Abstract:
A semiconductor pressure sensor can reduce the damage of bonding wires to increase their life time even under an environment in which the temperature and pressure change rapidly and radically. The semiconductor pressure sensor includes a package ( 1 ) made of a resin and having a concave portion ( 1   a ), a lead ( 2 ) formed integral with the package ( 1 ) by insert molding, with its one end exposed into the concave portion ( 1   a ) and its other end extended from the package ( 1 ) to the outside, a sensor chip ( 3 ) arranged in the concave portion ( 1   a ) for detecting pressure, and a bonding wire ( 4 ) electrically connecting the sensor chip ( 3 ) and the lead ( 2 ) with each other. An interface between the lead ( 2 ) and the package ( 1 ) on the side of the concave portion ( 1   a ) is covered with a first protective resin portion ( 6 ) of electrically insulating property, and the bonding wire ( 4 ) is covered with a second protective resin portion ( 7 ) that is softer than the first protective resin portion ( 6 ).

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor pressure sensor for detecting a pressure such as, for example, the pressure in an intake manifold of an internal combustion engine, the internal pressure of a tank, etc 
   2. Description of the Related Art 
   As a general pressure sensing element, there has been known a semiconductor pressure sensor using a piezoresistive effect, for example. 
   Such a semiconductor pressure sensor is constructed as follows. That is, a seat with a diaphragm bonded thereto is arranged in a concave portion of a package, and a strain gauge formed on the diaphragm serves to catch, as a change in resistance, a strain or distortion of the diaphragm that is caused by a pressure difference between a medium or fluid to be measured and a vacuum chamber defined between the diaphragm and the seat, so that the change in resistance is output as an electric signal to the outside through leads, and the pressure of the fluid to be measured is thereby detected. 
   The diaphragm and the leads are electrically connected with each other through bonding wires, and the diaphragm and the bonding wires are covered with and protected by an electrically insulating protective resin material or portion so as to ensure the corrosion resistance and the electrical insulation thereof to the medium to be measured, but as such a resin material, there is used a relatively soft one such as for example a gel so as not to obstruct the strain or distortion deformation of the diaphragm. 
   However, minute gaps or clearances are formed in interfaces between the package and the leads which are formed integral with the package by means of insert molding, so when the diaphragm and the bonding wires are covered with the protective resin portion, air existing in the interfaces is released into the protective resin portion, as a result of which a stress is applied to the bonding wires, thereby causing a fear that the bonding wires might be damaged. 
   In order to prevent such a situation, a countermeasure is taken in which work to cover the protective resin portion is carried out under a vacuum atmosphere so as to reduce the amount of air confined or trapped in the interfaces, but even in this case, when the diaphragm is subjected to a negative pressure lower than the atmospheric pressure, the air existing in the minute gap expands as air bubbles to invade into the protective resin portion, whereby the protective resin portion and the bonding wires are stressed, and hence there was still a problem that the damage of the bonding wires might be caused. 
   Here, note that a similar problem was generated by the air that invaded from the outside of the package through small gaps. 
   As a means for solving such problems, for example, a semiconductor pressure sensor is described in a first patent document (Japanese patent application laid-open No. H11-304619 ( FIG. 1 )). That is, a concave portion side, lower portions of the bonding wires and the leads on the interfaces between the leads and the package are covered with a first relatively hard, insulating protective resin portion thereby to confine air in the interface, and the diaphragm and upper portions of the bonding wires are covered with a second relatively soft protective resin portion. 
   However, in the above-mentioned semiconductor pressure sensor, the bonding wires are covered with the first protective resin portion and the second protective resin portion which are different from each other in the coefficient of linear expansion and the elastic modulus, so a difference or variation in the stress or distortion of the first protective resin portion and the second protective resin portion caused by a temperature change or a pressure change acts on the bonding wires as a large force as it is. Accordingly, even in this case, there was a problem that the bonding wires might be damaged. 
   SUMMARY OF THE INVENTION 
   The present invention is intended to obviate the above-mentioned problems, and has for its object to obtain a semiconductor pressure sensor in which the damage of bonding wires can be reduced to increase their life time even under an environment in which the temperature and pressure change rapidly and radically. 
   A semiconductor pressure sensor according to the present invention includes: a package made of a resin and having a concave portion; a lead formed integral with the package by insert molding, with its one end exposed into the concave portion and its other end extended from the package to the outside; a semiconductor chip arranged in the concave portion; and a bonding wire electrically connecting the semiconductor chip and the lead with each other. An interface between the lead and the package on the side of the concave portion is covered with a first protective resin portion of electrically insulating property, and the bonding wire is covered with a second protective resin portion that is softer than the first protective resin portion. 
   According to the semiconductor pressure sensor of the present invention, the damage of the bonding wires can be reduced even under an environment in which the temperature and pressure change rapidly or drastically, and hence the life time of the pressure sensor can be increased. 
   The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view showing a semiconductor pressure sensor according to a first embodiment of the present invention. 
       FIG. 2  is a cross sectional view of essential portions of the semiconductor pressure sensor into which leads different from those in  FIG. 1  are built. 
       FIG. 3  is a cross sectional view of essential portions of the semiconductor pressure sensor into which leads different from those in  FIG. 1  are built. 
       FIG. 4  is a cross sectional view of essential portions of the semiconductor pressure sensor into which leads different from those in  FIG. 1  are built. 
       FIG. 5  is a cross sectional view showing a semiconductor pressure sensor according to a second embodiment of the present invention. 
       FIG. 6  is a cross sectional view showing a semiconductor pressure sensor according to a third embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Now, preferred embodiments of the present invention will be described in detail while referring to the accompanying drawings. Throughout respective figures, the same or corresponding members or parts are identified by the same reference numerals and characters. 
   Embodiment 1 
     FIG. 1  is a cross sectional view that shows a semiconductor pressure sensor according to a first embodiment of the present invention. 
   In this semiconductor pressure sensor, a concave portion  1   a  for insulation of a semiconductor chip in the form of a sensor chip  3  is formed in a package  1  made of epoxy resin of a thermosetting property. 
   The sensor chip  3  is comprised of a glass seat  3   b  with a bonding portion  5  bonded to the bottom of the concave portion  1   a , and a diaphragm  3   a  made of a Si material and attached to the glass seat  3   b  through anode bonding. Formed between the diaphragm  3   a  and the glass seat  3   b  is a vacuum chamber  3   c  which serves as a reference for measured pressure. 
   A strain gauge, which constitutes a Wheatstone bridge circuit, is formed on the diaphragm  3   a.    
   Leads  2  are formed integral with the package  1  by insert molding, and have their one end exposed into the concave portion  1   a , and their other end extended from the package  1  to the outside. At the one end of each lead  2 , there is formed a bonding pad  2   a  that is bent in its immediate portion toward the diaphragm  3   a  in a stepwise fashion. A plurality of bonding wires  4  made of gold have their opposite ends connected with the bonding pads  2   a  and the edge of the diaphragm  3   a  by means of thermo-compression bonding using ultrasonic waves in combination. 
   In order to ensure protection, corrosion resistance and insulation against invasion of foreign matter into a medium to be measured, a first protective resin portion  6  and a second protective resin portion  7  both of electrically insulating property are formed in the concave portion  1   a.    
   The first protective resin portion  6  covers the bottom of the concave portion  1   a . The first protective resin portion  6  need only to cover at least interfaces between the leads  2  and the package  1  at least on the side of the concave portion  1   a . The first protective resin portion  6  is made of a gummy or gel material of relatively high hardness, and serves to primarily prevent air bubbles from being released from the interfaces between the leads  2  and the package  1  into the concave portion  1  a when the interior of the concave portion  1   a  is subjected to negative pressure. In other words, the first protective resin portion  6  has a sealing function. 
   Here, not that the bonding wires  4  and the leads  2  shown in  FIG. 1  serve as output paths from the Wheatstone bridge circuit, but for bonding wires (not shown) and leads (not shown) used for impressing a reference potential to the Wheatstone bridge circuit, the first protective resin portion  6  also serves, of course, to prevent release of air bubbles from interfaces between the leads and the package  1  into the concave portion  1   a.    
   The second protective resin portion  7  covering the first protective resin portion  6  is softer than the first protective resin portion  6 , and covers the bonding wires  4 , the bonding pads  2   a , and the diaphragm  3   a . In case where the semiconductor pressure sensor is used for detecting an intake air pressure in a motor vehicle for example, a fluorine-based resin with high chemical resistance such as gasoline, engine oil, etc., is used as the second protective resin portion  7 . 
   In the semiconductor pressure sensor as constructed above, when the pressure of the medium or fluid to be measured is applied from a direction of arrow A to the diaphragm  3   a , the diaphragm  3   a  is caused to strain deformed. As a result, a stress is applied to the strain gauge, and the resistance value of the strain gauge changes in proportion to the magnitude of the stress. 
   On the other hand, the reference potential is impressed to the strain gauge, which constitutes the Wheatstone bridge circuit, through the leads (not shown) and the bonding wires (not shown), so the output voltage from the Wheatstone bridge circuit changes in accordance with a change in the resistance value of the strain gauge. The amount of change in the output voltage of the Wheatstone bridge is output to the outside through the bonding wires  4  and the leads  2 , whereby the pressure of the fluid to be measured is detected. 
   According to the semiconductor pressure sensor as constructed above, since the interfaces between the leads  2  and the package  1  on the side of the concave portion  1   a  is covered with the first protective resin portion  6  of electrically insulating property, even if there exist air bubbles in minute gaps on the interfaces between the package  1  and the leads  2 , it is possible to prevent the air bubbles from being released into the concave portion  1   a , and hence it is also possible to prevent breakage or damage of the bonding wires  4  resulting from the air bubbles. 
   In addition, the bonding wires  4  are uniformly covered with the second protective resin portion  7  that is softer than the first protective resin portion  6 . Accordingly, there will be no damage of the bonding wires  4  due to a difference in the coefficient of linear expansion, the elastic modulus, etc., between different protection resin portions. 
   Moreover, since each of the leads  2  is provided at its one end with a bonding pad  2   a  that is formed by being bent in its immediate portion toward the diaphragm  3   a  in a stepwise fashion, the first protective resin portion  6  is formed without covering the bonding wires  4  at all. 
   Here, note that the configuration or shape of the one end of each lead  2  may be as shown in  FIG. 2 ,  FIG. 3  or  FIG. 4 . 
   In the case of a lead  2  shown in  FIG. 2 , one end of the lead  2  is bent at an angle of 90 degrees, and a bonding wire  4  is connected at its one end with a tip face or edge of the bent end of the lead  2 . 
   In this case, the lead  2  is bent at an angle of 90 degrees, so the thickness of a first protective resin portion  6  can be set without receiving the influence of the thickness of the lead  2 . Also, there is an advantage that a molding die used when the package  1  and the lead  2  are molded by insert molding also need only have a simple construction. 
   In addition, in the case of a lead  2  shown in  FIG. 3 , one end of the lead  2  is formed into a trapezoidal shape by press forming, and a bonding wire  4  is connected at its one end with a top side or face of the trapezoidal end of the lead  2 . 
   In this case, too, similar to the one shown in  FIG. 2 , the thickness of a first protective resin portion  6  can be set without receiving the influence of the thickness of the lead  2 . 
   Further, in the case of a lead  2  shown in  FIG. 4 , one end of the lead  2  is turned back or bent at an angle of 180 degrees, and a bonding wire  4  is connected at its one end with an upper face of the turned-back end of the lead  2 . 
   In this case, too, similar to the one shown in  FIG. 2 , the thickness of a first protective resin portion  6  can be set without receiving the influence of the thickness of the lead  2 . 
   Embodiment 2 
     FIG. 5  is a cross sectional view that shows a semiconductor pressure sensor according to a second embodiment of the present invention. 
   In this semiconductor pressure sensor, a sensor chip  3  is bonded to the bottom of a concave portion  1   a  through a first protective resin portion  6 . 
   The construction of this second embodiment other than the above is similar to that of the first embodiment. 
   According to the semiconductor pressure sensor of this embodiment, advantageous effects similar to those of the first embodiment can be achieved, and in addition, the first protective resin portion  6  has not only a function to seal interfaces between leads  2  and a package  1  on the side of the concave portion  1   a  but also a function to bond the sensor chip  3  to the package  1 , whereby a step of applying a bonding material to a bonding portion  5  required in the first embodiment becomes unnecessary and hence assembling efficiency is improved. 
   Embodiment 3 
     FIG. 6  is a cross sectional view that shows a semiconductor pressure sensor according to a third embodiment of the present invention. 
   In this semiconductor pressure sensor, a processor chip  8 , which serves to correct and amplify an electric signal from a sensor chip  3  for detecting pressure, is arranged in a concave portion  1   a  together with the sensor chip  3 . 
   The processor chip  8  in the form of a semiconductor chip is bonded to a protruded portion of the bottom of the concave portion  1   a  through a bonding portion  5 . 
   In this processor chip  8 , too, similar to the sensor chip  3 , a plurality of bonding wires  4  are connected at their opposite ends with bonding pads  2   a  and edges of the processor chip  8  by means of thermo-compression bonding using ultrasonic waves in combination. 
   The construction of this third embodiment other than the above is similar to that of the first embodiment, and the same advantageous effects as in the first embodiment can be achieved. 
   Here, note that in the above-mentioned first through third embodiments, a thermosetting resin is used as the material for the package  1  but a thermoplastic resin may be employed. 
   In addition, although the sensor chip has been described as the one using a piezoresistive effect, a semiconductor pressure sensor chip of a capacitance type can be used for example. 
   Moreover, the present invention can also be applied to a semiconductor pressure sensor that is constructed of an IC in which the functions of the sensor chip  3  and the processor chip  8  are formed on one and the same chip. 
   While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.