Airflow sensor test structure and packaging method and packaging structure thereof

Abstract

The invention relates to an airflow sensor testing structure and a packaging method and packaging structure thereof, each chip unit of an airflow sensor wafer is composed of a substrate (1), a vibrating diaphragm (2) and a back plate which are stacked, the substrate (1) is provided with a back cavity (42) penetrating in the thickness direction of the substrate (1), a slot (10) is formed in the bottom of the substrate (1), and the vibrating diaphragm (2) is arranged in the slot (10). The open groove (10) penetrates through the substrate (1) and the back cavity (42), and the open groove (10) is used for establishing a continuous air flow path in a space outside the back cavity (42) and the air flow sensor. During packaging, the airflow sensor chip is fixed on the packaging substrate through silica gel, a packaging shell is installed outside the airflow sensor chip, the open groove (10) is filled with the silica gel, and blocking and sealing of the open groove (10) are achieved. According to the invention, the requirement of each tube core on the test wafer can be met, the production cost is not increased, and the risk of wafer fragmentation can be effectively avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of MEMS airflow sensor, in particular to an airflow sensor test structure, a packaging method and a packaging structure. BACKGROUND

[0002] In the airflow sensor market, MEMS chip airflow sensor products based on Micro-Electro-Mechanical System (MEMS) manufacturing are increasingly accepted by the market. The MEMS chip mainly includes a diaphragm and a back plate, and has a gap between the diaphragm and the back plate. Changes in air pressure will cause the diaphragm to deform, and the capacitance value between the diaphragm and the back plate will change, thereby being converted into an electrical signal output. In order to confirm whether the MEMS chip differential pressure product meets the preset requirements, airflow is usually added for testing before shipment. This is the FT test (Final Test), i.e. the final product test.

[0003] For airflow sensor products, the packaging cost generally accounts for about 50% of the total cost. In order to reduce production loss, the MEMS wafer needs to be subjected to CP testing (Chip Probing), i.e. wafer testing, before packaging, in order to remove functionally abnormal or parameterally abnormal dies, thereby reducing subsequent packaging loss caused by abnormal MEMS chips.

[0004] The CP testing method is generally implemented in two ways:

[0005] (1) controlled airflow is added to the upper or lower surface of the wafer, the air pressure difference on both sides of the diaphragm causes the diaphragm to deform, and the capacitance value between the diaphragm and the back plate changes, thereby being tested.

[0006] (2) a direct current voltage is applied to the diaphragm and the back plate to generate an electrostatic attraction force, thereby causing the diaphragm to deform, and the capacitance value between the diaphragm and the back plate changes, thereby being tested.

[0007] Both of the above two methods require that the air pressure on both sides of the diaphragm be balanced in the initial state of testing, so as to ensure that C0 is the initial capacitance value of the sensor under the condition of not bearing the gas pressure, and to prevent the test system from detecting incorrect capacitance change values in the subsequent test.

[0008] Due to the device structure of the MEMS chip, the mechanical strength of the MEMS wafer is much smaller than that of the ordinary IC wafer, and the sensitivity of the MEMS chip to external particle pollution is extremely high. In order to ensure the safety of the wafer during production transfer and transportation, the industry generally practices pasting a UV film larger than the wafer on the back of the wafer, and the UV film is fixed by a ring larger than the wafer. In the subsequent production process, the wafer is transferred by clamping and fixing the ring.

[0009] However, after the UV film is pasted on the back of the MEMS wafer, the UV film and the back cavity and diaphragm of the MEMS chip form a closed cavity, and the air in the closed cavity will expand and contract with heat and cold, and the gas pressure cannot be consistent with the atmospheric pressure outside the wafer, that is, the air pressure on the upper and lower surfaces of the diaphragm cannot be balanced, which directly conflicts with the test requirements.

[0010] To solve this problem, the most common practice in the industry is to specially design a test die, which is uniformly and spacedly placed in normal dies, such as 10x10 or 20x20 normal dies. The only difference between the test die and the normal die is that several small holes are provided on the diaphragm, that is, several small air holes are provided on the closed cavity formed by the UV film and the back cavity and diaphragm of the MEMS chip. In this way, the air pressure on the upper and lower surfaces of the diaphragm can be balanced, and the requirement of accurately testing the initial capacitance value C0 of the sensor can be met. However, this method has two problems:

[0011] (1) The test die cannot be used normally, which reduces the number of normal dies on each wafer and causes a fixed die yield loss.

[0012] (2) The CP test can only test the test die, and the test die is spacedly arranged, so the CP test can only monitor the overall situation of the wafer, and cannot confirm whether a large number of normal dies are normal one by one. This will also cause some abnormal dies to be packaged, resulting in packaging abnormal loss.

[0013] Another method is to tear off the UV film before CP testing of the MEMS wafer, and then the wafer can be normally tested. After testing, the wafer is pasted with the UV film again, and then the wafer can be normally delivered and transported. This method also has two problems:

[0014] (1) Pasting the UV film again directly increases the production cost.

[0015] (2) Since the MEMS wafer is not protected by the UV film and the fixed ring, the risk of wafer breakage during the delivery and transfer of the CP test will be greatly increased.

[0016] Therefore, the above methods are not suitable for large-scale production.

[0017] Therefore, it is urgent to provide an airflow sensor test structure and packaging method and packaging structure, which can meet the requirements of testing each die on the wafer, without increasing the production cost, and can effectively avoid the risk of wafer breakage. SUMMARY

[0018] The application aims to provide an air flow sensor test structure, a packaging method and a packaging structure thereof, which can meet the requirement of each die on a test wafer, without increasing the production cost, and can effectively avoid the risk of wafer cracking.

[0019] Based on the same inventive concept, the application has three independent technical solutions.

[0020] 1. An air flow sensor test structure, an air flow sensor wafer comprising a plurality of chip units, each of which is composed of a substrate, a diaphragm and a back plate arranged in layers, the substrate having a back cavity penetrating through its thickness direction, a slot being arranged on the top of the bottom of the substrate, the slot penetrating through the substrate and the back cavity, the slot being used to establish a continuous air flow path between the back cavity and a space outside the air flow sensor.

[0021] Further, each chip unit is laterally provided with one slot, and the slots of the chip units in each row of chip units are in communication with each other and on the same straight line.

[0022] Further, a scribe groove is arranged between each adjacent chip unit, and the slot penetrates through the scribe groove.

[0023] Further, each chip unit is provided with two slots, a first slot being laterally arranged and a second slot being longitudinally arranged; the first slots of the chip units in each row of chip units are in communication with each other and on the same straight line; the second slots of the chip units in each column of chip units are in communication with each other and on the same straight line.

[0024] Further, the first slot and the second slot are perpendicular to each other.

[0025] Further, a scribe groove is arranged between each adjacent chip unit, the first slot penetrates through the scribe groove between each row of adjacent chip units, and the second slot penetrates through the scribe groove between each column of adjacent chip units.

[0026] Further, the slot is located at the lower part of the substrate.

[0027] 2. A packaging method of the above air flow sensor test structure, the air flow sensor chip is fixed on a packaging substrate by using silica gel, an outer packaging shell is mounted outside the air flow sensor chip, the silica gel is filled in the slot to achieve the plugging and sealing of the slot.

[0028] Further, a filter screen is attached to the top surface of the packaging shell, and the filter screen is used to prevent water, oil and dust particles from entering.

[0029] 3. A packaging structure of the above-mentioned airflow sensor test structure, the airflow sensor is fixed on a packaging substrate, an external packaging shell is arranged outside the airflow sensor, the slot is filled with silica gel, and the silica gel is used for plugging and sealing the slot; a filter screen is attached to the top surface of the packaging shell, and the filter screen is used for preventing water, oil and dust particles from entering.

[0030] Advantages:

[0031] The airflow sensor wafer comprises a plurality of chip units, each of which is composed of a substrate, a diaphragm and a back plate arranged in layers, the substrate has a back cavity penetrating in the thickness direction thereof, a slot is arranged on the top of the bottom of the substrate, the slot penetrates the substrate and the back cavity, and the slot is used to establish a continuous air flow path between the back cavity and the space outside the airflow sensor. After the UV film is attached to the back of the airflow sensor, since a continuous air flow path is established between the back cavity of the airflow sensor and the space outside the airflow sensor, the air pressure on the upper and lower sides of the diaphragm is balanced in the initial state of the CP test of the airflow sensor, the C0 in this state is the initial capacitance value of the sensor without bearing the air flow pressure, and the test system detects the wrong capacitance change value in the subsequent CP test. The airflow sensor can be tested without tearing off the UV film, the demand of testing each die on the wafer can be met, the production cost is not increased, and the risk of wafer fragmentation is effectively avoided.

[0032] Each chip unit is transversely provided with one slot, the slots of the chip units in each row of chip units are communicated with each other and are on the same straight line; or each chip unit is provided with two slots, a first slot is transversely arranged, and a second slot is longitudinally arranged; the first slots of the chip units in each row of chip units are communicated with each other and are on the same straight line; the second slots of the chip units in each column of chip units are communicated with each other and are on the same straight line, and the first slot and the second slot are perpendicular to each other. The test requirement of the airflow sensor is further ensured by the above-mentioned slot structure, and the airflow sensor is easy to process.

[0033] The packaging structure of the above-mentioned airflow sensor test structure, the airflow sensor is fixed on a packaging substrate, an external packaging shell is arranged outside the airflow sensor, the slot is filled with silica gel, and the silica gel is used for plugging and sealing the slot; a filter screen is attached to the top surface of the packaging shell, and the filter screen is used for preventing water, oil and dust particles from entering. By the above-mentioned packaging structure, it can be ensured that after the sensor is packaged, there is no connected air flow path leakage in the air on the upper and lower sides of the diaphragm in the circuit, thereby ensuring the sensitivity of the airflow sensor to the change of the air flow, and preventing the foreign pollutants entering from the slot structure from diffusing into the gap layer between the diaphragm and the back plate, thereby reducing the failure rate of the airflow sensor in the FT test and use. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other implementation methods can be obtained based on these drawings without creative effort.

[0035] Figure 1A This is a cross-sectional view of an existing conventional MEMS airflow sensor;

[0036] Figure 1B This is a bottom view of an existing conventional MEMS airflow sensor;

[0037] Figure 1C This is a top view of an existing conventional MEMS airflow sensor;

[0038] Figure 2A This is a cross-sectional view of multiple adjacent dies in a typical MEMS airflow sensor wafer after a UV film has been applied.

[0039] Figure 2B This is a bottom view of multiple adjacent dies in a localized area after a UV film has been applied to a conventional MEMS airflow sensor wafer.

[0040] Figure 3A This is a cross-sectional view of the MEMS airflow sensor according to Embodiment 1 of the present invention;

[0041] Figure 3B This is a bottom view of the MEMS airflow sensor according to Embodiment 1 of the present invention;

[0042] Figure 4A This is a cross-sectional view of multiple adjacent dies in a portion of the MEMS airflow sensor wafer after a UV film has been applied to it, according to Embodiment 1 of the present invention.

[0043] Figure 4B This is a bottom view of a portion of multiple adjacent dies after a UV film has been applied to the wafer of the MEMS airflow sensor according to Embodiment 1 of the present invention.

[0044] Figure 5A This is a cross-sectional view of the MEMS airflow sensor according to Embodiment 2 of the present invention;

[0045] Figure 5B This is a bottom view of the MEMS airflow sensor according to Embodiment 2 of the present invention;

[0046] Figure 6A This is a partial cross-sectional view of multiple adjacent dies after a UV film has been applied to the wafer of the MEMS airflow sensor according to Embodiment 2 of the present invention.

[0047] Figure 6B is the bottom view of a plurality of adjacent dies of the MEMS airflow sensor wafer of embodiment two after the UV film is attached to the MEMS airflow sensor wafer;

[0048] Figure 7 is a cross-sectional view of the MEMS airflow sensor package structure. DETAILED DESCRIPTION

[0049] The present application will be described in detail below with reference to the various embodiments shown in the drawings, but it should be noted that these embodiments are not limiting of the present application, and equivalent transformations or substitutions of function, method, or structure made by those of ordinary skill in the art based on these embodiments are within the scope of the present application.

[0050] As Figure 1A , 1B , 1C, the existing ordinary MEMS airflow sensor includes a substrate 1, a diaphragm 2, and a fixed backplate arranged in layers. The fixed backplate is composed of an insulating layer 31 and a conductive layer 32, and the substrate has a back cavity 4 that penetrates in the thickness direction thereof. The diaphragm 2 has a vibration sensitive region, and a gap layer is arranged between the vibration sensitive region and the fixed backplate, forming a variable capacitance between the diaphragm and the fixed backplate. A plurality of densely arranged release holes 72, 71 are arranged on the fixed backplate in a region directly above the vibration sensitive region of the diaphragm, the release hole 72 is within the coverage range of the conductive layer 32 in the fixed backplate, and the release hole 71 is outside the coverage range of the conductive layer 32 in the fixed backplate. The release hole is in communication with the gap layer. The diaphragm and the substrate have a first support body 5, and the fixed backplate and the diaphragm have a second support body 6.

[0051] As Figure 2A , 2B shown, as described in the foregoing background section, after the UV film 9 is attached to the back of the ordinary MEMS airflow sensor wafer, the UV film 9 and the back cavity 4, diaphragm 2 form a closed cavity 41, and the sealed air therein will expand and contract with heat, and the gas pressure and the atmospheric pressure outside the wafer cannot remain consistent, i.e., the air pressure on the upper and lower surfaces of the diaphragm cannot be balanced.

[0052] Embodiment one

[0053] Airflow sensor test structure

[0054] As Figure 4A , Figure 4B shown, the airflow sensor wafer includes a plurality of chip units (dies), and a scribe groove 8 is arranged between each adjacent chip unit, and the UV film 9 is attached to the back of the airflow sensor wafer. As Figure 3A , 3BAs shown, each chip unit is composed of a substrate 1, a diaphragm 2 and a back plate, the substrate 1 has a back cavity 42 through its thickness direction, the diaphragm 2 has a vibration sensitive area, a gap layer is arranged between the vibration sensitive area and the fixed back plate, and a variable capacitor is formed between the diaphragm and the fixed back plate. On the fixed back plate, a plurality of densely arranged release holes 72, 71 are arranged in the area directly above the vibration sensitive area of the diaphragm, the release hole 72 is within the coverage range of the conductive layer 32 in the fixed back plate, and the release hole 71 is outside the coverage range of the conductive layer 32 in the fixed back plate. The release hole is in communication with the gap layer. The diaphragm and the substrate have a first support body 5, and the fixed back plate and the diaphragm have a second support body 6. The above is the prior art.

[0055] As shown in Figure 3A , 3B , as shown in Figure 4A , Figure 4B , a slot 10 is arranged on the bottom surface of the substrate 1, the slot 10 passes through the substrate 1 and the back cavity 42, and the slot 10 is located in the lower part of the substrate 1. The slot 10 is used to establish a continuous air flow path between the back cavity 42 and the space outside the airflow sensor, that is, the slot 10 passes through the back cavity of each chip unit and the outermost edge of the airflow sensor wafer. As shown in Figure 4A , Figure 4B , each chip unit is transversely provided with one slot 10, and the slots of each chip unit in each row of chip units are in communication with each other and are in the same straight line. As shown in Figure 4A , a scribe groove 8 is arranged between each adjacent chip unit, and the slot 10 passes through the scribe groove 8.

[0056] After the UV film 9 is attached to the back of the airflow sensor, a continuous air flow path is established between the back cavity 42 of the airflow sensor and the space outside the airflow sensor, so that the air pressure on the upper and lower surfaces of the diaphragm is balanced in the initial state of the CP test of the airflow sensor, and the C0 in this state is the initial capacitance value of the sensor in the state of not bearing the airflow pressure, preventing the test system from detecting the wrong capacitance change value in the subsequent CP test. The present application can perform testing without tearing off the UV film 9, can meet the needs of testing each die on the wafer, will not increase the production cost, and can effectively avoid the risk of wafer cracking.

[0057] Example two

[0058] Airflow sensor test structure

[0059] As shown in Figure 5A , 5B , as shown in Figure 6A , Figure 6BAs shown, the difference between Embodiment 2 and Embodiment 1 is that each chip unit has two slots 10: a first slot in the horizontal direction and a second slot in the vertical direction. The first slots of each chip unit in each row are interconnected and on the same straight line. The second slots of each chip unit in each column are interconnected and on the same straight line. The first and second slots are perpendicular to each other. A dicing groove 8 is provided between each adjacent chip unit, with the first slot passing through the dicing groove between adjacent chip units in each row and the second slot passing through the dicing groove between adjacent chip units in each column. The remaining structure and working principle of Embodiment 2 are the same as those of Embodiment 1.

[0060] Example 3

[0061] A packaging method for the above-mentioned airflow sensor test structure

[0062] like Figure 7 As shown, the airflow sensor chip is fixed to the packaging substrate 12 using silicone. A packaging shell 13 is installed outside the airflow sensor chip, and silicone 101 is used to fill the slots, achieving a sealing effect. A filter 11 is attached to the top surface of the packaging shell 13, which is used for waterproofing, oil resistance, and preventing dust particles from entering. This packaging method ensures that after the sensor is packaged, there are no airflow paths between the upper and lower surfaces of the diaphragm inside the circuit, thus guaranteeing the sensitivity of the airflow sensor in sensing airflow changes. It also prevents external contaminants entering through the slotted structure from diffusing into the gap between the diaphragm and the backplate, thereby reducing the failure rate of the airflow sensor during FT testing and use.

[0063] Example 4

[0064] A packaging structure for the above-mentioned airflow sensor test structure

[0065] like Figure 7 As shown, the airflow sensor is fixed on the encapsulation substrate 12, and the airflow sensor is provided with an encapsulation shell 13. The slot is filled with silicone 101, which is used to seal the slot. A filter screen 11 is attached to the top surface of the encapsulation shell 13. The filter screen 11 is used to prevent water, oil and dust particles from entering.

[0066] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A test structure for an airflow sensor, wherein the airflow sensor wafer comprises multiple chip units, each chip unit consisting of a substrate (1), a diaphragm (2), and a backplate stacked together, wherein the substrate (1) has a cavity (42) extending through its thickness direction, characterized in that: A slot (10) is provided on the bottom of the base (1), the slot (10) passes through the base (1) and the back cavity (42), and the slot (10) is used to establish a continuous airflow path in the back cavity (42) and the space outside the airflow sensor.

2. The airflow sensor test structure according to claim 1, characterized in that: Each chip unit has one slot (10) in the horizontal direction. The slots of each chip unit in each row are interconnected and are on the same straight line.

3. The airflow sensor test structure according to claim 2, characterized in that: A dicing groove (8) is provided between each adjacent chip unit, and the slot (10) passes through the dicing groove (8).

4. The airflow sensor test structure according to claim 1, characterized in that: Each chip unit has two slots (10), with a first slot in the horizontal direction and a second slot in the vertical direction; the first slots of each chip unit in each row are interconnected and on the same straight line; the second slots of each chip unit in each column are interconnected and on the same straight line.

5. The airflow sensor test structure according to claim 4, characterized in that: The first slot and the second slot are perpendicular to each other.

6. The airflow sensor test structure according to claim 4, characterized in that: A dicing groove (8) is provided between each adjacent chip unit. The first groove passes through the dicing groove between each row of adjacent chip units, and the second groove passes through the dicing groove between each column of adjacent chip units.

7. The airflow sensor test structure according to any one of claims 1 to 6, characterized in that: The slot (10) is located at the lower part of the base (1).

8. A packaging method for the airflow sensor test structure according to any one of claims 1 to 7, comprising fixing the airflow sensor chip onto a packaging substrate using silicone, and mounting a packaging shell on the outside of the airflow sensor chip, characterized in that: The groove (10) is filled with silicone to achieve a blockage and seal of the groove (10).

9. The packaging method according to claim 8, characterized in that: A filter screen is attached to the top surface of the encapsulation shell. The filter screen is used to prevent water, oil, and dust particles from entering.

10. A packaging structure for a gas flow sensor test structure according to any one of claims 1 to 7, wherein the gas flow sensor is fixed on a packaging substrate, and a packaging shell is provided outside the gas flow sensor, characterized in that: The slot is filled with silicone, which is used to seal the slot. A filter screen is attached to the top surface of the encapsulation shell, which is used to prevent water, oil, and dust particles from entering.

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