JP2018185213A - Pressure sensor and method for equipping the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor that can suppress the influence of external stress, and a method for equipping the pressure sensor.SOLUTION: The present invention includes: a resin package 14; a pedestal 13 above the resin package 14 with a die-bond region 12 in between; and a pressure sensor element 11 above the pedestal 13 with the die-bond region 12 in between. The pedestal 13 has a route 13a for a pressure medium to go to the pressure sensor element 11, and is made of a material that has a coefficient of linear expansion of 0.5 to 1.5 times that of the resin package 14 and does not have a glass transition point and a melting point in the range of 20 to 200°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pressure sensor and a mounting method thereof.

  Conventionally, as a pressure sensor, a method of detecting pressure by converting a strain detected by a mechanical pressure sensitive element such as a diaphragm into an electric signal by a piezoresistor or the like has been developed. Patent Literature 1 describes a pressure sensor including a package configured to introduce a pressure detection fluid from an introduction pipe into a body that houses a sensor chip.

JP 2008-82969 A

  As the measurable pressure region becomes smaller and the measurement of finer pressure is required, the influence of external stress due to the deformation of the resin package cannot be ignored. Thereby, the fluctuation | variation of the offset voltage of sensor output becomes large. In particular, if the external temperature varies, stress may act on the sensor element due to the difference in thermal expansion coefficients of the materials constituting each part of the pressure sensor, and the characteristics of the pressure sensor may vary.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the pressure sensor which can suppress the influence of an external stress, and its mounting method.

  In order to solve the above problems, the present invention includes a resin package, a pedestal provided on the resin package via a die-bond resin, and a pressure sensor element provided on the pedestal via a die-bond resin. The pedestal has a path through which a pressure medium communicates with the pressure sensor element, and the pedestal is formed of a material having a linear expansion coefficient of 0.5 to 1.5 times the linear expansion coefficient of the resin package, The pedestal is formed of a material having no glass transition point and no melting point at least between 20 and 200 ° C., and provides a pressure sensor.

The pedestal may be made of a material having no glass transition point and no melting point at least between 20 and 300 ° C.
The resin package may include polyphenylene sulfide (PPS), and the pedestal may be formed of a metal selected from aluminum, brass, and copper alloy.

  In addition, the present invention provides a mounting method for the pressure sensor, the method including mounting a solder to a terminal electrically connected to the pressure sensor element and performing a reflow process. provide.

  According to the present invention, it is difficult for stress to act on the sensor element even if there is a change in temperature, and the characteristic change of the pressure sensor can be suppressed.

It is the (a) longitudinal cross-sectional view which shows the pressure sensor of embodiment, (b) The cross-sectional view which follows the AA line. It is a graph which shows the simulation result of the stress by the difference in a base. It is the graph which compared the offset fluctuation | variation in a reflow process.

Hereinafter, based on a preferred embodiment, the present invention will be described with reference to the drawings.
FIG. 1 shows a pressure sensor of this embodiment. The pressure sensor 10 of this embodiment generally includes a pressure sensor element 11, a die bond resin 12, a pedestal 13, and a resin package 14.

  As shown in FIG. 1A, the pressure sensor element 11 includes a detection unit 11a formed on a substrate 11b. An example of the detection unit 11a is a diaphragm. The sensitivity to pressure can be adjusted by the thickness, size, and the like of the detection unit 11a. Inside the pressure sensor element 11, a recess 11c into which a pressure medium is introduced from the outside of the pressure sensor 10 is provided. The pressure sensor element 11 may be made of a semiconductor such as silicon by, for example, MEMS technology.

The detector 11a can be deformed in accordance with a change in the difference between the pressure in the recess 11c and the pressure outside the pressure sensor element 11. The pressure sensor 10 of the present embodiment can take a configuration corresponding to the type such as absolute pressure, relative pressure (differential pressure, gauge pressure) and the like. For example, when the outside of the pressure sensor element 11 constitutes a pressure reference chamber that is closed by a lid or the like (not shown), the detection unit 11a is a pressure sensor according to a change in pressure of the pressure medium introduced into the recess 11c. 10 external pressure changes can be detected. When the spaces on both sides of the detection unit 11a communicate with the outside of the pressure sensor 10 through the pressure medium inlets, the detection unit 11a can detect the differential pressure between the spaces on both sides. When the pressure in one space indicates atmospheric pressure, the detection unit 11a can detect the gauge pressure in the other space.
When the pressure changes, the detection unit 11a is distorted. The distortion generated in the detection unit 11a can be converted into an electric signal such as a voltage by a piezoresistor or the like. The electric signal is taken out of the pressure sensor 10 through an external terminal such as a lead electrically connected to the pressure sensor element 11. When mounting the pressure sensor 10 on an external substrate or the like, it is preferable from the viewpoint of productivity to have a process of applying solder to the external terminal and performing reflow.

  The pressure sensor element 11 is disposed above the pedestal 13. The pressure sensor element 11 is provided on a pedestal 13 via a die bond resin 12. The pedestal 13 has a path 13 a through which the pressure medium communicates with the pressure sensor element 11. The material of the base 13 is a metal, for example. Examples of the path 13a include a hole (through hole) penetrating the pedestal 13. The pressure medium is a fluid such as gas or liquid.

  The pedestal 13 is provided at a location where the pressure sensor element 11 is mounted on the resin package 14. The pedestal 13 is provided on the resin package 14 via the die bond resin 12. The resin package 14 has a path 14a through which a pressure medium passes. Examples of the path 14a include a hole (through hole) penetrating the bottom of the resin package 14. The pressure medium path 14 a provided in the resin package 14 may be provided at a position overlapping the pressure medium path 13 a provided in the base 13. The pressure medium can contact the pressure receiving surface of the detection unit 11a through the paths 13a and 14a.

  The planar shape of the pedestal 13 may include all locations where the pressure sensor element 11 is fixed to the resin package 14 side. FIG. 1B shows an example in which the outer shape of the pedestal 13 is square and the path 13a is circular. These shapes are not particularly limited. For example, the outer shape of the pedestal 13 may be circular.

The resin package 14 can be made of a relatively inexpensive resin. Examples of the constituent material of the resin package 14 include polyphenylene sulfide (PPS) having a linear expansion coefficient of about 2.2 × 10 ⁻⁵ / K. For example, PPS has a heat distortion temperature of about 260 ° C. or higher and a melting point of about 280 ° C. The resin package 14 may have a glass transition point or a melting point between at least 20 to 300 ° C. It is preferable that the resin package 14 is a thermoplastic resin because molding is easy. Note that the resin package 14 can also be made of a thermosetting resin, a photocurable resin, or the like.

  The pedestal 13 is made of a material that maintains rigidity in the temperature range of the external environment when the pressure sensor 10 is mounted or used. The constituent material of the pedestal 13 is preferably a substance that does not have a glass transition point and a melting point at least between 20 and 200 ° C., and a substance that does not have a glass transition point and a melting point at least between 20 and 300 ° C. Is more preferable.

The pedestal 13 has a linear expansion coefficient close to that of the resin package 14. The linear expansion coefficient κ ₁ of the pedestal 13 is preferably in the range of 0.5 to 1.5 times the linear expansion coefficient κ ₂ of the resin package 14. The linear expansion coefficient κ ₁ of the pedestal 13 is more preferably in the range of 0.7 to 1.3 times the linear expansion coefficient κ ₂ of the resin package 14. For example, when the resin package 14 includes PPS, the pedestal 13 has aluminum (Al) with a linear expansion coefficient of about 2.4 × 10 ⁻⁵ / K and a linear expansion coefficient of about 2.1 × 10 ⁻⁵ / K. It is preferable that it is formed from brass or a copper alloy having a linear expansion coefficient close to that of PPS. Brass is also a kind of copper alloy (copper and zinc alloy), but is not particularly limited as long as the metal has an appropriate linear expansion coefficient, and other alloys may be used.

FIG. 2 shows the result of simulation for the stress applied to the vicinity of the through hole of the resin package 14 when the external environment is heated from 25 ° C. to 260 ° C. “Glass”, “Al”, and “brass” indicate the material of the base 13. “No pedestal” indicates a configuration in which the pedestal 13 is omitted and the pressure sensor element 11 is mounted on the resin package 14 via the die bond resin 12. The numerical value attached to the material of the base represents length L × width W × thickness T (unit: mm). In FIG. 2A, the Al pedestal was compared with a glass pedestal and no pedestal, and in FIG. 2B, the brass pedestal was compared with a glass pedestal and no pedestal. The linear expansion coefficient of the glass used for the pedestal in proportion is about 0.058 × 10 ⁻⁵ / K.

  From the result of FIG. 2, it can be seen that the stress applied to the resin package decreases in the order of glass, no pedestal, Al, and brass. This represents that the stress applied to the resin package becomes smaller as the difference in coefficient of linear expansion between the resin package and the pedestal becomes smaller. In addition, in this simulation, it was found that there was no significant difference in stress with respect to changes in the thickness and size of the pedestal. Therefore, it is significant to consider the material of the pedestal, especially the linear expansion coefficient of the pedestal.

Based on the above results, samples having different base materials and materials are prepared, and the results of comparing offset fluctuations are shown in the graph of FIG. In each sample, a resin using PPS as a main material was used for a resin package, and a MEMS pressure sensor element using silicon as a main material was used. There are four types of pedestal materials: glass, Al, brass, and copper alloy, and five types of levels including “no pedestal” are comparison targets. Table 1 shows the number of experimental inputs at each level, the thickness of the pedestal, and the coefficient of linear expansion (CTE). Note that the linear expansion coefficient of PPS is about 2.2 × 10 ⁻⁵ / K, and the linear expansion coefficient of silicon is about 0.26 × 10 ⁻⁵ / K.

  The offset fluctuation measurement method is to perform a reflow process with a maximum temperature of 270 ° C. for each sample, measure the offset output before the reflow process and the offset output after 30 minutes from the reflow process, % FS). Here, the reason that 30 minutes have passed immediately after the reflow is that the time required for the sample temperature to return to the same room temperature as that before the reflow process is taken into consideration.

  From the result of FIG. 3, it was found that the effect of suppressing the offset fluctuation is larger as the linear expansion coefficient of the pedestal becomes closer to the linear expansion coefficient of the resin package. That is, it was shown that the solution of the present invention is very likely to be effective.

The following mechanism can be considered for the offset fluctuation due to the reflow process.
(1) When the temperature of the resin package rises from room temperature, an elastic stress is generated in the pressure sensor element due to a difference in linear expansion coefficient and a temperature difference between the resin package and the pressure sensor element.
(2) When the temperature of the resin package reaches the melting point or the like (phase transition point) of the resin, the resin acquires viscosity and the elastic stress of the pressure sensor element decreases.
(3) While the temperature is equal to or higher than the freezing point of the resin (phase transition point) and the resin package is viscous, the resin package does not generate much stress. The thermoplastic resin may have a freezing point different from the melting point.
(4) When the temperature decreases until the resin package acquires elasticity, an elastic stress is generated in the pressure sensor element from the difference in linear expansion coefficient and the temperature difference between the resin package and the pressure sensor element.

  If the resin package does not acquire viscosity and remains elastic during the reflow process, the expansion due to the rise in temperature and the shrinkage due to the fall in temperature are almost balanced, so that it remains in the pressure sensor element when it returns to room temperature. The stress is thought to be small. However, in that case, there is a concern that the material of the resin package and the processing cost are high.

  As described above, when the resin package acquires viscosity during the reflow process, the stress of the pressure sensor element is relieved at a high temperature. However, in the process of cooling from the reflow process, the resin package contracts more than the pressure sensor element, thereby generating stress in the pressure sensor element. Therefore, even if the resin package has a phase transition point such as a glass transition point or a melting point within the reflow temperature range and can be thermally deformed, it is necessary to suppress the stress of the pressure sensor element.

  Since the linear expansion coefficients of the pressure sensor element 11 and the pedestal 13 are different, the pressure sensor element 11 receives stress when the temperature of the entire pressure sensor 10 rises due to the reflow process. However, since the deformation of the pressure sensor element 11 is an elastic change, the stress received by the pressure sensor element 11 disappears when the temperature returns to room temperature. On the other hand, deformation of the resin package 14 can be suppressed by reducing the difference in linear expansion coefficient between the base 13 and the resin package 14. Therefore, according to the present embodiment, since the influence of the deformation of the pedestal 13 received from the resin package 14 after the reflow process is reduced, the influence of the deformation of the pedestal 13 on the pressure sensor element 11 is also reduced.

  As mentioned above, although this invention has been demonstrated based on suitable embodiment, this invention is not limited to the above-mentioned embodiment, A various change is possible in the range which does not deviate from the summary of this invention.

  The above-described pressure sensor can also be used for a device that measures a physical quantity other than pressure based on the surrounding water pressure or atmospheric pressure, such as a water depth meter or an altimeter.

DESCRIPTION OF SYMBOLS 10 ... Pressure sensor, 11 ... Pressure sensor element, 12 ... Die bond resin, 13 ... Base, 14 ... Resin package.

Claims (4)

A resin package;
A pedestal provided on the resin package via a die bond resin;
A pressure sensor element provided on the base via a die bond resin,
The pedestal has a path through which a pressure medium communicates with the pressure sensor element;
The pedestal is formed of a material having a linear expansion coefficient of 0.5 to 1.5 times the linear expansion coefficient of the resin package,
The pedestal is formed of a material having no glass transition point and no melting point at least between 20 and 200 ° C.   The pressure sensor according to claim 1, wherein the pedestal is formed of a material having no glass transition point and no melting point at least between 20 and 300 ° C.   The pressure sensor according to claim 1, wherein the resin package includes polyphenylene sulfide (PPS), and the pedestal is formed of a metal selected from aluminum, brass, and copper alloy.   It is the mounting method of the pressure sensor of any one of Claims 1-3, Comprising: It has the process of providing solder and reflowing to the terminal electrically connected with the said pressure sensor element. Mounting method of pressure sensor.

Images