JP3405402B2 - Parallel transmission type optical module and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a parallel transmission type optical module for optical communication. The present invention also relates to the manufacturing method thereof.

[0002]

2. Description of the Related Art Optical communication uses optical fibers and semiconductor lasers (L
D), light emitting diodes (LEDs), photodiodes (PDs), optical switches, optical modulators, isolators, optical waveguides, and other passive and active devices have been expanding their application range due to high performance and high functionality. . In recent years, with the increasing demand for transmitting more information, parallel transmission, which performs data transmission between computer terminals, switches and large computers in parallel in real time, is drawing attention. There is a parallel transmission type module that integrates a plurality of light emitting or light receiving elements and a plurality of optical fibers to satisfy this function. Usually, a plurality of light emitting (light receiving) elements are monolithically arranged on the same semiconductor substrate, such as LD and PD arrays, and a plurality of optical fibers are arranged in one direction.

FIG. 7 shows an example of a parallel transmission optical module having a level of several hundreds of megahertz per channel. FIG. 7 (a) is a sectional view and FIG. 7 (b) is a plan view. The optical mounting board 24 and the ceramic electrical mounting board 28 are mounted on the common board 20 having good heat dissipation.
Are arranged. The optical mounting substrate 24 is usually made of silicon (Si) because of its heat dissipation and workability of the groove for mounting the optical fiber. An array of 12-channel LDs or PDs on the optical mounting substrate 24 with an insulating film such as SiO ₂ interposed therebetween.
21 (hereinafter, represented by LD21) is arranged. LD
The light emitted from 21 is coupled to the polymer-based optical waveguide 22 arranged in close proximity. The optical waveguide 22 converts the array pitch interval to a constant 250 μm, and the array optical fiber 23 is arranged at the emitting end. Array optical fiber 2
3 is usually formed in a ribbon shape, and is highly accurately fixed to the V groove 25 precisely formed by anisotropic wet etching.

As the electrical mounting substrate 28, an alumina substrate is usually used because of the ease of designing the multilayer wiring and the manufacturing cost. On the electric mounting substrate 28, electric elements such as the analog driver IC 26 of the LD 21 and the logic IC 27 are arranged. In the case of high speed driving, the electrical mounting substrate 28 is constructed in multiple layers. The optical mounting substrate 24 and the electrical mounting substrate 28 are electrically connected by wire bonds 29.

[0005]

In a parallel transmission type module that handles high-speed signals of gigahertz or higher, all channels must operate at high speed and independently, so that the wiring length between elements must be shortened, and Wire bonds need to be eliminated. Therefore, the module configuration of FIG. 7 has a problem that a problem of crosstalk between channels occurs.

On the other hand, by flip-chip mounting the electric element such as the IC 26 and the optical element such as the LD 21 on the same substrate, the distance between the elements can be reduced and the wire bond can be eliminated. However, there are the following problems. When the common substrate is Si, which is an optical mounting substrate, since Si is a semiconductor rather than an insulator, electrical crosstalk between channels occurs during high-speed operation. Further, since the substrate cannot be easily formed into a multi-layer structure, high speed operation is inconvenient. on the other hand,
When a ceramic multi-layer substrate such as alumina, which is advantageous for high-speed operation, is used as a common substrate, the alumina substrate has a heat conduction that is one digit or more worse than that of Si.
Becomes unstable. Further, since it is difficult to machine the ceramic substrate with high precision, it is difficult to form precision grooves for aligning optical fibers.

An object of the present invention is to solve the above problems and provide a parallel transmission type optical module in which both optical elements and electric elements are mounted together.

[0008]

A parallel transmission type optical module of the present invention is a Si substrate having an optical element mounted on a ceramic substrate.
The substrate is bonded, at least the electrical connection between the optical element and the ceramic substrate, the optical element is electrically connected to the metal electrode formed on the surface of the Si substrate through the insulating layer,
The metal electrode extends to the bottom surface of the Si substrate and is directly connected to the electrode formed on the ceramic substrate.

In addition to an optical element, an optical waveguide and an optical fiber are arranged on the Si substrate, the ceramic substrate is formed in a multilayer structure, and the electric element is a resin build-up formed on the ceramic substrate. The parallel transmission type optical module is arranged on a substrate.
Further, the electrical connection between the Si substrate and the ceramic substrate is performed through a through hole formed in the Si substrate, and in the through hole formed in the Si substrate, a metal electrode is formed after being insulated by an oxide film or the like after the penetration. , Connected to the electrodes formed on the ceramic substrate. The through hole is formed by polishing the rear surface of the Si substrate after anisotropic etching from the upper surface of the Si substrate. Furthermore, S of the ceramic substrate
The parallel transmission type optical module is characterized in that a heat dissipation via is provided in the i substrate joint portion.

Further, the present invention is a method of manufacturing a parallel transmission type optical module comprising a ceramic substrate and an Si substrate on which an optical element is mounted, which is bonded to the Si substrate surface through an insulating layer to the Si substrate bottom surface. A step of forming an extending metal electrode; a step of adhering the Si substrate on a ceramic substrate so that the metal electrode and an electrode formed on the ceramic substrate are directly connected; and an optical element electrically connected to the metal electrode. The present invention relates to a method for manufacturing a parallel transmission type optical module including a step of electrically connecting.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An LD, an optical waveguide, and an optical fiber are arranged on a Si substrate bonded on a ceramic substrate. The ceramic substrate is formed in a multilayer structure, and a control electric element such as a driver IC is arranged near the Si substrate. When high-density wiring is required, the electric element is arranged on a resin build-up board formed on a ceramic board. The electrical connection between the Si substrate and the ceramic is made through a through hole formed in the Si substrate. In the through hole,
A metal electrode is formed after being penetrated and insulated by an oxide film or the like, and connected to an electrode formed on the ceramic of the lower substrate. Here, the through hole is formed by anisotropic etching or mechanical processing, but the thickness of the Si substrate is reduced by polishing or the like in order to reduce the hole shape and the processing time. When the wiring length between the optical element and the electric element is made as short as possible, the electrode of the electric element is directly bonded to the electrode of the through hole.

Since the optical element and the electric element can be independently mounted on the respective substrates, the conventional problems such as wiring, substrate processing, and heat radiation caused by sharing the substrates can be solved. Further, the heat radiation of the LD can be further improved by providing the heat radiation via in the Si substrate bonding portion of the ceramic substrate.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is an example of a parallel transmission type optical module showing the present invention. FIG. 1 (a) is a sectional view and FIG. 1 (b) is a plan view. A Si substrate 5 on which an optical element is mounted is arranged on a mounting substrate, for example, a ceramic substrate 1 such as alumina. The Si substrate 5 is bonded to the ceramic substrate 1 with an adhesive, solder, or metal diffusion. The Si substrate 5 has the same structure as the optical substrate of a normal parallel transmission type optical module, and the LD array 2, the polymer array optical waveguide 3, and the optical fiber array 4 having a pitch of 250 μm are arranged.
In the polymer array optical waveguide 3, the pitch of the LD array 2 which is not uniform is converted into equal intervals. The optical fiber array 4 is accurately positioned in the V groove 6 formed by anisotropic wet etching or the like. Driver I of LD array 2
The C7 and the logic IC 8 are flip-chip mounted on the ceramic substrate 1 close to the Si substrate 5. LD array 2
And IC 7 are electrically connected to each other through through holes 10 formed in Si substrate 5 at the same pitch as LD array 2.
A through-hole electrode whose surface is, for example, gold (Au) is formed in advance in the through-hole 10 portion of the ceramic substrate 1 and is connected to the electrode 9 formed in the through-hole 10. The through hole 10 is formed by anisotropic wet etching similarly to the optical fiber V groove 6, for example. After the through hole 10 is formed, an insulating film such as a thermal oxide film is laminated on the Si surface of the hole portion, and the lead Au electrode 9 of the LD array 2 is further formed thereon. The lead electrode 9 and the through-hole electrode on the ceramic substrate 1 side are connected by, for example, melting gold-tin (AuSn) solder on the through-hole electrode. When a higher speed operation is required, the ceramic substrate 1 may have a multi-layer structure, or as shown in FIG.
The configuration is such that it is directly connected to the 0 through-hole electrode via the solder bump 11. Further, as shown in FIG. 3, by forming the heat dissipation vias 12 in the LD array 2 mounting portion of the ceramic substrate 1, the heat dissipation of the LD array 2 can be further improved.

Further, when the signal wiring is made high speed and high density, a multilayer buildup 12 is formed on the ceramic substrate 28 as shown in FIG.

As described above, by adopting the structure in which the Si substrate is laminated on the ceramic substrate and laminated, a mounting substrate which simultaneously satisfies the requirements for heat dissipation to optical elements, high-precision positioning, and high-speed electrical wiring for electrical elements is possible. Thus, it is possible to realize a high-speed parallel transmission type optical module at a gigahertz level, which has been difficult in the past.

In the present invention, a 12-channel LD having an array pitch of 250 μm is shown as an array element, but similar effects can be obtained with other pitches and channels. Also,
Although the polymer optical waveguide is arranged between the LD array and the optical fiber, the waveguide of another material or the waveguide may be omitted.

[0018]

EXAMPLE 1 A method of manufacturing the parallel transmission type optical module shown in FIG. 1 will be described with reference to process sectional views shown in FIG. 5 and a flow sheet shown in FIG. First, alumina powder, flux, organic binder, solvent and plasticizer are thoroughly mixed in a ball mill, and then spread on a carrier tape with a blade and dried to produce a green sheet. The green sheet is punched with a mold, filled with a conductive paste made of metal powder, and a plurality of printed conductor patterns are laminated,
Firing is performed to produce the ceramic multilayer wiring board 1 (step (a), FIG. 5 (a)).

Next, the V groove 6 and the through hole 10 are formed in the Si substrate 5 on which the optical element is mounted by anisotropic wet etching. When a 200 μm square etching window is provided on the Si substrate 5 and Si is etched, a quadrangular pyramid-shaped hole 10 having a depth of about 140 μm is formed. After forming a thermal oxide film on the surface of the Si substrate including the holes, the extraction Au electrode 9 of the LD array 2 is formed by the sputtering method (step (b), FIG. 5).
(B)). Next, the optical waveguide 3 is formed at a predetermined position. As the optical waveguide, conventionally known polymethylmethacrylate (PMMA), fluorinated polyimide, siloxane-based polymer or the like is used, and these resin solutions or precursor solutions are applied by spin coating and cured according to a predetermined curing method. Then, it is formed into a predetermined shape using photolithography (step (c), FIG. 5C). Next, the Si substrate 5 is polished from the back surface to a thickness of 100 μm, so that a through hole of about 60 μm square is formed at the bottom. The thickness of the Si substrate 5 after polishing depends on the pitch of the through holes 10, and if the through holes 10 are arranged in a staggered manner and the pitch is doubled, the thickness of the Si substrate 5 can also be doubled. .

The through hole of the Si substrate 5 for mounting the optical element thus formed is aligned so that it can be joined to the through hole electrode of the ceramic multilayer wiring substrate 1, and epoxy adhesive, solder, or metal diffusion. After bonding by, the gold-tin (AuSn) solder is melted on the through-hole electrode and joined to the extraction electrode 9 (step (e), FIG. 5 (e)).

Finally, the driver IC 7 and the logic IC 8 are flip-chip bonded onto the substrate 1, the 12-channel LD 2 having an array pitch of 250 μm and the optical fiber 4 are bonded onto the Si substrate 5, as shown in FIG. The parallel transmission type optical module is completed (step (f)).

In the above embodiment, a through hole is formed,
I have an electrical connection, but instead of, for example, a through hole,
The end portion of the substrate may be formed obliquely, and the metal electrode may be formed so as to continue from the top surface to the bottom surface of the substrate, and the metal electrode for electrical connection to the optical element is fixed on the Si substrate.
Any structure may be used as long as it can be directly connected to the ceramic substrate on the bottom surface of the substrate.

Example 2 A parallel transmission type optical module shown in FIG. 2 was manufactured. In this example, the size of the Si substrate 5 is such that it substantially covers the main surface of the ceramic substrate 1, and in addition to the through holes for optical elements shown in Example 1, electrical elements are mounted. After forming through-holes and forming a thermal oxide film inside each through-hole, Example 1
Similarly, the optical waveguide 3 is formed and bonded to a ceramic substrate. After that, the optical element is formed on the metal electrode 9 on the Si substrate, the optical fiber 4 is formed on the V groove 6, and the electric elements 7 and 8 are formed on the ceramic substrate by solder bumps. It was formed by connecting to the through-hole electrode.

Example 3 Similar to Example 1, after a required number of alumina green sheets were bonded together, a heat radiating via 12 was formed by making a hole using a mold. Then, as in Example 1, Si
The parallel transmission type optical module shown in FIG. 3 is completed by bonding the substrate 5 and mounting the optical element and the electric element. High heat dissipation can be obtained by setting the size of the heat dissipation via formed here to about φ500 μm. It is also possible to attach a radiation fin or the like via a radiation via.

Example 4 As in Example 1, after the Si substrate 5 is bonded, the resin buildup 13 is formed on the electric element mounting portion. The resin buildup 13 is formed by the following procedure. 1. A photosensitive insulating resin is applied to the substrate, and the insulating pattern is etched by exposure and development. 2. A conductive pattern is formed with photoresist. 3. Attach the conductor by electroless plating. 4. Remove photoresist. By repeating the above steps as many times as necessary, a buildup having a desired layer structure can be formed.

The electric elements 7 and 8 are mounted on the build-up 13.
Are flip-chip connected to complete the parallel transmission type optical module shown in FIG.

[0027]

As described above, according to the present invention, a parallel transmission type optical module capable of transmitting and receiving high speed signals can be realized. The reason is that a metal electrode for electrically connecting to an optical element is formed on a Si substrate, the metal electrode is extended to the bottom surface of the Si substrate, and the portion is directly connected to the ceramic substrate. This is because, as compared with the method using wire bonding, it is possible to connect the wiring inside the ceramic substrate with high reliability. Also, since wire bonding is unnecessary, crosstalk is eliminated, and
It is possible to bring the optical element and the electric element close to each other, and it is possible to cope with high-speed signals of gigahertz or higher.

[Brief description of drawings]

FIG. 1 is a cross-sectional view (a) and a top view (b) of a parallel transmission type optical module configuration of the present invention.

FIG. 2 is a cross-sectional view of a parallel transmission type optical module according to another embodiment of the present invention.

FIG. 3 is a sectional view of a parallel transmission type optical module according to another embodiment of the present invention.

FIG. 4 is a sectional view (a) and a top view (b) of a parallel transmission type optical module configuration according to another embodiment of the present invention.

5A to 5C are process cross-sectional views illustrating a method of manufacturing the parallel transmission type optical module shown in FIG.

6 is a flow sheet of the manufacturing method of FIG.

FIG. 7 is a cross-sectional view (a) and a top view (b) of a conventional parallel transmission type optical module.

[Explanation of symbols]

1 ... Ceramic substrate 2 ... LD array 3 ... Optical waveguide array 4 ... Optical fiber array 5: Si substrate 6 ... V groove 7 ... Driver IC 8 ... Logic IC 9 ... Electrode 10 ... through hole 11 ... Solder bump 12 ... Heat dissipation via 13 ... Build up

Continuation of front page (56) Reference JP-A-11-97797 (JP, A) JP-A-8-78657 (JP, A) JP-A-10-275957 (JP, A) JP-A-7-273401 (JP , A) JP-A-2-220491 (JP, A) JP-A-5-304306 (JP, A) JP-A-10-311936 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) H01S 5/00-5/50 G02B 6/42 H01L 33/00 H04B 10/00 JISST file (JOIS)

Claims (16)

(57) [Claims] 1. An S in which an optical element is mounted on a ceramic substrate.
The i substrate is bonded, and at least the electrical connection between the optical element and the ceramic substrate is electrically connected to the metal electrode formed on the surface of the Si substrate via the insulating layer, and the metal electrode is connected to the Si electrode. A parallel transmission type optical module, which is formed by directly connecting to an electrode formed on a ceramic substrate and extending to the bottom surface of the substrate. 2. The parallel transmission type optical module according to claim 1, wherein an optical waveguide and an optical fiber are further arranged on the Si substrate. 3. The parallel transmission type optical module according to claim 1, wherein the ceramic substrate is formed in a multilayer structure. 4. The parallel transmission type optical module according to claim 1, wherein the electric element is arranged on a resin buildup formed on a ceramic substrate. 5. The metal electrode for electrical connection between the optical element and the ceramic substrate extends to the bottom surface of the Si substrate through a through hole formed in the Si substrate. The parallel transmission type optical module according to any one of 1. 6. The parallel transmission type according to claim 5, wherein the through hole is formed by polishing the rear surface of the Si substrate after anisotropic etching from the upper surface of the Si substrate. Optical module. 7. The parallel transmission type optical module according to claim 1, wherein a heat dissipation via is provided in the Si substrate joint portion of the ceramic substrate. 8. The Si substrate is bonded to substantially the entire surface of the ceramic substrate, and the electric element is connected to the ceramic substrate through a through hole formed in the Si substrate. The parallel transmission type optical module described in. 9. A ceramic substrate on which an optical element is mounted, S
A method of manufacturing a parallel transmission type optical module, which comprises bonding i substrates together, the method comprising:
Forming a metal electrode extending to the bottom surface of the substrate;
A step of laminating a substrate on a ceramic substrate so that the metal electrode and an electrode formed on the ceramic substrate are directly connected; and a step of electrically connecting an optical element to the metal electrode. Method for manufacturing parallel transmission type optical module. 10. The Si substrate further includes an optical waveguide,
The method for manufacturing a parallel transmission type optical module according to claim 9, wherein an optical fiber is arranged, and a groove forming step for arranging the optical fiber is included. 11. The method of manufacturing a parallel transmission type optical module according to claim 9, further comprising the step of forming a ceramic substrate in a multilayer structure. 12. The method of manufacturing a parallel transmission type optical module according to claim 9, further comprising a step of forming a resin build-up on the ceramic substrate and a step of disposing an electric element on the build-up. 13. A through hole for extending a metal electrode for electrical connection between the optical element and the ceramic substrate to the bottom surface of the Si substrate is formed at the same time as forming a groove for arranging an optical fiber in the Si substrate. The method for manufacturing a parallel transmission type optical module according to claim 9 or 10, further comprising steps. 14. The method of manufacturing a parallel transmission type optical module according to claim 13, wherein the through hole is formed by anisotropically etching the upper surface of the Si substrate and then polishing the back surface of the Si substrate. . 15. The method of manufacturing a parallel transmission type optical module according to claim 9, further comprising the step of forming a heat dissipation via in a Si substrate bonding portion of the ceramic substrate. 16. A Si substrate covering substantially the entire surface of the ceramic substrate is bonded, and the electric element is connected to the ceramic substrate through a through hole formed in the Si substrate. 15. The method for manufacturing a parallel transmission type optical module according to item 15.