Abstract:
An electronic product comprises a heat radiating plate, an electronic component securely mounted on the heat radiating plate and including a high power transistor, an enveloper including a frame member securely associated with the heat radiating plate to encompass the electronic component, and a lid member securely attached to an upper opening end of the frame member, thereby accommodating and sealing the electronic component in the enveloper, and at least one electrically conductive element passing and extending through the frame member. The frame member is made of a suitable resin material, and the lid member is made of one material selected from the group consisting of a ceramic material, a metal material, and a composite material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic product equipped with a heat radiating plate, and more particularly relates to an electronic product wherein an electronic component, including a high power transistor, is mounted on and adhered to a heat radiating plate, and is encapsulated in an enveloper. 
     2. Description of the Related Art 
     In general, a high power transistor, such as a power MOSFET or the like, which is frequently utilized in an analog amplifier or the like, generates a large amount of heat in operation. Thus, when an electronic component includes the high power transistor, an electronic product which uses the electronic component including the high power transistor, is equipped with a heat radiating plate made of a suitable metal material, such as copper or the like, to thereby facilitate radiation of heat from the electronic component. 
     The electronic product is provided with an enveloper for encapsulating the electronic component, to protect the electronic component from the outside, and leads of the electronic component pass and extend through the enveloper. When the enveloper is made of a suitable thermosetting resin, the electronic product is called a resin-sealed package. Also, when the enveloper is made of a suitable ceramic material, the electronic product is called a suitable ceramic package. Further, when the enveloper is made of a suitable metal material, the electronic product is called a metal package. 
     Conventionally, the electronic product of resin-sealed package type including, for example, the power MOSFET, is manufactured as explained below. 
     The electronic component is mounted on and adhered to the heat radiating plate, such that electrode pads of the electronic component, provided on a bottom face thereof, are electrically connected to the heat radiating plate. Also, the electronic component has two sets of electrode pads provided on a top face thereof, and the respective sets of electrode pads are connected to inner lead sections of two leads through bonding-wires. Thereafter, the electronic component and the inner lead sections are put in a molding cavity of a metal mold, and then sealing-resin is injected into the molding cavity, whereby the electronic component and the inner lead sections are enclosed with and encapsulated in the molded resin, with outer lead sections of the leads being protruded from the molded resin. Thus, in the conventional resin-sealed package, the electronic component and the inner lead sections are in direct contact with the molded resin. 
     When electric power consumption of the high power transistor is too large, it generates a very large amount of heat during an operation of the electronic component, SO that the molded resin may be subjected to deterioration and exfoliation. In this case, the characteristics of the electronic products are changed, resulting in a decline in the operational reliability. 
     Also, as stated above, since the molded resin is in direct contact with the electronic component and the inner lead sections, it may serve as a dielectric layer, resulting in production of a parasitic capacitance. Accordingly, due to the interference based on the production of the parasitic capacitance, the frequency characteristics of the electronic product may be deteriorated in a high-frequency band of more than 1 GHz. In particular, the deterioration of the high-frequency characteristics causes serious problems in microwave applications of the electronic product. 
     In manufacturing the electronic product of ceramic or metal package type, the electronic component is mounted on and adhered to the heat radiating plate, such that the bottom electrode pads of the electronic component are electrically connected to the heat radiating plate. Then, a rectangular ceramic or metal frame member is securely attached to the heat radiating plate such that the electronic component is encompassed by the ceramic or metal frame. Thereafter, the respective two leads are put on tops of opposing side walls of the ceramic or metal frame, and the respective sets of top electrode pads are connected to the inner lead sections of the two leads through bonding-wires. After the electrical connections of the sets of top electrode pads to the inner lead sections of the lead are finished, a ceramic or metal lid member is securely adhered to the top opening end of the ceramic or metal frame, thereby forming the ceramic or metal package for accommodating and sealing the electronic component, with the outer lead sections of the leads being protruded from the interface between the frame member and the lid member. 
     The electronic product of ceramic or metal package type not be subjected to the aforesaid problems involved in the resin-sealed package. However, it is impossible to obtain the inherent advantages derived from the resin-sealed package, as stated below. 
     Historically, the ceramic or metal package has been used in a high-power transistor, such as the power MOSFET or the like, for obtaining a high operational reliability. However, it is desirable to realize an electronic product, including the high-power transistor, as a resin-sealed package, which can be manufactured with a high productivity at low cost. 
     Certainly, according to the ceramic or metal package, it is possible to obtain a higher operational reliability and a higher operational performance, in comparison with the resin-sealed package. Nevertheless, the manufacturing cost of the ceramic or metal package, including the cost of materials, is higher than that of the resin-sealed package. 
     Especially, before an operational reliability of the electronic product of ceramic package type can be enhanced, it is necessary to eliminate thermal stresses, resulting from variations in temperature, from the ceramic package as much as possible. To suppress the production of thermal stresses in the ceramic package, thermal expansion coefficients of materials for manufacturing must be matched with that of the ceramic enveloper. Nevertheless, the scope of choice of the materials for manufacturing the ceramic package is considerably restricted, because there are not many kinds of materials having thermal expansion coefficients which can be matched with that of the ceramic enveloper. Also, for metal materials, having thermal expansion coefficients which can be matched with that of the ceramic enveloper, although there are tungsten/copper alloy, molybdenum/copper alloy or the like, these metal materials are relatively expensive. 
     Accordingly, if the electronic product, which should be conventionally manufactured as a ceramic or metal package, is constituted as a resin-sealed package, it could be expected that the manufacturing cost of the electronic product can be considerably lowered. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide an electronic product comprising a heat radiating plate, an electronic component, including a high power transistor, mounted on the heat radiating plate, and an enveloper securely attached to the heat radiating plate, which can be constituted such that a superior operational reliability can be ensured during a high power operation of the electronic product. 
     Another object of the present invention is to provide an electronic product of the above-mentioned type, which is constituted so as to improve high-frequency-operational characteristics thereof. 
     Yet another object of the present invention is to provide an electronic product of the above-mentioned type, which can be manufactured at a low cost. 
     In accordance with a first aspect of the present invention, there is provided an electronic product which comprises a heat radiating plate, an electronic component securely mounted on the heat radiating plate, an enveloper including a frame member securely associated with the heat radiating plate to encompass the electronic component, and a lid member securely attached to an upper opening end of the frame member, thereby accommodating and sealing the electronic component in the enveloper, and at least one electrically conductive element passing and extending through the frame member. According to the present invention, the frame member is made of a suitable resin material, and the lid member is made of one material selected from the group consisting of a ceramic material, a metal material, and a composite material. 
     The composite material may be composed of a suitable resin material, and a suitable filler material comprising either an electrically conductive material or a non-conductive material. Also, the composite material may be composed of a metal sheet element enveloped as a core body in a resin plate element. Further, the composite material may comprise a resin plate element in which a metal sheet element is embedded in a surface of the resin plate element such that a surface of the metal sheet element is exposed. Furthermore, the composite material may be composed of a non-conductive plate element, and an electronic conductive layer formed on a surface of the non-conductive plate element. 
     In accordance with a second aspect of the present invention, at least a part of the lid member exhibits an electrical conductivity. To this end, the lid member may be made of a suitable metal material. Also, the lid member may be made of an electrically conductive resin material. Further, the lid member may be constituted as a composite lid member composed of an electrically conductive element and a non-conductive element. Furthermore, the lid member may comprise a non-conductive plate element, and an electronic conductive layer formed on a surface of the non-conductive plate element. The electronic conductive layer may comprise a suitable metal sheet securely adhered to the surface of the non-conductive plate element, and otherwise may be formed by coating the surface of the non-conductive plate element with a suitable electrically conductive paste material. 
     Preferably, the electronic conductive layer is configured such that a thermal expansion difference between the non-conductive plate element and the electronic conductive layer is mitigated. To this end, the electronic conductive layer may be formed from a plurality of thick portions and a plurality of thin portions which are regularly arranged on the surface of the plate element for the mitigation of the thermal expansion difference between the non-conductive plate element and the electronic conductive layer. Also, the electronic conductive layer may be formed with a plurality of openings for the mitigation of the thermal expansion difference between the non-conductive plate element and the electronic conductive layer. 
     In the second aspect of the present invention, preferably, the frame member is provided with an electrically conductive element through which the lid member is electrically connected to the heat radiating plate. When the frame member is molded from the resin by a molding process, the electrically conductive element may be embedded in the molded frame member. Alternatively, the electrically conductive element may be constituted as an electronic conductive layer formed on an inner wall face of the frame member. In this case, the electronic conductive layer may comprise a suitable metal sheet securely adhered to the inner wall face of the frame member, and otherwise may be formed by coating the inner wall face of the frame member with a suitable electrically conductive paste material. 
     Preferably, the electronic conductive layer is configured such that a thermal expansion difference between the frame member and the electronic conductive layer is mitigated. To this end, the electronic conductive layer may be formed from a plurality of thick portions and a plurality of thin portions which are regularly arranged on the inner wall face of the frame member for the mitigation of the thermal expansion difference between the frame member and the electronic conductive layer. Also, the electronic conductive layer may be formed with a plurality of openings for the mitigation of the thermal expansion difference between the frame member and the electronic conductive layer. 
     In the first and second aspects of the present invention, preferably, the frame member may be molded from the resin by a molding process, and the heat radiating plate is configured so as to be mechanically engaged with the molded frame member. For example, the heat radiating plate may be formed with at least one recess embedded in the molded frame member, so as to be mechanically engaged with the molded frame member. Also, the heat radiating plate may be formed with at least one projection arranged on a wall face forming the recess, thereby further ensuring the mechanical engagement between the radiating plate and the molded frame member. 
     In the first and second aspects of the present invention, preferably, the electrically conductive element is configured so as to be mechanically engaged with the molded frame member. To this end, the electrically conductive element may be formed with at least one perforation embedded in the molded frame member so as to be mechanically engaged with the molded frame member. Also, the electrically conductive element may be formed with an alignment of perforations embedded in the molded frame member. Further, the electrically conductive element may be formed with an alignment of perforations and endmost cutouts embedded in the molded frame member. 
     The electrically conductive element may be formed with another alignment of perforations arranged along an outer wall face of the molded frame member, to thereby reduce a rigidity of an outer sections of the electrically conductive element. 
     The electrically conductive element may be formed with a first alignment of perforations embedded in the molded frame member to be mechanically engaged with the molded frame member, and a second alignment of perforations arranged along an outer wall face of the molded frame member to thereby reduce a rigidity of an outer sections of the electrically conductive element. Preferably, the perforations included in the second alignment are alternately arranged with respect to the perforations included in the first alignment. 
     The lid member may be formed with two rectangular land portions, which are integrally swelled from opposing wall faces thereof, and which are symmetrically arranged with respect to a geometrical neutral plane of the lid member, and each land portion is sized to be fitted into the upper opening end of the frame member. 
     In the first and second aspects of the present invention, the heat radiating plate includes inner and outer portions which are divided and defined by the frame member. In this case, preferably, the inner portion of the heat radiating plate, which is inside the frame member, is surfaced with silver-plating, and the outer portion of the heat radiating plate, which are outside the frame member, are surfaced with gold-plating. The electrically conductive element also includes inner and outer lead sections which are divided and defined by the frame member, and preferably the inner and outer lead section are surfaced with gold-plating. 
     In the first and second aspects of the present invention, preferably, the electrically conductive element is derived from a lead frame, and the heat radiating plate is prepared as a part which is independent from the lead frame. 
     In the first and second aspects of the present invention, the electronic component may comprises a high power transistor. In this case, the aforesaid electrically conductive element is defined as a first lead, and the electronic product further comprises a second lead passing and extending through the frame member. The respective first and second leads are electrically connected to the high power transistor so as to form input and output terminals of the high power transistor, and the heat radiating plate is electrically connected to form a grounded terminal of the high power transistor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and other objects will be more clearly understood from the description set forth below, with reference to the accompanying drawings, wherein: 
         FIG. 1  is a partially-cutaway perspective view of a first embodiment of an electronic product according to the present invention; 
         FIG. 2  is a plan view of the electronic product, shown in  FIG. 1 , from which a lid member is removed; 
         FIG. 3  is a longitudinal cross-sectional view, taken along the III—III line of  FIG. 1 , but illustrating the lid member; 
         FIG. 4  is a lateral cross-sectional view, taken along the IV—IV line of  FIG. 1 , but illustrating the lid member; 
         FIG. 5  is a partially-cutaway perspective view of the electronic product shown in  FIG. 1 , observed from a bottom side of the electronic product; 
         FIG. 6  is a perspective view of a heat radiating plate forming a part of the electronic product; 
         FIG. 7A  is a plan view of the lid member; 
         FIG. 7B  is a side view of the lid member shown in  FIG. 7A ; 
         FIG. 7C  is an elevation view of the lid member shown  FIG. 7A ; 
         FIG. 8  is a partial plan view of a lead frame used in manufacturing the electronic product; 
         FIG. 9  is a partial longitudinal cross-sectional view of a metal mold for molding a rectangular frame member forming a part of the electronic product; 
         FIG. 10  is a partial lateral cross-sectional view of the metal mold shown in  FIG. 9 ; 
         FIG. 11  is a perspective view of an intermediate product for the electronic product; 
         FIG. 12A  is a perspective view of the intermediate product subjected to a first plating process; 
         FIG. 12B  is a perspective view of the intermediate product subjected to a second plating process; 
         FIG. 12C  is a perspective view of the intermediate product subjected to a third plating process; 
         FIG. 12D  is a perspective view of the intermediate product subjected to a fourth plating process; 
         FIG. 13  is a partial plan view of a modification of the lead frame shown in  FIG. 8 ; 
         FIG. 14  is a lateral cross-sectional view, similar to  FIG. 4 , showing a modification of the electronic product; 
         FIG. 15  is a lateral cross-sectional view, similar to  FIG. 4 , showing another modification of the electronic product; 
         FIG. 16  shows a lateral cross-sectional view showing a modification of a composite lid member shown in  FIG. 15 ; 
         FIG. 17  shows a lateral cross-sectional view showing another modification of the composite lid member shown in  FIG. 15 ; 
         FIG. 18  is a lateral cross-sectional view, similar to  FIG. 4 , showing a second embodiment of an electronic product according to the present invention; 
         FIG. 19  is a lateral cross-sectional view, similar to  FIG. 18 , showing a modification of the second embodiment of the electronic product; 
         FIG. 20  is a partial lateral cross-sectional view showing a modification of a lid member used in the electronic product in shown in either  FIG. 18  or  FIG. 19 ; 
         FIG. 21  is a partial lateral cross-sectional view showing another modification of the lid member used in the electronic product in shown in either  FIG. 18  or  FIG. 19 ; 
         FIG. 22  is a partially-cutaway perspective view, similar to  FIG. 1 , showing a third embodiment of an electronic product according to the present invention; 
         FIG. 23  is a partially-cutaway perspective view, similar to  FIG. 1 , showing a modification of the third embodiment of the electronic product according to the present invention; 
         FIG. 24  is a vertical cross-sectional view showing a modification of an electrically conductive layer formed on an inner wall face of a lateral side wall of a rectangular frame member which is used in the electronic product shown in  FIG. 23 ; and 
         FIG. 25  is a vertical cross-sectional view showing another modification of the electrically conductive layer formed on the inner wall face of the lateral side wall of the rectangular frame member which is used in the electronic product shown in  FIG. 23 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIGS. 1 to 8 , a first embodiment of an electronic product according to the present invention is generally indicated by reference  10 . 
     As shown in  FIGS. 1 to 4 , the electronic product  10  comprises a heat radiating plate  12  made of a suitable metal material such as copper or the like, and the heat radiating plate  12  is subjected to electroplating processes, as stated in detail hereinafter. The heat radiating plate  12  is formed with a pair of screw holes  12   a  at the ends thereof, and the screw holes  12   a  are used for attaching the electronic product  10  to a suitable base frame, such as an aluminum chassis or the like, by screws (not shown), when being assembled in a piece of electronic equipment. 
     Also, the electronic product  10  comprises an electronic component  14  mounted on and adhered to the heat radiating plate  12 . In this embodiment, the electronic component  14  includes a power MOSFET as a high power transistor, which is utilized in an analog amplifier or the like, and is provided with three sets of pads: first, second and third sets of pads. 
     In particular, as shown in  FIGS. 1 and 2 , the first set of pads, indicated by reference  16 , is provided on a top face of the electronic component  14 , and forms a drain (D) of the power MOSFET. Similarly, the second set of pads, indicated by reference  17 , is provided on the top face of the electronic component  14 , and forms a gate (G) of the power MOSFET. The third set of pads is provided on a bottom face of the electronic component  14  (not visible), and forms a source (S) of the power MOSFET. When the electronic component  14  is mounted on and adhered to the heat radiating plate  12 , the third set of pads are electrically connected to the heat radiating plate  12 , and thus the heat radiating plate  12  also serves as the source terminal (S) of the power MOSFET. 
     The electronic product  10  further comprises an enveloper  18  for encapsulating the electronic component  14  to thereby protect it from the outside. The enveloper  18  comprises a rectangular frame member  19  made of a suitable thermosetting resin such as epoxy resin or the like, and a lid member  20  securely attached to a top opening end of the frame member  19 . In this first embodiment, the lid member  20  is made of a suitable ceramic material. 
     The rectangular frame member  19  is formed by a molding process, and is mechanically engaged with and attached to the heat radiating plate  12  at a bottom end thereof when being molded. To ensure a securely-mechanical engagement between the heat radiating plate  12  and the frame member  14 , as best shown in  FIGS. 5 and 6 , the heat radiating plate  12  is provided with a pair of side recesses  12   b  formed along the opposing longitudinal sides thereof, and three projections  12   c  are integrally protruded from the inmost wall face of each side recess  12   b.  Thus, as best shown in  FIG. 5 , it is possible to establish the secure mechanical attachment of the frame member  14  to the heat radiating plate  12 . 
     As is apparent from  FIGS. 1 to 4 , the rectangular frame member  14  is provided with a pair of shelf elements  21  and  22 , which are integrally protruded from the inner wall faces of the opposing longitudinal side walls of the frame member  14 , and which are extended between the opposing lateral side walls of the frame member  14 . Note that the functions of the shelf elements  21  and  22  are explained hereinafter. 
     The lid member  20  may be securely adhered to the top opening end of the frame member  19 , using a suitable adhesive agent, to thereby close the top opening end of the frame member  19 . Thus, the electronic component  14  is encapsulated in the enveloper  18 , whereby it is possible to seal and protect the electronic component  14  from the outside. 
     Preferably, the lid member  20  is configured as shown in  FIGS. 7A to 7C . In particular, the lid member  20  is shaped as a rectangular plate having the same rectangular profile as that of the frame member  19 , and is formed with two rectangular land portions  20   a  and  20   b  integrally swelled from the opposing wall faces thereof. The land portions  20   a  are symmetrically arranged with respect to a geometrical neutral plane of the lid member  20 , and each land portion ( 20   a,    20   b ) is sized so as to be fitted into the upper opening end of the rectangular frame member  19 . Thus, it is possible to easily and accurately attach the lid member  20  to the upper opening end of the frame member  19 . Also, although the lid member  20  is subjected to variations in temperature, due to the symmetrical configuration of the lid member  20 , it is possible to considerably reduce warpage of the lid member  20 . 
     Furthermore, the electronic product  10  comprises a pair of leads  23  and  24  made of a suitable metal such as copper or the like, and the respective leads  23  and  24  pass and extend through the opposing longitudinal side walls of the frame member  19 , as shown in  FIGS. 1 ,  2 , and  4 . Each of the leads  23  and  24  is mechanically held by the corresponding longitudinal side wall of the frame member  19  when the frame member  19  is molded. Note that, similar to the heat radiating plate  12 , the pair of leads  23  and  24  are also subjected to electroplating processes, as stated in detail hereinafter. 
     With reference to  FIG. 8 , a part of a lead frame  30  is shown as a plan view, and the pair of leads  23  and  24  are obtained from the lead frame  30 . The lead frame  30  comprises an elongated metal (e.g. copper) sheet in which pairs of lead patterns  23 ′ and  24 ′ are successively formed in an openwork manner. As stated hereinafter, when the rectangular frame member  19  is molded by a metal mold, a pair of lead patterns  23 ′ and  24 ′ is disposed in a molding cavity of the metal mold together with the heat radiating plate  12 . After the molding of the frame member  19  is completed, the pair of lead patterns  23 ′ and  24 ′ is cut off from the lead frame  30 , thereby producing the pair of leads  23  and  24 . 
     As shown in  FIG. 8 , each lead pattern  23 ′ is formed with a first alignment of three slots or perforations  32  and two endmost cutouts  34 , and a second alignment of three through slots or perforations  36 . Similarly, each lead pattern  24 ′ is formed with a first alignment of three slots or perforations  38  and endmost cutouts  40  and a second alignment of three slots or perforations  42 . 
     As best shown in  FIG. 2 , when the rectangular frame member  19  is molded, the first alignment of perforations  32  and endmost cutouts  34  in the lead pattern  23 ′ and the first alignment of perforations  38  and endmost cutouts  40  in the lead pattern  24 ′ are respectively buried in the opposing longitudinal side walls of the frame member  19 , resulting in a mechanical and secure engagement between the lead patterns  23 ′ and  24 ′ and the opposing longitudinal side walls of the frame member  19 . Thus, it is possible to mechanically and firmly hold the respective leads  23  and  24  by the opposing longitudinal side walls of the frame member  19 . 
     The lead  23  has inner and outer lead sections  23   a  and  23   b,  which are divided and defined by the corresponding longitudinal side wall of the frame member  19 . also, the lead  24  has inner and outer lead sections  24   a  and  24   b,  which are divided and defined by the corresponding longitudinal side wall of the frame member  19 . Namely, the respective inner lead sections  23   a  and  24   a  are protruded from the inner wall faces of the opposing longitudinal side walls of the frame member  19 , and the respective outer lead sections  23   b  and  24   b  are protruded from the outer wall faces of the opposing longitudinal side walls of the frame member  19 . Note that the respective inner lead sections  23   a  and  24   a  are laid on the shelf elements  21  and  22 . 
     As best shown in  FIGS. 1 and 2 , the inner lead section  23   a  is electrically connected to the first set of pads  16  with bonding-wires  26 , and thus the outer lead section  23   b  forms the drain terminal (D) of the power MOSFET. Similarly, the inner lead section  24   a  is electrically connected to the second set of pads  17  with bonding-wires  28 , and thus the outer lead section  24   b  forms the gate terminal (G) of the power MOSFET. 
     The electronic product  10  as mentioned above may be manufactured below. 
     First, referring to  FIGS. 9 and 10 , the aforesaid metal mold for molding the rectangular frame member  19  is generally indicated by reference  44 . The metal mold  44  comprises upper and lower mold dies  44   a  and  44   b,  which define a molding cavity  46 , corresponding to the profile of the rectangular frame member  19 , when being combined with each other. Namely, an upper half of the molding cavity  46  is defined by the upper mold die  44   a,  and a lower half of the molding cavity  46  is defined by the lower mold die  44   b.    
     As shown in  FIGS. 9 and 10 , the heat radiating plate  12  and the pair of lead patterns  23 ′ and  24 ′ are sandwiched by the upper and lower mold dies  44   a  and  44   b  such that these elements  12 ,  23 ′, and  24 ′ are disposed in place in the molding cavity  46 . Then, liquid epoxy resin is injected into the molding cavity  26 , and is hardened. As is apparent from  FIG. 10 , the perforations  32  and  38  and cutouts  34  and  40  of the lead patterns  23 ′ and  24 ′ are filled with the injected resin, and thus the lead patterns  23 ′ and  24 ′ are mechanically and firmly engaged with the molded piece when being hardened. Thereafter, the metal mold  44  is opened, thereby obtaining an intermediate product  10 ′ as shown in  FIG. 11 . 
     Then, the intermediate product  10 ′ is subjected to plating processes in accordance with a plating flow diagram shown in  FIGS. 12A to 12D . 
     In a first plating process shown in  FIG. 12A , both the heat radiating plate  12  and the lead frame  30  (including the lead patterns  23 ′ and  24 ′) are plated with nickel (Ni), as represented by hatching in  FIG. 12A . Note that areas of these elements  12  and  30 , covered by the resin material of the rectangular frame member  19 , cannot be subjected to the nickel-plating. 
     In a second plating process shown in  FIG. 12B , the nickel-plating of the heat radiating plate  12  are further plated with silver (Ag), using an electroplating method, as represented by hatching in  FIG. 12B . In particular, the heat radiating plate  12  is immersed together with the lead frame  30  in a solution containing Ag ions, and a negative voltage is applied to the heat radiating plate  12 , whereby the nickel-plating of the heat radiating plate  12  is further subjected to the silver plating. 
     In a third plating process shown in  FIG. 12C , the nickel-plating surfaces of the lead frame  30  (including the lead patterns  23 ′ and  24 ′) are further plated with gold, using an electroplating method, as represented by hatching in  FIG. 12C . In particular, the lead frame  30  is immersed together with the heat radiating plate  12  in a solution containing Au ions, and a negative voltage is applied to the lead frame  30 , whereby the nickel-plating of the lead frame  30  is further subjected to the gold-plating. 
     In a fourth plating process shown in  FIG. 12D , the outer portions of the heat radiating plate  12 , which are outside the rectangular frame member  19 , are further plated with gold, using an electroplating method, as represented by hatching in  FIG. 12D . In particular, the inner portion of the heat radiating plate  12 , which is inside the rectangular frame member  19 , is masked with a photo-resist or the like, and the heat radiating plate  12  is immersed together with the lead frame  30  in a solution containing Au ions, and a negative voltage is applied to the heat radiating plate  12 , whereby only the silver-plating of the outer portions of the heat radiating plate  12  is further subjected to the gold-plating. 
     Then, the electronic component  14  is mounted on and adhered to the silver-plating surface of the heat radiating plate  12 , using a suitable electrically conductive bonding agent. Accordingly, as already stated, the third set of pads (not visible), provided on the bottom face of the electronic component  14 , are electrically connected to the heat radiating plate  12 , and thus the heat radiating plate  12  serves as the source terminal (S) of the power MOSFET. 
     Subsequently, a wire-bonding process is performed to establish the electrical connections between the first set of pads  16  and the inner lead section  23   a  of the lead pattern  23 ′ with the bonding-wires  26 , and between the second set pads  17  and the inner lead section  24   a  of the lead pattern  24 ′ with the bonding-wires  28 . During the wire-bounding process, the respective inner lead sections  23   a  and  24   a  lie on the shelf elements  21  and  22 , to thereby prevent deformation of the inner lead sections  21  and  22 . 
     After the wire-bounding process is finished, the intermediate product  10 ′ is removed from the lead frame  30  by cutting off the lead patterns  23 ′ and  24 ′ therefrom, and then the top opening end of the frame member  19  is closed by the lid member  20 , thereby encapsulating the electronic component  14  in the enveloper  18 , resulting in a completion of the manufacture of the electronic product  10  in which the electronic component  14  is sealed and protected in the enveloper  18  from the outside. 
     According to the aforesaid manufacturing process, it is possible to obtain various advantages as explained below. 
     For example, the molding process contributes to a flattening of the heat radiating plate  12 . In particular, the heat radiating plate  12  is frequently produced from a copper sheet, using a punching machine. In this case, the heat radiating plate  12  has a residual strain or stress, which is inevitably brought about when being punched, and thus may be warped due to the residual strain or stress. However, it is possible to flatten the warped heat radiating plate  12  during the molding process, because the warped heat radiating plate  12  is clamped by the upper and lower mold dies  44   a  and  44   b  while the metal mold  44  is closed, as is apparent from  FIGS. 9 and 10 . 
     In short, since the rectangular frame member  19  is molded in the metal mold  44  so as to be mechanically engaged with a part of the heat radiating plate  12 , the heat radiating plate  12  is necessarily clamped by the upper and lower mold dies  44   a  and  44   b,  resulting in achievement of the flattening of the warped heat radiating plate  12 . 
     Also, in accordance with the aforesaid manufacturing process, since the heat radiating plate  12  is prepared as a part which is independent from the lead frame  30 , and since the heat radiating plate  12  and the lead frame  30  are electrically isolated from each other, it is possible to individually and separately electroplate the heat radiating plate  12  and the lead frame  30  without masking either of the heat radiating plate  12  or the lead frame  30 . For example, as shown in  FIG. 12B , while the heat radiating plate  12  is subjected to the silver-plating, it is unnecessary to mask the lead frame  30 . Thus, the electroplating processes ( FIGS. 12A to 12D ) can be easily performed at a low cost. 
     In addition, due to the fact that the heat radiating plate  12  is independent from the lead frame  30 , the heat radiating plate  12  can be made thicker than the lead frame  30 , and thus it is possible to facilitate the radiation of heat from the heat radiating plate  12 . 
     The electronic component  10  itself according to the present invention also features various advantages. 
     For example, with the arrangement of the electronic component  10 , since the electronic component  14 , the inner lead sections  23   a  and  24   a,  and the bonding-wires  26  and  28  are arranged in the interior space of the enveloper  18 , i.e. since these elements ( 14 ,  23   a,    24   a,    26 ,  28 ) are not directly covered with and sealed in a molded resin, the electronic component  10  has no relation with problems accompanying production of parasitic capacitance, resulting in an improvement in high frequency characteristics thereof. Also, although the surface of the electronic component  14  is raised up due to the heating generated in a high-power operation of the electronic product  10 , the enveloper  18  cannot be subjected to a thermal influence from the heated electronic component  14 , because the enveloper  18  is not in direct contact with the electronic component  14 , resulting in improvement and preservation of an operational reliability of the electronic product  10  during a high-power-output operation. 
     Also, due to the formation of the second alignments of perforations  36  and  42  in the outer lead sections  23   b  and  24   b,  rigidity of the outer lead sections  23   b  and  24   b  is reduced, whereby the rectangular frame member  19  can be protected from being damaged. In particular, for example, while the lead patterns  23 ′ and  24 ′ are cut off from the lead frame  30  and/or while the electronic product  10  is assembled in a piece of electronic equipment, an excessive external force may be exerted on the outer lead sections  23   b  and  24   b.  If the rigidity of the outer lead sections  23   b  and  24   b  is too large, the excessive external force may damage the frame member  19 . However, in reality, the outer lead sections  23   b  and  24   b  exhibit a flexibility based on the reduction of the rigidity of the outer sections  23   b  and  24   b.  Thus, the excessive external force may be absorbed by the deformation of the outer lead sections  23   b  and  24   b,  resulting in the protection of the lead sections  23   b  and  24   b  from the damage. 
     Further, the electronic product  10  entirely exhibits a superior corrosive resistance, because the outer portions of the heat radiating plate  12 , which are outside the frame member  19 , are surfaced with the gold-plating, and because the outer lead sections  23   b  and  24   b  of the leads  23  and  24  are surfaced with the gold-plating. In addition, due to the gold-plating of the inner and outer lead sections ( 23   a;    23   b  and  24   a;    24   b ) of the leads  23  and  24 , it is possible to improve anti-migration characteristics on the leads  23  and  24 , resulting in promotion of operational reliability of the electronic product  10 . Also, since the inner area of the heat radiating plate  12 , encompassed by the frame member  19 , is surfaced not with the gold-plating but the silver-plating, it is possible to reduce cost required for the plating processes. 
     Furthermore, it is possible to obtain an advantage from the formation of the first alignment of perforations ( 32 ,  38 ) and endmost cutouts ( 34 ,  40 ) and the second alignment of perforations ( 36 ,  42 ) in the lead ( 23 ,  24 ). 
     In particular, when the electronic product  10  is assembled in a piece of electronic equipment, it is necessary to connect the outer lead sections  23   b  and  24   b  to electrical terminals, using solder and flux. In this case, fused solder and flux may be penetrated into interfaces between the resin frame member  19  and the leads  23  and  24 , and may be further invaded into the interior of the enveloper  18  through the aforesaid interfaces. However, it is possible to impede the penetration of the fused solder and flux into the interfaces between the resin frame member  19  and the leads  23  and  24  and the invasion of the fused solder and flux into the interior of the enveloper  18  through the aforesaid interfaces, due to the provision of the first alignment of perforations ( 32 ,  38 ) and endmost cutouts ( 34 ,  40 ) and the second alignment of perforations ( 36 ,  42 ) in the lead ( 23 ,  24 ). 
       FIG. 13  shows a modification of the lead frame  30  shown in  FIG. 8 . In this drawing, the modified lead frame is generally indicated by reference  30 ′, and the elements similar to those of the lead frame  30  are indicated by the same references elements. The modified lead frame  30 ′ is identical to the lead frame  30  of  FIG. 8 , except that a second alignment of four slots or perforations  36 ′ is substituted for the second alignment of three slots or perforations  36  in the lead pattern  23 ′, and that a second alignment of four slots  42 ′ is substituted for the second alignment of slots or perforations  42  in the lead pattern  24 ′. 
     As shown in  FIG. 13 , in the lead pattern  23 ′, the four perforations  36 ′ included in the second alignment are alternately arranged with respect to the three perforations  32  and endmost cutouts  34  included in the first alignment. In particular, each of the two endmost perforations  36 ′ in the first alignment is opposed to a space area between the corresponding endmost cutout  34  and the adjacent perforations  32 , and each of the two middle slots  36 ′, intervened between the two endmost perforations  36 ′, is opposed to a space area between the two corresponding adjacent perforations  32  in the second alignment. The same is true for a relationship between the second alignment of four perforations  42 ′ and the first alignment of three perforations  38  and two endmost cutouts  40 , formed in the lead pattern  24 ′. 
     When the modified lead frame  30 ′ is used for the manufacture of the electronic product  10 , it is possible to more effectively impede the penetration of the fused solder and flux into the interfaces between the resin frame member  19  and the leads  23  and  24  and the invasion of the fused solder and flux into the interior of the enveloper  18  through the aforesaid interfaces, due to the alternate arrangement of the four perforations ( 36 ′,  42 ′) in the second alignment with respect to the three perforations ( 32 ,  38 ) and two endmost cutouts ( 34 ,  40 ) in the first alignment. 
     As already mentioned above, in the first embodiment, the lid member  20  is made of the ceramic material. However, when a high frequency signal is processed in the electronic component  14 , it is preferable to modify the electronic product  10 , as shown in  FIG. 14 , corresponding to  FIG. 4 . Namely, the lid member  20  is made of a suitable metal material, such as, copper, silver or the like. The metal lid member  20  serves as an electromagnetic shield due to an electrical conductivity thereof, whereby it is possible to suppress an emission of high frequency noises from the electronic product  10 . 
     Further, the electronic product  10  may be modified as shown in  FIG. 15 . Namely, in this modified embodiment, the lid member  20  is made of a composite material composed of a suitable thermosetting resin, such as epoxy or the like, and suitable filler represented by a plurality of small open-triangles “Δ” in  FIG. 15 . When a low frequency signal is processed in the electronic component  14 , the filler may comprise a suitable non-conductive material, such as wood chips or pieces, ceramic chips or pieces or the like. When a high frequency signal is processed in the electronic component  14 , the filler should comprise a suitable conductive material, such as metal chips or pieces, carbon powder or the like. Namely, when the filler comprises the conductive material, the lid member  20  serves as an electromagnetic shield for suppressing the emission of high frequency noises from the electronic product  10 . 
       FIG. 16  shows a modification of the lid member  20 , a part of which exhibits an electrical conductivity. In particular, the modified lid member  20  is constituted as a composite lid member comprising a metal sheet element  21   a  made of a suitable metal material, such as copper, silver or the like, which is enveloped as a core body in a resin plate element  21   b  made of a suitable material, such as epoxy or the like. This composite lid member  20  also serves as the electromagnetic shield for suppressing the emission of high frequency noises from the electronic product  10 . 
       FIG. 17  shows another modification of the lid member  20 , a part of which also exhibits an electrical conductivity. In particular, the modified lid member is constituted as a composite lid member comprising a resin plate element  21   c  made of a suitable thermosetting resin material, such as epoxy or the like, in which a metal sheet element  21   d,  made of a suitable metal material, such as copper, silver or the like is embedded in a surface of the resin plate element  21   c  such that a surface of the metal sheet element  21   d  is exposed. Preferably, the embedding of the metal sheet element  21   d  is performed such that the surfaces of the resin plate element  21   c  and metal sheet element  21   d  are flush with each other, as shown in  FIG. 17 . Similar to the modification of  FIG. 16 , the composite lid member  20  serves as an electromagnetic shield for suppressing the emission of high frequency noises from the electronic product  10 . 
       FIG. 18 , similar to  FIG. 4 , shows a second embodiment of an electronic product according to the present invention. In this drawing, the elements similar to those of  FIG. 4 , are indicated by the same references. 
     In the second embodiment, the electronic product, generally indicated by reference  48 , is substantially identical to the electronic product  10  except that a lid member  50  is substituted for the lid member  20 . The lid member  50  comprises a rectangular ceramic plate element  52  having the same profile as the lid member  20  ( FIG. 7A ), and an electrically conductive layer  54  applied to a surface of the ceramic plate element  52 , and is adhered to the top opening end of the frame member  19  with a suitable adhesive agent. 
     The electrically conductive layer  54  may be formed by attaching or adhering a suitable metal sheet, made of copper, silver or the like, to the surface of the ceramic plate element  52 . Also, it is possible to perform the formation of the conductive layer  54  by a deposit of metal layer based on a sputtering process. Further, the conductive layer  54  may be formed by coating the surface of the ceramic plate element  52  with electrically conductive paste. 
     Of course, since the conductive layer  54  serves as an electromagnetic shield, the electronic product  48  is suited to the case where a high frequency signal is processed in the electronic component  14 . 
     The electronic product  10  may be modified as shown in  FIG. 19 . Namely, in this modified embodiment, a resin plate element  52 ′, made of a suitable thermosetting resin material, is substituted for the ceramic plate element  52  of the lid member  50 . Alternatively, the resin plate element  52 ′ may be replaced with a composite plate element which is made of a non-conductive composite material as explained with reference to  FIG. 15 . Namely, the composite plate element is composed of a suitable thermosetting resin, such as epoxy or the like, and a suitable non-conductive filler, such as wood chips or pieces, ceramic chips or pieces or the like. 
     In the embodiments shown in  FIGS. 18 and 19 , it is difficult to select materials for the plate element ( 52 ,  52 ′) and the conductive layer  54  such that a coefficient of thermal expansion of the plate element ( 52 ,  52 ′) is consistent with that of the conductive layer  54 , and thus the lid member  52  may be warped and deformed due to a thermal expansion difference between the plate element ( 52 ,  52 ′) and the conductive layer  54 . Eventually, the plate element ( 52 ,  52 ′) and the conductive layer  54  may be peeled from each other while being to subjected to variations in temperature over a period of long time. 
     To mitigate the thermal expansion difference between the plate element ( 52 ,  52 ′) and the conductive layer  54 , it is preferable to modify the lid member  50  as shown in  FIG. 20 . In particular, in this modified embodiment, the lid member  50  is provided with an electrically conductive layer  54   a,  a thickness of which is regularly varied. Namely, the conductive layer  54   a  is formed from a plurality of thick portions  56  and a plurality of thin portions  58  which are regularly arranged on the surface of the plate element ( 52 ,  52 ′). When the lid member  50  is subjected to variation in temperature, it is possible to absorb the thermal expansion difference between the plate element ( 52 ,  52 ′) and the conductive layer  54  by the regular-arrangement of the thick and thin portions  56  and  58 , resulting in mitigation of the thermal expansion difference between the plate element ( 52 ,  52 ′) and the conductive layer  54   a.    
       FIG. 21  shows another modification of the lid member  50  illustrated in either  FIG. 18  or  FIG. 19 . In this modification, the lid member  50  has an electrically conductive layer  54   b  which is regularly formed with a plurality of openings  60 . When the lid member  50  is subjected to variation in temperature, it is possible to absorb the thermal expansion difference between the plate element ( 52 ,  52 ′) and the conductive layer  54   b  by the regular-arrangement of the openings  60 , resulting in mitigation of the thermal expansion difference between the plate element ( 52 ,  52 ′) and the conductive layer  54   b.    
     In the aforesaid embodiments in which a whole or a part of the lid member ( 20 ,  50 ) exhibits an electrical conductivity, a parasitic capacitance may be produced due to the fact that the lid member ( 20 ,  50 ), exhibiting the electrical conductivity, is electrically floated. The production of the parasitic capacitance should be prevented, because the parasitic capacitance exerts a bad influence on an operation of the electronic component  14 . For example, the production of the parasitic capacitance delays transmission of signals in the electronic component  14 . 
       FIG. 22 , similar to  FIG. 1 , shows a third embodiment of an electronic product according to the present invention, which is directed to prevention of the production of the aforesaid parasitic capacitance. In this drawing, the elements similar to those of  FIG. 1 , are indicated by the same references. 
     In the third embodiment, the rectangular frame member  19  has an electrically conductive element  62  which is embedded in one of the opposing lateral side walls thereof. The conductive element  62  may be formed as a suitable plate-like element made of a suitable metal, such as copper, silver or the like. The conductive element  62  is put in the molding cavity of the metal mold  44  ( FIGS. 9 and 10 ) when the frame member  19  is molded, whereby the embedding of the conductive element  62  is achieved such that a lower end face of the conductive element  62  is in electrical contact with the heat radiating plate  12 . 
     As shown in  FIG. 22 , an upper end of the conductive element  62  is exposed. Thus, by electrically connecting the lid member ( 20 ,  50 ), exhibiting the electrical conductivity, to the upper end face of the conductive element  62 , the lid member ( 20 ,  50 ) is grounded to the heat radiating plate  12 , resulting in the prevention of the production of the parasitic capacitance. For example, the electrical connection of the lid member ( 20 ,  50 ) to the upper end face of the conductive element  62  can be established by adhering the lid member ( 20 ,  50 ) to the upper opening end of the frame member  19 , using an electrically conductive adhesive agent. 
     In the third embodiment, although the conductive element  62  is embedded in only one of the opposing lateral side walls thereof, it is possible to embed an electrically conductive element in the other lateral side wall. Also, an electrically conductive element may be embedded in at least one of the opposing longitudinal side walls of the frame member  19  without being in contact with the corresponding lead ( 23 ,  24 ). 
       FIG. 23 , similar to  FIG. 1 , shows a modification of the third embodiment shown in  FIG. 22 . In this drawing, the elements similar to those of  FIG. 1 , are indicated by the same references. 
     As shown in  FIG. 23 , in this modified embodiment, an electrically conductive layer  64  is applied to one inner wall face of the opposing lateral side walls of the frame member  19 . The electrically conductive layer  64  may be formed by attaching or adhering a suitable metal sheet, made of copper, silver or the like, to the inner surface of the lateral side wall of the frame member  19  with a suitable adhesive agent. Also, the conductive layer  64  may be formed by coating the inner surface of the lateral side wall of the frame member  19  with electrically conductive paste. 
     Similar to the third embodiment, the conductive layer  64  is in electrical contact with the heat radiating plate  12 , and is electrically connected to the lid member ( 20 ,  50 ), exhibiting electrical conductivity, by adhering the lid member ( 20 ,  50 ) to the upper opening end to the frame member  19  with a suitable electrically conductive adhesive agent. Thus, the lid member ( 20 ,  50 ) is grounded to the heat radiating plate  12 , resulting in the prevention of the production of the parasitic capacitance. 
     In the modified embodiments shown in  FIG. 23 , it is difficult to select materials for the frame member  19  and the conductive layer  64  so that a coefficient of thermal expansion of the frame member  19  is consistent with that of the conductive layer  64 , and thus the conductive layer  64  may be warped and deformed due to a thermal expansion difference between the frame member  19  and the conductive layer  64 . Eventually, the conductive layer  64  may be peeled from the lateral side wall of the frame member  19  while being to subjected to variations in temperature over a period of long time. 
     To mitigate the thermal expansion difference between the frame member  19  and the conductive layer  64 , it is preferable to modify the conductive layer  64  as shown in  FIG. 25 . In particular, the conductive layer  64  is replaced with an electrically conductive layer  64   a,  a thickness of which is regularly varied. Namely, the conductive layer  64   a  is formed from a plurality of thick portions  66  and a plurality of thin portions  68  which are regularly arranged on the inner wall face of the lateral side wall of the frame member  19 . When the conductive layer  64   a  is subjected to variation in temperature, it is possible to absorb the thermal expansion difference between the lateral side wall of the frame member  19  and the conductive layer  64   a  by the regular arrangement of the thick and thin portions  66  and  88 , resulting in mitigation of the thermal expansion difference between the lateral side wall of the frame member  19  and the conductive layer  64   a.    
       FIG. 25  shows another modification of the conductive layer  64  illustrated in  FIG. 24 . In particular, the conductive layer  64  is replaced with an electrically conductive layer  64   b  which is formed with a plurality of regular openings  70 . When the conductive layer  64   b  is subjected to variation in temperature, it is possible to absorb the thermal expansion difference between the lateral side wall of the frame member  19  and the conductive layer  64   b  by the regular arrangement of the openings  70 , resulting in mitigation of the thermal expansion difference between the lateral side wall of the frame member  19  and the conductive layer  64   b.    
     Finally, it will be understood by those skilled in the art that the foregoing description is of preferred embodiments of the product, and that various changes and modifications may be made to the present invention without departing from the spirit and scope thereof.