Etching process for thick copper plate and military circuit board
By performing acid etching on thick copper plates and then alkaline etching, combined with tin plating and detinning operations, the problems of small etching factors and large line width tolerance of thick copper plates are solved, and the stability of current and signal transmission is improved.
Patent Information
- Application Number
- CN202411909284.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-24
- Publication Date
- 2025-04-01
AI Technical Summary
The prior art cannot effectively solve the problems of small etching factors and large line width tolerances of thick copper plates, resulting in unstable current and signal transmission.
After acid etching on thick copper plates, an alkaline etching is performed, combined with tin plating and detinning operations, the thickness and protection of the etching layer and the line layer are controlled, and the etching factor and line width tolerance are improved.
The etching factor is greater than 2.5 and the line width tolerance is less than 15%, ensuring more stable current and signal transmission of thick copper plates, and is suitable for high current and high voltage electronic equipment.
Smart Images
Figure CN119743902A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the field of circuit boards, and in particular to an etching process for thick copper plates and a military circuit board. Background Art
[0002] Thick copper design of circuit boards, namely PCB (printed circuit board) thick copper board design, is a special application in modern electronic devices for high current, high voltage or better heat dissipation. With the development of the electronics industry, new energy vehicle products and military products will increasingly use thick copper design, especially for military products such as tanks, rockets, submarines, etc., which will use thick copper PCB boards with higher power resistance. For example, the surface copper thickness reaches 12OZ (ie 420um). In order to ensure the stability of the transmission signal, the line width tolerance of this type of thick copper design needs to be less than 15%, and the etching factor (the ratio between the vertical etching depth and the lateral side etching) must be greater than 2.5 to ensure the stability of the current and signal.
[0003] In traditional technology, the circuit board is acid-etched after exposure and development to erode the copper layer on the copper surface of the circuit board except for the circuit. However, acid etching is generally only performed once and the immersion time cannot be too long. This is because too long a time can easily cause the dry film to fall off and fail to protect the copper underneath. However, acid etching can only etch away a maximum of 210um of copper at a time, while the copper thickness on the surface of the thick copper plate is 420um. A single acid etching cannot meet the precision requirements for thick copper plate etching, resulting in a thick copper plate etching factor of less than 2.5 (generally only 1.0-1.5). At this time, the line width tolerance reaches 30%, which leads to unstable current and signal transmission of the circuit board.
[0004] Therefore, there is an urgent need for a thick copper etching method with a larger etching factor, smaller line width tolerance, and stable current and signal transmission. Summary of the invention
[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide an etching process for thick copper plates and military circuit boards with a larger etching factor and smaller line width tolerance, so that current and signal transmission are stable.
[0006] The purpose of this disclosure is achieved through the following technical solutions:
[0007] An etching process for thick copper plate, comprising:
[0008] Cutting the substrate to form a thick copper plate, wherein the copper thickness on the surface of the thick copper plate is 400 μm-450 μm;
[0009] Performing a lamination operation on the thick copper plate so that the dry film adheres to the surface of the thick copper plate;
[0010] Performing exposure and development operations on the thick copper plate;
[0011] Performing an acid etching operation on the thick copper plate, so that a circuit layer and an etching layer are formed on the surface of the thick copper plate, and the thickness of the circuit layer is greater than the thickness of the etching layer;
[0012] Performing a blocking operation on the etching layer so that the surface of the etching layer is covered with the blocking layer;
[0013] Tinning the thick copper plate so that the circuit layer is covered with a tin layer, and part of the tin layer is located between the circuit layer and the barrier layer, and the barrier layer is used to prevent the tin layer from being formed on the etching layer;
[0014] Performing a detachment operation on the thick copper plate to detach the barrier layer from the etching layer;
[0015] Performing alkaline etching on the thick copper plate to reduce the thickness of the etching layer;
[0016] The thick copper plate is subjected to a detinning operation so as to separate the tin layer from the circuit layer.
[0017] In one embodiment, performing a blocking operation on the etching layer specifically comprises the following steps:
[0018] Performing a screen printing operation on the thick copper plate so that the etching layer is covered with a wet film, wherein the wet film is used to prevent the etching layer from forming a tin layer;
[0019] performing a baking operation on the wet film;
[0020] The wet film is exposed and developed to solidify the wet film on the etching layer.
[0021] In one embodiment, the thickness of the wet film is 20 μm-30 μm.
[0022] In one embodiment, the thick copper plate is separated, and the steps include:
[0023] The thick copper plate is stripped using an alkaline solution to dissolve the wet film.
[0024] In one embodiment, the thick copper plate is subjected to an acid etching operation, specifically comprising the following steps:
[0025] The thick copper plate is immersed in an acidic etching solution for 3 minutes to 5 minutes.
[0026] In one embodiment, the thickness of the tin layer is 10 μm-23 μm.
[0027] In one of the embodiments, the current for tinning the thick copper plate is 8A-9A, and the tinning time is 40min-50min.
[0028] In one embodiment, the detinning operation is performed on the thick copper plate, specifically comprising the following steps:
[0029] heating the tin layer to melt the tin layer;
[0030] Scraping off the tin layer to separate the tin layer from the circuit layer;
[0031] The circuit layer is cleaned to remove tin slag on the circuit layer.
[0032] In one embodiment, the tin layer is heated at a temperature of 200° C.-250° C., and the heating time is 10s-15s.
[0033] A military circuit board is prepared by using the etching process for thick copper plates described in any of the above embodiments.
[0034] Compared with the prior art, the present invention has at least the following advantages:
[0035] The above-mentioned etching process for thick copper plate forms a thick copper plate after cutting the substrate, and the copper thickness on the surface of the thick copper plate is 400μm-450μm. After the dry film is attached to the surface of the thick copper plate, it is exposed and developed, so that the thick copper plate is acid-etched to form a circuit layer and an etching layer. However, the etching layer formed by the acid etching is relatively thick at this time, and it is necessary to further remove the etching layer, and then block the etching layer, so that during the tin plating process, the circuit layer is covered with a tin layer, and the etching layer is not plated with a tin layer, and then the blocking layer is separated from the etching layer. In this way, during the alkaline etching process, the etching layer reacts with the alkaline etching solution because it is not blocked, thereby reducing the thickness of the etching layer, and the side of the circuit layer is protected by the tin layer and will not be etched away. Specifically, alkaline etching is performed again after acid etching to reduce the thickness of the etching layer. At the same time, the side of the circuit layer is protected by the tin layer and will not be corroded. In this way, the etching factor of the etching layer is greater than 2.5, and the line width tolerance of the thick copper plate is reduced to less than 15%, making the current and signal transmission of the thick copper plate more stable, so as to adapt to high current and high voltage electronic equipment. BRIEF DESCRIPTION OF THE DRAWINGS
[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.
[0037] Figure 1 is a process flow chart of an etching process for a thick copper plate according to an embodiment;
[0038] Figure 2 use Figure 1 The etching process for thick copper plate is shown as a schematic diagram of the structural changes of the thick copper plate after etching. DETAILED DESCRIPTION
[0039] In order to facilitate the understanding of the present disclosure, the present disclosure will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present disclosure are given in the drawings. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present disclosure more thoroughly and comprehensively understood.
[0040] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.
[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present disclosure. The terms used herein in the specification of the present disclosure are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure. The term "and / or" used herein includes any and all combinations of one or more related listed items.
[0042] The present invention provides an etching process for a thick copper plate, comprising the following steps: cutting a substrate to form a thick copper plate, wherein the copper thickness on the surface of the thick copper plate is 400 μm-450 μm; performing a lamination operation on the thick copper plate to make a dry film adhere to the surface of the thick copper plate; performing an exposure and development operation on the thick copper plate; performing an acid etching operation on the thick copper plate to form a circuit layer and an etching layer on the surface of the thick copper plate, wherein the thickness of the circuit layer is greater than the thickness of the etching layer; performing a blocking operation on the etching layer to cover the surface of the etching layer with a blocking layer; performing a tin plating operation on the thick copper plate to cover the circuit layer with a tin layer, wherein the blocking layer is used to block the formation of a tin layer on the etching layer; performing a detachment operation on the thick copper plate to detach the blocking layer from the etching layer; performing an alkaline etching operation on the thick copper plate to reduce the thickness of the etching layer; performing a tin removal operation on the thick copper plate to detach the tin layer from the circuit layer.
[0043] The above-mentioned etching process for thick copper plate forms a thick copper plate after cutting the substrate, and the copper thickness on the surface of the thick copper plate is 400μm-450μm. After the dry film is attached to the surface of the thick copper plate, it is exposed and developed, so that the thick copper plate is acid-etched to form a circuit layer and an etching layer. However, the etching layer formed by the acid etching is relatively thick at this time, and it is necessary to further remove the etching layer, and then block the etching layer, so that during the tin plating process, the circuit layer is covered with a tin layer, and the etching layer is not plated with a tin layer, and then the blocking layer is separated from the etching layer. In this way, during the alkaline etching process, the etching layer reacts with the alkaline etching solution because it is not blocked, thereby reducing the thickness of the etching layer, and the side of the circuit layer is protected by the tin layer and will not be etched away. Specifically, alkaline etching is performed again after acid etching to reduce the thickness of the etching layer. At the same time, the side of the circuit layer is protected by the tin layer and will not be corroded. In this way, the etching factor of the etching layer is greater than 2.5, and the line width tolerance of the thick copper plate is reduced to less than 15%, making the current and signal transmission of the thick copper plate more stable, so as to adapt to high current and high voltage electronic equipment.
[0044] In order to better understand the technical solutions and beneficial effects of the present invention, the present invention is further described in detail below in conjunction with specific embodiments:
[0045] like Figure 1 As shown, an etching process for a thick copper plate according to an embodiment includes the following steps:
[0046] S100: cutting the substrate to form a thick copper plate, wherein the copper thickness on the surface of the thick copper plate is 400 μm-450 μm.
[0047] In this embodiment, a substrate with a surface copper thickness of 400μm-450μm is cut to form a thick copper plate of required size. The thick copper plate with a surface copper thickness of 400μm-450μm has higher current carrying capacity, less signal transmission loss and better heat dissipation performance, so as to be suitable for high current, high voltage and high power electronic equipment.
[0048] S200: performing a lamination operation on the thick copper plate so that the dry film is attached to the surface of the thick copper plate.
[0049] In this embodiment, a laminator is used to press the dry film onto the surface of the thick copper plate. The dry film has photosensitive properties, that is, it will solidify under ultraviolet light to achieve the function of pattern transfer.
[0050] S300: performing exposure and development operations on the thick copper plate.
[0051] In this embodiment, after the dry film is pressed onto the surface of the thick copper plate, the dry film is exposed to ultraviolet light through the pattern of the desired circuit design, and the exposed dry film is cured to protect the copper layer under the dry film from being corroded during the etching process, that is, the copper layer under the cured dry film is the circuit that needs to be retained; then, the thick copper plate is developed using a sodium carbonate solution, and the uncured dry film is dissolved under the action of the developer to expose the copper layer underneath, which needs to be corroded to form a circuit pattern.
[0052] S400: performing an acid etching operation on the thick copper plate, so that a circuit layer and an etching layer are formed on the surface of the thick copper plate, and the thickness of the circuit layer is greater than the thickness of the etching layer.
[0053] In this embodiment, an acidic etching solution (such as copper sulfate, copper chloride, etc.) is used to etch the thick copper plate. Since a solidified dry film is attached to part of the surface of the thick copper plate, during etching, the copper under the solidified dry film forms a circuit layer, and the copper without dry film protection forms an etching layer, that is, the etching layer is the copper that needs to be etched away, so after acid etching, the thickness of the formed circuit layer is greater than the thickness of the etching layer. It should be noted that, limited by the time and etching concentration of the acid etching, one acid etching can only etch away 200μm-220μm of copper at most, and if the acid etching time of the thick copper plate is increased, it is easy to cause the dry film to fall off, and then the copper under the dry film protection is etched away, and if the concentration of the acid etching solution is increased, the side etching will be aggravated, and the line width tolerance of the thick copper plate will be increased, that is, the etching layer has not been completely removed after the acid etching, and the copper of the etching layer needs to be further removed. Further, after the acid etching is completed, a strong alkali is used to dissolve the solidified dry film to expose the circuit layer.
[0054] S500: performing a blocking operation on the etching layer so that the surface of the etching layer is covered with the blocking layer.
[0055] In this embodiment, a barrier layer is covered on the surface of the etching layer, and the barrier layer is used to prevent the etching layer from being plated with a tin layer during the tinning operation, so as to play a blocking role. Further, the barrier layer can be a wet film or photosensitive ink, which is coated on the surface of the etching layer by silk screen printing.
[0056] S600: performing a tinning operation on the thick copper plate, so that the circuit layer is covered with a tin layer, and a portion of the tin layer is located between the circuit layer and the barrier layer, and the barrier layer is used to prevent the tin layer from being formed on the etching layer.
[0057] In this embodiment, the thick copper plate is tin-plated. Under the action of electric current and liquid medicine, the tin ions in the liquid medicine form a single substance of tin on the circuit layer and adhere to the surface of the circuit layer. Since the chemical stability of tin is more stable than that of copper, the tin will not react and dissolve during alkaline etching to protect the circuit layer under the tin layer. Further, since the etching layer is covered with a barrier layer, the barrier layer blocks the tin layer from being formed on the etching layer during the tin-plating operation. It should be noted that since the circuit layer is thicker than the etching layer, that is, there is a height difference between the circuit layer and the etching layer, that is, the side of the circuit layer is higher than the etching layer, during the tin-plating operation, the side of the circuit layer will also be plated with a tin layer, that is, part of the tin layer is located between the circuit layer and the barrier layer to protect the side of the circuit layer from being bitten in the alkaline etching, thus reducing the side etching phenomenon of the thick copper plate, that is, the ratio between the vertical etching depth of the thick copper plate and the horizontal side etching is increased, that is, the etching factor is improved, and the line width tolerance requirements of the thick copper plate are guaranteed.
[0058] S700: performing a detachment operation on the thick copper plate to detach the barrier layer from the etching layer.
[0059] In this embodiment, after the thick copper plate is tinned, a tin layer is attached to the circuit layer on the surface of the thick copper plate, and a barrier layer is attached to the etching layer. At this time, the thick copper plate is detached, and the barrier layer can be dissolved by chemical reagents to detach the barrier layer from the etching layer, thereby exposing the etching layer for subsequent alkaline etching process.
[0060] S800: performing an alkaline etching operation on the thick copper plate to reduce the thickness of the etching layer.
[0061] In this embodiment, an alkaline etching solution (such as sodium hydroxide) is used to etch the thick copper plate. Since the circuit layer on the surface of the thick copper plate is covered with a tin layer, the tin layer can well protect the circuit layer during the alkaline etching process, and the barrier layer on the etching layer has been detached, that is, the etching layer is exposed. During the alkaline etching process, the etching layer reacts with the alkaline etching solution, so that the etching layer is continuously eroded, that is, the thickness of the etching layer is continuously reduced, and finally the etching layer is completely eroded to expose the substrate under the etching layer, and the alkaline etching operation of the thick copper plate is completed at this time. Further, the side of the circuit layer is also plated with a tin layer during the tinning operation, so that during the alkaline etching process, the side of the circuit layer is protected by the tin layer and will not be bitten off, that is, the side etching of the thick copper plate is reduced, that is, the ratio between the vertical etching depth of the thick copper plate and the horizontal side etching is increased, that is, the etching factor is improved, and the line width tolerance requirements of the thick copper plate are guaranteed.
[0062] S900: performing a detinning operation on the thick copper plate to separate the tin layer from the circuit layer.
[0063] In this embodiment, the tin layer on the circuit layer is peeled off by chemical solution or physical method to expose the circuit layer, so as to ensure the integrity and accuracy of the thick copper plate pattern.
[0064] Furthermore, if Figure 2 As shown, Figure 2 Schematic diagram of structural changes of thick copper plate etching: the thick copper plate shown in a, the dry film (blue mark) is attached to the board surface of the thick copper plate, and the copper under the dry film is the circuit to be retained; the thick copper plate shown in b is subjected to acid etching operation, at which time the thick copper plate forms an etching layer and a circuit layer, and the thickness of the circuit layer is greater than the etching layer; the thick copper plate shown in c is subjected to a blocking operation, so that the surface of the etching layer is covered with a blocking layer (pink mark), so that the etching layer will not be plated with a tin layer during the tin plating operation; the thick copper plate shown in d is subjected to a tin plating operation, and the surface of the circuit layer is covered with a tin layer (blue mark), and the side surface where the circuit layer and the etching layer meet is also covered with a tin layer, and the tin layer is used to protect the circuit layer from being dissolved in the subsequent alkaline etching, so as to reduce the side corrosion of the circuit layer, thereby increasing the etching factor and ensuring the line width tolerance requirements of the thick copper plate; the thick copper plate shown in e is the final formed circuit, at which time the etching layer has been completely dissolved, leaving only the circuit layer, and the tin layer has been removed to expose the circuit layer.
[0065] The above-mentioned etching process for thick copper plate forms a thick copper plate after cutting the substrate, and the copper thickness on the surface of the thick copper plate is 400μm-450μm. After the dry film is attached to the surface of the thick copper plate, it is exposed and developed, so that the thick copper plate is acid-etched to form a circuit layer and an etching layer. However, the etching layer formed by the acid etching is relatively thick at this time, and it is necessary to further remove the etching layer, and then block the etching layer, so that during the tin plating process, the circuit layer is covered with a tin layer, and the etching layer is not plated with a tin layer, and then the blocking layer is separated from the etching layer. In this way, during the alkaline etching process, the etching layer reacts with the alkaline etching solution because it is not blocked, thereby reducing the thickness of the etching layer, and the side of the circuit layer is protected by the tin layer and will not be etched away. Specifically, alkaline etching is performed again after acid etching to reduce the thickness of the etching layer. At the same time, the side of the circuit layer is protected by the tin layer and will not be corroded. In this way, the etching factor of the etching layer is greater than 2.5, and the line width tolerance of the thick copper plate is reduced to less than 15%, making the current and signal transmission of the thick copper plate more stable, so as to adapt to high current and high voltage electronic equipment.
[0066] In one embodiment, performing a blocking operation on the etching layer specifically comprises the following steps:
[0067] Performing a screen printing operation on the thick copper plate so that the etching layer is covered with a wet film, wherein the wet film is used to prevent the etching layer from forming a tin layer;
[0068] performing a baking operation on the wet film;
[0069] The wet film is exposed and developed to solidify the wet film on the etching layer.
[0070] In this embodiment, the barrier layer adopts a wet film, and a layer of wet film is covered on the etching layer by screen printing, and then the wet film is baked to make the wet film adhere to the etching layer, and then the wet film is exposed to ultraviolet light to solidify the wet film on the etching layer, and finally the wet film on the etching layer is dissolved by a developer, leaving only the wet film on the etching layer. The wet film on the etching layer acts as a barrier to prevent the etching layer from forming a tin layer during the tin plating process.
[0071] In one embodiment, the thickness of the wet film is 20 μm-30 μm. It can be understood that the thickness of the wet film is 20 μm-30 μm, so as to play a blocking role and make the wet film easier to remove.
[0072] In one embodiment, the thick copper plate is separated, and the steps include:
[0073] The thick copper plate is stripped using an alkaline solution to dissolve the wet film.
[0074] In this embodiment, an alkaline solution (sodium hydroxide) is used to dissolve the wet film, so that the etching layer under the wet film is exposed, and the etching layer is dissolved in the alkaline etching process.
[0075] In one embodiment, the thick copper plate is subjected to an acid etching operation, specifically comprising the following steps:
[0076] The thick copper plate is immersed in an acidic etching solution for 3 minutes to 5 minutes.
[0077] It is understandable that the immersion time of the thick copper plate in the acid etching should not be too long, because a too long immersion time will cause the dry film to fall off the surface of the thick copper plate, and then fail to protect the copper under the dry film. In this embodiment, the thick copper plate is immersed in the acid etching solution for 5 minutes, so that the copper surface not covered by the dry film forms an etching layer, and the copper surface covered by the dry film forms a circuit layer, but the etching layer at this time is not completely dissolved and needs further etching.
[0078] In one embodiment, the thickness of the tin layer is 10 μm-23 μm. In this embodiment, the thickness of the tin layer is 23 μm, so that the tin layer can better protect the circuit layer and make the detinning of the tin layer more convenient.
[0079] In one embodiment, the current for tinning the thick copper plate is 8A-9A, and the tinning time is 40min-50min. In this embodiment, the current is 9A, and the tinning time is 50min, so that a tin layer of corresponding size is formed on the circuit layer, thereby protecting the circuit layer from being corroded during the alkaline etching process, and at the same time, the tin layer on the side of the circuit layer reduces the side corrosion phenomenon, thereby increasing the etching factor of the thick copper plate, and ensuring the line width tolerance requirements of the thick copper plate.
[0080] In one embodiment, the detinning operation is performed on the thick copper plate, specifically comprising the following steps:
[0081] heating the tin layer to melt the tin layer;
[0082] Scraping off the tin layer to separate the tin layer from the circuit layer;
[0083] The circuit layer is cleaned to remove tin slag on the circuit layer.
[0084] In this embodiment, the tin layer is removed physically, that is, the tin layer is heated with a hot air gun to melt the tin layer, and then the melted tin layer is scraped off from the circuit layer with a scraper. Finally, anhydrous ethanol or alcohol is used to clean the thick copper plate to remove the tin slag on the circuit layer, thereby exposing the circuit layer.
[0085] In one embodiment, the tin layer is heated at a temperature of 200°C-250°C for a heating time of 10s-15s. In this embodiment, the tin layer is heated at a temperature of 200°C for a heating time of 10s, so that the tin layer is melted by the heat, and then the tin layer is removed to expose the circuit layer.
[0086] It can be understood that after the thick copper plate is acid-etched, a circuit layer and an etching layer are formed. The end face of the circuit layer contacts the dry film, that is, the end face of the circuit layer has not been etched, that is, the end face of the circuit layer is relatively smooth, and the part of the thick copper plate that does not cover the dry film is etched to form an etching layer. At this time, there is a height difference between the circuit layer and the etching layer, and the part of the circuit layer side contacting the etching layer is also etched, that is, the circuit layer side is rougher than the circuit layer end face. At the same time, the dry film may still remain during the film removal operation, which will cause the surface roughness of the circuit layer side and the circuit layer end face to be inconsistent, that is, the bonding force between the circuit layer end face and the circuit layer side and the tin layer is inconsistent, which will lead to the problem of uneven tin plating thickness of the circuit layer side and the circuit layer end face during the tin plating operation, which will lead to inconsistent protection effect of the tin layer on the end face and side of the circuit layer, and there is a problem that the thickness of the tin layer on the end face of the circuit layer is thin, resulting in the copper under the tin layer being bitten during the alkaline etching process. Therefore, in order to solve the problem of uneven tin plating thickness of the thick copper plate, in one embodiment, the thick copper plate is tinned, specifically including the following steps:
[0087] Coating photosensitive ink on the side of the circuit layer adjacent to the etching layer;
[0088] The thick copper plate is subjected to a tinning operation, the tinning current is 8.5A-9.0A, and the tinning time is 10min-15min, so that the exposed end surface of the circuit layer is formed with a first tin layer;
[0089] Performing laser ablation on the side of the circuit layer to remove the photosensitive ink on the side of the circuit layer so as to expose the side of the circuit layer;
[0090] The thick copper plate is subjected to a secondary tin plating operation, the tin plating current is 8.0A-8.5A, and the tin plating time is 25min-35min, so that a second tin layer is formed on the surface of the first tin layer, and a third tin layer is formed on the side of the thick copper plate adjacent to the etching layer, wherein the sum of the thickness of the first tin layer and the thickness of the second tin layer is equal to the thickness of the third tin layer.
[0091] In this embodiment, since the end faces of the thick copper plate are covered with a dry film during acid etching, that is, the end faces of the thick copper plate are not etched, the end faces of the thick copper plate are relatively smooth, and the side faces of the circuit layer are connected to the etching layer. When the etching layer is formed by acid etching, the side faces of the circuit layer will inevitably be etched, that is, the side faces of the circuit layer are rougher than the end faces that have not been etched. This makes the bonding force between the tin layer and the end faces and sides of the circuit layer inconsistent during the tin plating operation, resulting in uneven thickness of the formed circuit layer, and even the risk of the tin layer falling off at the thinner part during alkaline etching. Therefore, in this embodiment, before the tin-plating operation is performed, a layer of photosensitive ink is first coated on the side of the circuit layer, and the photosensitive ink plays a barrier role. When the thick copper plate is tinned once, the tin layer will only form a first tin layer on the exposed end face of the circuit board. At the same time, the tin-plating current is controlled to be 8.5A-9.0A. The current in the first tin-plating operation is greater than the current in the second operation. This is because the end face of the circuit layer is relatively smooth, and the current needs to be increased to make the tin layer better combined with the end face of the circuit layer. At the same time, the time of the first tin-plating is controlled to be 10min-15min, so that a thinner first tin layer is formed on the end face of the circuit layer. Then, the photosensitive ink on the side of the circuit layer is ablated by a laser device, and at the same time, the wet film on the etching layer can be accurately avoided to prevent the wet film from being burned through, so that the side of the circuit layer is exposed. Finally, the thick copper plate is tinned for the second time. At this time, the end face of the circuit layer has formed the first tin layer, that is, the end face of the circuit layer before the second tin-plating is performed. The thickness is greater than the thickness of the side of the circuit layer. When the second tin plating is performed, the second tin layer will adhere to the first tin layer, and the third tin layer will adhere to the side of the circuit layer. Due to the large roughness of the side of the circuit layer, the rate at which the side of the circuit layer combines with the third tin layer is faster, that is, within the same tin plating time, the thickness of the third tin layer is greater than the thickness of the second tin layer, but due to the existence of the first tin layer, the thickness of the end face of the circuit layer is greater than the thickness of the side of the circuit layer, that is, although the thickness of the side of the circuit layer is smaller, the tin layer formed per unit time will be faster. By controlling the tin plating current at 8.0A-8.5A and the tin plating time at 25min-35min, within the preset tin plating time, the thickness of the first tin layer and the second tin layer finally formed can be equal to the thickness of the third tin layer, ensuring that the thickness of the tin layer coated on the surface of the circuit layer is uniform, thereby avoiding the problem of the tin layer on the surface of the circuit layer falling off during alkaline etching, and making the tin layer have a better protective effect on the circuit layer.
[0092] Furthermore, the end surface of the circuit layer is relatively smooth, so that the bonding force between the circuit layer and the first tin layer is relatively small, resulting in the thickness of the first tin layer not meeting the preset requirements under the preset parameters (current and time), which in turn results in the sum of the first tin layer and the second tin layer being greater than or less than the third tin layer after the secondary electrotinning operation, that is, the tin layer on the surface of the circuit layer still has an uneven thickness problem. Therefore, in order to further improve the uniformity of the thickness of the tin layer on the surface of the circuit layer, in one embodiment, the thick copper plate is subjected to a secondary tinning operation, specifically comprising the following steps:
[0093] Get the thickness of the first tin layer;
[0094] matching the thickness of the first tin layer with a preset thickness;
[0095] When the thickness of the first tin layer is greater than or equal to the preset thickness, the current of the secondary tin plating is increased and the time of the secondary tin plating is reduced.
[0096] In this embodiment, the preset thickness is a preset range of the thickness of the first tin layer. After the first tin layer and the second tin layer are combined within the preset range, the overall thickness will be equal to the thickness of the third tin layer, so that the thickness of the circuit layer surface is consistent, and the tin layer has a better protective effect on the circuit layer. However, in the actual production process, the end face of the circuit layer is relatively smooth, that is, the surface of the circuit layer has a poor bonding ability with the first tin layer, which will lead to the problem that the thickness of the first tin layer does not meet the predetermined requirements after one tin plating. Therefore, in this embodiment, after the circuit layer is subjected to a tin plating operation, the thickness of the first tin layer is detected, and the thickness of the first tin layer is compared with the preset thickness. When the thickness of the first tin layer is greater than or equal to the preset thickness, it indicates that the thickness of the first tin layer is high. At this time, the current of the secondary tin plating is increased. After the current is increased, the speed of forming the second tin layer and the third tin layer is accelerated. However, since the side of the circuit layer is etched, that is, the roughness of the side of the circuit layer is greater than that of the first tin layer. This is because for the etching process and tin plating process of the ultra-thick copper plate, a high-concentration etching solution will be selected for etching during the acid etching process, so that the etching solution will bite When the depth of copper etching is large, there will also be the problem of poor control of etching accuracy, resulting in a large roughness on the side of the formed circuit layer. The roughness of the first tin layer formed by the first tin plating is smaller than that of the side of the circuit layer. In this way, after increasing the current of the secondary tin plating, the increase in the forming speed of the third tin layer is higher. In this way, the thickness of the third tin layer formed in the same time is greater, and the thickness of the second tin layer formed is smaller than that of the third tin layer, so that the thickness of the third tin layer within the preset time is equal to the thickness and value of the first tin layer and the second tin layer, thereby ensuring that the thickness of the tin layer on the surface of the circuit layer is uniform, so that the tin layer has a better effect on protecting the circuit layer. Furthermore, increasing the current will lead to an intensified reaction and an increase in temperature in the electroplating tank, and the increase in temperature will affect the wet film on the etching layer, and the wet film will be damaged under long-term high temperature. Therefore, while increasing the current, the time of the secondary tin plating is reduced to avoid the problem of the wet film on the etching layer being damaged due to being at high temperature for a long time.
[0097] In another embodiment, after matching the thickness of the first tin layer with a preset thickness, the following steps are further included:
[0098] When the thickness of the first tin layer is less than a preset thickness, the current of the secondary tin plating is reduced and the time of the secondary tin plating is increased.
[0099] In this embodiment, the thickness of the first tin layer is detected, and the thickness of the first tin layer is compared with the preset thickness. When the thickness of the first tin layer is less than the preset thickness, it indicates that the thickness of the first tin layer after the first tin plating is smaller. At this time, the current of the second tin plating is reduced. After the current is reduced, the forming speed of the second tin layer and the third tin layer is reduced, that is, the thickness of the second tin layer and the third tin layer formed per unit time are both reduced. Since the roughness of the side of the circuit layer is greater than the roughness of the first tin layer, the reduction in the thickness of the third tin layer is greater than the reduction in the thickness of the second tin layer, thereby ensuring that after the second tin plating is completed, the thickness of the third tin layer is equal to the sum of the thickness of the second tin layer and the first tin layer, thereby making the tin layer better in protecting the circuit layer. Furthermore, while reducing the current, the time of the second tin plating is increased, so that the tin layer formed by the second tin plating is more uniform and less prone to defects.
[0100] Furthermore, in order to make the thickness of the tin layer on the end surface and the side surface of the circuit layer more consistent, in one embodiment, after the secondary tinning operation is performed on the thick copper plate, the following steps are also included:
[0101] Get the sum of the thickness of the first tin layer and the second tin layer;
[0102] Get the thickness of the third tin layer;
[0103] Performing differential processing on the sum of the thicknesses of the first tin layer and the second tin layer and the thickness of the third tin layer to obtain a calibrated thickness;
[0104] matching the calibration thickness with a preset calibration thickness;
[0105] When the calibration thickness is greater than the preset calibration thickness, a laser ablation operation is performed on the third tin layer.
[0106] It can be understood that since the roughness of the side of the circuit layer is greater than the roughness of the end face of the circuit layer, there is a situation where the sum of the first tin layer and the second tin layer formed within the preset time is less than the thickness of the third tin layer. At this time, the thickness of the tin layer on the surface of the circuit layer is uneven, and the protection effect on the circuit layer is not good. In this embodiment, after the secondary tin plating is completed, the thickness of the tin layer on the end face and the side face of the circuit layer is detected to obtain the sum of the thickness of the first tin layer and the second tin layer, and the thickness of the third tin layer. Then, the sum of the thickness of the first tin layer and the second tin layer is subtracted from the thickness of the third tin layer to obtain the calibration thickness. The calibration thickness is compared with the preset calibration thickness. The preset calibration thickness is the tolerable range of the difference in the thickness of the tin layer on the side and end face of the circuit layer, that is, the difference in the thickness of the tin layer within the preset calibration thickness range has a negligible effect on the circuit layer, that is, the difference in the thickness of the tin layer within the preset calibration thickness range does not need to be adjusted. When the calibration thickness is greater than the preset calibration thickness, it indicates that the thickness difference between the end face and the side face of the circuit layer is large and needs to be corrected. The third tin layer is laser ablated by laser to reduce the thickness of the third tin layer, thereby ensuring that the thickness difference between the end face and the side face of the circuit layer is within the preset calibration range, so that the thickness of the tin layer on the end face and the side face of the circuit layer is more uniform, and the protection effect of the circuit layer during alkaline etching is better.
[0107] The present application also provides a military circuit board, which is prepared using the etching process for thick copper plates described in any of the above embodiments.
[0108] Compared with the prior art, the present invention has at least the following advantages:
[0109] The above-mentioned etching process for thick copper plate forms a thick copper plate after cutting the substrate, and the copper thickness on the surface of the thick copper plate is 400μm-450μm. After the dry film is attached to the surface of the thick copper plate, it is exposed and developed, so that the thick copper plate is acid-etched to form a circuit layer and an etching layer. However, the etching layer formed by the acid etching is relatively thick at this time, and it is necessary to further remove the etching layer, and then block the etching layer, so that during the tin plating process, the circuit layer is covered with a tin layer, and the etching layer is not plated with a tin layer, and then the blocking layer is separated from the etching layer. In this way, during the alkaline etching process, the etching layer reacts with the alkaline etching solution because it is not blocked, thereby reducing the thickness of the etching layer, and the side of the circuit layer is protected by the tin layer and will not be etched away. Specifically, alkaline etching is performed again after acid etching to reduce the thickness of the etching layer. At the same time, the side of the circuit layer is protected by the tin layer and will not be corroded. In this way, the etching factor of the etching layer is greater than 2.5, and the line width tolerance of the thick copper plate is reduced to less than 15%, making the current and signal transmission of the thick copper plate more stable, so as to adapt to high current and high voltage electronic equipment.
[0110] The above-mentioned embodiments only express several implementation methods of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present disclosure, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure shall be subject to the attached claims.
Claims
1. An etching process for thick copper plate, characterized in that: The following steps are involved: Cutting the substrate to form a thick copper plate, wherein the copper thickness on the surface of the thick copper plate is 400 μm-450 μm; Performing a lamination operation on the thick copper plate so that the dry film adheres to the surface of the thick copper plate; Performing exposure and development operations on the thick copper plate; Performing an acid etching operation on the thick copper plate, so that a circuit layer and an etching layer are formed on the surface of the thick copper plate, and the thickness of the circuit layer is greater than the thickness of the etching layer; Performing a blocking operation on the etching layer so that the surface of the etching layer is covered with the blocking layer; Tinning the thick copper plate so that the circuit layer is covered with a tin layer, and part of the tin layer is located between the circuit layer and the barrier layer, and the barrier layer is used to prevent the tin layer from being formed on the etching layer; Performing a detachment operation on the thick copper plate to detach the barrier layer from the etching layer; Performing alkaline etching on the thick copper plate to reduce the thickness of the etching layer; The thick copper plate is subjected to a detinning operation so as to separate the tin layer from the circuit layer.
2. The etching process for thick copper plate according to claim 1, characterized in that: The blocking operation is performed on the etching layer, specifically comprising the following steps: Performing a screen printing operation on the thick copper plate so that the etching layer is covered with a wet film, wherein the wet film is used to prevent the etching layer from forming a tin layer; performing a baking operation on the wet film; The wet film is exposed and developed to solidify the wet film on the etching layer.
3. The etching process for thick copper plate according to claim 2, characterized in that: The thickness of the wet film is 20 μm-30 μm.
4. The etching process for thick copper plate according to claim 2, characterized in that: The thick copper plate is separated, and the steps are as follows: The thick copper plate is stripped using an alkaline solution to dissolve the wet film.
5. The etching process for thick copper plate according to claim 1, characterized in that: The thick copper plate is subjected to an acid etching operation, which specifically comprises the following steps: The thick copper plate is immersed in an acidic etching solution for 3 minutes to 5 minutes.
6. The etching process for thick copper plate according to claim 1, characterized in that: The thickness of the tin layer is 10 μm-23 μm.
7. The etching process for thick copper plate according to claim 1, characterized in that: The current for tinning the thick copper plate is 8A-9A, and the tinning time is 40min-50min.
8. The etching process for thick copper plate according to claim 1, characterized in that: The thick copper plate is subjected to a detinning operation, specifically comprising the following steps: heating the tin layer to melt the tin layer; Scraping off the tin layer to separate the tin layer from the circuit layer; The circuit layer is cleaned to remove tin slag on the circuit layer.
9. The etching process for thick copper plate according to claim 8, characterized in that: The tin layer is heated at a temperature of 200° C.-250° C., and the heating time is 10s-15s.
10. A military circuit board, characterized in that: The method is prepared by using the etching process for thick copper plates according to any one of claims 1 to 9.