Abstract:
A lid for sealing a ceramic container receiving a semiconductor device such as an acceleration sensor is provided. The lid has an electrodeposition coating layer having a thickness of approximately 10 μm, which is formed by plating the outer surface of the 42 alloy plate having a thickness of approximately 100 μm with chrome and by forming a black color compound at the chrome plating layer. The lid is fixed to the upper end of a sidewall part of the ceramic container by means of a thermosetting resin. The thickness of the thermosetting resin after thermosetting is adjusted to be approximately 20 to 30 μm. The conventional ceramic lid needs 200 μm or more in thickness in view of strength, and has difficulty in laser processing. The lid of the present invention allows decreasing the thickness by half, and facilitating the imprint by laser.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a package for a semiconductor device, and more particularly to the structure of a lid of a package for an acceleration sensor formed by a semiconductor.  
         [0003]     2. Description of the Related Art  
         [0004]      FIGS. 2A and 2B  are views showing the structure of a conventional acceleration sensor. Specifically,  FIG. 2A  is a perspective view of a sensor body, and  FIG. 2B  is a sectional view of a package having the sensor body incorporated therein.  
         [0005]     As shown in  FIG. 2A , the sensor body  10  includes a fixing part  11  for fixing the sensor body to the package, a weight part  13  supported by four beams  12  extending from the fixing part  11  such that the weight part  13  is displaced due to acceleration, and piezo resistance elements  14  respectively placed at surfaces of the beams  12 . The fixing part  11 , the beams  12 , and the weight part  13  are integrally shaped and made of silicon.  
         [0006]     As shown in  FIG. 2B , the package having the sensor body incorporated therein is formed by receiving the sensor body  10  in a ceramic container  20  and covering the ceramic container  20  with a ceramic lid  30 .  
         [0007]     The ceramic container  20  includes a bottom part  21  and a sidewall part  22 . The sensor body  10  is fixed to the bottom part of the ceramic container  20 . At the upper side of the sidewall part  22 , a step part  22   a  is formed. A metal terminal  23  penetrates through the sidewall part  22  so as to extend from the step part  22   a  to the outside of the bottom part  21 . The piezo resistance elements  14  placed at the surface of the sensor body  10  is connected to the metal terminal  23  via metal wires  24 . The ceramic lid  30  is fixed to the sidewall part  22  of the ceramic container  20  by means of an adhesive agent. Noted that the weight part  13  of the sensor body  10  is spaced apart from the ceramic container  20  and the ceramic lid  30  such that the weight part  13  does not come into contact with the ceramic container  20  and the ceramic lid  30  even though the weight part  13  is displaced due to acceleration.  
         [0008]     The acceleration sensor is mounted on an apparatus by means of the metal terminal  23  disposed at the rear side of the package. When acceleration is applied, the weight part  13  of the sensor body  10  is displaced, and then the four beams  12  are bent. As a result, resistance values of the piezo resistance elements  14  placed at the surfaces of the beams  12  are changed according to bending amounts of the respective beams  12 . Accordingly, a three-dimensional direction and a magnitude of the acceleration are calculated based on the resistance values of the piezo resistance elements  14 .  
         [0009]     Japanese Patent Kokai No. 5-251577 discloses a method of manufacturing a ceramic package that has a capability of electromagnetic shield by metallizing a ceramic lid and by sealing the metallized ceramic lid and a base substrate with a conductive sealer. Japanese Patent Kokai No. 8-17951 discloses a semiconductor device having excellent printing and heat radiating characteristics by bonding a light color metallic plate coated with a dark color paint on the surface of a package and by burning away the paint with laser beams for printing.  
         [0010]     Since the ceramic lid  30  is used to cover the ceramic container  20 , the above-described acceleration sensors have the following problems:  
         [0011]     (1) If the thickness of a ceramic plate is less than 0.2 mm, the ceramic plate may warp or crack. For this reason, it is difficult to provide a thinner ceramic plate, and making it difficult to reduce the overall thickness of the package. Furthermore, the acceleration sensors are more and more installed in mobile phones etc. having a function of a global position system (GPS). This leads to a demand for further miniaturization of the package.  
         [0012]     (2) Printing on the package using laser beams is superior to printing on the package using ink in view of processing speed and simplified processing. However, printing on the ceramic with the laser beams requires high energy. Consequently, the provision of a special high-power laser oscillator is required, and a conventional manufacturing unit cannot be used.  
       SUMMARY OF THE INVENTION  
       [0013]     An object of the present invention is to provide a thinner package for a semiconductor device and excellent printing properties that are readily available.  
         [0014]     According to the present invention, there is provided a package for a semiconductor device including a ceramic container having an internal space for receiving the semiconductor device, and a lid attached to an upper end of a sidewall part of the ceramic container for sealing the internal space of the ceramic container. The lid is formed by a black color electrodeposition coating layer applied either on the outer surface or the inner and outer surfaces of a stainless steel plate or a 42 alloy plate, or by applying copper coating layers on the inner and outer surfaces of a stainless steel plate and by black-finishing the copper coating layers by means of oxidization, or by a heat-resistant polyimide tape or a glass epoxy plate.  
         [0015]     The lid is formed by a metal plate such as stainless steel or 42 alloy, a heat-resistant polyimide tape, or a glass epoxy plate. Accordingly, the lid is thinner and stronger than a ceramic lid formed by a ceramic plate. Furthermore, the outer surface of the metal plate is black-finished, and therefore, it is possible to easily imprint characters without using a high-power laser beam.  
         [0016]     A thermosetting resin may be used to attach the lid to the ceramic container. Alternatively, the lid may be attached to the ceramic container by coating a thermoplastic resin on an entire surface of an inner side of the lid and by pressing the lid to the ceramic container while heating the thermoplastic resin. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a sectional view showing an acceleration sensor according to a first embodiment of the present invention;  
         [0018]      FIGS. 2A and 2B  are a perspective view and a sectional view, respectively, showing the structure of a conventional acceleration sensor;  
         [0019]      FIG. 3  is a sectional view showing an acceleration sensor according to a second embodiment of the present invention;  
         [0020]      FIG. 4  is a sectional view showing an acceleration sensor according to a third embodiment of the present invention;  
         [0021]      FIG. 5  is a sectional view showing an acceleration sensor according to a fourth embodiment of the present invention; and  
         [0022]      FIG. 6  is a sectional view showing an acceleration sensor according to a fifth embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings.  
       First Embodiment  
       [0024]     In  FIG. 1 , the same reference numerals are used for elements similar to those shown in  FIGS. 2A and 2B .  
         [0025]     As shown in  FIG. 1 , an acceleration sensor includes a sensor body  10  and a ceramic container  20  having the sensor body  10  received therein, which are similar to the sensor body  10  and the ceramic container  20  shown in  FIGS. 2A and 2B . The acceleration sensor further includes a lid  30 A for sealing a top part of the ceramic container  20 , which is different from the lid  30  shown in  FIGS. 2A and 2B .  
         [0026]     Specifically, as shown in  FIG. 2A , the sensor body  10 , for example, includes a fixing part  11  for fixing the sensor body to the package, a weight part  13  supported by four beams  12  extending from the fixing part  11  so as to be displaced due to acceleration, and piezo resistance elements  14  respectively placed at the surfaces of the beams  12 . The fixing part  11 , the beams  12 , and the weight part  13  are integrally shaped and made of silicon.  
         [0027]     The ceramic container  20  includes a bottom part  21  and a sidewall part  22 . A protrusion  21   a  is formed at the center of the bottom part  21 , to which the fixing part  11  of the sensor body  10  is fixed by means of an adhesive agent. At the upper side of the sidewall part  22 , a step part  22   a  is formed. A metal terminal  23  for an external connection penetrates through the sidewall part  22  so as to extend from the step part  22   a  to the outside of the bottom part  21 . The piezo resistance elements  14  placed at the surface of the sensor body  10  is connected to the metal terminal  23  via metal wires  24 .  
         [0028]     On the other hand, the lid  30 A is formed by applying a black color electrodeposition coating layer  32  on an outer surface of a 42 alloy plate  31 , which is made of an alloy composed of 42% nickel and 58% iron. The electrodeposition coating layer  32  may be formed by plating the outer surface of the 42 alloy plate  31  with chrome, and then by forming a black color compound at the chrome plating layer. The thickness of the 42 alloy plate  31  is approximately 100 μm, and the thickness of the electrodeposition coating layer  32  is approximately 10 μm.  
         [0029]     The lid  30 A is fixed to the upper end of the sidewall part  22  of the ceramic container  20  by means of thermosetting resin  41  in a hermetically sealed fashion such that no outside moisture is introduced into the internal space of the ceramic container  20 . The thickness of the thermosetting resin  41  after thermosetting is adjusted to be approximately 20 to 30 μm, and the difference in coefficient of thermal expansion between the lid  30 A and the ceramic container  20  is absorbed by plastic deformation of the thermosetting resin  41 . Noted that the weight part  13  of the sensor body  10  is spaced apart from the ceramic container  20  and the lid  30 A such that the weight part  13  does not come into contact with the ceramic container  20  and the lid  30 A even though the weight part  13  is displaced due to acceleration.  
         [0030]     Operation of the acceleration sensor is similar to that shown in  FIGS. 2A and 2B . Specifically, the acceleration sensor is mounted on an apparatus by means of the metal terminal  23  disposed at the rear side of the package. When acceleration is applied, the weight part  13  of the sensor body  10  is displaced, and then the four beams  12  are bent. As a result, resistance values of the piezo resistance elements  14  placed at the surfaces of the respective beams  12  are changed according to bending amounts of the beams  12 . Accordingly, a three-dimensional direction and a magnitude of the acceleration are calculated based on the resistance values of the piezo resistance elements  14 .  
         [0031]     The acceleration sensor according to the first embodiment of the present invention therefore has the following advantages:  
         [0032]     (a) The lid  30 A with the black color electrodeposition coating layer  32  applied on the outer surface of the 42 alloy plate  31  is used for a lid of the package. Consequently, it is possible to reduce the thickness of the lid to approximately 0.1 mm, and thus, to reduce the thickness of the entire package to approximately 1 mm. Noted that the width and length of the package are both approximately 6.2 mm.  
         [0033]     (b) Since the black color electrodeposition coating layer  32  is applied on the outer surface of the lid  30 A, printing with a low-power laser beam is possible, and therefore, conventional manufacturing apparatuses can be used.  
         [0034]     (c) Since the lid is made of a metal, the lid has excellent impact resistance.  
         [0035]     (d) The material used for the lid  30 A is less expensive than ceramic, and the material can be processed more easily than the ceramic. Consequently, a manufacturing cost can be reduced.  
         [0036]     Furthermore, the black color electrodeposition coating layer  32  may be applied by means of a so-called alumite which is formed by oxidizing an aluminum plating. The alumite has excellent insulation properties, and therefore, electric short due to contact of the lid and the metal wires  24  can be prevented when the alumite is formed on an inner surface of the lid.  
       Second Embodiment  
       [0037]      FIG. 3  is a sectional view showing an acceleration sensor according to a second embodiment of the present invention. In  FIG. 3 , the same reference numerals are used for elements similar to those used in  FIG. 1 .  
         [0038]     The acceleration sensor includes a sensor body  10  and a ceramic container  20  having the sensor body  10  received therein, which are similar to the sensor body  10  and the ceramic container  20  shown in  FIG. 1 . The acceleration sensor further includes a lid  30 B for sealing a top part of the ceramic container  20 , which is different from the lid  30 A shown in  FIG. 1 .  
         [0039]     The lid  30 B is formed by applying copper coating layers  34   a  and  34   b  each having a thickness of approximately 10 μm on opposite surfaces of a stainless steel  33  having a thickness of approximately 100 μm, respectively, and then by black-finishing the copper coating layers  34   a  and  34   b  by means of oxidization. The lid  30 B is fixed to the upper end of the sidewall part  22  of the ceramic container  20  by means of thermosetting resin  41  having a thickness of approximately 20 to 30 μm, in a similar manner as the first embodiment of the present invention. Other construction and operation of the lid  30 B are similar to those of the first embodiment.  
         [0040]     The acceleration sensor according to the second embodiment of the present invention therefore has the following advantages:  
         [0041]     (a) The lid  30 B with the black-finished copper coating layers  34   a  and  34   b  applied on the opposite surfaces of the stainless steel  33  is used for a lid of the package. Consequently, it is possible to reduce the thickness of the lid to approximately 0.1 mm, and thus, to reduce the thickness of the entire package to approximately 1 mm.  
         [0042]     (b) Since the surfaces of the lid  30 B are black-finished, it is possible to imprint characters with a low-power laser beam, and therefore, conventional manufacturing apparatuses can be used.  
         [0043]     (c) Since the lid is made of a metal, the lid has excellent impact resistance.  
         [0044]     (d) The material used for the lid is less expensive than ceramic, and the material can be processed more easily than the ceramic. Consequently, a manufacturing cost can be reduced.  
         [0045]     (e) The copper coating layers  34   a  and  34   b , which are black-finished by oxidization, have excellent insulation properties, and therefore, no electric short occurs even though the lid  30 B contacts with the metal wires  24 .  
       Third Embodiment  
       [0046]      FIG. 4  is a sectional view showing an acceleration sensor according to a third embodiment of the present invention. In  FIG. 4 , the same reference numerals are used for elements similar to those used in  FIG. 1 .  
         [0047]     The acceleration sensor includes a sensor body  10  and a ceramic container  20  having the sensor body  10  received therein, which are similar to the sensor body  10  and the ceramic container  20  shown in  FIG. 1 . The acceleration sensor further includes a lid  30 C for sealing a top part of the ceramic container  20 , which is different from the lid  30 A shown in  FIG. 1 .  
         [0048]     The lid  30 C is made of a heat-resistant polyimide tape  35  having a thickness of approximately 100 μm. The lid  30 C is fixed to the upper end of the sidewall part  22  of the ceramic container  20  by means of thermosetting resin  41  having a thickness of approximately 20 to 30 μm, in a similar manner as the first embodiment of the present invention. Other construction and operation of the lid  30 C are similar to those of the first embodiment of the present invention.  
         [0049]     The acceleration sensor according to the third embodiment of the present invention therefore has the following advantages:  
         [0050]     (a) The heat-resistant polyimide tape  35  is used for a lid of the package. Consequently, it is possible to reduce the thickness of the lid to approximately 0.1 mm, and thus, to reduce the thickness of the entire package to approximately 1 mm.  
         [0051]     (b) Since the lid  30 C is made of the heat-resistant polyimide, it is possible to imprint characters with a low-power laser beam, and therefore, conventional manufacturing apparatuses can be used.  
         [0052]     (c) The material used for the lid is less expensive than ceramic, and the material can be processed more easily than the ceramic. Consequently, a manufacturing cost can be reduced.  
         [0053]     (d) The heat-resistant polyimide has an excellent insulation property, and therefore, no electric short occurs even though the lid  30 C contacts with the metal wires  24 .  
         [0054]     It should be noted that a glass epoxy plate having a thickness of approximately 100 μm may be used instead of the heat-resistant polyimide tape  35 . The lid made of glass epoxy plate provides similar advantage as the lid  30 C made of the heat-resistant polyimide tape  35 .  
       Fourth Embodiment  
       [0055]      FIG. 5  is a sectional view showing an acceleration sensor according to a fourth embodiment of the present invention. In  FIG. 5 , the same reference numerals are used for elements similar to those used in  FIG. 1 .  
         [0056]     The acceleration sensor includes a sensor body  10  and a ceramic container  20  having the sensor body  10  received therein, which are similar to the sensor body  10  and the ceramic container  20  shown in  FIG. 1 . The acceleration sensor further includes a lid  30 D for sealing a top part of the ceramic container  20 , which is slightly different from the lid  30 A shown in  FIG. 1 .  
         [0057]     The lid  30 D is formed by applying a black color electrodeposition coating layer  32  on the outer surface of a 42 alloy plate  31  having a thickness of approximately 100 μm, in a similar manner as the first embodiment of the present invention, and by coating a thermoplastic resin  36  having a thickness of 20 to 30 μm on the entire surface of a back side, or an inner surface, of the 42 alloy plate  31 . The lid  30 D is fixed to the upper end of the sidewall part  22  of the ceramic container  20  by thermal pressing. Other construction and operation of the lid  30 D are similar to those of the first embodiment of the present invention.  
         [0058]     The acceleration sensor according to the fourth embodiment of the present invention therefore has the following advantages:  
         [0059]     (a) The lid  30 D with the black color electrodeposition coating layer  32  applied on the outer surface of the 42 alloy plate  31  is used for a lid of the package. Consequently, it is possible to reduce the thickness of the lid to approximately 0.1 mm.  
         [0060]     (b) Since the black color electrodeposition coating layer  32  is applied on the outer surface of the lid  30 D, it is possible to imprint characters with a low-power laser beam, and therefore, conventional manufacturing apparatuses can be used.  
         [0061]     (c) Since the lid is made of a metal, the lid has excellent impact resistance.  
         [0062]     (d) The material used for the lid is less expensive than ceramic, and the material can be processed more easily than the ceramic. Consequently, a manufacturing cost can be reduced.  
         [0063]     (e) Since the thermoplastic resin  36  is coated on the entire surface of the inside of lid, no electric short occurs even though the lid  30 D contacts with the metal wires  24 .  
         [0064]     (f) Since the coated thermoplastic resin  36  serves as an adhesive agent, application of the adhesive agent is not required when the ceramic container is covered with the lid.  
         [0065]     It should be noted that a stainless steel  33  may be used instead of the 42 alloy plate  31  and a black-finished copper coating layer  34  may be used instead of the black color electrodeposition coating layer  32 . This modification provides similar advantages as the fourth embodiment of the present invention.  
       Fifth Embodiment  
       [0066]      FIG. 6  is a sectional view showing an acceleration sensor according to a fifth embodiment of the present invention. In  FIG. 6 , the same reference numerals are used for elements similar to those used in  FIG. 1 .  
         [0067]     The acceleration sensor includes a sensor body  10  and a ceramic container  20  having the sensor body  10  received therein, which are similar to the sensor body  10  and the ceramic container  20  shown in  FIG. 1 . The acceleration sensor further includes a lid  30 E for covering the top part of the ceramic container  20 , which is slightly different from the lid  30 A shown in  FIG. 1 .  
         [0068]     The lid  30 E is formed by coating a thermoplastic resin  36  having a thickness of 20 to 30 μm on the entire surface of an inner side of a heat-resistant polyimide tape  35  having a thickness of approximately 100 μm. The lid  30 E is fixed to the upper end of the sidewall part  22  of the ceramic container  20  by thermal pressing. Other construction and operation of the lid  30 E are similar to those of the first embodiment of the present invention.  
         [0069]     The acceleration sensor according to the fifth embodiment of the present invention therefore has the following advantages:  
         [0070]     (a) The heat-resistant polyimide tape  35  is used for a lid of the package. Consequently, it is possible to reduce the thickness of the lid to approximately 0.1 mm, and thus, to reduce the thickness of the entire package to approximately 1 mm.  
         [0071]     (b) Since the lid  30 E is made of the heat-resistant polyimide, it is possible to imprint characters with a low-power laser beam, and therefore, conventional manufacturing apparatuses can be used.  
         [0072]     (c) The materials used for the lid are less expensive than ceramic, and the materials can be processed more easily than the ceramic. Consequently, a manufacturing cost can be reduced.  
         [0073]     (d) The heat-resistant polyimide and the thermoplastic resin have excellent insulation properties, and therefore, no electric short occurs even though the lid  30 E contacts with the metal wires  24 .  
         [0074]     (e) Application of an adhesive agent is not required when the ceramic container is covered with the lid.  
         [0075]     It should be noted that a glass epoxy plate having a thickness of approximately 100 μm may be used instead of the heat-resistant polyimide tape  35 . The lid made of glass epoxy plate provides similar advantage as the lid  30 E made of the heat-resistant polyimide tape  35 .  
         [0076]     This application is based on Japanese patent application No. 2004-371102 which is herein incorporated by reference.