Abstract:
A semiconductor device includes: a semiconductor chip; a package for accommodating the chip, wherein the package has a box shape with an opening and a bottom; and a cover for sealing the opening of the package. The semiconductor chip is disposed on the bottom of the package. The cover has a plate shape. The cover includes a protrusion, which is disposed at a center of the plate shape. The protrusion protrudes toward an outside of the package.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on Japanese Patent Application No. 2007-62166 filed on Mar. 12, 2007, the disclosure of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a physical quantity sensor and a semiconductor device having a package and a cover. 
   BACKGROUND OF THE INVENTION 
   A semiconductor device as a sensor includes a case and a cover, which is disclosed in U.S. Pat. No. 6,906,412 corresponding to JP-A-2004-3886. The case accommodates a semiconductor chip, and the cover seals an opening of the case. Specifically, the sensor includes the semiconductor sensor chip, a package as the case and a lid as the cover. The package has a rectangular box shape, and the lid has a rectangular plate shape. The sensor chip is mounted on an inner bottom of the package. A terminal base is formed on the inner bottom of the package, and a bonding pad is formed on the terminal base. The sensor chip is connected to the bonding pad through a bonding wire. The opening of the package is covered and sealed with the lid. 
   The above sensor is integrally molded together with other electric elements for providing a circuit for the sensor. However, since the lid has the rectangular plate shape, the lid may be deformed toward the package side by pressure in a molding process. When the lid is made of metal, the lid may contact the semiconductor chip or the bonding wire so that the deformation causes to short-circuit the chip. 
   When the lid is made of material other than metal, for example, when the lid is made of resin, the deformation may cause to generate stress in the bonding wire or the semiconductor chip. When the thickness of the lid becomes larger, the manufacturing cost of the sensor increases. Further, in case of thick lid, when the lid is fixed by a welding method, the welding becomes difficult because the thick lid radiates heat largely. 
   Thus, it is required for the sensor to improve pressure resistance of the lid. 
   SUMMARY OF THE INVENTION 
   In view of the above-described problem, it is an object of the present disclosure to provide a physical quantity sensor. It is another object of the present disclosure to provide a semiconductor device having a package and a cover. 
   According to a first aspect of the present disclosure, a physical quantity sensor includes: a case made of resin; a connector terminal molded in the case; and a sensing element molded in the case. The sensing element is electrically coupled with the connector terminal. The sensing element includes: a semiconductor chip; a package for accommodating the chip, wherein the package has a box shape with an opening and a bottom; and a cover for sealing the opening of the package. The semiconductor chip is disposed on the bottom of the package. The cover has a plate shape. The cover includes a protrusion, which is disposed at a center of the plate shape, and the protrusion protrudes toward an outside of the package. 
   In the above sensor, the mechanical strength of the cover is improved, so that the pressure resistance of the sensing element increases. Further, the deformation of the cover is reduced. Furthermore, the distance between the semiconductor chip and a bonding wire or the like is sufficiently secured, so that short-circuit of the sensing element is prevented. 
   According to a second aspect of the present disclosure, a semiconductor device includes: a semiconductor chip; a package for accommodating the chip, wherein the package has a box shape with an opening and a bottom; and a cover for sealing the opening of the package. The semiconductor chip is disposed on the bottom of the package. The cover has a plate shape. The cover includes a protrusion, which is disposed at a center of the plate shape, and the protrusion protrudes toward an outside of the package. 
   In the above device, the mechanical strength of the cover is improved, so that the pressure resistance of the semiconductor chip increases. Further, the deformation of the cover is reduced. Furthermore, the distance between the semiconductor chip and a bonding wire or the like is sufficiently secured, so that short-circuit of the semiconductor chip is prevented. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIG. 1  is a cross sectional view showing an acceleration sensor according to a first embodiment; 
       FIG. 2  is a cross sectional view showing a sensing element in the sensor; 
       FIG. 3  is a partial perspective view showing a lid in the sensor; 
       FIG. 4  is a graph showing a relationship between pressure and deformation of the lid in a first example case of the sensor; 
       FIG. 5  is a graph showing a relationship between pressure and deformation of the lid in a second example case of the sensor; 
       FIG. 6  is a graph showing a relationship between pressure and deformation of the lid in a third example case of the sensor; 
       FIG. 7  is a partial perspective view showing a lid in an acceleration sensor according to a second embodiment; 
       FIG. 8  is a graph showing a relationship between pressure and deformation of the lid in a fourth example case of the sensor; 
       FIG. 9  is a graph showing a relationship between pressure and deformation of the lid in a fifth example case of the sensor; 
       FIG. 10  is a graph showing a relationship between pressure and deformation of the lid in a sixth example case of the sensor; 
       FIG. 11  is a partial perspective view showing a lid in an acceleration sensor according to a third embodiment; 
       FIG. 12  is a graph showing a relationship between pressure and deformation of the lid in a seventh example case of the sensor; 
       FIG. 13  is a graph showing a relationship between pressure and deformation of the lid in an eighth example case of the sensor; 
       FIG. 14  is a graph showing a relationship between pressure and deformation of the lid in a ninth example case of the sensor; and 
       FIG. 15  is a cross sectional view showing a sensing element in an acceleration sensor according to a modification. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The inventors have studied about a semiconductor device having a case and a cover. Specifically, when a center of the cover protrudes toward an outside of the case, pressure resistance increases without thickening the thickness of the cover. 
   First Embodiment 
     FIG. 1  shows an acceleration sensor  1  as a semiconductor device for detecting acceleration, converting the detected acceleration to a signal and outputting the signal. 
   The acceleration sensor  1  includes an acceleration sensing element  2 , an electronic element such as a capacitor (not shown), multiple connector terminals  3  and a case  4 . The sensing element  2  and the electronic element are connected to the connector terminal  3 . The case  4  made of resin mold integrally seals the sensing element  2  and the electronic element. One end of the connector terminal  3  protrudes from a front of the case  4 . Further, a connector housing  40  is integrally formed around the one end of the connector terminal  3  such that the connector housing  40  surrounds the one end of the connector terminal  3 . A bushing  41  is integrally formed on a back of the case  4 . The sensor  1  is mounted on another equipment with the bushing  41 . 
     FIGS. 2 and 3  show the sensing element  2 . Specifically,  FIG. 3  shows a one-fourth part of a lid  22  in the sensing element  2 . The sensing element  2  includes a semiconductor sensor chip  20  as a semiconductor chip, a ceramic package  21  as a case and the lid as a cover. 
   The semiconductor sensor chip  20  is a semiconductor integrated circuit that detects acceleration, covert the detected acceleration to a signal and output the signal. The chip  20  includes an acceleration detection portion  200  and a converting circuit  201 . The acceleration detection portion  200  detects the acceleration, which is applied to the sensing element  2 . The converting circuit  201  converts the detected acceleration to the signal and outputs the signal. The acceleration detection portion  200  is disposed over and mounted on the converting circuit  201 . The acceleration detection portion  200  is electrically coupled with the converting circuit through a bonding wire or a lead. 
   The ceramic package  21  has a square cylindrical shape with a bottom  212 . The ceramic package  21  is made of ceramic, and accommodates the chip  20 . The package  21  has a sidewall  210  with a stage  211 , which is disposed inside of the package  21 . A bonding pad is formed on the stage  211 . The package  21  has the bottom  212 , on which the chip  20  is mounted. The chip  20  is electrically connected to the bonding pad through a bonding wire or a lead. A seal ring  214  is bonded to a top of the package  21  by a brazing method, the top which is disposed on an opening side of the package  21 . The package  21  has an opening  213 . 
   The lid  22  has a square plate shape, and made of metal. The lid  22  seals, i.e., covers the opening  213  of the package  21  so that the chip  20  is accommodated in the package  21 . The outline of the lid  22  is larger than the opening  213  of the package  21 . The lid  22  includes a protrusion  220 , which is disposed at a center of the lid  22 . The protrusion has a dome shape protruding toward the outside of the package  21  and having a predetermined curvature. Specifically, as shown in  FIG. 3 , the outline of the protrusion  22  is a circular shape so that the protrusion is a circular domed shape. The height h of the protrusion  220  and the thickness t of the lid  22  are defined as shown in  FIG. 3 . The height h is almost equal to the thickness t. In  FIG. 3 , the height h is overdrawn with respect to the thickness t. The periphery of the lid  22  is seal welded on the seal ring  214 . Thus, the lid  22  seals the opening  213  of the package  21 . 
     FIGS. 4 to 6  shows effects of the lid  22  having the dome shape.  FIGS. 4 to 6  are graphs showing analysis results of deformation amount of the lid  22  when external pressure is applied to the lid  22 . In  FIG. 4 , IVA shows a case where the lid  22  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  220  of 0.1 mm. IVB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.1 mm. In  FIG. 5 , VA shows a case where the lid  22  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  220  of 0.25 mm. VB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.15 mm. In  FIG. 6 , VIA shows a case where the lid  22  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  220  of 0.5 mm. VIB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.2 mm. 
   When the sensing element  2  is molded with the case  4 , molding pressure is applied to the sensing element  2 . However, the protrusion  220  is disposed at the center of the lid  22 . Further, the height h of the protrusion  220  is set to be equal to the thickness t of the lid  22 . Specifically, in this case, as shown in  FIG. 4 , the deformation amount of the lid  22  with respect to the pressure in the curve IVA is about 60% of that in the curve IVB. Accordingly, without increasing the thickness of the lid  22 , the pressure resistance of the sensing element  2  is improved. Thus, when the case  4  molds the sensing element  2 , the deformation of the lid  22  caused by the molding pressure is reduced. Further, since the protrusion  220  of the lid  22  protrudes toward the outside of the semiconductor sensor chip  20 , even when the lid  22  is deformed toward the sensor chip  20 , a distance between the chip  20  and a bonding wire or a lead is sufficiently maintained. Thus, short-circuit of the chip  20  is prevented from occurring. 
   When the thickness t of the lid  22  is 0.1 mm, and the height h of the protrusion  220  is 0.25 mm, as shown in  FIG. 5 , the deformation amount of the lid  22  in the curve VA becomes smaller than that in the curve VB, which represents that the thickness is 0.15 mm, and the lid has the plate shape without a dome. When the thickness t of the lid  22  is 0.1 mm, and the height h of the protrusion  220  is 0.5 mm, as shown in  FIG. 6 , the deformation amount of the lid  22  in the curve VIA becomes smaller than that in the curve VIB, which represents that the thickness is 0.2 mm, and the lid has the plate shape without a dome. 
   Second Embodiment 
     FIG. 7  shows a lid  23  according to a second embodiment. The lid  23  has a protrusion  230 , which is disposed at a center of the lid  23 . The protrusion  230  protrudes toward the outside of the package  21 , and has a curved dome shape. Specifically, the protrusion  230  has a square domed shape. 
     FIGS. 8 to 10  shows effects of the lid  23  having the dome shape.  FIGS. 8 to 10  are graphs showing analysis results of deformation amount of the lid  23  when external pressure is applied to the lid  23 . In  FIG. 8 , VIIIA shows a case where the lid  23  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  230  of 0.1 mm. VIIIB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.1 mm. In  FIG. 9 , IXA shows a case where the lid  23  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  230  of 0.25 mm. IXB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.15 mm. In  FIG. 10 , XA shows a case where the lid  23  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  230  of 0.5 mm. XB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.2 mm. 
   In a case where the thickness of the lid  23  is 0.1 mm, and the height of the protrusion  230  is 0.1 mm, as shown in  FIG. 8 , the deformation amount of the lid  23  with respect to the pressure in the curve VIIIA is about 60% of that in the curve VIIIB. When the thickness t of the lid  23  is 0.1 mm, and the height h of the protrusion  230  is 0.25 mm, as shown in  FIG. 9 , the deformation amount of the lid  23  in the curve IXA becomes smaller than that in the curve IXB, which represents that the thickness is 0.15 mm, and the lid has the plate shape. When the thickness t of the lid  23  is 0.1 mm, and the height h of the protrusion  230  is 0.5 mm, as shown in  FIG. 10 , the deformation amount of the lid  23  in the curve XA becomes smaller than that in the curve XB, which represents that the thickness is 0.2 mm, and the lid has the plate shape. 
   Accordingly, without increasing the thickness of the lid  23 , the pressure resistance of the sensing element  2  is improved. Further, short-circuit of the chip  20  is prevented from occurring. 
   Third Embodiment 
     FIG. 11  shows a lid  24  according to a third embodiment. The lid  24  has a protrusion  240 , which is disposed at a center of the lid  24 . The protrusion  240  protrudes toward the outside of the package  21 , and has a curved dome shape. Specifically, the protrusion  240  has a square domed shape. Further, the outline of the protrusion  240  is a square with four corners  241 . The dome shape has a top  242 . An edge  243  is formed on the dome shape from the top  242  to each corner  241 . Thus, the edge  243  is formed along with a diagonal line of the square domed shape. 
     FIGS. 12 to 14  shows effects of the lid  24  having the dome shape.  FIGS. 12 to 14  are graphs showing analysis results of deformation amount of the lid  24  when external pressure is applied to the lid  24 . In  FIG. 12 , XIIA shows a case where the lid  24  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  240  of 0.1 mm. XIIB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.1 mm. In  FIG. 13 , XIIIA shows a case where the lid  24  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  240  of 0.25 mm. XIIIB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.15 mm. In  FIG. 14 , XIVA shows a case where the lid  24  has the dome shape with the thickness of 0.1 mm and the height of the protrusion  240  of 0.5 mm. XIVB shows a case as a comparison where a lid has a plate shape without a dome, and the thickness of the lid is 0.2 mm. 
   In a case where the thickness of the lid  24  is 0.1 mm, and the height of the protrusion  240  is 0.1 mm, as shown in  FIG. 12 , the deformation amount of the lid  24  with respect to the pressure in the curve XIIA is about 60% of that in the curve XIIB. When the thickness t of the lid  24  is 0.1 mm, and the height h of the protrusion  240  is 0.25 mm, as shown in  FIG. 13 , the deformation amount of the lid  24  in the curve XIVA becomes smaller than that in the curve XIVB, which represents that the thickness is 0.15 mm, and the lid has the plate shape. When the thickness t of the lid  24  is 0.1 mm, and the height h of the protrusion  240  is 0.5 mm, as shown in  FIG. 14 , the deformation amount of the lid  24  in the curve XIVA becomes smaller than that in the curve XIVB, which represents that the thickness is 0.2 mm, and the lid has the plate shape. 
   Accordingly, without increasing the thickness of the lid  24 , the pressure resistance of the sensing element  2  is improved. Further, short-circuit of the chip  20  is prevented from occurring. 
   (Modifications) 
   The shape of a protrusion in the lid  22 - 24  may be another shape such as an ellipsoid domed shape and a polygonal domed shape. 
   The shape of a protrusion in the lid  22 - 24  may be another dome shape. For example, a top portion of the protrusion may be a flat shape so that the protrusion is composed of a partially flat curved dome shape. Further, the protrusion may be a planar domed shape. 
   Although the semiconductor device  1  is the acceleration sensor, the semiconductor device  1  may be a physical quantity sensor for detecting physical quantity such as pressure, temperature and angular speed. 
   Although the semiconductor device  1  is the acceleration sensor, the semiconductor device  1  may be a device other than the physical quantity sensor. 
   While the invention has been described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the preferred embodiments and constructions. The invention is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, which are preferred, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.