High-efficiency inner-layer bonding pad protection process for multi-layer rigid-flex board

Abstract

The invention discloses a multilayer rigid-flex board efficient inner layer pad protection process, which comprises the steps of prefabricating an inner layer board and an outer layer board, and performing circuit manufacturing of the inner layer board; a covering film is attached to the outer surface of the inner-layer plate; printing a water-soluble ink layer at the position of a bonding pad of the inner-layer plate; printing a solder resist ink layer at the position of a bonding pad of the inner layer board, wherein the solder resist ink layer covers the water-soluble ink layer; the inner-layer plate and the outer-layer plate are laminated to form a finished product plate; drilling a communicating hole for conducting on the finished board; carrying out copper plating treatment on the finished board; manufacturing a circuit of the outer layer board; and removing the water-soluble ink layer and the solder resist ink layer on the bonding pad. According to the process, the manufacturing steps are simplified, and the manufacturing cost is reduced; a layer of water-soluble ink is used for protecting a bonding pad, then a layer of solder resist ink is printed on the water-soluble ink to guarantee the completeness of the water-soluble ink, finally, the solder resist ink is removed, the water-soluble ink is made to make contact with water and directly fall off, the problems that in the prior art, uncovering is abnormal, and process oil returning is not thorough are solved, and the yield is increased.

Description

Technical Field

[0001] The present application relates to the technical field of circuit board processing, and in particular to a highly efficient inner pad protection process for a multi-layer rigid-flexible board. Background Art

[0002] As the types of electronic products increase, the functional requirements of circuit boards are also getting higher and higher. In order to meet the needs of different products, multi-layer rigid-flex boards have been born. Multi-layer rigid-flex boards are circuit boards with both FPC and PCB characteristics formed by combining flexible circuit boards and rigid circuit boards through lamination and other processes according to relevant process requirements.

[0003] The manufacturing process of the rigid-flex board in the prior art includes: inner layer circuit production; lamination film bonding of the inner layer flexible board; printing of solder mask oil; lamination of the outer layer rigid board and the inner layer flexible board; drilling; copper electroplating; outer layer circuit production; laser decapping; and solder mask oil removal.

[0004] The manufacturing process of the prior art is complicated, resulting in high manufacturing costs; and the time from printing solder mask ink to solder mask exposure is long, and it is exposed to high temperatures. In the solder mask exposure de-oiling process, there will be abnormalities such as unclean de-oiling, and the ink will stick to the outer hard board in a high-temperature pressing environment, resulting in a large number of scraps. Summary of the invention

[0005] The present application aims to solve one of the above technical problems in the prior art. To this end, the present application provides an efficient inner pad protection process for a multi-layer rigid-flex board.

[0006] The invention discloses an efficient inner pad protection process for a multi-layer rigid-flexible board, which includes prefabricating an inner layer board and an outer layer board, and manufacturing a circuit of the inner layer board; laminating a covering film on the outer surface of the inner layer board; printing a water-soluble ink layer at the pad position of the inner layer board; printing a solder resist ink layer at the pad position of the inner layer board, wherein the solder resist 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 a connecting hole for conduction on the finished board; copper plating the finished board; manufacturing a circuit of the outer layer board; and removing the water-soluble ink layer and the solder resist ink layer on the pad.

[0007] The above-mentioned multi-layer rigid-flexible board efficient inner pad protection process has at least the following beneficial effects: the process flow of the present application changes the laser opening of the cover to two layers of ink, which simplifies the production steps and reduces the manufacturing cost; a layer of water-soluble ink is used to protect the pad, and then a layer of solder mask ink is printed on the water-soluble ink to ensure the completeness of the water-soluble ink, and finally the solder mask ink is removed to allow the water-soluble ink to come into contact with water and fall off directly, thus solving the existing abnormal opening of the cover and the incomplete degreasing process, and greatly improving the yield.

[0008] According to the efficient inner pad protection process for a multi-layer rigid-flexible board described in an embodiment of the present application, the circuit manufacturing process of the inner layer board includes: presetting a copper layer on the surface of a prefabricated inner layer board, manufacturing inner layer circuits on the copper layer, protecting 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 efficient inner pad protection process for a multi-layer rigid-flex board described in an embodiment of the present application, a window is reserved in advance for the position of the prefabricated outer board corresponding to the inner board.

[0010] According to the efficient inner pad protection process for a multi-layer rigid-flexible board described in an embodiment of the present application, the covering film is a PI covering film, and the holes and points reserved on the covering film are aligned one by one with the holes and points reserved on the inner layer board and then pressed and shaped by a fast pressing machine.

[0011] According to the efficient inner pad protection process for a multi-layer rigid-flex board described in an embodiment of the present application, the coverage area of ​​the solder resist ink layer is larger than the coverage area of ​​the water-soluble ink layer to prevent the water-soluble ink layer from being exposed.

[0012] According to the efficient inner pad protection process for a multi-layer rigid-flexible board described in an embodiment of the present application, the holes and points reserved on the outer layer board are aligned one by one with the holes and points reserved on the inner layer board and then shaped by pressure transfer.

[0013] According to the efficient inner pad protection process for a multi-layer rigid-flexible board described in an embodiment of the present application, a copper layer is electroplated on the outer surface of the finished board and the inside of the connecting hole by electroplating, and the thickness of the copper layer is 35 to 50 μm.

[0014] According to the efficient inner pad protection process for a multi-layer rigid-flex board described in an embodiment of the present application, the circuit manufacturing process of the outer layer board includes: presetting a copper layer on the surface of the prefabricated outer layer board, manufacturing an outer layer circuit on the copper layer, protecting the required circuit positions by a developing solution, and etching away the copper of the circuit not protected by the developing solution by an etching solution.

[0015] According to the efficient inner pad protection process for a multi-layer rigid-flex board described in an embodiment of the present application, the solder resist ink layer is removed by an acidic solution, and the water-soluble ink layer is removed by water in the alkaline solution to expose the pads of the inner layer board.

[0016] According to the efficient inner pad protection process for a multi-layer rigid-flex board described in an embodiment of the present application, the working temperature of the acidic solution is set to 75° C. to 90° C.

[0017] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present application is further described below with reference to the accompanying drawings and embodiments;

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

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

[0021] Reference numerals: inner layer board 100 , outer layer board 200 , pad 210 , solder resist ink layer 300 . DETAILED DESCRIPTION

[0022] This section will describe in detail the specific embodiments of the present application. The preferred embodiments of the present application are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present application, but it cannot be understood as a limitation on the scope of protection of the present application.

[0023] In the description of the present application, it should be understood that descriptions involving orientation, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply 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 understood as a limitation on the present application.

[0024] In the description of this application, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, and "above", "below", "within", etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0025] In the description of this application, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in this application based on the specific content of the technical solution.

[0026] Reference Figure 1In the prior art, the window size of the opening position of the multi-layer rigid-flex board is smaller than the position of the pad 210, and the opening method is laser opening. The high temperature generated during the laser processing will cause the solder resist ink to adhere to the outer hard board, and it is easy for the solder resist ink to penetrate into the junction of the outer hard board and the inner soft board, which is not convenient for the subsequent solder resist exposure and degreasing, and it is easy to cause unclean degreasing, resulting in the scrapping of the entire finished board.

[0027] In order to solve the problem of incomplete ink removal and improve the yield rate, the present application provides a multi-layer rigid-flex board high-efficiency inner pad 210 protection process, which includes the following steps:

[0028] The inner layer board 100 and the outer layer board 200 are prefabricated, and the circuit of the inner layer board 100 is manufactured. Specifically, according to the required finished product size, a cutting machine is used to cut the inner layer board 100 substrate and the outer layer board 200 substrate to a predetermined size to form the inner layer board 100 and the outer layer board 200, and holes are opened on the inner layer board 100 and the outer layer board 200 according to the preset opening positions of the finished board. After the opening is completed, the circuit of the inner layer board 100 is first manufactured. At the same time, the window of the outer layer board 200 for exposing the pad 210 of the inner layer board 100 is also manufactured at the same time as the opening, so that there is no need to process on the finished board by laser opening, which affects the removal of solder mask ink.

[0029] Among them, the circuit manufacturing process of the inner layer board 100 includes: presetting a copper layer on the two side surfaces of the prefabricated inner layer board 100, manufacturing an inner layer circuit on the copper layer, protecting the required circuit position with a developing solution, and etching away the copper of the circuit not protected by the developing solution with an etching solution.

[0030] Specifically, a laminator is used to laminate a layer of photosensitive film on the surface of the inner layer board 100 to prepare for the subsequent formation of the inner layer circuit; the photosensitivity of the photosensitive film is used in conjunction with an exposure machine to stimulate UV ultraviolet light to cause a polymerization reaction in the photosensitive film, and the required pattern is transferred to the copper layer on the surface of the inner layer board 100 through the film; a weak base is used to dissolve the unexposed part of the photosensitive film to expose part of the copper surface; an etching solution is used to dissolve the exposed copper surface to form the required circuit pattern on the surface of the inner layer board 100; the exposed part of the photosensitive film on the inner substrate is removed to obtain the inner layer board 100 containing the inner layer circuit.

[0031] After the inner circuit of the inner layer board 100 is completed, a cover film is attached to the outer surface of the inner layer board 100. The cover film is a PI cover film, and the reserved holes and points on the cover film are aligned one by one with the reserved holes and points on the inner layer board 100, and then pressed and shaped by a fast press. The laminating film is also provided with a hollow hole for exposing the pad 210. The cover film and the inner layer board 100 are aligned and pressed together, and the pressing temperature, pressure, time and other factors will affect the pressing effect.

[0032] After the inner layer board 100 and the laminating film are pressed together, a water-soluble ink layer is printed on the pad 210 of the inner layer board 100. The printing of the water-soluble ink layer can be achieved by screen printing, and the pad 210 of the inner layer board 100 is protected by the water-soluble ink layer.

[0033] Among them, Figure 2 As shown, the size of the window opening 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 resist ink layer 300 is printed at the pad 210 of the inner layer board 100. The solder resist ink layer 300 covers the water-soluble ink layer, wherein the coverage area of ​​the solder resist ink layer 300 is larger than the coverage area of ​​the water-soluble ink layer to prevent the water-soluble ink layer from being exposed. The solder resist ink layer 300 protects the water-soluble ink layer to prevent the water-soluble ink from dissolving in contact with water, thereby achieving the purpose of protecting the water-soluble ink layer. The existing process is to directly brush the solder resist ink layer 300 at the pad 210 of the inner layer board 100. When degreasing in the subsequent degreasing process, it is easy for the solder resist ink to remain on the pad 210 or the outer layer board 200.

[0035] After the solder resist ink layer 300 is printed, a drying process is performed. Specifically, the inner layer board 100 is baked until the solder resist ink layer 300 is solidified. The baking is performed twice, the first baking temperature is controlled at 76-84° C. for 20 minutes, and 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 stacked and pressed together 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, and the reserved holes and points on the outer layer board 200 are aligned one by one with the reserved holes and points on the inner layer board 100, and then pressed together by pressure transmission to form a finished board. Pressing is to combine the layers of the multi-layer circuit board together by fully curing the PP resin under high temperature and high pressure, so as to ensure the electrical and mechanical properties of the multi-layer circuit board.

[0037] After the finished board is pressed together, connecting holes for conduction are drilled on the finished board, and the connecting holes run through both sides of the finished board.

[0038] After the connecting holes are made, the finished board is copper plated to form a copper layer on the surface of the finished board and the connecting holes. A copper layer is electroplated on the outer surface of the finished board and the inside of the connecting holes, and the thickness of the copper layer is 35 to 50 μm.

[0039] The electroplating process includes the following steps: upper plate → degreasing → double water washing → micro-etching → double water washing → acid immersion → copper plating → water washing → lower plate → acid washing → overflow water washing → overflow water washing → drying → plate collection.

[0040] Degreasing: It is to remove the grease on the board surface and adjust the charge in the hole.

[0041] Copper plating: Copper plating is performed on the entire board of the product, the surface copper is thickened, and the connecting holes are plated with the required copper thickness.

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

[0043] Stripping: Remove copper powder and plating on the Feiba fixture.

[0044] Water washing: clean the excess residual liquid in the hole and on the surface.

[0045] Drying: Avoid oxidation of the board surface.

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

[0047] After the electroplating is completed, the circuit is fabricated on the surface of the outer layer board 200. The circuit fabrication process of the outer layer board 200 includes: pre-setting a copper layer on the surface of the prefabricated outer layer board 200, fabricating an outer layer circuit on the copper layer, protecting the required circuit position with a developing solution, and etching away the copper of the circuit that is not protected by the developing solution with an etching solution.

[0048] Specifically, a laminator is used to adhere a layer of photosensitive film to the surface of the finished board to prepare for the subsequent formation of the outer layer circuit; the photosensitivity of the photosensitive film is used in conjunction with an exposure machine to stimulate UV ultraviolet light to cause a polymerization reaction in the photosensitive film, and the required pattern is transferred to the copper layer on the surface of the finished board through the film; a weak base is used to dissolve the unexposed part of the photosensitive film to expose part of the copper surface; an etching solution is used to dissolve the exposed copper surface to form the required circuit pattern on the surface of the inner layer board 100; the exposed part of the photosensitive film on the inner layer substrate is removed to obtain an inner layer board 100 containing inner layer circuits.

[0049] After the outer circuit is completed, the water-soluble ink layer and the solder resist ink layer 300 on the pad 210 are removed. When the solder resist is de-oiled through the de-oiling line, the solder resist 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 resist ink layer 300 will not remain on the pad 210. If there is any residue in the water-soluble ink layer, it will be de-oiled again when it comes into contact with water in the subsequent process, ensuring that there is no residue in the water-soluble ink layer.

[0050] In a specific embodiment, the solder resist ink layer 300 is removed by an acid solution, and the water-soluble ink layer is removed by water in an alkaline solution, so that the pads 210 of the inner layer board 100 are exposed.

[0051] The acidic solution is composed of an organic acid, an organic solvent, a surfactant, a corrosion inhibitor, etc. The working temperature of the acidic solution is set to 75° C. to 90° C.

[0052] The characteristics of this acidic solution are that it can quickly peel off the ink layer; it can be peeled off cleanly and thoroughly without any dead corner residue; it does not need to be heated for a long time and will not damage the finished board and metal; the product has no strong irritating odor and is not easy to evaporate.

[0053] The specific operation process is: mount the finished board to be cleaned of ink and immerse it in the tank liquid for about 10-20 minutes. The specific time is based on the removal effect. Take out the finished board and soak it in warm water for 1-2 times (3-5 minutes) to clean the surface tank liquid and reduce the residual agent on the surface of the substrate to facilitate subsequent operations.

[0054] The existing multi-layer rigid-flexible boards first print a solder resist ink layer 300 on the pad 210 of the inner board 100 to protect the pad 210, then combine the inner board 100 and the outer board 200, and then use laser cutting and cover opening at the position of the finished board corresponding to the pad 210 of the inner board 100, and finally de-oil the solder resist to expose the pad 210 of the inner board 100. The whole manufacturing process is complicated, resulting in high manufacturing costs; and the time from printing the solder resist ink to solder resist exposure is long, and after being exposed to high temperature, there will be an abnormality of unclean de-oiling during the solder resist exposure de-oiling process, and the ink will stick to the outer board 200 in a high-temperature pressing environment, resulting in a large number of scraps.

[0055] The present application removes the existing laser decapping process, and processes the window when prefabricating the outer layer board 200. A layer of water-soluble ink is printed on the inner pad 210 to cover the pad 210, and a layer of solder mask ink is printed on the water-soluble ink layer to cover the water-soluble ink layer to protect the inner and outer layers of the water-soluble ink layer. After the combination, the solder mask is de-oiled. The original solder mask ink layer 300 is prone to residue after high temperature, but there is a water-soluble ink layer on the lower layer. The water-soluble ink will fall off when it comes into contact with water, and the solder mask ink will not remain on the pad 210.

[0056] The present application changes the laser decapping process to brushing two layers of ink, which simplifies the production steps and reduces the manufacturing cost; a layer of water-soluble ink is used to protect the pad 210, and then a layer of solder mask ink is printed on the water-soluble ink to ensure the completeness of the water-soluble ink, and finally the solder mask ink is etched to allow the water-soluble ink to come into contact with water and fall off directly, thereby solving the existing abnormalities of decapping and incomplete degreasing, and greatly improving the yield.

[0057] The embodiments of the present application are described in detail above in conjunction with the accompanying drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present application.

Claims

1. A multi-layer rigid-flex board high-efficiency inner pad protection process, characterized in that: The method comprises the following steps: Prefabricate inner and outer panels, and make circuits on the inner panels; The outer surface of the inner plate is attached with a covering film; Printing a water-soluble ink layer at the pad position of the inner layer board; Printing a solder resist ink layer at the pad position of the inner layer board, wherein the solder resist ink layer covers the water-soluble ink layer; The inner layer plate and the outer layer plate are laminated and pressed together to form a finished plate; Drilling a connecting hole for conduction on the finished board; Performing copper plating on the finished board; Conducting circuit production of the outer layer board; The water-soluble ink layer and the solder resist ink layer on the pad are removed.

2. The high-efficiency inner pad protection process for a multi-layer rigid-flex board according to claim 1 is characterized in that: The circuit manufacturing process of the inner layer board includes: presetting a copper layer on the surface of the prefabricated inner layer board, manufacturing inner layer circuits on the copper layer, protecting the required circuit positions by developing solution, and etching away the copper of the circuits not protected by the developing solution by etching solution.

3. The high-efficiency inner pad protection process for a multi-layer rigid-flex board according to claim 1 is characterized in that: A window is reserved in advance at a position of the prefabricated outer layer plate corresponding to the inner layer plate.

4. The high-efficiency inner pad protection process for a multi-layer rigid-flex board according to claim 1 is characterized in that: The covering film is a PI covering film, and the holes and points reserved on the covering film are aligned one by one with the holes and points reserved on the inner layer board and then pressed and shaped by a fast pressing machine.

5. The high-efficiency inner pad protection process for a multi-layer rigid-flex board according to claim 1 is characterized in that: The coverage area of ​​the solder resist ink layer is greater than the coverage area of ​​the water-soluble ink layer to prevent the water-soluble ink layer from being exposed.

6. The high-efficiency inner pad protection process for a multi-layer rigid-flex board according to claim 1 is characterized in that: The holes and points reserved on the outer plate are aligned one by one with the holes and points reserved on the inner plate and are shaped by pressure transmission.

7. The high-efficiency inner pad protection process for a multi-layer rigid-flex board according to claim 1 is characterized in that: A copper layer is electroplated on the outer surface of the finished board and the inside of the connecting hole by electroplating, and the thickness of the copper layer is 35-50 μm.

8. The high-efficiency inner pad protection process for a multi-layer rigid-flex board according to claim 1 is characterized in that: The circuit manufacturing process of the outer layer board includes: presetting a copper layer on the surface of the prefabricated outer layer board, manufacturing an outer layer circuit on the copper layer, protecting the required circuit position by a developing solution, and etching away the copper of the circuit not protected by the developing solution by an etching solution.

9. The high-efficiency inner pad protection process of a multi-layer rigid-flex board according to claim 1 is characterized in that: The solder resist ink layer is removed by an acid solution, and the water-soluble ink layer is removed by water in the alkaline solution, so that the pads of the inner layer board are exposed.

10. The high-efficiency inner pad protection process of a multi-layer rigid-flex board according to claim 9, characterized in that: The working temperature of the acid solution is set to 75°C to 90°C.

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