CN113038703B

CN113038703B - Flexible circuit board, manufacturing method thereof and electronic equipment

Info

Publication number: CN113038703B
Application number: CN202110288172.3A
Authority: CN
Inventors: 肖云瀚; 王志强; 梁恒镇
Original assignee: BOE Technology Group Co Ltd; Chengdu BOE Optoelectronics Technology Co Ltd
Current assignee: BOE Technology Group Co Ltd; Chengdu BOE Optoelectronics Technology Co Ltd
Priority date: 2021-03-17
Filing date: 2021-03-17
Publication date: 2022-08-05
Anticipated expiration: 2041-03-17
Also published as: CN113038703A

Abstract

The embodiment of the disclosure discloses a flexible circuit board, a manufacturing method thereof and an electronic device, wherein the flexible circuit board at least comprises: the main FPC layer and the switching FPC layer are connected through an adhesive layer and solder paste; the main FPC layer and the switching FPC layer are FPCs with double-layer copper foils, a pad area of the switching FPC layer is of a concave structure relative to a pad area of the main FPC layer, the pad area of the main FPC layer is of a convex structure relative to the pad area of the switching FPC layer, both the concave structure and the convex structure are copper foils, the thickness of the copper foil corresponding to the concave part in the concave structure is not more than the sum of the thickness of the upper layer and the lower layer of the copper foil of the switching FPC layer and the thickness of a base material, and the height of the copper foil corresponding to the convex part of the convex structure is lower than the outer surface of the copper foil, close to one side of the main FPC layer, of the switching FPC layer. The embodiment of the disclosure increases the welding area, has small influence on the welding state of the solder paste, is not easy to cause poor cold welding, and has firm welding.

Description

Flexible circuit board, manufacturing method thereof and electronic equipment

Technical Field

The present disclosure relates to the field of display, and in particular, to a flexible printed circuit board, a method for manufacturing the same, and an electronic device.

Background

In order to reduce the cost of a Flexible Printed CirCuit (FPC) used in an OLED product and improve the problem of line signal crosstalk, a design combining a plurality of double-layer FPCs may be used and applied to the existing project.

In the existing multiple FPC assembly processes, the transfer FPC and the main FPC are soldered together by molten solder paste, for example, as shown in fig. 1 and 2 (the figures are schematic diagrams, and the specific structures of all the FPCs are not shown), and two double-layer FPCs are soldered and combined, so that the two double-layer FPCs have performances which are incomparable with a single double-layer board. The welding process mainly adopts pressure welding, but the existing manufacturing process has the problem of poor welding (insufficient welding and less tin), so that Open disconnection of welding points (namely Open NG) is caused.

In the manufacturing process of the combination of the multiple FPCs, the heat deformation degree of the switching FPC is large, as shown in figure 3 (deformation mainly causes two forms, namely convex and concave at welding point positions), so that the distances between welding points of an upper bonding pad and a lower bonding pad are different, and the bad welding state of solder paste can be caused if the distances are serious; meanwhile, the space of a welding spot area is very small, and the welding area cannot ensure better peeling resistance. Therefore, different tin-climbing phenomena (as shown in fig. 4) occur during the soldering process, which may cause problems of less tin and even insufficient soldering, resulting in poor soldering.

Therefore, different types of tin-climbing phenomena can occur in the welding process of the existing multiple FPC combination process, so that the problems of less tin and insufficient welding are caused, and poor welding is caused.

Disclosure of Invention

In view of this, the present disclosure provides a flexible circuit board, a manufacturing method thereof and an electronic device, so as to solve the following problems in the prior art: the existing multiple FPC combination process can generate different tin climbing phenomena in the welding process, so that the problems of less tin and insufficient welding are caused, and poor welding is caused.

In one aspect, an embodiment of the present disclosure provides a flexible circuit board, which at least includes: the main FPC layer and the switching FPC layer are connected through an adhesive layer and solder paste; the main FPC layer and the switching FPC layer are FPCs with double-layer copper foils, a pad area of the switching FPC layer is of a concave structure relative to a pad area of the main FPC layer, the pad area of the main FPC layer is of a convex structure relative to the pad area of the switching FPC layer, the concave structure and the convex structure are copper foils, the thickness of the copper foil corresponding to a concave part in the concave structure is not more than the sum of the thicknesses of the upper layer and the lower layer of the copper foil of the switching FPC layer and the thickness of a base material, and the height of the copper foil corresponding to a convex part of the convex structure is lower than that of the switching FPC layer close to the outer surface of the copper foil on one side of the main FPC layer.

In some embodiments, the surface area of the cross-section of the convex structure convex portion is greater than the surface area of the cross-section of the concave structure concave portion.

In some embodiments, the convex structure protruding portion and the concave structure concave portion are both cylinders, and the cross sections of the two cylinders have the same circle center corresponding to the circle.

In some embodiments, the horizontal portions on both sides of the convex structure have recessed grooves, which surround the convex structure.

In some embodiments, the recess depth of the groove is less than the thickness of the copper foil on the side of the main FPC layer close to the relay FPC layer.

In some embodiments, the groove is adjacent to the convex structure.

In some embodiments, the interior of the concave structure has a boss.

In some embodiments, the height of the boss does not exceed the depth of the recessed portion of the female structure.

On the other hand, an embodiment of the present disclosure provides an electronic device, which at least includes: the flexible circuit board of any embodiment of this disclosure.

On the other hand, an embodiment of the present disclosure provides a method for manufacturing a flexible circuit board, which is used for manufacturing the flexible circuit board according to any embodiment of the present disclosure, and at least includes: connecting the main FPC layer with the transfer FPC layer through glue; and soldering tin paste on the convex structure of the main FPC layer and the concave structure of the switching FPC layer through a preset soldering process.

The through hole position of the original switching FPC layer is filled, so that a concave structure is formed in the pad area, and further, no through hole with tin climbing possibility exists, and the tin climbing problem can not occur again; in order to make the welding more firm, all designed the convex structure with the pad region on the main FPC layer, reduce the welding distance between main FPC layer and the switching FPC layer, also make molten state's tin cream scramble more easily, increased the welding area of tin cream. The embodiment of the disclosure increases the welding area, has small influence on the welding state of the solder paste, is not easy to cause poor cold welding, and has firm welding.

Drawings

In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only some embodiments described in the present disclosure, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic cross-sectional structure of an FPC provided in the prior art;

FIG. 2 is a schematic cross-sectional view of a land of a FPC provided in the prior art;

FIG. 3 is a schematic diagram of a deformation of an FPC provided by the prior art;

FIG. 4 is a schematic diagram illustrating a solder-climbing phenomenon of an FPC provided in the prior art;

fig. 5 is a schematic cross-sectional structure diagram of a flexible circuit board according to an embodiment of the present disclosure;

fig. 6 is a schematic cross-sectional structure diagram of a flexible circuit board according to an embodiment of the present disclosure;

fig. 7 is a first schematic diagram illustrating a cross-sectional view of a full-area bonding area of a flexible circuit board according to an embodiment of the present disclosure;

fig. 8 is a schematic cross-sectional structure diagram of a flexible circuit board according to an embodiment of the present disclosure;

fig. 9 is a schematic cross-sectional view of a full-area bonding region of a flexible circuit board according to an embodiment of the disclosure.

Reference numerals:

1-main FPC layer, 2-switching FPC layer, 3-solder paste, 4-adhesive layer, 5-copper foil, 6-substrate, 22-concave structure, 11-convex structure and 12-groove.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be described below clearly and completely with reference to the accompanying drawings of the embodiments of the present disclosure. It is to be understood that the described embodiments are only a few embodiments of the present disclosure, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the disclosure without any inventive step, are within the scope of protection of the disclosure.

Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure belongs. The use of "first," "second," and similar terms in this disclosure is not intended to indicate any order, quantity, or importance, but rather is used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that the element or item listed before the word covers the element or item listed after the word and its equivalents, but does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships may also be changed accordingly.

To maintain the following description of the embodiments of the present disclosure clear and concise, a detailed description of known functions and known components have been omitted from the present disclosure.

A first embodiment of the present disclosure provides a flexible circuit board, a cross-sectional structure of which is schematically shown in fig. 5, and which at least includes:

the main FPC layer 1 and the switching FPC layer 2 are connected through an adhesive layer 4 and solder paste 3; wherein the content of the first and second substances,

the main FPC layer and the switching FPC layer are both FPCs with double-layer copper foils, a pad area of the switching FPC layer is of a concave structure 22 relative to the pad area of the main FPC layer, the pad area of the main FPC layer is of a convex structure 11 relative to the pad area of the switching FPC layer, the concave structure and the convex structure are copper foils 5, the thickness of the copper foil corresponding to a concave part in the concave structure is not more than the sum of the thickness of the upper copper foil 5 and the lower copper foil 5 of the switching FPC layer and the thickness of a base material 6, and the height of the copper foil corresponding to a convex part of the convex structure is lower than the outer surface of the copper foil on one side, close to the main FPC layer, of the switching FPC layer.

In the concrete implementation, the surface area of the cross section of the convex part of the convex structure is larger than that of the cross section of the concave part of the concave structure, so that solder paste in a molten state can be more easily dropped on the convex structure, and the welding area is increased. Preferably, the convex portion of the convex structure and the concave portion of the concave structure are both cylinders, and the corresponding circles of the cross sections of the two cylinders have the same circle center, however, this structure is only an example, and those skilled in the art can design the shapes of the convex structure and the concave structure according to actual requirements, for example, the shapes are designed into a cone, a cuboid, etc., and are not described herein again.

In order to further increase the welding area and make the welding more firm, the horizontal part on both sides of the convex structure is provided with a downward embedded groove 12, and the groove 12 surrounds the convex structure 11. The depth of the recess 12 is less than the thickness of the copper foil on the side of the main FPC layer adjacent to the via FPC layer to form a blind groove rather than a through groove. When the welding structure is specifically arranged, the welding effect is best when the groove is adjacent to the convex structure.

In order to further increase the welding area and make the welding more firm, the inside of the concave structure is provided with a boss. The height of the boss is not more than the depth of the concave part of the concave structure, so that the distance between the concave structure and the convex structure is further shortened, and a better welding effect is realized.

The above structure will be further explained with reference to the drawings.

The embodiment of the disclosure designs the sinking groove and convex structure of the main FPC bonding pad area. Firstly, a groove with a proper size is formed in a main FPC bonding pad area, the range of the groove is required to be not beyond a circular bonding pad area, and the depth of the groove is required to be not beyond the thickness of copper foil in the bonding pad area; then, a convex structure with a certain height is plated in the groove, the material can be copper foil, and the height of the convex structure is required not to reach the transfer FPC layer. In addition, the through hole design of the switching FPC layer is changed into a closed type, and the through hole is packaged by green ink, so that the soldering tin is welded between the two FPC layers; here, the bonding pad area of the transfer FPC layer may be only a concave structure, the single solder joint has a cross section as shown in fig. 6, and the entire surface of the bonding pad has a cross section as shown in fig. 7; of course, reference may also be made to the design of the main FPC layer, i.e. adding a boss inside the concave structure, with a single solder joint cross-section as shown in fig. 8 and a full solder joint cross-section as shown in fig. 9.

The design of the sinking groove increases the space of the pad area, so that the molten state prepared solder paste can flow into the groove and be stored in the groove when the tin soldering preparation process is carried out, and the periphery of the central convex structure can be relied on, thereby increasing the adhesion area of the solder paste and being beneficial to improving the soldering stability and firmness; when the furnace returning welding and pressure welding process is carried out, the convex structure has a certain height and is closer to the concave structure, so that the allowed FPC deformation is more sufficient, and the problem of insufficient soldering caused by less tin or even no tin in the main FPC layer due to deformation is solved; and because no punching technology is used in the manufacture of the hollow board, the structural strength of the whole surface area of the switching FPC layer is enhanced, and the risk caused by deformation is reduced.

In the existing welding effect detection method, because the through-connection FPC layer is designed to be a through hole, and part of solder paste is finally pressed onto a pad area of the main FPC from the through hole through a pressure welding process, when the welding effect is detected, the welding effect can be judged in an auxiliary mode through CCD (charge coupled device) manual observation of a tin-emitting form, and whether the welding reaches the standard is judged by matching with X-ray and functional electrical property tests, but the mode cannot completely eliminate poor insufficient welding, and manual judgment specification cannot be standardized.

Aiming at the double-layer flexible circuit board provided by the embodiment of the disclosure, through hole design is structurally cancelled, the traditional appearance detection method cannot be corresponded, but the defective products of the insufficient solder joint cannot be completely eliminated by means of common X-ray and functional electrical test, so that 3dX-ray or 5dX-ray can be used for replacing X-ray to carry out dynamic monitoring, and the effect of eliminating defective products of less tin and insufficient solder joint can be achieved by combining the electrical test.

The embodiment of the disclosure designs a sinking groove and convex structure in the FPC bonding pad area, and increases the welding area; meanwhile, the design of a through hole of the conventional switching FPC layer is cancelled, so that solder paste is welded between the two FPC layers, and the risk of deformation of a welding area caused by a mechanical punching process is reduced.

The embodiment of the present disclosure further provides an electronic device, which at least includes the flexible circuit board in the above embodiments, and the specific structure of the flexible circuit board is not described herein again.

The embodiment of the present disclosure further provides a method for manufacturing a flexible circuit board, which is used for manufacturing the above-mentioned double-layer flexible circuit board, and the method at least includes the following steps: connecting the main FPC layer with the switching FPC layer through glue; and soldering tin paste on the convex structure of the main FPC layer and the concave structure of the switching FPC layer through a preset soldering process.

In a specific implementation, the predetermined welding process may be an existing welding process, and is not described herein again.

Moreover, although exemplary embodiments have been described herein, the scope thereof includes any and all embodiments based on the disclosure with equivalent elements, modifications, omissions, combinations (e.g., of various embodiments across), adaptations or alterations. The elements of the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. It is intended, therefore, that the specification and examples be considered as exemplary only, with a true scope and spirit being indicated by the following claims and their full scope of equivalents.

The above description is intended to be illustrative and not restrictive. For example, the above-described examples (or one or more versions thereof) may be used in combination with each other. For example, other embodiments may be used by those of ordinary skill in the art upon reading the above description. In addition, in the foregoing detailed description, various features may be grouped together to streamline the disclosure. This should not be interpreted as an intention that a non-claimed disclosed feature is essential to any claim. Rather, the subject matter of the present disclosure may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that these embodiments may be combined with each other in various combinations or permutations. The scope of the disclosure should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

While the present disclosure has been described in detail with reference to the embodiments, the present disclosure is not limited to the specific embodiments, and those skilled in the art can make various modifications and alterations based on the concept of the present disclosure, and the modifications and alterations should fall within the scope of the present disclosure as claimed.

Claims

1. A flexible circuit board, characterized by comprising at least:

the main FPC layer and the switching FPC layer are connected through an adhesive layer and solder paste; wherein the content of the first and second substances,

the main FPC layer and the transfer FPC layer are FPCs with double-layer copper foils, pad areas of the transfer FPC layer are of concave structures relative to pad areas of the main FPC layer, pad areas of the main FPC layer are of convex structures relative to pad areas of the transfer FPC layer, the concave structures and the convex structures are copper foils, the thickness of the copper foil corresponding to concave parts in the concave structures is not more than the sum of the thickness of the copper foils on the upper layer and the lower layer of the transfer FPC layer and the thickness of a base material, and the height of the copper foil corresponding to convex parts of the convex structures is lower than the outer surface of the copper foil on one side, close to the main FPC layer, of the transfer FPC layer;

wherein the surface area of the cross section of the convex structure convex part is larger than that of the cross section of the concave structure concave part.

2. The flexible circuit board of claim 1, wherein the convex structure raised portion and the concave structure depressed portion are both cylinders, and the corresponding circles of the cross sections of the two cylinders have the same center.

3. The flexible circuit board of claim 1, wherein the horizontal portion of both sides of the convex structure has a recessed groove thereon, the recessed groove surrounding the convex structure.

4. The flexible circuit board of claim 3, wherein a recess depth of the groove is smaller than a thickness of a copper foil of the main FPC layer on a side close to the relay FPC layer.

5. The flexible circuit board of claim 3, wherein the groove is adjacent to the convex structure.

6. The flexible circuit board according to any one of claims 1 to 5, wherein the concave structure has a boss inside.

7. The flexible circuit board of claim 6, wherein the height of the raised platform does not exceed the depth of the recessed portion of the female structure.

8. An electronic device, characterized in that it comprises at least: the flexible circuit board of any one of claims 1 to 7.

9. A manufacturing method of a flexible circuit board for manufacturing the flexible circuit board according to any one of claims 1 to 7, characterized by comprising at least:

connecting the main FPC layer with the switching FPC layer through glue;

and soldering tin paste on the convex structure of the main FPC layer and the concave structure of the switching FPC layer through a preset soldering process.