An optical module daughter board structure

Abstract

The present invention discloses an optical module sub-board structure, comprising a heat sink disposed on a PCB board and a sub-board designed to match the shape of the heat sink, wherein an optical fiber array, a laser assembly, a PIC chip, and a driver chip are all disposed on the heat sink; the sub-board is disposed around the driver chip and the PIC chip, and the upper surface of the sub-board is flush with the chip surfaces of the driver chip and the PIC chip; an array of wire bonding pads is disposed on the upper surface of the sub-board near the periphery of the driver chip and the PIC chip, and the sub-board is connected to the PCB board via the pad array. Advantages: The sub-board arrangement of the present invention ensures that the upper surface of the sub-board is flush with the PIC chip and the driver chip, minimizing the height difference and shortening the bonding distance, thereby greatly improving high-frequency performance; the sub-board arrangement controls the height conversion within the sub-board, and through reasonable layout and differential line impedance matching within the sub-board, the degradation in high-frequency performance caused by the vias required for height conversion is compensated.

Description

Technical Field

[0001] The invention relates to an optical module sub-board structure. Background Art

[0002] With the development of the internet and data centers, the demand for transmission bandwidth is increasing. Optical modules have evolved from 100G to 400G and even 800G. Despite these increases in transmission rates and channel counts, the size of optical modules has remained constant, and even needs to be reduced to increase port density. Furthermore, DSP has been introduced to increase speeds, posing significant challenges to optical module PCB wiring. Currently, 800G cabling in QSFP modules is already extremely limited. Meeting these cabling requirements within limited space has become a pressing issue.

[0003] This existing technology is currently used in 400G PIC chips. To ensure high-frequency performance, traditional PCB solutions place the PIC chip and driver chip on the same plane as the PCB. This minimizes the height difference between the bonding wires and shortens the bonding wire length, which improves high-frequency performance.

[0004] The PIC chip and driver chip have heat sinks underneath them. These heat sinks are much taller than the chips themselves, necessitating a cutout in the PCB to accommodate the heat sink. A typical PCB is 1mm thick, so the cutout depth can be up to 0.7mm. Because the PIC chip's width nearly covers the entire width of the PCB, most wiring can only be routed within 0.3mm. Excluding the power and ground planes, only two or three layers are available for routing.

[0005] Since 400G requires almost half as many wires for connection, routing is still relatively easy within the 2-3 layers after 0.3mm.

[0006] The existing solution involves hollowing out the PCB, placing the top surface of the PIC and driver chips flush with the PCB. However, the PCB is 1mm thick, and the hollowing out is 0.7mm thick, leaving only 0.3mm. Consequently, most wiring must be routed within this 0.3mm. Excluding the power and ground planes, only two or three layers are available for routing. 800G circuits are extremely complex, involving 8x100G transmitters and 8x100G receivers, making routing within these two or three layers extremely challenging.

[0007] If the PIC chip and driver chip are elevated, the chip's top surface will be 0.7 mm higher than the PCB, and the bond wire height difference will be 0.7 mm. The bond wire length must be at least 0.8 mm. For high-frequency signals like 100G, such a long wire length is unacceptable. Eye diagrams will be severely degraded. The shorter the wire length, the better, and it should generally be kept within 0.15 mm.

[0008] Existing solutions are widely used in 400G modules, but are not suitable for 800G applications. Summary of the Invention

[0009] The present invention proposes an optical module daughter board structure. The specific technical solution is an optical module daughter board structure, wherein the optical module includes an upper cover and a lower cover that are embedded in each other, and a PCB board, a driver chip, a PIC chip, an optical fiber array, an optical fiber plug and a laser assembly encapsulated between the upper cover and the lower cover. The characteristic is that the PCB board is arranged on the lower cover, and a wiring gap is left between the PCB board and the lower cover; a heat sink and a daughter board designed to match the shape of the heat sink are arranged on the PCB board, the optical fiber array, the laser assembly, the PIC chip and the driver chip are all arranged on the heat sink, and the side panels of the heat sink are perpendicularly arranged at the edge near the heat source, and the heat sink side panels extend and protrude between the lower cover and the side wall of the upper cover through thermal pads; 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; a wire bonding pad array is provided on the upper surface of the daughter board near the periphery of the driver chip and the PIC chip, and the daughter board is connected to the PCB board through the pad array.

[0010] In the technical solution of the present invention, the provision of a heat sink is used to solve the heat dissipation problem of the optical module. The provision of a daughterboard solves the problem of the PIC chip and driver chip being elevated by the heat sink within the optical module structure equipped with the heat sink, making wiring impossible. The daughterboard configuration makes the upper surface of the daughterboard flush with the PIC chip and driver chip, minimizing the height difference and shortening the wiring distance, greatly improving high-frequency performance. The daughterboard configuration controls the height conversion within the daughterboard. Through reasonable layout and differential line impedance matching within the daughterboard, the high-frequency performance degradation caused by the vias required for height conversion is compensated.

[0011] In a preferred embodiment of the technical solution of the present invention, the daughter board and the PCB board are made of the same material, and the daughter board and the PCB board are fixed by welding.

[0012] In a preferred embodiment of the present invention, the heat sink includes a first mounting portion for mounting the PIC chip, a second mounting portion for mounting the driver chip, and a third mounting portion for mounting the fiber array and laser assembly. The first mounting portion is a first flat plate of the same size as the PIC chip, with the upper surface of the first flat plate forming a first mounting plane, on which the PIC chip is mounted. The second mounting portion is disposed adjacent to the first mounting portion and arranged along the length of the lower cover. The number of second mounting portions corresponds to the number of driver chips. The second mounting portion is a second flat plate of the same size as the driver chip, with the upper surface of the second flat plate forming a second mounting plane, on which the driver chip is mounted. A gap is left between each adjacent second mounting portion. The third mounting portion is disposed adjacent to the first mounting portion and arranged along the length of the lower cover. The upper surface of the third mounting portion forms a third mounting plane, on which the fiber array and laser assembly are mounted. The heat sink's heterogeneous structural design ensures that the fiber array and laser assembly, the optical integrated circuit chip, and the driver chip share a single platform, and also ensures that the fiber array, laser assembly, optical integrated circuit chip, and driver chip, which serve as heat sources, can dissipate heat effectively.

[0013] In a preferred embodiment of the present invention, the edge of the daughterboard is provided with a plurality of extension protrusions for filling the gaps around the driver chip and the PIC chip. The provision of the extension protrusions allows the daughterboard to be closer to the driver chip and the PIC chip, which is conducive to shortening the wire bonding distance.

[0014] In a preferred embodiment of the technical solution of the present invention, soldering bumps are provided on the surface of the daughter board in contact with the PCB and on the surface of the extended protrusion in contact with the PCB.

[0015] In a preferred embodiment of the technical solution of the present invention, the heat dissipation plate is an integrated structure and is made of tungsten-copper alloy.

[0016] In a preferred embodiment of the present invention, a rear heat dissipation protrusion is provided on the surface of the heat sink that contacts the PCB, opposite the heat source. This protrusion extends through a slot in the PCB and connects to the lower cover via a thermal pad. This protrusion is located close to the heat source, further increasing the heat dissipation area of ​​the heat source.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The optical module sub-board structure of the present invention and the arrangement of the sub-board solve the problem of being unable to perform wiring in an optical module structure equipped with a heat sink due to the fact that the PIC chip and the driver chip are elevated by the arrangement of the heat sink. The arrangement of the sub-board ensures that the upper surface of the sub-board is flush with the PIC chip and the driver chip, minimizing the height difference and shortening the wiring distance, thereby greatly improving high-frequency performance. The arrangement of the sub-board controls the height conversion within the sub-board. Through reasonable layout and differential line impedance matching in the sub-board, the degradation of high-frequency performance caused by the vias required for the height conversion is compensated. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. 4 is a three-dimensional diagram of the optical module of this embodiment (the upper cover is hidden in the diagram).

[0020] Figure 2 yes Figure 1 main view.

[0021] Figure 3 yes Figure 2 AA cross-section diagram.

[0022] Figure 4 This is a three-dimensional structural diagram of a preferred sub-board in this embodiment.

[0023] Figure 5 yes Figure 4 Plan view of the.

[0024] Figure 6 It is a three-dimensional diagram of the heat sink.

[0025] Figure 7 yes Figure 6 Plan view of the. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is described in detail below, but the protection scope of the present invention is not limited to the embodiments.

[0027] In order to make the content of the present invention more clear and easy to understand, the following Figure 1-Figure 7 The specific implementation methods are further described.

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] Example 1:

[0030] like Figure 1 and 2Figure 1 shows an optical module daughterboard structure. The optical module includes an upper cover and a lower cover 1 that fit together, a PCB 2, a driver chip 3, a PIC chip 4, an optical fiber array 5, an optical fiber plug 7, and a laser assembly 6 encapsulated between the upper and lower covers 1. The PCB 2 is mounted on the lower cover 1, with a wiring gap between the PCB 2 and the lower cover 1.

[0031] The optical module mentioned in this embodiment is a known product in the art and is well known to those skilled in the art.

[0032] like Figure 1 and 2 As shown, a heat sink 8 and a daughterboard 9 designed to match the heat sink 8 are mounted on the PCB 2. The fiber array 5, laser assembly 6, PIC chip 4, and driver chip 3 are all arranged on the heat sink 8. Heat sink side panels 81 are perpendicularly mounted on the side panels of the heat sink 8 near the heat source. These panels extend beyond the lower cover 1 and contact the sidewalls of the upper cover via thermal pads.

[0033] Within the optical module structure, the fiber array 5, laser assembly 6, PIC chip 4, and driver chip 3 all serve as heat sources. This embodiment arranges these heat sources on a heat sink 8, improving the module's heat dissipation performance. This embodiment's heat sink 8 is an integrated structure made of tungsten-copper alloy, a readily available material. Leveraging its excellent thermal conductivity, the heat from the heat source is transferred to the upper cover for dissipation.

[0034] like Figure 1 and 2 As shown, 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; a wire bonding pad array is set on the upper surface of the daughter board 9 near the periphery of the driver chip 3 and the PIC chip 4, and the daughter board 9 is connected to the PCB board 2 through the pad array.

[0035] There are heat sinks beneath the PIC chip 4 and driver chip 3. The height of the heat sinks is much greater than the height of the chips. To ensure easy wiring, the PCB needs to be hollowed out to accommodate the heat sinks. Typically, the PCB is 1 mm thick, and the hollowing depth can reach up to 0.7 mm. Because the width of the PIC chip almost completely overlaps the width of the PCB, most wiring can only be routed within 0.3 mm. After deducting the power and ground layers, only 2-3 layers are available for wiring. In this embodiment, however, the daughterboard 9 structure is used. To ensure high-frequency performance, the PIC chip and driver chip are aligned with the PCB. This minimizes the height difference between the three bonding layers, shortens the bonding length, and improves high-frequency performance.

[0036] like Figure 3As shown, in this embodiment, the top surface of daughterboard 9 is flush with the PIC chip 4 and driver chip 3, minimizing the height difference and shortening the wiring distance, significantly improving high-frequency performance. The bottom surface is connected to the PCB 2 via a pad array. Height conversion is controlled within daughterboard 9. Reasonable layout and differential line impedance matching within the daughterboard compensate for the high-frequency performance degradation caused by the vias required for height conversion. While the vias have a negative impact, the high-frequency performance is still acceptable compared to other solutions.

[0037] like Figure 3 As shown, the daughter board 9 in this embodiment is attached to the top of the PCB board 2, and the PCB board 2 is not hollowed out accordingly.

[0038] like Figure 1 、 2 As shown in Figures 4 and 5, daughterboard 9 is made of the same material as PCB 2 and is soldered to PCB 2. A plurality of extended protrusions 91 extend from the edge of daughterboard 9 to fill the gaps around driver chip 3 and PIC chip 4. Soldering bumps 92 are provided on the surface of daughterboard 9 that contacts PCB 2 and on the surface of extended protrusions 91 that contacts PCB 2.

[0039] like Figure 6 As shown, in this embodiment, the heat sink 8 is an integrated structure and is made of tungsten-copper alloy. Tungsten-copper alloy is an existing material. The good thermal conductivity of tungsten-copper alloy is utilized to transfer heat from the heat source to the upper cover for heat dissipation.

[0040] like Figure 6 As shown, the heat sink 8 includes 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 assembly 6 .

[0041] The heterogeneous structural design of the heat sink 8 ensures that the optical fiber array 5 and the laser assembly 6 are on one platform, the optical integrated circuit chip 4 is on one platform, and the driver chip 3 is on one platform. It also ensures that the optical fiber array, laser assembly, optical integrated circuit chip and driver chip, which serve as heat sources, can dissipate heat well.

[0042] like Figure 6As shown, the first mounting portion 83 is a first flat plate of identical size to the PIC chip 4. The top surface of the first flat plate is a first mounting plane, and the PIC chip 4 is mounted in contact with the first mounting plane. The second mounting portion 84 is positioned adjacent to the first mounting portion 83 and arranged along the length of the lower cover 1. The number of second mounting portions 84 corresponds one-to-one with the number of driver chips 3. The second mounting portions 84 are second flat plates of identical size to the driver chips 3. The top surface of the second flat plate is a second mounting plane, and the driver chips 3 are mounted in contact with the second mounting plane. A gap is left between each adjacent second mounting portion 84. The third mounting portion 85 is positioned adjacent to the first mounting portion 83 and arranged along the length of the lower cover 1. The top surface of the third mounting portion 85 is a third mounting plane, and the fiber array 5 and laser assembly 6 are mounted in contact with the third mounting plane.

[0043] like Figure 6 As shown, the purpose of setting the first mounting plane, the second mounting plane and the third mounting plane is to ensure the bonding effect of chip mounting.

[0044] like Figure 6 As shown, the heat sink side plate 81 is arranged on the side of the third mounting portion 85 of the heat sink 8. The laser assembly is the main heat source of the optical module. The heat sink side plate is arranged on the side of the third mounting portion closer to the heat source to improve the heat dissipation effect.

[0045] Furthermore, in this embodiment, the heat sink side panels 81 are preferably designed to have a length greater than 2.5 mm in contact with the upper cover and a width greater than 4 mm in contact with the upper cover. Given the structural dimensions of the optical module, the heat sink side panels 81 are designed to be as large as possible to maximize the contact area between the heat sink and the upper cover, resulting in better heat dissipation.

[0046] like Figure 1 and 2 As shown, the first mounting plane where the optical integrated circuit chip 4 is attached and the third mounting plane where the optical fiber array 5 and laser assembly 6 are attached are not at the same height. The first mounting plane is higher than the third mounting plane. This is to compensate for the height difference between the chips.

[0047] like Figure 6 As shown, the surface of the heat sink 8 that contacts the PCB 2 is provided with a rear heat dissipation protrusion 86 at a position opposite the heat source. The rear heat dissipation protrusion 86 extends through a through slot provided in the PCB 2 and contacts the lower cover 1 via a thermal pad. The rear heat dissipation protrusion is located close to the heat source, further increasing the heat dissipation area of ​​the heat source.

[0048] like Figure 7As shown, this embodiment features a backside heat dissipation protrusion 86. The size and shape of this protrusion are designed to be as close to all heat sources as possible without interfering with the optical module wiring. The surface where the backside heat dissipation protrusion 86 contacts the lower cover 1 is flat, improving heat dissipation performance. A 0.3-0.5mm thick thermal pad is placed between the contact surfaces of the backside heat dissipation protrusion 86 and the lower cover 1.

[0049] like Figure 6 As shown, the contact areas between the end surfaces of the heat sink 8 and the inner wall surfaces of the side panels of the lower cover 1 are all connected via thermal pads. The purpose of the thermal pads is to improve heat conductivity and further enhance the heat dissipation effect. In this embodiment of the optical module side heat dissipation structure, all thermal pads have a thickness of 0.3-0.5mm.

[0050] like Figure 6 As shown, the optical module side heat dissipation structure of this embodiment further comprises heat dissipation protrusions 82 perpendicularly disposed on both sides of the third mounting portion of the heat sink 8. The end faces of the heat dissipation protrusions 82 contact the inner wall surfaces of the side panels of the lower cover 1 via thermal pads. The height of the heat dissipation protrusions 82 is lower than the height of the side panels of the lower cover 1. The purpose of providing the heat dissipation protrusions 82 is to ensure that the heat sink contacts the side of the lower cover, thereby increasing the heat dissipation area and improving the heat dissipation effect.

[0051] like Figure 1 and 2 As shown, the optical module's side heat dissipation structure in this embodiment features a raised heat sink side panel that is higher than the lower cover. This portion of the panel contacts the upper cover via a thin layer of thermal padding, resulting in a larger contact area and lower thermal resistance. The gap between the raised heat sink side panel and the upper cover is minimal, resulting in a larger contact area and significantly improved thermal resistance. Specific embodiments

[0052] like Figure 4 and 5 As shown, in this embodiment, the PIC chip 4 used in the optical module structure is an 8X100G silicon photonic modulation chip. The width of the PIC chip 4 almost covers the width of the PCB. Therefore, when 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 protrusions 91 for filling the gaps around the driver chip 3 and the PIC chip 4. The setting of the extension protrusions 91 makes the daughter board closer to the driver chip and the PIC chip, which is conducive to shortening the wiring distance. There are multiple wire bonding pad arrays on both sides for the purpose of leading out the wires of the PIC chip. As shown Figure 4 and 5 As shown, the overall shape of the sub-plate 9 is approximately U-shaped.

[0053] If so, in this embodiment, the PIC chips in the optical module structure are two 4X100G chips, and the daughter board can also be in an F-shaped shape. The two sides of the F-shaped board are respectively connected to a 4X100G chip by wire bonding.

[0054] Therefore, the shape of the daughter board 9 in this embodiment is also not fixed and depends on the structural requirements of the actual optical module.

[0055] The parts not involved in the present invention are the same as the existing technology or can be implemented by using the existing technology.

[0056] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. An optical module sub-board structure, the optical module comprising an upper cover and a lower cover (1) that are interlocked with each other, a PCB board (2), a driver chip (3), a PIC chip (4), an optical fiber array (5), an optical fiber plug (7) and a laser assembly (6) encapsulated between the upper cover and the lower cover (1), characterized in that: The PCB board (2) is arranged on the lower cover (1), and a wiring gap is left between the PCB board (2) and the lower cover (1); a heat sink (8) and a sub-board (9) designed to match the shape of the heat sink (8) are arranged on the PCB board (2); the optical fiber array (5), the laser assembly (6), the PIC chip (4) and the driver chip (3) are all arranged on the heat sink (8); the heat sink (8) includes a third mounting portion (85) for mounting the optical fiber array (5) and the laser assembly (6); a heat sink side plate (81) is vertically arranged on the side of the third mounting portion (85) of the heat sink (8) at an edge close to a heat source; and the heat sink side plate (81) is provided on the heat sink side plate. The board (81) extends and protrudes from the lower cover (1), and the portion protruding from the lower cover (1) contacts the side wall of the upper cover via a heat-conducting 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); a wire bonding pad array is provided on the upper surface of the daughter board (9) near the periphery of the driver chip (3) and the PIC chip (4), and the daughter board (9) is connected to the PCB board (2) via the pad array; the daughter board (9) and the PCB board (2) are made of the same material, and the daughter board (9) and the PCB board (2) are fixed by welding.

2. The optical module sub-board structure according to claim 1, characterized in that: The heat sink (8) further includes a first mounting portion (83) for mounting the PIC chip (4) and a second mounting portion (84) for mounting the driver chip (3). The first mounting portion (83) is a first flat plate having the same size as the PIC chip (4), the upper surface of the first flat plate being a first mounting plane, and the PIC chip (4) is arranged in contact with the first mounting plane; The second mounting portion (84) is arranged adjacent to the first mounting portion (83) and is 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); the second mounting portion (84) is a second flat plate having the same size as the driver chip (3); the upper surface of the second flat plate is a second mounting plane, and the driver chip (3) is arranged in contact with the second mounting plane; a gap is left between each two adjacent second mounting portions (84); The third mounting portion (85) is arranged adjacent to the first mounting portion (83) and is 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 assembly (6) are arranged in contact with the third mounting plane.

3. The optical module sub-board structure according to claim 2, characterized in that: The edge of the daughter board (9) is extended with a plurality of extension protrusions (91) for filling the gaps around the driver chip (3) and the PIC chip (4).

4. The optical module sub-board structure according to claim 2, characterized in that: Welding bumps (92) are provided on the surface of the sub-board (9) in contact with the PCB (2) and on the surface of the extended protrusion (91) in contact with the PCB (2).

5. The optical module sub-board structure according to claim 2, characterized in that: The heat dissipation plate (8) is an integrated structure and is made of tungsten-copper alloy.

6. The optical module sub-board structure according to claim 5, characterized in that: A back heat dissipation protrusion (86) is provided on the surface of the heat dissipation plate (8) that is in contact with the PCB board (2) at a position opposite to the heat source. The back heat dissipation protrusion (86) passes through a through groove provided on the PCB board (2) and is in contact with the lower cover (1) through a thermal pad.

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