Background
The high temperature resistant sensor has very important application in various industries and fields, such as high temperature pressure and vibration resistant sensors for detecting high temperature pressure and vibration in an aeroengine, high temperature pressure resistant sensors for measuring loop pressure of a high temperature reactor of a nuclear power station, and high temperature pressure and vibration sensors for monitoring operation safety of a high temperature industrial reaction kettle and a smelting tower.
The high temperature resistant sensor can normally work in a high temperature environment, and has the key problems that (1) the sensor chip can normally work in the high temperature environment, and (2) the sensor packaging structure can normally play roles of supporting, electric connection, sealing and the like in the high temperature environment. With the progress of technology, sensor chip materials capable of working normally at high temperature are continuously discovered, and the first key problem faced by high temperature resistant sensors is effectively solved. However, the sensor packaging structure often involves combination and fixation of various materials, and at high temperature, the problems of inconsistent thermal expansion of heterogeneous materials, high-temperature oxidation of materials, softening and falling of connecting pieces and the like are easily caused, so that the sensor chip supporting structure is invalid, electrical connection is short-circuited or broken, even the sensor chip is broken, and the sensor performance is deteriorated even permanently invalid.
The most important ring in the sensor package is to form an effective electrical connection between the electrode of the sensor chip and the electrode on the package structure, so that the signal measured by the sensor chip can be smoothly transmitted. The packaging mode commonly used at present adopts a metal lead bonding mode for connection. Chinese patent CN105236343a, for example, discloses a dielectric-isolated pressure sensor package structure in which a pressure sensor package module with a MEMS chip is connected to a wire by wire bonding. The connecting mode is simple in structure and convenient to operate, but when the connecting mode is used in a high-temperature environment, bonding points between the lead and the sensor packaging module and between the lead and the lead are easy to fall off due to softening at a high temperature, and failure risks exist.
Aiming at the problem of metal lead bonding, chinese patent CN102928150A discloses a leadless packaged metal film pressure sensor, wherein a sensor chip and a glass sealing cover are connected together in a bonding mode, and the leadless packaged metal film pressure sensor is prepared by vacuum annealing through a through hole corresponding to a lead bonding pad of the sensor chip on the glass sealing cover, conductive metal materials filled in the through hole and conductive metal pins inserted into the through hole filled with the conductive metal materials. The packaging mode adopted in the patent effectively solves the problem that the metal lead bonding type packaging is not resistant to high temperature, but has two problems in actual operation, namely (1) because the size of the MEMS chip is small, the sizes of the lead bonding pad and the corresponding through hole are very small (in micron level), the micropore effect can lead the conductive metal material to be difficult to effectively fill the whole through hole in practice, so that bubbles and holes exist in the through hole filled with the conductive metal material, the lead bonding pad, the conductive metal material and the conductive metal lead pin cannot be fully contacted, even contact is not realized at all, and (2) even though the annealing aims at sintering the conductive metal material, the lead bonding pad, the conductive metal material and the conductive metal lead pin can be fixedly connected and form good electrical connection, because the conductive metal material can generate thermal deformation and volatilize bubbles in the actual sintering process, the volume of the conductive metal material after annealing is reduced, the internal bubbles are caused, and even the conditions of open circuit among the lead bonding pad, the conductive metal material and the conductive metal lead pin are caused by inconsistent thermal expansion coefficients of different materials are generated. Due to the problems of the two aspects, the success rate of actually obtaining the packaging structure is not high.
Chinese patent CN109781334a discloses a leadless package structure of piezoresistive sensor, in which conductive paste (composed of silver, glass, organic binder, solvent, etc.) has a problem of generating thermal stress after sintering and curing, in order to make the sintered and cured conductive paste stably play a role of a connection structure, noble metal gold is further used as a transition layer, and the thermal stress is reduced by using good ductility of gold. However, the transition layer cannot solve the problem that the conductive paste itself generates thermal deformation and volatilizes bubbles in the actual sintering and curing process. In addition, the size of the through hole penetrated by the valve pin still needs to be limited to a smaller range, so that the reliability of the connection structure is still affected by the micropore effect. Meanwhile, the patent also uses a glass slurry mainly comprising a PbO-ZnO-B2O3 system to form another transition layer, the softening point of the glass system can be adjusted according to the lead content, and a composite glass slurry formed by adding a low expansion coefficient and a negative expansion material such as PbTiO3, cordierite, eucryptite, spodumene, quartz glass and the like on the basis of PbO-ZnO-B2O3 according to the requirement, so as to adjust the thermal expansion coefficient and improve the effects of chemical stability and mechanical strength. However, the slurry has high viscosity and limited application modes and range.
Disclosure of Invention
In order to solve the technical problems of the existing high-temperature-resistant sensor packaging structure, the invention provides a leadless packaging structure and method of a high-temperature-resistant sensor.
In order to achieve the above purpose, the invention adopts the following technical scheme:
The leadless packaging structure of the high temperature resistant sensor comprises a sensor chip, a sensor shell for supporting the sensor chip and metal pins arranged on the sensor shell, wherein the metal pins are connected with metal electrodes of the sensor chip through a high temperature resistant conducting layer, and the metal electrodes are externally arranged on the surface of the sensor shell or internally arranged in the sensor shell.
Preferably, the sensor housing comprises a base body and a chip packaging groove arranged on the base body, the sensor chip is connected with the sensor housing through a sealing layer arranged at the bottom of the chip packaging groove, and the sensor chip is flush with the surface of the sensor housing.
Preferably, the sealing layer is formed by curing a high temperature resistant adhesive applied to the bottom of the chip package groove.
Preferably, the high-temperature-resistant adhesive comprises a glass paste of a PbO-ZnO-B2O3 system, and the thermal expansion coefficient of the sealing layer is between that of the sensor shell and that of the sensor chip.
Preferably, the sensor housing further comprises a cavity channel arranged on the substrate, and the cavity channel is connected with the bottom of the chip packaging groove.
Preferably, the sensor housing further comprises a through hole arranged on the substrate, wherein a conductive sealing block is arranged in the through hole, and the conductive sealing block is filled between the part of the metal pin in the through hole and the inner wall of the through hole.
Preferably, the conductive sealing block is formed by curing a conductive glass paste injected into the inner space of the sensor housing along the through hole to bond a portion of the metal pin located in the through hole (bonding the portion with the sensor housing).
Preferably, the components of the conductive glass paste comprise a glass paste of a PbO-ZnO-B2O3 system and a nano conductive material.
Preferably, the substrate is columnar, the chip packaging groove is formed in 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 where the chip packaging groove is formed.
Preferably, the through hole of the sensor housing is connected with the bottom of the chip packaging groove, and the high-temperature resistant conductive layer is arranged between the metal pin and the metal electrode of the sensor chip in a superposition manner (namely, the metal electrode is built-in), or the through hole of the sensor housing is arranged outside the chip packaging groove on the end face of the substrate, and the high-temperature resistant conductive layer is arranged between the metal pin and the metal electrode of the sensor chip in a direct writing manner (namely, the metal electrode is external).
Preferably, the high temperature resistant conductive layer is prepared by coating and curing a modified slurry containing an adhesive, a high temperature antioxidant and a nano conductive material (i.e. the adhesive is modified by the high temperature antioxidant and the nano conductive material), or by coating and curing a modified slurry containing an adhesive, a high temperature antioxidant, a toughness agent and a nano conductive material (i.e. the adhesive is modified by the high temperature antioxidant, the toughness agent and the nano conductive material).
Preferably, the components of the adhesive comprise glass paste of PbO-ZnO-B2O3 system, namely the adhesive can adopt the high-temperature-resistant adhesive glue.
Preferably, the sensor housing further comprises an annular groove provided on a side of the base body.
A leadless packaging method of a high temperature resistant sensor comprises the following steps:
1) Processing a chip packaging groove and a through hole on a substrate to obtain a sensor shell;
2) The metal pins and the sensor chip are correspondingly bonded with the sensor shell through the through holes and the chip packaging grooves respectively and then are solidified, and a high-temperature resistant conductive layer which simultaneously covers the metal pins and the metal electrodes of the sensor chip is formed by preset sizing agents (such as the modified sizing agents) which cross the two sides of the boundary position of the sensor shell and the sensor chip in solidification, so that a high-temperature resistant sensor leadless packaging structure with external metal electrodes is obtained;
Or bonding the metal pins with the sensor shell through the through holes, and placing the slurry (for example, the slurry which is the same as the preset slurry) for forming the high-temperature-resistant conductive layer into the chip packaging groove before bonding the sensor chip with the sensor shell through the chip packaging groove, so that the metal pins and the metal electrodes of the sensor chip are in butt joint with the high-temperature-resistant conductive layer through solidification, and the leadless packaging structure of the high-temperature-resistant sensor with the built-in metal electrodes is obtained.
Preferably, the step 1) further comprises the step of processing a cavity connected with the bottom of the chip packaging groove on the substrate.
Preferably, in the step 2), the conductive glass paste is injected into the through hole, and a gap between a portion of the metal pin located in the through hole and an inner wall of the through hole is filled with the conductive glass paste, so that the metal pin is bonded to the sensor housing.
Preferably, in the step 2), the high temperature resistant adhesive is coated on a certain area of the bottom of the chip packaging groove (when the end surfaces of the through holes are positioned at the bottom of the chip packaging groove, as the high temperature resistant conductive layers are required to be formed on the areas where the end surfaces are positioned, the high temperature resistant adhesive is coated on the bottom surface of the chip packaging groove except for the areas, when the end surfaces of the through holes are positioned outside the chip packaging groove, the bottom surface of the chip packaging groove is coated, the connecting part between the cavity and the bottom of the chip packaging groove cannot be coated), the sensor chip is placed in the chip packaging groove and contacted with the coated high temperature resistant adhesive until the sensor chip is flush with the surface of the sensor shell, so that the sensor chip is bonded on the sensor shell.
The beneficial effects of the invention are as follows:
In the high-temperature-resistant sensor packaging structure, the lead-free packaging is realized by introducing the conductive layer which accords with the application temperature grade of the sensor, the reliability of the electric connection between the metal pins in the packaging structure and the metal electrodes of the sensor chip is improved, the defect of the traditional packaging structure in the aspect of heat stability is solved fundamentally, and meanwhile, the packaging mode of the sensor chip is flexible, and the packaging method is low in process difficulty and high in yield.
Furthermore, the sensor chip and the sensor shell are packaged in a flush way, so that the sensor chip is directly contacted with a measured high-temperature medium for the pressure sensor, the attenuation influence of a tube cavity effect on the dynamic performance of the sensor is avoided, the problems of response time lag and frequency distortion caused by the tube cavity effect are solved, and the sensor has higher response speed and higher resonant frequency.
Furthermore, the packaging materials directly connected with the sensor chip are few in types (only a few materials with the same glass paste component such as sensor shell materials and cured high-temperature-resistant adhesive) so that the thermal expansion coefficients of the packaging materials and the sensor chip materials are easy to match (the thermal expansion coefficients of the packaging materials and the sensor chip materials are very similar), the possibility of thermal stress mismatch between heterogeneous materials is reduced, and meanwhile, the packaging can be completed through one-time curing, so that the process steps are simplified.
Furthermore, the thermal expansion coefficient of the high-temperature-resistant adhesive adopted by the invention after solidification is between that of the existing sensor shell and that of the sensor chip, so that the thermal expansion internal stress between the sensor shell and the sensor chip can be effectively relaxed, and the high-temperature stability and the thermal stress damage resistance of the sensor chip are improved.
Furthermore, the cavity (such as a channel structure and the like) at the bottom of the chip packaging groove and the through hole for bonding the metal pin are used as a stress release structure for the thermal expansion of the sensor shell, so that the internal stress caused by the thermal expansion difference between the sensor shell and the sensor chip is reduced.
Further, the through hole arrangement mode adopted by the invention (particularly when the end face of the through hole is positioned outside the chip packaging groove) is beneficial to increasing the aperture of the through hole, so that the packaging material (such as the cured conductive glass paste) based on the glass paste with higher viscosity can be used for realizing more reliable fixing of the metal pins.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples. The examples are given solely for the purpose of illustration and are not intended to limit the scope of the invention.
Aiming at the problems existing in the existing leadless packaging (particularly the packaging of high-temperature-resistant sensors with the temperature of more than 600 ℃) when conducting metal materials are poured into fine packaging through holes and sintered, such as high operation difficulty and low yield (due to air resistance and pore canal effect in micro-pores, the conducting metal materials are difficult to fill the packaging through holes, and hole structures are easy to generate in the conducting metal materials in the curing process, and finally metal lead pins cannot be well electrically connected with lead pads on a sensor chip), the invention provides the leadless packaging structure of the high-temperature-resistant sensor.
Example 1
As shown in fig. 1, the overall package structure of the high temperature resistant sensor includes a sensor housing 1, metal pins 2, and a sensor chip 5. The sensor chip 5 is fixed on the upper end face of the sensor shell 1 in a jogged mode through a sealing layer 6 formed by cured high-temperature-resistant adhesive glue, wherein the sensor chip 5 faces upwards, the upper end of the metal pin 2, the cured conductive glass paste and the front face of the sensor chip 5 are all flush with the upper end face of the sensor shell 1, the lower end of the metal pin 2 extends out of the lower end face of the sensor shell 1, and the back face of the sensor chip 5 is opposite to a channel or an inner cavity structure positioned in the sensor shell 1. The high-temperature resistant conductive layer 4 which is formed by direct-writing conductive silver paste solidification and is continuously distributed in a strip shape is attached to the junction position of the upper end face of the sensor shell 1 and the front face of the sensor chip 5 and corresponding areas on two sides, and the circuit structure of the front face of the sensor chip 5 is connected with the upper ends of the metal pins 2 and the solidified conductive glass paste through the high-temperature resistant conductive layer 4.
As shown in fig. 2, the sensor housing 1 is formed by processing a cylindrical substrate, and the substrate is specifically processed with a circular through hole 101, a chip packaging groove 102, a groove bottom cavity 103 of the chip packaging groove and an annular groove 104.
The chip packaging groove 102 is located in the middle of the upper end surface of the sensor housing 1, and is mainly used for placing the sensor chip 5, and the length and width dimensions (the chip packaging groove 102 in fig. 2a is rectangular) or the diameter dimensions of the chip packaging groove 102 are matched with those of the sensor chip 5, so that the sensor chip 5 can be tightly contacted with the side wall of the chip packaging groove 102 after being mounted in, the depth of the chip packaging groove 102 is slightly greater than the thickness of the sensor chip 5, thereby reserving a space for coating a certain thickness of high-temperature-resistant adhesive on the bottom of the chip packaging groove 102, and enabling the front surface of the sensor chip 5 to be flush with the upper end surface of the sensor housing 1.
The cavity 103 is located below the bottom of the chip packaging groove 102 and is in communication with the chip packaging groove 102. The main function of this channel 103 is (1) to act as a stress relief structure for the thermal expansion of the sensor housing 1, reducing the thermal stresses transmitted to the sensor chip 5. (2) For the pressure sensor, if the cavity 103 directly penetrates the lower end surface of the sensor housing 1 and is in communication with the outside (as shown in fig. 2b, i.e., a channel structure is adopted), the corresponding pressure sensor can be used as a gauge pressure sensor, and if the cavity 103 does not penetrate the lower end surface of the sensor housing 1 (i.e., an inner cavity structure), the corresponding pressure sensor can be used as an absolute pressure sensor through vacuum encapsulation.
The number and relative positions of the circular through holes 101 of the sensor housing 1 are generally determined according to the circuit structure of the front surface of the sensor chip 5, for example, in fig. 2a, the 5 circular through holes 101 are arranged at intervals in two rows, and the arrangement positions of the circular through holes 101 on the end surface of the sensor housing 1 are all located outside the chip packaging groove 102.
The annular groove 104 has the functions of (1) placing an annular sealing ring so that after the sensor is installed in a tested pipeline, a good sealing effect is formed between the sensor and the inner wall of the pipeline, and the detection accuracy is ensured, and (2) fixing the sensor as a positioning clamping groove.
The upper end face and the lower end face of the sensor housing 1 are not provided with edges (for example, the edges of the upper end face and the lower end face of the substrate are provided with fillets), so that people or other objects are prevented from being scratched by sharp right angles, and when the pressure sensor is used in some pipes or cavities, the cylindrical structure with the fillets is beneficial to the flow and outward diffusion of air flow and liquid flow, and vortex is not generated due to the existence of the sharp right angles, so that the actual measurement accuracy is not affected.
When the materials of the sensor housing 1 and the sensor chip 5 are selected, materials with the same or similar thermal expansion coefficients are selected, so that thermal expansion matching under a high-temperature environment is realized, the internal thermal stress of the sensor is ensured to be small, and the high-temperature stability of the sensor is ensured to be good. For example, the sensor case 1 is made of an insulating material AlN having a thermal expansion coefficient of 4.1×10-6/°c, and the sensor chip 5 is made of a material SiC having a thermal expansion coefficient of 3.7×10-6/°c for manufacturing the MEMS chip.
As shown in fig. 3, the metal pins 2 are generally cylindrical elongated bar structures (so called metal pins), and have a specific number and relative positions corresponding to those of the circular through holes 101 provided in the sensor housing 1. I.e. a metal pin 2 is mounted and fixed in a circular through hole 101 by using a conductive sealing block 3 formed by curing conductive glass paste.
As shown in fig. 4-1 and 4-2, the sensor chip 5 is a MEMS miniaturized chip fabricated by a micro-nano manufacturing process. For example, for the sensor chip 5 shown in fig. 4-1a, the front circuit structure of the sensor chip includes 5 metal electrodes 501, one end of the metal wire 503 is closely connected to the metal electrodes 501, and the other end is closely connected to the semiconductor sensitive resistor 504. If the sensor chip 5 is a pressure sensor chip, a cavity 502 should be formed on the back of the chip, the cavity 502 may be rectangular (including square), circular (fig. 4-2 b) or other shapes, and the size of the cavity 502 and the relative position between the cavity and the semiconductor sensitive resistor 504 should satisfy the arrangement rule of the pressure sensor sensitive film and the sensitive resistor. If the sensor chip 5 is a vibration sensor chip, the back side of the chip should be correspondingly processed with a mass and cantilever structure. The number and positions of the metal electrodes 501 and the semiconductor sensitive resistors 504 on the front surface of the sensor chip 5 can be changed according to actual needs. The number and positions of the circular through holes 101 located outside the sensor chip 5 can be determined according to the number and positions of the metal electrodes 501 on the front surface of the sensor chip 5. In addition, when the back of the sensor chip 5 is provided with the concave cavity 502, the cavity 103 below the bottom of the chip packaging groove 102 is opposite to the back of the sensor chip 5, and the upper end opening of the cavity 103 is aligned to the opening of the concave cavity 502 through matching, so that the shape and the size of the opening can be adjusted to be consistent, the chip packaging groove 102 is utilized to stably support the back of the sensor chip 5 except the area corresponding to the concave cavity 502, the reliability of the sensor packaging structure is improved, the fact that only the area corresponding to the concave cavity 502 on the sensor chip 5 is movable and other areas are fixed is ensured, the sensor chip 5 can be measured according to a preset theoretical state, and the measurement accuracy is ensured.
The high-temperature-resistant adhesive is a high-temperature adhesive and has good electrical insulation performance at high temperature. The high-temperature-resistant adhesive is glass slurry mainly composed of a PbO-ZnO-B2O3 system, and can be mixed with lead titanate (PbTiO3), cordierite, eucryptite, spodumene and quartz glass (SiO2) as components besides components composing the PbO-ZnO-B2O3 system.
The formula of the glass paste (namely high-temperature resistant adhesive) based on the PbO-ZnO-B2O3 system is as follows (in mass percent):
①PbO:73%~77%
②B2O3:7%~13%
③ZnO:8%~13%
④PbTiO3 . 0-5% of cordierite, eucryptite, spodumene and quartz glass.
The high-temperature-resistant adhesive needs to be cured at high temperature by sintering to form the sealing layer 6, and the specific application is as follows:
1) In addition to controlling the thickness of the coating, it should be noted that the coating can be used to form a complete sealing ring between the back of the sensor chip and the bottom of the chip packaging slot, and not enter the cavity 502 of the back of the sensor chip 5, so as to avoid affecting the movable structure (such as sensitive film, mass, etc.) inside the sensor chip 5, that is, the shape and size of the high temperature resistant adhesive coated on the bottom of the chip packaging slot 102 should match the shape and size of the back of the sensor chip 5.
2) Curing
Heating from room temperature to 270 ℃ at 2 ℃ per minute for 25 minutes, then uniformly heating to 550 ℃ for 5 minutes, then uniformly reducing the temperature to 540 ℃ within 10 minutes for 20 minutes, then reducing from 540 ℃ to 495 ℃ within 20 minutes for 20 minutes, then reducing from 495 ℃ to 455 ℃ within 20 minutes for 20 minutes, and then reducing to room temperature at a rate of 2 ℃ per minute.
By adopting the procedure to sinter the high-temperature-resistant adhesive, the sealing layer 6 obtained by sintering has no quality defects such as holes, cracks and the like, and the sintering strength and compactness are ensured.
After the high-temperature-resistant adhesive is cured, the thermal expansion coefficient of the high-temperature-resistant adhesive is between the thermal expansion coefficients of the sensor shell 1 and the sensor chip 5 (namely between 3.7X10-6/° C and 4.1X10-6/° C), and the thermal expansion coefficients of the high-temperature-resistant adhesive are very close to each other, so that the back surface of the sensor chip 5 can be tightly fixed in the chip packaging groove 102 of the sensor shell 1 to achieve the effects of adhesion and sealing, and the high-temperature-resistant adhesive can be used as a thermal expansion transition layer to alleviate the thermal expansion internal stress between the sensor shell 1 and the sensor chip 5 and improve the high-temperature stability and the thermal stress damage resistance of the sensor chip.
The conductive glass paste is prepared into high-temperature-resistant conductive paste, namely, the conductive glass paste is formed by further mixing nano conductive silver powder on the basis of the components contained in the high-temperature-resistant adhesive, and the mass fraction of the mixed nano conductive silver powder can be optimized according to the actual conductivity of the conductive glass paste after solidification.
The specific use description of the conductive glass paste is as follows:
1) Filling
And injecting conductive glass slurry into the circular through hole of the sensor shell by adopting a needle tube injector, and filling the gap between the part of the metal pin, which is placed in the through hole, and the inner wall of the through hole.
2) High temperature curing
The sintering procedure refers to the high temperature resistant adhesive.
The conductive glass paste is cured (namely, the conductive sealing block 3) and has the main characteristics of (1) high temperature resistance, good long-term use stability and difficult denaturation under a high-temperature environment, (2) conductivity, low resistance value and small degree of change of the resistance value along with temperature change, (3) thermal expansion coefficient of 3.7X10-6/DEG C to 4.1X10-6/DEG C, and is matched with a sensor shell and a chip material, (4) strong adhesiveness and good adhesiveness, and metal pins can be firmly fixed in circular through holes of the sensor shell.
The direct-writing type conductive silver paste is a multi-component mixed paste which consists of the high-temperature resistant adhesive and a modifier (not only comprises nano conductive silver powder, but also comprises components such as a toughness agent such as micro-nano metal fiber and the like, a high-temperature antioxidant such as ferric oxide powder and the like). And forming physical connection between the metal electrode 501 on the front surface of the sensor chip 5 and the upper end of the corresponding metal pin 2 (flush with the upper end surface of the sensor shell 1) in a 3D printing or spraying mode, and then performing high-temperature curing (a sintering procedure refers to the high-temperature-resistant adhesive) on the direct-writing type conductive silver paste formed physical connection to form a functional structural layer which is tightly adhered on a plane formed by the upper end of the metal pin 2, the corresponding metal electrode 501, the upper end surface of the sensor shell 1 positioned between the upper end and the upper end of the conductive glass paste (the upper end of the conductive sealing block 3) and the corresponding area on the front surface of the sensor chip 5. The functional structural layer has high temperature resistance and low resistance conductive property (so is also called high temperature resistance conductive layer 4), and has a thermal expansion coefficient similar to that of the sensor housing and the chip material (namely, between 3.7X10-6/DEG C and 4.1X10-6/DEG C), meanwhile, the problem of oxidation failure (the disappearance of conductivity due to surface oxidation) occurring at high temperature is avoided, and the problem of fracture at the interface of the sensor housing and the sensor chip is avoided, so that stable electric connection can be formed between the metal pins 2 and the metal electrodes 501 on the front surface of the sensor chip 5.
In the high-temperature working environment of the sensor, the high-temperature resistant conductive layer 4 formed by curing the direct-writing conductive silver paste has good conductivity, toughness and high-temperature oxidation resistance, and stable and reliable electrical connection is provided between the sensor chip 5 and an external circuit connected to the metal pin 2. Meanwhile, the conductive sealing block 3 formed by curing the conductive glass paste adopted by the invention has an additional function of ensuring reliable electrical connection between the metal electrode 501 and the metal pin 2 on the front surface of the sensor chip 5. Although the metal leads 2 and the metal electrodes 501 of the sensor chip 5 are indirectly connected by the cured direct-write conductive silver paste, even if a circuit break occurs between the cured direct-write conductive silver paste and the metal leads 2, the electrical connection reliability of the sensor is not affected because the glass paste for bonding the metal leads 2 in the circular through holes is conductive after curing, and an electrical signal can be transferred to the cured conductive glass paste through the cured direct-write conductive silver paste and then to the metal leads 2.
The whole packaging structure of the high temperature resistant sensor of the embodiment can be obtained by adopting the following packaging process flow:
1) Processing sensor housing
The method comprises the steps of processing 1 chip packaging groove 102 with the size and shape matched with those of a sensor chip 5 and 1 channel (serving as a groove bottom cavity 103 of the chip packaging groove) extending from the bottom of the chip packaging groove 102 to the lower end face of the cylindrical substrate on the upper end face of the cylindrical substrate, referring to a circuit structure of the front face of the sensor chip 5 needing to be placed in the chip packaging groove 102, processing 5 circular through holes 101 which have the same diameter and penetrate through the upper end face and the lower end face of the cylindrical substrate and are spaced a certain distance from the position of a metal electrode 501 on the front face of the sensor chip 5 on the cylindrical substrate, and processing 1 annular groove 104 on the side face of the cylindrical substrate.
2) Bonding sensor chip and metal pins
The method comprises the steps of inserting 5 metal pins 2 into corresponding circular through holes 101 of a sensor housing 1 obtained by processing in the step 1 (the upper ends of the 5 metal pins are flush with the upper end face of the sensor housing 1), injecting conductive glass paste into the circular through holes 101 containing the metal pins 2 at the lower end face of the sensor housing 1, wherein the injection amount of the conductive glass paste is based on the fact that the conductive glass paste can fully contact the metal pins 2 and the circular through holes 101 (fig. 8 a), coating high-temperature-resistant adhesive on the bottom of a chip packaging groove 102 of the sensor housing 1, and then placing the sensor chip 5, so that the sensor chip 5 is tightly embedded into the chip packaging groove 102, and the front face of the sensor chip 5 is flush with the upper end face of the sensor housing 1.
3) A physical connection is formed between the metal electrode 501 on the front side of the sensor chip 5 and the corresponding metal pin 2 on the outer side by using direct-writing conductive silver paste.
4) The embedded sensor chip 5 is fixed on the corresponding end face of the sensor housing 1 through high-temperature curing (namely, the sensor chip 5 is firmly fixed in the chip packaging 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 pins 2 (to realize electric connection), and fixes the metal pins 2 in the circular through hole 101 (namely, the metal pins 2 are fixed with the sensor housing 1), and the 5 flat high-temperature resistant conductive layers 4 formed through the high-temperature curing realize electric connection of the metal pins 2 and the metal electrodes 501.
Example 2
The above example 1 is directed to the sensor chip operating environment being relatively friendly, such as where the chip is not directly exposed to moisture, dust or corrosive substances. If the sensor chip is operated in an environment containing moisture, dust or corrosive substances, it is necessary to consider protecting the circuit structure of the front side of the sensor chip with a package structure, so embodiment 2 is proposed.
As shown in fig. 5a, the overall packaging structure of the high temperature resistant sensor in this embodiment is mainly different from that in embodiment 1 in that the sensor chip 5 is flip-chip in the chip packaging groove 102, that is, the back surface of the sensor chip 5 faces upward, the arrangement positions of the circular through holes 101 on the end surface of the sensor housing 1 are all located inside the chip packaging groove 102, that is, the upper ends of the circular through holes 101 are also communicated with the chip packaging groove 102, and the position of the groove bottom channel 103 is unchanged, that is, the channel 103 is surrounded in the middle of the sensor housing 1 by the circular through holes 101.
The whole packaging structure of the high temperature resistant sensor of the embodiment can be obtained by adopting the following packaging process flow:
1) Processing sensor housing
As shown in FIG. 5b, 1 chip package groove 102 matching the size and shape of the sensor chip 5 and 1 channel (as chip package groove bottom channel 103) extending from the bottom of the chip package groove 102 to the lower end face of the cylindrical substrate are processed on the upper end face of the cylindrical substrate, referring to the circuit structure of the front face of the sensor chip 5 to be placed in the chip package groove 102, 5 circular through holes 101 having the same diameter and penetrating the cylindrical substrate and being capable of facing the metal electrodes 501 of the sensor chip 5 are further processed on the cylindrical substrate, and 1 annular groove 104 is processed on the side face of the cylindrical substrate.
2) Bonding metal pin
As shown in fig. 6a and 8b, referring to step 2) in embodiment 1, the metal pins 2 are bonded in the circular through holes 101 by conductive glass paste.
3) As shown in fig. 6b, a direct writing type conductive silver paste is applied to the end face of each metal pin 2 at the bottom of the chip package groove 102 and the inside of the edge of the corresponding circular through hole 101 (the upper end of the conductive glass paste filling area).
4) As shown in fig. 7, the bottom of the chip packaging groove 102 is removed from the direct writing conductive silver paste coating area and other areas except the opening of the channel structure, high temperature resistant adhesive is coated, the sensor chip 5 is placed in the chip packaging groove 102 in such a way that the back (with the concave cavity 502) faces upwards (the sensor chip 5 is inverted) and each metal electrode 501 is aligned with each direct writing conductive silver paste coating area, so that the sensor chip 5 is tightly embedded in the chip packaging groove 102, and the front surface of the sensor chip 5 is flush with the upper end surface of the sensor housing 1.
5) After sintering, and along with complete solidification of the conductive glass paste in the circular through hole 101 and the direct writing conductive silver paste and the high temperature resistant adhesive in the chip packaging groove 102, the sensor chip 5 and the metal pins 2 are firmly fixed on the sensor shell 1, and a high temperature resistant conductive layer 4 is formed between the metal pins 2 and the opposite ends of the metal electrode 501 (and the conductive sealing block 3).
It should be specially noted that (1) each metal pin 2, the conductive sealing block 3 formed by curing conductive glass paste, and the high temperature resistant conductive layer 4 formed by curing direct writing conductive silver paste are in one-to-one correspondence with the positions of the metal electrodes 501 of the sensor chip 5 and are located on the same axis, so that complete electrical connection can be formed after the sensor package is completed, (2) the depth of the chip package groove 102, the coating thickness of the high temperature resistant adhesive and the direct writing conductive silver paste, and the thickness of the sensor chip 5 are matched, so that the back surface of the sensor chip and the upper end surface of the sensor housing are flush after the sensor package is completed.
The sensor chip flip-chip package adopted in the embodiment has the advantages that (1) the circuit structure on the front side of the sensor chip 5 is effectively protected from being damaged by water vapor, dust and corrosive substances in the external environment, the service life of the sensor is long, the environmental adaptability is strong, and (2) for the pressure sensor, the measured medium applies pressure on the back side of the sensor chip 5, the stability of electric connection among the metal electrode 501 on the front side of the sensor chip 5, the conductive sealing block 3 formed after the conductive glass paste is cured, the metal pin 2 and the high-temperature resistant conductive layer 4 formed after the direct writing type conductive silver paste is cured can be effectively promoted, and the connection stability can be higher along with long-time use of the sensor.
In a word, the high-temperature-resistant leadless packaging structure and the packaging process thereof provided by the invention solve the problems of reliability disintegration and even failure of the conventional metal lead bonding packaging technology in a high-temperature environment, simplify the lead packaging mode, and have the advantages of simplicity in operation, high yield, high reliability in actual use, suitability for mass production, low cost and high cost performance. Meanwhile, the invention improves the working stability and long-term reliability of the sensor in a high-temperature environment by selecting and simplifying the packaging material, and the sensor chip has the advantage of good dynamic response characteristic by adopting flush packaging.