Printed circuit board with opto-via holes and process of forming the opto-via holes

[0001] 1. Field of the Invention

[0002] The present invention pertains, in general, to a printed circuit board with opto-via holes and a process of forming the opto-via holes and, in particular, to a printed circuit board with opto-via holes for transmitting an optical signal to an optical waveguide in the printed circuit board, and a process of forming the opto-via holes.

[0003] 2. Description of the Prior Art

[0004] As well known to those skilled in the art, a printed circuit board (PCB) functions to connect various electronic components to each other on a board along a predetermined pattern, and is applied to various electronic goods such as home appliances including a digital TV and advanced telecommunication equipments.

[0005] A conventional PCB comprises a copper plate on which a circuit pattern is formed, and an inner and an outer layer. However, recently, an electro-optical circuit board (EOCB) is frequently used instead of the conventional PCB. At this time, the EOCB is formed by inserting an optical waveguide comprising polymer and glass fiber, for transmitting and receiving an optical signal and into the PCB.

[0006] In other words, the EOCB is the PCB into which the optical waveguide and a glass plate are inserted after a circuit pattern is already formed on the PCB, and it transmits and receives both an electrical signal and an optical signal. Additionally, the EOCB functions to convert the optical signal into the electrical signal so as to store data or process signals in a component mounted on the PCB, and a very high speed data telecommunication is realized when the electrical signal is interfaced into the optical signal in the PCB.

[0007] Meanwhile, an opto-via hole acts as a medium for connecting the optical signal to an entrance of the optical waveguide component of an inner layer of the PCB, and is a kind of via hole of the PCB functioning to transmit signals in the PCB to a photodiode (PD) or vertical-cavity surface-emitting laser (hereinafter referred to as VCSEL) acting as a light source component located outside the PCB. When the optical waveguide is formed, there is a need to form the opto-via hole which acts as a channel for connecting the outer layer of the PCB to the inner layer of the PCB and easily transmits the optical signal from the inner layer to the outer layer.

[0008] In detail, in accordance with the recent trend of rapid increase in the use of the Internet and improvements of service quality on the internet, an amount of data to be processed and transmitted is rapidly increased, so it is necessary to expand a bandwidth and rapidly to process signals. Accordingly, it is required to use the EOCB as the medium of optical interfacing. That is to say, the electrical signal used in the conventional PCB is undesirably affected by electromagnetic susceptibility (EMS) characteristics during a high-speed switching process at a GHz band, so there remains a need to adopt optical interfacing which is not limited by the EMS characteristics.

[0009] A detailed description of the optical interfacing in the PCB will be given, below.

[0010] FIG. 1 schematically illustrates a beam coupling in the case of using a beam reflecting micro mirror in a conventional manner.

[0011] With reference to FIG. 1, an electrical signal transmitted from a processor board 2 is converted into an optical signal by a laser diode 1 in a transmitting module 3, transported via left lenses 8a, 8b, and then reflected by a left micro mirror 4a inserted into the PCB. The reflected signal is transported through the optical waveguide, reflected by a right reflecting mirror 4b, and then transported through right lenses 8c, 8d to a photo diode 6 in a receiving module 7. At this time, the optical waveguide is embedded within a low loss multimode polymer waveguide core 5a, 5b, and a waveguide clad 9 is formed on an upper and a lower part of the core. Therefore, the electrical signal transmitted from the left processor board 2 is converted into the optical signal and transported to a photo diode 6, and the optical signal is then converted into the electrical signal by the photo diode 6 and transported to a right processor board.

[0012] However, there is no commercial process by which the waveguide or glass plate is inserted into the PCB and connected to components outside the PCB, even though it has been ten years or more since the EOCB was first proposed. Additionally, a process of fabricating the PCB depends on a method of applying the optical signal to the PCB. Accordingly, it is necessary to desirably determine the procedure of forming the via hole so that the via hole is less affected by chemicals used to fabricate the PCB.

[0013] Furthermore, a conventional process of forming the PCB with opto-via holes is disadvantageous in that the optical waveguide component and the glass fiber are undesirably affected by physical and chemical stresses during a fabrication process of the PCB, thereby readily degrading the light transmissivity of the PCB, so there is a problem in forming the desired opto-via hole in accordance with different processes.

[0014] Therefore, the present invention has been made keeping in mind the above disadvantages occurring in the conventional arts, and an object of the present invention is to provide a PCB with opto-via holes, each of which allows a signal to stably pass therethrough while minimizing damage to an optical waveguide directly exposed to an outside of the PCB, and into which the optical waveguide is inserted, and a process of forming the opto-via holes.

[0015] The above object can be accomplished by providing a process of forming an opto-via hole, comprising forming a plurality of via holes on a plurality of copper clad laminates using a drill, plating an inner wall of each via hole, exposing and etching plated portions of an upper and lower side of each copper clad laminate to form a circuit pattern on the upper and lower side of the copper clad laminate, layering a plurality of patterned copper clad laminates each other using an insulating resin adhesive, and removing the insulating resin adhesive in the predetermined via holes to form opto-via holes.

[0016] At this time, the opto-via holes comprise electric-via holes and opto-via holes.

[0017] Additionally, it is preferable that the opto-via holes are formed by a CO₂ laser beam or a mechanical bit in the removing step, and an epoxy resin with 95% more light transmissivity is filled in the opto-via holes.

[0018] Further, the present invention provides a process of forming an opto-via hole for an optical waveguide, comprising forming circuit patterns on a plurality of copper clad laminates, respectively. Each of the copper clad laminates includes an insulating layer and copper-clad layers coated on an upper and a lower side of the insulating layer. The process also includes firstly layering the patterned copper clad laminates each other using an adhesive, firstly drilling a plurality of electric- and opto-via holes on desired positions of the patterned copper clad laminate, plating inner walls of the firstly drilled electric- and opto-via holes, exposing and etching plated portions of an upper and a lower side of each copper clad laminate to form a circuit pattern on the upper and lower side of the copper clad laminate, and secondly drilling a plurality of second opto-via holes on the copper clad laminate.

[0019] The process further comprises forming a stepped part in the vicinity of the opto-via hole and attaching the optical waveguide to the stepped part.

[0020] In addition, it is preferable that an epoxy resin with 95% more light transmissivity is filled in the opto-via holes.

[0021] Furthermore, the present invention provides a printed circuit board with an opto-via hole for an optical waveguide, comprising a plurality of copper clad laminates with a plurality of via holes formed by a drill, and a plated layer formed on an inner wall of each via hole. A circuit pattern layer is formed by exposing and etching plated portions on an upper and a lower side of each copper clad laminate, and an insulating resin adhesive is used to layer a plurality of patterned copper clad laminates on each other. Additionally, the printed circuit board in the present invention also includes a plurality of opto-via holes formed by removing the insulating resin adhesive in the via holes, and an optical waveguide for transmitting an optical signal through each opto-via hole.

[0022] The opto-via holes comprise electric-via holes and opto-via holes.

[0023] The opto-via holes are formed by a CO₂ laser beam or a mechanical bit.

[0024] Further, an epoxy resin with 95% or more light transmissivity is filled in the opto-via holes.

[0025] Moreover, the present invention provides a printed circuit board with an opto-via hole for an optical waveguide, comprising a plurality of copper clad laminates with an insulating layer and copper layers coated on an upper and a lower side of the insulating layer. Each of the copper clad laminates includes a circuit pattern formed thereon. The patterned copper clad laminates are firstly layered on each other using an adhesive. The printed circuit board in the present invention also includes a plurality of electric-via holes formed by firstly drilling desired points on the copper clad laminates, and a plurality of first opto-via holes formed at the same time as the electric-via holes. A plated layer is formed on an inner wall of each electric-via hole and first opto-via hole, and a circuit pattern layer is formed by exposing and etching plated portions on an upper and a lower side of each copper clad laminate. Additionally, a plurality of second opto-via holes are formed by secondly drilling desired points on the copper clad laminates, and an optical waveguide transmits an optical signal through the first and second opto-via holes.

[0026] At this time, an epoxy resin with 95% or more light transmissivity is filled in the second opto-via holes.

[0027] Therefore, the present invention is advantageous in that the electric- and opto-via holes are all formed on the PCB for the optical waveguide, thereby stably transmitting a signal from an outer layer of the PCB to an inner layer of the PCB without damage to the optical waveguide directly exposed to an external environment.

[0028] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0029] FIG. 1 schematically illustrates a beam coupling in the case of using a beam reflecting micro mirror according to a conventional art;

[0030] FIGS. 2a to 2f are sectional views stepwisely illustrating the formation process of opto-via holes in an outer layer of a PCB according to an embodiment of the present invention;

[0031] FIGS. 3a to 3f are sectional views stepwisely illustrating the formation process of opto-via holes in an inner layer of a PCB according to the present invention; and

[0032] FIGS. 4a to 4g are sectional views stepwisely illustrating the fabrication process of the PCB after the opto-via holes are formed according to the present invention.

[0033] Reference numerals are made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.

[0034] First Process: a Process of Forming Opto-via Holes in an Outer Layer

[0035] FIGS. 2a to 2f are sectional views stepwisely illustrating the formation process of the opto-via holes in the outer layer of a PCB according to an embodiment of the present invention.

[0036] In detail, FIG. 2a illustrates a forming step of a plurality of via holes on a copper clad laminate (CCL) using a drill, FIG. 2b illustrates a plating step of an inner wall of each via hole, and FIG. 2c illustrates a patterning step of a plated portion on the copper clad laminate by an exposing and an etching process. Additionally, FIG. 2d illustrates a layering step of the patterned copper clad laminates using an insulating resin adhesive, and in FIG. 2e, the adhesive on a position on which the opto-via holes are to be formed is removed, thereby forming the opto-via holes in the copper clad laminate.

[0037] With reference to FIGS. 2a to 2e, the via holes are formed on the copper clad laminate (CCL) using a drill, in which a copper layer is coated on an upper and a lower side of an insulating panel 12 made of epoxy and a glass fiber (FIG. 2a). The via holes (a) thus formed act as electric-via holes or the opto-via holes. Additionally, the drill may be a mechanical drill. At this time, the electric-via hole has the same diameter as a via-hole of a conventional PCB, and the opto-via hole has larger diameter than the electric-via hole so as to interface light to the optical waveguide.

[0038] The via hole is then subjected to an electroless or electrolytic Cu plating (FIG. 2b), thereby plating an inner wall of the via hole (b) by a conventional plating process.

[0039] The plated copper clad laminate is then patterned by an exposing and etching process (FIG. 2c) to form a circuit pattern (c) on the plated copper clad laminate, and a detailed description of a process of forming the circuit pattern will be omitted in this specification because the present invention relates to a process of forming the opto-via holes on the circuit pattern.

[0040] Referring to FIG. 2d, the copper clad laminates on which the circuit patterns are formed are layered on each other using an insulating resin adhesive, for example, prepreg. At this time, a reference numeral 13 denotes an adhesive, and one CCL is layered on the other CCL. Each CCL comprises a panel or an epoxy insulating layer 12, 12 which is coated with the copper layer 11, 11 at an upper and a lower side thereof and subjected to a drilling, a plating, and a patterning process. A process of FIGS. 2a to 2d is conducted in a manner similar to a conventional process of forming the via hole.

[0041] The resulting structure is then processed by a CO₂ laser or a mechanical bit to form the opto-via holes (d) (FIG. 2e). In other words, the insulating resin adhesive is removed from the resulting structure and the opto-via holes are formed. Additionally, a stepped part 15 may be formed in the vicinity of the opto-via holes (FIG. 2f), and the optical waveguide 14 is attached to the stepped part 15.

[0042] Therefore, the PCB fabricated according to the process of FIGS. 2a to 2f is used as an outer layer of a multi-layered PCB for the optical waveguide.

[0043] Second Process: a Process of Forming Opto-via Holes in an Inner Layer

[0044] FIGS. 3a to 3f are sectional views stepwisely illustrating the formation process of opto-via holes in an inner layer of a PCB according to another embodiment of the present invention.

[0045] With reference to FIGS. 3a to 3f, an insulating panel 22 made of epoxy and the glass fiber is coated with a copper layer 21 at an upper and a lower side thereof to produce a CCL, and a circuit pattern (e) is formed on the CCL (FIG. 3a).

[0046] The copper layer 24 is then covered on an upper and a lower side of a circuit pattern layer of FIG. 3a (FIG. 3b). At this time, a reference numeral 23 denotes an adhesive for attaching layers to each other.

[0047] Referring to FIG. 3c, the resulting structure is subjected to a first drilling process to simultaneously form electric- and opto-via holes (f) using a drill. At this time, the drill may be a mechanical drill.

[0048] The drilled structure is then plated in an electrolytic or electroless manner (FIG. 3d) to form a plated layer (g).

[0049] A predetermined circuit pattern (h) is then formed on an outer layer of the plated structure (FIG. 3e).

[0050] The patterned structure is secondly drilled to form the opto-via hole (i) (FIG. 3f). In other words, the opto-via holes are formed in the CCL by the first and second drilling processes.

[0051] In the case of the first embodiment as shown in FIGS. 2a to 2e, the opto-via holes are formed in the inner layer of the PCB by removing an adhesive, but in the case of the second embodiment, the opto-via holes are formed by a separate second drilling process, as shown in FIG. 3f.

[0052] Therefore, the PCB fabricated by the process of FIGS. 3a to 3f is useful as the inner layer of the multi-layered PCB for the optical waveguide.

[0053] Third Process: a Process of Attaching the Outer Layer to the Inner Layer

[0054] FIGS. 4a to 4g are sectional views stepwisely illustrating the fabrication process of a PCB after opto-via holes are formed according to the present invention.

[0055] Each of the layers 10, 20, 30 with an optical waveguide 35, 36 is layered on each other with the use of an insulating resin adhesive 38 (FIG. 4a). At this time, the optical waveguide 35, 36 is attached to a predetermined position of an outer layer in which the opto-via holes are formed (FIG. 2f). The outer layers 10, 20 according to the first embodiment are layered on an upper and a lower side of the inner layer 30 according to the second embodiment, thereby forming the PCB with the optical waveguide. The inner layer 30 may have various shapes according to the intended use of the PCB, and plural inner layers may be inserted between the outer layers 10, 20. At this time, the number of inner and outer layers are prepared to correspond to the number of layers of the multi-layered PCB, and the electric- and opto-via holes are previously formed on the inner and outer layers, as in the first and second embodiments.

[0056] Referring to FIG. 4b, a part B of FIG. 4a, that is, the copper-clad part 37 is exposed and etched. In detail, after the outer layers 10, 20 are firstly layered on a CCL, the inner layer 30 is secondly layered on the resulting structure. The copper-clad part 37 is then removed to form an entrance for an optical-interfacing.

[0057] In FIG. 4c, a highly pure epoxy resin packing material 0.39 is filled into the entrance, i.e. a part C of the FIG. 4b in which the copper-clad part is removed. At this time, it is preferable that the epoxy resin packing material 39 has 95% or more light transmissivity so as to easily transmit light therethrough. If the packing material 39 is not filled into the entrance C, the entrance is easily deformed by an external impact.

[0058] Turning now to FIG. 4d, a drilling process is conducted, thereby forming via holes D in the multi-layered PCB. Each via hole is electroless- or electrolytic-plated on its inner wall, as shown in FIG. 4e. Reference numeral 40 denotes a plated layer.

[0059] In FIG. 4f, a circuit pattern E is formed on the multi-layered PCB.

[0060] The patterned multi-layered PCB is subjected to a solder resist 41 and gold plating step (FIG. 4g). The solder resist 41 is coated on the patterned multi-layered PCB so as to protect the insulated positions of the outer layer from an external impact or a surface treatment, and the gold plating step is conducted in order to improve solderability of a position on which electronic parts are to be mounted (PAD).

[0061] Therefore, a process of forming opto-via holes according to the present invention is advantageous in that an optical signal is stably transmitted from an outer layer of a PCB to an inner layer of the PCB without damage to an optical waveguide directly exposed to an external environment, because the inner layer is attached to the outer layer after the opto-via holes are previously formed in the inner and outer layers of the PCB.

[0062] Another advantage of the present invention is that the optical waveguide suitable to physical properties of the material constituting the PCB is easily inserted between the inner layer and the outer layer.

[0063] The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.