Leadless Package Structure and Method for a High-Temperature Sensor

Abstract

The present invention discloses a leadless packaging structure and method for a high-temperature sensor. The leadless packaging structure includes a sensor chip, a sensor housing for supporting the sensor chip, and metal pins disposed on the sensor housing. The metal pins are connected to the metal electrodes of the sensor chip through a high-temperature conductive layer, and the metal electrodes are externally disposed on the surface of the sensor housing or internally disposed in the sensor housing. On the one hand, the present invention solves the problem that the reliability of the conventional metal lead bonding packaging technology degenerates or even fails in a high-temperature environment. On the other hand, it simplifies the packaging lead method, has simple operation, high yield, high reliability in actual use, is suitable for mass production, has low cost, and has a very high cost performance. At the same time, the present invention improves the working stability and long-term reliability of the sensor in a high-temperature environment by selecting and simplifying the packaging materials, and the sensor chip has the advantage of good dynamic response characteristics by adopting a flush packaging.

Description

Technical Field

[0001] The present invention relates to a high-temperature resistant sensor, and particularly to a leadless packaging structure and method for the sensor. Background Art

[0002] High-temperature resistant sensors have very important applications in many industries and fields. For example, high-temperature resistant pressure and vibration sensors for detecting high-temperature pressure and vibration inside aeroengines, high-temperature resistant pressure sensors for measuring the pressure of the primary loop of a high-temperature reactor in a nuclear power plant, and high-temperature pressure and vibration sensors for monitoring the operation safety of high-temperature industrial reaction kettles and smelting towers.

[0003] The key issues for high-temperature resistant sensors to work properly in a high-temperature environment are as follows: (1) the sensor chip itself can work properly in a high-temperature environment, and (2) the sensor packaging structure can play the roles of support, electrical connection, sealing, etc. properly in a high-temperature environment. With the progress of technology, sensor chip materials that can work properly at high temperatures have been continuously discovered, effectively solving the first key problem faced by high-temperature resistant sensors. However, the sensor packaging structure often involves the combination and fixation of multiple materials, which are very likely to cause problems such as inconsistent thermal expansion of heterogeneous materials, high-temperature oxidation of materials, and softening and falling off between connectors at high temperatures, resulting in the failure of the sensor chip support structure, electrical connection short circuit or open circuit, and even the rupture of the sensor chip, causing the deterioration or even permanent failure of the sensor performance.

[0004] The most important part in sensor packaging is to form an effective electrical connection between the electrodes of the sensor chip and the electrodes on the packaging structure, so that the signals measured by the sensor chip can be transmitted smoothly. The currently commonly used packaging method is to use metal wire bonding for connection. For example, Chinese Patent CN105236343A discloses a dielectric isolation type pressure sensor packaging structure, in which a pressure sensor packaging module with an MEMS chip is connected to a wire through wire bonding. This connection method has a simple structure and convenient operation, but when used in a high-temperature environment, the bonding points between the wire and the sensor packaging module, and between the wire and the wire are likely to fall off due to softening at high temperatures, posing a risk of failure.

[0005] In view of the problems existing in metal wire bonding, Chinese Patent CN102928150A discloses a leadless packaged metal thin film pressure sensor. In this sensor, the sensor chip and the glass seal cover are connected together by bonding. Through the through holes corresponding to the lead pads of the sensor chip on the glass seal cover, the conductive metal material filled in the through holes, and the conductive metal pins inserted into the through holes filled with the conductive metal material, and through vacuum annealing, a leadless packaged metal thin film pressure sensor is obtained. The packaging method adopted in this patent effectively solves the problem that the metal wire bonding type packaging is not resistant to high temperature. However, there are two problems in actual operation: (1) Due to the small size of the MEMS chip, the sizes of the lead pads and the corresponding through holes are very small (in the micron range). The micropore effect makes it actually very difficult for the conductive metal material to effectively fill the entire through hole, resulting in air bubbles and holes inside the through hole filled with the conductive metal material, making it impossible for the lead pads, the conductive metal material, and the conductive metal pins to make full contact, or even no contact at all; (2) Although the purpose of annealing is to sinter the conductive metal material so that the lead pads, the conductive metal material, and the conductive metal pins can be solidly connected and form a good electrical connection, during the actual sintering process, the conductive metal material will undergo thermal deformation and volatilize air bubbles, which will inevitably cause the volume of the conductive metal material to shrink and there to be air bubbles inside after annealing. Even due to the inconsistent thermal expansion coefficients of different materials, an open circuit may occur among the lead pads, the conductive metal material, and the conductive metal pins. Due to the above two problems, the success rate of the actually obtained packaging structure is not high.

[0006] Chinese Patent CN109781334A discloses a leadless packaging structure for a piezoresistive sensor. The conductive paste (composed of components such as silver, glass, organic binder, and solvent) in this patent has the problem of generating thermal stress after sintering and curing. In order to enable the sintered and cured conductive paste to stably play the role of a connecting structure, it further uses noble metal gold as a transition layer to utilize the good ductility of gold to reduce thermal stress. However, the transition layer cannot solve the problems of thermal deformation and volatilization of air bubbles of the conductive paste itself during actual sintering and curing. In addition, the size of the through hole into which the valve pin penetrates still needs to be limited within a small range, so the reliability of the connecting structure will still be affected by the micropore effect. At the same time, this patent also uses a glass paste based on the PbO-ZnO-B 2 O 3 system to form another transition layer. The softening point of this glass system can be adjusted according to the lead content, and low expansion coefficient and negative expansion materials such as PbTiO 2 O 3 can be added on the basis of PbO-ZnO-B 3, Cordierite, spodumene, spodumene, fused silica, etc. constitute a composite glass paste, which is used to adjust the coefficient of thermal expansion and improve chemical stability and mechanical strength. However, due to the high viscosity of the paste, the application method and scope are limited. Summary of the Invention

[0007] In order to solve the technical problems existing in the existing high-temperature resistant sensor packaging structure, the present invention provides a leadless packaging structure and method for a high-temperature resistant sensor.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A leadless packaging structure for a high-temperature resistant sensor, the leadless packaging structure includes a sensor chip, a sensor housing for supporting the sensor chip, and metal pins provided on the sensor housing, the metal pins are connected to the metal electrodes of the sensor chip through a high-temperature resistant conductive layer, and the metal electrodes are externally disposed on the surface of the sensor housing or internally disposed in the sensor housing.

[0010] Preferably, the sensor housing includes a base body and a chip packaging groove provided on the base body, the sensor chip is connected to the sensor housing through a sealing layer provided at the bottom of the chip packaging groove, and the sensor chip is flush with the surface of the sensor housing.

[0011] Preferably, the sealing layer is formed by curing a high-temperature resistant adhesive applied to the bottom of the chip packaging groove.

[0012] Preferably, the components of the high-temperature resistant adhesive include a glass paste of the PbO-ZnO-B 2 O 3 system, and the coefficient of thermal expansion of the sealing layer is between the coefficient of thermal expansion of the sensor housing and the coefficient of thermal expansion of the sensor chip.

[0013] Preferably, the sensor housing further includes a cavity provided on the base body, and the cavity is connected to the bottom of the chip packaging groove.

[0014] Preferably, the sensor housing further includes a through hole provided on the base body, and a conductive sealing block is provided in the through hole, and the conductive sealing block fills the part of the metal pin located in the through hole and the inner wall of the through hole.

[0015] Preferably, the conductive sealing block is formed by curing a conductive glass paste injected into the internal space of the sensor housing along the through hole to bond the part of the metal pin located in the through hole (bonding this part to the sensor housing).

[0016] Preferably, the components of the conductive glass paste include PbO-ZnO-B 2 O 3Glass paste and nano conductive materials of the system.

[0017] Preferably, the substrate is columnar, the chip packaging groove is opened on one end face of the substrate, one end of the through hole is located on the other end face of the substrate, and the other end of the through hole extends to the end face of the substrate with the chip packaging groove opened.

[0018] Preferably, the through hole of the sensor housing is connected to the bottom of the chip packaging slot, and the high temperature resistant conductive layer is arranged in a stacked manner between the metal pin and the metal electrode of the sensor chip (that is, the metal electrode is built-in); or, the through hole of the sensor housing is arranged on the end face of the substrate so as to be located outside the chip packaging slot, and the high temperature resistant conductive layer is arranged in a direct writing manner between the metal pin and the metal electrode of the sensor chip (that is, the metal electrode is external).

[0019] Preferably, the high temperature resistant conductive layer is made of a modified slurry containing an adhesive, a high temperature antioxidant and a nano-conductive material (i.e., the adhesive is modified using a high temperature antioxidant and a nano-conductive material) and is coated and cured, or the high temperature resistant conductive layer is made of a modified slurry containing an adhesive, a high temperature antioxidant, a toughening agent and a nano-conductive material (i.e., the adhesive is modified using a high temperature antioxidant, a toughening agent and a nano-conductive material) and is coated and cured.

[0020] Preferably, the adhesive comprises PbO-ZnO-B 2 O 3 The glass paste of the system, that is, the adhesive, can adopt the above-mentioned high temperature resistant adhesive.

[0021] Preferably, the sensor housing further comprises an annular groove arranged on a side surface of the base body.

[0022] A leadless packaging method for a high temperature resistant sensor comprises the following steps:

[0023] 1) Processing chip packaging grooves and through holes on the substrate to obtain a sensor housing;

[0024] 2) bonding the metal pins and the sensor chip to the sensor housing through the through holes and the chip packaging grooves respectively, and then curing them. During the curing, a pre-placed slurry (such as the modified slurry described above) across both sides of the interface between the sensor housing and the sensor chip is used to form a high-temperature conductive layer that covers the metal pins and the metal electrodes of the sensor chip at the same time, thereby obtaining a high-temperature sensor leadless packaging structure with an external metal electrode;

[0025] Alternatively, bond the metal pins to the sensor housing through through-holes, and place the paste for forming the high-temperature resistant conductive layer (for example, the same paste as the above-mentioned pre-set paste) into the chip encapsulation groove before bonding the sensor chip to the sensor housing through the chip encapsulation groove, so as to make the metal pins and the metal electrodes of the sensor chip dock with the high-temperature resistant conductive layer through curing, and obtain a leadless encapsulation structure of a high-temperature resistant sensor with built-in metal electrodes.

[0026] Preferably, step 1) further includes the following steps: process a cavity on the substrate that is connected to the bottom of the chip encapsulation groove.

[0027] Preferably, in step 2), inject the above-mentioned conductive glass paste into the through-holes, and fill the gap between the part of the metal pin located in the through-hole and the inner wall of the through-hole with the conductive glass paste, so as to bond the metal pin to the sensor housing.

[0028] Preferably, in step 2), apply the above-mentioned high-temperature resistant adhesive to a certain area at the bottom of the chip encapsulation groove (when the end face of the through-hole is located at the bottom of the chip encapsulation groove, since a high-temperature resistant conductive layer needs to be formed in the areas where these end faces are located, the high-temperature resistant adhesive is applied to the bottom surface of the chip encapsulation groove except for these areas; when the end face of the through-hole is located outside the chip encapsulation groove, then the bottom surface of the chip encapsulation groove is fully coated; the connection part between the cavity and the bottom of the chip encapsulation groove cannot be coated), place the sensor chip into the chip encapsulation groove, and make it contact with the applied high-temperature resistant adhesive until the surface of the sensor chip is flush with the surface of the sensor housing, so as to bond the sensor chip to the sensor housing.

[0029] The beneficial effects of the present invention are as follows:

[0030] In the high-temperature resistant sensor encapsulation structure proposed by the present invention, leadless encapsulation is realized by introducing a conductive layer that meets the temperature grade requirements of sensor applications, improving the reliability of the electrical connection between the metal pins and the metal electrodes of the sensor chip in the encapsulation structure, and helping to fundamentally solve the deficiencies in thermal stability of the existing encapsulation structure; at the same time, the encapsulation method of the sensor chip is flexible, the process difficulty of the encapsulation method is low, and the yield is high.

[0031] Furthermore, in the present invention, the sensor chip and the sensor housing are flush-mounted. For a pressure sensor, the sensor chip is directly in contact with the measured high-temperature medium, avoiding the attenuation effect of the pipe cavity effect on the dynamic performance of the sensor, eliminating the response time lag and frequency distortion problems caused by the pipe cavity effect, and enabling the sensor to have a faster response speed and a higher resonance frequency.

[0032] Furthermore, in the present invention, the types of packaging materials directly connected to the sensor chip are few (only involving a few materials such as the sensor housing material and the cured high-temperature resistant adhesive, etc., which have the same glass paste composition), making it easy to match the thermal expansion coefficients of the packaging material and the sensor chip material (making the thermal expansion coefficients of the two very close), reducing the possibility of thermal stress mismatch between heterogeneous materials; at the same time, the packaging can be completed through one-time curing, simplifying the process steps.

[0033] Furthermore, the high-temperature resistant adhesive used in the present invention has a thermal expansion coefficient after curing that is between the thermal expansion coefficients of the existing sensor housing and the sensor chip, which can effectively relieve the internal thermal expansion stress between the sensor housing and the sensor chip, improving the high-temperature stability and thermal stress resistance of the sensor chip.

[0034] Furthermore, in the present invention, the cavity (such as a channel structure, etc.) at the bottom of the chip packaging groove and the through hole for bonding the metal pins are used as stress release structures for the thermal expansion of the sensor housing, reducing the internal stress caused by the thermal expansion difference between the sensor housing and the sensor chip.

[0035] Furthermore, the through hole arrangement method adopted in the present invention (especially when the end face of the through hole is outside the chip packaging groove) helps to increase the through hole diameter, so that a more reliable fixation of the metal pins can be achieved using a packaging material based on a more viscous glass paste (such as a cured conductive glass paste). Description of the Drawings

[0036] Figure 1 Schematic diagrams of the overall high-temperature resistant sensor packaging structure (a) and its longitudinal sectional structure (b) in Embodiment 1;

[0037] Figure 2 Schematic diagrams of the sensor housing (a) and its longitudinal sectional structure (b) in Embodiment 1;

[0038] Figure 3 Schematic diagram of the metal pins in Embodiment 1;

[0039] Figure 4-1 Schematic diagrams of the sensor chip (a) and its longitudinal sectional structure (b) in Embodiment 1;

[0040] Figure 4-2 Schematic diagram of the shape and size matching of the cured high-temperature resistant adhesive (a) and the back of the sensor chip (b) in Embodiment 1;

[0041] Figure 5 Schematic diagrams of the overall high-temperature resistant sensor packaging structure (a) and the sensor housing (b) in Embodiment 2;

[0042] Figure 6Schematic diagram of the metal pin, conductive glass paste (a) and direct-write conductive silver paste (b) packaging structure in Example 2;

[0043] Figure 7 Schematic diagram of the high-temperature resistant adhesive (a) and sensor chip (b) packaging structure in Example 2;

[0044] Figure 8 Schematic diagram of the state of the conductive glass paste injected into the circular channel (the dark area is the cured packaging structure of the conductive glass paste, i.e., the conductive sealing block); where: (a) Example 1, (b) Example 2;

[0045] In the figure: 1 - sensor housing; 2 - metal pin; 3 - conductive sealing block; 4 - conductive layer; 5 - sensor chip; 6 - sealing layer; 101 - through hole; 102 - chip packaging groove; 103 - cavity; 104 - annular groove; 501 - metal electrode; 502 - concave cavity; 503 - metal wire; 504 - semiconductor sensitive resistor. Detailed implementation manners

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments are only used to explain the present invention, rather than limiting the protection scope of the present invention.

[0047] Aiming at the problems existing in the pouring and sintering of conductive metal materials into fine packaging through holes in the existing leadless packaging (especially for the packaging of high-temperature resistant sensors above 600 °C), such as high operation difficulty and low yield (due to the air resistance and channel effect inside the micropores, it is difficult for the conductive metal material to fill the packaging through holes, and holes are easily generated inside during the curing process of the conductive metal material, ultimately resulting in poor electrical connection between the metal pins and the lead pads on the sensor chip); the present invention proposes a leadless packaging structure for high-temperature resistant sensors. In the packaging of high-temperature resistant sensors, on the one hand, the electrical connection packaging between the metal pins and the metal electrodes of the sensor chip is carried out by means of direct writing of conductive silver paste, etc., and on the other hand, the sensor chip and the sensor housing are flush-mounted through a high-temperature resistant adhesive, thereby improving the packaging success rate of high-temperature resistant sensors, and the packaging structure is stable and reliable, and the packaging process is simple to operate, having strong industrial application value.

[0048] Example 1

[0049] As Figure 1As shown in the figure, the overall encapsulation structure of the high-temperature resistant sensor includes a sensor housing 1, metal pins 2, and a sensor chip 5. A part of the metal pins 2 is fixed inside the sensor housing 1 through a conductive sealing block 3 formed by cured conductive glass paste, and the sensor chip 5 is fixed on the upper end surface of the sensor housing 1 in an embedded manner through a sealing layer 6 formed by cured high-temperature resistant adhesive; among them, the front side of the sensor chip 5 faces upward, and the upper ends of the metal pins 2, the cured conductive glass paste, and the front side of the sensor chip 5 are all flush with the upper end surface of the sensor housing 1. The lower ends of the metal pins 2 extend out of the lower end surface of the sensor housing 1, and the back side of the sensor chip 5 faces a channel or inner cavity structure located inside the sensor housing 1. At the intersection position between the upper end surface of the sensor housing 1 and the front side of the sensor chip 5 and the corresponding areas on both sides, there is a high-temperature resistant conductive layer 4 formed by curing direct-write conductive silver paste and distributed continuously in a strip shape. The circuit structure on the front side of the sensor chip 5, the upper ends of the metal pins 2, and the cured conductive glass paste are connected through the high-temperature resistant conductive layer 4.

[0050] As Figure 2 shown, the sensor housing 1 is processed from a cylindrical base body, and specifically, a circular through-hole 101, a chip packaging groove 102, a cavity channel 103 at the bottom of the chip packaging groove, and an annular groove 104 are processed on the base body.

[0051] The chip packaging groove 102 is located in the middle of the upper end surface of the sensor housing 1 and is mainly used to place the sensor chip 5. The length and width dimensions ( Figure 2 in Figure a, the chip packaging groove 102 is rectangular) or the diameter dimension of the chip packaging groove 102 matches that of the sensor chip 5, so that the edge of the sensor chip 5 can be in close contact with the side wall of the chip packaging groove 102 after being installed. The depth of the chip packaging groove 102 is slightly greater than the thickness of the sensor chip 5, so as to reserve space for applying a certain thickness of high-temperature resistant adhesive at the bottom of the chip packaging groove 102 and make the front side of the sensor chip 5 flush with the upper end surface of the sensor housing 1.

[0052] The cavity channel 103 is located below the bottom of the chip packaging groove 102 and is connected to the chip packaging groove 102. The main functions of the cavity channel 103 are: (1) As a stress release structure for the thermal expansion of the sensor housing 1, reducing the thermal stress transmitted to the sensor chip 5. (2) For a pressure sensor, if the cavity channel 103 directly penetrates to the lower end surface of the sensor housing 1 and is connected to the outside (as Figure 2 shown in Figure b, that is, a channel structure is adopted), then the corresponding pressure sensor can be used as a gauge pressure sensor. If the cavity channel 103 does not penetrate the lower end surface of the sensor housing 1 (that is, an inner cavity structure is adopted), then the corresponding pressure sensor can be used as an absolute pressure sensor through vacuum packaging.

[0053] The circular through-hole 101 completely penetrates the upper and lower end faces of the sensor housing 1, and this through-hole is mainly used to install the metal pins 2 of the sensor; the number and relative positions of the circular through-holes 101 in the sensor housing 1 are generally determined according to the circuit structure on the front side of the sensor chip 5. For example Figure 2 In Figure a, five circular through-holes 101 are arranged at intervals in two rows, and the arrangement positions of the circular through-holes 101 on the end face of the sensor housing 1 are all located outside the chip encapsulation groove 102.

[0054] The functions of the annular groove 104 include: (1) placing an annular sealing ring so that after the sensor is installed in the pipeline to be tested, a good sealing effect is formed between the sensor and the inner wall of the pipeline, ensuring the detection accuracy; (2) fixing the sensor as a positioning card slot.

[0055] The upper and lower end faces of the sensor housing 1 have no sharp corners (for example, by machining rounded corners at the edges of the upper and lower end faces of the base). On the one hand, it avoids sharp right angles from scratching people or other objects. On the other hand, when the pressure sensor is used in some pipes and cavities, the cylindrical structure with rounded corners is conducive to the flow and outward diffusion of air flow and liquid flow, and will not generate vortices due to the existence of sharp right angles, affecting the actual measurement accuracy.

[0056] It should be noted that when selecting the materials of the sensor housing 1 and the sensor chip 5, materials with the same or similar thermal expansion coefficients should be selected, so as to achieve thermal expansion matching in a high-temperature environment, ensure small internal thermal stress of the sensor and good high-temperature stability of the sensor. For example, the sensor housing 1 is made of the insulating material AlN with a thermal expansion coefficient of 4.1×10 -6 / °C, and the sensor chip 5 is made of SiC with a thermal expansion coefficient of 3.7×10 -6 / °C for manufacturing MEMS chips.

[0057] As Figure 3 shown, the metal pins 2 are generally cylindrical slender bar structures (so they are also called metal needles), and their specific numbers and relative positions are the same as the numbers and relative positions of the circular through-holes 101 in the sensor housing 1. That is, one metal pin 2 is installed and fixed in one circular through-hole 101 by using a conductive sealing block 3 formed by curing conductive glass paste.

[0058] As Figure 4-1 and Figure 4-2 shown, the sensor chip 5 is a MEMS miniaturized chip processed by micro-nano manufacturing technology. For example, for Figure 4-1The shown sensor chip 5 has 5 metal electrodes 501 in the circuit structure on its front side. One end of the metal wire 503 is tightly connected to the metal electrode 501, and the other end is tightly connected to the semiconductor sensitive resistor 504. If the sensor chip 5 is a pressure sensor chip, then a concave cavity 502 should also be processed on the back side of the chip. The shape of the concave cavity 502 can be rectangular (including square), circular ( Figure 4-2 b) or other shapes. The size of the concave cavity 502 and its relative position to the semiconductor sensitive resistor 504 should satisfy the layout rules of the sensitive film and sensitive resistor of the pressure sensor. If the sensor chip 5 is a vibration sensor chip, then a mass block and a cantilever beam structure should be processed on the back side of the chip accordingly. The number and position of the metal electrodes 501 and semiconductor sensitive resistors 504 on the front side of the sensor chip 5 can be changed according to actual needs. According to the number and position of the metal electrodes 501 on the front side of the sensor chip 5, the number and position of the circular through holes 101 located outside the sensor chip 5 can be determined. Additionally, when the back side of the sensor chip 5 has a concave cavity 502, the cavity 103 located below the bottom of the chip encapsulation groove 102 is opposite to the back side of the sensor chip 5, and through matching, the upper end opening of the cavity 103 is aligned with the opening of the concave cavity 502. In this way, by adjusting the opening shapes and sizes to be consistent, the chip encapsulation groove 102 can stably support the area on the back side of the sensor chip 5 except for the area corresponding to the concave cavity 502, improve the reliability of the sensor encapsulation structure, and ensure that only the area corresponding to the concave cavity 502 on the sensor chip 5 is movable while other areas are fixed, enabling the sensor chip 5 to perform measurements according to the pre-set theoretical state and ensuring the measurement accuracy.

[0059] The high-temperature resistant adhesive is a high-temperature adhesive with good electrical insulation performance at high temperatures. The high-temperature resistant adhesive is a glass paste mainly based on the PbO-ZnO-B 2 O 3 system. In addition to the components constituting the PbO-ZnO-B 2 O 3 system, lead titanate (PbTiO 3 ), cordierite, spodumene, petalite, and quartz glass (SiO 2 ) can also be mixed as components.

[0060] The formula of the glass paste (i.e., the high-temperature resistant adhesive) mainly based on the PbO-ZnO-B 2 O 3 system is as follows (by mass fraction):

[0061] ① PbO: 73% - 77%

[0062] ② B 2 O 3 : 7% - 13%

[0063] ③ZnO: 8% - 13%

[0064] ④PbTiO 3 、 cordierite, spodumene, spodumene, fused silica: 0 - 5%.

[0065] The high-temperature resistant adhesive needs to be sintered for high-temperature curing to form the sealing layer 6. The specific usage instructions are as follows:

[0066] 1) Apply the high-temperature resistant adhesive to the bottom of the chip packaging groove 102; in addition to controlling the coating thickness, it should also be noted that when applying the high-temperature resistant adhesive, it is necessary to form a complete sealing ring between the back of the sensor chip and the bottom of the chip packaging groove, and it should not enter the concave cavity 502 inside the back of the sensor chip 5 to avoid affecting the movable structures (such as sensitive films, mass blocks, etc.) inside the sensor chip 5. That is to say, the shape and size of the high-temperature resistant adhesive applied to the bottom of the chip packaging groove 102 should match the shape and size of the back of the sensor chip 5.

[0067] 2) Curing

[0068] Heat up from room temperature to 270°C at a rate of 2°C per minute and hold for 25 minutes; then uniformly increase the temperature to 550°C within 135 minutes and hold for 5 minutes; then uniformly decrease the temperature to 540°C within 10 minutes and hold for 20 minutes; then decrease from 540°C to 495°C within 20 minutes and hold for 20 minutes; then decrease from 495°C to 455°C within 20 minutes and hold for 20 minutes; then cool down to room temperature at a rate of 2°C per minute.

[0069] Sintering the applied high-temperature resistant adhesive using the above procedure can achieve a sealing layer 6 obtained by sintering without quality defects such as voids and cracks, ensuring the sintering strength and density.

[0070] After the high-temperature resistant adhesive is cured, its coefficient of thermal expansion is between the coefficients of thermal expansion of the sensor housing 1 and the sensor chip 5 (i.e., between 3.7×10 -6 / °C and 4.1×10 -6 / °C), and the coefficients of thermal expansion of the three are very close. Thus, it can not only firmly fix the back of the sensor chip 5 in the chip packaging groove 102 of the sensor housing 1, achieving an adhesive and sealing effect; but also serve as a thermal expansion transition layer to relieve the thermal expansion internal stress between the sensor housing 1 and the sensor chip 5, improving the high-temperature stability and thermal stress resistance of the sensor chip.

[0071] The conductive glass paste is a high-temperature resistant conductive paste obtained by formulation, that is, the conductive glass paste is formed by further mixing nano-conductive silver powder on the basis of the components contained in the above-mentioned high-temperature resistant adhesive. The mass fraction of the mixed nano-conductive silver powder can be optimized according to the actual conductivity of the conductive glass paste after curing.

[0072] The specific usage instructions of the conductive glass paste are as follows:

[0073] 1) Filling

[0074] Inject the conductive glass paste into the circular through-hole of the sensor housing using a syringe, and fill the gap between the part of the metal pin placed in the through-hole and the inner wall of the through-hole.

[0075] 2) High-temperature curing

[0076] The sintering procedure refers to the above-mentioned high-temperature resistant adhesive.

[0077] The main characteristics of the conductive glass paste after curing (i.e., the conductive sealing block 3) are as follows: (1) It has the characteristic of high-temperature resistance, with good stability and not easy to deform during long-term use in a high-temperature environment; (2) It has conductivity, and the resistance value is low, and the degree of change of the resistance value with temperature is small; (3) The coefficient of thermal expansion is between 3.7×10 -6 / °C and 4.1×10 -6 / °C, which is compatible with the sensor housing and chip materials; (4) It has strong adhesiveness and good adhesion, and can firmly fix the metal pin in the circular through-hole of the sensor housing.

[0078] The direct-write conductive silver paste is a multi-component mixed paste composed of the above-mentioned high-temperature resistant adhesive and modifiers (including not only nano-conductive silver powder, but also toughening agents such as micro-nano metal fibers and high-temperature antioxidants such as iron oxide powder). The direct-write conductive silver paste is used to form a physical connection between the metal electrode 501 on the front of the sensor chip 5 and the upper end of the corresponding metal pin 2 (flush with the upper end surface of the sensor housing 1) by 3D printing or spraying, and then the direct-write conductive silver paste forming the physical connection is subjected to high-temperature curing (the sintering procedure refers to the above-mentioned high-temperature resistant adhesive), so as to form a functionalized structure layer tightly adhering to the plane jointly composed of the upper end of the metal pin 2, the corresponding metal electrode 501, the upper end surface of the sensor housing 1 located therebetween, the conductive glass paste (the upper end of the conductive sealing block 3) cured around the metal pin 2 and the corresponding area on the front of the sensor chip 5. This functionalized structure layer has the characteristics of high-temperature resistance and low-resistance conductivity (so it is also called the high-temperature resistant conductive layer 4), and has a coefficient of thermal expansion similar to that of the sensor housing and chip materials (i.e., between 3.7×10 -6 / °C and 4.1×10 -6(between / ℃), while avoiding the problem of oxidation failure occurring at high temperatures (the conductivity disappears due to surface oxidation), and avoiding the problem of fracture occurring at the junction between the sensor housing and the sensor chip, so that a stable electrical connection can be formed between the metal pin 2 and the metal electrode 501 on the front surface of the sensor chip 5.

[0079] In the high-temperature working environment of the sensor, the high-temperature conductive layer 4 formed by curing the direct-write conductive silver paste has good electrical conductivity, toughness and high-temperature oxidation resistance, providing a stable and reliable electrical connection between the sensor chip 5 and the external circuit connected to the metal pin 2. At the same time, the conductive sealing block 3 formed after curing the conductive glass paste used in the present invention has an additional function, which is to ensure a reliable electrical connection between the metal electrode 501 on the front surface of the sensor chip 5 and the metal pin 2. Although the metal pin 2 and the metal electrode 501 of the sensor chip 5 are indirectly connected through the cured direct-write conductive silver paste, even if there is an open circuit between the cured direct-write conductive silver paste and the metal pin 2, it will not affect the electrical connection reliability of the sensor, because the glass paste used to bond the metal pin 2 in the circular through-hole is conductive after curing, and the electrical signal can be transmitted to the cured conductive glass paste through the cured direct-write conductive silver paste, and then transmitted to the metal pin 2.

[0080] The overall packaging structure of the high-temperature sensor in this embodiment can be obtained by the following packaging process flow:

[0081] 1) Process the sensor housing

[0082] On the upper end surface of a cylindrical substrate, process 1 chip packaging groove 102 that matches the size and shape of the sensor chip 5 and 1 channel extending from the bottom of the chip packaging groove 102 to the lower end surface of the cylindrical substrate (as the bottom cavity 103 of the chip packaging groove); referring to the circuit structure on the front surface of the sensor chip 5 that needs to be placed in the chip packaging groove 102, process 5 circular through-holes 101 with the same diameter on the cylindrical substrate, which penetrate the upper and lower end surfaces of the cylindrical substrate and are spaced a certain distance from the positions of the metal electrodes 501 on the front surface of the sensor chip 5; process 1 annular groove 104 on the side surface of the cylindrical substrate.

[0083] 2) Bond the sensor chip and the metal pin

[0084] Insert 5 metal pins 2 into the corresponding circular through-holes 101 of the sensor housing 1 processed in step 1 (the upper ends of the 5 metal pins are flush with the upper end surface of the sensor housing 1), and inject the conductive glass paste into the circular through-holes 101 containing the metal pins 2 at the lower end surface of the sensor housing 1. The injection amount of the conductive glass paste is based on its ability to fully contact the metal pins 2 and the circular through-holes 101 ( Figure 8a); Apply high-temperature resistant adhesive to the bottom of the chip encapsulation groove 102 of the sensor housing 1, and then place the sensor chip 5 so that the sensor chip 5 is tightly embedded in the chip encapsulation groove 102, and the front surface of the sensor chip 5 is flush with the upper end surface of the sensor housing 1.

[0085] 3) Use direct-write conductive silver paste to form a physical connection between the metal electrodes 501 on the front surface of the sensor chip 5 and the corresponding metal pins 2 on the outside.

[0086] 4) Fix the embedded sensor chip 5 on the corresponding end surface of the sensor housing 1 through high-temperature curing (that is, the sensor chip 5 is firmly fixed in the chip encapsulation groove 102); the conductive sealing block 3 formed through the high-temperature curing not only seals one end of the circular through-hole 101 close to the sensor chip 5, but also enables the cured conductive glass paste to be tightly and reliably combined with the metal pin 2 (to achieve electrical connection), and fixes the metal pin 2 in the circular through-hole 101 (that is, fixes the metal pin 2 to the sensor housing 1); the five flat high-temperature resistant conductive layers 4 formed through the high-temperature curing achieve the electrical connection between the metal pin 2 and the metal electrode 501.

[0087] Example 2

[0088] The above Example 1 is for the case where the working environment of the sensor chip is relatively friendly, for example, the chip does not directly contact water vapor, dust or corrosive substances. If the sensor chip works in an environment containing water vapor, dust or corrosive substances, it is necessary to consider using the encapsulation structure to protect the circuit structure on the front surface of the sensor chip, so Example 2 is proposed.

[0089] As Figure 5 As shown in a, the main difference between the overall encapsulation structure of the high-temperature resistant sensor in this embodiment and that in Example 1 is that: the sensor chip 5 is buckled in the chip encapsulation groove 102, that is, the back surface of the sensor chip 5 faces up, and the arrangement positions of the circular through-holes 101 on the end surface of the sensor housing 1 are all inside the chip encapsulation groove 102, that is, the upper end of the circular through-hole 101 is also connected to the chip encapsulation groove 102, and the position of the bottom cavity 103 remains unchanged, that is, this cavity 103 is surrounded by each circular through-hole 101 in the middle of the sensor housing 1.

[0090] The overall encapsulation structure of the high-temperature resistant sensor in this embodiment can be obtained by the following encapsulation process flow:

[0091] 1) Process the sensor housing

[0092] As Figure 5As shown in Fig. b, a chip encapsulation groove 102 matching the size and shape of the sensor chip 5 and a channel (as the bottom cavity channel 103 of the chip encapsulation groove) extending from the bottom of the chip encapsulation groove 102 to the lower end surface of the cylindrical substrate are machined on the upper end surface of a cylindrical substrate; referring to the circuit structure on the front surface of the sensor chip 5 to be placed in the chip encapsulation groove 102, five circular through holes 101 with the same diameter, penetrating the cylindrical substrate and capable of being directly opposite to the positions of the metal electrodes 501 of the sensor chip 5 are machined on the cylindrical substrate; an annular groove 104 is machined on the side surface of the cylindrical substrate.

[0093] 2) Bond the metal pins

[0094] As Figure 6 a, Figure 8 As shown in Fig. b, refer to step 2) in Embodiment 1 to bond the metal pins 2 in the circular through holes 101 through conductive glass paste.

[0095] 3) As Figure 6 As shown in Fig. b, direct-write conductive silver paste is applied to the end faces of the metal pins 2 at the bottom of the chip encapsulation groove 102 and within the edges of the corresponding circular through holes 101 (above the upper end of the conductive glass paste filling area).

[0096] 4) As Figure 7 As shown, high-temperature resistant adhesive is applied to other areas of the bottom of the chip encapsulation groove 102 except for the direct-write conductive silver paste application area and the channel structure opening. The sensor chip 5 is placed into the chip encapsulation groove 102 in the manner that the back surface (with the cavity 502) faces upward (the sensor chip 5 is placed upside down) and each metal electrode 501 is respectively aligned with each direct-write conductive silver paste application area, so that the sensor chip 5 is tightly embedded in the chip encapsulation groove 102, and the front surface of the sensor chip 5 is flush with the upper end surface of the sensor housing 1.

[0097] 5) After sintering, with the complete curing of the conductive glass paste in the circular through holes 101, the direct-write conductive silver paste in the chip encapsulation groove 102, and the high-temperature resistant adhesive, the sensor chip 5 and the metal pins 2 are firmly fixed on the sensor housing 1, and a high-temperature resistant conductive layer 4 is formed between the opposite ends of the metal pins 2 and the metal electrodes 501 (and the conductive sealing block 3).

[0098] It should be specifically noted that: (1) The positions of each metal pin 2, the conductive sealing block 3 formed after curing the conductive glass paste, and the high-temperature conductive layer 4 formed after curing the direct-write conductive silver paste correspond one by one to the metal electrode 501 of the sensor chip 5 and are on the same axis, ensuring that a complete electrical connection can be formed after the sensor is encapsulated; (2) The depth of the chip encapsulation groove 102, the coating thickness of the high-temperature adhesive and the direct-write conductive silver paste, and the thickness of the sensor chip 5 should be matched so that the back surface of the sensor chip and the upper end surface of the sensor housing are flush after the sensor is encapsulated.

[0099] The advantages of the inverted encapsulation of the sensor chip adopted in this embodiment are as follows: (1) It effectively protects the circuit structure on the front surface of the sensor chip 5 from being damaged by moisture, dust, and corrosive substances in the external environment, with a long sensor life and strong environmental adaptability; (2) For a pressure sensor, the measured medium applies pressure to the back surface of the sensor chip 5, which can effectively promote the stability of the electrical connection between the metal electrode 501 on the front surface of the sensor chip 5, the conductive sealing block 3 formed after curing the conductive glass paste, and the metal pin 2 and the high-temperature conductive layer 4 formed after curing the direct-write conductive silver paste. This connection stability will be higher as the sensor is used for a long time.

[0100] In summary, the high-temperature leadless encapsulation structure and its encapsulation process proposed by the present invention, on the one hand, solve the problem of the degradation or even failure of the reliability of the conventional metal lead bonding encapsulation technology in a high-temperature environment. On the other hand, it simplifies the encapsulation lead method, has simple operation, high yield, high reliability in actual use, is suitable for mass production, low cost, and has a very high cost performance. At the same time, the present invention improves the working stability and long-term reliability of the sensor in a high-temperature environment by selecting and simplifying the encapsulation materials. And the sensor chip has the advantage of good dynamic response characteristics by adopting a flush encapsulation.

Claims

1. A leadless package structure for a high-temperature resistant sensor, characterized in that: The leadless package structure includes a sensor chip (5), a sensor housing (1) for supporting the sensor chip (5), and metal pins (2) provided on the sensor housing (1). The metal pins (2) are connected to the metal electrodes (501) of the sensor chip (5) through a high-temperature conductive layer (4). The metal electrodes (501) are externally disposed on the surface of the sensor housing (1) or internally disposed in the sensor housing (1); The sensor housing (1) includes a base body and a chip packaging groove (102) provided on the base body. The sensor chip (5) is connected to the sensor housing (1) through a sealing layer (6) provided at the bottom of the chip packaging groove (102). The sensor chip (5) is flush with the surface of the sensor housing (1); The sensor housing (1) further includes a cavity (103) provided on the base body. The cavity (103) is connected to the bottom of the chip packaging groove (102), that is, the cavity (103) communicates with the chip packaging groove (102). The cavity (103) adopts a channel structure communicating with the outside, or the cavity (103) adopts an internal cavity structure; The sensor housing further includes a through hole (101) provided on the base body. A conductive sealing block (3) is provided in the through hole (101). The conductive sealing block (3) fills the space between the part of the metal pin (2) located in the through hole (101) and the inner wall of the through hole (101).

2. The leadless package structure for a high-temperature resistant sensor according to claim 1, characterized in that: The sealing layer (6) is formed by curing a high-temperature resistant adhesive applied to the bottom of the chip packaging groove (102); the components of the high-temperature resistant adhesive include a glass paste of the PbO-ZnO-B 2 O 3 system.

3. The leadless package structure for a high-temperature resistant sensor according to claim 1, characterized in that: The conductive sealing block (3) is formed by curing the conductive glass paste injected into the inner space of the sensor housing (1) along the through hole (101); the components of the conductive glass paste include the glass paste of the PbO-ZnO-B 2 O 3 system.

4. The leadless package structure for a high-temperature resistant sensor according to claim 1, characterized in that: The base body is columnar. The chip packaging groove (102) is opened on one end face of the base body. One end of the through hole (101) is located on the other end face of the base body, and the other end of the through hole (101) extends to the end face of the base body where the chip packaging groove (102) is opened.

5. The leadless package structure for a high-temperature resistant sensor according to claim 4, characterized in that: The through hole (101) of the sensor housing (1) is connected to the bottom of the chip packaging groove (102), and the high-temperature resistant conductive layer (4) is arranged between the metal pin (2) and the metal electrode (501) of the sensor chip (5) in a stacked manner; alternatively, the arrangement position of the through hole (101) of the sensor housing (1) on the substrate end face is outside the chip packaging groove (102), and the high-temperature resistant conductive layer (4) is arranged between the metal pin (2) and the metal electrode (501) of the sensor chip (5) in a direct writing manner; the high-temperature resistant conductive layer (4) is made of a modified paste mainly composed of a glass paste in the PbO-ZnO-B 2 O 3 system and is formed by coating and curing.

6. The leadless package structure for a high-temperature resistant sensor according to claim 4, characterized in that: The sensor housing (1) further includes an annular groove (104) provided on the side surface of the base body.

7. A packaging method for the leadless package structure of a high-temperature resistant sensor as claimed in claim 1, characterized in that: comprises the following steps: 1) Processing a chip packaging groove (102), a cavity (103) at the bottom of the chip packaging groove (102), and a through hole (101) on the base body to obtain the sensor housing (1); wherein the cavity (103) communicates with the chip packaging groove (102). The cavity (103) adopts a channel structure communicating with the outside, or the cavity (103) adopts an internal cavity structure; 2) After the metal pin (2) and the sensor chip (5) are respectively adhesively bonded to the sensor housing (1) through the through holes (101) and the chip packaging grooves (102), curing is carried out, and during the curing, a high-temperature resistant conductive layer (4) that simultaneously covers the metal pin (2) and the metal electrode (501) of the sensor chip (5) is formed by using a pre-placed paste across both sides of the junction position between the sensor housing (1) and the sensor chip (5), obtaining a leadless package structure of a high-temperature resistant sensor with an external metal electrode; Alternatively, the metal pin (2) is adhesively bonded to the sensor housing (1) through the through hole (101), and before the sensor chip (5) is adhesively bonded to the sensor housing (1) through the chip packaging groove (102), the paste for forming the high-temperature resistant conductive layer (4) is placed into the chip packaging groove (102), so that during curing, the metal pin (2) and the metal electrode (501) of the sensor chip (5) are simultaneously butt-jointed with the high-temperature resistant conductive layer (4), obtaining a leadless package structure of a high-temperature resistant sensor with an internal metal electrode.

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