A packaging structure for an intake manifold pressure sensor

Abstract

The utility model provides a kind of packaging structure for intake manifold pressure sensor.It is related to pressure sensor technical field, especially high-precision MAP sensor for engine.The existing packaging due to the difference of thermal expansion coefficient, resulting in thermal mechanical stress is directly transmitted to sensitive MEMS sensor chip, causes the technical problem of measurement signal drift, precision decline.Solution: between SSOP8 lead frame and MEMS bare chip, add a ceramic sheet, the ceramic sheet is fixed on the frame bottom by first silicone glue layer, MEMS bare chip is fixed on ceramic sheet by second silicone glue layer, and constitute the composite structure of "rigid and flexible".Beneficial effect is: ceramic sheet provides stable rigid reference, ensure chip flatness;Double-layer silicone glue effectively absorbs and isolates thermal stress, significantly improves the measurement accuracy, linearity and stability of sensor in full temperature range, while improving the process of chip mounting and wire bonding.

Description

Technical Field

[0001] This utility model relates to the field of pressure sensor structure technology, and in particular to a packaging structure for an intake manifold pressure sensor. Background Technology

[0002] The Manifold Absolute Pressure Sensor (MAP sensor) is one of the core sensing components in the electronic control system of an automotive engine. Its function is to accurately detect the absolute pressure value within the intake manifold and convert it into an electrical signal, which is then transmitted to the engine control unit (ECU). This provides the ECU with crucial information for accurately calculating key parameters such as fuel injection quantity and controlling ignition timing. Therefore, the measurement accuracy of the MAP sensor directly affects the engine's power, fuel economy, and emissions cleanliness.

[0003] Currently, most mainstream MAP sensors on the market employ a structure where a MEMS (Micro-Electro-Mechanical Systems) pressure sensing chip is directly mounted within a lead frame (such as an SSOP8 package). This MEMS chip typically operates based on the Wheatstone bridge principle and is extremely sensitive to mechanical stress. However, existing packaging structures have inherent drawbacks: the coefficients of thermal expansion of the lead frame and the epoxy molding compound (EMC) encapsulating the chip differ significantly from those of the MEMS chip material. When the sensor operates in the drastically changing high and low temperature environment of an engine compartment, this difference leads to significant thermomechanical stress within the package. This stress is directly transmitted to the sensitive MEMS chip, causing a drift in the resistance value of the Wheatstone bridge that is not caused by pressure factors, thus introducing errors into the output signal and severely limiting further improvements in sensor accuracy. Existing technologies face the following main technical bottlenecks:

[0004] 1. Limited accuracy: Due to the aforementioned packaging stress, the accuracy of conventional MAP sensors mostly hovers between 1% and 2% FS (full scale), which is difficult to meet the control accuracy requirements of next-generation high-efficiency and clean engines.

[0005] 2. High cost challenge: To achieve higher accuracy (such as 0.5% to 1% FS), special materials or extremely complex compensation algorithms and manufacturing processes are often required, which significantly increases the manufacturing cost of sensors and makes it difficult to promote and apply them on a large scale.

[0006] 3. Poor processability: Insufficient flatness of the lead frame itself and the EMC material after molding will lead to a decrease in the yield and efficiency (UPH) of the die bond and wire bond processes, affecting production stability and product consistency.

[0007] Therefore, there is an urgent need for an innovative chip packaging structure that can effectively isolate or absorb thermomechanical stress at the physical level, thereby improving the measurement accuracy of sensors while taking into account the feasibility and economy of manufacturing. Utility Model Content

[0008] The purpose of this invention is to overcome the problems in the prior art and provide a packaging structure for an intake manifold pressure sensor.

[0009] The core technical idea of ​​this invention lies in constructing a "rigid-flexible" composite packaging structure by embedding a ceramic substrate between the MEMS sensor chip and the lead frame, and bonding them together using two layers of silicone grease. This structure utilizes the excellent dimensional stability of ceramics to provide a flat and robust support reference for the chip, while the flexibility of the silicone grease layer absorbs and isolates thermomechanical stress caused by temperature changes, thereby significantly reducing the measurement error of the sensing signal. Ultimately, while ensuring manufacturability, it achieves a fundamental improvement in sensor accuracy and reliability.

[0010] To achieve the above-mentioned utility model objectives, the present utility model adopts the following technical solution: a packaging structure for an intake manifold pressure sensor, including an SSOP8 lead frame housing and a MEMS die, and also including a ceramic sheet. The ceramic sheet is fixed to the bottom of the SSOP8 lead frame housing by a first silicone grease layer, and the MEMS die is fixed to the ceramic sheet by a second silicone grease layer.

[0011] Furthermore, the ceramic sheet has length and width dimensions ranging from 1.5mm × 1.5mm to 2.0mm × 2.0mm. This size setting ensures that the ceramic sheet can fully cover and support the MEMS die, providing it with a stable reference plane, while avoiding interference with the internal space of the lead frame due to excessive size, thus ensuring the feasibility and reliability of the packaging structure.

[0012] Furthermore, the thickness of the ceramic sheet ranges from 0.2 mm to 0.6 mm. This thickness range allows the ceramic sheet to possess sufficient rigidity and strength to resist deformation while also fitting into the limited internal space of the SSOP8 lead frame housing, thereby achieving miniaturization of the package while ensuring structural stability.

[0013] Furthermore, the thickness of both the first and second silicone grease adhesive layers is between 10 μm and 30 μm. Silicone grease adhesive layers within this thickness range can form an effective flexible buffer zone, sufficient to absorb and isolate stress caused by mismatches in the thermal expansion coefficients of the materials, while avoiding excessive thickness that could affect the overall stability and thermal conductivity of the structure.

[0014] Furthermore, the bottom area of ​​the ceramic sheet is smaller than the internal mounting surface size of the SSOP8 leadframe housing, but larger than the bottom surface size of the MEMS die. The bottom dimensions of the SSOP8 leadframe housing are 2.53mm × 4.3mm, and the dimensions of the MEMS die are 1.0mm × 1.0mm. This dimensional relationship ensures that the ceramic sheet can be smoothly assembled into the leadframe and fully support the MEMS die, thus providing an excellent flatness foundation for chip mounting and wire bonding processes, effectively improving production yield and efficiency.

[0015] Furthermore, the MEMS die is a Wheatstone bridge pressure sensor chip. This chip is extremely sensitive to mechanical stress. The packaging structure of this invention, through the combination of a ceramic sheet and silicone adhesive, creates a stable, low-stress working environment for it, directly solving the core problem of output signal drift caused by stress interference in the Wheatstone bridge, thereby significantly improving the measurement accuracy of the sensor.

[0016] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0017] 1. This invention brings significant benefits by introducing a "rigid-flexible" structure combining a ceramic sheet and a silicone grease layer. The core improvement lies in utilizing the excellent thermal stability and mechanical strength of ceramic materials to provide a near-ideal working reference surface for the stress-sensitive MEMS Wheatstone bridge chip. Simultaneously, the flexible connection formed by the two layers of silicone grease effectively absorbs and isolates the thermomechanical stress from the lead frame and epoxy molding compound caused by drastic temperature changes. This fundamentally reduces errors introduced by non-pressure signals from a physical structural perspective, ensuring that the sensor maintains excellent measurement linearity and accuracy stability even under harsh operating conditions of alternating high and low temperatures.

[0018] 2. This packaging structure not only improves product performance but also optimizes manufacturing processes and long-term reliability. The extremely high flatness of the ceramic sheet itself provides an excellent operating platform for subsequent chip mounting and wire bonding processes, significantly reducing process difficulty and equipment alarm rates, thereby improving production efficiency and first-pass yield. Furthermore, because the ceramic sheet maintains shape and performance stability under long-term high-pressure, high-speed gas media, and corrosive environments, this structure also greatly enhances the overall mechanical robustness and lifespan of the sensor, providing a solid hardware foundation for achieving high-performance, high-precision pressure sensing at a cost-effective price. Attached Figure Description

[0019] The accompanying drawings are provided to further understand the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation thereof.

[0020] Figure 1This is a schematic diagram of the ceramic sheet assembly structure of this utility model;

[0021] Figure 2 This is a schematic diagram of the newly added ceramic sheet structure in this utility model;

[0022] Figure 3 This is a schematic diagram of the assembly of the MEMS bare die in this utility model;

[0023] Figure 4 This is a schematic diagram of the exploded structure of this utility model.

[0024] The attached figures are labeled as follows: 1. SSOP8 lead frame housing; 2. Ceramic sheet; 3. MEMS die; 4. Gold wire; 5. Top cover; 6. First silicone grease layer; 7. Second silicone grease layer. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described herein are only for explaining this utility model and are not intended to limit it.

[0026] Example

[0027] The core of this invention lies in providing a high-precision chip packaging structure for intake manifold pressure sensors (MAP sensors). This structure aims to fundamentally solve the industry problem of decreased sensor measurement accuracy due to thermomechanical stress in traditional packaging.

[0028] I. Structural Composition

[0029] Please see Figures 1 to 4 The packaging structure described in this utility model mainly consists of the following components: SSOP8 lead frame housing 1, ceramic sheet 2, MEMS bare die 3, gold wire 4, top cover 5, first silicone grease adhesive layer 6, and second silicone grease adhesive layer 7.

[0030] SSOP8 leadframe housing 1 and top cover 5: This is the main structure of the package, made of metal, which supports internal components, provides external pins, and offers physical protection. It forms an internal cavity.

[0031] Ceramic sheet 2: This is one of the core innovative components of this utility model. It is a precisely sized square ceramic sheet, preferably made of ceramic materials such as alumina, which have high hardness, high thermal conductivity and extremely low coefficient of thermal expansion.

[0032] MEMS die 3: This refers to the microelectromechanical system pressure sensing chip, which is the core of the sensor's functionality. In this embodiment, the die is a piezoresistive chip operating based on the Wheatstone bridge principle.

[0033] Gold wire 4: Metal lead used to achieve electrical connection, usually gold wire, connecting the bare die pad to the lead frame pad. The advantage of using gold wire is that it is easy to bond with the pad and resistant to harsh media.

[0034] First silicone grease adhesive layer 6 and second silicone grease adhesive layer 7: These are another core innovative component of this utility model. They are flexible thermally conductive adhesive layers coated on the connection interface.

[0035] The spatial layout and connection relationships of each component are as follows:

[0036] Underlying foundation: The SSOP8 lead frame housing 1 forms the base of the entire structure.

[0037] First connection: At the bottom of the inner cavity of the housing 1, the ceramic sheet 2 is bonded and fixed by a first layer of silicone grease 6. The ceramic sheet 2 is flatly attached to the bottom of the housing 1, and its lower surface is bonded to the housing 1 by the silicone grease 6.

[0038] Second connection: The MEMS die 3 is bonded and fixed to the upper surface of the ceramic sheet 2 by a second silicone grease adhesive layer 7. Therefore, the MEMS die 3 is not directly mounted on the lead frame, but is supported on the ceramic sheet 2.

[0039] Electrical connection: The electrode pads on the MEMS die 3 are electrically interconnected with the corresponding pin pads on the SSOP8 lead frame housing 1 through gold wires 4, thereby leading out the signal.

[0040] Final packaging: After the internal components are assembled and wire bonded, the SSOP8 lead frame cover 5 or epoxy molding compound EMC is used for potting and encapsulation to form a complete integrated structure.

[0041] III. Functions of Each Component and the Technical Problems Solved

[0042] 1. The function of ceramic plate 2:

[0043] Providing a rigid reference: The excellent dimensional stability of the ceramic material ensures that it hardly deforms under different temperature conditions, thus providing an extremely flat and stable mechanical mounting reference for the MEMS die. This directly solves the problem of inherent deformation of sensor chips caused by EMC or unevenness of the frame substrate or thermal expansion and contraction in traditional packaging.

[0044] Resistance to external deformation: Its high hardness can resist mechanical stress and long-term pressure load from the outside of the package, maintain the geometric integrity of the internal structure, and ensure the long-term stability of the sensor.

[0045] 2. The functions of the first silicone grease layer 6 and the second silicone grease layer 7:

[0046] Forming a stress buffer zone: The silicone adhesive has a certain degree of elasticity and flexibility after curing. The first adhesive layer 6 is located between the ceramic sheet 2 and the lead frame 1, and is used to absorb and buffer thermal stress from the lead frame and external EMC materials. The second adhesive layer 7 is located between the ceramic sheet 2 and the MEMS die 3, and is used to further isolate any residual stress that may be transmitted, and to flexibly compensate for the thermal expansion of the chip itself.

[0047] Achieving thermal stress decoupling: These two flexible connections together form a "stress isolation system," successfully decoupling the temperature-sensitive MEMS die 3 from the package body, which is susceptible to temperature-induced deformation. This solves the core technical problem in existing technologies where thermomechanical stress is directly transmitted to the Wheatstone bridge, causing bridge resistance drift and measurement errors.

[0048] 3. Effect of MEMS die 3 on the overall structure:

[0049] Through the combined effect of the above structures, the MEMS die 3 can operate in a low-stress, highly stable local microenvironment. The resistance change of its Wheatstone bridge is caused only by the actual intake manifold pressure, greatly reducing signal interference caused by ambient temperature variations. The ultimate result is a significant improvement in the sensor's measurement accuracy, linearity, and repeatability across the entire temperature range.

[0050] The working process of the packaging structure of this utility model is as follows:

[0051] When the MAP sensor is mounted on the engine intake manifold, the absolute pressure within the intake manifold acts on the sensing area of ​​MEMS die 3 (not shown in the diagram) through a pressure inlet on the package. This pressure causes deformation of the piezoresistor in the Wheatstone bridge on MEMS die 3, altering its resistance and disrupting the bridge balance. This results in a millivolt-level differential voltage signal proportional to the pressure. This signal is transmitted to the external engine control unit (ECU) via gold wire 4 and the lead frame pins.

[0052] Throughout the operation, the drastic temperature changes within the engine compartment cause thermal expansion and contraction of the SSOP8 lead frame and epoxy molding compound, generating significant internal stress. However, this stress is effectively absorbed and buffered by the first silicone grease layer 6. Even if a small amount of stress is transmitted to the ceramic sheet 2, its rigidity prevents deformation. Finally, any remaining trace amounts of residual stress are further isolated by the second silicone grease layer 7. Therefore, the stress transmitted to the MEMS die 3 is minimized, ensuring the authenticity and accuracy of the Wheatstone bridge output signal and achieving high-precision pressure measurement.

[0053] In summary, this utility model, through its ingenious structural design that combines rigidity and flexibility, achieves the fundamental goal of improving sensor accuracy in a simple and reliable physical way, while also possessing good manufacturability and long-term reliability.

[0054] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A packaging structure for an intake manifold pressure sensor, comprising an SSOP8 lead frame housing (1) and a MEMS die (3), characterized in that: It also includes a ceramic sheet (2), which is fixed to the bottom of the SSOP8 lead frame housing (1) by a first silicone grease adhesive layer (6), and the MEMS die (3) is fixed to the ceramic sheet (2) by a second silicone grease adhesive layer (7).

2. The packaging structure for an intake manifold pressure sensor according to claim 1, characterized in that: The length and width of the ceramic sheet (2) are both in the range of 1.5mm×1.5mm to 2.0mm×2.0mm.

3. The packaging structure for an intake manifold pressure sensor according to claim 2, characterized in that: The thickness of the ceramic sheet (2) ranges from 0.2 mm to 0.6 mm.

4. The packaging structure for an intake manifold pressure sensor according to claim 1, characterized in that: The thickness of the first silicone grease layer (6) and the second silicone grease layer (7) is 10 μm to 30 μm.

5. The packaging structure for an intake manifold pressure sensor according to claim 1, characterized in that: The bottom area of ​​the ceramic sheet (2) is smaller than the internal mounting surface size of the SSOP8 lead frame housing (1) and larger than the bottom surface size of the MEMS die (3).

6. The packaging structure for an intake manifold pressure sensor according to claim 1, characterized in that: The MEMS die (3) is a Wheatstone bridge pressure sensor chip.

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