An efficient inner layer pad protection process for multi-layer rigid-flex printed circuit boards

Abstract

The present application discloses an efficient inner layer pad protection process for a multi-layer rigid-flex printed circuit board, which includes prefabricating an inner layer board and an outer layer board, and fabricating circuits on the inner layer board; laminating a cover film on the outer surface of the inner layer board; printing a water-soluble ink layer at the pad positions of the inner layer board; printing a solder mask ink layer at the pad positions of the inner layer board, and the solder mask ink layer covers the water-soluble ink layer; laminating and pressing the inner layer board and the outer layer board to form a finished board; drilling communication holes for conduction on the finished board; performing copper plating treatment on the finished board; fabricating circuits on the outer layer board; removing the water-soluble ink layer and the solder mask ink layer on the pads. The process of the present application simplifies the manufacturing steps and reduces the manufacturing cost; uses a layer of water-soluble ink to protect the pads, prints a layer of solder mask ink on the water-soluble ink to ensure the integrity of the water-soluble ink, and finally removes the solder mask ink to allow the water-soluble ink to come into contact with water and directly fall off, solving the problems of abnormal opening and incomplete process oil removal in the prior art and improving the yield.

Description

Technical Field

[0001] This application relates to the technical field of printed circuit board processing, and particularly to an efficient inner layer pad protection process for multi-layer flexible-rigid printed circuit boards. Background Art

[0002] With the increasing variety of electronic products, the functional requirements for printed circuit boards are also getting higher and higher. To meet the needs of different products, multi-layer flexible-rigid printed circuit boards have emerged. A multi-layer flexible-rigid printed circuit board is a circuit board formed by laminating a flexible printed circuit board and a rigid printed circuit board through processes such as lamination and combining them according to relevant process requirements, having the characteristics of both FPC and PCB.

[0003] The existing manufacturing process flow for flexible-rigid printed circuit boards includes: inner layer circuit manufacturing; covering film lamination of the inner layer flexible board; printing solder mask oil; lamination of the outer rigid board and the inner layer flexible board; drilling; electroplating copper; outer layer circuit manufacturing; laser opening of the cover; solder mask oil removal.

[0004] The existing manufacturing process is complex, resulting in high manufacturing costs; and the time from printing solder mask ink to solder mask exposure is long and involves high temperatures. There are abnormalities such as incomplete oil removal in the solder mask exposure and oil removal process, and the ink will adhere to the outer rigid board reversely in the high-temperature lamination environment, causing a large number of scraps. Summary of the Invention

[0005] This application aims to solve one of the above technical problems in the existing technology. To this end, an embodiment of this application provides an efficient inner layer pad protection process for multi-layer flexible-rigid printed circuit boards.

[0006] According to the efficient inner layer pad protection process for multi-layer flexible-rigid printed circuit boards provided by this application, it includes prefabricating an inner layer board and an outer layer board, and performing circuit manufacturing on the inner layer board; covering the outer surface of the inner layer board with a covering film; printing a water-soluble ink layer at the pad positions of the inner layer board; printing a solder mask ink layer at the pad positions of the inner layer board, and the solder mask ink layer covers the water-soluble ink layer; laminating the inner layer board and the outer layer board to form a finished board; drilling through holes for conduction on the finished board; performing copper plating treatment on the finished board; performing circuit manufacturing on the outer layer board; removing the water-soluble ink layer and the solder mask ink layer on the pads.

[0007] The above-mentioned efficient inner layer pad protection process for multi-layer flexible-rigid printed circuit boards has at least the following beneficial effects: The process flow of this application changes laser opening of the cover to two layers of ink, streamlines the manufacturing steps, and reduces the manufacturing cost; uses a layer of water-soluble ink to protect the pads, prints a layer of solder mask ink on the water-soluble ink to ensure the integrity of the water-soluble ink, and finally removes the solder mask ink, allowing the water-soluble ink to come into contact with water and directly fall off, solving the existing abnormalities such as abnormal opening of the cover and incomplete oil removal in the process, and greatly improving the yield.

[0008] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, the process of fabricating the inner - layer circuit includes: presetting a copper layer on the surface of the pre - fabricated inner - layer board, fabricating the inner - layer circuit on the copper layer, protecting the required circuit positions with a developing solution, and etching away the copper of the circuits not protected by the developing solution with an etching solution.

[0009] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, windows are reserved in advance at the positions of the pre - fabricated outer - layer board corresponding to the inner - layer board.

[0010] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, the cover film is a PI cover film. After the holes and dots reserved on the cover film are aligned one - to - one with the holes and dots reserved on the inner - layer board, they are pressed and shaped by a fast - press machine.

[0011] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, the covering area of the solder mask ink layer is larger than that of the water - soluble ink layer to prevent the exposure of the water - soluble ink layer.

[0012] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, after the holes and dots reserved on the outer - layer board are aligned one - to - one with the holes and dots reserved on the inner - layer board, they are shaped by pressure transfer.

[0013] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, a copper layer is electroplated on the outer surface of the finished board and inside the communication holes, and the thickness of the copper layer is 35 - 50 μm.

[0014] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, the process of fabricating the outer - layer circuit includes: presetting a copper layer on the surface of the pre - fabricated outer - layer board, fabricating the outer - layer circuit on the copper layer, protecting the required circuit positions with a developing solution, and etching away the copper of the circuits not protected by the developing solution with an etching solution.

[0015] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, the solder mask ink layer is removed by an acidic solution, and the water - soluble ink layer is removed by water of the alkaline solution to expose the pads of the inner - layer board.

[0016] According to the high - efficiency inner - layer pad protection process for multi - layer rigid - flexible printed circuit boards according to the embodiments of the present application, the operating temperature of the acidic solution is set at 75°C - 90°C.

[0017] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Brief Description of the Drawings

[0018] The present application will be further described below in conjunction with the drawings and embodiments;

[0019] Figure 1 is a schematic surface view of a multi-layer rigid-flex printed circuit board in the prior art;

[0020] Figure 2 is a schematic surface view of a multi-layer rigid-flex printed circuit board in an embodiment of the present application.

[0021] Reference numerals: inner layer board 100, outer layer board 200, solder pad 210, solder mask ink layer 300. Detailed Description of the Embodiments

[0022] This part will describe in detail the specific embodiments of the present application. The preferred embodiments of the present application are shown in the drawings. The function of the drawings is to supplement the description in the text part of the specification, enabling people to intuitively and vividly understand each technical feature and the overall technical solution of the present application. However, it should not be construed as a limitation on the protection scope of the present application.

[0023] In the description of the present application, it should be understood that for orientation descriptions, such as up, down, front, back, left, right, etc., the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present application.

[0024] In the description of the present application, the meaning of "several" is one or more, the meaning of "multiple" is two or more, "greater than", "less than", "exceeding", etc. are understood as not including the recited number, and "above", "below", "within", etc. are understood as including the recited number. If there is a description of "first" and "second", it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence of the indicated technical features.

[0025] In the description of the present application, unless otherwise clearly defined, words such as "set", "installed", "connected", etc. should be understood in a broad sense. Those skilled in the art can reasonably determine the specific meanings of the above words in the present application in combination with the specific content of the technical solution.

[0026] Refer to Figure 1, in the prior art, the window size at the opening position of the multi-layer rigid-flex printed circuit board is smaller than the position of the solder pad 210, and the opening method is laser opening. The high temperature generated during the laser processing will cause the solder mask ink to adhere to the outer rigid board, and it is easy for the solder mask ink to penetrate into the joint between the outer rigid board and the inner flexible board, which is inconvenient for subsequent solder mask exposure and deinking, and it is easy to have incomplete deinking, resulting in the scrapping of the entire finished board.

[0027] To solve the problem of incomplete ink removal and improve the yield rate. The present application provides an efficient inner layer solder pad 210 protection process for a multi-layer rigid-flex printed circuit board, and this process includes the following steps:

[0028] Pre-fabricate the inner layer board 100 and the outer layer board 200, and perform the circuit production of the inner layer board 100. Specifically, according to the required finished product size, use a cutting machine to cut the substrates of the inner layer board 100 and the outer layer board 200 to the predetermined size to form the inner layer board 100 and the outer layer board 200. Open holes on the inner layer board 100 and the outer layer board 200 according to the preset opening positions of the finished board. After the hole opening is completed, first perform the circuit production of the inner layer board 100. At the same time, when opening the holes, the windows for the exposure of the solder pads 210 of the outer layer board 200 for the inner layer board 100 are made at the same time, so as to avoid affecting the removal of the solder mask ink by processing on the finished board through the laser opening method subsequently.

[0029] Among them, the process of making the inner layer circuit of the inner layer board 100 includes: preset copper layers on both surfaces of the pre-fabricated inner layer board 100, make inner layer circuits on the copper layers, protect the required circuit positions through the developing solution, and etch away the copper of the circuits not protected by the developing solution through the etching solution.

[0030] Specifically, laminate a photosensitive film on the surface of the inner layer board 100 with a laminating machine to prepare for the subsequent formation of the inner layer circuit; utilize the photosensitivity of the photosensitive film to cooperate with the exposure machine to emit UV ultraviolet light for irradiation to cause the photosensitive film to undergo a polymerization reaction, and transfer the required pattern to the copper layer on the surface of the inner layer board 100 through the negative film; dissolve the unexposed part of the photosensitive film with a weak base to expose part of the copper surface; use the etching solution to dissolve the exposed copper surface to form the required circuit pattern on the surface of the inner layer board 100; remove the photosensitive film on the already exposed part of the inner layer substrate to obtain the inner layer board 100 containing the inner layer circuit.

[0031] After the inner layer circuit of the inner layer board 100 is completed, laminate a cover film on the outer surface of the inner layer board 100. Among them, the cover film is a PI cover film. After the holes and dots reserved on the cover film are aligned with the holes and dots reserved on the inner layer board 100, they are pressed and shaped through a fast press. The cover film is also provided with hollow holes for the exposure of the solder pads 210. Align the cover film with the inner layer board 100 and then press them together. Among them, factors such as the temperature, pressure, and time of pressing will affect the pressing effect.

[0032] After the inner layer board 100 is laminated with the composite film, a water-soluble ink layer is printed at the pad 210 position of the inner layer board 100. The printing of the water-soluble ink layer can be achieved by screen printing, and the pad 210 position of the inner layer board 100 is protected through the water-soluble ink layer.

[0033] Among them, as Figure 2 shown, the window opening size of the outer layer board 200 is larger than the size of the pad 210 of the inner layer board 100.

[0034] After the water-soluble ink layer is printed and dried, a solder mask ink layer 300 is printed at the pad 210 position of the inner layer board 100. The solder mask ink layer 300 covers the water-soluble ink layer. Among them, the covering area of the solder mask ink layer 300 is larger than the covering area of the water-soluble ink layer to prevent the water-soluble ink layer from being exposed. The water-soluble ink layer is protected through the solder mask ink layer 300 to avoid the water-soluble ink from contacting and dissolving with water, achieving the purpose of protecting the water-soluble ink layer. The existing process is to directly brush the solder mask ink layer 300 at the pad 210 position of the inner layer board 100. During the subsequent de-inking process, it is easy for the solder mask ink to remain on the pad 210 or the outer layer board 200.

[0035] After the solder mask ink layer 300 is printed, it is dried. Specifically, the inner layer board 100 is baked until the solder mask ink layer 300 is cured. The baking is carried out in two times. The first baking temperature is controlled at 76 - 84 °C for 20 minutes; the second baking temperature is controlled at 150 - 160 °C for 60 minutes.

[0036] The inner layer board 100 and the outer layer board 200 are laminated and pressed to form a finished board. Before pressing, the window of the outer layer board 200 is aligned with the pad 210 position of the inner layer board 100. After the holes and dots reserved on the outer layer board 200 are aligned with the holes and dots reserved on the inner layer board 100 one by one, they are shaped and pressed through pressure transfer to form a finished board. Pressing is achieved by using the resin of PP to be completely cured under high temperature and high pressure to bond the layers of the multi-layer circuit board together, ensuring the electrical performance and mechanical performance of the multi-layer circuit board.

[0037] After the finished board pressing is completed, through holes for conduction are drilled on the finished board, and the through holes penetrate both sides of the finished board.

[0038] After the through holes are made, the finished board is copper-plated so that a copper layer is formed on the surface and through holes of the finished board. A copper layer is electroplated on the outer surface and the inside of the through holes of the finished board through electroplating, and the thickness of the copper layer is 35 - 50 μm.

[0039] The electroplating process includes the following steps: loading the board → degreasing → double water washing → micro-etching → double water washing → acid dipping → copper plating → water washing → unloading the board → pickling → overflow water washing → overflow water washing → drying → collecting the board.

[0040] Degreasing: Remove the grease on the board surface and adjust the charge in the holes.

[0041] Copper plating: Electroplate the entire board of the product to thicken the surface copper and deposit the required copper thickness on the through holes.

[0042] Pickling: Remove the copper surface oxides and impurity ions.

[0043] Strip hanging: Remove the copper powder and plating layer on the flying bar fixture.

[0044] Water washing: Wash the excess residual chemical solution inside the holes and on the surface.

[0045] Drying: Prevent the board surface from oxidation.

[0046] After electroplating, a copper layer with a copper thickness of 35 - 50 μm is formed on the upper and lower surfaces of the outer layer board 200.

[0047] After electroplating is completed, circuit production is carried out on the surface of the outer layer board 200. Among them, the circuit production process of the outer layer board 200 includes: presetting a copper layer on the surface of the prefabricated outer layer board 200, making the outer layer circuit on the copper layer, protecting the required circuit positions through the developing solution, and etching and removing the copper of the circuits not protected by the developing solution through the etching solution.

[0048] Specifically, laminate a photosensitive film on the surface of the finished board using a laminator to prepare for the formation of the subsequent outer layer circuit; utilize the photosensitivity of the photosensitive film to cooperate with an exposure machine to emit UV ultraviolet light for irradiation to cause the photosensitive film to undergo a polymerization reaction, and transfer the required pattern to the copper layer on the surface of the finished board through the negative film; dissolve the unexposed part of the photosensitive film using a weak base to expose part of the copper surface; use the etching solution to dissolve the exposed copper surface to form the required circuit pattern on the surface of the inner layer board 100; remove the photosensitive film on the exposed part of the inner layer substrate to obtain the inner layer board 100 containing the inner layer circuit.

[0049] When the outer layer circuit production is completed, remove the water-soluble ink layer and the solder mask ink layer 300 on the solder pads 210. Through the degreasing line for solder mask degreasing, the solder mask ink layer 300 will fall off, and the inner water-soluble ink layer will dissolve and fall off when it comes into contact with water, ensuring that the solder mask ink layer 300 will not remain on the solder pads 210. If there is any residue of the water-soluble ink layer, it will achieve the degreasing purpose again when contacting water in the subsequent process to ensure that there is no residue of the water-soluble ink layer.

[0050] In a specific embodiment, the solder mask ink layer 300 is removed by an acidic solution, and the water-soluble ink layer is removed by water of an alkaline solution to expose the solder pads 210 of the inner layer board 100.

[0051] The acidic solution is composed of organic acids, organic solvents, surfactants, corrosion inhibitors, etc., and the working temperature of the acidic solution is set at 75°C to 90°C.

[0052] The characteristics of the acidic solution are as follows: the speed of stripping the ink layer is fast; it can be stripped cleanly without dead-angle residues; it does not require long-term heating treatment, and does not damage the finished board and metal; the product has no strong pungent smell and is not easy to volatilize.

[0053] The specific operation process is as follows: Place the finished board to be removed of ink on the rack and immerse it in the bath solution for about 10 - 20 minutes, and the specific time depends on the removal effect; take out the finished board and soak it in warm water and wash it 1 - 2 times (3 - 5 minutes) to clean the bath solution on the surface and reduce the residue of the agent on the substrate surface to facilitate subsequent operations.

[0054] In the existing multi-layer rigid-flexible printed circuit boards, a solder mask ink layer 300 is first printed at the pad 210 position of the inner layer board 100 to protect the pad 210, then the inner layer board 100 and the outer layer board 200 are combined. After combination, laser cutting and opening are performed at the position corresponding to the pad 210 of the inner layer board 100 on the finished board, and finally, the solder mask ink is removed to expose the pad 210 of the inner layer board 100. The entire manufacturing process is complex, resulting in high manufacturing costs; moreover, the time from printing the solder mask ink to solder mask exposure is long, and it goes through high temperatures. There will be an abnormality of incomplete solder mask ink removal during the solder mask exposure and de-inking process, and the ink will stick to the outer layer board 200 under the high-temperature lamination environment, causing a large number of scraps.

[0055] This application removes the existing laser opening process. When prefabricating the outer layer board 200, a window is processed together. A layer of water-soluble ink layer is printed on the inner layer pad 210, which needs to cover the pad 210. A layer of solder mask ink is printed on the water-soluble ink layer, which needs to cover the water-soluble ink layer to protect the combination of the inner and outer layers of the water-soluble ink layer. After combination, the solder mask ink is removed. The original solder mask ink layer 300 is prone to residue after high temperature, but there is a water-soluble ink layer below. The water-soluble ink will fall off when it meets water, and the solder mask ink will not remain on the pad 210.

[0056] This application changes the laser opening process to brushing two layers of ink, streamlines the manufacturing steps, and reduces the manufacturing cost; uses a layer of water-soluble ink to protect the pad 210, prints a layer of solder mask ink on the water-soluble ink to ensure the integrity of the water-soluble ink, and finally etches the solder mask ink to make the water-soluble ink contact water and directly fall off, solving the existing abnormalities of opening and incomplete de-inking in the process, and greatly improving the yield.

[0057] The above has described the embodiments of the present application in detail with reference to the drawings. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art in the technical field, various changes can be made without departing from the purpose of the present application.

Claims

1. An efficient inner layer pad protection process for a multi-layer rigid-flex printed circuit board, characterized in that Including the following steps; Pre-fabricate the inner layer board and the outer layer board, and perform circuit production on the inner layer board; Attach a cover film to the outer surface of the inner layer board; Print a water-soluble ink layer at the pad positions of the inner layer board; Print a solder mask ink layer at the pad positions of the inner layer board. The solder mask ink layer covers the water-soluble ink layer, and the coverage area of the solder mask ink layer is larger than that of the water-soluble ink layer to prevent the water-soluble ink layer from being exposed. After the solder mask ink layer is printed, it is dried. Among them, the baking is carried out in two times. The first baking temperature is controlled at 76-84°C and baked for 20 minutes; the second baking temperature is controlled at 150-160°C and baked for 60 minutes; Stack and press the inner layer board and the outer layer board to form a finished board; Drill through holes for conduction on the finished board; Perform copper plating on the finished board. A copper layer is electroplated on the outer surface of the finished board and inside the through holes by electroplating. The thickness of the copper layer is 35-50μm; Perform circuit production on the outer layer board; Remove the water-soluble ink layer and the solder mask ink layer on the pads. Among them, the solder mask ink layer is removed by an acidic solution, and the water-soluble ink layer is removed by water with an alkaline solution to expose the pads of the inner layer board.

2. The high-efficiency inner-layer pad protection process for a multi-layer rigid-flex printed circuit board according to claim 1, characterized in that: The process of circuit production on the inner layer board includes: preset a copper layer on the surface of the pre-fabricated inner layer board, make inner layer circuits on the copper layer, protect the required circuit positions with developing solution, and etch away the copper of the circuits not protected by the developing solution with etching solution.

3. The high-efficiency inner layer pad protection process for multi-layer rigid-flex printed circuit boards according to claim 1, characterized in that: Windows are reserved in advance at the positions of the pre-fabricated outer layer board corresponding to the inner layer board.

4. The high-efficiency inner layer pad protection process for the multi-layer rigid-flex printed circuit board according to claim 1, wherein: The cover film is a PI cover film. After the holes and dots reserved on the cover film are aligned with the holes and dots reserved on the inner layer board one by one, they are pressed and shaped by a fast press.

5. The high-efficiency inner-layer pad protection process for a multi-layer rigid-flex printed circuit board according to claim 1, wherein: After the holes and dots reserved on the outer layer board are aligned with the holes and dots reserved on the inner layer board one by one, they are shaped by pressure transfer.

6. The high-efficiency inner-layer pad protection process for a multi-layer rigid-flex printed circuit board according to claim 1, wherein: The process of circuit production on the outer layer board includes: preset a copper layer on the surface of the pre-fabricated outer layer board, make outer layer circuits on the copper layer, protect the required circuit positions with developing solution, and etch away the copper of the circuits not protected by the developing solution with etching solution.

7. The high-efficiency inner layer pad protection process for the multi-layer flexible-rigid printed circuit board according to claim 1, characterized in that: The working temperature of the acidic solution is set at 75°C to 90°C.

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