A stepped substrate suitable for high-speed laser packages

Abstract

The application discloses a stepped substrate suitable for high-speed laser package, which comprises a first substrate, a first solder metal layer and a second solder metal layer arranged on the first substrate, and the second solder metal layer is arranged on the side of the first solder metal layer; a second substrate, a third solder metal layer arranged on the second substrate; wherein the third solder metal layer of the second substrate is soldered and fixed with the second solder metal layer of the first substrate, and the thickness of the second substrate is equivalent to the height of a laser device attached on the first solder metal layer. The application can reduce the wire length between the laser device and the transmission line, and further reduce the signal reflection caused by the inductance effect.

Description

Technical Field

[0001] This application belongs to the field of optoelectronic device technology, specifically relating to a stepped substrate suitable for high-speed laser packaging. Background Technology

[0002] In fiber optic communication technology, semiconductor lasers are primarily used as signal sources. With the continuous improvement of laser chip fabrication technology, not only has the cost of laser chips been significantly reduced, but the modulation frequency of a single laser chip has also reached 10 GHz or even tens of GHz. Currently, the key factor restricting the characteristics and cost of the signal source lies mainly in packaging technology. In the packaging process, the packaging substrate must provide the laser with a high-frequency signal. To meet the requirements of high-frequency transmission and signal coupling, multilayer ceramic or multilayer high-resistivity silicon structures are generally used to form microstrip lines or coplanar microwave waveguides.

[0003] Lasers are typically surface-mounted on a substrate, with transmission lines connected to the laser electrodes via wire bonding. For advanced edge-emitting lasers, the modulation signal can exceed 35 GHz. For high-frequency electromagnetic signals, the inductive effect of the wire bonding is significant, leading to signal reflection. Reducing the wire bonding length is an effective way to mitigate the inductive effect; however, current conventional packaging substrates are planar, and with laser heights ranging from 100 to 200 micrometers, the wire bonding length must be at least greater than the laser height. Therefore, it is necessary to improve existing packaging substrates to reduce the wire bonding length, thereby reducing signal reflection caused by the inductive effect. Summary of the Invention

[0004] In view of the shortcomings or deficiencies of the prior art, the technical problem to be solved by this application is a stepped substrate suitable for high-speed laser packaging, which can reduce the wire bonding length between the laser and the transmission line, thereby reducing signal reflection caused by inductive effect.

[0005] To solve the above-mentioned technical problems, this application provides the following technical solution: This application proposes a stepped substrate suitable for high-speed laser packaging, the stepped substrate comprising: A first substrate, wherein a first welding metal layer and a second welding metal layer are disposed on the first substrate, and the second welding metal layer is disposed on the side of the first welding metal layer; A second substrate, on which a third welding metal layer is disposed; The third welding metal layer of the second substrate is welded and fixed to the second welding metal layer of the first substrate, and the thickness of the second substrate is approximately equal to the height of the laser mounted on the first welding metal layer.

[0006] Alternatively, the first welding metal layer and the second welding metal layer are disposed in parallel, and the area of ​​the first welding metal layer is smaller than the area of ​​the second welding metal layer.

[0007] Alternatively, a cantilever beam structure can be fabricated on the first substrate using MEMS technology, and the first welding metal layer can be welded through the cantilever beam structure for mounting the laser.

[0008] Further optionally, the second substrate is further provided with a connecting metal layer and a transmission line metal layer, wherein the connecting metal layer connects the transmission line metal layer and the third welding metal layer together, wherein the third welding metal layer and the transmission line metal layer are respectively disposed on both sides of the second substrate; And / or, the width of the third welding metal layer is greater than the width of the transmission line metal layer, and the length of the third welding metal layer is not less than the length of the transmission line metal layer; And / or, the thickness of the transmission line metal layer is 0.1~2µm.

[0009] Optionally, the second substrate is provided with a plurality of through holes extending through the second substrate along the thickness direction, and the connecting metal layer is located in the through holes; the through holes are partially filled with a high thermal conductivity metal to help conduct the heat generated by the transmission line to the first substrate.

[0010] Alternatively, the transmission line metal layer may be a coplanar waveguide / microstrip line with a gradient or stepped variation.

[0011] Further optionally, the transmission line metal layer is formed by a combination of one or more materials such as titanium, gold, aluminum, copper, silver, and platinum; And / or, the third weld metal layer is a metal layer formed of copper-tin, silver-tin, or gold-tin alloy material.

[0012] Alternatively, a thin-film thermoelectric cooler (TEC) is further integrated on the second substrate, the thin-film thermoelectric cooler (TEC) being composed of a bismuth tellurium compound and fabricated using thin-film deposition technology.

[0013] Further optionally, a microchannel or a highly thermally conductive material is integrated inside the first substrate, near the bottom of the first weld metal layer; And / or, thin-film resistors and capacitors are also integrated on the first substrate.

[0014] Further optionally, the first substrate is a ceramic substrate, a silicon substrate, a silicon-ceramic composite substrate, or a glass-silicon-glass composite substrate. And / or, the second substrate is a photosensitive glass substrate or a glass substrate that can be strengthened by ion exchange. And / or, the first weld metal layer is a gold-tin alloy layer, And / or, the second weld metal layer is a copper-tin alloy layer.

[0015] Compared with the prior art, this application has the following technical effects: The stepped substrate provided in this application bonds a second substrate to a first substrate, thereby forming a second substrate higher than the first substrate next to the mounted laser. This makes the height of the mounted laser comparable to the height of the second substrate, thus minimizing the wire bonding length between the microstrip line and the laser electrode and reducing inductive effects. Furthermore, since the signal transmission section is located on a glass substrate, the glass has a low dielectric constant and low loss, making it easy to achieve 70 GHz signal transmission. Attached Figure Description

[0016] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This application includes a cross-sectional view of a stepped substrate for high-speed laser packaging according to one embodiment. Figure 2 : A top view of the first substrate in one embodiment of this application; Figure 3 : A top view of the second substrate in one embodiment of this application; Figure label: 1-First substrate, 11-First welding metal layer, 12-Second welding metal layer, 2-Second substrate, 21-Transmission line metal layer, 22-Third welding metal layer, 23-Connection metal layer. Detailed Implementation

[0017] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] like Figure 1-3 As shown in one embodiment of this application, a stepped substrate suitable for high-speed laser packaging is provided, the stepped substrate comprising a first substrate 1 and a second substrate 2.

[0019] The first substrate 1 is a flat plate structure with uniform thickness throughout. Considering the mechanical strength of the device and the optical path requirements of the laser, the thickness of the first substrate 1 is preferably between 100 and 500 μm. The first substrate 1 can be a ceramic substrate, a silicon substrate, a silicon-ceramic composite substrate, or a glass-silicon-glass composite substrate. When there is a need for integrated capacitors, a silicon substrate is preferred. Furthermore, the first substrate 1 is preferably made using low-temperature co-fired ceramic (LTCC) or thin-film ceramic processes, embedding high-Q inductors, capacitor arrays with specific capacitance values, or even simple impedance matching networks between the ceramic layers to achieve three-dimensional integration of passive devices, rather than being limited to surface mounting; changing from passive carrier to active functional integration, reducing package size, thereby improving high-frequency performance (reducing parasitic parameters).

[0020] The first substrate 1 is further provided with a first bonding metal layer 11 for mounting a laser and a second bonding metal layer 12 located next to the first bonding metal layer 11 for mounting a second substrate 2. In this embodiment, the first bonding metal layer 11 is a gold-tin alloy layer formed by metal deposition and photolithography, and the second bonding metal layer 12 is a copper-tin alloy layer formed by metal deposition and photolithography. Preferably, the second bonding metal layer 12 is arranged parallel to the first bonding metal layer 11.

[0021] Optionally, in this embodiment, a cantilever beam structure is fabricated on the first substrate 1 using MEMS technology. The first welding metal layer 11 is then welded onto the cantilever beam structure for mounting the laser. The cantilever beam structure is made of silicon nitride, with the first welding metal layer 11 fabricated on it for mounting the laser. A second substrate 2 is fabricated beside the cantilever beam structure, and a coplanar waveguide is fabricated on the second substrate 2. The cantilever beam structure allows adjustment of the laser's height to precisely match the height of the second substrate, thereby minimizing the wire bonding length.

[0022] Optionally, thin-film resistors and capacitors can also be mass-integrated on the first substrate 1. Simultaneously, transmission lines, vias, and bonding layers are mass-fabricated on the glass wafer (second substrate). Then, wafer-level bonding techniques (such as thermoforming and anodic bonding) are used to align and bond the two wafers. Finally, dicing yields thousands of individual stepped substrates. This setup achieves high consistency, high-volume, and low-cost manufacturing, aligning with modern semiconductor packaging technology trends.

[0023] The second substrate 2 is a photosensitive glass substrate or an ion-exchange-strengthened glass substrate. High aspect ratio vias can be formed more precisely through photolithography and chemical etching. Ion exchange processes can form a compressive stress layer on the glass surface, significantly improving mechanical strength and allowing the use of thinner glass substrates (e.g., <100µm) to further reduce RF losses. This improves processing accuracy and substrate reliability, laying the foundation for higher frequency applications (e.g., above 70 GHz).

[0024] The second substrate 2 has the same dimensions as the area of ​​the second bonding metal layer on the first substrate 1, and the thickness of the second substrate 2 is approximately the same as the thickness of the laser to be mounted. A transmission line metal layer 21 is provided on the top surface of the second substrate 2. This transmission line metal layer 21 can be a microstrip line or a coplanar waveguide structure, which can support the transmission of signals up to 70 GHz.

[0025] On the second substrate 2, in addition to the aforementioned transmission line metal layer 21, a thin-film thermoelectric cooler (TEC) is also integrated. The TEC is composed of a bismuth-tellurium compound and is fabricated using thin-film deposition technology. The TEC can control the temperature of the laser, thereby improving output power and wavelength stability.

[0026] In this embodiment, the transmission line metal layer 21 on the surface of the second substrate 2 is taken as an example as a coplanar waveguide structure. The coplanar waveguide structure is formed by multiple metal layers composed of one or more materials such as titanium, gold, aluminum, copper, silver, and platinum. Considering the skin effect and economic effect of high-frequency signals, the thickness of the metal layer is between 0.1 and 2 μm.

[0027] More preferably, the transmission line metal layer 21 employs a coplanar waveguide / microstrip line with a gradient or stepped variation. At the end closer to the laser mounting area, the linewidth and spacing are optimized for the low impedance of the laser electrodes; at the end further away, they are optimized for a standard 50-ohm interface. This gradient structure enables broadband impedance transformation. These features significantly broaden the effective bandwidth, improve the transmission integrity of high-frequency signals (e.g., above 70 GHz), and reduce return loss.

[0028] Furthermore, inside the first substrate 1, near the bottom of the first welded metal layer 11, microchannels (suitable for silicon substrates to be realized through deep etching process) or highly thermally conductive materials (such as CVD diamond sheets, oriented carbon nanotube arrays) are integrated.

[0029] A third welding metal layer 22 is disposed on the bottom surface of the second substrate 2. This third welding metal layer 22 can be a copper-tin, silver-tin, or gold-tin alloy. This third welding metal layer 22 can be welded and fixed to the second welding metal layer 12 on the first substrate 1, thereby fixing the second substrate 2 onto the first substrate 1. Simultaneously, the third welding metal layer 22 also serves as a reference ground layer for the transmission line metal layer 21. Preferably, the width of the third welding metal layer 22 is greater than the width of the transmission line metal layer 21, and its length is not less than the length of the transmission line.

[0030] In another preferred embodiment, the second substrate 2 is further provided with a connecting metal layer 23, which connects the transmission line metal layer 21 and the third welding metal layer 22 to further improve the electrical performance of the transmission line. The connecting metal layer 23 can be a metal layer formed on the sidewall of the second substrate 2, or it can be formed by creating multiple through-holes along the thickness direction through the second substrate 2, and forming a metal layer connecting the transmission line metal layer 21 and the third welding metal layer 22 within the through-holes. The transmission line metal layer 21 and the connecting metal layer 23 are formed using additive manufacturing techniques based on aerosol spraying or precision electroplating. This allows for the fabrication of three-dimensional transmission line structures with superior shapes (such as curved corners instead of right angles), further reducing signal reflection and radiation loss. This configuration overcomes the two-dimensional planar limitations of traditional photolithography and etching processes, enabling flexible fabrication of high-performance three-dimensional microwave transmission structures.

[0031] More preferably, the through-hole is partially filled with a high thermal conductivity metal (such as silver paste) to help conduct the heat generated by the transmission line to the first substrate 1. This can solve the core thermal management problem in high-speed laser packaging and improve the power density and long-term reliability of the device.

[0032] After the second substrate 2 is soldered onto the first substrate 1, a second substrate 2 is formed next to the mounted laser, higher than the first substrate 1. This ensures that the height of the mounted laser is roughly equivalent to the height of the second substrate 2, thus minimizing the wire bonding length between the transmission line and the laser electrode and reducing inductive effects. Furthermore, since the signal transmission section is located on a glass substrate, the low dielectric constant and low loss of the glass facilitate 70 GHz signal transmission.

[0033] In one preferred embodiment, an aluminum nitride ceramic substrate with a thickness of 0.2 mm is preferably used as the first substrate. Resistor and gold-tin solder regions are formed on the surface of the ceramic substrate using thin film deposition and photolithography. A 3 μm thick solder layer, of copper-tin alloy, is deposited in the region parallel to the gold-tin solder.

[0034] Schott AG's BF33 glass was used as the second substrate, with a thickness of 0.15 mm chosen to account for the laser's height. First, the transmission line structure was optimized based on electromagnetic wave transmission line theory. Following the optimization, multiple grounding vias were etched into the glass substrate using laser-induced etching, and copper was then electroplated into the vias. After completion, a coplanar waveguide structure or microstrip line structure was formed on the front side of the glass substrate using photolithography and thin-film deposition techniques, while a 3 μm thick copper-tin layer was deposited on the back side. The glass is cut and then attached to the solder area of ​​an aluminum nitride ceramic substrate using a pick-and-place machine to form a stepped high-speed laser packaging substrate. Electromagnetic field simulation shows that the bandwidth of the transmission line can meet the 70GHz requirement.

[0035] The stepped substrate provided in this application bonds a second substrate to a first substrate, thereby forming a second substrate higher than the first substrate next to the mounted laser. This ensures that the height of the mounted laser is roughly equivalent to the height of the second substrate, minimizing the wire bonding length between the microstrip line and the laser electrode, and reducing inductive effects. Furthermore, since the signal transmission section is located on a glass substrate, the low dielectric constant and low loss of the glass facilitate 70 GHz signal transmission. In summary, this application has promising market application prospects.

[0036] In the description of this application, unless otherwise expressly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0037] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0038] In the description of this embodiment, the terms "upper," "lower," "left," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and 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. Therefore, they should not be construed as limitations on this application. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0039] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. The preferred embodiments have been described in detail. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the claims of this application.

Claims

1. A stepped substrate suitable for high-speed laser packaging, characterized in that, The stepped substrate includes: A first substrate, wherein a first welding metal layer and a second welding metal layer are disposed on the first substrate, and the second welding metal layer is disposed on the side of the first welding metal layer; A second substrate, on which a third welding metal layer is disposed; In this embodiment, the third welding metal layer of the second substrate is welded and fixed to the second welding metal layer of the first substrate, and the thickness of the second substrate is approximately equal to the height of the laser mounted on the first welding metal layer; The second substrate is further provided with a connecting metal layer and a transmission line metal layer, wherein the connecting metal layer connects the transmission line metal layer and the third welding metal layer together, wherein the third welding metal layer and the transmission line metal layer are respectively disposed on both sides of the second substrate.

2. The stepped substrate as described in claim 1, characterized in that, The first welding metal layer and the second welding metal layer are arranged in parallel, and the area of ​​the first welding metal layer is smaller than the area of ​​the second welding metal layer.

3. The stepped substrate as described in claim 1, characterized in that, A cantilever beam structure is fabricated on the first substrate using MEMS technology, and the first welding metal layer is welded through the cantilever beam structure for mounting the laser.

4. The stepped substrate as described in claim 1, characterized in that, The width of the third welding metal layer is greater than the width of the transmission line metal layer, and the length of the third welding metal layer is not less than the length of the transmission line metal layer; And / or, the thickness of the transmission line metal layer is 0.1~2µm.

5. The stepped substrate as described in claim 4, characterized in that, The second substrate is provided with a plurality of through holes penetrating the second substrate along the thickness direction, and the connecting metal layer is located in the through holes; the through holes are partially filled with a high thermal conductivity metal to help conduct the heat generated by the transmission line to the first substrate.

6. The stepped substrate as described in claim 4, characterized in that, The transmission line metal layer adopts a coplanar waveguide / microstrip line with a gradient or stepped variation.

7. The stepped substrate as described in claim 4, 5, or 6, characterized in that, The transmission line metal layer is formed by a combination of one or more materials such as titanium, gold, aluminum, copper, silver, and platinum. And / or, the third weld metal layer is a metal layer formed of copper-tin, silver-tin, or gold-tin alloy material.

8. The stepped substrate as described in claim 1, characterized in that, A thin-film thermoelectric cooler (TEC) is also integrated on the second substrate. The thin-film thermoelectric cooler (TEC) is composed of bismuth tellurium compound and is fabricated by thin-film deposition technology.

9. The stepped substrate as described in claim 1, characterized in that, Inside the first substrate, a microchannel or a highly thermally conductive material is integrated or embedded near the bottom of the first welding metal layer; And / or, thin-film resistors and capacitors are also integrated on the first substrate.

10. The stepped substrate as described in claim 1, characterized in that, The first substrate is a ceramic substrate, a silicon substrate, a silicon-ceramic composite substrate, or a glass-silicon-glass composite substrate. And / or, the second substrate is a photosensitive glass substrate or a glass substrate that can be strengthened by ion exchange. And / or, the first weld metal layer is a gold-tin alloy layer, And / or, the second weld metal layer is a copper-tin alloy layer.

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