41 on the circuit board 3. A second opening hole 56 corresponding to the light-emitting unit group 4 is formed on the foamed reflection layer 53, and the light-emitting unit group 4 is located within the second opening hole 56 corresponding thereto. A sidewall of the second opening hole 56 can form the reflection wall 52. In some embodiments, the foamed reflection layer 53 can include a foamed material, in which multiple densely distributed bubbles are formed. The finer and denser the bubbles are, the higher the reflectivity of the foamed reflection layer is. The base material of the foamed reflection layer can be polyethylene terephthalate, and the foamed reflection layer can further include a master particle encapsulated in the base material. During the formation process of the foamed reflection layer, bubbles can be formed at the position where the master particle is located by pulling the base material. In some embodiments, the master particle can be materials such as titanium oxide, barium sulfate, calcium carbonate, etc. The foamed reflection layer can achieve a reflectivity of 98%.

In some embodiments, as shown in FIG. 8, the microstructure film layer can further include a first wavelength conversion layer 54, which can be configured to convert a wavelength of the light passing through it, and the first wavelength conversion layer 54 can conformally cover the sidewall of the second opening hole 56. The first wavelength conversion layer 54 can be a quantum dot layer or a fluorescence layer. The first wavelength conversion layer 54 can fine tune the color of the output light of the backlight module. For example, when the color of the output light of the backlight module is blue, the first wavelength conversion layer 54 can be configured to convert the blue light into the red light and the green light. For example, when the color of the output light of the backlight module is purple, the first wavelength conversion layer 54 can be configured to convert the blue light into the green light. As shown in FIG. 8, the first wavelength conversion layer 54 can also conformally cover an entire side of the foamed reflection layer 53 away from the circuit board 3.

In some embodiments, as shown in FIG. 8, the microstructure film layer can further include a transparent protection layer 55, which can conformally cover a side of the first wavelength conversion layer 54 away from the foamed reflection layer 53. The transparent protection layer 55 can be made of polyethylene terephthalate material. The transparent protection layer 55 can be used to protect the first wavelength conversion layer 54.

As shown by the arrow in FIG. 8, the light emitted by the light-emitting unit 41 can follow two kinds of transmission paths. Part of the light emitted by the light-emitting unit 41 can directly pass through the second wavelength conversion layer 6, to form white light emitted from the second wavelength conversion layer 6. Part of the light emitted by the light-emitting unit 41 can pass through the transparent protection layer 55 and the first wavelength conversion layer 54, be reflected on the sidewall of the second opening hole 56, and then incident into the second wavelength conversion layer 6 through the first wavelength conversion layer 54 and the transparent protection layer 55, to emit from the second wavelength conversion layer 6.

In some embodiments, as shown in FIG. 8, the light-emitting unit 41 can further include transparent glue 412, which forms an encapsulation on a side of the light-emitting chip 411 away from the circuit board 3, for fixing the light-emitting chip 411 onto the circuit board 3. The transparent glue 412 can provide physical protection for the light-emitting chip 411.

In some embodiments, as shown in FIG. 8, the second opening hole 56 can include a gradually-varied extension section 561, and an area of the opening hole on a side where the gradually-varied extension section 561 is away from the circuit board 3 is greater than an area of the opening hole on a side where the gradually-varied extension section 561 is close to the circuit board 3. That is, the area of the opening hole for the gradually-varied extension section 561 gradually increases from a side of the circuit board 3 to a side away from the circuit board 3. Such arrangement can enable the microstructure film layer 5 to have a larger light outlet, thereby reducing the risk of forming dark regions in non-light outlet regions. As shown in FIG. 8, a sidewall of the gradually-varied extension section 561 can form a curved surface, and a tangent D at any position on the sidewall of the gradually-varied extension section 561 can be located on a side of the sidewall of the gradually-varied extension section 561 facing towards the circuit board 3. Such arrangement can enable a slope of the sidewall of the gradually-varied extension section 561 at a position close to the light-emitting unit 41, in a direction parallel to the circuit board 3, to be smaller than a slope at a position away from the light-emitting unit 41. Therefore, in the direction parallel to the circuit board 3, high-intensity light at the position close to the light-emitting unit 41 can be reflected through the sidewall with a smaller slope to a position away from the light-emitting unit 41, and low-intensity light at the position away from the light-emitting unit 41 can be reflected through the sidewall with a larger slope, to emit out in a direction having a smaller angle with an extension direction of the first opening hole 51. In some embodiments, the extension direction of the first opening hole 51 can be a direction perpendicular to the circuit board 3. Such arrangement, on the one hand, can ensure that the light emitted by the light-emitting unit 41 mixes evenly within the first opening hole 51, thereby improving the uniformity of the light intensity at the outlet of the first opening hole 51, and on the other hand, such arrangement can improve the collimation of the light emitted by the light-emitting unit.

It should be noted that in some embodiments, since the first wavelength conversion layer 54 conformally covers on the sidewall of the second opening hole 56, and the transparent protection layer 55 conformally covers on a side of the first wavelength conversion layer 54 away from the foamed reflection layer 53, the first opening hole 51 and the second opening hole 56 can have the same shape.

In some embodiments, the foamed reflection layer 53 can be molded by a mold. When manufacturing the backlight module, the molded foamed reflection layer 53 can be assembled on a circuit board provided with a light-emitting unit.

As shown in FIGS. 6 and 8, the first opening hole 51 includes a first opening 511 on a side where the first opening hole is away from the circuit board 3 and a second opening 512 on a side where the first opening hole is close to the circuit board 3. An orthographic projection of the second opening 512 on circuit board 3 has a minimum size S3 in a direction passing through the opening's centroid, and an orthographic projection of the light-emitting unit 41 on the circuit board has a maximum size S4 in the direction passing through the opening's centroid, where S3 is greater than S4. As shown in FIG. 5, if the orthographic projection of the light-emitting unit 41 on the circuit board is a rectangle, the maximum size of the orthographic projection of the light-emitting unit 41 on the circuit board in the direction passing through the opening's centroid is a length of a diagonal of the orthographic projection of the light-emitting unit 41 on the circuit board. If the orthographic projection of the second opening 512 on the circuit board is a circle, the minimum size of the orthographic projection of the second opening 512 on the circuit board 3 in the direction passing through the opening's centroid is a diameter of the circle. In some embodiments, S3 is set slightly larger than S4, so that a certain assembly error can be reserved when assembling the foamed reflection layer 53, which facilitates the assembly of the foamed reflection layer 53. In some embodiments, S3-S4 can be 0.2 mm-0.6 mm, for example, S3-S4 can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, etc.

It should be understood that in some embodiments, the first opening 511 can also be any one of polygonal, elliptical, or irregular shapes, and the second opening 512 can also be any one of polygonal, elliptical, or irregular shapes.

In some embodiments, as shown in FIGS. 6 and 8, the gradually-varied extension section 561 can include a third opening 5613 on a side where the gradually-varied extension section is away from the circuit board 3 and a fourth opening 5614 on a side where the gradually-varied extension section is close to the circuit board 3. A distance between the third opening 5613 and the fourth opening 5614 in a direction perpendicular to the circuit board is S2. A minimum distance between an edge of an orthographic projection of the third opening 5613 on the circuit board and an edge of an orthographic projection of the fourth opening 5614 on the circuit board in a first horizontal direction is S1. In some embodiments, the first horizontal direction is a direction parallel to the circuit board and passing through a centroid of the orthographic projection of the fourth opening 5614 on the circuit board. In some embodiments, a centroid of the orthographic projection of the third opening 5613 on the circuit board and the centroid of the orthographic projection of the fourth opening 5614 on the circuit board can coincide with each other, and the orthographic projections of the third opening 5613 and the fourth opening 5614 on the circuit board are both circles. Correspondingly, the minimum distance between the edge of the orthographic projection of the third opening 5613 on the circuit board and the edge of the orthographic projection of the fourth opening 5614 on the circuit board in the first horizontal direction is a width of a ring formed by the edge of the orthographic projection of the third opening 5613 on the circuit board and the edge of the orthographic projection of the fourth opening 5614 on the circuit board. In some embodiments, S1/S2 can be 1-4, for example, S1/S2 can be 1, 2, 3, 4, etc. In some embodiments, S2 can be 0.15 mm-0.3 mm, for example, S2 can be 0.15 mm, 0.18 mm, 0.2 mm, 0.25 mm, 0.3 mm.

It should be understood that in some embodiments, the third opening 5613 can also be any one of polygonal, elliptical, or irregular shapes, and the fourth opening 5614 can also be any one of polygonal, elliptical, or irregular shapes. For example, the orthographic projections of the third opening 5613 and the fourth opening 5614 on the circuit board can be a concentric square, with orthographic projections of one side edge of the third opening 5613 and one side edge of the fourth opening 5614 on the circuit board being able to be parallel to each other. Correspondingly, the minimum distance between the edge of the orthographic projection of the third opening 5613 on the circuit board and the edge of the orthographic projection of the fourth opening 5614 on the circuit board in the first horizontal direction is a distance between orthographic projections of the above parallel side edges on the substrate.

In some embodiments, a thickness of the circuit board 3 is relatively thin. For example, the thickness of the circuit board 3 can be 0.12 mm, and a material of the circuit board 3 is relatively soft, which can easily lead to an uneven surface of the circuit board. The unevenness of the surface of the circuit board can affect the flatness of the microstructure film layer 5, which in turn affects the display effect. As shown in FIG. 9, a schematic diagram of a structure of an example backlight module according to embodiments of the present disclosure is provided. A groove 7 is further formed on a side of the foamed reflection layer 53 facing towards the circuit board 3. An area of a groove opening where the groove 7 is close to the circuit board 3 is greater than an area of a groove opening where the groove 7 is away from a side of the circuit board. That is, the groove opening of the groove 7 gradually decreases from a side of the circuit board 3 to a side away from the circuit board 3. An orthographic projection of a sidewall 71 of the groove 7 on the circuit board 3 intersects with an orthographic projection of a sidewall of the gradually-varied extension section 561 on the circuit board. Such arrangement can reduce a contact area between the microstructure film layer 5 and circuit board 3 while ensuring good support for the microstructure film layer 5, thereby avoiding the unevenness of the microstructure film layer 5 caused by the unevenness of the circuit board 3.

As shown in FIG. 9, the sidewall 71 of the groove 7 can form a curved surface, and a tangent E at any position on the sidewall 71 of the groove 7 can be located on a side of the sidewall 71 of the groove 7 facing towards the circuit board 3. The foamed reflection layer 53 of this structure has a certain elastic deformation ability, which can reduce the risk of damage to the foamed reflection layer. In addition, the groove 7 and the second opening hole 56 are arranged in the matching manner, which can enable the foamed reflection layer 53 to form a film layer with a relatively uniform thickness. In some embodiments, a maximum thickness of the foamed reflection layer between the sidewall 71 of the groove and the sidewall of the gradually-varied extension section is X, and a minimum thickness of the foamed reflection layer between the sidewall 71 of the groove and the sidewall of the gradually-varied extension section is Y, where (X−Y)/Y can be greater than or equal to 0 and less than or equal to 1.8. For example, (X−Y)/Y can be 0, 0.5, 1, 1.5, 1.8, etc.

As shown in FIGS. 10 and 11, FIG. 10 is a schematic diagram of a structure of an example backlight module according to embodiments of the present disclosure, and FIG. 11