CN115087191A - High bandwidth EML substrate - Google Patents

Abstract

The invention relates to an EML substrate with high bandwidth, which comprises a PCB (printed circuit board), an CUW substrate and an ALN substrate; wherein the PCB processes high-speed digital signals; the ALN substrate is provided with a front surface and a back surface, wherein a circuit for processing a high-speed analog signal is arranged on the front surface of the ALN substrate; one side of the back surface of the ALN substrate is provided with a step-shaped recess in the thickness direction, an EML chip is arranged in the step-shaped recess, and the depth of the step-shaped recess is greater than the thickness of the EML chip, so that the EML chip is not exposed out of the back surface of the ALN substrate when the EML chip is welded in the step-shaped recess in a gold-tin solder ball mode; the non-step recessed portion of the back surface of the ALN substrate is attached to the CUW substrate in a manner that facilitates heat conduction; CUW the substrate is connected to the PCB board such that the ALN substrate and the PCB board are not in direct contact with each other. The invention can optimize the-3 dB bandwidth of the high-speed link of the EML substrate from the existing 40GHz to more than 70 GHz.

Description

High bandwidth EML substrate

Technical Field

The invention relates to a photoelectric conversion device in optical fiber communication, belongs to the technical field of optical communication, and particularly relates to a high-bandwidth EML (electro absorption Modulated Laser) substrate structure. In particular to an EML substrate with a-3 dB bandwidth larger than 70GHz and a high bandwidth, which is suitable for the high-speed link requirement of the next generation of single-wave 200G optical module.

Background

In recent years, the continuous development of cloud computing and data centers has increasingly demanded short-distance broadband transmission. The generation of 5G communication and the change of communication architecture will cause large data burst, requiring the speed of optical module in data center to be higher and higher, the single channel speed of optical module is developed from 10Gb/s to today's 100Gb/s and future 200Gb/s, and the bandwidth demand of high speed link of optical module is also higher and higher. In short-range applications, although Direct Modulation Lasers (DMLs) have the advantages of low cost and low power consumption, their modulation bandwidth and transmission distance are limited by the relaxation oscillation frequency and frequency chirp. Electro-absorption modulated lasers (EMLs) have advantages over DMLs in terms of chirp, extinction ratio, eye diagram, jitter, transmission distance, etc., and can achieve higher rates and longer distance transmission.

The EML is monolithically integrated by a Distributed Feedback (DFB) laser and an Electric Absorption (EA) modulator, the DFB laser part adopts a multi-quantum well active region to provide gain, and the selection of a lasing wavelength is realized by utilizing a grating so as to ensure single-mode operation; EA modulators use the Quantum Confinement Stark Effect (QCSE) of quantum well materials under an applied electric field to achieve intensity modulation of the output light of the laser.

However, in the technical scheme of the EML substrate in the prior art, the driving circuit, the high-frequency coupling capacitor and the high-speed bias-T circuit are arranged on the PCB, the EML chip is arranged on the ALN (aluminum nitride) substrate through silver paste, the ALN substrate is arranged on the CUW (copper-tungsten) substrate, and the CUW substrate is adhered to the PCB through black paste. The PCB and the EML substrate are connected through a gold wire WB1, and the EML impedance matching capacitor and the resistor on the ALN substrate are connected with the EML chip through a gold wire WB 2. In the technical scheme, the elements on the PCB and the elements on the ALN substrate are distributed and dispersed, the high-speed loss of the PCB is large, and the insertion loss of part of high-speed routing on the PCB is large, so that the bandwidth is influenced; and WB bonding pads and WB gold threads for connecting the PCB, the ALN substrate and the EML chip have equivalent inductance, so that the WB bonding pads and the WB gold threads are a bottleneck for limiting a link to carry out high-speed transmission, the bandwidth of the current high-speed link scheme is limited to 40GHz, the lifting space is limited, and the performance requirement that the-3 dB bandwidth of a next-generation single-wave 200G optical module is larger than 70GHz cannot be met.

Specifically, when the current 100G optical module adopts a PAM4 modulation mode, the-3 dB bandwidth of a high-speed link of the optical module is required to be controlled within 40 GHz; when the single channel rate is increased to 100Gb/s, that is, the single wave transmission rate of the optical module reaches 200G, so as to meet the transmission requirements of 4-channel 800G and 8-channel 1.6T optical modules, the-3 dB bandwidth requirement of a high-speed link is about 70GHz, and the existing high-speed link connection scheme cannot meet the high bandwidth requirement, so that a new technical breakthrough is needed.

Disclosure of Invention

In order to solve the above technical problem, the present invention provides an EML substrate with high bandwidth, which includes a PCB, an CUW substrate, and an ALN substrate; the ALN substrate is arranged on the CUW substrate, and the CUW substrate is connected with the PCB, so that the ALN substrate and the PCB are not in direct contact with each other; the PCB processes high-speed digital signals; the ALN substrate is provided with a front surface and a back surface, wherein a circuit for processing a high-speed analog signal is arranged on the front surface of the ALN substrate; one side of the back surface of the ALN substrate is provided with a recess in the thickness direction, an EML chip is arranged in the recess, and the depth of the recess is greater than the thickness of the EML chip, so that when the EML chip is welded in the recess in a gold-tin solder ball mode, the EML chip is not exposed out of the back surface of the ALN substrate; the EML chip is electrically connected to the front side of the ALN substrate through a gold wire through hole; the non-stepped recessed portion of the backside of the ALN substrate and the CUW substrate are bonded together in a manner that facilitates thermal conduction.

In the above technical solution, the ALN substrate is an aluminum nitride substrate, and the CUW substrate is a copper-tungsten substrate.

In the above technical solution, the ALN substrate is bonded to the CUW substrate through silver paste; the CUW base plate is connected with the PCB plate through black glue.

In the technical scheme, the recess of the EML chip arranged on the back surface of the ALN substrate is a step-shaped recess; the EML chip is arranged in a step-shaped recess on the back surface of the ALN substrate and an enclosed space of the CUW substrate, and a gap between the EML chip and the enclosed space is filled with heat-conducting silver adhesive.

In the above technical solution, the PCB board is provided with an ODSP circuit, and the ODSP circuit includes an optical DSP chip.

In the above technical solution, the circuit for processing the high-speed analog signal disposed on the front surface of the ALN substrate includes a high-frequency coupling capacitor, an impedance matching resistor, a coupling capacitor, a driving circuit, and a bias T circuit.

In the technical scheme, the ODSP circuit connects an electric signal to the front surface of the ALN substrate through a connecting wire, the ODSP circuit is connected with the data sending pins TD + and TD-of the driving circuit, the output of the driving circuit is connected to the via hole through a high-frequency coupling capacitor, and two ends of the high-frequency coupling capacitor are respectively connected to the positive voltage VCC and the negative voltage VEE of the power supply through the bias T circuit.

In the above technical solution, the high-frequency driving signal, the power ground GND and the laser bias signal on the front surface of the ALN substrate are respectively led to the back surface of the ALN substrate through the via holes and connected to the EML chip through the corresponding solder balls.

In the above technical solution, the bias T circuit connected to VCC includes a resistor and a low-frequency inductor connected in parallel and then connected in series with the high-frequency magnetic bead.

In the above technical solution, the bias T circuit connected to the VEE includes connecting a resistor and a low-frequency inductor in parallel and then connecting the resistor and the low-frequency inductor in series with the high-frequency magnetic bead.

The invention achieves the following technical effects:

1. the invention replaces the process of connecting the gold wire with the EML chip, which causes bandwidth limitation in the prior art, with the high-speed solder ball, thereby eliminating the influence of the wire inductance effect caused by the gold wire connection and increasing the bandwidth of the substrate;

2. the invention transfers the high-speed devices which are arranged on the PCB board and used for processing the high-frequency analog signals in the prior art to the ALN substrate, so that the distance between the high-speed devices is shortened, and the insertion loss is reduced;

3. the invention replaces the high-speed wiring on the PCB board in the prior art with the high-speed wiring on the ALN substrate, and the insertion loss of the high-speed wiring on the ALN substrate is far less than that of the wiring on the PCB board, thereby further improving the high-speed bandwidth.

Drawings

FIG. 1 is a top view of a high bandwidth EML substrate structure of the present invention;

fig. 2 is a side view of a high bandwidth EML substrate structure of the present invention.

The labels in the figure are: the circuit comprises a 10-PCB, a 20-CUW substrate, a 30-ALN substrate, a 40-bias-T circuit, a 50-EML chip, an 11-ODSP circuit, a 12-connecting wire, a 31-high-frequency coupling capacitor, a 32-impedance matching resistor, a 33-coupling capacitor, a 34-driving circuit, a 35-via hole, a 41-resistor, a 42-low-frequency capacitor, a 43-high-frequency magnetic bead, a 44-resistor, a 45-low-frequency capacitor, a 46-high-frequency magnetic bead, a 51-solder ball, a 52-power supply GND solder ball, a 53-laser bias signal solder ball and 54-silver adhesive.

Detailed Description

The invention is described in further detail below in connection with the accompanying drawings and the detailed description, in order to facilitate understanding and implementation of the invention by those skilled in the art.

In order to optimize the-3 dB bandwidth of the high-speed link of the EML substrate of the optical module from the current 40GHz to greater than 70GHz and enable the single-wave transmission rate of the optical module to reach 200G to meet the transmission requirements of the optical module of 4-channel 800G and 8-channel 1.6T, the invention provides the EML substrate of high bandwidth, as shown in fig. 1-2, which comprises a PCB board 10, an CUW substrate 20 and an ALN substrate 30, wherein the ALN substrate 30 is bonded on the CUW substrate 20 through silver paste, and the CUW substrate 20 is connected with the PCB board 10 through black paste, so that the ALN substrate 30 and the PCB board 10 are not in direct contact with each other.

The ALN substrate 30 has front and back surfaces, wherein the front surface of the ALN substrate 30 is provided with a high-frequency coupling capacitor 31, an impedance matching resistor 32, a coupling capacitor 33, a driving circuit 34, and a bias-T circuit 40, one side of the back surface of the ALN substrate 30 has a step-shaped recess in the thickness direction, the EML chip 50 is disposed in the step-shaped recess, and the depth of the step-shaped recess is greater than the thickness of the EML chip 50, so that the EML chip 50 does not expose the back surface of the ALN substrate 30 when the EML chip 50 is soldered in the step-shaped recess in a gold-tin solder ball manner, and preferably, a certain distance is provided between the top of the EML chip 50 and the back surface of the ALN substrate 30; the non-stepped recessed portion of the backside of the ALN substrate 30 and the CUW substrate 20 are attached together in a manner that facilitates thermal conduction. Preferably, as shown in fig. 1, the CUW substrate 20 has a larger area than the ALN substrate 30 when viewed from above; that is, after the ALN substrate 30 is bonded to the CUW substrate 20, the CUW substrate 20 has a constant extending protrusion from the ALN substrate 30 in all directions in the circumferential direction when viewed from above; as shown in fig. 2, the EML chip 50 is disposed in the space enclosed by the step-shaped recess on the back surface of the ALN substrate 30 and the CUW substrate 20, and preferably, the space between the EML chip 50 and the substrate CUW is filled with the thermal conductive silver paste 54.

The PCB board 10 is provided with an ODSP circuit 11, and the ODSP circuit 11 is an optical DSP circuit and includes an optical DSP chip. The ODSP circuit 11 connects the electrical signals to the front surface of the ALN substrate 30 via the connection lines 12, the electrical signals connected by the connection lines 12 include at least TD + signals and TD-signals, GND and Laser Bias (Laser Bias) signals, preferably, a signal ground GND or a power ground GND are also correspondingly arranged on two sides of a signal line connected with a transmission data pin TD + and a transmission data pin TD-of the driving circuit 34, respectively, an output of the driving circuit 34 is connected to the via hole 35 through the high-frequency coupling capacitor 31, two ends of the high-frequency coupling capacitor 31 are connected to a positive voltage VCC and a negative voltage VEE of a power supply through a Bias T circuit 40 (namely, a Bias T circuit), the Bias T circuit 40 connected to VCC comprises a resistor 41 and a low-frequency inductor 42 which are connected in parallel and then connected in series with a high-frequency magnetic bead 43, and the Bias T circuit 40 connected to VEE comprises a resistor 44 and a low-frequency inductor 45 which are connected in parallel and then connected in series with a high-frequency magnetic bead 46. The via 35 is further connected to the power ground GND through the resistor 32 and the coupling capacitor 33 so as to lead the power ground GND on the front surface of the ALN substrate 30 to the EML chip 50 on the back surface of the ALN substrate 30, and the via 35 is further electrically connected to the EML chip 50 on the back surface of the ALN substrate 30 and the high-frequency coupling capacitor 32 on the front surface of the ALN substrate 30; alternatively, the high-frequency driving signal, the power ground GND and the Laser Bias (Laser Bias) signal are respectively led from the front surface of the ALN substrate 30 to the back surface of the ALN substrate 30 through three via holes 35, and are respectively connected to the EML chip 50 through solder balls 51, power GND solder balls 52 and Laser Bias signal solder balls 53.

Therefore, the PCB 10 and the electronic devices thereon are mainly used for processing high-speed digital signals, the ALN substrate 30 is an aluminum nitride substrate, and the CUW substrate 20 is a copper-tungsten substrate. The electronic devices on the ALN substrate 30 are mainly used for high-speed analog signal processing and photoelectric conversion, the ALN substrate 30 itself also functions as a heat sink, and the CUW substrate 20 mainly functions to support heat dissipation.

According to the technical scheme, the components (such as the high-frequency coupling capacitor 31, the impedance matching resistor 32, the coupling capacitor 33, the driving circuit 34, the bias-T circuit 40 and the EML chip 50) for processing the high-frequency analog signal part are arranged on the ALN substrate 30, and all the high-frequency components are connected through the high-speed wiring on the ALN substrate 30. The ALN substrate 30 is formed into an inverted step shape relative to the CUW substrate 20, and the high-speed wires are connected to the step recesses on the back of the ALN substrate 30 from the front of the ALN substrate 30 through one or more gold wire through holes 35 to form gold-tin solder balls 51, power supply GND solder balls 52 and laser bias signal solder balls 53. The EML chip 50 is inversely welded below the step, and a high-speed radio frequency link, a power supply GND and a laser bias signal required by the work of the EML chip 50 are connected with the ALN substrate 30 through a gold tin solder ball 51, a power supply GND solder ball 52 and a laser bias signal solder ball 53. Therefore, the invention has the following technical effects:

1. the technology of gold wire connection (WB) EML chips causing bandwidth limitation in the prior art is replaced by high-speed solder balls, so that the influence of a lead inductance effect caused by gold wire connection is eliminated, and the substrate bandwidth is increased;

2. high-speed devices which are arranged on a PCB board in the prior art and used for processing high-frequency analog signals are transferred to an ALN substrate, so that the distance between the high-speed devices is shortened, and the insertion loss is reduced;

3. the high-speed wiring on the PCB board in the prior art is replaced by the high-speed wiring on the ALN substrate, and the insertion loss of the high-speed wiring on the ALN substrate is far smaller than that of the wiring on the PCB board, so that the high-speed bandwidth is further improved.

Therefore, the-3 dB bandwidth of the high-speed link of the EML substrate can be optimized to be larger than 70GHz from the existing 40GHz, the single-wave transmission rate of the optical module can reach 200G, and the transmission requirements of the optical module with 4-channel 800G and 8-channel 1.6T can be met.

Those of skill in the art will understand that reference throughout the specification to "one embodiment," "some embodiments," "an example," "a specific example" or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Moreover, the various embodiments or examples and features of the various embodiments or examples described in this specification can be combined and combined by those skilled in the art without being mutually inconsistent.

Although embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are exemplary and not to be construed as limiting the present invention, and that changes, modifications, substitutions and alterations can be made to the above embodiments by those skilled in the art within the scope of the present invention.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (10)

1. A high-bandwidth EML substrate comprises a PCB board, an CUW substrate and an ALN substrate; the ALN substrate is arranged on the CUW substrate, and the CUW substrate is connected with the PCB, so that the ALN substrate and the PCB are not in direct contact with each other; the method is characterized in that:

the PCB processes high-speed digital signals;

the ALN substrate is provided with a front surface and a back surface, wherein a circuit for processing a high-speed analog signal is arranged on the front surface of the ALN substrate; one side of the back surface of the ALN substrate is provided with a recess in the thickness direction, an EML chip is arranged in the recess, and the depth of the recess is greater than the thickness of the EML chip, so that when the EML chip is welded in the recess in a gold-tin solder ball mode, the EML chip is not exposed out of the back surface of the ALN substrate; the EML chip is electrically connected to the front side of the ALN substrate through a gold wire through hole; the non-stepped recessed portion of the backside of the ALN substrate and the CUW substrate are bonded together in a manner that facilitates thermal conduction.

2. The high bandwidth EML substrate of claim 1, wherein: the ALN substrate is an aluminum nitride substrate, and the CUW substrate is a copper-tungsten substrate.

3. The high bandwidth EML substrate of claim 2, wherein: the ALN substrate is bonded on the CUW substrate through silver adhesive; the CUW base plate is connected with the PCB plate through black glue.

4. The high bandwidth EML substrate of claim 3, wherein: the back of the ALN substrate is provided with a step-shaped recess of the EML chip; the EML chip is arranged in a step-shaped recess on the back surface of the ALN substrate and an enclosed space of the CUW substrate, and a gap between the EML chip and the enclosed space is filled with heat-conducting silver adhesive.

5. The high bandwidth EML substrate of claim 1, wherein: and an ODSP circuit is arranged on the PCB and comprises an optical DSP chip.

6. The high bandwidth EML substrate of claim 5, wherein: the circuit for processing the high-speed analog signal arranged on the front surface of the ALN substrate comprises a high-frequency coupling capacitor, an impedance matching resistor, a coupling capacitor, a driving circuit and a bias T circuit.

7. The high bandwidth EML substrate of claim 6, wherein: the ODSP circuit connects an electric signal to the front side of the ALN substrate through a connecting line, a data sending pin TD + and a data sending pin TD-of the driving circuit are connected, the output of the driving circuit is connected to the via hole through a high-frequency coupling capacitor, and two ends of the high-frequency coupling capacitor are connected to a positive voltage VCC and a negative voltage VEE of a power supply through a bias T circuit respectively.

8. The high bandwidth EML substrate of claim 7, wherein: the high-frequency driving signal, the power ground GND and the laser bias signal on the front surface of the ALN substrate are respectively led to the back surface of the ALN substrate through via holes and are connected to the EML chip through corresponding solder balls.

9. The high bandwidth EML substrate of claim 8, wherein: and the bias T circuit connected to the VCC comprises a resistor and a low-frequency inductor which are connected in parallel and then connected in series with the high-frequency magnetic bead.

10. The high bandwidth EML substrate of claim 8, wherein: and the bias T circuit connected to the VEE comprises a resistor and a low-frequency inductor which are connected in parallel and then connected in series with the high-frequency magnetic beads.

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