Flow sensor packaging structure

Abstract

The utility model relates to a flow sensor packaging structure, which belongs to the technical field of micro electro mechanical sensors and comprises a substrate and a chip, a first bonding pad is arranged on the upper surface of the substrate, a second bonding pad is arranged at the top of the chip, and the first bonding pad and the second bonding pad are electrically connected through a wire. The upper surface of the substrate is concave inwards to form a chip mounting groove, the chip is arranged in the chip mounting groove, and the upper surface of the chip and the upper surface of the substrate are located on the same plane; according to the utility model, the chip is arranged in the chip mounting groove on the substrate, so that the upper surface of the chip and the upper surface of the substrate are positioned on the same plane, the height difference between the chip and the substrate is eliminated, and the accuracy and the stability of measuring the flow velocity of fluid are improved; the chip and the substrate are bonded and sealed through the sealant, so that the bottom of the chip does not need to be connected with the substrate through glue, and inclination of the upper surface of the chip caused by uneven glue at the bottom of the chip and thermal expansion and cold contraction of the glue is prevented.

Description

Technical Field

[0001] The utility model relates to a flow sensor packaging structure, belonging to the technical field of micro-electromechanical sensors. Background Art

[0002] MEMS (Micro Electro Mechanical Systems) flow sensor is a fluid measurement method based on the principle of heat exchange. Due to its unique advantages such as small size, low power consumption, wide range ratio, high sensitivity, and ultra-low starting flow, MEMS flow sensor is widely used in many fields such as industry, medical treatment, semiconductor, and new energy. The packaging method of MEMS flow sensor has an important impact on the performance and reliability of the product. The packaging structure ensures that the medium flowing through the sensor is laminar flow and ensures that the sensor is not damaged in the application of sudden pressure changes.

[0003] The Chinese utility model patent with announcement number CN216038651U discloses a sensor structure and an electronic device, the sensor structure comprising: a silicon substrate; a film structure arranged on one side of the silicon substrate, wherein a cavity is arranged on the side of the silicon substrate away from the film structure; a packaging substrate, the packaging substrate is arranged on the side of the silicon substrate away from the film structure; a connecting layer, arranged between the silicon substrate and the packaging substrate, a first gap is formed in the connecting layer, and the first gap is used to connect the cavity with the environment outside the sensor structure. The sensor structure provided by the embodiment of the application can simplify the process, improve production efficiency and reduce costs, but still has the following shortcomings:

[0004] 1. After the chip is bonded to the substrate, there is a certain height difference between the substrate and the chip surface. When the fluid flows over the chip surface, especially at a high flow rate, obvious eddy currents are generated on the chip surface, thus affecting the accurate measurement and stability of the fluid flow rate;

[0005] 2. The flow sensor chip is connected to the substrate by glue packaging, which may easily cause the chip surface to tilt. When the fluid medium flows through the chip surface, it is easy to cause medium fluctuations and affect the measurement accuracy. Moreover, due to the small base area of ​​the sensor chip and the use of glue packaging, the glue is easy to overflow into the thermal isolation cavity of the sensor, which will cause the zero-point output of the sensor to be too large.

[0006] Therefore, there is a need for a flow sensor packaging structure to achieve a flat chip surface and improve the accuracy and stability of measuring fluid flow rate. Utility Model Content

[0007] The technical problem to be solved by the utility model is: in order to overcome the deficiencies of the prior art, a flow sensor packaging structure is provided which can realize the flatness of the chip surface and improve the accuracy and stability of measuring the flow velocity of a fluid.

[0008] The technical solution adopted by the utility model to solve the above problems is: a flow sensor packaging structure, including a substrate and a chip, the upper surface of the substrate is provided with a first pad, the upper surface of the chip is provided with a second pad, the first pad and the second pad are electrically connected through a wire, the upper surface of the substrate is concave to form a chip loading groove, the chip is arranged in the chip loading groove, and the upper surface of the chip and the upper surface of the substrate are in the same plane;

[0009] A copper coating is provided at the bottom of the chip loading slot, the lower surface of the chip is in contact with the copper coating, and the front, back, left, and right sides of the chip are respectively connected to the front, back, left, and right side walls of the chip loading slot through sealant;

[0010] A pressure balance hole is provided on the upper surface of the copper cladding layer, and the pressure balance hole extends upward to the lower surface of the substrate;

[0011] The chip includes a dielectric layer and a substrate distributed in sequence from top to bottom, a thermal isolation cavity is provided on the lower surface of the substrate, the thermal isolation cavity extends to the upper surface of the substrate, the thermal isolation cavity is directly connected to the pressure balance hole, the position of the dielectric layer directly opposite the thermal isolation cavity is a suspended sensitive film area, and three thermistors are provided in the suspended sensitive film area.

[0012] Preferably, the first pad, the second pad and the wire are coated with a coating adhesive.

[0013] Preferably, a gap is provided between the suspended sensitive film area and the coating adhesive.

[0014] Preferably, the substrate is made of FR4 or ceramic.

[0015] Preferably, the length, width and height of the chip loading slot are respectively 0.15mm, 0.15mm and 0.1mm larger than the length, width and height of the chip.

[0016] Preferably, the copper cladding layer has a thickness of 48um to 52um, with a specific value of 50um.

[0017] Preferably, the conductive wire is a gold wire or an aluminum wire.

[0018] Preferably, two groups of first silk screen layers are provided on the upper surface of the substrate, and the two groups of first silk screen layers are arranged symmetrically about the film loading slot. Each group of first silk screen layers is provided with two, and the two first silk screen layers in the same group are respectively arranged on the left and right sides of the suspended sensitive film area.

[0019] Preferably, an annular second silk-screen layer is provided on the upper surface of the substrate, and the coating glue is placed in the annular hole of the second silk-screen layer.

[0020] Preferably, the thickness of the sealant is 68um to 72um, with a specific value of 70um.

[0021] Compared with the prior art, the advantages of the utility model are:

[0022] 1. By placing the chip in the chip loading slot on the substrate, the upper surface of the chip and the upper surface of the substrate are in the same plane, eliminating the height difference between the chip and the substrate, and improving the accuracy and stability of measuring the fluid flow rate;

[0023] 2. The chip and substrate are bonded and sealed with sealant, so that the bottom of the chip does not need to be connected to the substrate with glue, to prevent the glue on the bottom of the chip from being uneven and the thermal expansion and contraction of the glue from causing the upper surface of the chip to tilt, thereby avoiding changes in the fluid medium above the suspended sensitive film area and affecting the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a structural schematic diagram of a flow sensor packaging structure of the utility model;

[0025] Figure 2 This is a top view of a flow sensor packaging structure of the utility model;

[0026] Figure 3 This is the relationship diagram between the sensor output and the set air flow rate.

[0027] in:

[0028] Substrate 1, chip 2, chip loading slot 3, pressure balance hole 4, first solder pad 5, second solder pad 6, wire 7, copper cladding layer 8, sealant 9, coating glue 10, first silk screen layer 11, second silk screen layer 12;

[0029] Dielectric layer 201 , substrate 202 , thermal isolation cavity 203 , suspended sensitive film region 204 , thermistor 205 . DETAILED DESCRIPTION

[0030] like Figure 1-3 As shown, a flow sensor packaging structure in this embodiment includes a substrate 1 and a chip 2, the upper surface of the substrate 1 is concave to form a chip loading slot 3, the chip 2 is arranged in the chip loading slot 3, the upper surface of the substrate 1 is provided with a first pad 5, the upper surface of the chip 2 is provided with a second pad 6, the first pad 5 and the second pad 6 are electrically connected through a wire 7, the wire 7 is a gold wire or an aluminum wire, and the upper surface of the chip 2 and the upper surface of the substrate 1 are in the same plane;

[0031] The substrate 1 is made of FR4 or ceramic. FR4 is a common composite material and is widely used in the electronic and electrical industry. FR4 is a thermosetting plastic composite material composed of glass fiber and epoxy resin, and has excellent insulation, mechanical strength and heat resistance.

[0032] The first pad 5, the second pad 6 and the wire 7 are coated by a coating adhesive 10;

[0033] A copper coating 8 is provided at the bottom of the chip loading slot 3, and the lower surface of the chip 2 is bonded to the copper coating 8. The thickness of the copper coating 8 is 48um to 52um, and the specific value is 50um. The front, back, left, and right sides of the chip 2 are respectively connected to the front, back, left, and right side walls of the chip loading slot 3 through a sealant 9.

[0034] A pressure balance hole 4 is provided on the upper surface of the copper cladding layer 8, and the pressure balance hole 4 extends upward to the lower surface of the substrate 1;

[0035] The length, width and height of the chip loading slot 3 are respectively 0.15mm, 0.15mm and 0.1mm larger than those of the chip 2;

[0036] The chip 2 includes a dielectric layer 201 and a substrate 202 which are sequentially arranged from top to bottom. A thermal isolation cavity 203 is arranged on the lower surface of the substrate 202. The thermal isolation cavity 203 extends to the upper surface of the substrate 202. The thermal isolation cavity 203 is directly connected to the pressure balance hole 4. The position of the dielectric layer 201 directly opposite the thermal isolation cavity 203 is a suspended sensitive film area 204. Three thermistors 205 are arranged in the suspended sensitive film area 204. Here, the pressure balance hole 4 is used to protect the suspended sensitive film area 204 to prevent the suspended sensitive film area 204 from being damaged due to a sudden pressure change.

[0037] A gap is provided between the suspended sensitive film area 204 and the coating adhesive 10;

[0038] Two groups of first silk-screen layers 11 are arranged on the upper surface of the substrate 1, and the two groups of first silk-screen layers 11 are arranged symmetrically with respect to the chip loading slot 3. Each group of first silk-screen layers 11 is provided with two, and the two first silk-screen layers 11 in the same group are arranged on the left and right sides of the suspended sensitive film area 204, respectively. The first silk-screen layers 11 facilitate quick alignment of the suspended sensitive film area 204 with the pressure balance hole 4 when the chip 2 is loaded;

[0039] The upper surface of the substrate 1 is provided with an annular second silk-screen layer 12, and the coating glue 10 is placed in the annular hole of the second silk-screen layer 12. The coating range of the coating glue 10 is determined by the second silk-screen layer 12 to prevent the coating glue 10 from being too large or too small in area and affecting the product yield;

[0040] The thickness of the sealant 9 is 68um to 72um, and the specific value is 70um;

[0041] The sealant 9 is epoxy glue, which has a small thermal expansion coefficient and helps to stabilize the size of the sensor package;

[0042] In summary, the chip 2 and the substrate 1 are bonded and sealed by the sealant 9, so that the bottom of the chip 2 does not need to be connected to the substrate 1 by glue, which prevents the glue on the bottom of the chip 2 from being uneven and the thermal expansion and contraction of the glue from causing the upper surface of the chip 2 to tilt, thereby avoiding the change of the fluid medium on the suspended sensitive film area 204 and affecting the measurement accuracy. Secondly, by arranging the chip 2 in the chip loading slot 3 on the substrate 1, the upper surface of the chip 2 and the upper surface of the substrate 1 are in the same plane, eliminating the height difference between the chip 2 and the substrate 1, and improving the accuracy and stability of measuring the fluid flow rate;

[0043] In addition, according to the curve of sensor output and set air flow rate, it can be concluded that this packaging structure can make the surface of chip 2 flush with the surface of substrate 1. When the fluid passes through the surface of chip 2 from the surface of substrate 1, the fluid disturbance will not be introduced due to the uneven surface and affect the measurement accuracy. It can also increase the range ratio of the sensor to more than 300:1, expanding the application scenarios of the product.

[0044] In addition to the above embodiments, the present invention also includes other implementation modes. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the protection scope of the claims of the present invention.

Claims

1. A flow sensor packaging structure, comprising a substrate (1) and a chip (2), wherein a first pad (5) is disposed on the upper surface of the substrate (1), a second pad (6) is disposed on the top of the chip (2), the first pad (5) and the second pad (6) are electrically connected via a wire (7), the upper surface of the substrate (1) is concave to form a chip loading groove (3), the chip (2) is disposed in the chip loading groove (3), the upper surface of the chip (2) and the upper surface of the substrate (1) are in the same plane, and characterized in that: A copper cladding layer (8) is provided at the bottom of the chip loading slot (3), the lower surface of the chip (2) is in contact with the copper cladding layer (8), and the front, back, left, and right sides of the chip (2) are respectively connected to the front, back, left, and right side walls of the chip loading slot (3) via a sealant (9); A pressure balance hole (4) is provided on the upper surface of the copper cladding layer (8), and the pressure balance hole (4) extends upward to the lower surface of the substrate (1); The chip (2) comprises a dielectric layer (201) and a substrate (202) which are sequentially arranged from top to bottom; a thermal isolation cavity (203) is arranged on the lower surface of the substrate (202); the thermal isolation cavity (203) extends to the upper surface of the substrate (202); the thermal isolation cavity (203) is directly connected to the pressure balance hole (4); the position of the dielectric layer (201) directly opposite the thermal isolation cavity (203) is a suspended sensitive film area (204); and three thermistors (205) are arranged in the suspended sensitive film area (204).

2. A flow sensor packaging structure according to claim 1, characterized in that: The first solder pad (5), the second solder pad (6) and the wire (7) are coated by a coating adhesive (10).

3. A flow sensor packaging structure according to claim 2, characterized in that: A gap is provided between the suspended sensitive film area (204) and the coating glue (10).

4. A flow sensor packaging structure according to claim 1, characterized in that: The substrate (1) is made of FR4 or ceramic.

5. The flow sensor packaging structure according to claim 1, characterized in that: The length, width and height of the chip loading slot (3) are respectively 0.15 mm, 0.15 mm and 0.1 mm greater than the length, width and height of the chip (2).

6. The flow sensor packaging structure according to claim 1, characterized in that: The copper cladding layer (8) has a thickness of 48 um to 52 um.

7. The flow sensor packaging structure according to claim 1, characterized in that: The conductive wire (7) is a gold wire or an aluminum wire.

8. The flow sensor packaging structure according to claim 1, characterized in that: Two groups of first silk-screen layers (11) are provided on the upper surface of the substrate (1), the two groups of first silk-screen layers (11) are arranged symmetrically front and back about the film loading slot (3), each group of first silk-screen layers (11) is provided with two, and the two first silk-screen layers (11) in the same group are respectively arranged on the left and right sides of the suspended sensitive film area (204).

9. A flow sensor packaging structure according to claim 2, characterized in that: The upper surface of the substrate (1) is provided with an annular second silk-screen layer (12), and the coating glue (10) is placed in the annular hole of the second silk-screen layer (12).

10. The flow sensor packaging structure according to claim 1, characterized in that: The thickness of the sealant (9) is 68 um to 72 um.

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