An optoelectronic co-packaging bonding method and bonding apparatus

Abstract

The application discloses an optoelectronic co-encapsulation bonding method and a bonding device, and is applied to the technical field of optoelectronic integration and semiconductor packaging, and the bonding method comprises the following steps: obtaining an optical chip, and preparing a micro bump on a pad of the optical chip; the micro bump comprises a gold ball base and a solder ball, the gold ball base is covered on the pad of the optical chip, and the solder ball is located on the gold ball base; placing a packaging substrate on a heating base, and the micro bump of the optical chip faces the packaging substrate; sealing the four sides of the optical chip by using a nitrogen gas curtain, and physically flushing and chemically reducing the micro bump of the optical chip by using formic acid vapor; and bonding processing is performed by using a hot-press bonding control gap method. According to the bonding method, the micro bump structure of the gold ball base and the solder ball is adopted, the interconnection reliability is significantly improved, the gold ball base and the laser solder ball form stable metallurgical bonding, the process is simplified, the cost is reduced, no flux is involved in the whole process, the process transfer is reduced, and the production efficiency is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic integration and semiconductor packaging technology, and in particular to an optoelectronic co-packaging bonding method and bonding apparatus. Background Technology

[0002] With the explosive growth of artificial intelligence, high-performance computing, and data center traffic, CPO (Co-Packaged Optics, an advanced optoelectronic integration technology that integrates optical modules and optical chips in the same package) has become the core path to break through the power consumption wall of electrical interconnect I / O (Input / Output). Microbumps with a medium diameter of 40~100μm have become the mainstream size for interconnecting optical chips and electrical chips due to their balance between interconnect density and process feasibility.

[0003] In related technologies, for optoelectronic co-packaging of micro-bumps with fine diameters of 40~100μm, existing interconnect solutions cannot simultaneously meet the core requirements of "rapid iterative verification, single-chip adaptation, process compatibility, high cleanliness, and efficient cleaning." Specific problems are as follows: 1. Gold ball + stencil printed solder paste flip-chip bonding solution: This solution is a traditional interconnect method. It requires first implanting gold balls on the chip, and then using stencil printing solder paste to achieve flip-chip bonding with the substrate. It is only suitable for scenarios with microbump diameter ≥100μm and pitch ≥150μm (or even 200μm or more). It cannot adapt to the high-density interconnect requirements of 40~100μm medium-fine diameter and ≤150μm pitch. Moreover, the stencil printed solder paste is prone to uneven spreading, resulting in irregular microbump shapes, high bridging risk, and flux residue can easily contaminate the optical waveguide port, affecting optical signal transmission.

[0004] 2. Gold ball base + solder paste dip flip bonding solution: This solution achieves interconnection by placing gold balls on the chip as a base and then dipping them in solder paste. Although it can adapt to small and medium diameter micro bumps, the uniformity of the solder paste application is completely uncontrollable. This can easily lead to insufficient solder, resulting in cold solder joints, or excessive solder, resulting in solder overflow, leading to poor interconnect reliability. Furthermore, flux residue in the solder paste is difficult to completely remove, failing to meet the high cleanliness requirements of optical chips. At the same time, the process efficiency is not optimized for rapid verification scenarios, and the cost and cycle advantages are not obvious when processing small batches.

[0005] 3. Copper Pillar Microbump Process: This process can cover diameters from 5μm to 100μm and offers high efficiency in whole-wafer fabrication. However, its process architecture is significantly mismatched with the requirements of optoelectronic co-packaging, which demands rapid iteration and multiple verifications. On one hand, copper pillar microbump fabrication requires chip design to consider the current continuity of whole-wafer electroplating, which cannot tolerate deep trench structures. Optical chips, to improve the coupling efficiency between the waveguide and the fiber, often design the waveguide as a cantilever beam structure, which is incompatible with the copper pillar microbump electroplating process, easily leading to uneven Cu pillar growth and electroplating failure. On the other hand, the copper pillar electroplating process requires the fabrication of a Ni / Au layer on the copper pillar surface and involves a complete set of processes including electroplating, photolithography, and annealing. This process is complex, time-consuming, and extremely cost-effective for small-batch processing of single chips. Furthermore, the copper pillar microbumps need to be fabricated simultaneously during the tape-out stage, making it unsuitable for the single-chip replenishment needs of scattered chips after panelization tape-out, thus failing to fully realize the cost advantages of panelization tape-out.

[0006] 4. Existing fluxless bonding technology: In the existing technology, the fluxless path of formic acid vapor reduction has core defects: (1) The gas path design is unreasonable. It often adopts the mode of "single-sided gas inlet near the light port and exhaust far from the light port". The airflow is relatively gentle. After the formic acid reducing gas diffuses freely in the gas cavity, it diffuses to the surface of the micro-bumps. It lacks active flushing effect, the oxide layer removal efficiency is low, and the reduction products are easy to remain; (2) The pre-cleaning process takes a long time, the process is complicated and the cycle is long; (3) The airflow flushing effect is not optimized for micro-bumps with fine diameter and high density distribution of 40~100μm. It is easy to cause cleaning dead corners due to the shielding effect; the shielding effect refers to the effect of the shielding effect in micro-pitch interconnects caused by the shielding effect. If the microbump spacing is too small or the airflow is not smooth, some microbump surfaces cannot fully contact the reactive gas, resulting in incomplete cleaning; (4) There is a lack of dedicated microbump configurations and processes adapted to the independent preparation of single chips, the core energy parameters of laser ball planting are not clearly defined, the bonding pressure control method is prone to poor soldering or tin overflow, the process reproducibility is poor, and it cannot meet the flexible processing needs of scattered chips after panelization and fabrication; Panelization refers to the mode of combining multiple or multiple different optical chip design schemes on the same wafer for fabrication and manufacturing. The core purpose is to share the high cost of whole wafer fabrication. After fabrication, it is cut into independent scattered optical chips, which need to complete the final interconnect process separately.

[0007] Therefore, how to effectively improve the efficiency and reliability of optoelectronic co-packaging is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to provide an optoelectronic co-packaging bonding method and bonding apparatus to improve processing efficiency and quality while reducing costs.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A method for optoelectronic co-packaging bonding includes: Step S100: Obtain an optical chip and prepare microbumps on the pads of the optical chip; the microbumps include a gold ball substrate and solder balls, the gold ball substrate covers the pads of the optical chip, and the solder balls are located on the gold ball substrate; Step S200: Place the packaging substrate on the heating base and move the optical chip above the packaging substrate, with the micro-bumps of the optical chip facing the packaging substrate; Step S300: Use a nitrogen gas curtain to seal the periphery of the optical chip, and use formic acid vapor to physically flush and chemically reduce the micro-bumps of the optical chip; Step S400: Using the thermo-press bonding gap control method, the optical chip is controlled to move toward the pads of the packaging substrate and bonded.

[0010] On the other hand, step S1 includes: Step S101: Gold balls are implanted onto the optical chip using a gold wire bonding machine; Step S102: The gold balls are pressed using a soft-press flattening die-attachment machine to form the gold ball substrate, wherein the diameter of the gold ball substrate is larger than the diameter of the pads of the optical chip; Step S103: Use a laser ball-mounting machine to prepare solder balls on the gold ball substrate, wherein the solder balls and the gold ball substrate form the micro-bumps.

[0011] On the other hand, step S101 includes: controlling the gold wire bonding machine to implant the gold balls on the aluminum pads of the optical chip with gold wires with a diameter of 25~38μm. Step S102 includes: controlling the soft pressing and flattening machine to flatten the gold ball with a pressure of 5~10N, removing the tail filament of the gold ball and trimming the height of the gold ball to 15~25μm and the diameter to 30~80μm to form a flat gold ball substrate. Step S103 includes: the solder ball is a Sn96.5Ag3.0Cu0.5 alloy solder ball or a Sn-Ag alloy lead-free solder ball, and by adjusting the laser current and pulse width, outputting a single pulse energy of 3~7mJ, the solder ball with a height of 15~40μm is prepared on the gold ball substrate.

[0012] On the other hand, the total height of the micro-bumps is 30~65μm, the diameter is 40~100μm, and the distance between adjacent micro-bumps is ≤150μm; Furthermore, in step S103, when the diameter of the alloy tin ball is 60μm±5μm, a single pulse energy of 3~3.5mJ is output; when the diameter of the alloy tin ball is 80μm±5μm, a single pulse energy of 4.5~5mJ is output; and when the diameter of the alloy tin ball is 100μm±5μm, a single pulse energy of 6~7mJ is output.

[0013] On the other hand, step S300 includes: Step S301: Control the compressed nitrogen gas to enter the protective cover, and the compressed nitrogen gas flows out through the nitrogen gas curtain outlet on the protective cover, forming a nitrogen gas curtain around the optical chip; Step S302: Control the injection of compressed nitrogen into the formic acid solution to form bubbles, generate a mixed gas of formic acid and nitrogen, control the injection of the mixed gas onto the surface of the micro-bumps to pre-clean the surface of the micro-bumps, and control the by-products to be discharged through the waste spray pipe. Step S303: Control the heating base to heat to 150~195℃, and control the pre-cleaning of the mixed gas to ≤10s.

[0014] On the other hand, step S200 includes: Step S201: At room temperature, transfer the optical chip into a nitrogen-sealed system, place the packaging substrate on the heating platform, and heat the heating platform to 150℃±10℃; Step S202: Use a thermosetting bonding head to adsorb the optical chip and align the microbumps with the pads of the packaging substrate; Step S203: Orient the optical waveguide port in the optical chip toward the formic acid vapor inlet on the protective cover, so that the optical waveguide port is away from the exhaust gas collection port on the protective cover, control the protective cover to descend, and form a closed micro-reaction cavity between the protective cover and the heating base; the optical chip and the packaging substrate are both located in the closed micro-reaction cavity.

[0015] On the other hand, step S400 includes: Step S401: Using a vision alignment system in conjunction with a Z-axis displacement sensor, locate the contact position between the microbump and the pad of the packaging substrate; Step S402: Based on the contact position, control the thermosetting bonding head to continue pressing down on the optical chip by 5~10μm; Step S403: During the bonding process, the temperature of the hot-press bonding head is controlled at 250~340℃, the temperature of the heating base is controlled at 150℃±10℃, formic acid vapor is continuously supplied, and the oxygen concentration in the system is maintained at ≤100ppm through the nitrogen curtain.

[0016] On the other hand, after step S400, the method further includes: Step S500: Close the formic acid vapor, open the purging nitrogen inlet, and control the compressed nitrogen to purge through the purging nitrogen inlet for 3-5 seconds until the hot-press bonding head and the heating base are cooled to below 80°C; after purging, temporarily close the nitrogen curtain inlet to supply nitrogen, open the system pick-and-place port to remove the bonding device, which includes the bonded optical chip and the packaging substrate.

[0017] An optoelectronic co-packaging bonding device includes a microbump fabrication system and a nitrogen-sealed hot pressing system; The microbump fabrication system includes a gold wire bonding machine, a soft pressing and flattening chip bonding machine, and a laser ball bonding machine. The gold wire bonding machine is used to bond gold balls on the optical chip, the soft pressing and flattening chip bonding machine is used to extrude the gold balls, and the laser ball bonding machine is used to prepare solder balls on the gold ball substrate. The nitrogen-sealed thermopressing system includes a thermopressing bonding head, a heating base, a vision alignment system, and a protective cover. The thermopressing bonding head is used to press down the optical chip. The vision alignment system is used to locate the contact position between the microbumps and the pads of the packaging substrate. The protective cover is used to guide the compressed nitrogen and formic acid vapor to form a nitrogen curtain and direct the formic acid vapor toward the microbumps of the optical chip.

[0018] On the other hand, the protective cover includes a protective cover body and a nozzle. The first side of the protective cover body is provided with a nitrogen curtain inlet, a nitrogen curtain outlet, a formic acid vapor inlet and a purging nitrogen inlet. The nozzle is installed on the second side of the protective cover body, and the extension direction and cross-section of the nozzle are both U-shaped. The top of the nozzle is an open structure, and the top of the nozzle is fitted to the second side of the protective cover body so that the nozzle is connected to the formic acid vapor inlet and the purging nitrogen inlet; the bottom of the nozzle is provided with an array of vents for the purging nitrogen and formic acid vapor to flow out. The second side of the protective cover body is provided with a nozzle mounting groove. The formic acid vapor inlet and the purging nitrogen inlet are both connected to the nozzle mounting groove. An exhaust gas collection port is also provided on the side of the nozzle mounting groove opposite to the formic acid vapor inlet.

[0019] The optoelectronic co-packaging bonding method provided by the present invention includes: Step S100: Obtaining an optical chip and preparing microbumps on the pads of the optical chip; the microbumps include a gold ball substrate and solder balls, the gold ball substrate covering the pads of the optical chip, and the solder balls located on the gold ball substrate; Step S200: Placing the packaging substrate on a heating platform and moving the optical chip above the packaging substrate, with the microbumps of the optical chip facing the packaging substrate; Step S300: Sealing the optical chip around its perimeter using a nitrogen gas curtain, and physically rinsing and chemically reducing the microbumps of the optical chip using formic acid vapor; Step S400: Using a thermo-press bonding control gap method, controlling the movement of the optical chip toward the pads of the packaging substrate and performing bonding processing. The optoelectronic co-packaging bonding method provided by this invention employs a micro-bump structure of a gold ball substrate and solder balls, significantly improving interconnect reliability. Furthermore, the gold ball substrate and laser solder balls form a stable metallurgical bond, resulting in excellent long-term performance. The gold ball substrate completely covers the pads of the optical chip, forming an inert metal barrier layer that completely isolates formic acid vapor from contact with the pads, eliminating any corrosion risk. No additional Ni / Au barrier layer is required, simplifying the process and reducing costs. The entire process is flux-free, eliminating residue risks and ensuring high optical port cleanliness, perfectly matching the high cleanliness requirements of optical chips and avoiding optical signal attenuation issues caused by flux residue. The use of a controlled gap method instead of traditional pressure control significantly improves bonding consistency and reliability compared to traditional solutions. Moreover, the integrated bonding process reduces process transfers, significantly improving production efficiency.

[0020] In one embodiment, step S200 includes: step S201: at room temperature, transferring the optical chip into a nitrogen-sealed system, placing the packaging substrate on the heating platform, and heating the heating platform to 150℃±10℃; step S202: using a thermosetting bonding head to adsorb the optical chip, aligning the microbumps with the pads of the packaging substrate; step S203: orienting the optical waveguide in the optical chip toward the formic acid vapor inlet, controlling the protective cover to descend, forming a sealed micro-reaction cavity between the protective cover and the heating platform; the optical chip and the packaging substrate are both located within the sealed micro-reaction cavity. The above configuration, by orienting the optical waveguide port in the optical chip toward the formic acid vapor inlet (i.e., the optical waveguide port in the optical chip is away from the exhaust gas collection port), can prevent contamination of the optical waveguide port. With the help of the nitrogen sealing system, the physical scouring and chemical reduction of formic acid vapor can achieve flux-free cleaning, hot-press bonding, and port protection integrated into the same nitrogen sealing system. This enables transfer-free processing of the bonding process, avoids secondary oxidation and contamination, ensures cleanliness and processing efficiency, and meets the needs of both R&D verification and industrial production, adapting to all scenarios from small-batch laboratory prototyping to mass production in the factory.

[0021] The optoelectronic co-packaging bonding apparatus provided by this invention includes a microbump fabrication system and a nitrogen-sealed thermopressing system. The microbump fabrication system includes a gold wire bonding machine, a soft-press flattening placement machine, and a laser ball-mounting machine. The gold wire bonding machine is used to place gold balls on the optical chip, the soft-press flattening placement machine is used to extrude the gold balls, and the laser ball-mounting machine is used to prepare solder balls on the gold ball substrate. The nitrogen-sealed thermopressing system includes a thermopressing bonding head, a heating platform, a vision alignment system, and a protective cover. The thermopressing bonding head is used to press down on the optical chip, the vision alignment system is used to locate the contact position between the microbumps and the solder pads of the packaging substrate, and the protective cover is used to guide the compressed nitrogen and formic acid vapor to form a nitrogen curtain and to direct the formic acid vapor toward the microbumps of the optical chip. The optoelectronic co-packaging bonding device provided by this invention supports independent fabrication of single-chip optical assembly and flexible processing of multi-specification optical chips through a fabrication process of "gold wire bonding and ball placement - soft pressing and flattening - laser ball placement and capping". It can adjust parameters individually to complete the fabrication of microbumps for scattered optical chips of different specifications after wafer fabrication, greatly improving process flexibility. At the same time, the nitrogen-sealed hot pressing system can create a nitrogen atmosphere through dynamic sealing of nitrogen curtain, control the oxygen concentration ≤100ppm, and achieve transfer-free processing of "independent microbump fabrication - integrated cleaning - hot pressing bonding - cooling", which takes into account process flexibility and integration efficiency, and is suitable for bonding microbumps with medium and fine diameters of 40~100μm to optoelectronic chips. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A flowchart illustrating a specific embodiment of the optoelectronic co-packaging bonding method provided by the present invention; Figure 2 for Figure 1 A flowchart of a specific implementation of step S100 in the method shown; Figure 3 for Figure 1 A flowchart of a specific implementation of step S200 in the method shown; Figure 4 for Figure 1 A flowchart of a specific implementation of step S300 in the method shown; Figure 5 for Figure 1 A flowchart of a specific implementation of step S400 in the method shown; Figure 6 for Figure 1 A flowchart of another specific implementation of the method shown; Figure 7 for Figure 1 The diagram shows the formic acid reduction hot-press bonding process curve in the method shown. Figure 8-1 This is a schematic diagram of the process of the microbump fabrication system in the optoelectronic co-packaging bonding device provided by the present invention. Figure 8-2 for Figure 8-1 Enlarged schematic diagram of structure A in the middle; Figure 9 This is a schematic diagram of a specific embodiment of the nitrogen-sealed hot-pressing system in the optoelectronic co-encapsulation bonding device provided by the present invention; Figure 10-1 for Figure 9 A schematic diagram of the top structure of the protective cover in the nitrogen-sealed thermopressing system shown. Figure 10-2 for Figure 9 A schematic diagram of the bottom structure of the protective cover in the optoelectronic co-packaging bonding device shown; Figure 10-3 for Figure 10-2 A structural schematic diagram of the protective shield from another perspective; Figure 10-4 for Figure 9 The diagram shows the structure of the nozzle in the optoelectronic co-encapsulation bonding device. Figure 10-5 for Figure 9 The diagram shows the structure of the nozzle and protective cover assembled in the optoelectronic co-encapsulation bonding device.

[0024] Figure label: 1-Optical chip; 2-Aluminum pad; 3-Gold ball substrate; 4-Ceramic nozzle; 5-Gold wire lead; 6-Gold wire fused ball; 7-Gold pad; 8-Soft pressure head; 9-Solder ball; 10-Laser ball-planting nozzle; 11-Compressed nitrogen; 12-Formic acid solution; 13-Bubble; 14-Nitrogen curtain; 15-Formic acid vapor; 16-Protective cover; 17-Thermopressing bonding head; 18-Optical chip; 19-Micro bump; 20-Heating base; 21-Waste spray pipe; 22-Optical waveguide; 23-Purge nitrogen inlet; 24-Formic acid vapor inlet; 25-Protective cover mounting bracket; 26-Waste gas collection port; 27-Nozzle mounting groove; 28-Nozzle; 29-Orifice array; 30-Packaging substrate; 31-Nitrogen curtain inlet; 32-Nitrogen curtain outlet; 33-Gas guide groove. Detailed Implementation

[0025] The core of this invention is to provide an optoelectronic co-packaging bonding method and bonding device that can balance flexibility and integration efficiency while reducing product residue.

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0027] This invention addresses several issues encountered in rapid iterative verification of optoelectronic integrated optical chips, including incompatibility between the copper pillar microbump 19 process and the structure of the optical chip 1, poor reliability and residue of traditional solder paste solutions, low cleaning efficiency / product residue / long pre-cleaning time due to gas path design defects in existing flux-free technologies, lack of dedicated microbump 19 configuration and precise process parameters, unreasonable bonding control methods leading to cold solder joints or solder overflow, and inability to adapt to single-chip 1 rework after panelization. The invention proposes a gold-tin composite microbump 19 configuration and flux-free bonding method for optoelectronic co-packaging.

[0028] The core objectives of this invention are: 1. To propose a novel gold-tin composite microbump 19 configuration of "gold ball base + laser ball implantation," optimizing the microbump 19 size parameters, with a laser ball height of 15-40 μm and a total composite microbump 19 height of 30-65 μm, adapting to the requirements of airflow scouring and high-density interconnection; 2. To innovatively design the nozzle 28 structure, with air intake on three sides (optical chip 1, optical port direction, left and right sides) and exhaust on one side, achieving a dual effect of physical scouring and chemical reduction of formic acid vapor 15 on the microbump 19 through directional spraying, shortening the pre-cleaning time, improving cleaning efficiency, and reducing product residue; 3. To design a matching gold-tin composite microbump 19 preparation process, clarifying core parameters such as the single-pulse energy of laser ball implantation, and adjusting... 4. Optimize the hot-press bonding control method by using a controlled gap method instead of traditional pressure control to avoid poor soldering or solder overflow, thus improving bonding reliability; 5. Achieve process compatibility between the microbump 19 configuration and fabrication process and the cantilever beam structure of the optical chip 1, avoiding current continuity conflicts during copper pillar plating; 6. Construct a segmented process flow of "new microbump 19 configuration fabrication + integrated bonding", ensuring high cleanliness and low damage during the bonding process and eliminating flux residue through efficient flux-free cleaning and collaborative optical port protection design; 7. Balance flexibility and integration efficiency, accelerating the technological iteration of the optoelectronic integrated optical chip 1 while ensuring CPO packaging performance.

[0029] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Please refer to Figures 1 to 6In this embodiment, the optoelectronic co-packaging bonding method includes: Step S100: Obtain the optical chip 1 and prepare microbumps 19 on the pads of the optical chip 1; the microbumps 19 include a gold ball substrate 3 and solder balls 9, the gold ball substrate 3 covers the pads of the optical chip 1, and the solder balls 9 are located on the gold ball substrate 3; Step S200: Place the packaging substrate 30 on the heating base 20, and move the optical chip 1 above the packaging substrate 30, with the micro bumps 19 of the optical chip 1 facing the packaging substrate 30. Step S300: Use nitrogen gas curtain 14 to seal the periphery of optical chip 1, and use formic acid vapor 15 to physically flush and chemically reduce the micro-bumps 19 of optical chip 1. Step S400: Using the thermo-press bonding gap control method, the optical chip 1 is controlled to move toward the pads of the packaging substrate 30 and to perform bonding processing.

[0031] Specifically, this method is particularly applicable to optical chip 1 with optical waveguide 22 ports, such as optical chip 1, and high-reliability heterogeneous interconnection with interposer / packaging substrate 30; packaging substrate 30 can be PCB (Printed Circuit Board) board or HDI (High Density Interconnector) board, and microbump 19 is Au / Sn (gold / tin) microbump 19; the pads of optical chip 1 can be aluminum pads 2, and the pads of packaging substrate 30 are copper pads. The microbump 19 in this invention is a gold-tin composite microbump 19, which is composed of a gold ball substrate 3 formed by gold wire bonding process and a solder ball 9 formed by laser ball bonding process. It can be directly flip-chip mounted onto the copper pads of the packaging substrate 30. The microbump 19 is a medium-fine diameter microbump 19, which refers to a microbump 19 with a diameter of 40~100μm. It is the mainstream size of optoelectronic integrated packaging. The spacing of the microbump 19 is ≤150μm. It is electroless, low-damage, and highly clean. It can be independently fabricated by a single optical chip 1 and is suitable for the back-end interconnection and rapid packaging and testing verification scenarios of the chip 1 in the chip fabrication process.

[0032] The optoelectronic co-packaging bonding method provided by this invention adopts a micro-bump 19 structure of gold ball substrate 3 and solder balls 9, which significantly improves interconnect reliability. The gold ball substrate 3 and laser solder balls 9 form a stable metallurgical bond, resulting in excellent long-term performance. The gold ball substrate 3 completely covers the pads of the optical chip 1, forming an inert metal barrier layer, which can completely isolate the contact between formic acid vapor 15 and the pads, eliminating any risk of corrosion. It also eliminates the need for additional Ni / Au barrier layer preparation, simplifying the process and reducing costs. No flux is involved throughout the process, eliminating the risk of residue and ensuring high cleanliness of the optical port, perfectly matching the high cleanliness requirements of the optical chip 1 and avoiding optical signal attenuation problems caused by flux residue. The use of a controlled gap method instead of traditional pressure control significantly improves bonding consistency and reliability compared to traditional solutions. Furthermore, the integrated bonding process reduces process transfers and significantly improves production efficiency.

[0033] In some implementations, such as Figure 8-1 and Figure 8-2 As shown, step S1 includes: Step S101: Gold balls are implanted on the optical chip 1 using a gold wire bonding machine; Step S102: The gold balls are extruded using a soft-press flattening die-attachment machine to form a gold ball substrate 3. The diameter of the gold ball substrate 3 is larger than the diameter of the pad of the optical chip 1. Step S103: Use a laser ball-mounting machine to prepare solder balls 9 on the gold ball substrate 3. The solder balls 9 and the gold ball substrate 3 form micro-bumps 19.

[0034] In some embodiments, step S101 includes: controlling a gold wire bonding machine to implant gold balls onto the aluminum pads 2 of the optical chip 1 using gold wire leads 5 with a diameter of 25~38μm; the gold wire bonding machine is equipped with ceramic nozzles 4; specifically, the gold wire bonding machine controls the 25~38μm gold wire leads 5 to implant gold balls onto the aluminum pads 2 of the optical chip 1, ensuring that the diameter of the gold balls is 30~80μm to match the diameter of the target microbumps 19 (40~100μm) and completely cover the aluminum pads 2; Step S102 includes: controlling a soft-press flattening pick and place machine to flatten the gold balls with a pressure of 5~10N, removing the tail wires of the gold balls and trimming the height of the gold balls to 15~25μm and the diameter to 30~80μm to form a flat gold ball substrate 3. The gold ball substrate 3 is the gold pad 7, which provides a stable reference for laser soldering. The soft-press flattening pick and place machine is equipped with a 60~80HA soft pressure head 8. Step S103 includes: Solder balls 9 are Sn96.5Ag3.0Cu0.5 (SAC305) alloy solder balls or other lead-free solder balls 9 such as Sn-Ag alloy. By adjusting the laser current and pulse width, a single pulse energy of 3~7mJ is output to prepare solder balls 9 with a height of 15~40μm on the gold ball substrate 3. Laser single pulse energy: The total energy output by a single laser pulse during laser ball placement is the core process parameter controlling the melting degree and spreading morphology of the solder. It can be precisely controlled by adjusting the laser current and pulse width. The laser is output through the laser ball placement nozzle 10, and the single pulse energy is controlled by the coordinated control of current and pulse width, so that the solder balls 9 are completely fused onto the gold pads 7, forming a stable metallurgical bond, adapting to the forming requirements of solder balls 9 of different sizes.

[0035] The above configuration results in a gold ball substrate 3 with a height of 15-25 μm after flattening. The surface is flat and completely covers the aluminum pad 2, forming an inert barrier layer to prevent formic acid vapor 15 from corroding the aluminum pad 2, eliminating the need for an additional Ni / Au layer. The height of the microbumps 19 is reserved with sufficient space for airflow to balance scouring efficiency and gas utilization. The above process is without electroplating or photolithography and is fully compatible with the cantilever beam waveguide 22 structure of the optical chip 1.

[0036] In some embodiments, the total height of the microbumps 19 is 30~65μm, the diameter is 40~100μm, and the spacing between adjacent microbumps 19 is ≤150μm; ensuring high-density interconnection and morphological consistency; Furthermore, in step S103, when the diameter of the alloy solder ball is 60μm±5μm, a single pulse energy of 3~3.5mJ is output; when the diameter of the alloy solder ball is 80μm±5μm, a single pulse energy of 4.5~5mJ is output; and when the diameter of the alloy solder ball is 100μm±5μm, a single pulse energy of 6~7mJ is output. By setting the above parameters, the processing consistency can be improved, the efficiency can be increased, and the precise forming of the solder ball 9 can be achieved through the coordinated control of current and pulse width.

[0037] In some implementations, step S300 includes: Step S301: Control the compressed nitrogen gas 11 to enter the protective cover 16. The compressed nitrogen gas 11 flows out through the nitrogen gas curtain outlet 32 ​​on the protective cover 16 and forms a nitrogen gas curtain 14 around the optical chip 1. Step S302: Control the injection of compressed nitrogen gas 11 into the formic acid solution 12 to form bubbles 13, generating a mixed gas of formic acid and nitrogen. Control the injection of the mixed gas onto the surface of the micro-bumps 19 to pre-clean the surface of the micro-bumps 19, and control the discharge of by-products through the waste spray pipe 21. Specifically, the mixed gas is directionally injected onto the surface of the micro-bumps 19 through the nozzle 28 and the air hole array 29, and the by-products are discharged through the waste spray pipe 21, shortening the pre-cleaning time. During the cleaning process, the nitrogen curtain 14 continues to work to prevent external air from entering the system. Step S303: Control the heating base 20 to heat to 150~195℃, and control the pre-cleaning of the mixed gas to ≤10s.

[0038] In some implementations, step S200 includes: Step S201: At room temperature, transfer the optical chip 1 into the nitrogen sealing system, place the packaging substrate 30 on the heating base 20, and heat the heating base 20 to 150℃±10℃. Step S202: Use the thermosetting bonding head 17 to adsorb the light chip 1 and align it with the pads of the microbump 19 and the packaging substrate 30. Step S203: Orient the optical waveguide 22 port in the optical chip 1 toward the formic acid vapor inlet 24 on the protective cover 16, so that the optical waveguide 22 port is away from the exhaust gas collection port 26 on the protective cover 16, control the protective cover 16 to descend, and form a closed micro-reaction cavity between the protective cover 16 and the heating base 20; both the optical chip 1 and the packaging substrate 30 are located in the closed micro-reaction cavity.

[0039] The above configuration, by orienting the optical waveguide 22 port in the optical chip 1 toward the formic acid vapor inlet 24, i.e., the optical waveguide 22 port in the optical chip 1 away from the exhaust gas collection port 26, can prevent contamination of the optical waveguide 22 port. With the help of the nitrogen sealing system, and through the physical scouring and chemical reduction of formic acid vapor 15, flux-free cleaning, hot-press bonding, and port protection are integrated into the same nitrogen sealing system, achieving transfer-free processing of the bonding process, avoiding secondary oxidation and contamination, ensuring cleanliness and processing efficiency, taking into account the needs of R&D verification and industrial production, and adapting to all scenarios from small-batch laboratory prototyping to mass production in the factory.

[0040] In some implementations, step S400 includes: Step S401: Using a vision alignment system in conjunction with a Z-axis displacement sensor, locate the contact position between the micro-bump 19 and the pad of the packaging substrate 30; the Z-axis displacement sensor is integrated on the thermo-bonding head 17; Step S402: Based on the contact position, control the thermosetting bonding head 17 to continue pressing down on the optical chip by 15~10μm to ensure full contact and no solder overflow; Step S403: During the bonding process, the temperature of the hot-press bonding head 17 is controlled at 250~340℃, the temperature of the heating base 20 is controlled at 150℃±10℃, formic acid vapor 15 is continuously supplied, and at the same time, the oxygen concentration in the system is maintained at ≤100ppm through the nitrogen curtain 14 to prevent oxidation of the micro-bumps 19 and the solder joint surface at high temperature.

[0041] In some implementations, after step S400, the following steps are also included: Step S500: Close formic acid vapor 15, open purging nitrogen inlet 23, control compressed nitrogen 11 to purge through purging nitrogen inlet 23 for 3~5s, until the hot-press bonding head 17 and heating base 20 are cooled to below 80℃; after purging, temporarily close nitrogen curtain inlet 31 to supply nitrogen, open system pick-up and drop port to take out bonding device, bonding device includes bonded optical chip 1 and packaging substrate 30, no additional cleaning process is required throughout the process.

[0042] This invention utilizes formic acid vapor 15 to reduce the oxides on the surface of Au / Sn microbumps 19, solder balls 9, and the pads of the packaging substrate 30. The gold ball substrate 3, i.e., the gold pads 7, does not participate in the reaction and protects the pads of the optical chip 1. The reaction products are all gases with no residue. During the reduction process, a modular nitrogen sealing system maintains a low-oxygen environment through a nitrogen curtain 14. The nitrogen curtain 14 is supplied with nitrogen by the nitrogen curtain inlet 31 to prevent the oxidation reaction from proceeding in reverse.

[0043] The reduction reaction of formic acid vapor 15 with tin oxide SnO: 2HCOOH(g)+SnO(s)→(HCOO)2Sn(s)+H2O(g); (HCOO)2Sn(s)→Sn(s)+2CO2(g)+H2(g); The reduction reaction of formic acid vapor (15) with copper oxide (CuO): 2HCOOH(g)+CuO(s)→(HCOO)2Cu(s)+H2O(g); (HCOO)2Cu(s)→Cu(s)+2CO2(g)+H2(g).

[0044] Furthermore, such as Figure 7 As shown, the Z-axis position of the bonding head is: Pre-cleaning height: the initial distance between the bonding head and the target surface, ranging from 1-3mm, used for positioning during the pre-treatment stage; Bonding height: the final contact height between the bonding head and the target surface during the bonding process, which is the height of the microbumps or solder balls, for example, 50μm, to ensure bonding accuracy and pressure control. Bonding head temperature (T... BHThe process is divided into three temperature ranges: 150℃-195℃: preheating or formic acid pre-cleaning stage, providing a temperature environment for the reduction reaction and ensuring efficient removal of oxides from chip microbumps and substrate pads; 250℃-340℃: core bonding stage, where high temperature promotes the melting and metallurgical bonding of gold-tin composite microbumps; 140℃-150℃: cooling or solidification stage, stabilizing the bonding structure. Shielding gas (Va): gas flow rate range of 10 LPM-16 LPM, forming a nitrogen curtain to isolate air during the process and prevent oxidation or contamination; the later flow rate is 0 LPM, indicating that nitrogen supply is stopped at this stage. Formic acid vapor (FA): flow rate range of 1 LPM-8 LPM, participating in the reaction as a reducing agent to remove the oxide layer on the metal surface and improve bonding quality. Nitrogen (N2): flow rate range of 1 LPM-8 LPM, used after bonding to purge the chip and microbump gaps, removing reaction residues and preventing contamination.

[0045] In addition to the above-described optoelectronic co-packaging bonding method, the present invention also provides an optoelectronic co-packaging bonding apparatus capable of performing the optoelectronic co-packaging bonding method as described above.

[0046] like Figure 9 As shown, the optoelectronic co-encapsulation bonding method includes a microbump 19 fabrication system and a nitrogen-sealed hot pressing system; The micro-bump 19 fabrication system includes a gold wire bonding machine, a soft pressing and flattening chip bonding machine, and a laser ball bonding machine. The micro-bump 19 fabrication system can operate independently and supports flexible fabrication of single-optical chip 1. The gold wire bonding machine is used to bond gold balls on the optical chip 1, the soft pressing and flattening chip bonding machine is used to extrude the gold balls, and the laser ball bonding machine is used to fabricate solder balls 9 on the gold ball substrate 3. The nitrogen-sealed thermocompression system includes a thermocompression bonding head 17, a heating base 20, a vision alignment system, and a protective cover 16. The thermocompression bonding head 17 is used to press down the optical chip 1. The vision alignment system is used to locate the contact position between the microbumps 19 and the pads of the packaging substrate 30. The protective cover 16 is used to guide the compressed nitrogen gas 11 and formic acid vapor 15, so that the compressed nitrogen gas 11 forms a nitrogen curtain 14 and the formic acid vapor 15 is directed towards the microbumps 19 of the optical chip 1. Specifically, the nitrogen-sealed thermocompression system is not a closed structure. Dynamic sealing is achieved through the nitrogen curtain 14. It integrates three functional units: a flux-free formic acid cleaning unit, a thermocompression bonding unit, and an optical chip 1 port protection unit, avoiding secondary contamination caused by process transfer. Specifically, precise bonding is achieved by using a controlled gap method to avoid cold solder joints or solder overflow. The thermocompression bonding head 17 is equipped with a guiding mechanism to ensure that the movement is free from rotational offset, improving motion accuracy and bonding quality.

[0047] The optoelectronic co-packaging bonding device provided by this invention supports independent fabrication of single-chip 1 and flexible processing of multi-specification optical chips 1 through the fabrication process of "gold wire bonding and ball planting - soft pressing and flattening - laser ball planting and capping". It can adjust parameters individually to complete the fabrication of microbumps 19 for scattered optical chips 1 of different specifications after panelization and fabrication, which greatly improves the process flexibility. In other words, this method can realize the independent fabrication of single-chip 1 or the fabrication of microbumps 19 for scattered optical chips 1 after panelization and fabrication, without the need for synchronous processing during the fabrication stage. At the same time, the nitrogen-sealed hot pressing system can create a nitrogen atmosphere through the dynamic sealing of nitrogen curtain 14 and control the oxygen concentration ≤100ppm to achieve the transfer-free processing of "independent fabrication of microbumps 19 - integrated cleaning - hot pressing bonding - cooling", which takes into account the process flexibility and integration efficiency and is suitable for the bonding requirements of microbumps 19 with medium and fine diameters of 40~100μm and optoelectronic chips 1.

[0048] In some embodiments, the nitrogen-sealed hot-press system includes a reducing gas chamber and a hot-press bonding chamber. The reducing gas chamber contains formic acid solution 12 and compressed nitrogen gas 11. In the hot-press bonding chamber, the hot-press bonding head 17 absorbs the optical chip 1 through vacuum adsorption, and the heating base 20 positions the encapsulation substrate 30 through vacuum adsorption to ensure stability.

[0049] In some implementations, such as Figures 10-1 to 10-5 As shown, the protective cover 16 includes a main body and a nozzle 28. The first side of the main body of the protective cover 16 is provided with a nitrogen curtain inlet 31, a nitrogen curtain outlet 32, a formic acid vapor inlet 24, and a purging nitrogen inlet 23. The nozzle 28 is installed on the second side of the main body of the protective cover 16, and the extension direction and cross-section of the nozzle 28 are both U-shaped. A nitrogen curtain 14 is formed by supplying nitrogen through the nitrogen curtain inlet 31 and exhausting nitrogen through the nitrogen curtain outlet 32. There are numerous nitrogen curtain outlets 32 arranged in a ring. A dynamic nitrogen protective atmosphere is constructed through the nitrogen curtain 14. The modular design can be adapted to the processing of multiple specifications of optical chips 1, realizing the non-transfer processing of cleaning-bonding-cooling, and avoiding secondary oxidation caused by the exposure of the optical chip 1 and micro-bumps 19 to air between processes.

[0050] Furthermore, the nozzle 28, through its surrounding arrangement, forms a layout with the formic acid vapor generating module of "optical waveguide 22 direction + left and right sides" for three-sided air intake and single-sided exhaust. The directional spray enhances physical scouring and shortens the pre-cleaning time. Compressed nitrogen 11 is continuously introduced through the nitrogen curtain inlet 31, forming a ring-shaped nitrogen curtain 14 inside the system. The nitrogen is discharged in an orderly manner through the nitrogen curtain outlet 32, creating a dynamically sealed nitrogen protective atmosphere. This stabilizes the oxygen concentration in the system at ≤100ppm, replacing the traditional rigid sealed structure. This ensures both sealing effect and facilitates the removal and placement of the optical chip 1 and equipment maintenance.

[0051] In some embodiments, the top of the nozzle 28 is an open structure, and the top of the nozzle 28 is fitted to the second surface of the main body of the protective cover 16 so that the nozzle 28 is connected to the formic acid vapor inlet 24 and the purging nitrogen inlet 23. The formic acid vapor inlet 24 and the purging nitrogen inlet 23 can be arranged close to each other to facilitate the arrangement of pipelines. The bottom of the nozzle 28 is provided with a vent array 29, which allows the purging nitrogen and formic acid vapor 15 to flow out. The vent array 29 includes a number of vent units, which can be inclined and should face the micro protrusion 19. The inclination of the vent units should depend on the position of the micro protrusion 19.

[0052] In some embodiments, the second side of the main body of the protective cover 16 is provided with a nozzle mounting groove 27. The formic acid vapor inlet 24 and the purging nitrogen inlet 23 are both connected to the nozzle mounting groove 27. An exhaust gas collection port 26 is also provided on the side of the nozzle mounting groove 27 away from the formic acid vapor inlet 24. After installation, the nozzle 28 protrudes from the nozzle mounting groove 27, and the air hole array 29 is located outside the nozzle mounting groove 27 to facilitate gas discharge. Specifically, the nozzle mounting groove 27 can be square, the nozzle 28 can be U-shaped, the nozzle 28 is located on three sides of the nozzle mounting groove 27, and an exhaust gas collection port 26 is provided on the other side of the nozzle mounting groove 27. The nozzle mounting groove 27 not only facilitates the installation of the nozzle 28, but also plays a role in guiding the flow. Furthermore, the nozzle 28 is fixed in the nozzle mounting groove 27 by interference fit. The nozzle 28 surrounds the optical chip 1. The height of the nozzle 28 is precisely matched with the total height of the micro-bump 19. It is as close as possible to the side of the micro-bump 19 below the optical chip 1, but does not interfere with the hot-press bonding pressing operation.

[0053] In some embodiments, the pore diameter of the individual pores in the pore array 29 is 60~100μm, the pore spacing is 100~200μm, the height direction is tilted at 15~30° toward the micro-protrusion 19, and the width direction is tilted at 0~45° toward the center of the micro-protrusion 19, so as to achieve three-sided directional spraying.

[0054] Specifically, formic acid vapor 15 enters the nozzle 28 through the formic acid vapor inlet 24 and is sprayed onto the surface of the micro-bumps 19 through the vent array 29. The reaction byproducts are discharged through the waste gas collection port 26 and the waste spray pipe 21. The chemical reduction and physical rinsing work together, with no risk of residue. During the cleaning process, nitrogen is continuously supplied from the nitrogen curtain inlet 31 to form a nitrogen curtain 14, maintaining a low-oxygen environment in the system and avoiding secondary oxidation of the surface of the micro-bumps 19.

[0055] In some embodiments, the optical waveguide 22 port faces the formic acid vapor inlet 24, which is upstream of the fresh gas, reducing contact with byproducts; the inner side of the protective cover 16 is provided with an airflow guide groove to guide the formic acid vapor 15 to flow preferentially through the micro-protrusion 19 area, accelerating the flow of byproducts to the exhaust gas collection port 26; the exhaust gas collection port 26 and the vent array 29 on the side of the formic acid vapor inlet 24 are symmetrically arranged to form a straight airflow channel, which utilizes the pressure difference to quickly exhaust the gas without the need for a complex protection module; during the protection process, the airflow barrier formed by the nitrogen curtain 14 can block the diffusion of external air and reaction byproducts to the optical waveguide 22 port, further improving the protection effect.

[0056] In some embodiments, the inner side of the protective cover 16 is provided with an airflow guide groove, which is located on the outer periphery of the nozzle mounting groove 27. The airflow guide groove guides the airflow direction and is connected to the nitrogen curtain inlet 31. The protective cover 16 is provided with a cover plate, and the nitrogen curtain outlet 32 ​​is located on the cover plate. The cover plate is fastened to the airflow guide groove.

[0057] The optoelectronic co-packaging bonding method provided by this invention employs a 40-100μm proprietary gold-tin composite microbump 19 configuration. The microbump 19 on the aluminum pad 2 of the optical chip 1 is an integrated composite structure of "gold ball substrate 3 + laser solder ball 9", which can be directly flip-chip bonded to the copper pad of the packaging substrate 30. The gold ball substrate 3 forms an inert metal barrier layer, eliminating the need for additional Ni / Au barrier layer preparation, and is compatible with the cantilever beam structure of the optical chip 1, making it suitable for flux-free cleaning scenarios using formic acid vapor 15. The single-pulse energy is controlled by adjusting the laser current and pulse width, with 3-3.5 mJ for 60μm diameter solder balls 9 (with a height of 15-25μm after placement) and 4.5-5 mJ for 80μm diameter solder balls 9 (with a height of 25-35μm after placement). The solder balls 9 with a diameter of 100μm (with a height of 35~40μm after placement) have a heat output of 6~7mJ. The solder balls 9 are precisely formed through the coordinated control of current and pulse width. The entire process is completed in a nitrogen atmosphere with O2≤100ppm. It can be used to independently prepare single-light chips 1 or to supplement microbumps 19 for scattered light chips 1 after panelization and fabrication, without the need for synchronous processing during the fabrication stage. The thermo-press bonding adopts the gap control method, and the contact position between the microbumps 19 and the copper pads of the substrate is accurately detected by the Z-axis displacement sensor. Based on the contact position, the thermo-press bonding head 17 continues to press down by 5~10μm, replacing the traditional pressure control, ensuring that there is no cold solder joint and no solder overflow. It is suitable for composite microbumps 19 with a total height of 30~65μm, and the bonding consistency and reliability are significantly improved.

[0058] Furthermore, this method employs a segmented processing mode of fabrication and integrated bonding using a novel microbump 19 configuration. Independent fabrication and integrated bonding work in tandem to achieve segmented processing of "fabrication-cleaning-bonding-cooling," balancing process flexibility and integration efficiency. A nozzle 28 is installed inside the protective cover 16, its height precisely matched to the total height of the composite microbump 19, surrounding the optical chip 1 to be cleaned. A uniformly distributed array of pores 29 is provided on the inner wall of the nozzle 28, forming a three-sided air intake structure: "optical port direction + left and right sides." The optical waveguide 22 port of the optical chip 1 is oriented towards the formic acid vapor inlet 24, located upstream of the fresh gas. The exhaust gas collection port 26 is symmetrically arranged with the pore array 29 on the formic acid vapor inlet 24 side, utilizing airflow pressure difference to achieve rapid exhaust and prevent byproducts from accumulating and contaminating the optical port. Figure 7 As shown, the formic acid vapor 15 cleaning temperature is 150~195℃, cleaning time ≤10s, hot pressing bonding temperature is 250~340℃, bonding time is 8~12s, and the pressure drop is controlled by a gap method of 5~10μm. The single-pulse energy of laser ball implantation is precisely matched with the size of the solder ball 9. The gas atmosphere, temperature, gap and other parameters of the microbump 19 preparation and bonding process are matched in a coordinated manner to ensure the quality of configuration and bonding reliability. It is suitable for the preparation and interconnection of independent microbumps 19 of scattered optical chips 1 after panelization and tape-out; it is suitable for small-batch prototyping and rapid functional testing scenarios, eliminating the need for whole wafer fabrication, reducing costs and cycle time; it is suitable for optical chip 1 packaging with cantilever beam structure, and is compatible with the high-cleanliness and high-density interconnection requirements of optoelectronic co-packaging.

[0059] Furthermore, the segmented processing mode of fabrication and integrated bonding of the new microbump 19 configuration in this case is not only applicable to optical chip 1, but also to the chip interconnect process of flip-chip bonding of optoelectronic integrated electrical chips or switching chips to substrates or interposers.

[0060] Specific Example 1: Preparation of gold-tin composite microbumps 19; This embodiment focuses on the preparation of the micro-bump 19 configuration of "gold ball base + laser ball implantation". The micro-bump 19 is formed without electroplating and with high cleanliness through a three-step addition process, which corresponds to the complete process.

[0061] Preparation equipment and parameters: Core equipment: Gold wire bonding machine (including ceramic nozzle 4), soft pressing and flattening chip mounter (including soft pressing head 8), laser ball mounting machine (including laser ball mounting nozzle 10); Consumable specifications: Gold wire 5 with a diameter of 25μm, Sn96.5Ag3.0Cu0.5 (SAC305) alloy solder ball (diameter of 60μm); Environmental parameters: Compressed nitrogen 11 is introduced through the nitrogen curtain inlet 31 of the modular nitrogen sealing system to form a nitrogen curtain 14, and exhaust is carried out through the nitrogen curtain outlet 32 ​​to control the oxygen concentration in the system to ≤100ppm, with oxygen-free protection throughout the process.

[0062] Preparation steps: (1) Gold wire bonding and ball placement: The ceramic nozzle 4 of the gold wire bonding machine delivers a 25μm gold wire lead 5, which is precisely discharged above the aluminum pad 2 of the optical chip 1, melting the end of the gold wire lead 5 into a gold wire ball 6. Then, it is pressed down to form a metallurgical bond between the gold wire ball 6 and the aluminum pad 2, and finally forms a gold ball with a diameter of 30μm, which completely covers the aluminum pad 2; (2) Soft pressing and flattening: The soft pressing head 8 of the soft pressing and flattening machine applies a 5N pressure vertically to the surface of the gold ball for 2 seconds to remove the gold wire tails remaining on the top of the gold ball. After trimming, a height of 15μm and a diameter of 40μm are formed, with a surface flatness of ±1μm. The gold ball substrate 3, i.e. the gold pad 7; (3) Laser ball planting capping: The laser ball planting nozzle 10 of the laser ball planting machine is aligned with the center of the gold ball substrate 3, and the laser current and pulse width are adjusted so that the single pulse energy reaches 3mJ, and the 40μm diameter solder ball is accurately melted onto the surface of the gold ball substrate 3; after the solder ball is completely melted, it forms an Au-Sn intermetallic compound with the gold pad 7, and after cooling, it forms a laser solder ball 9 with a height of 15μm and a diameter of 40μm, and finally obtains the Au / Sn micro bump 19 of "gold ball substrate 3 + laser solder ball 9", with a total height of 30μm, a spacing of 80μm, and a height consistency of ±2μm.

[0063] Preparation results: Microbump 19 morphology: The Au / Sn microbump 19 surface is free of oxidation and cracks, and the solder ball 9 is tightly bonded to the gold ball without delamination defects; Process compatibility: No electroplating or photolithography is required throughout the process, and there is no conflict with the cantilever beam waveguide 22 structure of the optical chip 1, and no damage is caused to the surface of the optical chip 1 or the aluminum pad 2; Adaptability: The size of the microbump 19 fully meets the requirements of high-density interconnection with medium and fine diameters of 40~100μm, and can be directly used for subsequent fluxless bonding.

[0064] Specific Implementation Example 2: Flux-free hot-press bonding process; This embodiment, based on the gold-tin composite microbumps 19 prepared in specific embodiment 1, elaborates in detail the complete process of integrated flux-free cleaning-hot pressing bonding-cooling, corresponding to the collaborative working logic of each functional unit in the modular nitrogen sealing system.

[0065] 1. Bonding equipment and parameters; Core equipment: Modular nitrogen sealing system (integrating three functional units, including nitrogen curtain 14, nitrogen curtain inlet 31, and nitrogen curtain outlet 32), thermocompression bonding head 17 (including guiding mechanism), heating base 20, and waste spray pipe 21; Gas parameters: Compressed nitrogen 11 purity ≥ 99.999%, formic acid solution 12 concentration 90wt%-96wt%, for example 93wt%, mixed gas pre-cleaning temperature 150℃; Bonding parameters: Thermocompression bonding head 17 temperature 260℃ (higher than the melting point of solder balls), heating base 20 temperature 150℃, bonding time 8s, controlled gap method pressure 5μm; Sealing parameters: Nitrogen is supplied through nitrogen curtain inlet 31 and exhausted through nitrogen curtain outlet 32 ​​to form nitrogen curtain 14, and the oxygen concentration in the system is controlled at ≤100ppm.

[0066] 2. Bonding steps; (1) Transfer and alignment of optical chip 1: Nitrogen is supplied by opening the nitrogen curtain inlet 31 of the modular nitrogen sealing system. After the nitrogen curtain 14 is formed and the oxygen concentration in the system is ≤100ppm, the optical chip 1 with prepared Au / Sn microbumps 19 is transferred into the modular nitrogen sealing system and placed on the packaging substrate 30 (PCB / HDI board) of the heating base 20. The thermosetting bonding head 17 adsorbs the optical chip 1, and the Au / Sn microbumps 19 are precisely aligned with the pads of the packaging substrate 30 through the vision alignment system (alignment accuracy ±1μm). (2) Integrated flux-free cleaning: Turn on the supply of compressed nitrogen 11, inject compressed nitrogen 11 into the bottom of the formic acid solution 12 to form bubbles 13, and the bubbles 13 carry formic acid molecules to form formic acid vapor 15 during the rising process; the formic acid vapor 15 is introduced into the modular nitrogen sealing system through the gas path and sprayed directionally onto the surface of Au / Sn microbumps 19 at a flow rate of 1 LPM. Through the dual action of chemical reduction and physical scouring, it is cleaned for 6 seconds; the reaction byproducts are collected through the waste gas collection port 2. 6. Enter the waste spray pipe 21 for discharge; during the cleaning period, nitrogen is continuously supplied to the nitrogen curtain inlet 31, and the nitrogen curtain 14 maintains a low oxygen environment in the system to avoid oxidation of the microbumps 19; (3) Integrated hot-press bonding: after cleaning, the hot-press bonding head 17 descends smoothly under the action of the guide mechanism. The contact position between the Au / Sn microbumps 19 and the substrate pads is detected by the Z-axis displacement sensor. After recording the coordinates, it continues to press down by 5μm to make the microbumps 19 fully contact the substrate pads; the hot-press bonding head 17 is heated to 260℃ and held for 8s, during which nitrogen is continuously supplied. Acid vapor 15 prevents the surface of micro-bumps 19 from oxidizing again at high temperature; at the same time, nitrogen curtain 14 maintains a low oxygen environment to prevent high temperature oxidation; (4) Integrated nitrogen purging and cooling: shut off the supply of formic acid vapor 15, open the nitrogen inlet, and purge the micro-reaction chamber with compressed nitrogen 11 at a flow rate of 3 LPM for 3 seconds to remove residual formic acid vapor 15 and byproducts; the hot-press bonding head 17 and the heating base 20 are cooled to below 80°C in sync, the nitrogen curtain inlet 31 is shut off to supply nitrogen, the protective cover 16 rises with the hot-press bonding head 17, and the completed optoelectronic integrated component is taken out.

[0067] 3. Bonding effect; Interconnect reliability: Solder joint void rate ≤5%, resistance change rate ≤10% after thermal cycling (-40℃~125℃, 1000 cycles), no defects such as cold solder joints or solder overflow; Optical port cleanliness: No formic acid residue or by-products adhering to the 22-port of the optical waveguide, and optical signal transmission attenuation ≤0.5dB; Process efficiency: No transfer throughout the cleaning-bonding-cooling process, with a total time of ≤30s, which is more than 30% shorter than the traditional process.

[0068] Specific Implementation Example 3: Improved Structure and Application of Protective Cover 16; This embodiment focuses on the innovative design of the protective cover 16, and elaborates in detail the structural features and airflow guiding effect of the annular nozzle 28 and the air hole array 29, as well as the internal assembly relationship of the protective cover 16.

[0069] Improved structural parameters of protective cover 16: Core structure: Protective cover 16 (stainless steel), protective cover mounting bracket 25, annular nozzle 28 (stainless steel), vent array 29, nozzle mounting groove 27, formic acid vapor inlet 24, exhaust gas collection port 26; Key dimensions: Annular nozzle 28 has an inner diameter of 2mm and an outer diameter of 2.5mm, precisely matching the total height (30μm) of Au / Sn microbumps 19, close to the microbump 19 side below the optical chip 1, but without interfering with the hot-press bonding operation; Vent array 29 has a pore diameter of 80μm. The hole spacing is 150μm, and the height direction is tilted at 0°-15° towards the array of micro-protrusions 19; Assembly relationship: the annular nozzle 28 is installed in the nozzle mounting groove 27 on the inner wall of the protective cover 16 by interference fit, surrounding the optical chip 1. The formic acid vapor inlet 24 is connected to the annular nozzle 28, and the exhaust gas collection port 26 is symmetrically arranged with the formic acid vapor inlet 24 (with an included angle of 180°); the protective cover 16 and the nitrogen curtain 14 of the modular nitrogen sealing system work together to build an integrated environment for sealing and cleaning.

[0070] The working principle of the improved structure: (1) Airflow distribution: Formic acid vapor 15 enters the annular nozzle 28 through the formic acid vapor inlet 24. The closed-loop structure of the annular nozzle 28 makes the gas evenly distributed to the surrounding vent array 29, avoiding the airflow deviation caused by traditional single-sided air intake; (2) Directional scouring: The vent array 29 in the width direction is designed with a 0°-20° inclination, so that the formic acid vapor 15 is sprayed from the "optical waveguide 22 direction + left and right sides" three sides toward the center of the Au / Sn micro-bump 19 array, forming an enveloping airflow, which fully scours the sidewalls and top surface of the micro-bump 19. (3) Rapid exhaust: The exhaust gas collection port 26 and the formic acid vapor inlet 24 are symmetrically arranged. The gas flow pressure difference forms a straight airflow channel, and the reaction by-products can quickly enter the exhaust gas collection port 26 without detour, avoiding stagnation in the micro-reaction chamber; (4) Sealing and coordination: During the operation, the nitrogen curtain 14 (nitrogen supplied by the nitrogen curtain inlet 31) surrounds the inner side of the protective cover 16 to prevent external air from entering the cleaning area, while preventing the formic acid vapor 15 from leaking outward, taking into account both sealing and environmental protection requirements.

[0071] Application effect verification: Cleaning uniformity: Ten Au / Sn micro-bumps 19 in the edge and central areas of the optical chip 1 were selected for oxide layer detection. The oxide layer removal rate was ≥99.5% with no local residue, which is significantly improved compared with the traditional single-sided air intake structure. Structural compatibility: The modular assembly design of the annular nozzle 28 and the protective cover 16 can be quickly adapted to different sizes of optical chips 1 (maximum compatible with 60mm×60mm optical chips 1) without replacing the entire protective cover 16. Protection stability: After 100 consecutive bonding experiments, the protective cover 16 showed no deformation, the annular nozzle 28 showed no blockage, and the spray angle of the air hole array 29 showed no deviation, demonstrating excellent structural stability.

[0072] The beneficial effects are as follows: 1. Perfectly resolves the compatibility conflict between optical chip 1 and microbump 19 process; The gold-tin composite microbump 19 configuration and its proprietary fabrication process of this invention adopt an additive method without electroplating or photolithography, eliminating the need to consider the current continuity requirements of whole-wafer electroplating. It is fully compatible with the cantilever beam structure of the optical waveguide 22 in the optical chip 1, which improves coupling efficiency. This completely avoids the electroplating failure problem of the copper pillar microbump 19 caused by the special structure of the optical chip 1, broadens the range of packaging process options for the optoelectronic integrated optical chip 1, and provides a reliable interconnection solution for the optical chip 1 with special structure.

[0073] 2. Breaking through the density and reliability bottlenecks of traditional solutions; The dimensions of the microbump 19 were optimized (laser solder ball 9 height 15~40μm, total height of composite microbump 19 30~65μm) to adapt to more application scenarios. A new configuration of "gold ball base + laser ball placement" and supporting manufacturing process were proposed. The diameter of the microbump 19 is 40~100μm and the spacing is ≤150μm, which can accurately meet the needs of high-density interconnection. The laser ball placement process achieves precise single-pulse energy control of 3~7mJ (3~3.5mJ for 60μm solder balls, 4.5~5mJ for 80μm solder balls, and 6~7mJ for 100μm solder balls) by combining the coordinated adjustment of current and pulse width. This solves the problems of uneven solder amount, cold solder / overflow of solder in traditional solder paste dipping solutions, as well as the limitation of stencil printing solder paste which is only suitable for large diameter and large spacing. The microbump 19 has a high forming yield and significantly improved interconnection reliability. Moreover, the gold ball substrate 3 and the laser solder ball 9 form a stable metallurgical bond, which has excellent long-term performance.

[0074] 3. Significantly improved bonding reliability, avoiding cold solder joints or solder overflow; The innovative method of using a controlled gap to replace traditional pressure control ensures sufficient contact between the microbump 19 and the substrate pad (preventing cold solder joints) by precisely detecting the contact position and applying pressure of 5~10μm. This also limits solder overflow caused by excessive pressure (preventing solder overflow). No complex pressure calibration is required. It is suitable for composite microbumps 19 with a total height of 30~65μm. The bonding consistency and reliability are significantly improved compared to traditional solutions, solving the core defects of existing bonding control methods.

[0075] 4. Precise and efficient optical port protection, adaptable to various application scenarios; Based on the airflow scouring characteristics of the 28-channel annular nozzle, the optical port is always kept in a fresh airflow environment through a synergistic structure of "directional arrangement + airflow guidance + symmetrical exhaust". This allows reaction byproducts to be discharged quickly, effectively avoiding optical port contamination. The structure is simple and does not require additional complex modules, solving the problems of insufficient targeting and poor protection effect of existing optical port protection schemes, and ensuring the stable communication performance of optical chip 1.

[0076] 5. The process is precise and reproducible, optimizing both flexibility and integration efficiency; By clarifying the single-pulse energy (3~7mJ) of laser ball implantation and its compatibility with the size of the solder ball 9, and combining the adjustment method of "current + pulse width", the process parameters can be precisely controlled and stably reproduced, avoiding the problem of poor processing consistency caused by the ambiguity of parameters in existing technologies. The exclusive preparation process of "gold wire bonding ball implantation - soft pressing and flattening trimming - laser ball implantation capping" supports independent rework of single optical chip 1 and flexible processing of multiple specifications of optical chip 1. It can adjust the parameters individually to complete the preparation of micro-bumps 19 for scattered optical chips 1 of different specifications after the panelization and fabrication, which greatly improves the process flexibility. Flux-free cleaning, hot pressing bonding, and port protection are integrated into the same nitrogen sealing system to achieve transfer-free processing of the bonding process, avoid secondary oxidation and contamination, ensure cleanliness and processing efficiency, take into account the needs of R&D verification and industrial production, and adapt to the whole scenario from small-batch sampling in the laboratory to mass production in the factory.

[0077] 6. Flux-free, clean and efficient, with no aluminum pad corrosion; The gold ball substrate 3 completely covers the aluminum pad 2 to form an inert metal barrier layer, which can completely isolate the formic acid vapor 15 from contact with the aluminum pad 2, eliminating any risk of corrosion. No additional Ni / Au barrier layer is needed, simplifying the process and reducing costs. The 30~65μm height of the microbumps 19 forms a reasonable gap suitable for airflow, and the ±3μm height consistency allows formic acid vapor 15 to fully contact the surface of all microbumps 19, resulting in excellent oxide layer removal and completely eliminating cleaning dead zones. No flux is involved throughout the process, eliminating residue risks and ensuring high optical port cleanliness, perfectly matching the high cleanliness requirements of the optical chip 1 and avoiding optical signal attenuation problems caused by flux residue. The three-sided directional spray design of the annular nozzle 28 increases the physical scouring effect, significantly shortening the pre-cleaning time and improving cleaning efficiency.

[0078] 7. Adapts to rapid verification scenarios, with significant optimization of cost and cycle time; The dedicated fabrication process supports independent processing of single optical chip 1 without the need for whole wafer fabrication, significantly reducing the cost and cycle time of small-batch prototyping and avoiding the high cost and long cycle time problems caused by whole wafer fabrication in traditional processes; the integrated bonding process reduces process transfer and significantly improves production efficiency; it can fully leverage the cost sharing advantages of panel fabrication, allowing R&D teams to complete the packaging and functional verification of optical chip 1 at a lower cost and faster speed, accelerating the technological iteration of optoelectronic integrated optical chip 1.

[0079] 8. Green manufacturing, meeting energy conservation and environmental protection requirements; The products of the formic acid reduction reaction are all gases such as CO2, H2, and H2O, with no solid / liquid residues. No flux or additional cleaning process is required throughout the process, and no wastewater or waste residue is generated, thus avoiding environmental pollution. The directional injection gas path design reduces the waste of formic acid and nitrogen, lowers resource consumption, and meets the industry development requirements of green manufacturing and energy conservation and environmental protection.

[0080] The optoelectronic co-packaging bonding method and bonding apparatus provided by this invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of this invention.

Claims

1. A method for optoelectronic co-packaging bonding, characterized in that, include: Step S100: Obtain an optical chip (1) and prepare microbumps (19) on the pads of the optical chip (1); the microbumps (19) include a gold ball substrate (3) and solder balls (9), the gold ball substrate (3) covers the pads of the optical chip (1), and the solder balls (9) are located on the gold ball substrate (3); Step S200: Place the packaging substrate (30) on the heating base (20) and move the optical chip (1) above the packaging substrate (30), with the micro bumps (19) of the optical chip (1) facing the packaging substrate (30). Step S300: Use a nitrogen gas curtain (14) to seal the periphery of the optical chip (1), and use formic acid vapor (15) to physically flush and chemically reduce the micro-bumps (19) of the optical chip (1); Step S400: Using the hot-press bonding gap control method, the optical chip (1) is controlled to move toward the pads of the packaging substrate (30) and perform bonding processing.

2. The optoelectronic co-packaging bonding method according to claim 1, characterized in that, Step S1 includes: Step S101: Gold balls are implanted onto the optical chip (1) using a gold wire bonding machine; Step S102: The gold balls are pressed using a soft-press flattening die-attachment machine to form the gold ball substrate (3), the diameter of which is larger than the pad diameter of the optical chip (1); Step S103: Use a laser ball-planting machine to prepare solder balls (9) on the gold ball substrate (3), and the solder balls (9) and the gold ball substrate (3) constitute the micro-bumps (19).

3. The optoelectronic co-packaging bonding method according to claim 2, characterized in that, Step S101 includes: controlling the gold wire bonding machine to implant the gold ball onto the aluminum pad (2) of the optical chip (1) with a gold wire lead (5) with a diameter of 25~38μm; Step S102 includes: controlling the soft pressing and flattening machine to flatten the gold ball with a pressure of 5~10N, removing the tail filament of the gold ball and trimming the height of the gold ball to 15~25μm and the diameter to 30~80μm to form a flat gold ball substrate (3). Step S103 includes: the solder ball (9) is a Sn96.5Ag3.0Cu0.5 alloy solder ball or a Sn-Ag alloy lead-free solder ball (9). By adjusting the laser current and pulse width, a single pulse energy of 3~7mJ is output, and the solder ball (9) with a height of 15~40μm is prepared on the gold ball substrate (3).

4. The optoelectronic co-packaging bonding method according to claim 3, characterized in that, The total height of the micro-bumps (19) is 30~65μm, the diameter is 40~100μm, and the distance between adjacent micro-bumps (19) is ≤150μm; Furthermore, in step S103, when the diameter of the alloy tin ball is 60μm±5μm, a single pulse energy of 3~3.5mJ is output; when the diameter of the alloy tin ball is 80μm±5μm, a single pulse energy of 4.5~5mJ is output; and when the diameter of the alloy tin ball is 100μm±5μm, a single pulse energy of 6~7mJ is output.

5. The optoelectronic co-packaging bonding method according to claim 1, characterized in that, Step S300 includes: Step S301: Control the compressed nitrogen (11) to enter the protective cover (16). The compressed nitrogen (11) flows out through the nitrogen curtain outlet (32) on the protective cover (16) and forms a nitrogen curtain (14) around the optical chip (1). Step S302: Control the compressed nitrogen (11) to be injected into the formic acid solution (12) to form bubbles (13), generate a mixed gas of formic acid and nitrogen, control the mixed gas to be sprayed onto the surface of the micro-bumps (19) to pre-clean the surface of the micro-bumps (19), and control the by-products to be discharged through the waste spray pipe (21); Step S303: Control the heating base (20) to heat to 150~195℃, and control the pre-cleaning of the mixed gas to ≤10s.

6. The optoelectronic co-packaging bonding method according to any one of claims 1 to 5, characterized in that, Step S200 includes: Step S201: At room temperature, the optical chip (1) is transferred into the nitrogen sealing system, the packaging substrate (30) is placed on the heating base (20), and the heating base (20) is heated to 150℃±10℃; Step S202: Use a hot-press bonding head (17) to adsorb the optical chip (1) and align the microbump (19) with the pads of the packaging substrate (30); Step S203: Orient the optical waveguide (22) port in the optical chip (1) toward the formic acid vapor inlet (24) on the protective cover (16) so that the optical waveguide (22) port is away from the exhaust gas collection port (26) on the protective cover (16), control the protective cover (16) to descend, and form a closed micro-reaction cavity between the protective cover (16) and the heating base (20); the optical chip (1) and the packaging substrate (30) are both located in the closed micro-reaction cavity.

7. The optoelectronic co-packaging bonding method according to claim 6, characterized in that, Step S400 includes: Step S401: Using a vision alignment system in conjunction with a Z-axis displacement sensor, locate the contact position between the micro-bump (19) and the pad of the packaging substrate (30); Step S402: Based on the contact position, control the thermo-press bonding head (17) to continue pressing down the optical chip (1) by 5~10μm; Step S403: During the bonding process, the temperature of the hot-press bonding head (17) is controlled at 250~340℃, the temperature of the heating base (20) is controlled at 150℃±10℃, formic acid vapor (15) is continuously supplied, and the oxygen concentration in the system is maintained at ≤100ppm through the nitrogen curtain (14).

8. The optoelectronic co-packaging bonding method according to claim 6, characterized in that, After step S400, the method further includes: Step S500: Close the formic acid vapor (15), open the purging nitrogen inlet (23), control the compressed nitrogen (11) to purge through the purging nitrogen inlet (23) for 3~5s, until the hot-press bonding head (17) and the heating base (20) are cooled to below 80℃; after purging, temporarily close the nitrogen curtain inlet (31) to supply nitrogen, open the system pick-up and drop-out port to take out the bonding device, the bonding device including the bonded optical chip (1) and the packaging substrate (30).

9. An optoelectronic co-packaging bonding apparatus for performing the optoelectronic co-packaging bonding method as described in any one of claims 1 to 8, characterized in that, This includes a micro-bump (19) fabrication system and a nitrogen-sealed hot pressing system; The microbump (19) fabrication system includes a gold wire bonding machine, a soft pressing and flattening chip bonding machine and a laser ball bonding machine. The gold wire bonding machine is used to bond gold balls on the optical chip (1), the soft pressing and flattening chip bonding machine is used to extrude the gold balls, and the laser ball bonding machine is used to prepare solder balls (9) on the gold ball substrate (3). The nitrogen-sealed thermopressing system includes a thermopressing bonding head (17), a heating base (20), a vision alignment system, and a protective cover (16). The thermopressing bonding head (17) is used to press down the optical chip (1). The vision alignment system is used to locate the contact position between the microbump (19) and the pad of the packaging substrate (30). The protective cover (16) is used to guide the compressed nitrogen gas (11) and formic acid vapor (15) so that the compressed nitrogen gas (11) forms a nitrogen curtain (14) and the formic acid vapor (15) is directed towards the microbump (19) of the optical chip (1).

10. The optoelectronic co-packaging bonding device according to claim 9, characterized in that, The protective cover (16) includes a main body and a nozzle (28). The first side of the main body of the protective cover (16) is provided with a nitrogen curtain inlet (31), a nitrogen curtain outlet (32), a formic acid vapor inlet (24), and a purging nitrogen inlet (23). The nozzle (28) is installed on the second side of the main body of the protective cover (16), and the extension direction of the nozzle (28) and the cross-section of the nozzle (28) are both U-shaped. The top of the nozzle (28) is an open structure, and the top of the nozzle (28) is fitted to the second side of the main body of the protective cover (16) so that the nozzle (28) is connected to the formic acid vapor inlet (24) and the purging nitrogen inlet (23); the bottom of the nozzle (28) is provided with a vent array (29) for purging nitrogen and formic acid vapor (15) to flow out; The second side of the main body of the protective cover (16) is provided with a nozzle mounting groove (27). The formic acid vapor inlet (24) and the purging nitrogen inlet (23) are both connected to the nozzle mounting groove (27). The nozzle mounting groove (27) is also provided with a waste gas collection port (26) on the side away from the formic acid vapor inlet (24).

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