MEMS pressure sensor low-stress packaging structure and method

Abstract

The invention provides an MEMS pressure sensor low-stress packaging structure and method. The MEMS pressure sensor low-stress packaging structure comprises an MEMS pressure sensor plastic packaging shell, a stress isolation structure, an MEMS pressure chip, a bonding material and a low-stress carrier plate. The infiltration area of the bonding material accounts for 60%-75% of the back area of the MEMS pressure chip, and the rest area is filled with stress isolation glue. The stress isolation structure is obtained by curing stress isolation glue. The stress isolation structure surrounds the periphery of the MEMS pressure chip, the thickness of the stress isolation structure is uniform, the stress isolation structure is located on the lower edge of the inverted trapezoid of the plastic package shell, the stress isolation structure does not make contact with the force-sensitive film structure of the MEMS pressure chip, and all the parts, except for the force-sensitive film structure, of the MEMS pressure chip are protected by the stress isolation material. The influence of accumulated stress on the device is reduced, a good stress isolation effect and stable signal output are achieved, and the reliability and long-term stability of the MEMS device are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS pressure sensor packaging, and in particular relates to a low-stress packaging structure and method for a MEMS pressure sensor. Background Art

[0002] Micro-electro-mechanical-systems (MEMS) is a micro-system that integrates electricity and mechanics. It uses micro-machining technology to integrate micro-mechanical structure, signal conversion, signal processing and other functions into a complete and complex system, which is used to achieve sensitive monitoring and precise conversion of force or pressure changes.

[0003] Most MEMS pressure chips use silicon-based materials, and use micromachining technology to make a force-sensitive diaphragm in the middle of the material. Impurities are then diffused on the diaphragm to form four strain resistors. The resistors are then connected into a circuit using a Wheatstone bridge to obtain highly sensitive mechanical output.

[0004] MEMS pressure sensor packaging is a bridge between MEMS pressure chips and electronic systems, and is also an important process for protecting silicon-based materials. Packaging usually involves sticking the MEMS pressure chip to the bonding pad of the carrier board using a specific glue, and then going through processes such as gold wire bonding and plastic encapsulation casting to obtain the final usable device.

[0005] Plastic packaging accounts for an increasingly larger share in electronic device packaging due to its advantages such as simple shell manufacturing, suitability for automated production, light weight, small size and low cost. However, the problem that urgently needs to be solved in plastic packaging is the residual stress of the plastic packaging material when it transforms from liquid to solid.

[0006] MEMS pressure chips, stress isolation materials, adhesive materials and carrier materials generate large packaging stresses due to the mismatch of material thermal expansion coefficients. These packaging stresses will directly cause warping and deformation of the MEMS pressure chip.

[0007] The packaging stress caused by material property mismatch and the residual stress caused by the liquid-solid transformation of the plastic packaging material, the accumulation of these stresses causes the output signal of the packaged MEMS device to shift. At the same time, the packaging stress gradually changes over time, seriously affecting the reliability and long-term stability of the MEMS device. Summary of the invention

[0008] In order to solve the problem that the reliability and long-term stability of MEMS devices fail due to packaging stress caused by material property mismatch and residual stress from liquid-solid transformation of plastic packaging materials, as well as the packaging stress gradually changing over time, the present invention provides a low-stress packaging structure and method for MEMS pressure sensors.

[0009] A low stress packaging structure of a MEMS pressure sensor, comprising a MEMS pressure sensor plastic package housing, a stress isolation structure, a MEMS pressure chip, an adhesive material and a low stress carrier;

[0010] The low-stress carrier board has a gold finger structure in appearance and includes a carrier platform for the MEMS pressure chip. The mounting plane of the carrier platform and the plane of the entire carrier board are designed on two different planes; the mounting plane of the carrier platform is connected to the entire carrier board through two hanging ears.

[0011] Furthermore, the gold finger structure is specifically manifested in each inner pin, whereby precious metals such as Au / Pd are deposited on the surface and back of the carrier board by electrochemical methods to form a ring structure, thereby enhancing the conductivity of the device pad, effectively transmitting electrical signals, and improving the corrosion and oxidation resistance of the exposed metal of the device.

[0012] Furthermore, the low stress carrier plate is divided into n large groups by the stress release grooves, where n≥1, and each large group is composed of a plurality of MEMS pressure sensor device unit groups.

[0013] Furthermore, the two ears are designed with a bending depth of 0.1 mm to 0.3 mm. The purpose of this design is to prevent the deformation of the bonding structure caused by the expansion of packaging stress during the bonding process of the MEMS pressure chip.

[0014] The MEMS pressure chip is fixed on the mounting surface of the low-stress carrier by adhesive materials. The pads of the MEMS pressure chip are connected to the gold finger structure of the low-stress carrier by bonding wires. The stress isolation structure blocks the diffusion of residual stress during the liquid-solid transformation of the plastic shell material.

[0015] The wetting area of ​​the adhesive material on the mounting plane of the carrier platform accounts for 60% to 75% of the back area of ​​the MEMS pressure chip; the adhesive material does not climb on the four sides of the MEMS pressure chip; the remaining wetting area on the mounting plane is filled with stress isolation glue.

[0016] Furthermore, the bonding material uses light-curing and heat-curing glue, and the hardness Shore A after curing is controlled at 55 to 70. If the hardness is too low, the bonding strength is insufficient, and if the hardness is too high, the packaging stress is too high.

[0017] The stress isolation structure is obtained by curing the stress isolation glue. The stress isolation structure is evenly located around the MEMS pressure chip at the lower edge of the inverted trapezoid of the plastic package shell, and does not contact the MEMS pressure chip force-sensitive membrane structure. The MEMS pressure chip force-sensitive membrane structure is protected by stress isolation materials.

[0018] Furthermore, the viscosity of the stress isolation glue is 11000-18000 mPa·s (Shear rate: 10 1 / s|Gap: 500 μm), the hardness Shore D after curing is controlled at 40-50, the Young's modulus is less than 1 MPa, and it is cured at room temperature or medium and low temperature.

[0019] Furthermore, there is a spacing of 0.005 mm to 0.015 mm between the stress isolation structure and the force-sensitive membrane structure of the MEMS pressure chip.

[0020] Furthermore, the thickness of the stress isolation structure on the upper surface of the MEMS pressure chip is 1.2 to 1.5 times the thickness of the four side surfaces of the MEMS pressure chip.

[0021] Furthermore, an ASIC conditioning chip is pasted into the low stress packaging structure of the MEMS pressure sensor.

[0022] Furthermore, the plastic-sealed shell is made of improved epoxy resin plastic-sealed material by casting, and the filler content of the plastic-sealed material accounts for 45% to 65% (wt%) of the entire component.

[0023] Furthermore, the plastic package shell above the force-sensitive membrane structure of the MEMS pressure chip has an inverted trapezoidal opening structure.

[0024] According to the technical solution provided by the present invention, the low stress packaging design of the MEMS pressure sensor of the present invention is different from the conventional IC packaging design and the shell type sensor packaging design, which is specifically manifested in that the conventional IC packaging and the shell type sensor packaging require the adhesive material to reach 100% coverage with the back of the chip when the chip is bonded, and a certain amount of adhesive material climbing is required on the four sides of the chip. The low stress packaging design of the present invention is characterized by the following four aspects:

[0025] According to the technical solution provided by the present invention, as the third aspect of the present invention, the low stress packaging method of MEMS pressure sensor is characterized by the following two aspects:

[0026] Aspect 5: This is also different from the plastic packaging materials used for IC packaging and shell-type sensor packaging. IC packaging requires that the filler ratio is greater than 75%, and shell-type sensor packaging requires that the filler ratio is less than 45%.

[0027] Aspect 6: Stress isolation structure, specifically involving stress isolation layer materials and stress isolation layer structure.

[0028] The stress isolation layer material is characterized in that: the material is required to have good fluidity and filling properties, and a certain hardness after curing, and can absorb the residual stress when the epoxy resin plastic packaging material is transformed from liquid to solid in the cured state.

[0029] The present invention also provides a method for preparing a low-stress packaging structure of a MEMS pressure sensor, the steps of which are:

[0030] (1) The bonding position of the MEMS pressure chip is set on the carrier of the carrier, and the adhesive material is applied. The chip is fixed on the carrier of the carrier through the adhesive material to form an adhesive layer of a specific shape and size, so that a certain gap is left around the bottom of the MEMS pressure chip and the carrier.

[0031] (2) Fill the remaining gap at the bottom of the MEMS pressure chip with stress isolation glue and solidify the whole thing.

[0032] (3) Heating and gold wire bonding.

[0033] (4) Use stress isolation glue to draw glue around the MEMS pressure chip, heat and cure it to form a stress isolation structure higher than the MEMS pressure chip.

[0034] (5) After heating, the improved epoxy resin plastic packaging material is pushed into the mold cavity to fill the cavity of the above structure, thereby forming a final plastic packaging shell.

[0035] (6) The monomer is divided, marked, and cleaned to form a MEMS pressure sensor device.

[0036] Furthermore, in step (1), the ASIC conditioning chip is fixed on the carrier of the packaging carrier by means of an adhesive material.

[0037] According to the technical solution provided by the present invention, as the fourth aspect of the present invention, the technical effect brought about by the present application is explained, which is manifested in solving the offset of the MEMS device output signal caused by stress superposition in the packaging of the MEMS pressure sensor, thereby improving the reliability and long-term stability of the MEMS device; the use of improved epoxy resin molding materials realizes large-scale packaging, improves mass production efficiency, and reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the overall design appearance diagram of the low stress packaging carrier of the MEMS pressure sensor of the present invention.

[0039] Figure 2 This is a right view of the bonding structure of a single unit of the low stress package of the MEMS pressure sensor of the present invention.

[0040] Figure 3 This is a front view of a single unit bonding structure of a low stress package of a MEMS pressure sensor of the present invention.

[0041] Figure 4 It is a partial schematic diagram in the dotted frame of the low stress package of the MEMS pressure sensor according to an embodiment of the present invention.

[0042] Figure 5 It is a front cross-sectional view of a single unit bonding structure of a low stress package of a MEMS pressure sensor of the present invention.

[0043] Figure 6 This is a front cross-sectional view of a single MEMS pressure sensor after packaging according to the low-stress package of the MEMS pressure sensor of the present invention.

[0044] Specific manufacturing method

[0045] In order to make the technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. The same functions are represented by the same numbers in the accompanying drawings. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the description of the present invention refer to the directions in the accompanying drawings.

[0046] In the description of this application, it should be noted that the terms "first", "second" and "third" are only used for the purpose of describing the application and cannot be understood as indicating or implying relative importance.

[0047] The overall structure of the carrier board (number 100), such as Figure 1 As shown, the entire carrier board is divided into four blocks (numbered 101) by the stress relief grooves, and each block has several units ( Figure 2 , Figure 3 , Figure 4 ), each unit is also a MEMS pressure sensor unit in the present invention.

[0048] The pattern of a single unit bonding structure includes 16 gold finger structures (No. 102), 2 ear structures (No. 103), 1 MEMS pressure chip (No. 104), 1 ASIC conditioning circuit chip (No. 105), MEMS pressure chip bonding material (No. 106), ASIC conditioning circuit chip bonding material (No. 107), such as Figure 2-5 As shown, the mounting plane (numbered 108 - 1 ) and the carrier plane (numbered 102 - 1 ) belong to two different planes.

[0049] Specifically, before making the embodiment, the gold finger carrier board No. 100 must be inspected to confirm that there are no scratches, deformations, color differences and other defects. In particular, the height difference between the two planes No. 108-1 and No. 102-1 must be measured. This height difference determines the exposure of the gold wire after packaging, packaging stress transfer and bonding reliability.

[0050] Specifically, after No. 100 passes the inspection, No. 100 is placed at the set position of the bonding equipment track, and the bonding equipment dispensing system applies No. 106 bonding material to the first set position coordinate point. At this time, No. 106 bonding material is irradiated by the UV light of the bonding equipment to dry the surface of No. 106 bonding material. At this time, No. 104 MEMS pressure chip is picked up by the chip picking device of the bonding equipment and transported to the top of No. 106 bonding material and a certain pressure is applied to squeeze out the undried colloid inside No. 106 bonding material to form a bonding layer of a specific shape and size. Thereafter, No. 107 ASIC conditioning chip bonding material is also dispensed by the dispensing system at the second set position coordinate point, and No. 105 ASIC conditioning chip is also picked up by the bonding equipment and transported to the top of No. 107 ASIC conditioning chip bonding material and a certain pressure is applied.

[0051] During this process, after the operation, it is necessary to ensure that there is enough space under number 111, which is the location for the subsequent filling of the stress protection layer glue 112.

[0052] At this point, the mounting process of a MEMS pressure sensor device is completed, and then the entire carrier is transported to the curing furnace for thermal curing, and the entire bonding structure is completed by slowly heating up and curing at medium and low temperatures. It should be noted that in this embodiment, only one Block (number 101) is completed, and the specific number is set according to the experimental requirements.

[0053] After the above bonding structure is completed, the entire carrier is placed on the track of the fully automatic gold wire bonding machine. The lower part of the bonding table (No. 108-2) is supported by a heating block, and the upper part No. 102 is clamped with the pressure plate, thus completing the fixation of the automatic gold wire bonding equipment product. Heating the lower part of the bonding table can greatly reduce the stress damage to the bonding structure caused by the bonding heat, and can also reduce the residual thermal stress of the bonding structure package. Figure 6 The fact that the gold wires and gold balls are not shown does not mean that there are no gold wires and gold balls in the device.

[0054] Specifically, after the above structure is completed, the next step is to work on the stress protection layer. The above structure is placed on the visual glue painting machine storage table, and the pressure, glue painting machine speed, glue painting machine needle height and other parameters are adjusted to achieve Figure 4 The tetragonal structure numbered 112 (W1:W2≈1.2~1.5 times), Figure 6 Only the glue application on one side of the MEMS pressure chip is shown. In actual operation, the square structure numbered 112 is a full circle around numbered 104. In this embodiment, the glue application machine has a gas source pressure range of 2.0 Bar to 4.0 Bar, a running speed of 0.5 mm / s to 1 mm / s, and a needle height of 110 um to 130 um (the height zero point is above numbered 102).

[0055] Specifically, after the operation is completed according to the above parameters, the entire carrier is placed in a hot oven with a heating rate of 3°C to 5°C / Min, a maximum temperature of <80°C, and a holding time of 30Min to 60Min. After baking, the temperature is cooled to room temperature with the oven.

[0056] Specifically, after the stress protection layer is completed, the entire structure is placed in the mold cavity of the Boschman plastic packaging machine, and the FAM film-assisted technology is used to heat the improved epoxy resin plastic packaging material and push it into the mold cavity to fill the cavity of the above structure, thereby forming the final plastic packaging shell (No. 113) wherein the open cavity structure is Figure 6 Number 110.

[0057] Specifically, after the above-mentioned plastic packaging is completed, the manufacturing of a MEMS pressure sensor device is completed through processes such as monomer segmentation, laser marking, and cleaning.

Claims

1. A low stress packaging structure for a MEMS pressure sensor, characterized in that: It includes a MEMS pressure sensor plastic package shell, a stress isolation structure, a MEMS pressure chip, bonding materials and a low-stress carrier board; The low stress carrier has a gold finger structure in appearance, and includes a carrier for the MEMS pressure chip. The carrier plane and the entire carrier plane are designed on two different planes. The carrier plane is connected to the entire carrier through two hanging ears. The MEMS pressure chip is fixed on the upper surface of the carrier platform of the low-stress carrier by adhesive glue, and the pad of the MEMS chip is connected to the gold finger structure of the low-stress carrier by bonding wires; The wetting area of ​​the adhesive material on the mounting plane of the carrier platform accounts for 60% to 75% of the back area of ​​the MEMS pressure chip; the adhesive material does not climb on the four sides of the MEMS pressure chip; The stress isolation structure is obtained by curing the stress isolation glue; The remaining wetted area on the mounting plane is filled with stress isolation glue; the stress isolation structure is uniformly thick around the MEMS pressure chip and is located at the lower edge of the inverted trapezoid of the plastic package shell, and does not contact the MEMS pressure chip force-sensitive membrane structure. All parts except the MEMS pressure chip force-sensitive membrane structure are protected by stress isolation materials.

2. The low stress packaging structure of the MEMS pressure sensor according to claim 1, characterized in that: The gold finger structure is present on each inner pin, and Au and Pd precious metals are deposited on the surface and back of the carrier by electrochemical methods to form a ring structure; the bending depth of the ear is designed to be 0.1mm to 0.3mm.

3. The low stress packaging structure of the MEMS pressure sensor according to claim 1, characterized in that: The bonding material uses glue with two curing modes: light curing and heat curing, and the hardness Shore A after curing is controlled at 55-70.

4. The low stress packaging structure of the MEMS pressure sensor according to claim 1, characterized in that: The plastic-sealed shell is made of improved epoxy resin plastic-sealed material by casting, and the filler content of the epoxy resin plastic-sealed material accounts for 45% to 65% (wt%) of the whole component.

5. The low stress packaging structure of the MEMS pressure sensor according to claim 1, characterized in that: The stress isolation structure is obtained by curing the stress isolation glue; the stress isolation structure is uniformly thick around the MEMS pressure chip and is located at the lower edge of the inverted trapezoid of the plastic package shell, and has no contact with the force-sensitive membrane structure of the MEMS pressure chip. All parts except the force-sensitive membrane structure of the MEMS pressure chip are protected by the stress isolation material.

6. The low stress packaging structure of the MEMS pressure sensor according to claim 5, characterized in that: The viscosity of the stress isolation glue is 11000-18000 mPa·s (Shear rate: 10 1 / s|Gap: 500 μm), the hardness Shore D after curing is controlled at 40-50, the Young's modulus is less than 1 MPa, and it is cured at room temperature or medium and low temperature; the stress isolation structure and the force-sensitive membrane structure of the MEMS pressure chip have a spacing of 0.005 mm to 0.015 mm, and the thickness on the upper surface of the MEMS pressure chip is 1.2 to 1.5 times the thickness of the four sides of the MEMS pressure chip.

7. The low stress packaging structure of the MEMS pressure sensor according to claim 1, characterized in that: An ASIC conditioning chip is pasted on the carrying plane of the carrier.

8. The low stress packaging structure of the MEMS pressure sensor according to claim 1, characterized in that: The plastic package shell is made of improved epoxy resin plastic package material by casting, and the filler content of the plastic package material accounts for 45% to 65% (wt%) of the entire component; the plastic package shell has an inverted trapezoidal open cavity structure above the force-sensitive membrane structure of the MEMS pressure chip.

9. A method for preparing a low-stress packaging structure of a MEMS pressure sensor, characterized in that: The steps are: (1) Setting the bonding position of the MEMS pressure chip on the carrier of the carrier, applying adhesive material, and fixing the chip on the carrier of the carrier through the adhesive material to form an adhesive layer of a specific shape and size, so that a certain gap is left around the bottom of the MEMS pressure chip and the carrier; (2) Fill the remaining gap at the bottom of the MEMS pressure chip with stress isolation glue and solidify the whole chip; (3) heating and performing gold wire bonding; (4) Using stress isolation glue to draw glue around the MEMS pressure chip, heating and curing to form a stress isolation structure higher than the MEMS pressure chip; (5) After heating, the improved epoxy resin plastic packaging material is pushed into the mold cavity to fill the cavity of the above structure to form a final plastic packaging shell; (6) The monomer is divided, marked, and cleaned to form a MEMS pressure sensor device.

10. The method for preparing the low stress packaging structure of the MEMS pressure sensor according to claim 9, characterized in that: In step (1), the ASIC conditioning chip is fixed on the carrier of the packaging carrier by means of an adhesive material.

Images