Step-type substrate suitable for packaging high-speed laser

Abstract

The invention relates to a stepped substrate suitable for high-speed laser packaging, which comprises a first substrate and a second substrate, the top surface of the first substrate is provided with a first welding metal layer and a second welding metal layer, the top surface of the second substrate is provided with a transmission line metal layer, and the bottom surface of the second substrate is provided with a third welding metal layer; wherein the third welding metal layer of the second substrate is welded and fixed with the second welding metal layer of the first substrate, and the thickness of the second substrate is equivalent to the height of a laser mounted on the first welding metal layer; according to the step-type substrate, the routing length between the transmission line and the laser electrode can be reduced to the greatest extent, and the inductive effect is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic devices, and particularly to a stepped substrate suitable for high-speed laser packaging. Background Art

[0002] In optical fiber communication technology, semiconductor lasers are mainly used as signal sources. With the continuous improvement of laser chip preparation technology, not only the cost of laser chips has been greatly reduced, but also the modulation frequency of a single laser chip has reached 10 GHz or even dozens of GHz. Currently, the key factors restricting the characteristics and cost of signal sources mainly lie in packaging technology. In the packaging process, the packaging substrate needs to provide high-frequency signals to the laser. In order to meet high-frequency transmission and signal coupling, a microstrip line or coplanar microwave waveguide structure is generally formed by using multi-layer ceramics or multi-layer high-resistance silicon.

[0003] Lasers are generally surface-mounted on the surface of the substrate, and wire bonding is used to connect the transmission line and the laser electrode. For advanced edge-emitting lasers, the modulation signal will be higher than 35 GHz. For high-frequency electromagnetic signals, the inductance effect of wire bonding is very obvious, which will cause signal reflection. Reducing the wire bonding length is an effective method to reduce the inductance effect. However, the current conventional packaging substrate is flat, and the height of the laser is 100 - 200 microns. The wire bonding length must be at least greater than the height of the laser. Therefore, it is necessary to improve the existing packaging substrate to reduce the wire bonding length, thereby reducing the signal reflection caused by the inductance effect. Summary of the Invention

[0004] The purpose of the present invention is to provide 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 the signal reflection caused by the inductance effect.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A stepped substrate suitable for high-speed laser packaging, comprising:

[0007] A first substrate, the top surface of the first substrate has a first welding metal layer and a second welding metal layer, and the second welding metal layer is located beside the first welding metal layer;

[0008] A second substrate, the top surface of the second substrate is provided with a transmission line metal layer, and the bottom surface of the second substrate is provided with a third welding metal layer;

[0009] Wherein, 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 equivalent to the height of the laser mounted on the first welding metal layer.

[0010] In one embodiment, the second welding metal layer is arranged in parallel with the first welding metal layer.

[0011] In one embodiment, the second substrate is further provided with a connecting metal layer, and the connecting metal layer connects the transmission line metal layer and the third welding metal layer.

[0012] In one embodiment, the second substrate is provided with a plurality of through holes penetrating the second substrate in the thickness direction, and the connecting metal layer is located in the through holes.

[0013] In one embodiment, 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.

[0014] In one embodiment, the thickness of the transmission line metal layer is 0.1 - 2 um.

[0015] In one embodiment, the transmission line metal layer is a metal layer formed by combining one or more materials such as titanium, gold, aluminum, copper, silver, platinum, etc., and the third welding metal layer is a metal layer formed by copper tin, silver tin or gold tin alloy material.

[0016] In one embodiment, the first substrate is a ceramic substrate or a silicon substrate, and the second substrate is a glass substrate.

[0017] In one embodiment, thin film resistors and capacitor elements are also integrated on the first substrate.

[0018] In one embodiment, the first welding metal layer is a gold tin alloy layer, and the second welding metal layer is a copper tin alloy layer.

[0019] Adopting the above technical solution, the beneficial effect of the present invention is that the stepped substrate provided by the present invention welds the second substrate to the first substrate, thereby forming a second substrate higher than the first substrate beside the mounted laser, so that the height after the laser is mounted is equivalent to the height of the second substrate, thus minimizing the wire bonding length between the microstrip line and the laser electrode and reducing the inductance effect. In addition, since the signal transmission part is arranged on the glass substrate, the glass has a small dielectric constant, low loss, and it is easy to achieve 70G Hz signal transmission. Description of the Drawings

[0020] Figure 1 Shows a top view of the first substrate.

[0021] Figure 2 Shows a top view of the second substrate.

[0022] Figure 3 Shows a cross-sectional view of the stepped substrate. Detailed Embodiments

[0023] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, so as to more clearly understand the purpose, features and advantages of the present invention. It should be understood that the embodiments shown in the drawings are not a limitation on the scope of the present invention, but only to illustrate the essential spirit of the technical solution of the present invention.

[0024] In the following description, certain specific details are set forth in order to provide a thorough understanding of the various disclosed embodiments. However, one of ordinary skill in the relevant art will recognize that the embodiments may be practiced without one or more of these specific details. In other instances, well-known devices, structures, and techniques associated with the present application may not be shown or described in detail so as not to unnecessarily obscure the description of the embodiments.

[0025] Unless the context requires otherwise, throughout the specification and claims, the words "comprising" and its variants, such as "comprises" and "having", shall be construed in an open, inclusive sense, i.e., to mean "including, but not limited to".

[0026] References to "an embodiment" or "one embodiment" in the specification throughout mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of "in an embodiment" or "in one embodiment" in various places throughout the specification are not necessarily all referring to the same embodiment. Additionally, the particular features, structures, or characteristics may be combined in any manner in one or more embodiments.

[0027] As used in this specification and the appended claims, the singular forms "a" and "the" include plural referents unless the context clearly dictates otherwise. It should be noted that the term "or" is generally used in its inclusive sense of "and / or" unless the context clearly dictates otherwise.

[0028] In the following description, in order to clearly show the structure and working mode of the present invention, many directional terms will be used for description. However, words such as "front", "rear", "left", "right", "outer", "inner", "outward", "inward", "up", "down", etc. should be understood as convenient terms and should not be understood as limiting terms.

[0029] Furthermore, terms such as "horizontal", "vertical", "overhanging", etc. do not imply that the components are absolutely horizontal or overhanging, but may be slightly inclined. For example, "horizontal" merely means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but may be slightly inclined.

[0030] In the description of the present application, it should also be noted that unless otherwise clearly specified and limited, the terms "arranged", "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0031] As Figures 1-3 shown, the present invention provides a stepped substrate applicable to high-speed laser packaging. The stepped substrate includes a first substrate 1 and a second substrate 2.

[0032] The first substrate 1 is a flat plate structure with equal thickness everywhere. 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 um. The first substrate 1 can be a ceramic substrate or a silicon substrate. In the case of an integrated capacitor requirement, a silicon substrate is preferred.

[0033] The top surface of the first substrate 1 has a first soldering metal layer 11 for mounting the laser and a second soldering metal layer 12 located beside the first soldering metal layer 11 for mounting the second substrate 2. In this embodiment, the first soldering metal layer 11 is a gold-tin alloy layer obtained by metal deposition and photolithography techniques, and the second soldering metal layer 12 is a copper-tin alloy layer obtained by metal deposition and photolithography techniques. Preferably, the second soldering metal layer 12 is arranged parallel to the first soldering metal layer 11.

[0034] Optionally, thin film resistors and capacitor elements can also be integrated on the first substrate 1.

[0035] The second substrate 2 is a glass substrate. The size of the second substrate 2 is consistent with the area of the second soldering metal layer on the first substrate 1, and the thickness of the second substrate 2 is approximately equivalent to the thickness of the mounted laser. A transmission line metal layer 21 is provided on the top surface of the second substrate 2. The transmission line metal layer 21 can be a microstrip line or a coplanar waveguide structure, and it can support the transmission of signals up to 70 GHz at most. In this embodiment, the transmission line metal layer 21 on the surface of the second substrate 2 is taken as an example of a coplanar waveguide structure. The coplanar waveguide structure is composed of multiple metal layers formed by combining 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 um.

[0036] The bottom surface of the second substrate 2 is provided with a third welding metal layer 22, which can be a copper-tin, silver-tin or gold-tin alloy. The 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 on the first substrate 1. At the same time, the third welding metal layer 22 also serves as the reference ground layer of 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 the length is not less than the length of the transmission line.

[0037] Another preferably, 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 side wall of the second substrate 2, or a plurality of through holes penetrating the second substrate 2 in the thickness direction are formed in the second substrate 2, and a metal layer connecting the transmission line metal layer 21 and the third welding metal layer 22 is formed in the through holes.

[0038] After welding the second substrate 2 to the first substrate 1, a second substrate 2 higher than the first substrate 1 is formed beside the mounted laser, so that the height after the laser is mounted is 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 the inductance effect. In addition, since the signal transmission part is arranged on the glass substrate, the glass has a small dielectric constant, low loss, and it is easy to realize 70G Hz signal transmission.

[0039] Embodiment 1

[0040] An aluminum nitride ceramic substrate is used as the first substrate, and its thickness is 0.2 mm. Resistors and gold-tin solder regions are formed on the surface of the ceramic substrate by thin film deposition and photolithography techniques. A solder layer with a thickness of 3 um is deposited in the side region parallel to the gold-tin solder, and the solder is a copper-tin alloy.

[0041] Schott's BF33 glass is used as the second substrate, and a thickness of 0.15 mm is selected considering the height of the laser. First, according to the electromagnetic wave transmission line theory, the transmission line structure is optimized. According to the optimization results, a plurality of grounding through holes are etched on the glass substrate by laser-induced etching technology, and copper is filled in the holes by electroplating. After completion, a coplanar waveguide structure or a microstrip line structure is formed on the front surface of the glass substrate by photolithography and thin film deposition techniques, and a 3 um thick copper-tin layer is evaporated on the back surface.

[0042] The glass is cut and pasted on the solder area of the aluminum nitride ceramic substrate by a chip mounter, and a stepped high-speed laser packaging substrate can be formed. Through electromagnetic field simulation, the bandwidth of the transmission line can meet the requirements of 70 GHz.

[0043] The preferred embodiments of the present invention have been described in detail above. However, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention. These equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims

1. A stepped substrate applicable to high-speed laser packaging, characterized in that, Including: A first substrate, the top surface of the first substrate having a first solder metal layer and a second solder metal layer, the second solder metal layer being located beside the first solder metal layer; A second substrate, the top surface of the second substrate being provided with a transmission line metal layer, and the bottom surface of the second substrate being provided with a third solder metal layer; Wherein, the third solder metal layer of the second substrate is welded and fixed to the second solder metal layer of the first substrate, and the thickness of the second substrate is equivalent to the height of a laser mounted on the first solder metal layer.

2. The stepped substrate according to claim 1, wherein The second solder metal layer is arranged parallel to the first solder metal layer.

3. The stepped substrate according to claim 1, wherein The second substrate is further provided with a connecting metal layer, and the connecting metal layer connects the transmission line metal layer and the third solder metal layer.

4. The stepped substrate according to claim 3, wherein The second substrate is provided with a plurality of through holes penetrating the second substrate in the thickness direction, and the connecting metal layer is located in the through holes.

5. The stepped substrate according to claim 1, wherein, The width of the third solder metal layer is greater than the width of the transmission line metal layer, and the length of the third solder metal layer is not less than the length of the transmission line metal layer.

6. The stepped substrate according to claim 1, wherein The thickness of the transmission line metal layer is 0.1 - 2 um.

7. The stepped substrate according to claim 1, wherein, The transmission line metal layer is a metal layer formed by combining one or more materials such as titanium, gold, aluminum, copper, silver, platinum, etc., and the third solder metal layer is a metal layer formed by a copper-tin, silver-tin or gold-tin alloy material.

8. The stepped substrate according to claim 1, characterized in that, The first substrate is a ceramic substrate or a silicon substrate, and the second substrate is a glass substrate.

9. The stepped substrate according to claim 1, wherein, The first substrate is further integrated with thin film resistors and capacitor elements.

10. The stepped substrate according to claim 1, wherein The first solder metal layer is a gold-tin alloy layer, and the second solder metal layer is a copper-tin alloy layer.

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