residue is left on the product, and the product design requirement is met.

[0030] 4. The application improves the structural integrity and mechanical strength of the Inner Lead area line, directly improves the success rate of the subsequent chip binding process, reduces the product failure risk, and has important significance for improving the overall good product rate and long-term reliability of high-end flexible circuit boards. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below.

[0032] Figure 1 Process for adding the light shielding pattern on the surface of the quartz glass of the application; Figure 2 Process for exposing the photoresist glue by the high-pressure UV lamp of the application; Figure 3 Product state diagram after the exposed photoresist glue is developed; Figure 4 Left view of the product before etching of the application; Figure 5 State diagram of the product after etching of the application; Figure 6 Microscopic diagram of the end of the copper line in the Inner Lead area after etching by the etching method of Comparative Example 1 of the application; Figure 7 Microscopic diagram of the end of the copper line in the Inner Lead area after etching by the etching method of Example 1 of the application; Markings in the figure: 1, high-pressure UV lamp; 2, quartz glass; 3, base material; 4, copper foil; 5, first light shielding pattern; 6, second light shielding pattern; 7, first non-irradiated photoresist glue; 8, second non-irradiated photoresist glue; 9, irradiated photoresist glue; 10, pitch. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0034] The raw materials used in the application are commercially available, specifically: Photoresist, from MCS, model FR1000.

[0035] The etching solution is from MAG, model EXE-6105. Example

[0036] This embodiment provides an etching method for reducing the etching at the ends of copper traces on flexible circuit boards, including the following steps: S1. Coating: A layer of photoresist is uniformly coated onto the copper-clad substrate of the flexible circuit board. S2, Exposure and Development: Expose and develop the photoresist; S3, Etching: Performing the etching process; S4. Post-processing: Perform the stripping and cleaning process to remove all residual photoresist.

[0037] In step S1, the thickness of the photoresist is 1.5 μm. In step S2, a second light-shielding pattern is added while retaining the first light-shielding pattern in the empty area at the end of the Inner Lead area on the upper surface of the quartz glass. The quartz glass and the light-shielding pattern together form a photomask.

[0038] The distance between the second light-shielding pattern and the end of the Inner Lead area line is S, and the length is L.

[0039] The value of S is 9.5 μm and the value of L is 4 μm.

[0040] In step S2, the specific steps of the exposure are as follows: using a projection exposure machine, the exposure illuminance is 80mw / cm². 2 The exposure was 75mj.

[0041] In step S2, the specific development steps are as follows: The exposed flexible circuit board is passed through the developing solution at a rate of 4 m / min using a tank-type immersion developing machine to complete the photoresist development. Step S3 involves etching using an etching solution.

[0042] The specific steps of the etching process are as follows: the etching solution is sprayed onto the surface of the flexible circuit board strip through a nozzle at a certain pressure to perform copper etching.

[0043] Microscopic image of the copper trace end in the Inner Lead region after etching using the aforementioned etching method, see Figure 6 . Example

[0044] This embodiment provides an etching method to reduce the undercut at the ends of copper lines on a flexible circuit board. Specifically, it is the same as in Embodiment 1, except that S = 9.5 μm and L = 3 μm. Example

[0045] The embodiment provides an etching method for reducing the undercut of the copper circuit end of a flexible circuit board, and the embodiment 1 is specifically the same except that S=9.5 μm and L=5 μm.

[0046] Comparative Example 1 The comparative example provides an etching method, and the embodiment 1 is specifically the same except that a traditional etching method is used, and a second shading pattern is additionally provided without the first shading pattern reserved in the empty area at the end of the circuit of the Inner Lead area on the upper surface of the quartz glass.

[0047] The microscopic diagram of the copper circuit end of the Inner Lead area after etching by the etching method is shown in Figure 7 .

[0048] Comparative Example 2 The comparative example provides an etching method for reducing the undercut of the copper circuit end of a flexible circuit board, and the embodiment 1 is specifically the same except that S=8 μm and L=4 μm.

[0049] Comparative Example 3 The comparative example provides an etching method for reducing the undercut of the copper circuit end of a flexible circuit board, and the embodiment 1 is specifically the same except that S=11 μm and L=4 μm.

[0050] Comparative Example 4 The comparative example provides an etching method for reducing the undercut of the copper circuit end of a flexible circuit board, and the embodiment 1 is specifically the same except that S=9.5 μm and L=2 μm.

[0051] Comparative Example 4 The comparative example provides an etching method for reducing the undercut of the copper circuit end of a flexible circuit board, and the embodiment 1 is specifically the same except that S=9.5 μm and L=6 μm.

[0052] Performance Test The cross-section results after etching of the embodiment 1-3 and the comparative examples 1-5 are observed, and Table 1 is shown.

[0053] Table 1 Cross-section results

[0054] As shown in Table 1, the undercut of the copper circuit end of the Inner Lead area is effectively inhibited after etching of the embodiment 1-3, and the “bow” defect is eliminated. The comparative example 1 is the existing condition, and the S and L values of the comparative examples 2-5 are not all within the range of the application, and therefore there are still problems such as undercut or residue.

[0055] The microscopic diagrams of the copper circuit end of the Inner Lead area after etching by the etching method of the embodiment 1 and the comparative example 1 are respectively shown inFigure 7 and Figure 6 By comparison Figure 6 and Figure 7 It can be seen that the etching method described in the application effectively inhibits the etching of the end of the copper line in the Inner Lead area, eliminates the "bow" defect, and ensures the reliability of subsequent chip binding.

[0056] The above is the preferred embodiment of the application, it should be pointed out that, for those skilled in the art, without departing from the principles described in the application, can also make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. An etching method for reducing undercutting at the ends of copper traces on a flexible circuit board, characterized in that, Includes the following steps: S1. Coating: A layer of photoresist is uniformly coated onto the copper foil substrate of the flexible circuit board. S2, Exposure and Development: Expose and develop the photoresist; S3, Etching: Performing the etching process; S4. Post-processing: Perform film removal and cleaning processes to remove all residual photoresist. In step S2, a second light-shielding pattern is added while retaining the first light-shielding pattern in the empty area at the end of the Inner Lead area on the upper surface of the quartz glass. The quartz glass and the light-shielding pattern together form a mask.

2. The etching method for reducing undercutting at the ends of copper traces on flexible circuit boards according to claim 1, characterized in that, The distance between the second light-shielding pattern and the end of the Inner Lead area line is S, and the length is L.

3. The etching method for reducing undercutting at the ends of copper traces on flexible circuit boards according to claim 2, characterized in that, The value of S is 9~10μm, and the value of L is 3~5μm.

4. The etching method for reducing undercutting at the ends of copper traces on flexible circuit boards according to claim 1, characterized in that, In step S1, the thickness of the photoresist is 1~2μm.

5. The etching method for reducing undercutting at the ends of copper traces on flexible circuit boards according to claim 1, characterized in that, Step S3 employs a wet etching process.

6. The etching method for reducing undercutting at the ends of copper traces on flexible circuit boards according to claim 5, characterized in that, The specific steps of the etching process are as follows: using wet etching, the etching solution etches the copper surface without photoresist, and through copper breaking, coarse etching, downward etching, and fine etching, the copper circuit is finally formed.

7. The etching method for reducing undercutting at the ends of copper traces on flexible circuit boards according to claim 6, characterized in that, The main components of the etching solution are CuCl2, H2O2, HCl, and H2O.

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