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 in FIG. 8 attached hereto. A sensing member 20 is contained in a resin casing 10 having a conductor member 30 embedded therein. The sensing member 20 is composed of a glass base 22 and a diaphragm-type semiconductor sensor chip mounted on the glass base 22. The sensing member 20 is connected to the casing 10 with adhesive 23. The sensing element 20 is electrically connected to the conductor member 30 serving as a terminal with a bonding wire 40. The boundaries between the conductor members 30 and the casing 10 are encapsulated with an encapsulating member 50. The encapsulating member 50 is made of a material such as fluorine-rubber which is liquid when applied and is hardened afterward. The encapsulating member 50 prevents air bubbles from coming out through the boundaries between the casing 10 and the conductor members 30 when the pressure sensor is exposed to a negative pressure. A protecting member 60 made of a material such as fluorine gel is further disposed on the sensing member 20 and the encapsulating member 50 to protect them from chemical erosion.
The encapsulating member 50 is applied to the position when it is in liquid state, and it is hardened thereafter. In the conventional pressure sensor, as shown in FIG. 8, the conductor member 30 is positioned below the surface of the sensing member 20 in order to prevent the encapsulating member 50 from flowing toward the sensing member 20 and from sticking to the surface thereof. For this purpose the conductor member 30 has to be positioned at a bottom portion of the casing 10. Accordingly, a step is made between the surfaces of the sensing member 20 and the conductor member 30. This step is not advantageous for a process of forming the bonding wire 40 between the sensing member 20 and the conductor member 30. Further, the step makes the thickness (a vertical dimension of the pressure sensor shown in FIG. 8) large. For keeping the encapsulating member 50 in position when it is applied, the conductor member 30 has to be positioned lower than the sensing member 20 in the casing 10. Therefore, the casing 10 cannot be freely designed.