CN103148977B - Based on the passive and wireless pressure transducer had from encapsulation function of flexible base, board - Google Patents

Abstract

The invention discloses a passive wireless pressure sensor with self-encapsulation function based on a flexible substrate, which comprises an upper flexible substrate, an upper metal layer, a middle flexible substrate, a lower metal layer and a lower flexible substrate arranged in sequence from top to bottom and fixedly connected. The substrate, the middle flexible substrate is provided with electrical through holes and cavities; the upper metal layer includes a planar inductance coil and a capacitor upper plate located in the middle of the planar inductance coil, and the inner connector of the planar inductance coil is connected to the capacitor upper plate; the lower The metal layer includes the lower plate of the capacitor which is the same size as the upper plate of the capacitor and the position is opposite, and the interconnection line connected with the lower plate of the capacitor; The dielectric column is connected with the interconnection line of the lower metal layer, and the cavity of the middle flexible substrate is located between the upper pole plate of the capacitor and the lower pole plate of the capacitor. The pressure sensor has excellent performances of self-encapsulation, non-contact, high sensitivity and high quality factor. <b />

Description

Self-encapsulating passive wireless pressure sensor based on flexible substrate

technical field

The invention belongs to the technical field of sensors, and in particular relates to a passive wireless pressure sensor based on a flexible substrate and having a self-packaging function.

Background technique

Pressure sensors are widely used in many occasions. In some special applications, such as: inside the human body, food packaging and other sealed environments, pressure sensors are required to have wireless telemetry capabilities. There are currently two types of wireless telemetry pressure sensors: active telemetry and passive telemetry. Active telemetry means that the sensing system has a power source. This type of telemetry can transmit sensor signals in both directions over long distances, but the system is complex, large in size, and the battery needs to be replaced. Passive telemetry means that there is no power source in the sensing system, and signals are acquired by using inductive coupling or radio frequency (RF) reflection modulation. This telemetry method has a short signal transmission distance, but is small in size and does not need to replace batteries. In theory, it can be used indefinitely. Work. Among them, LC passive wireless pressure sensor is the most important type in passive telemetry. The LC passive wireless pressure sensor is usually an LC resonant circuit composed of a pressure-sensitive capacitor and an inductance coil. The inductance coil is the inductance element in the LC circuit and also undertakes the wireless output function of the pressure signal. When the pressure changes, the capacitance changes accordingly, which in turn affects the resonant frequency of the LC circuit, and transmits the signal through inductive coupling.

At present, LC passive wireless pressure sensors are usually composed of micro-electro-machining (hereinafter referred to as: MEMS) piezo-sensitive capacitors and inductors. The inductance can be an on-chip inductance integrated with a capacitive sensor, but it is generally difficult to obtain a high quality factor Q for this inductance, thereby limiting the overall characteristics of the device; in addition, an externally wound metal wire inductance coil can also be used. But this will increase the size of the device, and it is difficult to process in batches. In addition, MEMS pressure-sensitive capacitors also need to solve two major technical difficulties: the lead wire of the capacitor plate and the sealing of the cavity.

Contents of the invention

Technical problem: The technical problem to be solved by the present invention is to provide a passive wireless pressure sensor with self-encapsulation function based on a flexible substrate. Excellent performance of contact, high sensitivity and high quality factor.

Technical solution: In order to solve the above technical problems, the present invention adopts a passive wireless pressure sensor with self-encapsulation function based on a flexible substrate. The pressure sensor includes an upper flexible substrate, an upper metal layer, The middle flexible substrate, the lower metal layer and the lower flexible substrate are provided with electrical vias and cavities on the middle flexible substrate; the upper metal layer includes a planar inductance coil and a capacitor upper plate located in the middle of the planar inductance coil, and the planar inductance The inner connection head of the coil is connected to the upper plate of the capacitor; the lower metal layer includes the lower plate of the capacitor with the same size as the upper plate of the capacitor and the opposite position, and the interconnection line connected to the lower plate of the capacitor; the The outer connection head of the planar inductance coil on the upper metal layer is connected to the interconnection line of the lower metal layer through the conductive medium column located in the electrical through hole, and the cavity of the middle flexible substrate is located between the upper plate of the capacitor and the lower plate of the capacitor.

Further, the cavity is located in the middle of the middle flexible substrate.

Further, the thickness of the upper metal layer is 10-20 microns, and the thickness of the lower metal layer is 10-20 microns.

Beneficial effects: compared with the prior art, the technical solution of the present invention has the following advantages:

(1) It has self-encapsulation function and low packaging cost. After the sensor of the present invention is manufactured and laminated, the upper flexible substrate and the lower flexible substrate can protect the upper metal layer, the middle flexible substrate and the lower metal layer between the upper flexible substrate and the lower flexible substrate, that is, the capacitance and inductance of the sensor are protected. , no additional encapsulation structure is required. In this way, the upper flexible substrate and the lower flexible substrate of the present invention simultaneously perform the function of packaging, reducing the cost of packaging.

(2) High quality factor. Among the many factors affecting the Q value of the inductance quality factor, the thickness of the metal layer is the most important. The higher the thickness of the metal layer, the higher the quality factor Q value. The metal layer based on the microelectronic processing technology is usually obtained by a sputtering process, and the metal layer is usually about 1-2 μm, while the upper metal layer and the lower metal layer of the pressure sensor of the present invention are obtained by an electroplating process, and the upper metal layer and the lower metal layer The thickness of the layers can reach tens of microns respectively. The thickness of the metal layer of the pressure sensor of the present invention is far greater than that of the existing pressure sensor. Therefore, the quality factor Q value of the pressure sensor of the present invention is high. The higher the quality factor Q value of the pressure sensor, the smaller the loss of the coil and the lower the power consumption.

(3) High sensitivity. In the pressure sensor of the present invention, the upper flexible substrate, the lower flexible substrate, the capacitor upper plate, the capacitor lower plate and the middle flexible substrate constitute a plate capacitor. The upper flexible substrate and the lower flexible substrate are opposite to each other, and the cavity is located between the upper flexible substrate and the lower flexible substrate. When the pressure changes, both the upper flexible substrate and the lower flexible substrate on both sides of the cavity deform. That is to say, both the upper flexible substrate and the lower flexible substrate are pressure sensitive elements. Setting two pressure sensitive elements in one pressure sensor is beneficial to increase the sensitivity of the sensor.

(4) The structure is simple. The pressure sensor of the present invention is completely based on the processing technology of the flexible substrate, and the manufacturing technology is simple. The pressure sensor of the present invention comprises an upper flexible substrate, an upper metal layer, a middle flexible substrate, a lower metal layer and a lower flexible substrate, and has a simple structure. The upper flexible substrate and the lower flexible substrate are not only used as carriers for making capacitor plates and inductors, but also protect the internal structure of the sensor. When used, no additional packaging structure is required.

(5) Has a non-contact structure. The pressure sensor of the present invention is non-contact measurement during testing, uses the induction signal of the structure as the output signal, and has the advantage of low power consumption.

(6) The pressure sensor of the present invention uses a conductive medium column located in the electrical through hole to connect the single-layer planar spiral planar inductance coil and the planar capacitor in parallel, avoiding external lead wires, reducing the length of the interconnection line, and reducing the parasitic inductance , to reduce the parasitic effect, the equivalent electrical model can be simplified.

Description of drawings

Figure 1 is an exploded view of components of the present invention.

Fig. 2 is a longitudinal sectional view of the present invention.

Fig. 3 is a schematic diagram of the device for pressure measurement in the present invention.

In the figure, there are: upper flexible substrate 1, upper metal layer 2, middle flexible substrate 3, lower metal layer 4, lower flexible substrate 5, conductive medium column 6, capacitor upper plate 7, capacitor lower plate 8, planar inductance coil 9 , cavity 10, inner connector 11, outer connector 12, interconnection wire 13, electrical via 14, external readout coil 20, external readout system 21.

detailed description

The technical solution of the present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figures 1 and 2, a passive wireless pressure sensor with self-encapsulation function based on a flexible substrate of the present invention includes an upper flexible substrate 1, an upper metal layer 2, Middle flexible substrate 3 , lower metal layer 4 and lower flexible substrate 5 . The upper flexible substrate 1, the middle flexible substrate 3 and the lower flexible substrate 5 are all made of flexible materials, such as polyimide (PI), liquid crystal polymer (LCP), or polyethylene terephthalate. Alcohol esters (PET). Electrical vias 14 and cavities 10 are provided on the middle flexible substrate 3 . Preferably, the cavity 10 is located in the middle of the middle flexible substrate 3 . The cavity 10 is located in the middle of the middle flexible substrate 3, which can reduce the volume of the sensor. Considering the inductance and Q value of the planar inductor comprehensively, the planar inductor generally adopts a hollow structure. This places planar capacitance in this area without increasing the overall size of the device. The upper metal layer 2 includes a planar inductance coil 9 and a capacitor upper plate 7 . The capacitor upper plate 7 is located in the middle of the planar inductance coil 9 . That is to say, the planar inductance coil 9 is wound around the outer periphery of the upper plate 7 of the capacitor. The planar inductance coil 9 is provided with an inner connector 11 and an outer connector 12 . The inner connection head 11 of the planar inductance coil 9 is connected to the capacitor upper plate 7 . The lower metal layer 4 includes a capacitor lower plate 8 and interconnection lines 13 . The capacitor lower plate 8 has the same size as the capacitor upper plate 7 , and the capacitor lower plate 8 is opposite to the capacitor lower plate 8 . One end of the interconnection wire 13 is connected to the lower plate 8 of the capacitor. The outer connection head 12 of the planar inductance coil 9 of the upper metal layer 2 is connected to the interconnection line 13 of the lower metal layer 4 through the conductive medium column 6 in the electrical via 14 . The cavity 10 of the middle flexible substrate 3 is located between the capacitor upper plate 7 and the capacitor lower plate 8 .

Further, the upper flexible substrate 1 , the middle flexible substrate 3 and the lower flexible substrate 5 have the same size. Adopting the same size is beneficial to the subsequent alignment lamination process and facilitates manufacturing.

Further, the thickness of the upper metal layer 2 is 10-20 microns, and the thickness of the lower metal layer 4 is 10-20 microns. The thickness of the upper metal layer 2 and the lower metal layer 4 is larger than that of the existing sensor metal layer, which is beneficial to improve the Q value of the inductance quality factor.

In the pressure sensor with the above structure, the capacitive upper plate 7 , the capacitive lower plate 8 and the cavity 10 on the middle flexible substrate 3 form a plate capacitor. The cavity 10 of the middle flexible substrate 3 is a cavity of a flat panel capacitor. The plate capacitance is used as the pressure sensitive device of the pressure sensor. The pressure sensor also includes a planar inductive coil 9 . The inner connector 11 of the planar inductance coil 9 is connected to the upper plate 7 of the capacitor, and the outer connector 12 of the planar inductance coil 9 is connected to the interconnection line 13 of the lower metal layer 4 through the conductive medium column 6 in the electrical through hole 14 . Both ends of the plate capacitor and the planar inductance coil 9 are connected to each other to form an LC (LC corresponds to "LCtank" in English, and corresponds to inductance and capacitance circuit in Chinese) resonant circuit. Both the upper flexible substrate 1 and the lower flexible substrate 5 in the pressure sensor are deformed under the action of external pressure, thereby significantly increasing the sensitivity of the pressure sensitive capacitance.

The resistance loss of the metal coil is the most important factor that suppresses the quality factor Q value of the planar inductor, and the two basic ways to reduce the resistance of a coil with a certain length are to increase the conductivity and increase the cross-sectional area. In traditional on-chip sputtered metal inductors, the thickness of the sputtered metal is limited (usually less than two microns). To manufacture inductors with the same width, the cross-sectional area of the on-chip inductor is small, but the cross-sectional area of the inductor manufactured by the method of the present invention is larger, thereby improving the Q value of the inductor.

As shown in FIG. 3 , when using the pressure sensor with the above-mentioned structure, it is necessary to use an external readout coil 20 and an external readout system 21 . The external readout system 21 is typically an impedance analyzer or a network analyzer. The external readout coil 20 is connected to an external readout system 21 . An external readout coil 20 is located close to the planar inductive coil 9 of the pressure sensor. The external readout coil 20 is not in contact with the planar inductive coil 9 . The external sense coil 20 and the planar inductive coil 9 constitute a loosely coupled transformer.

The pressure measurement process of the pressure sensor with the above structure is: when the pressure changes, the upper flexible substrate 1 and the lower flexible substrate 5 located on both sides of the cavity 10 are deformed. The deformation of the upper flexible substrate 1 and the lower flexible substrate 5 will drive the deformation of the upper metal layer 2 and the lower metal layer 4, thereby causing the capacitance size and capacitance value of the plate capacitor to change, thereby causing the resonant frequency of the LC circuit to change. The impedance phase of the external sense coil 20 has a dip point at the resonant frequency of the pressure sensor LC loop. The external readout system 21 is used to analyze the impedance frequency characteristic of the external readout coil 20, and thereby determine the resonant frequency of the LC circuit of the pressure sensor, thereby realizing the passive wireless measurement of the pressure signal. The pressure signal of the pressure sensor is wirelessly output through inductive coupling.

The pressure sensor of the present invention is completely manufactured by the flexible substrate processing technology. The manufacturing process of the pressure sensor is as follows: first, two flexible copper-clad laminates are selected as the upper flexible substrate 1 and the lower flexible substrate 5 respectively. The flexible copper-clad laminate is generally formed by laminating polyimide layers and copper foils, and the copper foils are processed into the upper metal layer 2 and the lower metal layer 4 respectively through a wet etching process. Next, a polyimide layer is selected, and a cavity 10 is opened in the middle thereof as the middle flexible substrate 3 . The above-mentioned multi-layer structure is then aligned and laminated together by lamination technology in the flexible substrate processing process. The connection between the upper metal layer 2 and the lower metal layer 4 is realized through the conductive dielectric pillar 6 in the electrical via 14 .

Claims (3)

1. A passive wireless pressure sensor with self-encapsulation function based on a flexible substrate, characterized in that the pressure sensor includes an upper flexible substrate (1) and an upper metal layer (2) arranged in sequence from top to bottom and fixedly connected , the middle flexible substrate (3), the lower metal layer (4) and the lower flexible substrate (5), the middle flexible substrate (3) is provided with electrical through holes (14) and cavities (10); The upper metal layer (2) includes a planar inductance coil (9) and a capacitor upper plate (7) located in the middle of the planar inductance coil (9), and the inner connector (11) of the planar inductance coil (9) and the capacitor The upper plate (7) is connected; The lower metal layer (4) includes a capacitor lower plate (8) having the same size as the capacitor upper plate (7) and opposite in position, and an interconnection line (13) connected to the capacitor lower plate (8); The outer connection head (12) of the planar inductance coil (9) of the upper metal layer (2) passes through the interconnection line between the conductive medium column (6) and the lower metal layer (4) in the electrical through hole (14) (13) connection, the cavity (10) of the flexible substrate (3) is located between the capacitor upper plate (7) and the capacitor lower plate (8); The thickness of the upper metal layer (2) is 10-20 microns, and the thickness of the lower metal layer (4) is 10-20 microns. 2. The passive wireless pressure sensor with self-encapsulation function based on a flexible substrate according to claim 1, wherein the cavity (10) is located in the middle of the flexible substrate (3). 3. The passive wireless pressure sensor with self-encapsulation function based on flexible substrate according to claim 1, characterized in that, the upper flexible substrate (1), the middle flexible substrate (3) and the lower flexible substrate (5 ) have the same dimensions.