A high-speed optical module with optical components directly soldered to a circuit board

Abstract

This utility model discloses a high-speed optical module with direct soldering between optical components and a circuit board. It includes a TOSA (Optical Transmitter Component) optical transmitter, a ROSA (Optical Receiving Component), a PCB assembly, and a reflow solder paste layer. Both the TOSA and ROSA have a row of gold-plated copper alloy pins with a pin diameter of 0.24-0.26 mm. The PCB assembly surface has teardrop-shaped gradient pads corresponding to the pins. These teardrop-shaped gradient pads transition to a standard 50Ω single-ended or 100Ω differential transmission line via an impedance gradient transmission line. This application, through the above design, solves problems such as impedance discontinuity, increased loss, aggravated crosstalk, and thermomechanical stress, ensuring signal integrity and achieving the same performance and reliability as using an FPC (Flexible Printed Circuit).

Description

Technical Field

[0001] This utility model relates to the field of optical communication technology, and in particular to a high-speed optical module for optical modules with speeds of 10Gbps and above, which enables direct welding of optical devices and PCB components. Background Technology

[0002] High-speed optical modules (10Gbps and above) generally consist of a structural housing, optical components, and a PCB (Printed Circuit Board) assembly. In existing technologies, the electrical connection between the optical components and the PCB assembly uses a flexible printed circuit board (FPC) to ensure impedance matching and signal integrity. However, FPCs are expensive, and the connection between the FPC and the PCB assembly, and between the FPC and the optical components, requires two separate soldering processes, resulting in complex workflows, low yields, and long production cycles. If the FPC is eliminated entirely and the optical component pins are soldered directly to the PCB assembly, the following challenges arise:

[0003] 1. Impedance discontinuity: Conventional optical devices have a pin diameter of 0.45mm, resulting in large parasitic inductance and capacitance, which leads to impedance abrupt changes and degrades the integrity of high-speed signals;

[0004] 2. Secondary thermal shock during reflow soldering: After the two soldering processes of FPC are changed to one reflow soldering process, the reliability of the solder joints of optical devices and PCB components must be met simultaneously.

[0005] 3. Crosstalk and loss: When the pin layout, pads and transmission line structure of optical devices are not optimized, the crosstalk and insertion loss between differential pairs increase significantly.

[0006] 4. Thermomechanical stress: The thermal expansion coefficients of the metal casing of optical devices and PCBs differ greatly, and direct soldering is prone to cracking and poor soldering. Utility Model Content

[0007] A brief overview of embodiments of the present invention is provided below to provide a basic understanding of certain aspects of the invention. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0008] To address the aforementioned technical problems, this application provides a high-speed optical module with direct soldering between optical components and a circuit board, comprising an optical emitting component (TOSA), an optical receiving component (ROSA), a PCB assembly, and a reflow solder paste layer. Both the TOSA and ROSA have a row of gold-plated copper alloy pins with a pin diameter of 0.24-0.26 mm. The PCB assembly surface has teardrop-shaped gradient pads corresponding to the pins, which transition to a standard 50Ω single-ended or 100Ω differential transmission line via an impedance gradient transmission line. The teardrop-shaped gradient pads are the signal pads soldered to the optical component pins.

[0009] Furthermore, the optical emitting component TOSA and the optical receiving component ROSA are respectively encapsulated in a metal housing. The bottom surface of the metal housing of both the optical emitting component TOSA and the optical receiving component ROSA is less than 1mm from the surface of the pads of the PCB assembly, so as to minimize the pin suspension length.

[0010] Furthermore, the tops of the metal housings of the optical emitting component TOSA and the optical receiving component ROSA are flat, mirror-finished surfaces with a flatness of ≤0.05mm, allowing them to be directly picked up by the vacuum nozzle of the placement machine without manual clamping.

[0011] Furthermore, a continuous GND reference plane is provided below and around the teardrop-shaped gradient pad, and a coplanar waveguide structure is adopted. A ground hole array is arranged around the signal pad with a spacing of <100μm to form a low-inductance backflow path; the spacing between adjacent signal pads is ≥0.8mm, and the differential pair positive and negative signal path length matching error is ≤1mil (25.4μm).

[0012] Furthermore, the PCB assembly is provided with vent holes located within the PCB assembly area between the TOSA projection area of ​​the light emitting component and the ROSA projection area of ​​the light receiving component, for thermal balance during the reflow soldering process.

[0013] Preferably, the diameter of the gold-plated copper alloy pins of the optical emitting component TOSA and the optical receiving component ROSA is 0.25 mm.

[0014] Furthermore, the reflow solder paste layer has a thickness of 0.20mm–0.30mm, forming a reliable solder joint with the 0.24-0.26mm diameter leads.

[0015] Furthermore, the gold-plated copper alloy pins of the optical transmitting component TOSA and the optical receiving component ROSA are arranged in the following order: signal ground—signal positive—signal negative—signal ground. The signal grounds on both sides provide a return path for high-speed signals and reduce electromagnetic interference.

[0016] Furthermore, the optical emitting component TOSA is a single-row 4-pin device, and the optical receiving component ROSA is a single-row 5-pin device. The pin surfaces are plated with a thick gold layer with a thickness ≥0.1μm to reduce contact resistance and skin loss.

[0017] Furthermore, the PCB assembly inserts ground wires or ground shielding via arrays between high-frequency signal pairs to suppress crosstalk; the ground via array is arranged coplanarly with the signal pads to form a near 360° electromagnetic shielding structure.

[0018] Furthermore, the PCB assembly uses FR-4 or high-frequency mixed-pressure board material with a dielectric constant tolerance of ≤±3% to ensure impedance consistency.

[0019] Furthermore, the bottom edges of the metal housings of the optical emitting component TOSA and the optical receiving component ROSA are chamfered with an angle of 30°–45°, which is used for self-positioning and releasing thermal stress during reflow soldering.

[0020] Through the above structure, the present invention achieves the following technical effects:

[0021] 1. Eliminating FPC reduces material costs by 25%–30%;

[0022] 2. The process has been reduced from two welding operations to one reflow soldering operation, shortening the cycle time from 180 seconds / piece to 45 seconds / piece, thus increasing production efficiency by 75%.

[0023] 3. The 0.25mm pin diameter combined with teardrop-shaped gradient pads ensures continuous impedance, return loss ≤-20dB@10GHz, and signal integrity at the same level as FPC.

[0024] 4. Yield improvement of 8%–12%, reduction of labor costs by more than 30%, and significant reduction of static electricity and contamination risks.

[0025] In summary, this application solves the problems of impedance discontinuity, increased loss, aggravated crosstalk, and thermomechanical stress through the above design, ensuring signal integrity and achieving the same performance and reliability as using an FPC. Attached Figure Description

[0026] This invention can be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which the same or similar reference numerals are used throughout the drawings to denote the same or similar parts. These drawings, together with the following detailed description, are incorporated in and form part of this specification, and are used to further illustrate preferred embodiments of the invention and explain the principles and advantages of the invention. In the drawings:

[0027] Figure 1 This is a schematic diagram of the welding structure for optical devices;

[0028] Figure 2 This is a schematic diagram of the assembled high-speed optical module of this utility model. Detailed Implementation

[0029] Embodiments of the present invention will now be described with reference to the accompanying drawings. Elements and features described in one drawing or embodiment of the present invention may be combined with elements and features shown in one or more other drawings or embodiments. It should be noted that, for clarity, representations and descriptions of components and processes unrelated to the present invention and known to those skilled in the art have been omitted from the drawings and description.

[0030] In the description of this utility model, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0031] This application optimizes the optical module structure, thereby enabling direct soldering of optical devices to PCBAs without the need for a flexible FPC transition, thus reducing the cost of optical modules and improving production efficiency.

[0032] In actual implementation, the following challenges were found: One of the core advantages of FPC is that its impedance can be precisely controlled (usually designed as 50Ω single-ended or 100Ω differential), and its structure is relatively uniform. When directly soldered, the signal path will experience a series of regions with drastic impedance changes. To address these challenges, this application has optimized the pin signal arrangement and pin size of TOSA and ROSA, and optimized the pad structure and gradient transmission line structure of the PCB assembly.

[0033] For details, see Figure 1 and Figure 2This embodiment provides a high-speed optical module with direct soldering between optical components and a circuit board, including an optical transmitter component TOSA1, a receiver component ROSA2, a PCB assembly 3, a reflow solder paste layer, and a structural housing 4. The TOSA is the main component of the optical transmitter module, primarily converting electrical signals to optical signals. The ROSA is the optical receiver component, and the PCB assembly forms the main structure and is also the main component of the module. In high-data-rate optical modules, PIN or ADP photodiodes and TIAs are typically assembled in a sealed metal housing to form the receiver component. The optical transmitter component TOSA1, the receiver component ROSA2, and the structural housing 4, when assembled, constitute a high-speed optical module for fiber optic communication.

[0034] The pin signal arrangement of the optical transmitter TOSA1 and receiver ROSA2 is signal ground, signal positive, signal negative, and signal ground again. The two signal grounds are located on opposite sides, forming an electrical signal return path for the positive and negative signal pins, effectively reducing electrical signal interference. Simultaneously, the pins of the optical devices (optical transmitter TOSA1 and receiver ROSA2) are designed with a diameter of 0.25mm (compared to 0.45mm for conventional optical devices). This reduces parasitic inductance and capacitance, and matches the impedance of the PCB component signal lines, effectively ensuring high-frequency signal integrity.

[0035] In addition, the light emitting component TOSA1 and the receiving component ROSA2 each have a metal housing. The top of the metal housing is mirror-polished with a flatness of ≤0.05mm, allowing the pick-and-place machine's vacuum nozzle to directly pick up and accurately place the components without manual clamping. The bottom surface of the metal housing has a 30° chamfer around its perimeter, which facilitates reflow soldering self-positioning and thermal stress release.

[0036] PCB assembly 3 has teardrop-shaped gradient pads on its surface, corresponding one-to-one with the pins of the light emitting assembly TOSA1 and the receiving assembly ROSA2. In a specific embodiment, the pad width gradually transitions from 0.25mm to 0.40mm before connecting to a standard 50Ω / 100Ω transmission line, achieving a smooth impedance transition. A continuous GND reference plane is placed 0.1mm below the pads, and ground vias are arranged in an array with 0.08mm spacing around the pads, forming a coplanar waveguide structure to ensure low impedance in the return path. The path lengths of the differential pair's positive and negative signals are laser-adjusted, with an error ≤0.8mil.

[0037] Among them, teardrop-shaped gradient pads refer to the transition between the pad and the trace in a teardrop shape, which is used to reduce impedance abrupt changes and improve mechanical strength. Generally, its outline dimensions are: pad major axis 0.40mm, minor axis 0.25mm, transition angle 45°; copper thickness 35µm, solder mask opening 50µm on one side.

[0038] PCB assembly 3 has a through-hole vent between the light emitting component TOSA1 and the receiving component ROSA2. As a specific embodiment, the vent has a diameter of 0.8mm and is designed to penetrate the PCB assembly to achieve thermal balance during reflow soldering, reduce the thermal gradient during the reflow soldering process, and minimize the risk of PCB warpage.

[0039] The optical components are placed as close as possible to the PCB assembly to ensure that the pin overhang length and the total length of the connection path are shortened, which is controlled to <1mm in this embodiment.

[0040] The structural shell 4 is designed to enclose the light emitting component TOSA1, the receiving component ROSA2, and the PCB component 3.

[0041] During assembly, after TOSA1 and ROSA2 are picked up by the pick-and-place machine, their pins fall directly onto the reflow solder paste layer on the teardrop-shaped gradient pad 31. The reflow soldering completes all solder joints in one go. Then, it is installed into the structural housing 4 to form a high-speed optical module that conforms to the SFP / SFP+ protocol.

[0042] This application is implemented using the aforementioned single-row pin TOSA, ROSA, and PCB assembly, and solves problems such as impedance discontinuity, increased loss, aggravated crosstalk, and thermomechanical stress through the following improvements:

[0043] 1. The pins use 0.24-0.26mm (preferably 0.25mm) gold-plated material to reduce parasitic inductance and capacitance, and match the impedance of the PCB component signal lines to effectively ensure the integrity of high-frequency signals. In particular, reducing the pin size from the traditional 0.45mm to 0.25mm reduces the equivalent cylindrical conductor cross-sectional area by about 69%, which greatly reduces parasitic inductance and capacitance, thereby achieving low insertion loss and low thermal stress.

[0044] 2. The pin signal layout is as follows: signal ground, signal positive, signal negative, signal ground; the two signal grounds are located on both sides, forming an electrical signal return to the positive and negative pins, which can effectively reduce electrical signal interference.

[0045] 3. Designed with dedicated, optimized teardrop-shaped gradient pads; the teardrop-shaped gradient pads form a smaller wetting angle with the 0.25mm fine leads, thus providing high solder paste self-alignment capability;

[0046] In summary, this application, through the above-mentioned solution, ensures signal integrity and achieves the same performance and reliability as using an FPC.

[0047] In the above description of specific embodiments of the present invention, features described and / or shown for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0048] Although the present invention has been disclosed above through the description of specific embodiments, it should be understood that all the embodiments and examples described above are exemplary and not restrictive. Those skilled in the art can design various modifications, improvements, or equivalents to the present invention within the spirit and scope of the appended claims. These modifications, improvements, or equivalents should also be considered to be included within the protection scope of the present invention.

Claims

1. A high speed optical module with optical device directly soldered to a circuit board, characterized in that, The system includes an optical emitting component (TOSA), an optical receiving component (ROSA), a PCB assembly, and a reflow solder paste layer. Both the TOSA and ROSA have a row of gold-plated copper alloy pins with a pin diameter of 0.24-0.26 mm, arranged in the order of signal ground—signal positive—signal negative—signal ground. The PCB assembly has teardrop-shaped gradient pads on its surface corresponding to the pins. These teardrop-shaped gradient pads are transitioned to a standard 50Ω single-ended or 100Ω differential transmission line via an impedance gradient transmission line.

2. The high-speed optical module of claim 1, wherein, The teardrop-shaped gradient pads are provided with a continuous GND reference plane below and around them, and a ground hole array is arranged at a spacing of <100μm to form a coplanar waveguide structure, and the spacing between adjacent teardrop-shaped gradient pads is ≥0.8mm.

3. The high-speed optical module with optical device and circuit board direct soldering connection of claim 1, wherein, The optical emitting component TOSA and the optical receiving component ROSA are respectively encapsulated in a metal shell, and the bottom surface of the metal shell of both the optical emitting component TOSA and the optical receiving component ROSA is less than 1mm from the surface of the solder pads of the PCB assembly.

4. The high-speed optical module of claim 3, wherein the optical device is directly soldered to the circuit board. The tops of the metal casings of both the optical emitting component TOSA and the optical receiving component ROSA are flat and mirror-finished.

5. The high-speed optical module with optical device and circuit board direct soldering connection of claim 1, wherein, The PCB assembly is provided with vent holes located within the PCB assembly area between the TOSA projection area of ​​the light emitting component and the ROSA projection area of ​​the light receiving component.

6. The high-speed optical module with direct welding of optical devices and circuit boards according to claim 1, characterized in that, The diameter of the gold-plated copper alloy pins of the optical emitting component TOSA and the optical receiving component ROSA is 0.25 mm.

7. The high-speed optical module with direct soldering between the optical device and the circuit board according to claim 1, characterized in that, The thickness of the reflow solder paste layer is 0.20mm–0.30mm.

8. The high-speed optical module with direct welding of optical devices and circuit boards according to claim 1, characterized in that, The optical transmitting component TOSA is a single-row 4-pin device, and the optical receiving component ROSA is a single-row 5-pin device.

9. The high-speed optical module with direct soldering between the optical device and the circuit board according to claim 1, characterized in that, The PCB assembly inserts a ground wire or ground shielding via array between high-frequency signal pairs. The ground wire or ground shielding via array is arranged coplanarly with teardrop-shaped gradient pads to form a near 360° electromagnetic shielding structure.

10. The high-speed optical module with direct welding of optical devices and circuit boards according to claim 3, characterized in that, The bottom edge of the metal housing of the optical emitting component TOSA and the optical receiving component ROSA is chamfered at 30°–45°.

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