FPC for SMT component welding and manufacturing method thereof

Abstract

The invention relates to the technical field of printed circuit board manufacturing, and discloses an FPC for SMT component welding and a manufacturing method thereof.The manufacturing method comprises the steps that a substrate is provided, the substrate comprises a metal layer and a dielectric layer, the metal layer comprises a bending area and a non-bending area, the non-bending area comprises a first connecting part, a second connecting part and a third connecting part, the non-bending area is provided with a via hole, and the first connecting part is connected with the second connecting part; a conductive material is arranged on the inner wall of the via hole; arranging an electroplated layer in the non-bending area, wherein the electroplated layer comprises a first electroplated part, a second electroplated part and a third electroplated part; and the fourth connecting part is removed, so that the first connecting part and the first electroplating part form a bonding pad, the second connecting part and the second electroplating part form a hole ring at the hole opening of the via hole, and the third connecting part forms a circuit. The FPC for SMT component welding and the manufacturing method thereof provided by the invention are used for improving the welding yield and reliability of the FPC.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printed circuit board manufacturing, and particularly relates to an FPC for SMT component welding and a manufacturing method thereof. BACKGROUND

[0002] FPC (Flexible Printed Circuit) is widely used in electronic products due to its advantages such as bendability and small size. In order to ensure the electrical connection reliability of the through hole and the flexibility of the FPC as a whole, the industry generally adopts a pattern plating process, that is, selective copper plating is performed only on the through hole and the circuit part that needs electrical connection. This process will form a protruding "hole ring" at the position of the through hole, and the height of the "hole ring" is usually 15-30 microns.

[0003] With the development of electronic products towards miniaturization and high density, the number of components to be assembled on the FPC increases, and the distance between the components decreases. Many pads for welding components are arranged around the through hole, the pad and the trace, which will cause serious quality problems in the subsequent SMT (Surface Mount Technology) component welding process, such as tin connection (bridging), virtual welding and component monument, etc., resulting in low welding yield and poor reliability of the FPC. SUMMARY

[0004] The present application provides an FPC for SMT component welding and a manufacturing method thereof, which is used to improve the welding yield and reliability of the FPC.

[0005] In a first aspect, the present application provides a manufacturing method of an FPC for SMT component welding, comprising: providing a substrate, the substrate comprising a metal layer and a dielectric layer stacked, the metal layer comprising a bending area and a non-bending area, the non-bending area comprising a first connecting part, a second connecting part and a third connecting part, the non-bending area being a fourth connecting part except the first connecting part, the second connecting part and the third connecting part, the non-bending area being provided with a through hole, the through hole penetrating through the second connecting part and the dielectric layer, an inner wall of the through hole being provided with a conductive material, the conductive material being connected with the second connecting part and electrically connected; providing a plating layer in the non-bending area, the plating layer exposing the third connecting part and the fourth connecting part, the plating layer comprising a first plating part, a second plating part and a third plating part, the first plating part covering the first connecting part, the second plating part covering the second connecting part, and the third plating part covering the conductive material; removing the fourth connecting part, so that the first connecting part and the first electroplated part form a pad, the second connecting part and the second electroplated part form a hole ring at an aperture of the via, and the third connecting part forms a line, the pad is used for welding a component, and the hole ring is connected to the component and electrically connected.

[0006] In some embodiments, the electroplating layer is arranged on the non-bending area, including: arranging a first film on the substrate, the first film covering the bending area, the third connecting part and the fourth connecting part; electroplating the substrate to form the electroplated layer; removing the first film.

[0007] In some embodiments, the removing the fourth connecting part, including: arranging a second film on the substrate, the second film including a first covering part, a second covering part and a third covering part, the first covering part covering the first electroplated part, the second covering part covering the second electroplated part and the aperture of the via, and the third covering part covering the third connecting part, and the second film exposing the fourth connecting part; removing the fourth connecting part by etching; removing the second film.

[0008] In some embodiments, a projection of the first electroplated part on a side of the dielectric layer facing the metal layer is inside a projection of the first connecting part on the side of the dielectric layer facing the metal layer, and the first covering part further covers the first connecting part around the first electroplated part.

[0009] In some embodiments, a distance between an edge of a projection of the first electroplated part on a side of the dielectric layer facing the metal layer and an edge of a projection of the first connecting part on the side of the dielectric layer facing the metal layer is 0.05mm-0.10mm.

[0010] In some embodiments, the electroplating the substrate to form the electroplated layer, including: first electroplating the substrate by using a first current; second electroplating the substrate by using a second current, the second current being smaller than the first current; third electroplating the substrate by using a third current, the third current being smaller than the first current, and the third current being greater than the second current.

[0011] In some embodiments, the metal layer further comprises a power stealing pad located at a process edge of the substrate, the power stealing pad being connected to and electrically conducting with the non-bending region.

[0012] In some embodiments, the sum of the thicknesses of the first connecting part and the first electroplated part is equal to the sum of the thicknesses of the second electroplated part and the second connecting part.

[0013] In some embodiments, after the fourth connecting part is removed, a solder layer is deposited on the pad.

[0014] In a second aspect, the embodiments of the present application provide an FPC for SMT component soldering, which is processed by the method for manufacturing the FPC for SMT component soldering as described in the first aspect.

[0015] The method for manufacturing the FPC for SMT component soldering provided by the embodiments of the present application has the beneficial effects that: since the substrate comprises the metal layer and the dielectric layer which are stacked, the metal layer comprises the bending region and the non-bending region, the non-bending region comprises the first connecting part, the second connecting part and the third connecting part, the part of the non-bending region other than the first connecting part, the second connecting part and the third connecting part is the fourth connecting part, the non-bending region is provided with the through hole which penetrates through the second connecting part and the dielectric layer, the inner wall of the through hole is provided with the conductive material, the conductive material is connected to and electrically conducts with the second connecting part, the electroplated layer is first provided in the non-bending region, the electroplated layer exposes the third connecting part and the fourth connecting part, the electroplated layer comprises the first electroplated part, the second electroplated part and the third electroplated part, the first electroplated part covers the first connecting part, the second electroplated part covers the second connecting part, and the third electroplated part covers the conductive material; then the fourth connecting part is removed, so that the first connecting part and the first electroplated part form the pad, the second connecting part and the second electroplated part form the hole ring at the hole opening of the through hole, and the third connecting part forms the circuit, thus the sum of the thicknesses of the first connecting part and the first electroplated part can be close to or equal to the sum of the thicknesses of the second electroplated part and the second connecting part, so that when the component is subsequently soldered to the pad formed by the first connecting part and the first electroplated part, and the hole ring formed by the second connecting part and the second electroplated part is connected to and electrically conducts with the component, the height difference formed by the pad and the hole ring can be reduced or eliminated, and problems such as tin bridging, false soldering and component monument are less likely to occur, thereby improving the soldering yield and reliability of the FPC.

[0016] The FPC for SMT component soldering provided by the present application has the beneficial effects compared with the prior art, which can be explained by referring to the beneficial effects of the method for manufacturing the FPC for SMT component soldering provided by the present application, which will not be described herein again. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0018] Figure 1 is a flow chart of the FPC for SMT component welding in one of the embodiments of the present application; Figure 2 is a structural schematic diagram of the FPC for SMT component welding in one of the embodiments of the present application; Figure 3 is Figure 2 is a cross-sectional view of the FPC for SMT component welding shown in the figure; Figure 4 is a relative position schematic diagram of the solder pad and the cover film of the FPC for SMT component welding in one of the embodiments of the present application.

[0019] The meaning marked in the figure is: 10, substrate; 1001, dielectric layer; 111, first connecting part; 112, second connecting part; 113, third connecting part; 1101, bending area; 1102, non-bending area; 114, line connecting part; 20, through hole; 30, first electroplated part; 31, welding area; 40, second electroplated part; 50, cover film; 51, windowing. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present application more clear, the following will further describe the present application in combination with the drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not used to limit the present application.

[0021] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0022] In addition, the terms "first", "second", etc. are used only for descriptive purposes and do not connote or imply relative importance or a quantity of the indicated features. Thus, a feature defined with "first", "second", etc. can include one or more of that feature. In the description of the application, the meaning of "a plurality" is two or more, unless explicitly specified otherwise.

[0023] Reference within the specification of this application to "one embodiment", "some embodiments" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. Thus, the appearances of the phrases "in one embodiment", "in some embodiments", "in other embodiments", "in additional embodiments", and so on, in various places throughout this specification are not necessarily all referring to the same embodiment, unless otherwise specifically specified. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0024] FPC (Flexible Printed Circuit, flexible printed circuit board) has been widely used in electronic products due to its advantages such as bendability and small size. In order to ensure the electrical connection reliability of the through hole and the flexibility of the FPC as a whole, the industry generally adopts a pattern plating process, that is, selective copper plating is only performed on the through hole and the circuit part that needs electrical connection. This process will form a protruding "hole ring" at the position of the through hole, and the height is usually 15-30 microns.

[0025] With the development of electronic products towards miniaturization and high density, the number of components to be assembled on the FPC increases, and the pitch decreases. Many pads around the pads used for soldering components are arranged with through holes, pads and traces at the same time, which will cause serious quality problems in the subsequent SMT (Surface Mount Technology, surface mount technology) component welding process: Tin connection (bridging): when applying solder paste and performing reflow soldering, due to the lower surface of the pad than the surface of the hole ring, the molten solder will be blocked by the hole ring wall and cannot be evenly filled into the pad recess, and will easily flow to the adjacent pad or component pin, causing short circuit between the pins.

[0026] Virtual welding: the pins of the components do not contact the recessed pads well, and the solder cannot form an effective solder meniscus, resulting in unreliable electrical connection or open circuit.

[0027] Component monument: due to the uneven surface of the pad, the surface tension of the solder during melting is uneven, which may cause one end of the chip component to be lifted up, forming a "monument" defect.

[0028] Due to the height difference between the pad and the hole ring surface, it is easy to cause low welding yield and poor reliability of the FPC.

[0029] Therefore, the application provides an FPC for SMT component welding and a manufacturing method thereof. Since the substrate includes a metal layer and a dielectric layer arranged in layers, the metal layer includes a bending area and a non-bending area, the non-bending area includes a first connecting part, a second connecting part and a third connecting part, the part of the non-bending area other than the first connecting part, the second connecting part and the third connecting part is a fourth connecting part, the non-bending area is provided with a through hole, the through hole penetrates the second connecting part and the dielectric layer, the inner wall of the through hole is provided with a conductive material, the conductive material is connected with the second connecting part and electrically conductive, and a plating layer is first arranged in the non-bending area, the plating layer exposes the third connecting part and the fourth connecting part, the plating layer includes a first plating part, a second plating part and a third plating part, the first plating part covers the first connecting part, the second plating part covers the second connecting part, and the third plating part covers the conductive material; then the fourth connecting part is removed, so that the first connecting part and the first plating part form a pad, the second connecting part and the second plating part form a hole ring at the hole opening of the through hole, and the third connecting part forms a circuit, so that the sum of the thicknesses of the first connecting part and the first plating part is close to or equal to the sum of the thicknesses of the second plating part and the second connecting part, and then the component is welded to the pad formed by the first connecting part and the first plating part, and the hole ring formed by the second connecting part and the second plating part is connected with the component and electrically conductive, so that the height difference between the pad and the hole ring is reduced or eliminated, a relatively flat welding surface is obtained, problems such as tin bridging, false welding and component monument are not easy to occur, and the welding yield and reliability of the FPC are improved.

[0030] In order to illustrate the technical solutions of the application, the specific embodiments will be described below with reference to the specific drawings.

[0031] Please refer to Figures 1 to 3 , in a first aspect, the embodiments of the application provide a manufacturing method of an FPC for SMT component welding, comprising: S100: providing a substrate 10, the substrate 10 includes a metal layer and a dielectric layer 1001 arranged in layers, the metal layer includes a bending area 1101 and a non-bending area 1102, the non-bending area 1102 includes a first connecting part 111, a second connecting part 112 and a third connecting part 113, the part of the non-bending area 1102 other than the first connecting part 111, the second connecting part 112 and the third connecting part 113 is a fourth connecting part, the non-bending area 1102 is provided with a through hole 20, the through hole 20 penetrates the second connecting part 112 and the dielectric layer 1001, and the inner wall of the through hole 20 is provided with a conductive material, the conductive material is connected with the second connecting part 112 and electrically conductive.

[0032] The metal layer can be a copper layer, an aluminum layer, or a silver layer, etc. The dielectric layer 1001 can include PI (Polyimide), resin, glass cloth, etc. For example, the substrate 10 is a polyimide flexible substrate covered with a 12 μm thick copper foil. The dielectric layer 1001 can be provided with a metal layer on both sides. The via hole 20 can be processed by drilling, and then the via hole 20 can be subjected to chemical copper plating, black hole or black shadow treatment to form a conductive material.

[0033] The first connecting part 111, the second connecting part 112, the third connecting part 113, and the fourth connecting part can be connected together and are different parts of the non-bending area 1102. Part of the fourth connecting part can be located around the first connecting part 111, part of the fourth connecting part can be located around the second connecting part 112, and part of the fourth connecting part can be located around the third connecting part 113. The via hole 20 is located around the first connecting part 111, and the first connecting part 111, the second connecting part 112, and the via hole 20 can be provided with multiple. The material of the conductive material can be copper or carbon, etc.

[0034] S200: A plating layer is provided on the non-bending area 1102, the plating layer exposes the third connecting part 113 and the fourth connecting part, and the plating layer includes a first plating part 30, a second plating part 40, and a third plating part, the first plating part 30 covers the first connecting part 111, the second plating part 40 covers the second connecting part 112, and the third plating part covers the conductive material.

[0035] The plating layer can be provided on the non-bending area 1102 by copper plating, and the plating layer does not cover the third connecting part 113 and the fourth connecting part.

[0036] S300: The fourth connecting part is removed, so that the first connecting part 111 and the first plating part 30 form a pad, the second connecting part 112 and the second plating part 40 form a hole ring at the hole opening of the via hole 20, and the third connecting part 113 forms a line, the pad is used for welding components, and the hole ring is connected with the components and electrically connected.

[0037] The fourth connecting part can be removed by plasma etching or chemical etching, and one hole ring can correspond to multiple pads. After removing the fourth connecting part, an FPC for SMT component welding is obtained.

[0038] It can be understood that the bending area 1101 includes a line connecting part 114, which can be connected with the fourth connecting part. When the fourth connecting part is removed, the part of the bending area 1101 except the line connecting part 114 can be removed together, so that the line connecting part 114 forms a line. After removing the fourth connecting part, the original position of the fourth connecting part, the inside of the via hole, and the original position of the line connecting part 114 can be filled with an insulating filling layer.

[0039] From the above, the manufacturing method of the FPC for SMT component welding provided by the embodiment of the application is known. The substrate 10 includes the metal layer and the dielectric layer 1001 arranged in layers. The metal layer includes the bending area 1101 and the non-bending area 1102. The non-bending area 1102 includes the first connecting part 111, the second connecting part 112, and the third connecting part 113. The part of the non-bending area 1102 except the first connecting part 111, the second connecting part 112, and the third connecting part 113 is the fourth connecting part. The non-bending area 1102 is provided with the through hole 20. The through hole 20 penetrates the second connecting part 112 and the dielectric layer 1001. The inner wall of the through hole 20 is provided with the conductive material. The conductive material is connected with and electrically connected with the second connecting part 112. The electroplating layer is first arranged in the non-bending area 1102. The electroplating layer exposes the third connecting part 113 and the fourth connecting part. The electroplating layer includes the first electroplating part 30, the second electroplating part 40, and the third electroplating part. The first electroplating part 30 covers the first connecting part 111. The second electroplating part 40 covers the second connecting part 112. The third electroplating part covers the conductive material. Then, the fourth connecting part is removed. The first connecting part 111 and the first electroplating part 30 form the solder pad. The second connecting part 112 and the second electroplating part 40 form the hole ring at the hole opening of the through hole 20. The third connecting part 113 forms the circuit. Therefore, the sum of the thicknesses of the first connecting part 111 and the first electroplating part 30 is close to or equal to the sum of the thicknesses of the second electroplating part 40 and the second connecting part 112. Subsequently, the component is welded to the solder pad formed by the first connecting part 111 and the first electroplating part 30. When the hole ring formed by the second connecting part 112 and the second electroplating part 40 is connected with and electrically connected with the component, the height difference formed by the solder pad and the hole ring can be reduced or eliminated. The problems such as tin bridging, false welding, and component monument are not easy to occur. The welding yield and reliability of the FPC are improved.

[0040] The manufacturing method for the FPC for SMT component welding provided in the embodiments of the present application reduces or eliminates the height difference formed by the soldering pad and the hole ring, forms a relatively perfect flat welding surface, and provides an ideal substrate for the mounting and welding of high-density and fine-pitch components. Meanwhile, the flat welding surface ensures that the solder paste can be evenly distributed on the soldering pad, and the molten solder can form a good soldering meniscus during reflow soldering, thereby fundamentally eliminating quality problems such as tin connection, false welding and component standing caused by the height difference, and greatly improving the assembly yield and product reliability. In addition, the manufacturing method for the FPC for SMT component welding provided in the embodiments of the present application has good process compatibility and is highly compatible with the existing FPC standard production process, and all steps are easy to implement on the existing production line without the need for expensive new equipment investment, and has high industrial application value. In addition, the manufacturing method for the FPC for SMT component welding provided in the embodiments of the present application only performs planarization processing on the non-bending area 1102 domain that needs to be welded, does not affect the bending and flexibility of other areas of the FPC, and perfectly retains the core advantages of the FPC.

[0041] For reference Figures 1 to 3 In some embodiments, the electroplating layer is arranged on the non-bending area 1102, including: First, a first film is arranged on the substrate 10, and the first film covers the bending area 1101, the third connecting part 113 and the fourth connecting part.

[0042] The first film can be a dry film or a wet film, etc. The first film exposes the first connecting part 111, the second connecting part 112 and the conductive material.

[0043] Secondly, electroplating is performed on the substrate 10 to form an electroplating layer.

[0044] The electroplating layer can be arranged by copper electroplating.

[0045] Thirdly, the first film is removed.

[0046] The first film can be removed by a film removal process.

[0047] By adopting the above scheme, the electroplating layer can be arranged on the non-bending area 1102 relatively conveniently, and the electroplating layer avoids covering the bending area 1101, the third connecting part 113 and the fourth connecting part.

[0048] Optionally, the fourth connecting part is removed, including: First, a second film is arranged on the substrate 10, and the second film includes a first covering part, a second covering part and a third covering part, the first covering part covers the first electroplating part 30, the second covering part covers the second electroplating part 40 and the hole of the through hole 20, and the third covering part covers the third connecting part 113, and the second film exposes the fourth connecting part.

[0049] The second film can be a dry film or a wet film, etc.

[0050] Secondly, the fourth connecting part is removed by etching.

[0051] The fourth connecting part can be removed by plasma etching or chemical etching.

[0052] Thirdly, the second film is removed.

[0053] The second film can be removed by a film removal process.

[0054] By adopting the above scheme, the fourth connecting part can be removed conveniently, and the first electroplated part 30, the second electroplated part 40 and the third connecting part 113 are avoided from being damaged.

[0055] It can be understood that the second film covers part of the bending area.

[0056] For reference Figures 1 to 4 As an implementable manner, the orthographic projection of the first electroplated part 30 on the side of the dielectric layer 1001 facing the metal layer is located inside the orthographic projection of the first connecting part 111 on the side of the dielectric layer 1001 facing the metal layer, and the first covering part also covers the first connecting part 111 around the first electroplated layer.

[0057] By adopting the above scheme, the pad formed by the first connecting part 111 and the first electroplated part 30 is a stepped structure, so that when the fourth connecting part is removed, only the fourth connecting part around the first connecting part 111 needs to be removed, the fourth connecting part around the first connecting part 111 can be removed better, and the etching circuit yield is improved.

[0058] It should be noted that if the pad formed by the first connecting part 111 and the first electroplated part 30 is not a stepped structure, i.e., the size of the first connecting part 111 and the first electroplated part 30 is relatively thick, then due to the relatively thick thickness of the pad, the fourth connecting part around the pad cannot be etched and removed better when the fourth connecting part is removed.

[0059] Optionally, the distance between the edge of the orthographic projection of the first electroplated part 30 on the side of the dielectric layer 1001 facing the metal layer and the edge of the orthographic projection of the first connecting part 111 on the side of the dielectric layer 1001 facing the metal layer is 0.05-0.10 mm, such as 0.05 mm, 0.07 mm, 0.08 mm, 0.10 mm, etc.

[0060] In this way, the pad formed by the first connecting part 111 and the first electroplated part 30 is a stepped structure protruding from the first electroplated part 30, so that when the fourth connecting part is removed, only the fourth connecting part around the first connecting part 111 needs to be removed, and the fourth connecting part around the first connecting part 111 can be removed better.

[0061] For example, the second film is a dry film with a thickness of about 38um. The dry film can be attached to the first plated part 30, the second plated part 40 and the third connecting part 113 by applying temperature and pressure, and then exposed by using a UV mask that only exposes the first plated part 30, the second plated part 40 and the third connecting part 113. The size of the exposed area is 0.05mm-0.10mm larger than the single side of the first plated part 30, so that the dry film above the pad and the circuit area is exposed. Then, the dry film is removed by developing, etching and stripping, and the dry film in the unexposed area is completely removed to expose the flat pad and the required circuit. At this time, the exposed pad forms a smooth step structure due to the difference in the size of the first film and the second film.

[0062] It can be understood that when the pad formed by the first connecting part 111 and the first plated part 30 is a step structure, the pad plating area can be reduced to balance the current density of the pad and the through hole 20, so that the height of the pad and the hole ring after plating is closer, and when there are other circuit designs between the pads, the distance between the pad and the circuit is increased, thereby reducing the problem of tin connection between the pad and the circuit.

[0063] Optionally, the sum of the thicknesses of the first connecting part 111 and the first plated part 30 is equal to the sum of the thicknesses of the second plated part 40 and the second connecting part 112.

[0064] In this way, the sum of the thicknesses of the first connecting part 111 and the first plated part 30 is equal to the sum of the thicknesses of the second plated part 40 and the second connecting part 112, so that when the device is subsequently welded to the pad formed by the first connecting part 111 and the first plated part 30, and the hole ring formed by the second connecting part 112 and the second plated part 40 is connected to the device and electrically connected, the height difference between the pad and the hole ring can be eliminated, and problems such as tin connection (bridging), false welding and device monument are less likely to occur, thereby improving the welding yield and reliability of the FPC.

[0065] It should be noted that after the fourth connecting part is removed, a covering film 50 can be attached to the surface of the metal layer, and the covering film 50 completely covers other places except the pad to protect the surface of the metal layer from being contaminated and corroded. At this time, the opening 51 of the covering film 50 is smaller than the size of the pad required for welding by 0.075mm, the edge of the opening 51 of the covering film 50 is completely pressed on the step of the pad and does not reach the surface of the pad, and the welding area 31 of the pad is not less than 85% of the required size.

[0066] Optionally, after the fourth connecting part is removed, a welding layer is deposited on the pad.

[0067] In this way, the pad forms a weldable surface.

[0068] For example, the solder layer can be deposited on the pad by electroless nickel immersion gold, silver plating, tin plating, or tin spraying, etc., to complete the preparation of the solder surface.

[0069] For reference Figures 1 to 3 In some embodiments, the substrate 10 is electroplated to form an electroplated layer, including: First, the substrate 10 is electroplated for the first time using a first current.

[0070] In this embodiment, the VCP (Vertical Continuous Plating) large current is used for electroplating to flash-plating a layer of electroplated layer, such as a layer of thin copper, on the surface of the conductive material in the through hole 20, the first connection part 111 and the second connection part 112, to improve the TP (Throwing Power) value and improve the efficiency of subsequent electroplating.

[0071] Second, the substrate 10 is electroplated for the second time using a second current, and the second current is smaller than the first current.

[0072] In this embodiment, the small current is used for electroplating, and the small current does not plate copper or bite copper.

[0073] Third, the substrate 10 is electroplated for the third time using a third current, and the third current is smaller than the first current and larger than the second current.

[0074] In this embodiment, the normal current density is used for electroplating.

[0075] By using the above scheme, the thickness of the pad and the hole ring is consistent, and the planarization structure of the hole ring and the PAD is achieved.

[0076] It should be noted that in the VCP, the current density is not uniform in the distribution of the substrate 10 and the hole of the through hole 20. Due to the edge effect, the current density of the board surface (especially the edge of the lead and the hole of the through hole 20) is much higher than the middle of the hole, which will cause the copper to be deposited preferentially on the board surface and the hole, and the copper in the hole center is deposited slowly, forming a "dog bone" shaped electroplated layer with thick ends and thin middle, and in severe cases, the hole will be closed and there will be no copper in the hole, which is called "hollow". In the embodiment of the present application, the through hole 20 and the pad are electroplated at the same time, and the first aspect is that the electroplated unit area of the pad is normal compared to the through hole 20, and the second aspect is that the copper plating capacity in the through hole 20 is poorer than the pad on the board surface. Therefore, if the conventional electroplating parameters are used, the pad will be higher than the PTH hole ring after electroplating, and the flatness of the hole ring will also be poor, so it is necessary to adjust the electroplating parameters to improve the problem.

[0077] For example, the substrate 10 can be electroplated in the following manner to form an electroplated layer, which is a copper layer.

[0078] First, the substrate 10 is electroplated for a first time using a first current.

[0079] In particular, the VCP high current flash plating can be used to quickly establish a continuous and compact "seed layer" of copper within the hole of the via 20.

[0080] The principle is that: (1) Overcome activation overpotential: the hole wall of the via 20 after chemical copper deposition is very thin (usually less than 1 micron) and its crystal structure is not as dense as electrolytic copper. Directly applying a normal electroplating current, due to the difficulty of mass transfer within the hole, the effective current density may not be sufficient to overcome the "activation energy barrier" (i.e. activation overpotential) of electrochemical deposition, resulting in a difficult or very slow start of the deposition reaction. The use of a transient high current can provide a strong electrochemical driving force to ensure that every active site within the hole can quickly start the reduction reaction of copper.

[0081] (2) Occupy adsorption sites: the electroplating solution usually contains various organic additives (such as carriers, leveling agents, brighteners). These additives will compete for adsorption on the cathode (substrate) surface, and the leveling agent especially likes to adsorb in the high current density area (such as the hole), which inhibits the deposition of copper. In the moment of high current flash plating, the reduction and deposition of copper ions is extremely fast, and a thin layer of copper can be quickly formed within the entire via 20 before the additives (especially the leveling agent) have not had time to completely adsorb and inhibit the deposition within the hole.

[0082] (3) Improve the distribution of electric field: the initial conductive material is very thin and has relatively poor conductivity. The electrolytic copper layer flash plated has excellent conductivity. Once this layer of copper is formed, it is equivalent to establishing a "internal electrode" with good conductivity within the hole, making the electric field distribution within the hole more uniform during subsequent electroplating, and laying a solid foundation for subsequent normal electroplating.

[0083] Second, the substrate 10 is electroplated for a second time using a second current, which is smaller than the first current.

[0084] In particular, the substrate 10 can be electroplated for a second time using a small current stop plating. The purpose of small current stop plating is to allow the additives (especially the leveling agent) to redistribute and play a role, in preparation for entering the normal electroplating stage.

[0085] The principle is that: (1) "rest" and re-adsorption: in the VCP high current plating stage, the high speed deposition of high current disrupts the normal adsorption balance of additives. After entering the low current stage, the deposition rate of copper drops sharply, even close to zero ("no copper plating"). At the same time, due to the small current, the anodic dissolution of copper ("copper bite") will not occur.

[0086] (2) the advantage of adsorption of leveling agent: in this "still" or "quasi-still" stage, the additives in the electroplating solution, especially the leveling agent, have enough time to diffuse and adsorb to the cathode surface. Because the leveling agent has stronger adsorption to high current density area, they will preferentially and massively adsorb to the orifice and surface area of the via and board just after flash plating, which has relatively high current density.

[0087] (3) establish the inhibition layer: these adsorbed leveling agent molecules form an effective inhibition film, greatly reducing the deposition rate of these areas in subsequent electroplating. This makes preparations for the next stage of "suppressing strong and supporting weak".

[0088] Thirdly, the substrate 10 is plated for a third time using a third current, the third current being less than the first current and greater than the second current.

[0089] Among them, normal current density can be used for electroplating. The purpose of normal current density electroplating is to realize uniform and efficient copper layer growth in the hole of the via 20 and the surface of the substrate 10 on the basis of the established advantages.

[0090] The principle is that: (1) "suppressing strong and supporting weak" effect: at this time, due to the strong inhibition of the orifice and surface of the via 20 by the leveling agent, and the weak inhibition in the hole. When the normal electroplating current is applied, the current will be "driven" to the area with weak inhibition, that is, the middle part of the hole, which ensures that the current distribution in the hole is much more uniform than direct normal electroplating.

[0091] (2) based on good foundation: the hole of the via 20 has already had a good conductive copper layer provided by flash plating, the electric field distribution has been improved, and now the "intelligent" leveling effect of the additives is added, so that copper can continuously and stably deposit in the hole, continuously thicken, and thus obtain ideal hole plating uniformity (high TP value), while avoiding premature closure of the orifice.

[0092] Specifically, if the VCP copper plating tank is 6 sections, sections 1-2 select flash plating high current, the core task is to seize time and establish an initial copper layer in the hole of the via 20, section 3 is small current stop plating, the core task is to level, let the additives redistribute and inhibit the orifice of the via 20, and sections 4-6 are normal current electroplating, the core task is to build, under the optimized conditions, to efficiently and uniformly complete the final copper plating and form the electroplated layer.

[0093] Optionally, the metal layer further comprises a rush electricity pad, the rush electricity pad is located at the process edge of the substrate 10, and the rush electricity pad is connected with the non-bending area 1102 and electrically connected.

[0094] In this way, the plated area can be increased through the rush electricity pad, and the electroplating is balanced.

[0095] It should be noted that the rush electricity pad can be added on the film for pattern electroplating copper during the pattern electroplating copper, the rush electricity pad is designed around the electroplating pinch point of the process edge and the independent pad in the unit, for increasing the plated area, the electroplating is performed in a way of flash plating + electroplating, the thickness of the first connecting part 111 and the second connecting part 112 is increased by about 25 μm after electroplating, the non-plated area is recessed relative to the plated area, and the hole ring is in the same height as the pad.

[0096] In a second aspect, the embodiments of the present application provide an FPC for SMT component welding, which is processed by the method for manufacturing the FPC for SMT component welding as in the first aspect.

[0097] The FPC for SMT component welding provided by the embodiment of the present application has the following advantages: the substrate 10 comprises a metal layer and a dielectric layer 1001 arranged in layers, the metal layer comprises a bending area 1101 and a non-bending area 1102, the non-bending area 1102 comprises a first connecting part 111, a second connecting part 112 and a third connecting part 113, the part of the non-bending area 1102 other than the first connecting part 111, the second connecting part 112 and the third connecting part 113 is a fourth connecting part, the non-bending area 1102 is provided with a through hole 20, the through hole 20 penetrates the second connecting part 112 and the dielectric layer 1001, the inner wall of the through hole 20 is provided with a conductive material, the conductive material is connected with and electrically connected with the second connecting part 112, and a plating layer is first arranged on the non-bending area 1102, the plating layer exposes the third connecting part 113 and the fourth connecting part, the plating layer comprises a first plating part 30, a second plating part 40 and a third plating part, the first plating part 30 covers the first connecting part 111, the second plating part 40 covers the second connecting part 112, and the third plating part covers the conductive material; then the fourth connecting part is removed, so that the first connecting part 111 and the first plating part 30 form a pad, the second connecting part 112 and the second plating part 40 form a hole ring at the hole opening of the through hole 20, and the third connecting part 113 forms a circuit, so that the sum of the thicknesses of the first connecting part 111 and the first plating part 30 is close to or equal to the sum of the thicknesses of the second plating part 40 and the second connecting part 112, and when a component is subsequently welded to the pad formed by the first connecting part 111 and the first plating part 30 and the hole ring formed by the second connecting part 112 and the second plating part 40 is connected with and electrically connected with the component, the height difference formed by the pad and the hole ring can be reduced or eliminated, and problems such as tin bridging, false welding and component monument are less likely to occur, and the welding yield and reliability of the FPC are improved.

[0098] It should be noted that the FPC for SMT component welding provided by the embodiment of the present application has uniform solder paste printing in subsequent SMT mounting, and there is no tin bridging or false welding phenomenon after reflow soldering, and the welding quality is significantly improved.

[0099] The above embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for some technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for manufacturing an FPC for SMT component soldering, characterized in that, include: A substrate is provided, the substrate including a metal layer and a dielectric layer stacked thereon, the metal layer including a bending region and a non-bending region, the non-bending region including a first connecting portion, a second connecting portion and a third connecting portion, the portion of the non-bending region other than the first connecting portion, the second connecting portion and the third connecting portion being a fourth connecting portion, the non-bending region being provided with a through hole, the through hole penetrating the second connecting portion and the dielectric layer, the inner wall of the through hole being provided with a conductive material, the conductive material being connected to and electrically conductive with the second connecting portion; An electroplating layer is provided in the non-bending area, the electroplating layer exposing the third connection portion and the fourth connection portion, the electroplating layer including a first electroplating portion, a second electroplating portion and a third electroplating portion, the first electroplating portion covering the first connection portion, the second electroplating portion covering the second connection portion, and the third electroplating portion covering the conductive material; The fourth connecting portion is removed so that the first connecting portion and the first electroplated portion form a pad, the second connecting portion and the second electroplated portion form a ring at the opening of the through hole, the third connecting portion forms a circuit, the pad is used to solder components, and the ring is connected to the components and electrically conductive.

2. The method for manufacturing an FPC for SMT component soldering according to claim 1, characterized in that, The provision of an electroplated layer in the non-bending area includes: A first film is disposed on the substrate, the first film covering the bending area, the third connecting portion and the fourth connecting portion; The substrate is electroplated to form the electroplated layer; Remove the first membrane.

3. The method for manufacturing an FPC for SMT component soldering according to claim 2, characterized in that, The removal of the fourth connecting portion includes: A second film is disposed on the substrate. The second film includes a first covering portion, a second covering portion, and a third covering portion. The first covering portion covers the first electroplated portion, the second covering portion covers the second electroplated portion and the opening of the through hole, the third covering portion covers the third connecting portion, and the second film exposes the fourth connecting portion. The fourth connecting portion is removed by etching. Remove the second membrane.

4. The method for manufacturing an FPC for SMT component soldering according to claim 3, characterized in that, The first electroplated portion is located inside the first connecting portion in the projection of the dielectric layer toward the metal layer, and the first covering portion also covers the first connecting portion around the first electroplated layer.

5. The method for manufacturing an FPC for SMT component soldering according to claim 4, characterized in that, The distance between the edge of the first electroplated part projected onto the side of the dielectric layer facing the metal layer and the edge of the first connecting part projected onto the side of the dielectric layer facing the metal layer is 0.05mm-0.10mm.

6. The method for manufacturing an FPC for SMT component soldering according to claim 2, characterized in that, The electroplating of the substrate to form the electroplated layer includes: The substrate is electroplated for the first time using a first current; The substrate is electroplated a second time using a second current, which is less than the first current. The substrate is electroplated a third time using a third current, wherein the third current is less than the first current and greater than the second current.

7. The method for manufacturing an FPC for SMT component soldering according to claim 2, characterized in that, The metal layer also includes a power-blocking PAD located on the process edge of the substrate, and the power-blocking PAD is connected to and electrically conductive to the non-bending area.

8. The method for manufacturing an FPC for SMT component soldering according to claim 1, characterized in that, The sum of the thicknesses of the first connecting portion and the first electroplated portion is equal to the sum of the thicknesses of the second electroplated portion and the second connecting portion.

9. The method for manufacturing an FPC for SMT component soldering according to any one of claims 1 to 8, characterized in that, After the fourth connection portion is removed, a solder layer is deposited on the solder pad.

10. An FPC for SMT component soldering, characterized in that, It is manufactured by the method of fabricating an FPC for SMT component soldering as described in any one of claims 1 to 9.

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