Patent ID: 12236028

In the drawings:1. first bonding area;2. bending area;3. flexible substrate;31. notch;41. first bonding pin;42, conductor layer;51. first protective layer;52. conductive layer;53, third protective layer;54, electronic device;55, metal support;56, insulation layer;57, first trench;6. touch module;61, second protective layer;62, first cover layer;63, touch layer;64, second cover layer;65, rigid substrate;66, second bonding pin;67, first trench;7. bonding indenter;8. conductive particle;9. silicone pad;10. flexible circuit board;11. protective glue layer;12. protective film;131. first conductive metal layer;132. second conductive metal layer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms, and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention will be comprehensive and complete, and fully convey the concept of the example embodiments to those skilled in the art. The same reference numerals in the figures indicate the same or similar structures, and thus their detailed descriptions will be omitted.

Referring to the structural schematic diagram of the flexible circuit board in the related art shown inFIG.1, the first bonding pins41in the flexible circuit boards are flush with the edge of the flexible substrate3. During the bonding process, under the squeezing effect of the bonding indenter7, the conductive particles8will flow toward the edge of the flexible substrate3, thereby causing a short circuit between the first bonding pins41. This problem is exacerbated when the flexible circuit board is designed to be thin.

An exemplary embodiment first provides a flexible circuit board, referring to the schematic structural diagrams of the flexible circuit board according to the present invention shown inFIG.2andFIG.5. The flexible circuit board has a first bonding area1and a bending area2. The flexible circuit board may include a flexible substrate3, a conductor layer42, a first protective layer51, and a plurality of first bonding pins41. The bonding pins41are provided in the first bonding area1on the flexible substrate3. The orthographic projection on the flexible substrate3of an edge line of each bonding pin41is located within the edge of the flexible substrate3, which edge line is located at an end along the extension direction of the first bonding pin41. The conductor layer42is provided in the bending area2on the flexible substrate3, and the conductor layer42is connected to the first bonding pins41. The first protective layer51is provided on the side of the conductor layer42away from the flexible substrate3.

In an exemplary embodiment, referring toFIGS.2and12, a plurality of first bonding pins41are provided, in the first bonding area1of the flexible circuit board, on the flexible substrate3, and the plurality of first bonding pins41are are arranged side by side. The orthographic projection on the flexible substrate3of an edge line of the first bonding pin41is located within the edge of the flexible substrate3, which edge line is located at an end along the extension direction of the first bonding pin41. That is, the first bonding pin41does not extend to the edge of the flexible substrate3. During the bonding process, even if the conductive particles8are squeezed to the edge of the flexible substrate3causing the conductive particles8to gather, it will not cause a short circuit among the plurality of first bonding pins41.

With reference toFIGS.3and12, in another exemplary embodiment of the present invention, an end of the first bonding pin41close to the edge of the flexible substrate3may be set in a trapezoidal shape, which the short base of the trapezoid is close to the edge of the flexible substrate3, rendering the width of an end of the first bonding pin41close to the edge of the flexible substrate3to be smaller than the width of the part of the first bonding pin41away from the edge of the flexible substrate3. Of course, the end of the first bonding pin41close to the edge of the flexible substrate3can also be set to be a triangle, so that the end of the first bonding pin41close to the edge of the flexible substrate3forms a sharp angle. An end of the first bonding pin41close to the edge of the flexible substrate3can be also set to be a rectangle, but the width of the rectangle is smaller than the width of the portion of the first bonding pin41away from the edge of the flexible substrate3. In addition, an end of the first bonding pin41close to the edge of the flexible substrate3may also be set in an arc shape, for example, a semicircular shape, a semielliptical shape, and so on. This arrangement helps to increase the distance between the ends close to the edge of the flexible substrate3of two adjacent first bonding pins41, so as to provide a larger gap for the conductive particles8to flow out of the edge. On the one hand, a short circuit will not be caused by the aggregation of conductive particles8at the edge. On the other hand, this design increases the overflow possibility of the conductive particles8to a certain extent and reduces the problem of aggregation. Thereby, the short circuit among the plurality of first bonding pins41is further avoided.

Referring toFIGS.4and12, in another exemplary embodiment of the present invention, in addition to setting an end of the first bonding pin41close to the edge of the flexible substrate3to be narrow as in inFIG.2, a plurality of notches31may be provided at an end of the flexible substrate3close to the first bonding pins41, wherein each notch31is located between two adjacent first bonding pins41. The width of the opening part of the notch31is larger than the width of the side part of the notch31away from the opening part. The opening part of the notch31is designed to be relative wide, mainly for the smooth flow of the conductive particle glue and avoiding aggregation. The shape of the notch31may be a trapezoid, wherein the long base of the trapezoid coincides with the edge of the flexible substrate3, and the short base of the trapezoid is recessed into the flexible substrate3to form a notch31with an opening part larger than the bottom part. Of course, the shape of the notch31can also be a triangle, a semicircle, a semi-ellipse, etc., as long as the opening part of the notch31is designed to be relative wide, which will not be repeated here. The notch31further cuts off the physical connection between two adjacent first bonding pins41. On the one hand, no short circuit occurs because of conductive particles8generated on the edge. On the other hand, this design increases to a certain extent the overflowing possibility of the conductive particles8, thus reducing the problem of aggregation, and further avoiding a short circuit among the plurality of first bonding pins41.

It should be noted that the setting of the notch31may not be based on the narrower end of the first bonding pin41close to the edge of the flexible substrate3inFIG.2, but on the basis ofFIG.1.

With reference toFIG.5, in an exemplary embodiment, the flexible circuit board may further include a conductor layer42and a first protective layer51, wherein the conductor layer42is provided in the bending area2on the flexible substrate3, and the conductor layer42is connected to the first bonding pins41. That is, the conductor layer42and the first bonding pins41are located on the same side of the flexible substrate3, and the conductor layer42and the first bonding pins41are arranged in the same layer by the same material. That is, the conductor layer42and the first bonding pins41are formed through the same patterning process. The first protective layer51is provided on the side of the conductor layer42away from the flexible substrate3. That is, the first protective layer51is only provided on the side of the conductor layer42away from the flexible substrate3, but is not provided on the side of the first bonding pins41away from the flexible substrate3, and the first protective layer51covers the conductor layer42to protect the conductor layer42. The thickness of the flexible substrate3may be greater than or equal to 7 microns and less than or equal to 12 microns, the yielding degree of the flexible substrate is greater than 280 MPA, and the thickness of the conductor layer42and the first bonding pins41are greater than or equal to 8 microns and less than or equal to 10 microns.

In an example embodiment, each of the first bonding pins41and the conductor layer42may include a first conductive metal layer131and a second conductive metal layer132, wherein the first conductive metal layer131is fitted onto the flexible substrate3by pressing, and the second conductive metal layer132is formed on the side of the first conductive metal layer131away from the flexible substrate3by flash plating.

The flexible circuit board can be a single-layer flexible circuit board, or a double-layer flexible circuit board. Of course, it can also be a multilayer flexible circuit board.FIG.5shows a double-layer flexible circuit board. That is, a conductive layer52is provided on the side of the flexible substrate3away from the first bonding pins41and the conductor layer42, a third protective layer53is provided on the side of the conductive layer52away from the flexible substrate3, and a plurality of electronic devices54and a metal support55are provided on the side of the first protective layer51and the third protective layer53away from the flexible substrate3, wherein an insulating layer56is provided on the side of the metal support55close to the flexible substrate3.

Further, an example embodiment also provides a touch panel. As shown inFIG.6, the touch panel may include a touch module6and any one of the above-mentioned flexible circuit boards. The touch module6also has a second bonding area. The first bonding area1of the flexible circuit board10is bound to the second bonding area of the touch module6. The bonding adhesive layer is arranged between the second bonding area of the touch module6and the first bonding area1of the flexible circuit board10. The specific structure of the flexible circuit board10has been described in detail above, so it will not be repeated here.

In an example embodiment, as shown inFIG.7, the touch module6may include a second protective layer61, a first cover layer62, a touch layer63, and a second cover layer64. The first cover layer62is disposed on the second protective layer61, the touch layer63is disposed on the side of the first cover layer62away from the second protective layer61, and the second cover layer64is disposed on the side of the touch layer63away from the second protective layer61. The orthographic projection on the touch layer63of an edge line of an end of the second cover layer64is located within the touch layer63, so that part of the touch layer63is exposed to form the second bonding area of the touch module6. That is, the second cover layer64does not completely cover the touch layer63, but only covers a part of the touch layer63, so that a part of the touch layer63is exposed to form the second bonding area of the touch module6. The materials of the first cover layer62and the second cover layer64may be UV glue, that is, photosensitive glue. The thickness of the first cover layer62and the second cover layer64is approximately 2 microns. The bonding glue layer may be conductive particle glue with a diameter greater than or equal to 5 microns and less than or equal to 10 microns. That is, the diameter of the conductive particles in the conductive particle glue is greater than or equal to 5 microns and less than or equal to 10 microns. The diameter of conductive particles is set to be relative small for facilitating circulation. But it is easy to be squeezed out more during bonding, which is not conducive to bonding. When the diameter of conductive particles is set to be relatively large, it is not easy to be squeezed out more, thus being conducive to bonding, but it is easy to aggregate and cause a short circuit. Through lots of experiments, conductive particle glue with a diameter greater than or equal to 5 microns and less than or equal to 10 microns is less likely to be squeezed out during bonding, which is more conducive to bonding, and is less likely to aggregate and cause short circuits. Of course, the materials of the first cover layer62and the second cover layer64may also be an optical material such as Cyclic Olefin Polymer (COP), polyimide resin, or the like.

In an exemplary embodiment, the flexible circuit board may further include a protective film12, which is provided in the bending area2on the side of the flexible substrate3away from the conductor layer42. The protective film12can protect the flexible substrate3. On the other hand, the strength of the flexible substrate3itself can be improved to avoid breakage, making it not easy to deform under external conditions, and helping to maintain the bending appearance. Also, it is not easy to cause the risk of cracks in the flexible circuit board during installation or use of the whole machine.

Further, an example embodiment also provides a method for manufacturing a flexible circuit board, configured to manufacture the flexible circuit board described in any one of the above embodiments. The manufacturing method may include the following steps: after performing a shadow process on the via holes and before forming the photoresist, a first conductive material layer is formed on the conductor layer42by flash plating.

Referring toFIG.8, the method for flash-plated a flexible circuit board may include the following steps.

In step S11, a flexible substrate is provided, and conductor layers are formed on opposite sides of the flexible substrate.

In step S12, via holes are formed on the flexible substrate and the conductor layer.

In step S13, the via holes are cleaned.

In step S14, a shadow process is performed on the via holes.

In step S15, a first conductive material layer is formed by flash plating on the conductor layer.

In step S16, a photoresist is formed on the side of the first conductive material layer away from the flexible substrate.

In step S17, the photoresist is removed at the via holes.

In step S18, a second conductive material layer is formed on the side of the photoresist and the first conductive material layer away from the flexible substrate.

In step S19, the remaining photoresist and the second conductive material layer on the side of the photoresist away from the flexible substrate are removed.

Specifically, a flexible substrate3is provided, and the material of the flexible substrate3can be polyimide, polyester, or the like. A conductive material layer can be fitted onto both sides of the flexible substrate3by pressing. The thickness of the conductive material layer is about 12 microns, and the material of the conductive material layer can be high ductility copper. The conductive material layer subsequently forms the first bonding pins41and the first conductive metal layer131of the conductor layer42. Then, a thinning process can be performed on the conductive material layer. Via holes are formed on the conductive material layer and the flexible substrate3by laser drilling. That is, the via holes penetrate through the conductive material layer and the flexible substrate3. Then, the via holes are cleaned to remove the residue generated when the via holes are formed. Next, a shadow process is performed on the via holes, to facilitate subsequent electroplating and conduction. Then a flash plating process is performed on the entire surface. That is, a copper layer is formed by flash plating on the side of the conductive material layer away from the flexible substrate3. The thickness of the copper layer can be greater than or equal to 3 microns and less than or equal to 5 microns, and electroplating will be also performed at the via holes, thus causing part of the copper to be deposited on the wall of the via holes, so that the entire device has been turned on. The copper layer formed by flash plating subsequently forms the first bonding pins41and the second conductive metal layer132of the conductor layer42. Then photoresist is applied on the side of the flash-plated copper layer away from the flexible substrate3, and then the photoresist is exposed and cleaned at the via hole positions. Thus, the flash-plated copper layer at the via hole positions is exposed, while the flash-plated copper layer at other positions continues to be covered by photoresist. Then an electroplating process is carried out on the whole surface. However, due to the conductive effect of the flash-plated copper layer at the via holes, a large amount of electroplated copper is deposited at the via hole positions, and the electroplated copper is evenly deposited on the photoresist surface at other positions. Since the flash plating process of the entire surface has been electroplated at the via hole positions, this step further thickens the copper layer at the via hole positions, so as to improve the reliability of the entire flexible circuit board. Finally, the photoresist is removed. At the same time as the photoresist is removed, the electroplated copper layer on the surface of the photoresist will also be removed. Then the thickness and conductivity of the deposited copper at the via hole positions are detected.

In an exemplary embodiment, the materials plated by the flash plating process of the entire surface and the electroplating process of the entire surface are all copper. It is understandable that, in other exemplary embodiments of the present invention, the material plated by the flash plating process of the entire surface and the electroplating process of the entire surface may be materials with good conductivity such as silver and gold.

Since the flexible circuit board according to the present invention is an ultra-thin flexible circuit board, the method for manufacturing a flexible circuit board in the prior art can effectively ensure that only the via holes are covered with electroplated copper. However, due to the thinning of the flexible substrate3, the manufactured flatness is difficult to guarantee, which makes the manufacture of via hole electroplating more difficult. At the same time, it is relatively difficult to form via holes with a smaller diameter on the flexible substrate3due to process limitations after the flexible substrate3is thinned according to the present invention. When the photoresist is removed, exposed and developed, there is a part of the remaining photoresist, which makes the electroplated copper layer at the via holes appear inhomogeneous, and even makes a short-circuit phenomenon occur.

Compared with the prior art, the method for manufacturing the flexible circuit board according to the present invention adds a flash plating process on the entire surface after performing the shadow process on the via holes and before the process of photoresist coating. Through the above method, a flexible circuit board with stable performance can be produced. The flexible circuit board manufactured by this method can effectively ensure the conduction. It is verified by experiments that the thickness of the conductive material layer is reduced and the flash-plated copper layer is increased, so as to make the thicknesses of the conductor layer42and the conductive layer52remain unchanged. However, the thickness of the copper layer at the via holes is increased, and the conductivity is strengthened, thereby significantly enhancing the overall reliability. Therefore, the flexible circuit board manufactured by this method has good mass production.

Further, an example embodiment also provides a method for manufacturing a touch panel. As shown inFIG.9, the method for manufacturing a touch panel may include the following steps.

In step S10, a flexible circuit board is provided, and the flexible circuit board is manufactured according to any one of the manufacturing methods of the flexible circuit board described above.

In step S20, a touch module6is provided.

In step S30, the touch module6is bonded to the flexible circuit board10.

The steps of the manufacturing method of the touch panel are described in detail below.

The manufacturing method of the flexible circuit board has been described in detail above, so it will not be repeated here.

Before providing a touch module6, it is required to manufacture the touch module6. As shown inFIG.10, the method of manufacturing the touch module6may include the following steps.

In step S21, a rigid substrate65is provided.

In step S22, a first cover layer62is formed on the rigid substrate65.

In step S23, a touch layer63is formed on the side of the first cover layer62away from the rigid substrate65.

In step S24, a second cover layer64is formed on the side of the touch layer63away from the rigid substrate65.

In step S25, the rigid substrate65is irradiated with ultraviolet light to peel off the first cover layer62from the rigid substrate65.

In step S26, the first cover layer62is fitted onto the second protective layer61.

Specifically, referring toFIG.11, a rigid substrate65is provided, and the rigid substrate65is made of transparent glass. A first cover layer62is formed on the rigid substrate65through processes such as coating and printing. The material of the first cover layer62is photosensitive glue, that is, UV glue. The touch layer63is formed on the side of the first cover layer62away from the rigid substrate65through coating, printing, deposition, evaporation and plating, and other processes. The touch layer63is subjected to photolithography and other processes to form a required pattern. A second cover layer64is formed on the side of the touch layer63away from the rigid substrate65through processes such as coating, printing, and deposition. The material of the second cover layer64is photosensitive glue, that is, UV glue. The rigid substrate65is irradiated with ultraviolet light to peel off the first cover layer62from the rigid substrate65, so that the first cover layer62, the touch layer63and the second cover layer64are all separated from the rigid substrate65. Finally, the first cover layer62is fitted onto the second protective layer61to form the structure shown inFIG.7. The material of the second protective layer61is the optical material COP.

Since the method for manufacturing the touch module6uses the first cover layer62and the second cover layer64, the touch layer63can be well protected when bending, and at the same time, the method can make the production of the entire touch layer63on glass, thus achieving good flatness. Therefore, the touch layer63can achieve a manufacturing process for a 100 nm-level composite layer. That is, the thickness of the touch module6is about 100 nm.

Compared with the prior art method of directly coating the touch layer63on the optical material COP, and the thinned structure of the flexible circuit board, the deformation of the touch module6during bonding becomes larger. Specifically, referring toFIG.12, when the bonding indenter7is pressed on the edge of the first bonding pin41, the deformation of the touch module6is mainly at the edge position, and at the same time, the lower layer of the touch module6undergoes a non-uniform force at the edge, leading to the problem of severely deforming at edge. As a result, the gap between the first trench57of the flexible circuit board10and the second trench67of the touch layer63is sharply reduced, which causes the overflow path of the inner conductive particles8to be destroyed, and causes the conductive particles8to gather. Referring toFIGS.13and14, in an exemplary embodiment, when the touch module6is bound to the flexible circuit board10, a silicone pad9is placed between the bonding indenter7and the flexible circuit board10. The silicone pad9can protect the flexible circuit board10. The bonding indenter7is pressed on the overlapping part, in the middle area thereof, between the second bonding pins66of the touch module6and the first bonding pins41of the flexible circuit board10, wherein the middle area refers to the middle area along the length direction of a plurality of first bonding pins41. Besides, the length of the bonding indenter7is greater than the length of the second bonding area, and is also greater than the length of the first bonding area. All the first bonding pins41and all the second bonding pins66are pressed. When the bonding indenter7is pressed on the first bonding pins41in the middle area thereof, the force bearing points of the touch module6are relatively uniform, and there are deformations in the whole. But the limit deformation becomes smaller than that shown inFIG.12. For example, the gap between the whole trenches is increased. When the middle area is compressed, the largest deformation is in the middle area, and the deformation at both ends is relatively small, which allows the conductive particles8in the middle area to move in both directions. The conductive particles8moving to the edge can be eliminated without gathering at the edge. This bonding method is conducive to the flow of conductive particles8at the trench of the flexible circuit board10from inside to outside. The problem of aggregation of conductive particles8is greatly reduced, and the yield of bonding is improved.

Moreover, the combination of the above-mentioned bonding method and the flexible circuit board10in an exemplary embodiment further avoids the short circuit caused by the aggregation of conductive particles8, thus greatly improving the overall reliability.

As mentioned earlier, in order to ensure the overall characteristics of the display device, the present invention proposes a flexible circuit board and a manufacturing method. The bending area2of the flexible circuit board is only provided with the flexible substrate3, the conductor layer42, and the first protective layer51. It is composed of three parts. With this structure, it can be matched with the ultra-thin touch module6to ensure good bending characteristics. At the same time, the present invention changes the production process and the design of the first bonding pins41, and thus the overall performance in various aspects of the module state can be guaranteed stably. However, because this structure will eventually be applied to a foldable terminal, it has a large amount of twisting in the use state. At the same time, because the whole machine will make the bending area2to be bent, this makes the flexible circuit board10at this position easy to deform or wear. In order to improve the performance of the device, protect the fragile surface of the device, and ensure the process characteristics of the flexible circuit board10, an exemplary embodiment proposes an outer-side gluing process, wherein in the bending area2of the flexible circuit board10, a protective glue layer11is formed on the side of the flexible substrate3away from the conductor layer42, and when the protective glue layer11is not dry, the flexible circuit board10is bent. Of course, the gluing process can be performed before the bonding process or after the bonding process. As shown inFIG.15, the protective glue layer11is coated on a side of the flexible substrate3located at an outer surface of the bending area, wherein the protective glue layer11can be UV glue (photosensitive glue), and at the same time, when manufacturing the touch panel, the bending process is completed while the UV glue is not dried. After the subsequent drying of the glue, an ultra-thin protective film12will be formed on the surface of the flexible substrate3. The protective film12has the function of protecting the flexible substrate3on the one hand, and on the other hand, improving the strength of the flexible substrate3itself to avoid breakage. It is not prone to deformation under external conditions, thus maintaining the bending appearance, and is also not prone to the risk of cracks in the flexible circuit board during installation or use of the whole machine. This allows the product to cope with a more severe environment. It has been verified by experiments that this method can effectively improve the defects of the whole machine.

The features, structures, or characteristics described above can be combined in one or more embodiments in any suitable manner. If possible, the features discussed in the embodiments are interchangeable. In the above description, many specific details are provided to give a sufficient understanding of the embodiments of the present invention. However, those skilled in the art will realize that the technical solutions of the present invention can be practiced without one or more of the specific details, or other methods, components, materials, etc. can be used. In other cases, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the present invention.

The term “about” and “approximately” used in this specification usually means within 20% of a given value or range, preferably within 10%, and more preferably within 5%. The quantity given here is an approximate quantity, rendering that the meaning of “about”, “approximately”, “approximately” and “approximately” can still be implied in the absence of specific instructions.

Although relative terms such as “upper” and “lower” are used in this specification to describe the relative relationship between one component represented by an icon and another component, these terms are used in this specification only for convenience, for example, based on the example direction as shown in the drawings. It can be understood that if the device represented by an icon is turned over and turned upside down, the component described as “upper” will become the “lower” component. When a structure is “on” another structure, it may mean that a certain structure is integrally formed on the other structures, or that a certain structure is “directly” installed on the other structures, or that a certain structure is “indirectly” installed on the other structures through a third structure.

In this specification, the terms “a”, “an”, “the” and “said” are used to indicate the presence of one or more elements/components/etc. The terms “including”, “comprising” and “having” are used to mean open-ended inclusion, and means that in addition to the listed elements/components/etc., there may be other elements/components/etc. The terms “first”, “second” and “third””, etc. are only used as markers, not as a restriction on the number of objects.

It should be understood that the present invention does not limit its application to the detailed structure and arrangement of the components proposed in this specification. The present invention can have other embodiments, and can be implemented and executed in various ways. The aforementioned deformations and modifications fall within the scope of the present invention. It should be understood that the present invention disclosed and defined in this specification extends to all alternative combinations of two or more individual features mentioned or obvious in the text and/or drawings. All these different combinations constitute multiple alternative aspects of the invention. The embodiments described in this specification illustrate the best mode known for implementing the present invention, and will enable those skilled in the art to utilize the present invention.