OPTICAL WAVEGUIDE CIRCUIT SUBSTRATE AND MANUFACTURING METHOD THEREOF

An optical waveguide circuit substrate includes a circuit board and an optical waveguide structure disposed on a lower surface of the circuit board. A plurality of pads are disposed on an upper surface of the circuit board. The optical waveguide structure includes a first cladding layer, a second cladding layer, a core layer and a reflective layer. The core layer has an imprinted opening of which an aperture gradually increases from the first cladding layer to the second cladding layer. A first portion of the second cladding layer fills the imprinted opening and has a connection surface. The reflective layer is located between the core layer and the first portion, and an angle between the reflective layer and the connection surface is in a range from 44 degrees to 46 degrees. An orthographic projection of the reflective layer on the upper surface is located between the pads.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 108134799, filed on Sep. 26, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention generally relates to a circuit substrate and a manufacturing method thereof, and in particular, to an optical waveguide circuit substrate and a manufacturing method thereof.

Description of Related Art

In general, with the increase of information capacity, light interconnection technologies of optical signals are actively developed in the field of information processing. In the current circuit substrate technology, a circuit substrate having an optical waveguide structure has been developed at present. This circuit substrate may serve as an optical transmission path to transmit an optical signal.

At present, a manufacturing method of such a circuit substrate having an optical waveguide structure usually involves forming an opening in a core layer via a laser process, generating total reflection based on a refractive index difference between air and the core layer and then transmitting the optical signal outward. However, it is difficult to use the laser process to form an opening at a specific angle of 45 degrees for generating the total reflection, and higher production costs are needed.

SUMMARY OF THE INVENTION

The invention provides an optical waveguide circuit substrate and a manufacturing method thereof, which require a simple manufacturing process, have a high yield and can reduce the manufacturing costs.

The optical waveguide circuit substrate of the invention includes a circuit board and an optical waveguide structure. The circuit board has an upper surface and a lower surface opposite to each other, and a plurality of pads disposed on the upper surface. The optical waveguide structure is disposed on the circuit board and located on the lower surface. The optical waveguide structure includes a first cladding layer, a second cladding layer, a core layer and a reflective layer. The second cladding layer includes a first portion and a second portion. The core layer is located between the first cladding layer and the second cladding layer and has an imprinted opening. The first cladding layer is located between the circuit board and the core layer. An aperture of the imprinted opening gradually increases from the first cladding layer to the second cladding layer. The first portion of the second cladding layer fills the imprinted opening and has a connection surface. The second portion of the second cladding layer is in contact with the connection surface and covers a bottom surface of the core layer. The connection surface is flush with the bottom surface. The reflective layer is located between the core layer and the first portion of the second cladding layer. An angle between the reflective layer and the connection surface is in a range from 44 degrees to 46 degrees, and an orthographic projection of the reflective layer on the upper surface of the circuit board is located between the plurality of pads.

A manufacturing method of an optical waveguide circuit substrate of the invention includes: providing a circuit board, the circuit board having an upper surface and a lower surface opposite to each other and a plurality of pads disposed on the upper surface; forming a first cladding layer on the lower surface of the circuit board; forming a core layer on the first cladding layer; forming an imprinted opening on the core layer by imprinting, an aperture of the imprinted opening gradually increasing from the first cladding layer to a direction away from the first cladding layer; forming a reflective layer on a sidewall of the imprinted opening, an orthographic projection of the reflective layer on the upper surface of the circuit board being located between the plurality of pads; and forming a second cladding layer on the core layer, the second cladding layer including a first portion and a second portion, the first portion filling the imprinted opening and having a connection surface, the second portion being in contact with the connection surface and covering a bottom surface of the core layer, and the connection surface being flush with the bottom surface. The reflective layer is located between the core layer and the first portion of the second cladding layer, and an angle between the reflective layer and the connection surface is in a range from 44 degrees to 46 degrees.

In an embodiment of the invention, the circuit board includes at least one insulating layer and at least one patterned circuit layer. The at least one patterned circuit layer includes a plurality of conducting circuits and the plurality of pads. The insulating layer is located between the patterned circuit layer and the optical waveguide structure.

In an embodiment of the invention, the circuit board further includes a solder resist layer and a surface treatment layer. The solder resist layer clads the plurality of conducting circuits. The surface treatment layer clads the plurality of pads.

In an embodiment of the invention, the circuit board further includes a supporting layer. The supporting layer is disposed between the insulating layer and the optical waveguide structure, and a first side of the supporting layer is retracted by a distance relative to a second side of the first cladding layer.

In an embodiment of the invention, the supporting layer has an opening. An orthographic projection of the opening on the upper surface is located between the plurality of pads.

In an embodiment of the invention, the first cladding layer fills the opening and covers part of the insulating layer.

In an embodiment of the invention, the orthographic projection of the opening on the upper surface and an orthographic projection of the imprinted opening on the upper surface partially overlap.

In an embodiment of the invention, an optical refractive index of the first cladding layer and an optical refractive index of the second cladding layer are different from an optical refractive index of the core layer.

In an embodiment of the invention, part of the second cladding layer is in direct contact with the first cladding layer.

In an embodiment of the invention, a cross-sectional shape of the first portion of the second cladding layer includes an isosceles trapezoid.

Based on the above, the first portion of the second cladding layer of the optical waveguide circuit substrate of the invention fills the imprinted opening of the first cladding layer, the reflective layer is located between the core layer and the first portion of the second cladding layer, and the angle between the reflective layer and the connection surface is in a range from 44 degrees to 46 degrees. Therefore, an optical signal subsequently entering via a space between the pads of the circuit board may be transmitted outward through total reflection in the core layer via the reflective layer. In addition, because the imprinted opening is manufactured by imprinting in the invention, compared with an opening formed by a conventional laser process, the optical waveguide circuit substrate of the invention is easy to manufacture and high in yield and can effectively reduce the production costs.

To make the features and advantages of the invention clear and easy to understand, the following gives a detailed description of embodiments with reference to accompanying drawings.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1illustrates a schematic cross-sectional diagram of an optical waveguide circuit substrate according to an embodiment of the invention. Referring toFIG. 1, in the present embodiment, the optical waveguide circuit substrate100includes a circuit board110and an optical waveguide structure120. The optical waveguide structure120includes a first cladding layer122, a core layer124, a reflective layer126and a second cladding layer128.

In detail, the circuit board110of the present embodiment has an upper surface110aand a lower surface110bopposite to each other and a plurality of pads114bdisposed on the upper surface110a. Furthermore, the circuit board110of the present embodiment may include at least one insulating layer (one insulating layer112is schematically illustrated inFIG. 1) and at least one patterned circuit layer (one patterned circuit layer114is schematically illustrated inFIG. 1). A material of the insulating layer112is, for example, polyimide. A material of the patterned circuit layer114is, for example, copper. The insulating layer112has the upper surface110aand the lower surface110b, and the insulating layer112is located between the patterned circuit layer114and the optical waveguide structure120. The patterned circuit layer114is located on the upper surface110aof the insulating layer112, and includes a plurality of conducting circuits114aand the plurality of pads114b. It should be noted that the invention does not limit the number of the insulating layers112and the number of the patterned circuit layers114, which may depend on the design requirements of the actual circuit board110.

Furthermore, in order to effectively maintain the characteristics of the patterned circuit layer114, the circuit board110of the present embodiment further includes a surface treatment layer115and a solder resist layer116. The surface treatment layer115clads the pads114b. A material of the surface treatment layer115is, for example, nickel, gold, silver, nickel gold, nickel silver, nickel palladium or other suitable metal materials. The solder resist layer116clads the conducting circuits114ato prevent oxidation of the conducting circuits114a. A material of the solder resist layer116is, for example, green lacquer. In addition, in order to improve the structural strength, the circuit board110of the present embodiment further includes a supporting layer118. The supporting layer118is disposed between the insulating layer112and the optical waveguide structure120, and a first side118aof the supporting layer118is retracted by a distance L relative to a second side122aof the first cladding layer122. As shown inFIG. 1, the supporting layer118of the present embodiment further has an opening118c. An orthographic projection of the opening118con the upper surface110ais located between the pads114b. The circuit board110may be, for example, a flexible circuit board, and a material of the supporting layer118is, for example, copper, but is not limited thereto.

Referring toFIG. 1again, the optical waveguide structure120of the present embodiment includes the first cladding layer122, the core layer124, and the second cladding layer128that are stacked on the circuit board110in sequence and located on the lower surface110b, and the reflective layer126that is located between the core layer124and the second cladding layer128. An optical refractive index of the first cladding layer122and an optical refractive index of the second cladding layer128are different from an optical refractive index of the core layer124.

In detail, the first cladding layer122of the optical waveguide structure120fills the opening118cof the supporting layer118, and covers part of the insulating layer112. Specifically, a side118bof the supporting layer118opposite to the first side118ais flush with a side122bof the first cladding layer122opposite to the second side122a. The first cladding layer122covers the first side118aof the supporting layer118and is in direct contact with part of the insulating layer112.

Furthermore, the core layer124of the optical waveguide structure120is disposed on the first cladding layer122, and the first cladding layer122is located between the insulating layer112and the core layer124. In detail, the core layer124has an imprinted opening124cof which an aperture gradually increases from the first cladding layer122to the second cladding layer128. That is, the aperture of the imprinted opening124cgradually increases from the first cladding layer122to a direction away from the first cladding layer122. In other words, the aperture of the imprinted opening124cgradually increases from a top surface124aof the core layer124to a bottom surface124bof the core layer124. In an embodiment, the orthographic projection of the opening118cof the supporting layer118on the upper surface110aand an orthographic projection of the imprinted opening124con the upper surface110apartially overlap.

In addition, the second cladding layer128of the optical waveguide structure120is disposed on the first cladding layer122. The core layer124is located between the first cladding layer122and the second cladding layer128. In an embodiment, the second cladding layer128is in direct contact with the first cladding layer122. Furthermore, the second cladding layer128includes a first portion128aand a second portion128bthat are connected to each other. The first portion128aof the second cladding layer128fills the imprinted opening124cof the core layer124. There is a connection surface128sbetween the first portion128aand the second portion128b. The connection surface128sis flush with the bottom surface124bof the core layer124. The second portion128bof the second cladding layer128is in contact with the connection surface128sand covers the bottom surface124bof the core layer124. In an embodiment, a cross-sectional shape of the first portion128aof the second cladding layer128is, for example, an isosceles trapezoid, but is not limited thereto.

Referring toFIG. 1again, the reflective layer126of the optical waveguide structure120of the present embodiment is located between the core layer124and the first portion128aof the second cladding layer128. In detail, an angle θ between the reflective layer126and the connection surface128sis, for example, in a range from 44 degrees to 46 degrees, preferably 45 degrees. The orthographic projection of the reflective layer126on the upper surface110aof the circuit board110is located between the pads114b. Furthermore, the reflective layer126is located on a sidewall124s, close to the opening118cof the supporting layer118, of the imprinted opening124cof the core layer124, and the reflective layer126faces the opening118cof the supporting layer118.

In an embodiment, a laser diode (not illustrated) may be disposed on the optical waveguide circuit substrate100of the present embodiment. The laser diode may be electrically connected to the pads114bof the circuit board110by flip chip to generate an optical signal. The optical signal sequentially passes through the pads114b, the insulating layer112, the opening118cof the supporting layer118and the first cladding layer122, then generates total reflection in the core layer124via the reflective layer126, and is transmitted to outside. The path that the optical signal passes through may be known as an optical transmission path. In an embodiment, after the optical signal leaves the core layer124, an optical fiber or a photodetector may be connected to convert the optical signal into an electrical signal, and the electrical signal may enter another electronic device, or the electrical signal may be transmitted again to the laser diode, so that the electrical signal is reconverted into the optical signal and returns to the optical waveguide circuit substrate100.

The above only describes the structure of the optical waveguide circuit substrate100of the invention, and does not describe a manufacturing method of the optical waveguide circuit substrate100of the invention. Therefore, the structure of the optical waveguide circuit substrate100inFIG. 1is used as an example below to describe a manufacturing process of the optical waveguide circuit substrate100of the invention in detail with reference toFIG. 2AtoFIG. 2D.

FIG. 2AtoFIG. 2Dillustrate schematic cross-sectional diagrams of a manufacturing method of the optical waveguide circuit substrate ofFIG. 1. Referring toFIG. 2Aat first, a manufacturing method of the optical waveguide circuit substrate100of the present embodiment includes that: firstly, a circuit board100is provided. In the present embodiment, the circuit board110has an upper surface110aand a lower surface110bopposite to each other and a plurality of pads114bdisposed on the upper surface110a. In detail, the circuit board110of the present embodiment includes an insulating layer112and a patterned circuit layer114. The insulating layer112has the upper surface110aand the lower surface110b, and the patterned circuit layer114is located on the upper surface110aof the insulating layer112, and includes a plurality of conducting circuits114aand pads114b. Furthermore, in order to effectively maintain the characteristics of the patterned circuit layer114, the circuit board110of the present embodiment further includes a surface treatment layer115and a solder resist layer116. The surface treatment layer115clads the pads114b, and the solder resist layer116clads the conducting circuits114a, so as to avoid oxidization of the conducting circuits114a. In addition, in order to improve the structural strength, the circuit board110of the present embodiment further includes a supporting layer118. The supporting layer118is disposed on the lower surface110bof the insulating layer112. As shown inFIG. 1, the supporting layer118of the present embodiment further has an opening118c. An orthographic projection of the opening118con the upper surface110ais located between the pads114b. The circuit board110may be, for example, a flexible circuit board.

Secondly, referring toFIG. 2B, a first cladding layer122is formed on the lower surface110bof the circuit board110. A material of the first cladding layer122is, for example, an insulating material. In an embodiment, the material of the first cladding layer122may be, for example, a photoresist material. A method for forming the first cladding layer122is, for example, a coating method, but is not limited thereto.

Referring toFIG. 2C, a core layer124is formed on the first cladding layer122. A material of the core layer124is, for example, an insulating material. A method for forming the core layer124is, for example, a coating method, but is not limited thereto. In an embodiment, the material of the first cladding layer122is different from that of the core layer124. Therefore, the first cladding layer122and the core layer124have different optical refractive indexes. Then, an imprinted opening124cis formed on the core layer124by imprinting. Because the imprinted opening124cis manufactured by imprinting in the present embodiment, compared with an opening formed by a conventional laser process, the imprinted opening124cat a specific angle (such as 44 degrees to 46 degrees) may be formed by a simpler process in the present embodiment, which can reduce the manufacturing costs of the optical waveguide circuit substrate100.

Then, referring toFIG. 2Cagain, a reflective layer126is formed on a sidewall124sof the imprinted opening124c. A material of the reflective layer126is metal, such as aluminum, but the invention is not limited thereto. A method for forming the reflective layer126is, for example, a sputtering method. In comparison to air, a refractive index difference between the imprinted opening124cformed by imprinting and other materials in the optical waveguide circuit substrate100is less obvious. Therefore, the reflective layer126is further formed on the sidewall124sof the imprinted opening124c, and the optical signal may have a good total reflection to improve the later photoelectric conversion efficiency.

Finally, referring toFIG. 2D, a second cladding layer128is formed on the core layer124. The second cladding layer128fills the imprinted opening124c. A material of the second cladding layer128is an insulating material or a photoresist material, and a method for forming the core layer124is, for example, a coating method. In an embodiment, the material of the second cladding layer128may be the same as or different from the material of the first cladding layer122. Preferably, the optical refractive index of the first cladding layer122and the optical refractive index of the second cladding layer128may be different from the optical refractive index of the core layer124, so as to ensure that the optical signal may generate the total reflection in the core layer124via the reflection of the reflective layer126. The manufacturing of the optical waveguide circuit substrate100has been completed.

Based on the above, the first portion of the second cladding layer of the optical waveguide circuit substrate of the invention fills the imprinted opening of the first cladding layer, the reflective layer is located between the core layer and the first portion of the second cladding layer, and the angle between the reflective layer and the connection surface is in a range from 44 degrees to 46 degrees. Therefore, an optical signal subsequently entering via a space between the pads of the circuit board may be transmitted outward through total reflection in the core layer via the reflective layer. In addition, because the imprinted opening is manufactured by imprinting in the invention, compared with an opening formed by a conventional laser process, the optical waveguide circuit substrate of the invention is easy to manufacture and high in yield and can effectively reduce the production costs.

Although the invention is described with reference to the above embodiments, the embodiments are not intended to limit the invention. A person of ordinary skill in the art may make variations and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the invention should be subject to the appended claims.