CN114641131A

CN114641131A - Optical module daughter board structure

Info

Publication number: CN114641131A
Application number: CN202210376231.7A
Authority: CN
Inventors: 孙涛; 程进; 于让尘; 叶学亮; 吕维亮; 许广伟
Original assignee: Xifeng Photoelectric Technology Nanjing Co ltd
Current assignee: Xifeng Photoelectric Technology Nanjing Co ltd
Priority date: 2022-04-11
Filing date: 2022-04-11
Publication date: 2022-06-17

Abstract

The invention discloses an optical module daughter board structure, which comprises a radiating plate and a daughter board, wherein the radiating plate and the daughter board are arranged on a PCB and are designed in a shape matched with the radiating plate; the daughter board is arranged around the driver chip and the PIC chip, and the upper surface of the daughter board is flush with the chip surfaces of the driver chip and the PIC chip; and routing pad arrays are arranged on the upper surface of the daughter board and close to the periphery of the driver chip and the PIC chip, and the daughter board is connected with the PCB board through the pad arrays. The advantages are that: according to the arrangement of the daughter board, the upper surface of the daughter board is flush with the PIC chip and the driver chip, the height difference is reduced to be minimum, the routing distance is shortest, and the high-frequency performance is greatly improved; the daughter board is arranged, the height conversion is controlled in the daughter board, and the high-frequency performance reduction caused by the via holes needed by the height conversion is compensated through reasonable layout and matching of differential line impedance in the daughter board.

Description

Optical module daughter board structure

Technical Field

The invention relates to an optical module daughter board structure.

Background

With the development of the internet and data centers, the requirement for transmission bandwidth is higher and higher. Optical modules have evolved from 100G to 400G to 800G. With such an increase in transmission rate and number of channels, the size of the optical module is not increased, and even in order to increase the port density, the size needs to be reduced. While DSPs have been introduced to increase speed, these are a huge challenge to the routing of optical module PCBs. In QSFP modules, 800G wiring is currently very tight. How to satisfy the wiring requirement in a limited space becomes a problem to be solved urgently.

The prior art is the scheme currently used for 400G PIC chips. In the traditional scheme of the PCB, in order to ensure the high-frequency performance, the PIC chip, the driver chip and the PCB are on the same plane, so that the height difference of wire bonding before the PIC chip, the driver chip and the PCB is the minimum, the length of the wire bonding is also shorter, and the improvement of the high-frequency performance is facilitated.

There are heat sinks under the PIC chip and the driver chip, the height of the heat sink is much greater than that of the chip, and it is necessary to dig a hole in the PCB for placing the heat sink, etc. Typically the PCB is 1 mm thick and the depth of the cut can be up to 0.7 mm. Since the width of the PIC die almost covers the width of the PCB, most of the wiring can only be routed from within 0.3 millimeters. The power supply layer and the ground layer are eliminated, and only 2-3 layers can be actually wired.

Almost half of the wires need to be connected since 400G. In the 2-3 layers after 0.3 mm, the wiring is still easier to be distributed.

The existing scheme is that a PCB is hollowed, the upper surfaces of a PIC chip and a driver chip are flush with the PCB, but the PCB is 1 mm thick, the hollowed part is 0.7 mm thick, and only 0.3 mm is left. Most of the wiring can only be routed from within 0.3 mm. The power supply layer and the ground layer are eliminated, and only 2-3 layers can be actually wired. The 800G circuit is very complex, with 8X100G transmitting terminals and 8X100G receiving terminal connections, and the 2-3 layers are very difficult to access.

If the PIC chip and the driver chip are raised. The upper surface of the chip is 0.7 mm higher than the PCB, the height difference of the routing is 0.7 mm, the routing length is at least more than 0.8 mm, and the routing length is unacceptable for the length of a high-frequency signal gold wire of 100G. Eye degradation is very severe. The length of the gold wire is preferably smaller, and is often controlled to be within 0.15 mm.

The existing scheme is largely used in a 400G module, but is not suitable for 800G application.

Disclosure of Invention

The invention provides an optical module daughter board structure, and the specific technical scheme is that the optical module daughter board structure comprises an upper cover and a lower cover which are mutually embedded, and a PCB (printed circuit board), a driver chip, a PIC (peripheral interface controller) chip, an optical fiber array, an optical fiber plug and a laser assembly which are packaged between the upper cover and the lower cover, wherein the PCB is arranged on the lower cover, and a wiring gap is reserved between the PCB and the lower cover; the PCB is provided with a heat dissipation plate and a daughter board which is designed to be matched with the heat dissipation plate in shape, the optical fiber array, the laser assembly, the PIC chip and the driver chip are all arranged on the heat dissipation plate, the side plate of the heat dissipation plate is vertically provided with a heat dissipation plate side plate at the edge close to a heating source, and the heat dissipation plate side plate extends to protrude out of the lower cover and is contacted with the side wall of the upper cover through a heat conduction pad; the daughter board is arranged around the driver chip and the PIC chip, and the upper surface of the daughter board is flush with the chip surfaces of the driver chip and the PIC chip; and routing pad arrays are arranged on the upper surface of the daughter board and close to the periphery of the driver chip and the PIC chip, and the daughter board is connected with the PCB board through the pad arrays.

In the technical scheme of the invention, the heat dissipation plate is arranged for solving the heat dissipation problem of the optical module. The daughter board is arranged, so that the problem that routing cannot be performed due to the fact that the PIC chip and the driver chip are raised due to the arrangement of the heat dissipation plate in the optical module structure provided with the heat dissipation plate is solved; the daughter board is arranged, the upper surface of the daughter board is flush with the PIC chip and the driver chip, the height difference is reduced to be minimum, the routing distance is shortest, and the high-frequency performance is greatly improved; the daughter board is arranged, the height conversion is controlled in the daughter board, and the high-frequency performance reduction caused by the via holes needed by the height conversion is compensated through reasonable layout and matching of differential line impedance in the daughter board.

According to the optimization of the technical scheme, the daughter board and the PCB are the same in quality, and the daughter board and the PCB are fixedly welded.

Preferably, the heat dissipation plate comprises a first installation part for installing a PIC chip, a second installation part for installing a driver chip and a third installation part for installing an optical fiber array and a laser assembly, wherein the first installation part is a first flat plate with the same PIC chip size, the upper surface of the first flat plate is a first installation plane, and the PIC chip is attached to the first installation plane; the second mounting part is arranged close to the first mounting part and arranged along the length direction of the lower cover; the number of the second installation parts corresponds to the number of the driver chips one by one, the second installation parts are second flat plates with the sizes completely consistent with the sizes of the driver chips, the upper surfaces of the second flat plates are second installation planes, and the driver chips are arranged in a manner of being attached to the second installation planes; a gap is reserved between every two adjacent second installation parts; the third mounting part is arranged close to the first mounting part and arranged along the length direction of the lower cover; the upper surface of the third installation part is a third installation plane, and the optical fiber array and the laser assembly are attached to the third installation plane. The heat dissipation plate has the advantages that the heat dissipation plate is designed in an opposite structure, namely, a platform of the optical fiber array and the laser assembly, a platform of the optical integrated circuit chip and a platform of the driver chip are guaranteed, and the optical fiber array, the laser assembly, the optical integrated circuit chip and the driver chip which are used as heating sources can be well dissipated.

Preferably, the edge of the daughter board is provided with a plurality of extending bulges for filling gaps around the driver chip and the PIC chip in an extending manner. The arrangement of the extension bulge enables the daughter board to be closer to the periphery of the driver chip and the PIC chip, and the routing distance is favorably shortened.

Preferably, the surface of the daughter board contacting the PCB and the surface of the extending protrusion contacting the PCB are both provided with bumps for welding.

Preferably, the heat dissipation plate is of an integrated structure and is made of tungsten-copper alloy.

Preferably, the surface of the heat dissipation plate, which is attached to the PCB, is convexly provided with a back heat dissipation bulge at a position opposite to the heating source, and the back heat dissipation bulge penetrates through the through groove formed in the PCB and is attached to the lower cover through the heat conduction pad. The back heat dissipation bulge is arranged at a position close to the heating source, and the heat dissipation area of the heating source is further increased due to the design of the back heat dissipation bulge.

Compared with the prior art, the invention has the beneficial effects that:

the optical module daughter board structure and the daughter board are arranged, so that the problem that routing cannot be performed due to the fact that the PIC chip and the driver chip are raised due to the arrangement of the heat dissipation plate in the optical module structure provided with the heat dissipation plate is solved; due to the arrangement of the daughter board, the upper surface of the daughter board is flush with the PIC chip and the driver chip, the height difference is reduced to be minimum, the routing distance is shortest, and the high-frequency performance is greatly improved; the daughter board is arranged, the height conversion is controlled in the daughter board, and the high-frequency performance reduction caused by the via holes needed by the height conversion is compensated through reasonable layout and matching of differential line impedance in the daughter board.

Drawings

Fig. 1 is a perspective view of the optical module of the present embodiment (the upper cover is hidden in the drawing).

Fig. 2 is a front view of fig. 1.

Fig. 3 is a sectional view taken along line a-a of fig. 2.

Fig. 4 is a perspective view of a sub-board preferred in the present embodiment.

Fig. 5 is a plan view of fig. 4.

Fig. 6 is a perspective view of the heat sink.

Fig. 7 is a plan view of fig. 6.

Detailed Description

The technical solution of the present invention is described in detail below, but the scope of the present invention is not limited to the embodiments.

In order to make the disclosure of the present invention more comprehensible, the following description is further made in conjunction with fig. 1 to 7 and the detailed description.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1:

as shown in fig. 1 and 2, an optical module daughter board structure includes an upper cover and a lower cover 1 which are mutually embedded, a PCB 2 packaged between the upper cover and the lower cover 1, a driver chip 3, a PIC chip 4, an optical fiber array 5, an optical fiber plug 7 and a laser assembly 6. The PCB board 2 is arranged on the lower cover 1, and a wiring gap is reserved between the PCB board 2 and the lower cover 1.

The light module mentioned in the present embodiment is a known product in the art and is well known to those skilled in the art.

As shown in fig. 1 and 2, a heat sink plate 8 and a daughter board 9 configured to fit the heat sink plate 8 are disposed on the PCB 2, and the optical fiber array 5, the laser module 6, the PIC chip 4, and the driver chip 3 are all disposed on the heat sink plate 8. The side plate of the heat radiation plate 8 is vertically provided with a heat radiation plate side plate 81 at the edge close to the heat generating source, and the heat radiation plate side plate 81 extends and protrudes out of the side wall of the lower cover 1 and contacts with the side wall of the upper cover through a heat conducting pad.

In the optical module structure, the optical fiber array 5, the laser component 6, the PIC chip 4 and the driver chip 3 are all heating sources of the module, and the heating sources are all arranged on the heat dissipation plate 8 in the optical module structure of the embodiment, so that the heat dissipation performance of the module is improved. The heat sink 8 of the present embodiment is an integral structure and is made of tungsten-copper alloy. Tungsten copper alloy is an existing material. The heat of the heating source is transferred to the upper cover by utilizing the good heat-conducting property of the tungsten-copper alloy for heat dissipation.

As shown in fig. 1 and 2, the daughter board 9 is arranged around the driver chip 3 and the PIC chip 4, and the upper surface of the daughter board 9 is flush with the chip surfaces of the driver chip 3 and the PIC chip 4; and routing pad arrays are arranged on the upper surface of the daughter board 9 and close to the periphery of the driver chip 3 and the PIC chip 4, and the daughter board 9 is connected with the PCB 2 through the pad arrays.

There are the heating panels PIC chip 4 and driver chip 3 below, and the height of heating panel is far greater than the height of chip, if it is convenient to guarantee the routing, needs to dig out in order to place fin etc. on the PCB. Typically the PCB is 1 mm thick and the depth of the cut can be up to 0.7 mm. Since the width of the PIC die almost covers the width of the PCB, most of the wiring can only be routed from within 0.3 millimeters. The power supply layer and the ground layer are eliminated, and only 2-3 layers can be actually wired. In this embodiment, the daughter board 9 is adopted, and in order to ensure high frequency performance, the PIC chip, the driver chip and the PCB are on the same plane, so that the height difference of the wire bonding among the PIC chip, the driver chip and the PCB is the smallest, and the wire bonding length is also shorter, which is beneficial to improving high frequency performance.

As shown in fig. 3, in this embodiment, the upper surface of the daughter board 9 is flush with the PIC chip 4 and the driver chip 3, the height difference is reduced to the minimum, the wire bonding distance is the shortest, and the high frequency performance is greatly improved. The lower surface is connected to the PCB board 2 by an array of pads. The height conversion is controlled in the daughter board 9, and the high-frequency performance reduction caused by the via holes needed by the height conversion is compensated through reasonable layout and matching of differential line impedance in the daughter board. So that the high frequency performance of the via is acceptable compared to other solutions, although it has a detrimental effect.

As shown in fig. 3, the daughter board 9 in this embodiment is attached to the PCB board 2, and the PCB board 2 is not hollowed out.

As shown in fig. 1, 2, 4 and 5, the daughter board 9 is made of the same material as the PCB 2, and the daughter board 9 is fixed to the PCB 2 by soldering. The daughter board 9 is extended at its edge with a plurality of extension bumps 91 for filling gaps around the driver chip 3 and the PIC chip 4. The surface of the daughter board 9 contacting the PCB 2 and the surface of the extended projection 91 contacting the PCB 2 are provided with bumps 92 for soldering.

As shown in fig. 6, in the present embodiment, the heat dissipation plate 8 is an integral structure and made of tungsten-copper alloy. Tungsten copper alloy is an existing material. The heat of the heating source is transferred to the upper cover by utilizing the good heat-conducting property of the tungsten-copper alloy for heat dissipation.

As shown in fig. 6, the heat dissipation plate 8 includes a first mounting portion 83 on which the PIC chip 4 is mounted, a second mounting portion 84 on which the driver chip 3 is mounted, and a third mounting portion 85 on which the optical fiber array 5 and the laser module 6 are mounted.

The opposite structure design of the heat dissipation plate 8 ensures that the optical fiber array 5 and the laser assembly 6 are on a platform, the optical integrated circuit chip 4 is on a platform, and the driver chip 3 is on a platform, and can also ensure that the optical fiber array, the laser assembly, the optical integrated circuit chip and the driver chip which are used as heating sources can be well dissipated.

As shown in fig. 6, the first mounting portion 83 is a first flat plate having the PIC chip 4 with a uniform size, the upper surface of the first flat plate is a first mounting plane, and the PIC chip 4 is disposed to be attached to the first mounting plane. The second mounting portion 84 is provided next to the first mounting portion 83 and arranged along the length direction of the lower cover 1; the number of the second mounting portions 84 corresponds to the number of the driver chips 3 one by one, the second mounting portions 84 are second flat plates having the size completely consistent with that of the driver chips 3, the upper surfaces of the second flat plates are second mounting planes, and the driver chips 3 are arranged in a manner of being attached to the second mounting planes; a gap is left between every two adjacent second mounting portions 84. The third mounting portion 85 is disposed next to the first mounting portion 83 and arranged along the length direction of the lower cover 1; the upper surface of the third mounting portion 85 is a third mounting plane, and the optical fiber array 5 and the laser module 6 are arranged in a manner of being attached to the third mounting plane.

As shown in fig. 6, the first mounting plane, the second mounting plane and the third mounting plane are provided to ensure the attaching effect of the chip mounting.

As shown in fig. 6, the heat sink side plate 81 is provided at a side of the third mounting portion 85 of the heat sink 8. The laser subassembly is the main source that generates heat of optical module, sets up the side of heating panel curb plate at the third installation department more be close to the source that generates heat, improves the radiating effect.

Further, in the present embodiment, the heat radiating plate side plate 81 is preferably designed to have a length of more than 2.5mm in contact with the upper cover and a width of more than 4mm in contact with the upper cover. Under the structural size condition of the optical module, the size of the radiating plate side plate 81 is as large as possible, so that the contact area between the radiating plate and the upper cover is as large as possible, and the radiating effect is better.

As shown in fig. 1 and 2, the first mounting plane to which the optical integrated circuit chip 4 is attached is not at the same height as the third mounting plane to which the optical fiber array 5 and the laser module 6 are attached, and the first mounting plane is higher than the third mounting plane. In order to compensate for the height difference between the chips.

As shown in fig. 6, a back heat dissipating protrusion 86 is protruded from a position opposite to the heat source on the surface of the heat dissipating plate 8 attached to the PCB 2, and the back heat dissipating protrusion 86 penetrates through the through groove formed in the PCB 2 and is attached to the lower cover 1 through the heat conductive pad. The back heat dissipation bulge is arranged at a position close to the heating source, and the heat dissipation area of the heating source is further increased due to the design of the back heat dissipation bulge.

As shown in fig. 7, the back heat dissipation protrusions 86 of the present embodiment are arranged, and the size and shape of the back heat dissipation protrusions 86 are arranged, so that the size and shape of the back heat dissipation protrusions 86 need to be designed to be as close as possible to all heat sources without affecting the wiring of the optical module. The contact surface of the back heat dissipation protrusion 86 and the lower cover 1 is a plane, so that the heat dissipation performance is improved. A heat conducting pad of 0.3-0.5mm is arranged between the contact surface of the back heat dissipation bulge 86 and the lower cover 1.

As shown in fig. 6, the end surfaces of both sides of the heat sink plate 8 are in contact with the inner side surfaces of the side plates of the lower cover 1 through heat conductive pads. The heat conducting pad is arranged to improve heat conductivity and further improve heat dissipation effect. In the lateral heat dissipation structure of the optical module of the embodiment, the thicknesses of all the heat conducting pads are 0.3-0.5 mm.

As shown in fig. 6, in the optical module side heat dissipation structure of this embodiment, heat dissipation protrusions 82 are vertically disposed on both sides of the third mounting portion of the heat dissipation plate 8, end surfaces of the heat dissipation protrusions 82 are in contact with inner side wall surfaces of both side plates of the lower cover 1 through heat conduction pads, and heights of the heat dissipation protrusions 82 are lower than heights of the side plates of the lower cover 1. The heat dissipating protrusions 82 are provided to allow the heat dissipating plate to contact the side of the lower cover, thereby increasing the heat dissipating area and improving the heat dissipating effect.

As shown in fig. 1 and 2, in the side heat dissipation structure of the optical module of this embodiment, the side plate of the heat dissipation plate with the raised side is higher than the lower cover, and this portion is in contact with the upper cover through a thin layer of heat conduction pad, which has a larger area and a smaller thermal resistance. The gap between the side plate of the radiating fin with the side face being heightened and the upper cover is small, the contact area is larger, and the thermal resistance is greatly improved.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

As shown in fig. 4 and 5, in the present embodiment, the PIC chip 4 used in the optical module structure is an 8 × 100G silicon optical modulation chip. The PIC chip 4 has a width almost covering the width of the PCB, and therefore, in designing the structure of the daughter board 9, in order to take into account the arrangement of the pad array, the edge of the daughter board 9 is extended with a plurality of extension bumps 91 for filling the gaps around the driver chip 3 and the PIC chip 4. The extension protrusion 91 is arranged to be closer to the periphery of the driver chip and the PIC chip, so that the routing distance can be shortened. The two sides are provided with a plurality of bonding pad arrays for bonding and leading out the PIC chip. As shown in fig. 4 and 5, the sub-board 9 has an overall shape similar to a U-shape.

In this embodiment, in the optical module structure, the PIC chip is two 4 × 100G chips, and the daughter board may be F-shaped. The two sides of the F-shaped chip are respectively connected with a 4X100G chip through wire bonding.

Therefore, the shape of the daughter board 9 of the present embodiment is also not fixed, and is required according to the actual configuration of the optical module.

The parts not involved in the present invention are the same as or can be implemented using the prior art.

As noted above, while the present invention has been shown and described with reference to certain preferred embodiments, it is not to be construed as limited thereto. Various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. An optical module daughter board structure comprises an upper cover and a lower cover (1) which are mutually embedded, and a PCB (2), a driver chip (3), a PIC (peripheral interface controller) chip (4), an optical fiber array (5), an optical fiber plug (7) and a laser assembly (6) which are packaged between the upper cover and the lower cover (1), wherein the PCB (2) is arranged on the lower cover (1), and a wiring gap is reserved between the PCB (2) and the lower cover (1); the PCB (2) is provided with a heat dissipation plate (8) and a sub-plate (9) which is matched with the heat dissipation plate (8) in shape, the optical fiber array (5), the laser component (6), the PIC chip (4) and the driver chip (3) are all arranged on the heat dissipation plate (8), a heat dissipation plate side plate (81) is vertically arranged on the edge of the side plate of the heat dissipation plate (8) close to a heating source, and the heat dissipation plate side plate (81) extends and protrudes out of the side wall of the lower cover (1) and is contacted with the side wall of the upper cover through a heat conduction pad; the daughter board (9) is arranged around the driver chip (3) and the PIC chip (4), and the upper surface of the daughter board (9) is flush with the chip surfaces of the driver chip (3) and the PIC chip (4); the periphery of the upper surface of the daughter board (9) close to the driver chip (3) and the PIC chip (4) is provided with a routing pad array, and the daughter board (9) is connected with the PCB (2) through the pad array.

2. An optical module daughter board structure according to claim 1, characterized in that the daughter board (9) is made of the same material as the PCB (2), and the daughter board (9) is fixed to the PCB (2) by welding.

3. The optical module daughter board structure of claim 1, wherein the heat dissipation plate (8) comprises a first mounting portion (83) for mounting the PIC chip (4), a second mounting portion (84) for mounting the driver chip (3), and a third mounting portion (85) for mounting the optical fiber array (5) and the laser module (6), the first mounting portion (83) is a first flat plate with the PIC chip (4) having a completely consistent size, the upper surface of the first flat plate is a first mounting plane, and the PIC chip (4) is arranged to fit the first mounting plane;

the second mounting part (84) is arranged next to the first mounting part (83) and arranged along the length direction of the lower cover (1); the number of the second mounting parts (84) corresponds to the number of the driver chips (3) one by one, the second mounting parts (84) are second flat plates with the sizes completely consistent with the sizes of the driver chips (3), the upper surfaces of the second flat plates are second mounting planes, and the driver chips (3) are arranged in a manner of being attached to the second mounting planes; a gap is reserved between every two adjacent second mounting parts (84); the third mounting part (85) is arranged next to the first mounting part (83) and is arranged along the length direction of the lower cover (1); the upper surface of the third installation part (85) is a third installation plane, and the optical fiber array (5) and the laser assembly (6) are attached to the third installation plane.

4. An optical module daughter board structure according to claim 3, characterized in that the edge of the daughter board (9) is extended with a plurality of extending bumps (91) for filling the gap around the driver chip (3) and the PIC chip (4).

5. An optical module daughter board structure according to claim 3, characterized in that the surface of the daughter board (9) contacting the PCB (2) and the surface of the extending projection (91) contacting the PCB (2) are provided with bumps (92) for soldering.

6. The optical module daughter board structure of claim 3, wherein the heat sink (8) is a unitary structure and is made of tungsten copper alloy.

7. The optical module daughter board structure of claim 6, wherein a back heat dissipating protrusion (86) is protruded from a surface of the heat dissipating plate (8) attached to the PCB (2) at a position opposite to the heat source, and the back heat dissipating protrusion (86) penetrates through a through groove formed in the PCB (2) and is attached to the lower cover (1) through a thermal pad.