Pressure sensor contained in casing

A pressure sensor for detecting, e.g., an intake manifold pressure of an internal combustion engine is composed of a resin casing, a sensing member contained in the casing and conductor members embedded in the resin casing. The conductor members are disposed around the sensing member, and the sensing member is electrically connected to the conductor members by wire-bonding. Boundaries between the resin casing and the conductor members are sealed with an encapsulating member which is applied to the position at liquid state and dried thereafter. To prevent the liquid encapsulating member from flowing out of the applied position toward the sensing member, a bank is formed between the sensing member and the position where the encapsulating member is applied. A depressed portion for retaining the encapsulating member therein may be additionally formed next to the bank.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority of Japanese Patent Application No. 2004-13380 filed on Jan. 21, 2004, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pressure sensor contained in a casing and encapsulated by an encapsulating member.

2. Description of Related Art

Examples of this kind of pressure sensor are disclosed in JP-A-11-304619 and JP-A-2001-304999. The pressure sensor is composed of a resin casing, a sensing member contained in the casing, conductor members embedded in the casing and electrically connected to the sensing member, and a member for encapsulating boundaries between the conductor members and the casing. A pressure such as an intake manifold pressure of an automobile is applied to the sensing member, and the sensing member outputs electrical signals corresponding to the applied pressure.

A relevant portion of a conventional pressure sensor is shown inFIG. 8attached hereto. A sensing member20is contained in a resin casing10having a conductor member30embedded therein. The sensing member20is composed of a glass base22and a diaphragm-type semiconductor sensor chip mounted on the glass base22. The sensing member20is connected to the casing10with adhesive23. The sensing element20is electrically connected to the conductor member30serving as a terminal with a bonding wire40. The boundaries between the conductor members30and the casing10are encapsulated with an encapsulating member50. The encapsulating member50is made of a material such as fluorine-rubber which is liquid when applied and is hardened afterward. The encapsulating member50prevents air bubbles from coming out through the boundaries between the casing10and the conductor members30when the pressure sensor is exposed to a negative pressure. A protecting member60made of a material such as fluorine gel is further disposed on the sensing member20and the encapsulating member50to protect them from chemical erosion.

The encapsulating member50is applied to the position when it is in liquid state, and it is hardened thereafter. In the conventional pressure sensor, as shown inFIG. 8, the conductor member30is positioned below the surface of the sensing member20in order to prevent the encapsulating member50from flowing toward the sensing member20and from sticking to the surface thereof. For this purpose the conductor member30has to be positioned at a bottom portion of the casing10. Accordingly, a step is made between the surfaces of the sensing member20and the conductor member30. This step is not advantageous for a process of forming the bonding wire40between the sensing member20and the conductor member30. Further, the step makes the thickness (a vertical dimension of the pressure sensor shown inFIG. 8) large. For keeping the encapsulating member50in position when it is applied, the conductor member30has to be positioned lower than the sensing member20in the casing10. Therefore, the casing10cannot be freely designed.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved pressure sensor, wherein the conductor member is freely positioned in the resin casing.

The pressure sensor detects a pressure such as a pressure in an intake manifold of an automotive vehicle. The pressure sensor is composed of a resin casing, a sensing member contained therein, and conductor members embedded in the resin casing and disposed around the sensing member. The conductor member is used as a terminal to which the sensing member is electrically connected by, e.g., wire-bonding. The sensing member may be composed of a diaphragm-type semiconductor sensor chip. A pressure to be detected is applied to the sensing member, and the sensing member outputs electrical signals corresponding to the pressure applied thereto.

Boundaries between the resin casing and the conductor members embedded in the casing are sealed with an encapsulating member after the sensing member is electrically connected to the conductor member by wire-bonding. The encapsulating member is in liquid state when it is applied to the position, and the encapsulating member is dried thereafter. To prevent the encapsulating member from flowing toward the sensing member and from sticking to the surface thereof, a bank projecting from the casing is formed between the sensing member and the place where the encapsulating member is applied.

The encapsulating member, in the liquid state, applied to the boundaries between the resin casing and the conductor member is retained there by the bank. Therefore, it is not necessary to position the surface of the conductor member lower than the surface of the sensing member as done in the conventional sensor device mentioned above. The position of the conductor member relative to the sensing member in the resin casing is freely chosen. When the surfaces of the sensing member and the conductor member are positioned in the same level, a step between both surfaces can be eliminated, and thereby the pressure sensor can be made thin.

A depressed portion for retaining the encapsulating member therein may be made next to the bank in the resin casing. A projected portion exposing to an upper space above the encapsulating member may be formed on the conductor member. In this case, the sensing member is electrically connected to the projected portion by wire-bonding. The projected portion may be formed by making a portion of the conductor member thicker than other portions or by bending a portion of the conductor member.

Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described with reference toFIG. 1. A pressure sensor100is used as a pressure sensor for detecting an intake manifold pressure in an automotive vehicle. Since this pressure sensor100is exposed to gasoline or other chemical substances, it has to be well protected from those substances.

As shown inFIG. 1, a sensing member20is contained in a resin casing10and electrically connected to conductor members30embedded in the casing10with bonding wires40. The sensing member20is covered with a protecting member60filling an upper space in the casing10. The casing10is made by molding a resin material such as polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), epoxy or the like. An opening11is formed at an upper portion of the casing10.

The conductor members30serving as terminals to be connected to the sensing member20are embedded in the resin casing10. The conductor member30is made of a conductive material such as copper. A portion of the conductor member30is exposed to the upper space in the casing10, as shown inFIG. 1. The exposed portion is plated with gold so that it serves as a bonding pad for making an electrical connection between the sensing member20and the conductor member30. The conductor member30is also electrically connected to an outside circuit (not shown).

The sensing member20is composed of a glass base22and a diaphragm-type semiconductor sensor chip21mounted on the glass base22. The sensor chip21may be formed by a thin diaphragm21aincluding known piezoelectric elements. The thin diaphragm21adistorts when a pressure is applied thereto, and the sensor chip21generates an electrical signal corresponding to the pressure. The sensing member20composed of the sensor chip21and the glass base22is bonded to the casing10with adhesive23such as silicone rubber. The sensing member20is electrically connected to the conductor members30through bonding wires40made of a material such as gold or aluminum.

The conductor members30embedded in the casing10are positioned around the sensing member20as shown inFIG. 1. In this embodiment, the upper surface of the conductor member30and the upper surface of the sensing member20are positioned at a substantially equal level. The step between both surfaces formed in the conventional pressure sensor shown inFIG. 8is eliminated. By eliminating the step, the pressure sensor is made thinner than the conventional one. The boundaries between the conductor members30and the resin casing10are sealed or encapsulated by the encapsulating member50made of an insulating material. Further, the upper space of the casing10is filled with a protecting member60made of an insulating material to cover the sensing member20, the bonding wires40and the encapsulating member50. Thus, the portions electrically connecting components are covered with the encapsulating member50and the protecting member60, and protected from erosion from outside.

As shown inFIG. 1, the encapsulating member50is disposed to cover the connecting portion between the bonding wire40and the conductor member30, and the boundaries between the casing10and the conductor member30, while leaving an upper portion of the bonding wire40exposed from the encapsulating member50. The encapsulating member50and the protecting member60may be made of the materials disclosed in the documents mentioned above (JP-A-11-304619, JP-A-2001-304999).

The encapsulating member50is made of a material having a high elasticity modulus to prevent generation of air bubbles at the boundaries between the conductor member30and the casing10. The encapsulating member50made of a material such as fluorine-rubber is soft or in liquid state when it is applied to the position (pasted), and thereafter the encapsulating member50is hardened. The protecting member60is made of a material having a low elasticity modulus so that it does not give a stress to the sensing member20and bonding wires40. The protecting member60may be made of a material such as fluorine-type gel or fluorosilicone gel. Both of the encapsulating member50and the protecting member60are made of a material that is highly resistive to chemical substances. As shown inFIG. 1, banks12projecting from the bottom surface of the casing10are formed integrally with the casing10. The bank12prevents the encapsulating member50from flowing toward the surface of the sensing member20and from sticking thereto.

The pressure sensor100described above is manufactured in the following manner. The resin casing10in which the conductor members30are embedded is formed by molding. The sensing member20is mounted on the casing10by bonding with the adhesive23. Then, the sensing element20and the conductor members30are electrically connected by wire-bonding. Then, the encapsulating member50is applied to the place and the protecting member60is supplied into the upper space of the casing10. Then, the encapsulating member50and the protecting member60are hardened. Thus, the pressure sensor100is completed. The pressure sensor100is mounted on the intake manifold of an engine, so that the opening11of the casing10communicates with the intake passage to detect the pressure in the intake manifold.

In the pressure sensor100described above, the banks12projecting from the bottom of the casing10are formed. Therefore, the encapsulating member50is effectively prevented from flowing to the surface of the sensing member20and from sticking thereto. The vertical position of the conductor member30may be equal to the surface of the sensing member. It is not necessary to position the conductor members30at the lower portion of the casing10as done in the conventional pressure sensor. By positioning the sensing member20and the conductor members30at the same vertical level, the step between the surfaces of both members, which was made in the conventional pressure sensor, is eliminated. Therefore, the process of wire-bonding is easily performed, and the vertical size (or the thickness) of the pressure sensor100can be made small.

A modified form of the first embodiment shown inFIG. 1is shown inFIG. 2. In this modified form, the conductor member30is positioned at a higher level than the sensing member20. The encapsulating member50pasted in the liquid state is prevented from flowing out by the bank12, though the liquid encapsulating member50is positioned hither than the sensing member20.

A second embodiment of the present invention is shown inFIG. 3. In this embodiment, a depressed portion13is additionally formed next to the bank12, so that the encapsulating member50is retained in the depressed portion13.FIG. 4shows the depressed portion13in a perspective view. As seen inFIG. 4, the depressed portion13is formed in shape of a groove surrounding the conductor member30. The encapsulating member50is more effectively prevented from flowing out by the depressed portion13and the bank12. In this embodiment, the portion connecting the bonding wire40to the conductor member30is not covered with the encapsulating member50, but this portion is covered only with the protecting member60.

A third embodiment of the present invention is shown inFIG. 5. In this embodiment, a projected portion31sticking out from the encapsulating member50is formed on the conductor member30. The projected portion31may be formed in the process of forming the conductor member30by presswork or by partially laminating a plate. The bonding wire40is connected to the projected portion31sticking out from the encapsulating member50. The connecting portion is not covered with the encapsulating member50, but it is covered with the protecting member60.

A fourth embodiment of the present invention is shown inFIG. 6. In this embodiment, a projected portion32is formed by bending the conductor member30in U-shape. The projected portion32can be easily formed in the process of forming the conductor member30by presswork.FIG. 7shows a modified form of the fourth embodiment. In this modified form, an angled portion32′ is formed by bending the tip of the conductor member30in the presswork for forming the conductor member30. In the fourth embodiment, the portion connecting the bonding wire40and the conductor member30is not covered with the encapsulating member50, but it is covered with the protecting member60.

The present invention is not limited to the embodiments described above, but it may be variously modified. For example, the casing10may be made of a material other than resin. The conductor member30is not limited to the terminal to be connected to the sensing member20. The sensing member20may not be limited to the diaphragm-type semiconductor chip. The sensing member20may be a capacitive-type or a piezoelectric-type. The protecting member60filling the upper portion of the casing10may be eliminated in a certain application. The sensing member20and the conductor member30may be electrically connected by other methods than wire-bonding. They may be connected by soldering or by conductive adhesive. The vertical level of the conductor member30relative to the sensing member20can be freely selected as long as the encapsulating member50is prevented from flowing out by the bank12and/or the depressed portion13. The pressure sensor according to the present invention is applicable as sensors other than the intake manifold pressure sensor.