CN113495384B

CN113495384B - Direct type backlight module, display device and manufacturing method of circuit board

Info

Publication number: CN113495384B
Application number: CN202010192539.7A
Authority: CN
Inventors: 黄明利; 陶士超; 李小庆
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2022-12-30
Anticipated expiration: 2040-03-18
Also published as: CN113495384A

Abstract

The application provides a direct type backlight module, a display device and a manufacturing method of a circuit board, wherein the direct type backlight module comprises a direct type backlight source and a light conduction film layer, wherein the projection of the light conduction film layer along the thickness direction of the direct type backlight module covers the projection of the direct type backlight source along the thickness direction of the direct type backlight module; the direct type backlight source comprises N light-emitting devices and a circuit board, wherein the circuit board comprises a first solder mask layer and a pad array layer. The pad array layer includes N pads bound with the light emitting device, and the first solder mask layer includes N fenestrations. And at least part of the welding pad is arranged in the corresponding window, and the upper surface of the welding pad is flush with the upper surface of the first solder mask layer. The direct type backlight module that this application embodiment provided does not have the difference in height between pad and the first solder mask, has reduced soldering tin short circuit problem, and the problem of carving is not existed to first solder mask simultaneously, has improved the light reflectivity of direct type backlight source, has promoted direct type backlight module's light-emitting brightness.

Description

Direct type backlight module, display device and manufacturing method of circuit board

Technical Field

The application relates to the technical field of display, in particular to a direct type backlight module, a display device and a manufacturing method of a circuit board.

Background

In the field of display technology, ultra-clear display has been one of the most concerned and pursued technical points of technicians and consumers, and especially with the further development of 5G, the demand for ultra-clear display is becoming stronger, and thus a direct type backlight source is adopted, for example, a Mini LED (Mini Light Emitting Diode) direct type backlight source is adopted as a backlight source of a liquid crystal display device, so that the advantages of the liquid crystal display device in the aspects of contrast, color reproducibility, cost, life, stability and the like are far superior to those of a traditional liquid crystal display device, and even exceed those of an organic Light Emitting display device.

However, when the liquid crystal display device adopts the direct type backlight, the circuit board of the direct type backlight needs to have a surface with high reflectivity so as to improve the brightness and reduce the power consumption. The common method is to cover reflective film layers such as white ink on the surface of the circuit board to achieve the effect of high reflectivity, and the effect of improving the brightness is more obvious when the thickness of the reflective film layers such as the white ink is higher. The white ink used in the direct-type backlight circuit board is usually a photosensitive ink with solder resist, and the increase in thickness of the photosensitive white ink brings many adverse risks, which affect the normal light emission of the backlight and the normal display of the display device, resulting in low light emission brightness of the backlight and low display brightness of the display device.

Disclosure of Invention

The application provides a direct type backlight source, a display device and a manufacturing method of a circuit board to solve the problems.

In a first aspect, the present application provides a direct type backlight module, including a direct type backlight source and a light conducting film layer, wherein a projection of the light conducting film layer along a thickness direction of the direct type backlight module covers a projection of the direct type backlight source along the thickness direction of the direct type backlight module; the direct type backlight source comprises N light-emitting devices and a circuit board, wherein the circuit board comprises a first solder mask layer and a pad array layer. The pad array layer comprises N pads bound with the light-emitting device, and the first solder mask layer comprises N windows. And at least part of the welding pad is arranged in the corresponding window, and the upper surface of the welding pad is flush with the upper surface of the first solder mask layer. Wherein N is a positive integer greater than or equal to 1.

In one implementation of the first aspect, the first solder mask layer is at least one of photosensitive white ink, white solder mask dry film, and white prepreg.

In one implementation of the first aspect, the first solder resist layer has a thickness of 30 μm or more and the pad has a height of 30 μm or more.

In one implementation manner of the first aspect, the area of the upper surface of the pad is equal to the area of the upper surface of the corresponding window.

In one implementation of the first aspect, the light emitting device is a blue LED chip.

In one implementation of the first aspect, the light-conducting film layer includes a quantum dot conversion layer.

In one implementation form of the first aspect, the light conductive film layer includes a silicone protective layer covering the light emitting device.

In a second aspect, the present application provides a display device, including the direct type backlight module and the display panel provided in the first aspect, wherein the display panel is disposed on a light emitting side of the direct type backlight module.

In one implementation manner of the second aspect, the display panel is one of a liquid crystal display panel and an organic light emitting display panel.

In one implementation of the second aspect, the display panel includes a display area and a non-display area; the vertical projection of the light-emitting surface of the direct type backlight module and the display area of the display panel in the thickness direction of the display device is superposed.

In a third aspect, the present application provides a method for manufacturing a circuit board, which is used to manufacture the circuit board included in the direct type backlight module provided in the first aspect.

In one implementation form of the third aspect, the method includes: electroplating a selective plating metal layer; patterning the selective plating metal layer to form a selective plating metal block; electroplating to form a primary bonding pad by using the selective plating metal block as base copper; and forming a primary first solder mask layer, wherein the primary first solder mask layer comprises a first part and a second part, the first part is arranged between the primary pads, the second part is arranged on the upper surface of the primary pads, the upper surface of the first part is flush with or lower than the upper surface of the primary pads, the first solder mask layer and the pads are formed by grinding the areas where the primary pads are located, and the upper surfaces of the pads are flush with the upper surface of the first solder mask layer.

In one implementation of the third aspect, forming the primary first solder resist layer includes screen printing or coating a photosensitive white ink, thermally curing the photosensitive white ink.

In one implementation of the third aspect, forming the first solder resist layer includes attaching a white dry solder resist film and thermally curing the white dry solder resist film.

In one implementation of the third aspect, forming the first solder resist layer includes attaching a white prepreg and thermally curing the white prepreg.

The backlight module used by the display device provided by the embodiment of the application is a direct type backlight module, and the problem of soldering short circuit is reduced because no height difference exists between a welding pad and a first solder mask in the direct type backlight module; meanwhile, the grinding process is adopted to expose the bonding pad, so that the adverse effect of the etching process is avoided; and the grinding process is carried out after the film layer where the first solder mask layer is arranged, so that the height of the first solder mask layer is adjustable.

Drawings

FIG. 1 is a top view of a circuit board of a backlight source in the prior art;

FIG. 2 (a) is a cross-sectional view along the AA' direction of the circuit board of FIG. 1;

FIG. 2 (b) is a cross-sectional view along the circuit board shown in FIG. 1 in the direction BB';

FIG. 3 is a cross-sectional view of a direct type backlight module according to an embodiment of the present disclosure;

FIG. 4 is a partial top view of a circuit board of a direct backlight provided in an embodiment of the present application;

FIG. 5 (a) is a cross-sectional view taken along the direction of the circuit board MM' shown in FIG. 4;

FIG. 5 (b) is a cross-sectional view taken along the NN' direction of the circuit board shown in FIG. 4;

fig. 6 is an exploded view of a display device provided in an embodiment of the present application;

FIG. 7 is a partial cross-sectional view of the display device shown in FIG. 6;

fig. 8 is a schematic view of a display device according to an embodiment of the present application;

fig. 9 is a schematic view of a manufacturing method of a circuit board according to an embodiment of the present application.

Detailed Description

The terminology used in the description of the embodiments section of the present application is for the purpose of describing particular embodiments of the present application only and is not intended to be limiting of the present application.

Fig. 1 is a top view of a circuit board of a backlight source in the prior art, fig. 2 (a) is a cross-sectional view along a direction AA 'of the circuit board shown in fig. 1, and fig. 2 (b) is a cross-sectional view along a direction BB' of the circuit board shown in fig. 1. When the Mini LED is used as the backlight of the display panel, the surface of the backlight needs to have a high reflectivity to improve the brightness of the backlight and realize the energy-saving effect. As shown in fig. 1, 2 (a) and 2 (b), in the prior art, a certain thickness of photosensitive white ink 01 is generally coated on a surface of a circuit board on which an LED chip is disposed to achieve a high reflectance of a backlight, and the reflectance of the photosensitive white ink 01 is higher as the thickness is larger.

However, the conventional art has many problems in that a large thickness of the photosensitive white ink 01 provides a high reflectance.

With continued reference to fig. 1, fig. 2 (a) and fig. 2 (b), the film layer where the pads 02 soldered to the LED chip are located is under the photosensitive white ink 01, and the photosensitive white ink 01 is provided with windows 01C to expose the pads 02. The photosensitive white ink 01 used in the prior art generally contains a photosensitive substance, and the window 01C can be formed by exposing, developing and etching the photosensitive white ink 01. In the exposure process, light is incident perpendicularly to the photosensitive white ink 01, the light is less and less absorbed from the surface to the bottom of the photosensitive white ink 01, and when the thickness of the photosensitive white ink 01 is too large, the light is less absorbed closer to the bottom, so that the curing degree of the photosensitive white ink 01 is obviously weakened. In the next developing process, the part of the photosensitive white ink 01 with insufficient curing degree is etched to generate the problem of edge undercut of the window 01C, for example, as shown in fig. 2 (a) and fig. 2 (b), the more the part of the photosensitive white ink 01 closer to the bottom is etched, the more the liquid medicine used in the developing and nickel-gold dissolving process exists at the bottom of the photosensitive white ink 01, and further the problems of burr falling off, gold infiltration short circuit, poor welding, pad deformation, CAF failure and the like of the photosensitive white ink 01 are caused.

In addition, the area of the bonding pad 02 welded with the LED chip in the circuit board for the direct type backlight source is small, so that the requirement of the resolution ratio of the display panel is met. When the area of the pad 02 is small, as shown in fig. 1, 2 (a) and 2 (b), in the process of forming the window 01C by exposing, developing and etching the photosensitive white ink 01, an over-etching problem is easily generated due to the influence of process precision, that is, although the area of the window 01C is only for exposing the pad 02, the area of the window 01C is increased, so that not only the pad 02 but also a part of the copper clad plate base material 03 is exposed, and the photosensitive white ink 01 between the adjacent pads 02 is reduced, and the solder corresponding to different pads 02 is easily short-circuited. Moreover, since the area of the window 01C is increased to expose the copper-clad plate substrate 03, the white copper-clad plate substrate 03 should be used to ensure that the reflectivity of the backlight meets the requirement, which increases the manufacturing cost.

When the area of the bonding pad 02 is small, the density is high, and the thickness of the photosensitive white ink 01 is large, the uniformity of the photosensitive white ink 01 is poor because the bonding pad 02 is lower than the photosensitive white ink 01, and excessive soldering tin is easily caused, so that the soldering tin corresponding to different bonding pads 02 is short-circuited. Due to the high density of the bonding pads 02, if the photosensitive white ink 01 is prepared by a screen printing process, an extremely thin steel mesh is usually used, the stability of the steel mesh is lower than that of a thick steel mesh, and the small area of the bonding pads 02 easily causes tin printing deviation.

The problems can cause that the LED chip and the bonding pad are difficult to bind or the bound signal is abnormal in the direct type backlight source, and the normal light emitting of the direct type backlight source and the normal display of the display device are influenced; in addition, since the thickness and the area of the photosensitive white ink 01 are limited, the emission luminance of the direct type backlight is low and the display luminance of the display device is low.

In order to solve the above problems, embodiments of the present disclosure provide a direct-type backlight module and a display device including the direct-type backlight module, and provide a method for manufacturing a circuit board in the direct-type backlight module.

Fig. 3 is a cross-sectional view of a direct type backlight module according to an embodiment of the present disclosure, as shown in fig. 3, the direct type backlight module according to the embodiment of the present disclosure includes a direct type backlight source 001 and a light conduction film layer 002, wherein a projection of the light conduction film layer 002 along a thickness direction of the direct type backlight module covers a projection of the direct type backlight source 001 along the thickness direction of the direct type backlight module, the direct type backlight source 001 can emit light, the light conduction film layer 002 is used for conducting light emitted from the direct type backlight source 001, and thus the direct type backlight module can provide backlight meeting requirements of brightness, chromaticity, uniformity, and the like.

Specifically, the direct type backlight 001 includes a circuit board 100 and N light emitting devices 200, the N light emitting devices 200 are disposed on the circuit board 100, and the circuit board 100 is used for controlling the light emitting devices 200 to emit light. Specifically, the N light emitting devices 200 may be specifically LED chips arranged in an array, such as Mini-LEDs or Micro-LEDs. Wherein N is a positive integer greater than or equal to 1.

Specifically, the light-conductive film layer 002 includes a silicone protective layer 300, and the silicone protective layer 300 is disposed on the direct type backlight 001 and completely covers the light emitting device 200. The silicone protective layer 300 may diffuse light emitted from the light emitting device 200, and in addition, the silicone protective layer 300 may protect the light emitting device. It should be noted that, in order to ensure that the intensity uniformity of the light diffused by the silicone protective layer 300 is better and the flatness of other film layers on the silicone protective layer 300 is better, the light-emitting side of the silicone protective layer 300 should have a flat surface. Therefore, the specific manner of disposing the silica gel protective layer 300 above the direct-type backlight 001 may be attaching a silica gel protective layer film, and then thermally curing the silica gel protective layer film to form the silica gel protective layer 300, so that the silica gel protective layer 300 tightly wraps the light emitting device 200 and has a smooth light emitting surface.

In addition, the light conductive film 002 of the direct type backlight module can also include other structures.

As shown in fig. 3, the light conductive film 002 may further include a diffusion plate 400, and the diffusion plate 400 may be disposed on a light-emitting surface side of the silica gel protective layer for further diffusing light.

As shown in fig. 3, the light-conductive film layer 002 may further include a quantum dot protective layer 500. The light emitting device 200 may be an LED chip emitting white light, or may be an LED chip emitting light of another color. When the light emitting device 200 employs an LED chip emitting non-white light, the light conductive film layer 002 typically further includes a quantum dot conversion layer 500 to convert light emitted from the light emitting device 200 into white light. For example, the light emitting device 200 may be a blue LED chip with high light emitting efficiency and excellent light emitting intensity, and the light conductive film layer 002 may include a blue quantum dot conversion layer to convert blue light emitted from the blue LED chip into white light. Generally, the quantum dot conversion layer 500 is disposed on the light emitting surface side of the diffusion sheet 400 or the silicone protective layer 300.

As shown in fig. 3, the light-conducting film layer 002 may further include a brightness enhancement film 600, and the prisms on the brightness enhancement film 600 converge the light, so that the light emitted from the direct-type backlight module is emitted substantially vertically, and the light-emitting intensity is increased.

Further, light conduction rete 002 can also include quantum dot thickening membrane 700, and the colour gamut of the light through quantum dot thickening membrane 700 is wider, consequently sets up quantum dot thickening membrane 700 in straight following formula backlight unit and can make the backlight that it provided possess wider colour gamut. In addition, the brightness enhancement film 600 and the quantum dot thickening film 700 can be disposed on a side close to the light exit surface of the direct-type backlight module, and the positions of the brightness enhancement film and the quantum dot thickening film can be interchanged.

Fig. 4 is a partial top view of a circuit board of a direct type backlight according to an embodiment of the present disclosure, fig. 5 (a) is a cross-sectional view along a MM 'direction of the circuit board shown in fig. 4, and fig. 5 (b) is a cross-sectional view along a NN' direction of the circuit board shown in fig. 4.

Referring to fig. 4, 5 (a) and 5 (b), the circuit board 100 includes a first solder mask layer 10 and a pad array layer including N pads 20. In addition, the circuit board 100 may further include a copper clad substrate 30 for carrying the pads 20, a circuit 50 disposed on the copper clad substrate 30, and a second solder mask layer 60. As shown in fig. 5 (a) and 5 (b), the bonding pad 20 may be disposed on one side of the copper-clad substrate 30, and the circuit 50 may be disposed on the other side of the copper-clad substrate 30. The line 50 may be connected to the pad 20 through a via for supplying a signal to the pad 20. The bonding pads 20 and the circuit 50 are arranged on different sides of the copper-clad plate base material 30, so that possibility is provided for arranging the bonding pads 20 with high density, meanwhile, the area of the bonding pads 20 can be relatively increased, and the problem of tin printing deviation is reduced. A second solder resist layer 60 covers the wiring 50 for protecting the wiring 50.

The first solder resist layer 10 is a solder resist layer having a light reflection effect. Since the direct type backlight module is used for providing the backlight generated by the direct type backlight module to the display panel positioned on the light-emitting side of the direct type backlight module, but the light emitted by the light-emitting device 200 can be emitted in all directions, the first solder mask layer 10 with the light reflection effect can reflect the light emitted by the light-emitting device 200 to the surface of the direct type backlight module and then emit the light from the light-emitting side of the direct type backlight module, so that the brightness of the backlight generated by the direct type backlight module is improved. The first solder resist layer 10 may specifically be a white solder resist layer, i.e. a solder resist layer that is white in color and that can reflect light. Of course, the first solder resist layer 10 may be a solder resist layer having a light reflection effect of another color. The first solder resist layer 10 also mainly functions to resist solder and protect the electronic structure covered by it from oxidation and damage. Specifically, the first solder resist layer 10 may be white ink having photosensitivity.

In addition, the first solder mask layer 10 includes N windows 101 corresponding to the pads 20 one to one, and the windows 101 are openings on the first solder mask layer 10 for exposing the pads 20, so that the pads 20 can be bonded to the light emitting device 200. At least part of the pad 20 is disposed in the corresponding window 101, that is, the first solder mask layer 10 surrounds at least part of the pad 20, and the upper surface of the pad 20 facing the side of the light exit surface of the direct type backlight source 001 is flush with the upper surface of the first solder mask layer 10. As shown in fig. 5 (a) and 5 (b), the lower surface of the pad 20 away from the backlight light-emitting surface may also be flush with the lower surface of the first solder mask layer 10 and be disposed on the surface of the copper-clad substrate 30, that is, the pad 20 may be completely disposed in the open window 101 of the first solder mask layer 10, and the upper and lower surfaces of the pad 20 and the first solder mask layer 10 are flush with each other. In this manner, the bonding pad 20 is exposed, facilitating the subsequent bonding of the bonding pad 20 with the light emitting device 200. Specifically, since the upper surface of the pad 20 is flush with the upper surface of the first solder resist layer 10, uniformity of solder is easily controlled in the process of bonding the pad 20 and the light emitting device 200 using the solder, thereby effectively preventing short circuit between different pads 20 through excessive solder.

Further, the area of the upper surface of the pad 20 is equal to the area of the upper surface of the corresponding window 101, and since the pad 20 is disposed in the window 101 and the pad 20 is flush with the upper surface of the first solder resist layer 10, the pad 20 and the corresponding window 101 are closely bonded substantially without a gap. That is to say, first solder mask 10 basically fills up the region between the pad 20 completely, then the width of first solder mask 10 between the adjacent pad 20 is enough big in order obviously to reduce the short circuit risk to thereby need not to choose for use the white substrate copper-clad plate that possesses the light reflection effect for use because the substrate of copper-clad plate also can not expose, the cost is reduced. In addition, the pad 20 is flush with the upper surface of the first solder mask layer 10, and the first solder mask layer 10 tightly surrounds the pad 20, so that no impurities remain between the pad 20 and the first solder mask layer 10, and the pad 20 is firm and has stable performance.

The first solder mask layer 10 included in the direct type backlight provided in the embodiment of the present application may specifically be at least one of photosensitive white ink, white solder mask dry film, and white prepreg. The first solder mask layer 10 can serve as a solder mask on one hand, and on the other hand, has high reflectivity so as to improve the brightness of the backlight source. The first solder resist layer 10 is preferably made of a material having a photosensitive property.

In order to ensure that the direct type backlight module has high reflectivity and brightness, in the direct type backlight provided in the embodiment of the present application, the thickness of the first solder mask layer 10 is greater than or equal to 30 μm, and correspondingly, the height of the pad 20 is also greater than or equal to 30 μm, for example, the heights of the first solder mask layer and the pad are both about 40 μm.

Fig. 6 is an exploded view of the display device in an embodiment of the present application, fig. 7 is a partial cross-sectional view of the display device shown in fig. 6, as shown in fig. 6 and 7, the display device includes the direct-type backlight module 0001 and the display panel 0002 provided in the embodiments, wherein the display panel 0002 is disposed on a light emitting side of the direct-type backlight module 0001, and light generated by the direct-type backlight module 0001 reaches the display panel 0002 to provide backlight for the display panel 0002. In addition, the display device may further include a back plate 0003, a front frame 0004 and a middle frame 0005, wherein the back plate 0003 is used for carrying the direct type backlight module 0001, and the back plate 0002, the front frame 0004 and the middle frame 0005 are used for encapsulating the display panel 0002 and the direct type backlight module 0001.

The direct type backlight module 0001 includes a circuit board 100 and a light emitting device 200, specifically, the light emitting device 200 is disposed on a side of the circuit board 100 facing the display panel 300, and the circuit board 10 controls the light emitting device 200 to emit light so as to provide backlight for the display panel 300.

As shown in fig. 7, the direct-type backlight module 0001 generates planar light, and the direct-type backlight module 0001 is disposed directly below the display panel 0002. The area of the direct type backlight module 0001 may be smaller than that of the display panel 0002, for example, as shown in fig. 7, the left side of the direct type backlight module 0001 is retracted with respect to the display panel 0002. Since the display panel 0002 includes the display area AA and the non-display area BB, the front frame 0002 can block the non-display area BB and the display area AA is used for light-emitting display during the process of packaging the display device. Therefore, the final light-emitting surface of the direct-type backlight module 0001 should substantially coincide with the vertical projection of the display area AA of the display panel in the thickness direction of the display device. In addition, since light emitted from the direct type backlight source 001 exits from the direct type backlight module 0001 after going through the diffusion, conversion, enhancement, and other processes of the light conduction film layer 002, and reaches the display panel 0002 to provide backlight for the display panel 0002, the area of the direct type backlight source 001 may be slightly smaller than the area of the display area AA of the display panel 0002, as long as it is ensured that the area of the final light exit surface of the direct type backlight module 0001 is substantially the same as the area of the display area AA. Of course, the area of the direct backlight 001 may be the same as the area of the substrate of the display area AA.

The circuit board in the direct type backlight source in the display device provided by the embodiment of the application includes a first solder mask layer 10 and a pad array layer, and the pad array layer includes a plurality of pads 20 bound with the light emitting devices 200. The first solder mask layer 10 includes a plurality of windows 101 disposed in one-to-one correspondence with the pads 20, and at least a portion of the pads 20 is disposed in the corresponding windows 101, and an upper surface of the pads 20 is flush with an upper surface of the first solder mask layer 10. Because there is no height difference between the pad 20 and the first solder mask layer 20, the pad 20 and the light emitting device 200 can have a good binding effect, and the entire surface of the direct type backlight source has uniformity, and further the backlight uniformity provided by the direct type backlight module is better, so that the display of the display device has uniformity. In addition, the upper surface of the pad 20 is flush with the upper surface of the first solder mask layer 10, and the thickness of the first solder mask layer 10 is not limited by the limitation that the height difference between the pad and the first solder mask layer 10 is not too large, so that the thickness of the first solder mask layer 10 can be set as thick as possible to improve the brightness of the direct type backlight source, thereby improving the brightness of the display device, for example, the thickness of the first solder mask layer 10 can be set to be more than 30 μm, and specifically, can be 40 μm.

In one embodiment of the present application, the display panel 300 may be a liquid crystal display panel, and since the liquid crystal display panel emits light passively, the direct-type backlight provides light required for display for the display panel.

In an embodiment of the present application, the display panel 300 may also be an organic light emitting display panel, and although the organic light emitting display panel is active light emitting, in order to improve color purity of a display device including the organic light emitting display panel, the direct type backlight provides different colors of light for the display device, and the LED chips 200 of the direct type backlight may correspond to pixels of the display panel 300 one to one. Specifically, the light emitting color of the LED chip 200 is the same as the light emitting color of the corresponding pixel in the display panel 300, so as to improve the color purity displayed by the display device.

Fig. 8 is a schematic view of a display device according to an embodiment of the present disclosure, and according to different application scenarios, as shown in fig. 8, the display device according to the embodiment of the present disclosure may be a television, and in addition, the display device according to the embodiment of the present disclosure may also be a computer, a tablet, a mobile phone, or the like. It should be noted that, in different application scenarios, the sizes of the display devices are different, and the viewing distances are different, so the sizes and densities of the light emitting devices 200 in the direct type backlight 001 are also different.

When the display device provided by the embodiment of the application is a television, the size of the light-emitting device 200 can be relatively large and the process is relatively simple because the distance for watching by human eyes is relatively long; the density of the light emitting device 200 can also be small, reducing power consumption and saving cost.

The backlight module used by the display device provided by the embodiment of the application is a direct type backlight module, and the problem of soldering short circuit is reduced because no height difference exists between a welding pad and a first solder mask in the direct type backlight module; meanwhile, the grinding process is adopted to expose the bonding pad, so that the adverse effect of the etching process is avoided; and the grinding process is carried out after the film layer where the first solder mask layer is arranged, so that the height of the first solder mask layer is adjustable. In addition, when the display device provided by the embodiment of the application is a television, the display device is easy to implement and has relatively low power consumption.

An embodiment of the present application further provides a method for manufacturing a circuit board, as shown in fig. 9, fig. 9 is a schematic diagram of a method for manufacturing a circuit board according to an embodiment of the present application, and is used for manufacturing the circuit board according to the embodiment.

The manufacturing method of the circuit board comprises the following steps:

s1: and electroplating a selective plating metal layer 201'. The step can be carried out after copper reduction treatment is carried out on the copper foil 202' on the copper-clad plate base material 30, drilling is carried out on the copper-clad plate, and chemical copper deposition is carried out, wherein the chemical copper deposition can enable the drilled hole wall to be metalized to form a copper film, the copper film can also be used as base copper of the electroplating selective plating metal layer 201', and at least part of the selective plating metal layer 201' covers the copper film formed on the hole wall through the chemical copper deposition, so that the part of the copper film is protected from subsequent processing.

S2: and patterning the selective plating metal layer 201' to form a selective plating metal block 201. The step can be specifically completed through a patterned dry film, that is, the dry film 40 is arranged on the selective plating metal layer 201', then the dry film 40 is patterned through exposure, development and etching, the dry film 40 at the position of the bonding pad 20 is reserved, and finally, the part of the selective plating metal layer 201' which is not protected by the dry film 40 is etched, and the part of the selective plating metal layer 201' which is protected by the dry film 40 is reserved, so that the selective plating metal block 201 is formed. Note that the copper foil 202' under the selective plating metal block 201 is also patterned in this step to form the bottom copper 202 of the pad 20.

S3: the primary pad 20' is formed by electroplating using the selectively plated metal block 201 as base copper. Specifically, the dry film 40 is disposed at a position except for the selective plating metal block 201, and electroplating is performed to form a primary copper pillar 203' by using the selective plating metal block 201 as base copper, and the primary copper pillar 203' is used as a part ' of the primary bonding pad. It should be noted that the dry film 40 in this step serves to protect the area outside the primary pad 20' from being plated with copper, and the dry film 40 needs to be removed after this step. In addition, electroless copper plating, which is advantageous for forming the primary copper pillar 203' by electrolytic copper plating, may be performed before the dry film 40 is disposed in this step. Since the entire surface is chemically deposited with copper, the copper film formed by chemically depositing copper in the region other than the primary pad 20' can be removed by flash etching after this step.

S4: a primary first solder resist layer 10' is formed, wherein the primary first solder resist layer 10' includes first portions disposed between the primary pads 20' and second portions of the upper surface of the primary pads 20', the upper surface of the first portions being flush with or lower than the upper surface of the primary pads 20'. Since the reflectance of the direct type backlight is related to the thickness of the first solder resist layer, the thickness of the primary first solder resist layer 10 'may be selected as desired, for example, when the first solder resist layer has a thickness exceeding 40 μm and the reflectance of the backlight reaches substantially the peak, the primary first solder resist layer 10' may be formed to have a thickness of 40 μm in order to provide the backlight with the highest reflectance. It should be noted that a glue removal process may also be performed before the formation of the primary first solder resist layer.

Also, preferably, the upper surface of the primary pad 20 'is higher than the upper surface of the first portion in the primary first solder resist layer 10', and as shown in fig. 6, the difference in height between the upper surface of the primary pad 20 'and the first portion in the primary first solder resist layer 10' is h. At this time, the lowest height of the first portion in the primary first solder resist layer 10 'may be set to a predetermined height of the first solder resist layer 10, and the upper surfaces of the primary copper pillar 203' and the primary solder resist layer 10 'may be ground to be flush with the lowest upper surface of the first portion in the primary first solder resist layer 10' with the lowest height as a reference in a subsequent grinding process.

In another implementation, the lowest height of the first portion in the primary first solder mask layer 10' may be set to be higher than the predetermined height of the first solder mask layer 10, the entire primary first solder mask layer 10' is ground to a predetermined thickness in a subsequent grinding process, and the primary copper pillar 203' is ground to make the first solder mask layer 10 flush with the upper surface of the pad 20. At this time, the first portion of the primary first solder resist layer 10' may or may not be flush with the upper surface of the second portion, and this is not particularly limited.

S5: the first solder mask layer 10 and the pad 20 are formed by grinding the area where the primary pad 20' is located, and the upper surface of the pad 20 is flush with the upper surface of the first solder mask layer 10. Wherein grinding the area where the primary pad 20' is located comprises grinding away a second portion of the primary first solder mask layer 10' above the primary pad 20' to form the first solder mask layer 10. In addition, if the upper surface of the primary pad 20' is higher than the upper surface of the first portion of the primary first solder resist layer 10', then grinding the area where the primary pad 20' is located includes grinding away the second portion of the primary first solder resist layer 10' above the primary pad 20', and then grinding away the portion of the primary pad 20' that is higher than the first portion of the primary first solder resist layer 10' to form the pad 20 so that the upper surface of the pad 20 is flush with the upper surface of the first solder resist layer 10, as shown in fig. 6, by this step, the second portion of the primary first solder resist layer 10' above the primary pad 20' is ground away, and a portion of the primary copper pillar 203' in the primary pad 20' is ground away to form the copper pillar 203, that is the pad 20 includes the copper pillar 203 and the upper surface of the pad 20 is flush with the upper surface of the first solder resist layer 10.

The primary copper pillar 203' is formed by electroplating in step S3 and is not processed by the polishing process in step S5, and the height required by the polishing of the primary copper pillar 203' becomes the copper pillar 203, and it should be noted that the height of the primary copper pillar 203' may be the same as or different from the height of the copper pillar 203 in the pad 20 of the circuit board 100 in the direct-type backlight provided in the embodiment of the present application. When the primary copper pillar 203' and the copper pillar 203 have the same height, the grinding means that the primary first solder resist layer 10' is ground so that the upper surface thereof is flush with the upper surface of the pad 20, and impurities on the upper surface of the primary copper pillar 203' are ground away to form the copper pillar 203; when the height of the primary copper pillar 203' is different from that of the copper pillar, the grinding means is to grind the primary first solder resist layer 10' and expose the primary copper pillar 203', and continue to grind the primary first solder resist layer 10' and the primary copper pillar 203' to a predetermined height and make the upper surfaces of the two flush to form the first solder resist layer 10 and the copper pillar 203.

The primary pad 20' corresponds to the primary copper pillar 203', the primary pad 20' corresponds to the primary copper pillar 203' before being polished, and the pad 20 corresponds to the copper pillar 203 formed after polishing the primary copper pillar 203'.

The first solder resist layer 10 'covers the entire surface of the copper clad plate with respect to the first solder resist layer 10, and a second portion of the first solder resist layer 10' in the region of the pad 20 is ground away, and a first portion in the other position is ground to a predetermined height, thereby forming the first solder resist layer 10.

In the manufacturing method of the circuit board provided by the embodiment of the application, the upper surface of the welding pad containing the copper column is flush with the first solder mask layer by controlling the height of the copper column formed by electroplating, so that no height difference exists between the welding pad and the first solder mask layer, and the risk of short circuit of soldering tin is reduced. In addition, the bonding pad is exposed through a grinding process, so that the problems of over-etching, incomplete windowing, undercut and the like caused in an etching process in the prior art are solved. And because the upper surface of the primary pad is higher than the upper surface of the first part in the first solder mask, the height of the first solder mask can be flexibly selected according to the requirement on the reflectivity of the backlight source, and the primary pad is ground to be flush with the upper surface of the first part of the first solder mask through a subsequent grinding process, so that the ultrahigh reflectivity of the backlight plate can be realized, and when the circuit board prepared by the embodiment of the application is applied to a direct type backlight source, the reflectivity of the backlight source is more than 90 percent and even can reach 95 percent. There is the grinding technology after forming elementary first soldermask, therefore the foreign matter on the pad can be ground away to can promote subsequent bonding yield.

The manufacturing method of the circuit board further comprises the steps of conventional surface treatment, appearance detection, electrical detection, appearance inspection, packaging and the like.

In one embodiment of the present application, forming the primary first soldermask layer 10' comprises first screen printing or spraying or applying a photosensitive white ink and then thermally curing the photosensitive white ink.

In one embodiment of the present application, forming the primary first solder resist layer 10' includes first attaching a white dry film solder resist by a vacuum laminator and then thermally curing the white dry film solder resist.

In one embodiment of the present application, forming the primary first solder resist layer 10' includes first attaching a white prepreg, and then thermally curing the white prepreg.

The first solder mask that adopts in this application possess thermosetting performance can, need not like the solder mask among the prior art need possess the light sense performance, consequently the optional scope of the first solder mask that adopts in this application is wide, and can reduce cost.

The above description is only an embodiment of the present application, and any person skilled in the art can easily conceive of changes or substitutions within the technical scope of the present disclosure, and all of them should be covered by the protection scope of the present application. The protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A direct type backlight module is characterized by comprising: the direct type backlight module comprises a direct type backlight source and a light conduction film layer, wherein the projection of the light conduction film layer along the thickness direction of the direct type backlight module covers the projection of the direct type backlight source along the thickness direction of the direct type backlight module;

the direct type backlight source comprises N light-emitting devices and a circuit board, wherein the circuit board comprises a first solder mask layer and a pad array layer; wherein the pad array layer comprises N pads, and the light emitting device is bonded with the pads; n is a positive integer greater than or equal to 1;

the first solder mask layer comprises N windows, and at least part of the welding pad is arranged in the corresponding window; the upper surface of the welding pad is flush with the upper surface of the first solder mask layer through grinding;

the circuit board also comprises a copper-clad plate base material and a circuit, wherein the bonding pad and the circuit are arranged on different sides of the copper-clad plate base material;

the first solder mask layer is a solder mask layer with a light reflection effect, and the thickness of the first solder mask layer is greater than or equal to 30 μm and less than or equal to 40 μm.

2. The direct type backlight module according to claim 1, wherein the first solder mask layer is at least one of a photosensitive white ink, a white dry solder mask film, and a white prepreg.

3. The direct type backlight module according to claim 1, wherein the height of the pads is equal to or greater than 30 μm.

4. The direct type backlight module according to claim 1, wherein the area of the upper surface of the bonding pad is equal to the area of the corresponding upper surface of the opening window.

5. The direct type backlight module according to claim 1, wherein the light emitting devices are blue LED chips.

6. The direct type backlight module according to claim 5, wherein the light conductive film layer comprises a quantum dot conversion layer.

7. The direct type backlight module according to claim 1, wherein the light conductive film layer comprises a silicone protective layer covering the light emitting devices.

8. A display device comprising the direct type backlight module as claimed in any one of claims 1 to 7 and a display panel, wherein the display panel is disposed on the light exit side of the direct type backlight module.

9. The display device according to claim 8, wherein the display panel is one of a liquid crystal display panel and an organic light emitting display panel.

10. The display device according to claim 8, wherein the display panel includes a display region and a non-display region; and the vertical projection of the light-emitting surface of the direct type backlight module and the display area of the display panel in the thickness direction of the display device is superposed.

11. A method for manufacturing a circuit board, wherein the method is used for manufacturing a circuit board included in the direct type backlight module according to any one of claims 1 to 7.

12. The method of claim 11, wherein the method comprises:

electroplating a selective plating metal layer;

patterning the selective plating metal layer to form a selective plating metal block;

electroplating by taking the selective plating metal block as base copper to form a primary bonding pad;

forming a primary first solder mask layer comprising a first portion disposed between primary pads and a second portion disposed on an upper surface of the primary pads, the upper surface of the first portion being flush with or lower than the upper surface of the primary pads;

and grinding the area where the primary welding pad is located to form a first welding resistance layer and the welding pad, wherein the upper surface of the welding pad is flush with the upper surface of the first welding resistance layer.

13. The method of claim 12, wherein the forming a primary first solder mask layer comprises:

screen printing photosensitive white ink or coating the photosensitive white ink;

thermally curing the photosensitive white ink.

14. The method according to claim 12, wherein said forming a first solder resist layer comprises,

attaching a white solder resist dry film;

and thermally curing the white solder resist dry film.

15. The method according to claim 12, wherein said forming a first solder resist layer comprises,

attaching a white prepreg;

and thermally curing the white prepreg.