Pattern electroplating method of circuit board

Abstract

The invention discloses a pattern electroplating method for a circuit board, which comprises the following steps of: forming an isolated line on the circuit board through copper plating, tin plating, film stripping and etching processes, and is characterized in that the current density of the tin plating process is set to be 7-10ASF, and the concentration of a tin brightening agent is 13-15ml / L; in the film stripping process, the film stripping liquid is DL-400, and the concentration of the film stripping liquid is 7-9 wt%. According to the pattern electroplating method of the circuit board provided by the invention, the tin dissolving amount of a film stripping process can be reduced, so that the problem of line looseness or line breakage of an isolated line after etching is effectively prevented.

Description

Technical Field

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

[0002] The role of isolated lines on circuit boards in circuits is mainly to transmit signals. During pattern electroplating, due to the principle of current distribution, the current at the position of isolated lines will be greater than the current in the large copper surface area. Therefore, the copper thickness of isolated lines is significantly greater than that of other large copper surfaces. The isolated lines on the circuit board are formed through a pattern electroplating process, specifically, after copper plating, tin plating, film stripping and etching processes, isolated lines are formed on the circuit board. In the existing process, isolated lines will have tin dissolution problems such as broken or thin lines in batches after alkaline etching, causing the product to be scrapped. The main reason for the circuit boards with such problems is that after film stripping, the local isolated lines are matte, without tin color, and the tin layer is extremely thin, while the tin thickness at the matte position after etching is less than 0.1um, resulting in serious tin dissolution problems such as thin lines and broken lines after etching.

[0003] In view of this, it is necessary to provide a new process to solve the problem of isolated line breakage or thin line on the circuit board. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for pattern electroplating of a circuit board, which can reduce the amount of tin dissolved in the film stripping process, thereby effectively preventing the problem of thin lines or broken lines in isolated lines after etching.

[0005] The technical solution of the present invention is as follows:

[0006] A method for pattern electroplating of a circuit board, wherein isolated lines are formed on the circuit board through copper plating, tin plating, film stripping and etching processes, wherein:

[0007] The current density of the tinning process is set at 7-10ASF, and the concentration of the tin polishing agent is 13-15ml / L;

[0008] In the film stripping process, the film stripping liquid is DL-400, and its concentration is 7-9wt%.

[0009] Furthermore, the current density of the tinning process was set to 8 ASF, and the electroplating time was set to 12 min.

[0010] Furthermore, the temperature of the film stripping liquid is 48-50° C., and the line speed of the film stripping process is 2.5 m / min.

[0011] Compared with the prior art, the pattern electroplating method of the circuit board provided by the present invention has the following beneficial effects:

[0012] The pattern electroplating method of the circuit board provided by the present invention optimizes the parameters of the tin plating and film stripping processes to ensure good tin plating quality and reduce the amount of tin dissolved in the film stripping process, thereby effectively preventing the occurrence of thin lines or broken lines in isolated lines after etching. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of 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 work.

[0014] Figure 1 It is a schematic diagram of the position of the isolated line position where the tape is partially applied and the film is removed in the present invention;

[0015] Figure 2 This is a diagram of the tin thickness at the location of the tape and microscopic observation in the present invention. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation modes of the present invention are further described below.

[0017] It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as there is no conflict between them.

[0018] In the present invention, firstly, it is verified that the disconnection or thinning of isolated lines after etching is related to the tinning and film stripping processes, and the method is as follows:

[0019] (1) Process: Use a certain type of test board → normal electroplating (tinning 6ASF*18min) → tape the isolated lines → remove the film to confirm the appearance;

[0020] (2) Locally apply tape to the isolated line position to remove the film. Figure 1 As shown: (film stripping conditions: the film stripping liquid is sodium hydroxide solution, its mass concentration is 11.4%, the temperature is 50°C, and the line speed is 2.5m / min);

[0021] (3) Compare the tin thickness at the tape location and the microscope observation diagram, such as Figure 2 shown.

[0022] Depend on Figure 2By comparison, the tin thickness of the tin dissolving position after film stripping is basically 0.2-0.5um, while the tin thickness of the adjacent tape position before film stripping is about 2.3um, which is thinner than other positions with normal tin thickness; from the 20X and 2K magnifications of the tin dissolving position and the non-tin dissolving position, there is no difference in the density of the tin layer before film stripping. Tin dissolving in a local position is related to the thin tin thickness, because the melting point of pure tin is relatively low, which is 232℃. Due to improper temperature control of the film stripping cylinder, the temperature will be too high, and the tin layer will reach the melting point and melt. After film stripping, the surface tin layer of the thin tin position is basically completely dissolved, and etching cannot effectively protect it.

[0023] Then, the influence of different tin plating parameters on tin dissolution was verified, as shown in the following table:

[0024]

[0025] The concentration of tin polish in different tin tanks is as follows:

[0026]

[0027] From the comparison of schemes numbered 1 and 2, it can be seen that under the same tin plating current density of 5ASF, the tin dissolution ratio decreases with the extension of tin plating time; from the comparison of schemes numbered 1, 2, and 4, it can be seen that increasing the tin plating current density will reduce the tin dissolution ratio even under lower power conditions; by comparing the data of different tin cylinders, from the comparison of schemes 1 / 5 / and 3 / 6, it can be seen that the tin dissolution ratio of the 16# tin cylinder with a lower tin brightener concentration is lower than that of the 18# tin cylinder.

[0028] Under different tinning parameters and different power conditions, the tin thickness at different locations is as follows:

[0029]

[0030]

[0031] From the comparison of the two sets of data of Scheme 1 / 3 and 5 / 7, it can be seen that as the current density increases, the tin thickness at the isolated line position becomes relatively thicker; from the comparison of the tin cylinders at different slots, it can be seen that as the current density increases, the difference in tin thickness between the large copper surface position and the isolated line position becomes smaller and smaller; from the comparison of the two sets of data of Scheme 1 / 5 and 2 / 6, it can be seen that under the same parameters, the difference in tin thickness between the large copper surface position and the isolated line position is smaller in the 16# tin cylinder than in the 18# tin cylinder. That is, the difference in tin thickness in the high and low current zones of the 16# tin cylinder is relatively smaller, and the overall is more uniform.

[0032] From this analysis, it can be seen that when the concentration of the brightener is high and the tin plating current density is low (≤6ASF), the isolated line position is prone to tin thinning.

[0033] Next, the effect of the film stripping process on the tin dissolution was verified. The results of the difference in tin dissolution under different film stripping conditions and different position conditions are as follows:

[0034]

[0035] From the above data, it can be seen that increasing the stripping solution concentration, raising the temperature and reducing the line speed, the amount of dissolved tin at the isolated line and the large copper surface are positively correlated; under the same stripping conditions, the amount of dissolved tin at the isolated line is greater than that at the large copper surface, that is, the isolated line is more vulnerable to the attack of the solution; as the stripping conditions are strengthened, the amount of dissolved tin at the isolated line / large copper surface will increase, but the overall bias of the isolated line area is greater.

[0036] According to the above comparison data, when the stripping solution concentration is increased to 11%, the tin surface thickness is likely to be thin in some places; the tin tank brightener concentration is too high, and the tin plating current density is too low (≤6ASF), which is likely to cause the tin surface thickness to be thin in some places. Therefore, it is necessary to adjust the tin plating and stripping parameters.

[0037] According to the influence of the above tin plating parameters and film stripping process parameters on the amount of dissolved tin, the parameters are adjusted to form the following embodiments:

[0038]

[0039] From the above data, it can be seen that lowering the stripping solution concentration to 7-9% (such as 8% in the above embodiment) and adjusting the current density value of the tin plating process to 8ASF can significantly improve the tin dissolution problem of isolated wires. In actual application, a total of 546 panels have been produced without any tin dissolution problem.

[0040] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations made to these embodiments without departing from the principles and spirit of the present invention are still within the protection scope of the present invention.

Claims

1. A method for pattern electroplating of a circuit board, characterized in that: After copper plating, tin plating, film stripping and etching processes, isolated lines are formed on the circuit board, where: The current density of the tinning process is set at 7-10ASF, and the concentration of the tin polishing agent is 13-15ml / L; In the film stripping process, the film stripping liquid is DL-400, and its concentration is 7-9wt%.

2. The pattern electroplating method of a circuit board according to claim 1, characterized in that: The current density of the tinning process was set to 8ASF and the electroplating time was 12min.

3. The pattern electroplating method of a circuit board according to claim 1, characterized in that: The temperature of the film stripping liquid is 48-50°C, and the line speed of the film stripping process is 2.5m / min.

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