A micro coaxial cable and its manufacturing method

Abstract

The present invention discloses a micro coaxial and a preparation method thereof. The preparation method includes: preparing a first conductor part on a first wafer and releasing the photoresist; preparing a second conductor part with a groove structure and an inner conductor in the second conductor part on a second wafer and releasing the photoresist; welding the first conductor part and the second conductor part to seal the groove on the second conductor part to form an outer conductor of the micro coaxial; wherein, the inner conductor and the outer conductor form the micro coaxial. In the micro coaxial preparation method of the present invention, the outer conductor is divided into a first conductor part and a second conductor part, which are respectively fabricated on the first end face of the first wafer and the second end face of the second wafer. Neither the first conductor part nor the second conductor part forms a closed structure, which facilitates the release of the photoresist on the first wafer and the second wafer, and reduces the difficulty of releasing the photoresist during the preparation of the micro coaxial.

Description

Technical Field

[0001] This application relates to the technical field of semiconductors, and particularly to a micro coaxial and a method for manufacturing the same. Background Art

[0002] A micro coaxial includes an outer conductor and an inner conductor. The outer conductor is a hollow cavity structure, and the inner conductor passes through the cavity structure of the outer conductor for signal transmission. Usually, the micro coaxial is integrated into a radio frequency functional module for receiving and transmitting high-frequency radio frequency signals. The traditional micro coaxial process is to fabricate the outer conductor and the inner conductor, and finally release the photoresist in the cavity between the outer conductor and the inner conductor. Since the inner conductor is already placed in the cavity of the outer conductor at this time, the photoresist can only be released from both ends of the micro coaxial, which will bring complexity to the process.

[0003] Therefore, how to reduce the difficulty of releasing the photoresist during the manufacturing process of the micro coaxial is a technical problem to be solved urgently at the present stage. Summary of the Invention

[0004] In view of the above technical problems, a micro coaxial and a method for manufacturing the same according to the present invention reduce the difficulty of releasing the photoresist during the manufacturing process of the micro coaxial.

[0005] Embodiments of the present invention provide the following solutions:

[0006] In a first aspect, an embodiment of the present invention provides a method for manufacturing a micro coaxial, including:

[0007] Fabricating a first conductor portion on a first wafer and releasing the photoresist;

[0008] Fabricating a second conductor portion with a groove structure and an inner conductor inside the second conductor portion on a second wafer and releasing the photoresist;

[0009] Welding the first conductor portion and the second conductor portion to seal the groove on the second conductor portion to form the outer conductor of the micro coaxial; wherein, the inner conductor and the outer conductor form the micro coaxial.

[0010] In an optional embodiment, the first conductor portion is fabricated as a copper layer with a planar structure.

[0011] In an optional embodiment, the outer contour of the first conductor portion fabricated is not less than 5 μm of the outer contour of the second conductor portion.

[0012] In an optional embodiment, the thickness of the first wafer is 200 - 300 μm, and the thickness of the second wafer is 700 μm.

[0013] In an optional embodiment, fabricating the second conductor portion on the second wafer includes:

[0014] Fabricate a first copper layer with a planar structure on the second wafer;

[0015] Fabricate a second copper layer on the first copper layer, the second copper layer including first copper wires and second copper wires that are parallel to each other;

[0016] Fabricate a third copper layer and the inner conductor on the second copper layer, the third copper layer including third copper wires and fourth copper wires that are parallel to each other, and the inner conductor being located between the third copper wires and the fourth copper wires;

[0017] Fabricate a fourth copper layer on the third copper layer, the fourth copper layer including fifth copper wires and sixth copper wires that are parallel to each other.

[0018] In an alternative embodiment, before fabricating the third copper layer and the inner conductor on the second copper layer, further include:

[0019] Fabricate a dielectric strip on the second copper layer for supporting the inner conductor.

[0020] In an alternative embodiment, the dielectric strip overlaps the first copper wire and the second copper wire, and the thickness of the dielectric strip is 10 μm.

[0021] In an alternative embodiment, the solder for welding the first wafer and the second wafer is tin.

[0022] In an alternative embodiment, the groove structure is filled with a filler having a low dielectric constant.

[0023] In a second aspect, an embodiment of the present invention further provides a micro coaxial cable fabricated by any of the methods in the first aspect.

[0024] Compared with the prior art, a micro coaxial cable and a preparation method thereof provided by the present invention have the following advantages:

[0025] In the micro coaxial cable preparation method of the present invention, the outer conductor is divided into a first conductor part and a second conductor part, and they are respectively fabricated on the first end face of the first wafer and the second end face of the second wafer. Neither the first conductor part nor the second conductor part forms a closed structure, which facilitates the release of the photoresist on the first wafer and the second wafer, and reduces the difficulty of releasing the photoresist during the preparation of the micro coaxial cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present specification or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present specification. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0027] Figure 1 Flow chart of a preparation method of a micro coaxial provided by an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the theoretical three-dimensional structure of the micro coaxial provided by an embodiment of the present invention;

[0029] Figure 3 is Figure 2 Schematic diagram of the cross-sectional structure;

[0030] Figure 4 Schematic diagram of the cross-sectional structure of the micro coaxial provided by an embodiment of the present invention;

[0031] Figure 5 Schematic diagram of the longitudinal-sectional structure of the micro coaxial provided by an embodiment of the present invention;

[0032] Figure 6 Schematic diagram of the structure after welding the first conductor part and the second conductor part provided by an embodiment of the present invention.

[0033] Explanation of reference numerals: 1 - first wafer, 2 - first conductor part, 3 - second wafer, 4 - second conductor part, 5 - outer conductor, 6 - inner conductor, 7 - dielectric strip, 8 - first copper layer, 9 - second copper layer, 91 - first copper wire, 92 - second copper wire, 10 - third copper layer, 101 - third copper wire, 102 - fourth copper wire, 11 - fourth copper layer, 111 - fifth copper wire, 112 - sixth copper wire, 12 - solder, 13 - SiO2 layer, 14 - chip, 15 - clearance groove. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope protected by the embodiments of the present invention.

[0035] Please refer to Figure 1 , Figure 1 which is a flow chart of a preparation method of a micro coaxial provided by an embodiment of the present invention, including:

[0036] S11. Prepare a first conductor part on a first wafer and release the photoresist.

[0037] Specifically, the micro coaxial is usually applied in a radio frequency chip to transmit radio frequency signals in a high-frequency manner. For the theoretical three-dimensional structure of the micro coaxial, please refer to Figure 2, including an inner conductor 6 and an outer conductor 5. The inner conductor 6 passes through the cavity structure in the middle of the outer conductor 5 for high-frequency signal transmission. Since the outer conductor 5 is grounded, a good shielding layer is formed, making the micro-coaxial structure have the advantage of low loss in high-frequency signal transmission. When preparing the micro-coaxial, it is usually divided into multiple layers, and copper layers are sequentially plated and etched. The copper layers are stacked to form the micro-coaxial. For details, please refer to Figure 3 , the outer conductor 5 includes 5 copper layers, namely Cu1 - Cu5. The first conductor part 2 may include Cu4 and Cu5. After the preparation of the first conductor part 2 is completed, the photoresist of Cu4 is released.

[0038] In the traditional manufacturing process, to ground the outer conductor 5, a ground copper layer (or GND layer) is separately fabricated and then covered and bonded to the top of the outer conductor 5. This method requires 6 copper layers to complete the preparation and grounding of the outer conductor 5, resulting in a relatively thick copper layer on the top layer of the outer conductor 5, and finally the overall module thickness of the prepared micro-coaxial is relatively large, which is not conducive to the integration of radio frequency chips.

[0039] The first conductor part 2 is fabricated on the first wafer 1. The first conductor part 2 may only include Cu5, that is, the first conductor part 2 is fabricated as a planar copper layer.

[0040] Specifically, when the first conductor part 2 is fabricated as a planar copper layer, this copper layer can be used as the top layer of the outer conductor 5 and can be grounded at the same time. In this way, when preparing and grounding the outer conductor 5, the fabrication of one copper layer can be reduced, and the overall module thickness of the prepared micro-coaxial is thinner. After the preparation of the first conductor part 2 is completed and the photoresist is released, step S12 is entered.

[0041] S12: Fabricate the second conductor part with a groove structure and the inner conductor inside the second conductor part on the second wafer, and release the photoresist.

[0042] Specifically, for details, please continue to refer to Figure 3 , the second conductor part 4 may include Cu1 - Cu4, or may include Cu1 - Cu3. The inner conductor 6 is located inside the second conductor part 4, and the outer periphery of the inner conductor 6 does not contact the inner wall of the second conductor part 4. Usually, to ensure the high-frequency signal transmission performance of the inner conductor 6, the inner conductor 6 is located at the center of the cavity of the outer conductor 5.

[0043] In a specific implementation manner, fabricating the second conductor part 4 on the second wafer 3 includes:

[0044] A first copper layer 8 with a planar structure is fabricated on the second wafer 3; a second copper layer 9 is fabricated on the first copper layer 8, and the second copper layer 9 includes a first copper wire 91 and a second copper wire 92 that are parallel to each other; a third copper layer 10 and an inner conductor 6 are fabricated on the second copper layer 9, the third copper layer 10 includes a third copper wire 101 and a fourth copper wire 102 that are parallel to each other, and the inner conductor 6 is located between the third copper wire 101 and the fourth copper wire 102; a fourth copper layer 11 is fabricated on the third copper layer 10, and the fourth copper layer 11 includes a fifth copper wire 111 and a sixth copper wire 112 that are parallel to each other.

[0045] Those skilled in the art can understand that the preparation of the first copper layer 8 to the fourth copper layer 11 includes processes such as copper layer plating, lithography, and chemical mechanical polishing, and any copper layer that can meet the requirements of the micro coaxial preparation process is acceptable. The specific implementation methods will not be elaborated here.

[0046] In specific implementation, since the metal copper is relatively soft, when fabricating the third copper layer 10 and the inner conductor 6 on the second copper layer 9, due to the bottom of the inner conductor 6 being a suspended structure, the inner conductor 6 is prone to deformation, which affects the signal transmission performance of the inner conductor 6.

[0047] In a specific implementation method, before fabricating the third copper layer 10 and the inner conductor 6 on the second copper layer 9, it further includes:

[0048] Fabricating a dielectric strip 7 for supporting the inner conductor 6 on the second copper layer 9.

[0049] Specifically, the dielectric strip 7 can be prepared from an insulating material, such as SU8 photoresist. After the second copper layer 9 is completed, the dielectric strip 7 is first fabricated on the second copper layer 9, and then the inner conductor 6 is fabricated. During the fabrication process of the inner conductor 6, it can be supported by the dielectric strip 7 to reduce the deformation occurring during the fabrication of the inner conductor 6 and improve the signal transmission performance of the inner conductor 6.

[0050] In a specific implementation method, the dielectric strip 7 overlaps the first copper wire 91 and the second copper wire 92, and the thickness of the dielectric strip 7 is 10 μm.

[0051] Specifically, please continue to refer to Figure 3 , the overlapping length of the dielectric strip 7 on the first copper wire 91 and the second copper wire 92 can be set according to the experience of technicians. Of course, calibration tests can also be conducted to determine it, as long as it can support the dielectric strip 7. It should be noted that the overlapping length of the dielectric strip 7 on the first copper wire 91 and the second copper wire 92 cannot interrupt the electrical conduction between the second copper layer 9 and the third copper layer 10 to prevent the shielding of the inner conductor 6 by the outer conductor 5 from failing. Steps S11 and S12 can also be prepared synchronously. After the photoresist on both the first wafer 1 and the second wafer 3 is released, it enters step S13.

[0052] S13. Weld the first conductor portion and the second conductor portion to seal the groove on the second conductor portion to form the outer conductor of the micro coaxial; wherein, the inner conductor and the outer conductor form the micro coaxial.

[0053] Specifically, please refer to Figure 4 and Figure 5 , both the first wafer 1 and the second wafer 3 include an Si layer and an SiO2 layer 12. When preparing the first conductor portion 2 and the second conductor portion 4 by plating a copper layer on the SiO2 layer 12, the chip 14 to be applied can be prepared simultaneously during the preparation process and connected through the inner conductor 6. Among them, if a larger chip 14 needs to be applied, an avoidance groove 15 can be opened on the first conductor portion 2. After the first end face and the second end face are welded face to face, the first conductor portion 2 and the second conductor portion 4 form a complete outer conductor 5. The welding method can be to coat the solder 12 on the first wafer 1 or the second wafer 3 first, then fit them together and heat to the welding process requirements. After cooling, the first wafer 1 and the second wafer 3 are welded into a whole. The first conductor portion 2 completely covers the groove on the second conductor portion 4. After the second conductor portion 4 is sealed, the outer conductor 5 of the micro coaxial is formed to complete the preparation of the micro coaxial. The solder 12 can be coated on the first wafer 1 or the second wafer 3. Of course, the solder 12 can also be coated simultaneously for welding. Among them, Figure 4 shows that the solder 12 is coated on the first wafer 1; Figure 5 shows that the solder 12 is coated on the first wafer 1 and the second wafer 3. In a specific implementation manner, the solder 12 for welding the first wafer 1 and the second wafer 3 is tin.

[0054] Please refer to Figure 6 , after the first wafer 1 and the second wafer 3 are welded, some solder 12 will overflow to the corner of the cavity of the outer conductor 5. After simulation verification, the influence of the overflowed solder on the transmission performance of the radio frequency signal is small.

[0055] During the specific implementation of welding, the first wafer 1 and the second wafer 3 need to be bonded and aligned for welding so that the first conductor portion 2 completely covers the top of the second conductor portion 4. However, due to the accuracy limit of the bonding alignment, it is possible that the first conductor portion 2 cannot completely cover the top of the second conductor portion 4 correspondingly, resulting in defective products in the prepared micro coaxial.

[0056] In a specific implementation manner, the outer contour of the first conductor portion 2 is not less than 5 μm of the outer contour of the second conductor portion 4.

[0057] Specifically, making the outer contour of the first conductor portion 2 slightly larger can ensure that it can completely cover the top of the second conductor portion 4 even when there is a bonding alignment error.

[0058] In a specific embodiment, the thickness of the first wafer 1 is 260 μm, and the thickness of the second wafer 3 is 700 μm.

[0059] Specifically, the thickness of the first wafer 1 is thinner than that of the second wafer 3, which is convenient for adopting TSV packaging (Through-Silicon Via, silicon through-hole technology). Through the filling of conductive substances such as copper, tungsten, and polysilicon in TSV packaging, vertical electrical interconnection of silicon through-holes is achieved. The silicon through-hole technology can reduce the interconnection length through vertical interconnection, reduce signal delay, reduce capacitance / inductance, achieve low-power and high-speed communication between RF chips, increase bandwidth, and realize miniaturization of device integration. When performing TSV packaging, the first conductor portion 2 prepared as a planar copper layer can serve as the metal UBM (underbump metallization, solder bottom film) of the TSV port, which can enhance the interconnection strength between the first conductor portion 2 and the second conductor portion 4.

[0060] In addition, in the micro-coaxial structure, since the texture of the inner conductor 6 material is relatively soft, for a micro-coaxial with a relatively long structure, if there is a vibration source in the external environment, the inner conductor 6 may be damaged.

[0061] In a specific embodiment, the groove structure is filled with a filler having a low dielectric constant.

[0062] Specifically, the filler can be a substance with a low dielectric constant such as polyimide. The liquid polyimide is filled into the groove structure, and the filling is completed after the polyimide is cured. It can be understood that other curable resins can also be selected as the filler, and the micro-coaxial is more robust and durable after filling.

[0063] Based on the same inventive concept as the micro-coaxial preparation method, the embodiment of the present invention also provides a micro-coaxial, which is obtained by any one of the methods in the micro-coaxial preparation method.

[0064] The technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0065] 1. The outer conductor is divided into a first conductor portion and a second conductor portion, which are respectively fabricated on the first end face of the first wafer and the second end face of the second wafer. Neither the first conductor portion nor the second conductor portion forms a closed structure, which is convenient for releasing the photoresist on the first wafer and the second wafer, and reduces the difficulty of releasing the photoresist during the preparation of the micro-coaxial.

[0066] 2. The first conductor portion is prepared as a planar copper layer. During the preparation of the micro-coaxial, the plating of one layer of copper can be reduced, the preparation process of the micro-coaxial is simplified, and the overall module thickness of the prepared micro-coaxial is thinner.

[0067] Since the electronic device introduced in this embodiment is the electronic device used to implement the information processing method in the embodiments of the present application, based on the information processing method introduced in the embodiments of the present application, those skilled in the art can understand the specific implementation manners and various variations of the electronic device in this embodiment. Therefore, the specific implementation of how this electronic device implements the method in the embodiments of the present application will not be described in detail here. As long as the electronic device used by those skilled in the art to implement the information processing method in the embodiments of the present application falls within the scope of protection of the present application.

Claims

1. A preparation method of a micro coaxial cable, characterized in that, Applied to the integration of radio frequency chips, including: Fabricate a first conductor part on a first wafer and remove the photoresist. Fabricate a second conductor part with a groove structure and an inner conductor within the second conductor part on a second wafer, and fabricate the chips to be applied. Connect the chips through the inner conductor and remove the photoresist. Weld the first conductor part and the second conductor part to seal the groove on the second conductor part to form an outer conductor of a micro coaxial; wherein, the inner conductor and the outer conductor form the micro coaxial; the outer contour of the first conductor part is not less than 5 μm of the outer contour of the second conductor part; the first conductor part is fabricated as a planar copper layer, and the copper layer serves as the top layer of the outer conductor and is grounded simultaneously. The thickness of the first wafer is 200 - 300 μm, and the thickness of the second wafer is 700 μm, so as to enhance the interconnection strength of the first conductor part and the second conductor part by using TVS packaging. Fabricating the second conductor part on the second wafer includes: Fabricate a first copper layer with a planar structure on the second wafer. Fabricate a second copper layer on the first copper layer, and the second copper layer includes first copper wires and second copper wires that are parallel to each other. Fabricate a third copper layer and the inner conductor on the second copper layer, the third copper layer includes third copper wires and fourth copper wires that are parallel to each other, and the inner conductor is located between the third copper wire and the fourth copper wire. Fabricate a fourth copper layer on the third copper layer, and the fourth copper layer includes fifth copper wires and sixth copper wires that are parallel to each other. Before fabricating the third copper layer and the inner conductor on the second copper layer, it further includes: Fabricate a dielectric strip on the second copper layer for supporting the inner conductor; the dielectric strip overlaps on the first copper wire and the second copper wire; the overlapping length of the dielectric strip on the first copper wire and the second copper wire cannot cut off the electrical conduction between the second copper layer and the third copper layer to prevent the shielding failure of the outer conductor to the inner conductor; the thickness of the dielectric strip is 10 μm; the solder for welding the first wafer and the second wafer is tin. The groove structure is filled with a filler with a low dielectric constant to make the micro coaxial more durable.

2. A micro coaxial cable, characterized in that, Obtained by the method according to claim 1.

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