, it ensures that all light emitted from the light-emitting diodes 220 be directed toward the side-lit surface 105 (i.e., all light travels within a vertical projection area of the side-lit surface 105 toward the light-emitting diodes 220). This prevents light from traveling along a path outside the vertical projection area of the side-lit surface 105 of the light guide plate 100 and thus failing to enter the light guide plate 100 from the side-lit surface 105. Furthermore, such a design can completely avoid the problem of light outside this vertical projection area becoming stray light (noise) that may disturb the light guiding of the light guide plate 100.

On the other hand, the composite light path adjustment layer 300 comprises a reflective layer 310 and a light-shielding layer 320. The reflective layer 310 covers the light-emitting diodes 220 and a portion of the top surface 101 of the light guide plate 100. The light-shielding layer 320 is disposed and stacked on the reflective layer 310 and relatively away from the light-emitting diodes 220 and the light guide plate 100 compared to the reflective layer 310. In other words, the light-shielding layer 320 is stacked on a surface 311 of the reflective layer 310 that is facing away from the light-emitting diodes 220 and the light guide plate 100. More specifically, the reflective layer 310 and the light-shielding layer 320 both extend from the top surface 221 of the light-emitting diodes 220 to the top surface 101 of the light guide plate 100 and completely cover the space S between the light-emitting diodes 220 and the light guide plate 100. In addition, the space S is located between the reflective layer 310 and the opaque reflective surface 211 of the flexible circuit board 210 along the direction vertical to the top surface 101 of the light guide plate 100. Therefore, light traveling within the space S is more concentrated as it enters the light guide plate 100 from the side-lit surface 105 through the reflection from the reflective layer 310 and the opaque reflective surface 211 of the flexible circuit board 210, thereby resolving the problem of the potential reduction in light intake that may occur due to the thinning of the light guide plate 100.

Furthermore, the light-shielding layer 320 is disposed relatively closer to the user compared to the reflectively layer 310 and is used for absorbing or shielding various outward-emitting light in the peripheral area PA, thereby preventing any impact on the user's visual experience. For example, the light-shielding layer 320 can absorb or shield light that directly penetrates through the reflective layer 310.

In some embodiments, when viewed from top (i.e., from the view in FIG. 1A), the reflective layer 310 and the light-shielding layer 320 can completely overlap. In other words, the vertical projection of the reflective layer 310 and the vertical projection of the light-shielding layer 320 toward the flexible circuit board 210 completely overlap, thereby achieving a better light-shielding effect. In some embodiments, an inner sidewall 303 of the composite light path adjustment layer 300 is relatively closer to the visible area VA compared to the inner sidewall 213 of the flexible circuit board 210. In other words, the inner sidewall 303 of the composite light path adjustment layer 300 is relatively away from the light-emitting diodes 220 compared to the inner sidewall 213 of the flexible circuit board 210. This ensures that the light can still be reflected and shielded by the composite light path adjustment layer 300 after being reflected by the opaque reflective surface 211 of the flexible circuit board 210, thereby achieving the effect of stabilizing the light.

In some embodiments, the light-shielding layer 320 can be formed on the reflective layer 310 through any suitable method, wherein the reflective layer 310 can be an ink coating layer, a chemical plating layer, or an electroplated layer, and is preferably white to increase the light reflectivity. The material of the light-shielding layer 320 can be polyimide, tape, etc., and preferably in dark color (such as black) to achieve a better effect of light absorption or light shielding. More specifically, the formation of the composite light path adjustment layer 300 can involve using the light-shielding layer 320 as a substrate, with white ink coated on one surface of the substrate to serve as the reflective layer 310. In some other embodiments, the composite light path adjustment layer 300 can be a substrate with white ink coated on one surface to form a reflective layer 310 and black ink coated on the opposite surface to form a light-shielding layer 320. In some embodiments, the reflective layer 310 is attached to the light guide plate 100 and the light-emitting diodes 220 by an optical adhesive. In some other embodiments, the reflective layer 310 itself can be an adhesive, allowing it to be directly attached to the light guide plate 100 and the light-emitting diodes 220. Overall, a thickness H2 of the composite light path adjustment layer 300 can be from 28 mm to 32 mm to stabilize the light while maintaining thin design.

In some embodiments, as shown in FIG. 1A, the plurality of light-emitting diodes 220 are arranged at intervals on the opaque reflective surface 211 of the flexible circuit board 210 along the side-lit surface 105 of the light guide plate 100. A pitch P of any two adjacent light-emitting diodes 220 is from 1.5 mm to 20 mm (e.g., 1.8 mm). In such embodiments, the pitch P is defined as the distance between the center points of two adjacent light-emitting diodes 220. Additionally, a distance “A” from the position where the light is emitted by each of the light-emitting diodes 220 in the front light guide module 10 to the point where the overall light is uniformly mixed (which may also be referred to as a distance from the light-emitting surface 225 of the light-emitting diodes 220 to the boundary between the visible area VA and the peripheral area VA) can be considered as a light-mixing region of the front light guide module 10. To achieve a better light-mixing effect while meeting the narrow bezel requirements of the product, the design that can satisfy the requirements requires the relationship of “A/P value greater than 0.8.” In other words, in the embodiments, by reducing the pitch P of two adjacent light-emitting diodes 220, not only is the difference in brightness and darkness between two adjacent light-emitting diodes 220 minimized, but also the width of the peripheral area PA is reduced, which increases the area of the visible area VA. In some preferable embodiments, a plurality of light-emitting diodes 220 are arranged at equal intervals on the opaque reflective surface 211 of the flexible circuit board 210 to increase the uniformity of light. In some embodiments, for example, the light-emitting diodes 220 can be mini light-emitting diodes (mini-LED). Since the size of the mini light-emitting diodes (mini-LED) is small, more light-emitting diodes 220 can be installed within a given unit volume. This allows more light to enter the light guide plate 100, thereby increasing the overall brightness. Additionally, light-emitting diodes 220 with small size help to reduce the pitch P between the light-emitting diodes 220 in the layout arrangement.

In some embodiments, a vertical distance D3 between the light-emitting surface 225 of the light-emitting diode 220 and the side-lit surface 105 of the light guide plate 100 can range from 0.01 mm to 0.6 mm (e.g., 0.5 mm). Thus, under the condition that the light-emitting diodes 220 are not too far from the light guide plate 100, the gap formed by the vertical distance D3 can ensure the light transmission efficiency from the light-emitting surface 225 of the light-emitting diodes 220 to the side-lit surface 105 of the light guide plate 100, thereby increasing the light intake of the light guide plate 100.

In some embodiments, the light source module 200 is an unshielded light source. In detail, the light-emitting diodes 220 in the light source module 200 are not covered by any shell or housing that acts as a light concentrator. In other words, the light emitted by the light-emitting diodes 220 is not being focused by reflecting from any shell or housing that acts as a light concentrator. Overall, due to the configuration of the opaque reflective surface 211 of the flexible circuit board 210, the design of the vertical distance D1 from the light-emitting diodes 220 to the flexible circuit board 210, the design of the vertical distance D2 from the light guide plate 100 to the flexible circuit board 210, and the configuration of the composite light path adjustment layer 300, most of the light emitted from the light-emitting diodes 220 can enter the light guide plate 100. Therefore, no additional light concentrators are required to increase the light utilization. This avoids structural discontinuities (gaps) between the light source module 200 and the light guide plate 100 due to the large size of a shielded light source, which helps improve the overall structural stability and contributes to the thin design of the entire device.

It is worth mentioning that, in the prior art, using a thicker light guide plate paired with larger-sized light-emitting diodes typically meets the requirement of sufficient light intake. However, the distance between two larger-sized light-emitting diodes tends to be greater, which can lead to uneven light mixing and create obvious bright and dark bands, thus resulting in hot spots. To solve this problem, light absorption layers are usually disposed near the light incident area to absorb the disordered (scattered) light before light enters the light-mixing region, thereby stabilizing the light and resolving the hot spot problems. However, since the light-emitting diodes 220 of the present disclosure can be mini light-emitting diodes with smaller size, the distance between two adjacent light-emitting diodes 220 can be easily reduced in their arrangement. This helps prevent the light emitted by the light-emitting diodes 220 from creating obvious (noticeable) bright and dark bands in the light-mixing region (i.e., the region of the light guide plate 100 close to the side-lit surface 105). Additionally, since a thinned light guide plate 100 is used in the present disclosure, light intake is the primary consideration. Therefore, it is neither necessary nor feasible to dispose light-absorbing layers at the position corresponding to the vertical projection of the light-mixing region, as this would otherwise impact light intake.

On the other hand, in the prior art, in order to stabilize light before the light enters the light-mixing region, light reflective layers (reflectors) are not considered in the design in order to prevent the light from being reflected constantly and thus not stabilized. However, in the present disclosure, due to the design of the small size of the light-emitting diodes 220, hot spot issues are not encountered, and therefore light reflective layers (i.e., the reflective layer 310 and the opaque reflective surface 211 of the flexible circuit board 210 of the present disclosure) can be disposed near the light incident area. This allows the light to be reflected by the functional layers with reflective properties, enhancing the light intake and ensuring that the overall brightness is maintained or even increased in the thin design of the light guide plate 100. Furthermore, since in the present disclosure, functional layers with reflective properties are disposed near the light incident area of the peripheral area PA to enhance light intake, there is no need to dispose additional reflective layers in the visible area VA to improve the brightness of the visible area VA. It should be noted that when a reflective layer is disposed in the visible area VA, the visibility requirements of the visible area VA must be considered, and this often requires using transparent materials for the reflective layers, which may affect the visibility of the visible area VA to a certain extent. Therefore, by not needing additional reflective layers in the visible area VA, the difficulties of material matching and the potential impacts on the visibility of the visible area VA can be prevented.

Additionally, in the prior art, in order to resolve the hot spot problems caused by a large-sized light source, the side-lit surface of the light guide plate is often designed to be a rough surface, such that light is more likely to be reflected multiple times at the side-lit surface and further enters the light guide plate due to the rough surface design of the side-lit surface, thereby enhancing light intake. However, in the present disclosure, based on the design of small-sized light-emitting diodes 220 and the configuration where the light-emitting diodes 220 are sandwiched from top and below between two reflective layers (the reflective layer 310 of the composite light path adjustment layer 300 and the opaque reflective surface 211 of the flexible circuit board 210), the hot spot problems can be resolved and brightness enhanced. Therefore, the side-lit surface 105 of the light guide plate 100 of the present disclosure can be substantially a flat (smooth) surface. In other words, there is no need to further process the side-lit surface 105 of the light guide plate 100 to create a rough surface, thereby simplifying the manufacturing process. Overall, the present disclosure can achieve the effect of enhancing brightness, improving light mixing, stabilizing light, and simplifying manufacturing process.

For improving the optical effects such as brightness, light mixing, and light stability, when the front light guide module 10 of the present disclosure is disposed on the reflective display 20, the measured average brightness is larger than 120 cd/m², and the measured brightness uniformity is larger than 80%. These optical characteristics are verified through various embodiments and comparative examples as described below. In the stacked structure of Comparative Examples 1-4 and Embodiment 1, the front light guide module is disposed on the reflective display. In the stacked structure of Comparative Examples 5-8 and Embodiment 2, the front light guide module and a touch sensor are sequentially disposed on the reflective display, with an adhesive layer (made of acrylic resin or silicone, with a thickness from 50 mm to 75 mm) bonding the front light guide module and the reflective display (and the touch sensor). For measurement, nine test points (labeled as #1-#9) are selected on the light-emitting surface from the top layer (i.e., the front light guide module in Comparative Examples 1-4 and Embodiment 1, and the touch sensor in the Comparative Examples 5-8 and Embodiment 2) of each stacked structure. A luminance meter is used to measure the brightness at these nine test points. Please refer to FIG. 4 for the method of selecting the test points, in which the actual dimensions of the light guide plate (including length L and width W) are used for labelling the test points, and the light-emitting diodes are disposed at the left side (near the side of #7-#9 test points) of the light guide plate. The brightness measurement results for each embodiment and comparative example are shown in Table 1. It should be understood that, without exceeding the scope of the present disclosure, the embodiments shown in Table 1 should not be used to limit the present disclosure.

TABLE 1

Brightness (unit: cd/m²)

Comparative
Comparative
Comparative
Comparative
Embodiment

Test point
Example 1
Example 2
Example 3
Example 4
1

#1
140.18
36.48
45.19
121.97
147.41

#2
146.47
34.07
40.92
118.62
144.23

#3
142.71
32.97
39.67
118.84
144.74

#4
143.92
45.93
54.29
121.21
145.76

#5
140.75
39.56
49.23
119.00
145.88

#6
141.72
36.26
46.81
112.87
143.84

#7
149.18
52.75
55.82
126.41
135.21

#8
142.94
39.12
48.13
106.25
127.58

#9
141.52
37.36
48.92
99.21
126.59

Average
143.3
39.4
47.7
116.0
127.5

brightness

Brightness
93.96%
62.50%
71.06%
78.48%
85.87%

Uniformity

Brightness (unit: cd/m²)

Comparative
Comparative
Comparative
Comparative
Embodiment

Test point
Example 5
Example 6
Example 7
Example 8
2

#1
127.6
33.2
41.12
111.0
134.1

#2
133.3
31.0
37.24
107.9
131.3

#3
129.9
30.0
36.10
108.1
131.7

#4
131.0
41.8
49.40
110.3
132.6

#5
128.1
36.0
44.80
108.3
132.8

#6
129.0
33.0
42.60
102.7
130.9

#7
135.8
48.0
50.80
115.0
123.0

#8
130.1
35.6
43.80
96.7
116.1

#9
128.8
34.0
44.52
90.3
115.2

Average
130.4
35.8
43.40
105.6
127.5

brightness

Brightness
93.96%
62.50%
71.06%
78.48%
85.87%

Uniformity

[Note 1]

Unless otherwise specified, the stacked structure of the front light guide module in each comparative example and each embodiment is as shown in FIG. 1B. The remaining details are as follows:

- Comparative Examples 1 and 5: conventional size of the LED, light guide plate with a thickness H1 of 0.4 mm, and no reflective layer used;
- Comparative Examples 2 and 6: conventional size of the LED, light guide plate with a thickness H1 of 0.15 mm, and no reflective layer are used;
- Comparative Examples 3 and 7: conventional size of the LED, light guide plate with a thickness H1 of 0.15 mm;
- Comparative Examples 4 and 8: mini-LED, light guide plate with a thickness H1 of 0.15 mm, and no reflective layer used;
- Examples 1 and 2: mini-LED, light guide plate with a thickness H1 of 0.15 mm.
  
  [Note 2]

The brightness uniformity is calculated as: (minimum brightness/maximum brightness)×100%.

[Note 3]

The conventional size of the LED used in the comparative examples is: 3 mm (length)×0.85 mm (width)×0.4 mm (height).

Please refer to Comparative Examples 1 and 5. The conventional design of non-thinned light guide plates is used in Comparative Examples 1 and 5, meaning a thicker light guide plate and conventional size of the LED are used in Comparative Examples 1 and 5. Therefore, the brightness and brightness uniformity are in compliance. Please refer to Comparative Examples 2, 3, 5, and 6. It can be seen that regardless of whether a reflective layer is used, when the light guide plate is thinned without corresponding reduction in the size of the LED, neither brightness nor brightness uniformity is improved. This provides evidence that the light intake is reduced when simply thinning the light guide plate, leading to insufficient brightness and poor light guiding, which results in lower brightness uniformity. Please refer to Comparative Examples 4 and 8 and Embodiments 1 and 2. It can be seen that when a thinned light guide plate and small size of LED are used, the brightness and brightness uniformity can be significantly improved, in which when a reflective layer is added, the brightness and brightness uniformity can be further enhanced. This demonstrates that the overall stacked structure design (i.e., stacked structure shown in FIG. 1B) of the front light guide module of the present disclosure has a significant effect on improving the optical performance. On the other hand, based on the results of the first set of experiments (Comparative Examples 1-4 and Embodiment 1) and the second set of experiments (Comparative Examples 5-8 and Embodiment 2), it seems that the presence of a touch sensor on the front light guide module does not have significant impact on the optical performance. In addition, since adhesive layers with high transmittance are used, the impact of the adhesive layers on the optical performance in each comparative example and each embodiment is negligible.

Please refer to FIG. 2, which is a schematic cross-sectional view of the touch display device 1 according to some embodiments of the present disclosure, with the cross-sectional position corresponding to cutting plane line A-A′ in FIG. 1A. The touch display device 1 has a visible area VA and a peripheral area PA located on at least one side of the visible area VA. The front light guide module 10 of the present disclosure can be integrated into the reflective touch display device 1. More specifically, the touch display device 1 comprises a front light guide module 10, a reflective display 20, and a touch sensor 30. The front light guide module 10 is disposed on the reflective display 20, and the touch sensor 30 is disposed on the front light guide module 10. In other words, the front light guide module 10 is disposed between the reflective display 20 and the touch sensor 30.

The touch display device 1 further comprises a cover 40. The cover 40 is disposed on the touch sensor 30 and relatively away from the front light guide module 10 compared to the touch sensor 30. More specifically, the cover 40 is disposed on the side of the light-emitting surface of the front light guide module 10, which is the side of the top surface 101 of the light guide plate 100. Since the material of the cover 40, such as glass, quartz, or suitable polymers (e.g., polycarbonates (PC) or polymethyl methacrylate (PMMA)), has a certain degree of stiffness, the cover 40 can provide the touch display device 1 with protection. Additionally, a shielding layer 42 is disposed on the side of the cover 40 facing the front light guide module 10 to define the peripheral area PA and enhance concealment of components located on the back side of the cover 40 in the peripheral area PA (e.g., a flexible circuit board 35 connected to the touch sensor 30). The shielding layer 42 can extend from the edge of the cover 40 to the visible area VA, creating a boundary between the defined peripheral area PA and the visible area VA.

It can be seen from the overall stacked structure of the touch display device 1 that, in comparison with the visible area VA, the number of the components in the peripheral area PA is greater, the stacking relationships in the peripheral area PA are more complex, and the heights of the components in the peripheral area PA are more inconsistent. This may easily lead to component damage during the subsequent lamination process. To avoid mechanical interference, the design often requires layout adjustments or openings, which may in turn reduce structural stability. However, in the present disclosure, the light-emitting diodes 220 are designed with reduced thickness to accommodate the thinned light guide plate 100, which helps minimize the structural discontinuities in height between the peripheral area PA and the visible area VA. This approach addresses the problems of structural interference in the peripheral area PA and enhances the overall structural stability. Additionally, it eliminates the need for thicker adhesive layers to overcome significant structural discontinuities in height, thereby achieving a thinner device. Moreover, the thickness H2 of the composite light path adjustment layer 300 (please refer to FIG. 1A) can range from 28 mm to 32 mm. Such a design not only can stabilize the light while maintaining thin design, as previously mentioned, but also reduces the structural discontinuities in height between the visible area VA and the peripheral area PA, thereby enhancing the overall structural stability.

In some embodiments, the touch display device 1 further comprises an adhesive layer to bond each layer. More specifically, the first adhesive layer 50 is disposed between the touch sensor 30 and the front light guide module 10, the second adhesive layer 60 is disposed between the front light guide module 10 and the reflective display 20, and the third adhesive layer 70 is disposed between the cover 40 and the touch sensor 30. In some embodiments, each of the adhesive layers can be an optically clear adhesive (OCA) with high transmittance. To cope with the thin design of the touch display device 1, the thickness T1 of the first adhesive layer 50 and the thickness T2 of the second adhesive layer 60 can be reduced, while the thickness T3 of the third adhesive layer 70 is relatively thicker to compensate for the structural discontinuities created by the shielding layer 42 of the cover 40. This prevents the third adhesive layer 70 from forming bubbles therein during lamination process due to insufficient thickness, which may affect the product yield. In other words, the thickness T3 of the third adhesive layer 70 is larger than the thickness T1 of the first adhesive layer 50, and the thickness T3 of the third adhesive layer 70 is larger than the thickness T2 of the second adhesive layer 60. More specifically, the thickness T3 of the third adhesive layer 70 can range from 100 mm to 125 mm, and each of the thickness T1 of the first adhesive layer 50 and the thickness T2 of the second adhesive layer 60 can range from 50 mm to 75 mm.

On the other hand, it is understood that when two stiff layers are adhered together during the lamination process, bubbles are more likely to be formed in the stiff layers. Additionally, in practice, after a stiff layer and a flexible layer are adhered together, the overall structure formed tends to exhibit stiffness. Based on this, during the manufacturing process of the touch display device 1 of the present disclosure, the bonding sequence of the lamination process is designed according to the stiffness of each component and the thickness requirements of each aforementioned adhesive layer, in which thicker adhesive layers are used for bonding stiff layers, while thinner adhesive layers are used for bonding where flexible layers are involved. The touch display device 1 of the present disclosure can be formed by sequentially performing the following bonding steps S10 to S30. Please refer to FIG. 3A to FIG. 3C for better understanding. FIG. 3A to FIG. 3C are schematic cross-sectional views of the touch display device 1 at different steps of the manufacturing method thereof according to some embodiments of the present disclosure. For simplicity, rectangular outlines are used to represent the front light guide module 10, the reflective display 20, the touch sensor 30, and the cover 40 in FIG. 3A to