Abstract:
A pressure detection device for detecting pressure of fluid that comprises a housing, a pressure-transmission medium, a sensor chip, at least one terminal pin, a sealant and a film. The pressure of the fluid is transmitted to the pressure-transmission medium such as silicone oil, and the sensor chip detects the pressure of the pressure-transmission medium. The terminal pin for the electrical connection between the sensor chip and an outside device is fixed into the housing, and a contact protrusion that is exposed in the housing for being electrically connected with the sensor chip is formed at one end of the terminal pin. The sealant such as poly-monochloro-para-xylylene is put around the contact protrusion for sealing the pressure-transmission medium. The film such as poly-monochloro-para-xylylene for avoiding the contact between the pressure-transmission medium and the sealant is coating the sealant.

Description:
INCORPORATION BY REFERENCE  
         [0001]    The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2001-311802, filed on Oct. 9, 2001. The contents of that application are incorporated herein by reference in their entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a pressure detection device, more particularly to a semiconductor pressure detection device.  
           [0004]    2. Discussion of the background  
           [0005]    A semiconductor pressure detection device is known as a kind of devices to detect pressure of fluid At the semiconductor pressure detection device, the pressure of the fluid received at a metal diaphragm which contacts with the fluid is transmitted to a silicon diaphragm of the semiconductor sensor chip through a pressure-transmission medium such as incompressible fluid, and the semiconductor sensor chip outputs signal corresponding to the pressure.  
           [0006]    Generally, such a semiconductor pressure detection device has a chamber for the pressure-transmission medium, which is defined by a concave portion of a housing and the metal diaphragm that is blocking up the concave portion The chamber is filled up with the pressure-transmission medium, and the semiconductor sensor chip is attached therein. A couple of power supply electrodes of the sensor chip is connected with terminal pins inserted into the housing via bonding wires. A detection signal electrode of the sensor chip is also connected with another terminal pin via a bonding wire. All terminal pins are unified with the housing, which is made of synthetic resin, by insert molding, and one end of each terminal pin is exposed in the chamber in order to be connected with the bonding wire. The exposed portion of each terminal pin except a portion which the bonding wire is connected with is coated by a sealant such as silicon rubber. A reason to coat the sealant is that it is difficult that the synthetic resin housing and the metal terminal pins completely adhere each other because of a difference of the materials, and it is possible that the pressure-transmission medium leaks from clearances between the housing and the terminal pins. That is, it is prevented that the pressure-transmission medium leaks from the clearances so that the sealant obstructs that the pressure-transmission medium reaches the clearance.  
           [0007]    However, the sealant swells in a case that silicon oil is used for the pressure-transmission medium, and is deteriorated in case that fluorine oil is used for the pressure-transmission medium. The swelling or the deterioration of the sealant causes declination of the sealing ability of the sealant. More particularly, the sealant becomes porously or clearances are generated between the sealant and the housing. The pressure-transmission medium arrives to the clearances between the housing and the terminal pins through the porous or the clearances between the sealant and the housing. Therefore, it is possible that the pressure-transmission medium leaks to outside.  
         SUMMARY OF THE INVENTION  
         [0008]    In view of the foregoing, it is an object of the present invention to provide an improved pressure detection device. In order to achieve the above and other objects, the present invention provides a pressure detection device for detecting pressure of fluid that comprises a housing, a pressure-transmission medium, a sensor chip, at least one terminal pin, a sealant and a film. The pressure of the fluid is transmitted to the pressure-transmission medium such as silicone oil and the sensor chip detects the pressure of the pressure-transmission medium. The terminal pin for the electrical connection between the sensor chip and an outside device is fixed into the housing, and a contact protrusion that is exposed in the housing for being electrically connected with the sensor chip is formed at one end of the terminal pin. The sealant such as poly-monochloro-para-xylylene is put around the contact protrusion for sealing the pressure-transmission medium The film such as poly-monochloro-para-xylylene for avoiding the contact between the pressure-transmission medium and the sealant is coating the sealant.  
           [0009]    Since the film coats the sealant, it is avoided that the pressure-transmission medium contacts with the sealant. Therefore, the deterioration of the sealant is significantly reduced. As a result, the leak of the pressure-transmission medium is prevented. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Various other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiments when considered in connection with the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1 is a cross-sectional view of a pressure detection device according to an embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a bottom view of a connector housing of the embodiment;  
         [0013]    [0013]FIG. 3 is a cross-sectional view enlarged a part of FIG. 1;  
         [0014]    [0014]FIG. 4 is a cross-sectional view enlarged a part of a pressure detection device as a modification of the embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a semiconductor pressure detection device  11  according to the embodiment of the present invention. As showing in FIG. 1, the semiconductor pressure detection device  11  mainly comprises a connector housing  12  and a sensor housing  13 . Hereinafter, it is defined that a side that the connector housing  12  is in (top in FIG. 1) is called “top” or “upper side” and a side that the sensor housing  13  is in (bottom in FIG. 1) is called “bottom” or “lower side” in this description.  
         [0016]    The semiconductor pressure detection device  11  mainly comprises the connector housing  12  which is made of synthetic resin and the sensor housing  13  which is made of metal. The connector housing  12  is formed as an approximate cylindrical shape wherein a diameter of an intermediate portion is smaller than the same of both ends. A housing stiffening plate  14  that is made of metal is molded at the intermediate portion of the connector housing  12 . The housing stiffening plate  14  has plurality pinholes  14   a  which terminal pins  19  (describe later) penetrate thereinto. A concavity  15  for electric connection is formed at the top of the connector housing  12 , and another concavity  16  is formed at the bottom of the connector housing  12 . As showing in FIG. 2 and FIG. 3, other three concavities  17  (only two are shown in FIG. 3) for sealant are formed in the concavity  16 . Three terminal pins  19  (only two are shown in FIG. 1) are attached in the connector housing  12  by insert molding. A couple of the terminal pins  19  is for power supply, and another of terminal pin  19  is for detecting signal. Each terminal pin  19  is penetrating the pinhole  14   a  so that one end of each terminal pin  19  is projecting into the concavity  15 . Another end of each terminal pin  19  is bent, and a contact protrusion  19   a  is formed thereon so that the contact protrusion  19   a  is in the concavity  17 . Silicon rubber (for example dimethyl-silicon-rubber) as sealant  20  is injected into each concavity  17  so that a periphery of each contact protrusion  19   a  is surrounded by the sealant  20 . A semiconductor sensor chip  21  that outputs electric signal corresponding to received pressure is disposed in the center of the concavity  16 . The semiconductor sensor chip  21  is electrically connected to the contact protrusions  19   a  of the couple of terminal pins  19  via bonding wires  22  so as to be supplied power thereto, and is electrically connected to the contact protrusion  19   a  of the other terminal pin  19  via a bonding wire  22  so as to output detection signal therefrom.  
         [0017]    On the other hand, the sensor housing  13  comprises a hollow portion at the upper side thereof and threaded portion  13   a  at the lower side thereof. A pressure introduction aperture  13   h  is formed in the center of the threaded portion  13   a.  One end of the pressure introduction aperture  13   h  is communicated to the hollow portion, and the fluid whose pressure would be measured is introduced to another end of the pressure introduction aperture  13   h.  A step as a sealing portion  13   b  is formed at the upper end of the pressure introduction aperture  13   h,  and a flexible diaphragm  25  made of metal is fluid-tightly attached with a cramping member (not shown) thereon by laser welding. The top portion of the sensor housing  13  is formed as a caulking piece  13   c.  The connector housing  12  and the sensor housing  13  arc unified, so that the lower side of the connector housing  12  is inserted in the hollow portion of the sensor housing  13  with a O-ring  26  and the caulking piece  13   c  is crimped inwardly. Then the concavity  16  closed by the diaphragm  25  defines an oil chamber  18 , and silicon oil S (for example dimethyl-silicon-oil) as pressure-transmission medium is filled up therein In other words, the silicon oil S is sealed up at the bottom of the oil chamber  18  by the diaphragm  25  and  0 -ring  26 , and is sealed up at the top of the oil chamber  18  by the sealant  20 .  
         [0018]    As shown in FIG. 3 that is enlarged about one pair of the sealant  20  and the concavity  17 , a film  23  made of parylene coating is put on a surface of each sealant  20 . The surface where the film  23  is put on is an area of the sealant  20 , which the silicon oil S contacts with if there is not the film  23 . The parylene coating as the film  23  is processed by a way that a film of poly-monochloro-para-xylylene (known as a trade name “Parylene”) is evaporated by CVD (chemical vapor deposition) method so as to be approximately uniform thickness that is 3 μm-5 μm. It is possible that the sealant  20  exfoliates at a border B 1  with the connector housing  12  and a border B 2  with the contact protrusion  19   a.  As a result, clearances occur at the borders B 1 , B 2 . Therefore, it is preferable that the film  23  is also put on the borders B 1 , B 2 .  
         [0019]    The pressure of the fluid is detected by the semiconductor pressure detection device  11  as follows. The pressure of the fluid that is introduced in to the pressure introduction aperture  13   h  is transmitted to the silicon oil S through the diaphragm  25 . A diaphragm (not shown) of the semiconductor sensor chip  21  is deflected by the pressure of the silicon oil S. Electrical signal in proportion to the deflection is output via the bonding wire  22  and the terminal pin  19 .  
         [0020]    According to the above-described construction, the semiconductor pressure detection device  11  can achieve following advantages.  
         [0021]    (1) Because each surface of the sealant  20  is coated with the film  23 , the silicon oil S does not contact with the sealant  20 . Therefore, the deterioration of the sealant  20  is significantly reduced, as a result, it is prevented that the silicon oil S leaks out through the clearances between the connector housing  12  and the terminal pins  19 .  
         [0022]    (2) The parylene coating as the film  23  is used in this embodiment. The parylene coating has abilities of oil resistance, permeability resistance for various fluids, electrical insulation, heat resistance, permeability for narrow clearance and low-temperature resistance. Further, porous in the film can not occur, and the strain caused during coating does not remain in sealant  20 . Therefore, the parylene coating prevents the contact between the silicon oil S and the sealant  20 . The electrical insulation of the film prevent a short-circuit of the terminal pins  19  and others.  
         [0023]    (3) The dimethyl-silicon-oil is used as the pressure-transmission medium (the silicon oil S) and the dimethyl-silicon-rubber is used as the sealant  20 . The reduction of cost can be achieved to use the dimethyl-silicon-oil, because the dimethyl-silicon-oil is cheaper than fluoro-silicon-oil that is conventionally used as the pressure-transmission medium. A combination of the dimethyl-silicon-oil and the dimethyl-silicon-rubber was conventionally avoided, because these molecular structures are similar, therefore swelling of the dimethyl-silicon-oil easily occur. However, this combination can be selected in the present invention, because the dimethyl-silicon-oil as the pressure-transmission medium does not contact with the dimethyl-silicon-rubber as the sealant  20 .  
         [0024]    Some modifications of the embodiment will be described hereinafter. It is possible that other kinds of film  23  instead of the parylene coating can be used, as long as the film has sealing ability. However, it is preferably that the film further has abilities of oil resistance, chemical resistance, permeability resistance for fluid, not making other components (the sensor chip  21 , the sealant  20  and the connector housing  12 ) deteriorate, and a strong tensile strength. More preferably, the film has abilities of affinity to the other components, electrical insulation, and easiness of making a thin coating.  
         [0025]    The film  23  is put on the surface of the sealant  20  which the silicon oil S contacts with if there is not the film  23 , and additionally on the clearances that occurred at the borders B 1 , B 2  in the embodiment. Further, it is preferable that the film  23  is put on surfaces of the bonding wires  22 , surfaces of the connector housing  12  and surfaces of contact protrusions  19   a,  which these surfaces contact with the silicon oil S if there is not the film  23  as shown in FIG. 4.  
         [0026]    The film  23  is approximately uniform thickness that is 3□m-5□m in the embodiment. However the thickness of the film  23  can be modified, as long as the sealing ability is not lost. Further, it is possible that the thickness of the film  23  is not uniform, for example, the films  23  of the surface of the sealant  20  and the clearances that occurred at the borders B 1 , B 2  are made thickly, and the films  23  of the surfaces of the bonding wires  22 , connector housing  12  and contact protrusions  19   a  are made thinly. On the other hand, it is possible that only the films  23  of the surface of the sealant  20  are made thickly, and others, i.e. the films  23  of the clearances that occurred at the borders B 1 , B 2 , the surfaces of the bonding wires  22 , connector housing  12  and contact protrusions  19   a , are made thinly. In other words, these mean that the surfaces where the sealing necessity is serious are made thickly, and others are made thinly.  
         [0027]    The parylene coating as the film  23  is made so that poly-monochloro-para-xylylene is evaporated by CVD method in the embodiment. However, other materials, for example poly-para-xylylene or poly-dichloro-para-xylylene, are acceptable, and other coating methods are useable.  
         [0028]    The silicon oil S is used as the pressure-transmission medium in the embodiment. However, other mediums, for example perfluoro polyether (fluorine oil), are acceptable. In a case that the perfluoro polyether is used, the accuracy of detection is improved because the volume changes of the perfluoro polyether that occur due to temperature variations are less than the same of the silicon oil.  
         [0029]    The pressure detection device that has three terminal pins is described in the embodiment. However, it will be clear that the present invention can be adapted to pressure detection devices that has two or more than three terminal pins.  
         [0030]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is thereby to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.