Optical module and method for manufacturing the optical module

Abstract

To provide an optical module which can be improved in high frequency characteristics, and a method for manufacturing the optical module.SOLUTION: An optical module comprises: a lid having a bump, wiring, and a through-via; a first IC which is flip-chip mounted; an optical modulator which is flip-chip mounted; a first heat radiation block which is connected to the first IC; a temperature adjustment element which is connected to the optical modulator; and a package which has an opening and accommodates the first IC, the optical modulator, the first heat radiation block, and the temperature adjustment element in the opening. The first IC is electrically connected to the optical modulator via the wiring and electrically connected to the bump via the through-via. The first heat radiation block and the temperature adjustment element are connected to an internal third plane of the package with a second heat conductive adhesive. The package is hermetically sealed by shutting the opening by the lid.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an optical module and a method for manufacturing the optical module.

Background Art

[0002] Patent Document 1 describes an optical module including an optical integrated circuit, an electronic integrated circuit, and a molded substrate in which the optical integrated circuit and the electronic integrated circuit are embedded. The molded substrate has a first redistribution layer disposed on a first surface and a second redistribution layer provided on a second surface. The first redistribution layer has an opening for connecting an optical fiber to the optical integrated circuit. The second redistribution layer has a BGA (Ball Grid Array). The first redistribution layer and the second redistribution layer are connected to each other via an electrical wiring.

[0003] Patent Document 2 describes an integrated package configuration including a circuit board, an electronic IC, an optical IC, a carrier, and a BGA. The electronic IC is connected to the optical IC and the circuit board. The carrier has a redistribution layer. The carrier, the electronic IC, and the optical IC are integrated by POP (Package On Package). The carrier is made of a molding material. The carrier encloses the electronic IC and the optical IC. The electronic IC is physically connected to the redistribution layer. The electronic IC is connected to the circuit board via the redistribution layer, a through mold via (TMV), and a BGA.

[0004] Patent Document 3 describes an optoelectronic module including an optical chip and a molded substrate. The optical chip is embedded in the molded substrate, and the surface of the optical chip is exposed. The molded substrate has a TMV. An IC chip is flip-chip mounted on the molded substrate. The IC chip is electrically connected to the optical chip and the TMV. An optical connector having an optical waveguide is flip-chip mounted on the molded substrate, and the optical connector is optically coupled to the optical chip.

[0005] Patent Document 4 describes a chip-scale surface mount package that includes a substrate, a lid, a seal ring, and a monolithic microwave integrated circuit (MMIC). The MMIC is mounted to the substrate within a cavity in the lid. The lid has an electromagnetic shield and through vias. The substrate has through-substrate vias and solder balls. The seal ring attaches the lid to the substrate. The electromagnetic shield is connected to the MMIC via the through vias. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2020 / 173561 [Patent Document 2] U.S. Patent No. 10025047 [Patent Document 3] US Patent Application Publication No. 2018 / 0180808 [Patent Document 4] US Patent Application Publication No. 2019 / 0259676 Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, in an optical module, the transmission line of a high-frequency signal may be long, and particularly in the case of a high-frequency signal, problems such as an increase in conductor loss of the transmission line wiring and dielectric loss of the insulator used for the wiring may occur. For example, when the high-frequency signal includes a frequency component of 50 GHz or more, the loss in the transmission line or the like causes the band of the high-frequency signal to decrease and the transmission characteristics of the optical signal to deteriorate. Further, in an optical module including a package, a driver IC, and an optical modulator, each of the driver IC and the package, and the driver IC and the optical modulator may be connected to each other via bonding wires. In this case, since wire bonding has a large parasitic inductance, there is a concern that the frequency characteristics of the high-frequency signal will not be good.

[0008] An object of the present disclosure is to provide an optical module capable of improving the frequency characteristics of a high-frequency signal and a method for manufacturing the optical module.

Means for Solving the Problems

[0009] The optical module according to the present disclosure includes bumps formed on a first surface, wirings formed on a second surface opposite to the first surface, through vias penetrating between the first surface and the second surface, a lid having airtightness, a first IC flip-chip mounted on the second surface, an optical modulator flip-chip mounted on the second surface, a first heat dissipation block connected to the first IC by a first thermally conductive adhesive, a temperature adjustment element connected to the optical modulator, and a package having an opening and accommodating the first IC, the optical modulator, the first heat dissipation block, and the temperature adjustment element in the opening. The first IC is electrically connected to the optical modulator via the wiring and is electrically connected to the bumps via the through vias. The first heat dissipation block and the temperature adjustment element are connected to a third surface inside the package by a second thermally conductive adhesive. The package is hermetically sealed by closing the opening with the lid.

[0010] The manufacturing method of the optical module according to the present disclosure has bumps formed on a first surface, wirings formed on a second surface opposite to the first surface, and through vias penetrating between the first surface and the second surface, and includes a step of preparing a lid having airtightness, a step of connecting a first IC to a first heat dissipation block with a first thermally conductive adhesive, a step of connecting an optical modulator to a temperature adjustment element, a step of flip-chip mounting the first IC and the optical modulator on the second surface of the lid to electrically connect the first IC to the optical modulator via the wiring and electrically connect the first IC to the bumps via the through vias, a step of applying a second thermally conductive adhesive to a third surface inside the package, a step of holding the first heat dissipation block, the first IC, the temperature adjustment element, and the optical modulator in the opening of the package and connecting the first heat dissipation block and the temperature adjustment element to the third surface of the package with the second thermally conductive adhesive, and a step of closing the opening of the package with the lid and hermetically sealing the package.

Effect of the Invention

[0011] According to the present disclosure, the frequency characteristics of high-frequency signals can be improved.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

[0013] [Description of Embodiments of the Present Disclosure] First, the contents of an embodiment of an optical module and a method for manufacturing the optical module according to the present disclosure will be listed and described. An optical module according to an embodiment includes bumps formed on a first surface, wirings formed on a second surface opposite to the first surface, through vias penetrating between the first surface and the second surface, a lid having airtightness, a first IC flip-chip mounted on the second surface, an optical modulator flip-chip mounted on the second surface, a first heat dissipation block connected to the first IC by a first thermally conductive adhesive, a temperature adjustment element connected to the optical modulator by solder such as gold-tin solder, and a package having an opening and accommodating the first IC, the optical modulator, the first heat dissipation block, and the temperature adjustment element in the opening. The first IC is electrically connected to the optical modulator via the wiring and is also electrically connected to the bumps via the through vias. The first heat dissipation block and the temperature adjustment element are connected to a third surface inside the package by a second thermally conductive adhesive. The package is hermetically sealed by closing the opening with the lid.

[0014] A method for manufacturing an optical module according to an embodiment includes: preparing a lid having airtightness, a bump formed on a first surface, wiring formed on a second surface opposite to the first surface, and a through via penetrating between the first surface and the second surface; connecting a first IC to a first heat dissipation block with a first thermally conductive adhesive; connecting an optical modulator to a temperature adjustment element; flip-chip mounting the first IC and the optical modulator on the second surface of the lid to electrically connect the first IC to the optical modulator via the wiring and electrically connect the first IC to the bump via the through via; applying a second thermally conductive adhesive to a third surface inside the package; holding the first heat dissipation block, the first IC, the temperature adjustment element, and the optical modulator in an opening of the package and connecting the first heat dissipation block and the temperature adjustment element to the third surface of the package with the second thermally conductive adhesive; and closing the opening of the package with the lid and hermetically sealing the package.

[0015] In an optical module and a method for manufacturing an optical module according to an embodiment, a first heat dissipation block and a temperature adjustment element are connected to a third surface of a package. A first IC is connected to the first heat dissipation block with a first thermally conductive adhesive, and an optical modulator is connected to the temperature adjustment element with solder such as gold-tin solder. The first IC and the optical modulator are connected to the second surface of the lid, and bumps for supplying an electrical signal from a circuit board to the lid are fixed to a first surface facing the opposite side of the second surface of the lid. Therefore, the first IC is connected to the second surface of the lid, and the bumps are fixed to the first surface of the lid. Since an electrical signal is supplied from the circuit board to the lid via the bumps, a high-frequency signal is supplied from the circuit board via the bumps and the lid. Therefore, the transmission line of the high-frequency signal can be shortened, and the loss of the high-frequency signal can be reduced. Thus, the high-frequency characteristics can be improved. In particular, by connecting to a circuit board such as an interposer capable of forming a fine circuit pattern using bumps (for example, bumps having a diameter of 300 μm or less) smaller in size than solder balls (for example, bumps having a spherical shape with a diameter of 300 to 500 μm) for the purpose of connection to a printed circuit board or the like, high-frequency signals exceeding 50 GHz can be transmitted well.

[0016] The lid may contain glass in the base material. In this case, the thermal resistance of the lid can be increased.

[0017] The second thermally conductive adhesive may have a thickness greater than that of the first thermally conductive adhesive.

[0018] The package may have a heat dissipation member, and the heat dissipation member may have a third surface. In this case, the heat dissipation performance from each of the first heat dissipation block and the temperature adjustment element placed on the third surface can be further enhanced.

[0019] The third surface of the package may be disposed to face the second surface of the lid.

[0020] The heat dissipation member may have an enclosure for accommodating the second thermally conductive adhesive on the third surface. In this case, when the second thermally conductive adhesive is applied to the third surface of the package, leakage of the second thermally conductive adhesive is suppressed by the enclosure.

[0021] The optical module may further include a second IC flip-chip mounted on the second surface. The second IC is electrically connected to the optical modulator via the first IC, and the second IC may be connected to the second heat dissipation block. The second heat dissipation block may be connected to the third surface by the second thermally conductive adhesive. In this case, since the second IC is connected to the second surface of the lid inside the package, a high-frequency connection with the first IC can be made via the second surface. Therefore, since the second IC and the first IC are directly connected by a transmission line with a characteristic impedance controlled via the lid, deterioration of the high-frequency signal with respect to the first IC can be more reliably suppressed.

[0022] [Details of Embodiments of the Present Disclosure] Specific examples of an optical module and a method for manufacturing the optical module according to embodiments of the present disclosure will be described below with reference to the drawings. It should be noted that the present invention is not limited to the following examples, but is intended to cover all modifications included in the scope of the claims and within the scope equivalent to the claims. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate. Also, the drawings may be drawn with some parts simplified or exaggerated for ease of understanding, and the dimensional ratios and the like are not limited to those described in the drawings.

[0023] FIG. 1 is a plan view showing the internal structure of the optical module 1 according to the present embodiment. FIG. 2 is a longitudinal sectional view showing the optical module 1. As shown in FIGS. 1 and 2, the optical module 1 is, for example, an optical transmission module (TOSA: Transmitter Optical Sub Assembly) including a rectangular parallelepiped package 2 and an optical connector 3. The package 2 is made of, for example, at least one of materials such as airtight ceramic, glass, and metal. The package 2 extends in a direction D1 which is the longitudinal direction of the package 2, a direction D2 which is the width direction of the package 2, and a direction D3 which is the height direction of the package 2. For example, the direction D1, the direction D2, and the direction D3 are orthogonal to each other.

[0024] The package 2 has a pair of first side walls 2b located at the end in the direction D1, a pair of second side walls 2c located at the end in the direction D2, and a heat sink 2d (heat radiating member) located at one end in the direction D3. The optical connector 3 penetrates the first side wall 2b. The heat sink 2d is made of, for example, copper tungsten (CuW). The heat sink 2d may be made of, for example, a metal material other than CuW or a ceramic such as aluminum nitride (AlN). An internal space 2A of the package 2 is defined in the region surrounded by the pair of first side walls 2b, the pair of second side walls 2c, and the heat sink 2d. Parts of the optical module 1 are accommodated in the internal space 2A. The optical module 1 further includes a lid 5 and a sealing material 6 that seal the internal space 2A. The lid 5 is made of, for example, a material that transmits visible light. The base material of the lid 5 contains, as an example, glass. For example, it is preferable that the linear expansion coefficient is adjusted according to the components mounted on the lid 5 by glass ceramic in which part of the glass components are crystallized or aluminosilicate glass. For example, the linear expansion coefficients of silicon semiconductors and InP compound semiconductors are 3.0 ppm / °C and 4.5 ppm / °C, respectively. Considering that, for example, an optical modulator 12 manufactured by an InP compound semiconductor is temperature-controlled at a constant temperature by a TEC 15, it is desirable to use a lid having airtightness in the range of a linear expansion coefficient of 0 to 4.5 ppm / °C. Thereby, for example, the stress on the bump connection described later can be relaxed with respect to the temperature change of the package 2. By relaxing the stress, a more reliable bump connection can be configured.

[0025] FIG. 1 shows the internal space 2A of the package 2 with the lid 5 and the sealing material 6 omitted, as viewed in a plan view from the direction D3. The internal space 2A is formed inside the opening 2C of the package 2, and a driver IC 11 (first IC), a light modulator 12, and an optical component 20 are provided in the opening 2C. The driver IC 11 is connected to the heat sink 2d via a first heat dissipation block 13 and a second thermally conductive adhesive 14. The first heat dissipation block 13 is adhered to the third surface 2f of the package 2 via the second thermally conductive adhesive 14. The driver IC 11 is adhered to the first heat dissipation block 13 via a first thermally conductive adhesive 18. The second thermally conductive adhesive 14 has a thickness greater than that of the first thermally conductive adhesive 18 in the direction D3.

[0026] The first thermally conductive adhesive 18 and the second thermally conductive adhesive 14 are, for example, silver paste. The first thermally conductive adhesive 18 and the second thermally conductive adhesive 14 may be adhesives having thermal conductivity and conductivity other than silver paste. The light modulator 12 is connected to the heat sink 2d via a temperature adjustment element, a TEC (Thermo Electric Cooler) 15, and the second thermally conductive adhesive 14. The TEC 15 is adhered to the third surface 2f of the package 2. For example, the third surface 2f is formed on the heat sink 2d. The package 2 has a surround 2k that projects along the direction D3 from the third surface 2f. The surround 2k is formed so as to surround the driver IC 11 and the light modulator 12 when the package 2 is viewed along the direction D3. For example, the shape of the surround 2k when viewed along the direction D3 is a rectangular frame shape. The second thermally conductive adhesive 14 is applied inside the surround 2k when viewed along the direction D3.

[0027] For example, the optical component 20 includes at least one of a lens, a mirror, a beam splitter, and an optical filter. The optical component 20 inputs and outputs an optical signal to and from the optical modulator 12. The optical component 20 is optically coupled to the optical connector 3. The optical module 1 has, for example, two optical connectors 3 arranged along the direction D2. Local light emission L2 from outside the optical module 1 is input into the internal space 2A of the optical module 1 through one of the two optical connectors 3. Signal light L1 is output from the inside of the optical module 1 to the outside of the package 2 through the other of the two optical connectors 3. The optical component 20 inputs and outputs the signal light L1 and the local light emission L2 to and from the optical connector 3 and the optical modulator 12. Regarding the direction, the direction in which the signal light L1 is output from the optical connector 3 to the outside of the package 2 may be referred to as front, front side, or forward, and the direction opposite to the front, front side, or forward may be referred to as rear, rear side, or backward. For example, the local light emission L2 output from the optical connector 3 rearward, to the rear side, or in the backward direction is input into the optical component 20 from the outside of the package 2. However, these directions are for convenience of explanation and do not limit the direction in which the components are arranged, etc.

[0028] The optical module 1 further includes a plurality of conductive bumps (first bumps) 7 fixed to the lid 5. For example, the plurality of bumps 7 are two-dimensionally arranged along directions D1 and D2 to form a BGA (Ball Grid Array). The lid 5 is electrically connected to the circuit board 8 by the bumps 7. The driver IC 11 and the optical modulator 12 are arranged side by side along direction D1, and the driver IC 11, the lid 5, the bumps 7, and the circuit board 8 are arranged side by side in this order along direction D3. The lid 5 has a first surface 5c to which the bumps 7 are fixed and a second surface 5b on which the driver IC 11 and the optical modulator 12 are flip-chip mounted. The first surface 5c is exposed outside the package 2. The second surface 5b faces the internal space 2A. That is, in the lid 5, the second surface 5b is the surface opposite to the first surface 5c. An optical component 20 is mounted on the second surface 5b, and the optical modulator 12 is optically coupled to the optical component 20. The lid 5 has a plurality of wirings 5d fixed to the second surface 5b, and the driver IC 11 has a plurality of wirings 11b and bumps 9b facing the lid 5. The wiring 5d and the wiring 11b are electrically connected to each other via the bumps 9b. Here, the bump 7 is a protruding metal for obtaining an electrical connection, and typical examples include solder balls, C4 bumps (solder bumps), gold bumps, silver bumps, copper bumps, indium bumps, etc. A solder ball is one in which the bump is made of solder and is a form of the bump.

[0029] The optical modulator 12 has a wiring 12b and bumps (second bumps) 9c facing the lid 5, and the wiring 5d and the wiring 12b are electrically connected to each other via the bumps 9c. For example, the wiring 5d, the bumps (second bumps) 9b, 9c, the wiring 11b, and the wiring 12b constitute high-frequency wiring. The bumps 9b, 9c are, for example, gold stud bumps made of gold (Au). Note that the portion of the wiring 12b to which the bump 9c is connected may be referred to as a pad. The optical modulator 12 may further have dummy bumps 9d (see FIG. 2). The dummy bumps 9d connect, for example, pads formed on the optical modulator 12 and pads formed on the lid 5. The dummy bumps may be referred to as dummy bumps including the pads connected by the dummy bumps. The dummy bumps 9d are formed to ensure sufficient mechanical strength between the optical modulator 12 and the lid 5 and do not contribute to electrical connection. For example, the dummy bumps 9 are connected to the ground potential or are electrically floating. The lid 5 is, for example, a glass substrate with micro vias (TGV: Through Glass Vias). That is, the lid 5 has through vias (TGV) 5f, and the wiring 5d of the lid 5 is electrically connected to bumps 7 fixed to the first surface 5c via the through vias 5f. The bumps 7 are, for example, electrically connected to the circuit board 8. By the connection via the bumps 7, an electrical signal can be supplied from the circuit board 8 to the wiring 5d of the lid 5 with a relatively short wiring length.

[0030] A high-frequency signal is supplied to the lid 5 from the first surface 5c of the lid 5 via the bump 7, and the high-frequency signal is supplied to the driver IC 11 via the lid 5 and the bump 9b. The driver IC 11 supplies an electrical signal with a controlled characteristic impedance to the optical modulator 12 via the bump 9b, the wiring 5d, and the bump 9c. More specifically, on the second surface 5b of the lid 5, for example, a transmission line is formed by the wiring 5d. For example, the transmission line is configured as a coplanar line by four wirings (GSSG wirings) that are parallel to each other and extend along the direction D1. The GSSG wiring is composed of a ground wiring (G), a signal wiring (S), a signal wiring (S), and a ground wiring (G) that are arranged along the direction D2. For example, a differential signal, which is a high-frequency signal, is transmitted from the driver IC 11 to the optical modulator 12 by the two central signal wirings S, S. By transmitting the high-frequency signal through the transmission line, the influence of the inductance of the signal wiring can be reduced and the frequency characteristics can be improved.

[0031] The wiring 5d that constitutes the transmission line may be composed of a single metal layer, may be composed of two metal layers laminated along the direction D3, or may be composed of three or more metal layers. When it is composed of two or more metal layers, an insulating film that insulates the electrical wiring of each metal layer may be formed on the second surface 5b of the lid 5. When the wiring 5d has two metal layers, the transmission line may be configured as a coplanar line with a ground layer, for example. In this case, for example, a ground layer is formed in the layer closer to the first surface 5c of the lid 5 (one of the two metal layers), the coplanar line layer described above is formed in the layer farther from the first surface 5c of the lid 5 (the other of the two metal layers), and the ground wiring (G) provided in the ground layer and the coplanar line layer may be electrically connected via a through hole. That is, the ground layer is disposed between the coplanar wiring layer and the lid 5.

[0032] Note that in the drawings, only the high-frequency wiring is illustrated for simplicity. Wiring such as power supply, ground, and control signals other than the high-frequency wiring is also electrically connected to the circuit board 8 via the lid 5 and the bumps 7, similar to the high-frequency wiring. For example, the lid 5 is housed in a recess 2j formed at an end of the package 2 opposite to the heat sink 2d of the package 2. The recess 2j defines the opening 2C of the package 2. The recess 2j has a rectangular shape, for example, outside the internal space 2A when viewed along the direction D3. The sealing material 6 is interposed between the lid 5 housed in the recess 2j and the package 2. The material of the sealing material 6 is not particularly limited, but is, for example, glass or solder.

[0033] Next, a method for manufacturing the optical module according to the present embodiment will be described. Hereinafter, a method for assembling the above-described optical module 1 will be described. First, as shown in FIG. 3, the driver IC 11 and the first heat dissipation block 13 are connected to each other (step of connecting the first IC to the first heat dissipation block). Then, the optical modulator 12 and the TEC 15 are connected to each other (step of connecting the optical modulator to the temperature adjustment element).

[0034] Also, the wiring 5d on the second surface 5b includes pads, and bumps 9b and 9c are formed on these pads (the step of forming bumps), and a lid 5 with a plurality of bumps 7 fixed to the first surface 5c of the lid 5 is prepared (the step of preparing a lid). Here, the bump 7 may be any of a C4 bump, a gold bump, a silver bump, a copper bump, an indium bump, etc., and may have a diameter smaller than that of a general-purpose solder ball, which is 300 to 500 μm. As shown in FIG. 4, a driver IC 11 is connected to the second surface 5b of the lid 5. Then, an optical modulator 12 is connected to the second surface 5b (the step of electrically connecting). Specifically, the driver IC 11 is flip-chip mounted on the lid 5 with the bump 9b fixed to the pad of the wiring 5d. At this time, the pad of the wiring 11b of the driver IC 11 is joined to the bump 9b. Also, the pad of the wiring 12b of the optical modulator 12 is joined to the bump 9c. Note that the bump 9b may be formed on the pad of the wiring 11b of the driver IC 11 and joined to the pad of the wiring 5d of the lid 5. Also, the bump 9c may be formed on the pad of the wiring 12b of the optical modulator 12 and joined to the pad of the wiring 5d of the lid 5.

[0035] As shown in FIG. 5, an optical component 20 is mounted on the second surface 5b of the lid 5 (the step of mounting an optical component). More specifically, optical alignment is performed with respect to the light input / output port of the optical modulator 12, which is the end face of the optical waveguide formed by cleavage of the modulator chip, and the optical component 20 is fixed to the second surface 5b with resin (the step of fixing an optical component with resin). In this optical alignment, for example, alignment of a lens that generates collimated light output from the optical modulator 12 to the optical connector 3, alignment of a lens that couples the collimated light output from the optical connector 3 to the waveguide end face of the optical modulator 12, and mounting of a mirror on the lid 5 are performed.

[0036] As shown in FIG. 6, a second thermally conductive adhesive 14 is applied to the inner portion of the enclosure 2k in the third surface 2f (step of applying the second thermally conductive adhesive). Then, the lid 5 on which the driver IC 11, the optical modulator 12, and the optical component 20 are mounted is housed in the recess 2j of the package 2. As shown in FIG. 7, the first heat dissipation block 13 and the TEC 15 are pressed against the second thermally conductive adhesive 14 to connect the third surface 2f of the package 2 to the first heat dissipation block 13 and the TEC 15 (step of connecting to the third surface of the package). At this time, the connection state of the first heat dissipation block 13 and the TEC 15 to the third surface 2f of the package 2 by the second thermally conductive adhesive 14 may be confirmed by looking through the lid 5 with visible light (step of confirming the connection state).

[0037] The total thickness of the thickness (length along the direction D3) of the driver IC 11, the thickness (length along the direction D3) of the first heat dissipation block 13, and the thickness of the first thermally conductive adhesive 18 varies due to manufacturing variations (manufacturing variations) of each. Regarding the coating thickness of the second thermally conductive adhesive 14, it is determined in consideration of the variations between the total thickness after soldering the optical modulator 12 and the TEC 15 connected by gold-tin solder or the like and the total thickness after joining the driver IC 11 and the first heat dissipation block 13 connected by the first thermally conductive adhesive 18. For example, the thickness variation of the TEC 15 composed of a plurality of members is the largest, having a manufacturing variation of about ±150 μm including the joint thickness of gold-tin solder at most. On the other hand, the total thickness variation of the driver IC 11 and the first heat dissipation block 13 connected by the first thermally conductive adhesive 18 is about ±100 μm at most. Therefore, if the first heat dissipation block 13 and the dimensions of the recess 2j of the package 2 are designed so that the average values of the respective total thicknesses are the same, by applying the second thermally conductive adhesive 14 thicker than 300 μm, the heat generated by the driver IC 11, the signal source IC 21, and the TEC 15 can be reliably dissipated through the third surface 2f of the package 2. At the same time, the lid 5 is housed in the recess 2j of the package 2, and the package 2 can be reliably hermetically sealed with the sealing material 6.

[0038] Further, the optical connector 3 (specific example: an optical fiber held by the stub of the optical connector 3) is aligned with respect to the optical component 20 so that the collimated light from the optical component 20 is optically coupled to the optical connector 3, and the optical connector 3 is fixed to the package 2 (step of fixing the optical connector). At this time, for example, it is hermetically sealed so that no gap is formed between the periphery of the portion of the optical connector 3 passing through the package 2 and the package 2. As shown in FIG. 8, a sealing material 6 is inserted between the lid 5 housed in the recess 2j of the package 2 and the package 2 to seal the package 2 (step of hermetically sealing the package). Then, after connecting the circuit board 8 to the bumps 7, a series of steps is completed.

[0039] Next, the effects obtained from the optical module 1 according to the present embodiment and the manufacturing method of the optical module will be described. First, the optical transmission module 100 according to the reference example will be described with reference to FIGS. 10 and 11. As shown in FIGS. 10 and 11, the optical transmission module 100 includes a package 101, a driver IC 103 fixed to the inner surface 101b of the package 101 via a heat dissipation block 102, and an optical modulator 105 fixed to the inner surface 101b via a temperature modulation element 104. The optical transmission module 100 further includes an optical component 106 that inputs and outputs an optical signal to and from the optical modulator 105, and an optical connector 107 that transmits and receives the optical signal to and from the outside of the package 101 with respect to the optical component 106.

[0040] The optical transmission module 100 makes an electrical connection of a high-frequency signal to a signal source IC 110 located outside the optical transmission module 100 via an FPC (Flexible Printed Circuit) 111. In the optical transmission module 100, a ceramic package 101 is used. The package 101 has an internal space 101c and a feed-through 101d, and the feed-through 101d penetrates the wall 101f of the package 101. A high-frequency signal is supplied to the internal space 101c of the optical transmission module 100 via the FPC 111 and the feed-through 101d. Therefore, the transmission line of the high-frequency signal is relatively long, and there may be a problem that the loss of the high-frequency signal increases.

[0041] Inside the optical transmission module 100, between the driver IC 103 and the package 101, and between the driver IC 103 and the optical modulator 105, each is connected to each other via a bonding wire 113. Wire bonding has a concern that the parasitic inductance is large and the frequency characteristics of the high-frequency signal become poor. In particular, when the high-frequency signal includes a frequency component of 50 GHz or more, a sufficient band cannot be obtained to pass them.

[0042] On the other hand, in the optical module 1 and the method of manufacturing the optical module according to the present embodiment, the first heat dissipation block 13 and the TEC 15 are connected to the third surface 2f of the package 2. The driver IC 11 is connected to the first heat dissipation block 13 by the first thermally conductive adhesive 18, and the optical modulator 12 is connected to the TEC 15. The driver IC 11 and the optical modulator 12 are connected to the second surface 5b of the lid 5, and a bump 7 for supplying an electrical signal from the circuit board 8 to the lid 5 is fixed to the first surface 5c of the lid 5 facing the outside of the package 2. Therefore, the driver IC 11 is connected to the second surface 5b of the lid 5, and the bump 7 is fixed to the first surface 5c of the lid 5. And since an electrical signal is supplied from the circuit board 8 to the lid 5 via the bump 7, a high-frequency signal is supplied from the circuit board 8 via the bump 7 and the lid 5. Therefore, since the wiring line of the high-frequency signal can be made relatively short, the loss of the high-frequency signal can be reduced. Therefore, the frequency characteristics of the high-frequency signal can be improved. Further, the bump 7 may be a bump having a diameter of 300 μm or less, and by connecting the circuit board (interposer) on which a finer circuit pattern is formed and the lid 5, the influence of the parasitic capacitance of the solder ball is reduced, and a high-frequency signal including a frequency component exceeding 50 GHz can be transmitted well.

[0043] The lid 5 may contain glass in the base material. In this case, the thermal resistance of the lid 5 can be increased.

[0044] The second thermally conductive adhesive 14 may have a thickness larger than the thickness of the first thermally conductive adhesive 18.

[0045] Package 2 may have a heat sink 2d, and the heat sink 2d may have a third surface 2f. In this case, the heat dissipation performance from each of the first heat dissipation block 13 and the TEC 15 placed on the third surface 2f can be further enhanced.

[0046] The third surface 2f of the package 2 may be arranged to face the second surface 5b of the lid 5.

[0047] The heat sink 2d may have an enclosure 2k for accommodating the second thermally conductive adhesive 14 on the third surface 2f. In this case, when the second thermally conductive adhesive 14 is applied to the third surface 2f of the package 2, leakage to the surroundings along the directions D1 and D2 of the second thermally conductive adhesive 14 is suppressed by the enclosure 2k.

[0048] Next, the optical module 1A according to the modified example will be described with reference to FIG. 9. FIG. 9 is a longitudinal sectional view of the optical module 1A. Some configurations of the optical module 1A are the same as those of the optical module 1 described above. Therefore, in the following description, the description of the overlapping parts with the configuration of the optical module 1 will be appropriately omitted with the same reference numerals.

[0049] The optical module 1A further includes a signal source IC 21 (second IC) and a second heat dissipation block 23. The total thickness of the thickness (length along the direction D3) of the signal source IC 21, the thickness (length along the direction D3) of the second heat dissipation block 23, and the thickness of the first thermally conductive adhesive 18, and the thickness (length along the direction D3) of the driver IC 11, the thickness (length along the direction D3) of the first heat dissipation block 13, and the total thickness of the thickness of the first thermally conductive adhesive 18 vary due to respective manufacturing variations. Regarding the coating thickness of the second thermally conductive adhesive 14, it is determined in consideration of the variations in the total thickness after joining the optical modulator 12 and the TEC 15 connected by gold-tin solder or the like, the total thickness after joining the driver IC 11 and the first heat dissipation block 13 connected by the first thermally conductive adhesive 18, and the total thickness after joining the signal source IC 21 and the second heat dissipation block 23 connected by the first thermally conductive adhesive 18. For example, the thickness variation of the TEC 15 composed of a plurality of members is the largest, having a manufacturing variation of up to about ±150 μm at most. On the other hand, the thickness variations of the driver IC 11, the first heat dissipation block 13, the signal source IC 21, and the second heat dissipation block 23 connected by the first thermally conductive adhesive 18 are variations of up to about ±100 μm at most. Therefore, if the dimensions of the first heat dissipation block 13 and the recess 2j of the package 2 are designed so that the average values of the respective thicknesses are the same, by applying the second thermally conductive adhesive 14 to a thickness greater than 300 μm, the heat generated by the driver IC 11, the signal source IC 21, and the TEC 15 can be reliably dissipated through the third surface 2f of the package 2. At the same time, the lid 5 is housed in the recess 2j of the package 2 and is reliably hermetically sealed by the sealing material 6.

[0050] The signal source IC21 is connected to the second heat dissipation block 23 via, for example, the first thermally conductive adhesive 18. The signal source IC21 has a function of multiplexing, for example, low-speed electrical signals (low-frequency signals) to generate high-speed electrical signals (high-frequency signals). For example, by the multiplexing function, four independent electrical signals with a communication speed of 12.5 Gbit / s are multiplexed to generate one electrical signal with a communication speed of 50 Gbit / s. The low-frequency signal has a communication speed lower than that of the high-frequency signal. The second heat dissipation block 23 is connected to the third surface 2f of the package 2 by the second thermally conductive adhesive 14. The signal source IC21 is flip-chip mounted on the second surface 5b of the lid 5. The signal source IC21 is electrically connected to the optical modulator 12 via the driver IC11. The signal source IC21 has a plurality of wirings 21b facing the lid 5. The lid 5 has a wiring 5g facing the signal source IC21 and a through via 5h extending from the wiring 5g in the direction D3.

[0051] The through via 5h, the wiring 5g, and the wiring 21b are electrically connected to each other via the bump 19b. For example, the wiring 5d, the bumps 9b, 9c, 19b, the wiring 11b, the wiring 12b, and the wiring 21b constitute a high-frequency wiring for transmitting high-frequency signals. For example, the wiring 21b, the bump 19b, the wiring 5g, the through via 5h, and the bump 7 constitute a low-frequency wiring for transmitting low-frequency signals. A plurality of low-frequency signals are supplied from the circuit board 8 to the signal source IC21 via the bump 7 and the through via 5h. The high-frequency signal generated by multiplexing from the plurality of low-frequency signals is supplied from the signal source IC21 to the driver IC11 via the wiring 5d and the bumps 9b, 19b of the lid 5. Thus, the high-frequency signal generated by the signal source IC21 is supplied to the driver IC11. The driver IC11 supplies a high-frequency signal (drive signal) with a controlled characteristic impedance to the optical modulator 12 via the bump 9b, the wiring 5d, and the bump 9c.

[0052] As described above, the optical module 1A according to the modification example further includes a signal source IC 21 flip-chip mounted on the second surface 5b. The signal source IC 21 is electrically connected to the optical modulator 12 via the driver IC 11, and the signal source IC 21 is connected to the second heat dissipation block 23. The second heat dissipation block 23 is connected to the third surface 2f by the second thermally conductive adhesive 14. By housing the signal source IC 21 having a multiplexing function inside the package 2 in this way, it is possible to eliminate the transmission of high-frequency signals between the circuit board 8 and the optical module 1. Therefore, it is possible to avoid the deterioration of the frequency characteristics due to loss or impedance mismatch caused by the high-frequency signal passing through the bump 7 and the through via 5h. Therefore, inside the internal space 2A of the package 2, the signal source IC 21, the driver IC 11, and the optical modulator 12 are mutually connected by a transmission line with controlled characteristic impedance via the lid 5, so that the deterioration of the frequency characteristics of the high-frequency signal transmitted from the signal source IC 21 to the optical modulator 12 can be more reliably suppressed. In addition, since only low-frequency signals pass through the bump 7, it is not necessary to use bumps with a small diameter, and a circuit board 8 that is easy to manufacture and inexpensive can be used. In addition, it becomes possible to use a socket for connecting the bump 7 to the circuit board, facilitating the attachment and maintenance of the optical module 1A.

[0053] The embodiments and modifications according to the present disclosure have been described above. However, the present invention is not limited to the above-described embodiments or modifications, and can be appropriately changed within the scope of the gist described in the claims. For example, in the above-described embodiment, the optical module 1 which is an optical transmission module has been described. However, the optical module may not be an optical transmission module, and for example, it may be an optical reception module. For example, in the optical reception module, instead of the driver IC 11 in the configuration of FIG. 2, a transimpedance amplifier IC (TIA), instead of the optical modulator 12, a light receiving element PD, instead of the first heat dissipation block 13, a first block, and instead of the TEC 15, a second block may be used respectively. Further, instead of the first thermally conductive adhesive, an adhesive (first adhesive), and instead of the second thermally conductive adhesive, an adhesive (second adhesive) may be used respectively. With such a configuration, the received signal (for example, photocurrent) generated by the light receiving element PD can be transmitted to the TIA via the transmission line formed by the wiring 5d of the lid 5. The parasitic inductance can be reduced compared to the connection by bonding wires by the wiring 5d formed on the lid 5, and the frequency characteristics of the received signal can be improved.

[0054] The first block and the second block described above may be made of a material having insulating properties. Further, the first adhesive and the second adhesive may each have insulating properties. Furthermore, instead of the signal source IC 21 in the configuration of FIG. 2, a signal processing IC having a separation function opposite to the multiplexing function may be used. Thereby, the high-frequency signal is transmitted between the light receiving element, the TIA, and the signal processing IC housed in the internal space 2A of the package 2 via the wiring 5d of the lid 5, and a plurality of low-frequency signals generated from the high-frequency signal by the signal processing IC are transmitted to the circuit board 8 via the through via 5h and the bump 7. With such a configuration, it is possible to avoid deterioration of the frequency characteristics due to loss or impedance mismatch when the high-frequency signal passes through the bump 7 and the through via 5h.

Description of Reference Numerals

[0055] 1,1A… Optical module 2… Package 2A… Internal space 2b… First side wall 2c… Second side wall 2C… Opening 2d… Heat sink (heat dissipation member) 2f… Third surface 2j… Recess 2k… Enclosure 3… Optical connector 5… Lid 5b… Second surface 5c… First surface 5d,5g… Wiring 5f,5h… Through via 6… Sealing material 7… Bump (first bump) 8… Circuit board 9b,9c… Bump (second bump) 9d… Dummy bump 11… Driver IC (first IC) 11b,12b… Wiring 12… Optical modulator 13… First heat dissipation block 14… Second thermally conductive adhesive 15… TEC (temperature adjustment element) 18… First thermally conductive adhesive 19b… Bump 20… Optical component 21… Signal source IC (second IC) 21b… Wiring 23… Second heat dissipation block 100… Optical transmission module 101… Package 101b… Inner surface 101c… Internal space 101d… Feed through 101f… Wall 102… Heat dissipation block 104… Temperature modulation element 105… Optical modulator 106… Optical component 107… Optical connector 111… FPC 113... Bonding wire D1, D2, D3... Directions L1... Signal light L2... Local emission

Claims

1. A lid having bumps formed on a first surface, wirings formed on a second surface opposite to the first surface, and through vias penetrating between the first surface and the second surface; A first IC flip-chip mounted on the second surface; An optical modulator flip-chip mounted on the second surface; A first heat dissipation block connected to the first IC by a first thermally conductive adhesive; A temperature adjustment element connected to the optical modulator; A package having an opening and accommodating the first IC, the optical modulator, the first heat dissipation block, and the temperature adjustment element in the opening; Comprising; The first IC is electrically connected to the optical modulator via the wiring and is also electrically connected to the bump via the through via; The first heat dissipation block and the temperature adjustment element are connected to a third surface inside the package by a second thermally conductive adhesive; The package is hermetically sealed by closing the opening with the lid. Optical module.

2. The lid contains glass in a base material. The optical module according to Claim 1.

3. The second thermally conductive adhesive has a thickness greater than the thickness of the first thermally conductive adhesive. The optical module according to Claim 1 or Claim 2.

4. The package has a heat dissipation member, and the heat dissipation member has the third surface. The optical module according to any one of Claims 1 to 3.

5. The third surface of the package is disposed opposite to the second surface of the lid. The optical module according to Claim 4.

6. The heat dissipation member has a surrounding for accommodating the second thermally conductive adhesive on the third surface. The optical module according to Claim 4 or Claim 5.

7. Further comprising a second IC flip-chip mounted on the second surface, The second IC is electrically connected between the first IC and the through via, The second IC is connected to a second heat dissipation block, The second heat dissipation block is connected to the third surface by the second thermally conductive adhesive. The optical module according to any one of Claims 1 to 6.

8. A step of preparing a lid having bumps formed on a first surface, wirings formed on a second surface opposite to the first surface, and through vias penetrating between the first surface and the second surface; A step of connecting a first IC to a first heat dissipation block by a first thermally conductive adhesive; A step of connecting an optical modulator to a temperature adjustment element; A step of flip-chip mounting the first IC and the optical modulator on the second surface of the lid, electrically connecting the first IC to the optical modulator via the wiring, and electrically connecting the first IC to the bump via the through via; A step of applying a second thermally conductive adhesive to a third surface inside the package; A step of holding the first heat dissipation block, the first IC, the temperature adjustment element, and the optical modulator in the opening of the package, and connecting the first heat dissipation block and the temperature adjustment element to the third surface of the package by the second thermally conductive adhesive; A step of closing the opening of the package with the lid and hermetically sealing the package; A method for manufacturing an optical module comprising the above steps.

Images