An ultralow temperature temperature sensor device and packaging method

Abstract

The application discloses an ultralow-temperature temperature sensor device and a packaging method, and relates to the technical field of semiconductor packaging, and comprises an adapter, a bare chip, an enameled copper wire and an aviation pin; the resistance surface of the bare chip is bonded to the adapter through epoxy resin; one end of the enameled copper wire is connected to the electrode of the bare chip, the other end is connected to the aviation pin, and after being wound and fixed on the surface of the adapter, an integrated heat sink is formed. The application solves the problems of large thermal hysteresis, easy failure of welding points and serious heat leakage of wires in traditional packaging, and significantly improves the temperature measurement accuracy, response speed and long-term stability of the ultralow-temperature temperature sensor.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging technology, and in particular to an ultra-low temperature sensor device and packaging method. Background Technology

[0002] In fields such as quantum computing, cryogenic superconductivity, deep space exploration, and fundamental physics research, sensors capable of precise temperature measurement in ultra-low temperature environments of 4.2 K, and even in the mK temperature range, play an irreplaceable and crucial role. Cryogenic sensors based on ruthenium oxide (RuO2) thick-film resistors have become one of the mainstream solutions in this temperature range due to their excellent resistance-temperature characteristics and stability.

[0003] The core temperature-sensing element of this type of sensor is a ruthenium oxide thick-film resistor die, which is made by screen printing ruthenium oxide resistive paste onto an alumina substrate and then sintering it at high temperature. This die cannot be directly used in ultra-low temperature environments, mainly because: firstly, direct exposure of the die makes it susceptible to interference from environmental heat exchange, leading to temperature measurement distortion; secondly, for ease of disassembly and maintenance, it needs to be encapsulated in an adapter.

[0004] The current mainstream packaging solution is to use gold-plated oxygen-free copper as the adapter. First, the bare die is bonded to the surface of the adapter with epoxy resin. Then, the bare die and the measurement leads are connected by manual indium soldering. Finally, the adapter is fixed to the cold plate under test by bolt connection.

[0005] However, the above-mentioned packaging solutions reveal inherent defects that severely limit sensor performance below 4.2 K, especially in the extremely low temperature range below 0.1 K.

[0006] First, the thermal hysteresis effect is significant: the thermal conductivity of the alumina substrate and the epoxy resin adhesive layer drops sharply at extremely low temperatures, forming a significant thermal resistance layer, which leads to a slow thermal response speed of the bare die. This is manifested as the resistance-temperature (RT) curves not coinciding during the heating and cooling processes, i.e., the thermal hysteresis phenomenon, which seriously affects the real-time performance and accuracy of temperature measurement.

[0007] Secondly, the electrical connection reliability is poor: the solder joints formed by manual indium soldering are usually large and uneven in size, which can easily cause short circuit risks; more importantly, the thermal mismatch between the solder and the material during repeated thermal cycling (from room temperature to extremely low temperature) can easily lead to solder joint fatigue, cracking or even detachment, causing the sensor to fail.

[0008] Furthermore, parasitic heat leakage introduces temperature measurement deviations: existing packaging structures often lack or fail to adequately treat the heat sinks of the leads. At extremely low temperatures, the minute heat leakage introduced along the leads can cause the actual temperature of the bare die to be higher than the temperature of the point being measured, resulting in a non-negligible systematic measurement error. Summary of the Invention

[0009] To address the aforementioned issues, this invention proposes an ultra-low temperature sensor device and packaging method, which solves problems such as large thermal hysteresis, easy solder joint failure, and severe heat leakage in wires in traditional packaging, significantly improving the temperature measurement accuracy, response speed, and long-term stability of the ultra-low temperature sensor.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an ultra-low temperature sensor device, comprising: an adapter, a bare die, an enameled copper wire, and an aviation pin; the resistive surface of the bare die is bonded to the adapter by epoxy resin; one end of the enameled copper wire is connected to the electrode of the bare die, and the other end is connected to the aviation pin, and after being wound and fixed on the surface of the adapter, it forms an integrated heat sink.

[0011] As an alternative implementation, the connection between the enameled copper wire and the electrode is formed by electronic spot welding technology to create an alloy weld point between the enameled copper wire and the electrode.

[0012] As an alternative implementation method, the electronic spot welding technology adopts a dual-pulse mode, with the following spot welding parameters: first pulse current 1000~1200 A, pulse width 3 ms; second pulse current 800~1000 A, pulse width 5 ms; electrode pressure 2 N.

[0013] As an alternative implementation, the diameter of the alloy solder joint is 150 μm.

[0014] As an alternative implementation, the adapter is made of oxygen-free copper and its surface is gold-plated with a thickness of 2~10 μm.

[0015] As an alternative implementation, the epoxy resin thickness is in the range of 5 to 15 μm.

[0016] As an alternative implementation, the epoxy resin coating and curing process includes: weighing the epoxy resin main agent and catalyst at a mass ratio of 100:3.5; placing the mixed epoxy resin in a vacuum degassing mixer and stirring and degassing at a speed of 800~1200 r / min and a vacuum degree of 100 Pa for 5~10 min until no visible bubbles are present in the mixture; taking the degassed epoxy resin and uniformly coating it on the resistive surface of the bare die; placing the bare die in the predetermined position of the adapter by applying a constant force and placing it in a vacuum drying oven for curing at 65°C for 2 hours.

[0017] As an alternative implementation, a heat sink is made by fixing enameled copper wires with varnish, and the thickness of the varnish coating on the adapter surface is less than 0.05 mm.

[0018] As an alternative implementation, the diameter of the aircraft insert is 0.4~0.8 mm.

[0019] Secondly, the present invention provides a packaging method for the above-mentioned ultra-low temperature sensor device, comprising: Clean the surface of the bare die and the adapter with acetone and isopropanol; With the resistive side of the bare die facing the adapter, use epoxy resin to attach the resistive side of the bare die to the surface of the adapter; Enameled copper wires are soldered to the surface of palladium-silver electrodes on bare wafers using an electronic spot welding machine; Wrap enameled copper wire around the adapter surface and secure it with varnish; Tin-lead soldering is used to solder enameled copper wire to aviation pins.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: Existing cryogenic sensor packaging technologies suffer from problems such as high thermal hysteresis, low connection reliability, and severe parasitic heat leakage, caused by epoxy resin bonding, manual indium soldering, and improper heat sink design. These issues have become key bottlenecks restricting the accuracy, stability, and reliability of ruthenium oxide thick-film resistor cryogenic sensors. Therefore, to achieve packaging with low thermal resistance, high reliability, and effective thermal management, this invention provides a cryogenic temperature sensor device and packaging method, including a copper adapter, a ruthenium oxide thick-film resistor die, enameled copper wire, solder joints, an epoxy resin layer, varnish, aviation pins, and a copper housing. The resistor surface of the die is bonded to the copper adapter through an ultra-thin epoxy resin layer to reduce interfacial thermal resistance. The solder joints are micro-alloyed solder joints formed by enameled copper wire and palladium-silver electrodes using electronic spot welding technology to improve connection reliability. The enameled copper wire is wound around the surface of the copper adapter and fixed with varnish to form an integrated heat sink to suppress parasitic heat leakage. The corresponding packaging method specifies in detail the key process steps such as precision epoxy resin coating and curing, electronic spot welding parameters, and heat sink fabrication. This invention effectively solves the problems of large thermal hysteresis, easy failure of solder joints and serious heat leakage of wires in traditional packaging, and significantly improves the temperature measurement accuracy, response speed and long-term stability of ultra-low temperature sensors.

[0021] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

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

[0023] Figure 1 This is an exploded structural diagram of the ultra-low temperature sensor device provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the assembly structure of the ultra-low temperature sensor device with a housing provided in Embodiment 1 of the present invention; Figure 3 A comparison of the temperature rise and fall (RT) curves of traditional packaged sensors in the 3.2 K-45 K temperature range; Figure 4 This is a comparison of the temperature rise and fall (RT) curves of the sensor packaged in Embodiment 1 of the present invention in the temperature range of 3.2 K-45 K; Figure 5 This is the RT curve of the sensor packaged in Embodiment 1 of the present invention in a wide temperature range of 10 mK-45 K; The components are: 1. Adapter; 2. Bare die; 3. Enameled copper wire; 4. Solder joint; 5. Epoxy resin; 6. Varnish; 7. Aviation pin; 8. Housing. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. Furthermore, it should be understood that the terms “comprising” and “including”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0027] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0028] Example 1 like Figure 1 and Figure 2 As shown, this embodiment provides an ultra-low temperature sensor device, including: a housing 8, an adapter 1, a bare die 2, an enameled copper wire 3, a solder joint 4, an epoxy resin 5, a varnish 6, and an aviation pin 7 disposed within the housing 8.

[0029] In this embodiment, the outer casing 8 is connected to the adapter 1 by threads to reduce the impact of thermal radiation on the performance of the bare die.

[0030] Both the adapter 1 and the housing 8 are made of high-purity oxygen-free copper (TUO) and the surface is gold-plated, with the gold plating thickness preferably being 2~10 μm.

[0031] Oxygen-free copper retains high thermal conductivity even at ultra-low temperatures, ensuring a high degree of temperature consistency between the bare die and the measured location. The main function of the gold plating layer is to prevent copper oxidation in air and ensure good thermal conductivity and surface uniformity at ultra-low temperatures. Furthermore, the gold plating layer has high reflectivity, effectively reducing the heating effect of thermal radiation on the sensor.

[0032] In this embodiment, the bottom surface of the adapter 1 is designed as a smooth plane with a through hole in the middle, which is used to tightly install it onto the cold plate to be tested by bolts, thereby fixing the ultra-low temperature sensor.

[0033] In this embodiment, the bare die 2 is a ruthenium oxide-based thick film resistor bare die, the electrode is a palladium-silver electrode, and the substrate is 96%~99% alumina ceramic. Both the ruthenium oxide resistor and the palladium-silver electrode are made by high-temperature sintering after screen printing.

[0034] The ruthenium oxide resistive paste comprises ruthenium-based oxide nanoparticles, borosilicate glass powder, and an organic carrier containing various organic solvents. The palladium-silver electrode is sintered from the palladium-silver paste.

[0035] In this embodiment, the resistive side (i.e. the side with the resistive pattern) of the bare die 2 is bonded to the adapter 1 with epoxy resin 5 to avoid the influence of the thermal resistance of the alumina substrate.

[0036] The palladium-silver electrode has a structure that surrounds the alumina substrate, extending from the front to the sides and back, which facilitates soldering.

[0037] Epoxy resin 5 is key to performance optimization. A low-thermal-stress, low-temperature-curing epoxy resin is selected. Through precise processing, its final thickness is controlled within the range of 5~15 μm, thereby minimizing interfacial thermal resistance while ensuring bond strength.

[0038] The thickness is controlled within the range of 5~15 μm based on two considerations: if it is too thick, it will increase the thermal resistance of the epoxy resin itself, increase thermal hysteresis, and easily lead to uneven epoxy resin layer, increasing the risk of deformation; if it is too thin, the insulation of the epoxy resin layer will be reduced, and it may even lead to short circuit, affecting the normal testing of the sensor.

[0039] In this embodiment, the process of precision coating and curing of epoxy resin includes: Weigh the epoxy resin main agent and catalyst precisely at a mass ratio of 100:3.5.

[0040] Place the mixed epoxy resin in a vacuum degassing mixer and stir at a speed of 800~1200 r / min and a vacuum of 100Pa for 5~10 min until no visible bubbles are present in the mixture.

[0041] Using a precision dispensing needle or scraper, take a small amount of degassed epoxy resin and coat it evenly onto the resistor surface of bare die 2.

[0042] Subsequently, a constant force is applied using a fixing clamp to place the bare die 2 in the predetermined position of the adapter 1. The entire assembly is then placed in a vacuum drying oven and cured at 65°C for 2 hours.

[0043] After curing, the thickness of epoxy resin 5 was measured to be 5~15 μm using a white light interferometer.

[0044] This precision process ensures the adhesive layer is ultra-thin and uniform.

[0045] In this embodiment, one end of the enameled copper wire 3 is connected to the electrode of the bare die 2, and the other end is connected to the aviation pin 7, which facilitates rapid insertion and removal testing. The conductor diameter of the enameled copper wire 3 is 0.1-0.3 mm, and it is coated with polyimide insulating varnish.

[0046] In this embodiment, solder point 4 is an alloy solder point formed by partially melting the enameled copper wire 3 and the palladium-silver electrode using an electronic spot welding machine. This solder point replaces the traditional manual indium solder point, which is prone to falling off, and has the advantages of high strength, low contact resistance, and good consistency.

[0047] The specific process is as follows: Using an electronic spot welding machine equipped with a micro-alignment system, first remove the insulating varnish about 2 mm from the end of the enameled copper wire 3 with a blade, and align the exposed copper wire end with the palladium-silver electrode of the bare die 2.

[0048] The spot welding parameters are set as follows: dual-pulse mode, first pulse current 1000~1200 A, pulse width 3 ms; second pulse current 800~1000 A, pulse width 5 ms; electrode pressure 2 N.

[0049] After the welding is triggered, a silver-copper alloy solder joint with a diameter of approximately 150 μm is formed.

[0050] These process parameters ensure sufficient fusion without damaging the fragile alumina substrate.

[0051] In this embodiment, after the solder joint 4 is fabricated, the enameled copper wire 3 is tightly wound 5-10 turns onto the cylindrical side of the adapter 1. Subsequently, a layer of GE Varnish varnish 6 is applied and cured, firmly fixing the wire to the surface of the adapter 1, forming a highly efficient wound heat sink. This structure utilizes the high thermal conductivity of copper to provide an excellent thermal anchor point for the wire.

[0052] In this embodiment, the aviation pin 7 has a diameter of 0.4~0.8 mm, is gold-plated, and is connected to the other end of the enameled copper wire 3 by soldering, and is fixed to the insulator of the housing 8 to realize the external electrical connection of the device.

[0053] The design of the aviation pin enables rapid connection and testing of sensors, while avoiding the inefficiency and unreliability problems caused by direct soldering of wires.

[0054] Based on the above-described structure of the cryogenic sensor device, a preferred packaging method for the cryogenic temperature sensor is described in detail, mainly including the following steps: Step S1: Surface cleaning and preparation.

[0055] Clean the adapter 1, housing 8, and bare chip 2 sequentially with acetone and isopropanol using ultrasonic cleaning for 10 minutes each, and then dry them with dry nitrogen gas for later use.

[0056] This step aims to remove organic contaminants and particles from the surface to ensure the quality of subsequent bonding and welding.

[0057] Step S2: Precision coating and curing of epoxy resin.

[0058] Weigh the epoxy resin main agent and catalyst precisely at a mass ratio of 100:3.5.

[0059] Place the mixed epoxy resin in a vacuum degassing mixer and stir at a speed of 800~1200 r / min and a vacuum of 100Pa for 5~10 min until no visible bubbles are present in the mixture.

[0060] Using a precision dispensing needle or scraper, take a small amount of degassed epoxy resin and coat it evenly onto the resistor surface of bare die 2.

[0061] Subsequently, a constant force is applied using a fixing clamp to place the bare die 2 in the predetermined position of the adapter 1. The entire assembly is then placed in a vacuum drying oven and cured at 65°C for 2 hours.

[0062] After curing, the thickness of the epoxy resin layer was measured to be 5~15 μm using a white light interferometer.

[0063] This precision process ensures the adhesive layer is ultra-thin and uniform.

[0064] Step S3: Electro-spot welding forms alloy weld points.

[0065] Using an electronic spot welding machine equipped with a micro-alignment system, first remove the insulating varnish about 2 mm from the end of the enameled copper wire 3 with a blade, and align the exposed copper wire end with the palladium-silver electrode of the bare die 2.

[0066] The spot welding parameters are set as follows: dual-pulse mode, first pulse current 1000~1200 A, pulse width 3 ms; second pulse current 800~1000 A, pulse width 5 ms; electrode pressure 2 N.

[0067] After the welding is triggered, a silver-copper alloy solder joint with a diameter of approximately 150 μm is formed.

[0068] These process parameters ensure sufficient fusion without damaging the fragile alumina substrate.

[0069] Step S4: Fabrication of the heat sink for the conductor.

[0070] Take the soldered enameled copper wire 3 and wrap it tightly and smoothly around the cylindrical surface reserved on the side of the adapter 1 for 5 to 10 turns.

[0071] Apply a small amount of GE Varnish 6 evenly to the wound line using a fine brush, and allow it to cure at room temperature for 24 hours to ensure it is firmly fixed.

[0072] This number of wrapping turns ensures sufficient thermally conductive contact area.

[0073] Step S5: External connection and final assembly.

[0074] Solder the other end of the enameled copper wire 3 to the aviation pin 7.

[0075] Finally, the housing 8 is connected to the adapter 1 with the bare die and wires via threads to complete the encapsulation of the entire device.

[0076] In this embodiment, the above-mentioned solution significantly reduces interface thermal resistance, effectively improves the thermal response of the bare die, and reduces thermal hysteresis by using a mounting method where the bare die resistor faces the adapter and a method of using epoxy resin. The use of micro-alloy solder joints formed by electronic spot welding to replace manual indium soldering greatly improves the long-term reliability of electrical connections. Through reasonable heat sink design, the temperature measurement deviation caused by parasitic heat leakage is significantly reduced. The key steps of the packaging method all have clearly defined process parameters, resulting in high process controllability and consistency.

[0077] To verify the effectiveness of this embodiment, the cryogenic sensor using the packaging method of this embodiment was tested at low temperature, and a sensor using the traditional method (resistive surface far from the adapter + manual indium soldering + conventional thick epoxy resin bonding + no wire winding) was used as a control.

[0078] Thermal hysteresis test: such as Figures 3-4 As shown, conventionally packaged sensors exhibit significant separation in their temperature rise and fall curves within the 3.2K-45K temperature range, indicating substantial thermal hysteresis. In contrast, the sensor packaged using this embodiment shows almost complete overlap in its temperature rise and fall curves, demonstrating the significant effect of the ultra-thin epoxy layer and optimized structure on improving thermal response.

[0079] Reliability and ultra-low temperature performance testing: The sensor in this embodiment was subjected to 200 liquid nitrogen thermal shocks, followed by testing in a dilution refrigerator. For example... Figure 5 As shown, the RT curve is smooth, continuous, and without jumps throughout the entire process from 45 K to 10 mK, indicating that the solder joint connection is extremely reliable. Especially in the extremely low temperature range below 0.1 K, the resistance value still increases monotonically and steadily with decreasing temperature, without curve distortion or sensitivity reduction caused by heat leakage from the wires, which fully proves the effectiveness of the wound heat sink structure.

[0080] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A cryogenic temperature sensor device, characterized in that, include: Adapters, bare chips, enameled copper wires, and aviation pins; The resistive surface of the bare die is bonded to the adapter via epoxy resin. The epoxy resin thickness is in the range of 5~15 μm; The epoxy resin coating and curing process includes: weighing the epoxy resin main agent and catalyst at a mass ratio of 100:3.5; placing the mixed epoxy resin in a vacuum degassing mixer and stirring at a speed of 800~1200 r / min and a vacuum degree of 100 Pa for 5~10 min until no visible bubbles are visible in the mixture; taking the degassed epoxy resin and uniformly coating it on the resistive surface of the bare die; placing the bare die in the predetermined position of the adapter by applying a constant force and placing it in a vacuum drying oven for curing at 65 ℃ for 2 hours; One end of the enameled copper wire is connected to the palladium-silver electrode of the bare die, and the other end is connected to the aviation pin. After being wound and fixed on the surface of the adapter, it forms an integrated heat sink. The palladium-silver electrode has a structure that surrounds the alumina substrate, extending from the front to the sides and back, which facilitates soldering. The connection between the enameled copper wire and the electrode is formed by electronic spot welding technology to create an alloy weld point between the enameled copper wire and the electrode. The electronic spot welding technology adopts a dual-pulse mode. The spot welding parameters are: first pulse current 1000~1200 A, pulse width 3 ms; second pulse current 800~1000 A, pulse width 5 ms; electrode pressure 2 N.

2. The ultra-low temperature sensor device as described in claim 1, characterized in that, The diameter of the alloy weld is 150μm.

3. The ultra-low temperature sensor device as described in claim 1, characterized in that, The adapter is made of oxygen-free copper and its surface is gold-plated with a thickness of 2~10 μm.

4. The ultra-low temperature sensor device as described in claim 1, characterized in that, The heat sink is made by fixing the enameled copper wire with varnish, and the thickness of the varnish coating on the adapter surface is less than 0.05 mm.

5. The ultra-low temperature sensor device as described in claim 1, characterized in that, The diameter of the aviation pin is 0.4~0.8 mm.

6. A packaging method for an ultra-low temperature sensor device, employing an ultra-low temperature sensor device as described in any one of claims 1-5, characterized in that, include: Clean the surface of the bare die and the adapter with acetone and isopropanol; With the resistive side of the bare die facing the adapter, use epoxy resin to attach the resistive side of the bare die to the surface of the adapter; Enameled copper wires are soldered to the surface of palladium-silver electrodes on bare wafers using an electronic spot welding machine; Wrap enameled copper wire around the adapter surface and secure it with varnish; Tin-lead soldering is used to solder enameled copper wire to aviation pins.

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