Patent Publication Number: US-2011074005-A1

Title: Semiconductor device, method for fabricating a semiconductor device and lead frame, comprising a bent contact section

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to European Patent Application No. EP 09012416.5, filed Sep. 30, 2009. 
     FIELD OF THE INVENTION 
     The invention relates to a semiconductor device, and in particular, to a semiconductor device having an integrated circuit die and a housing 
     BACKGROUND 
     Electronic chip cards such as integrated circuit cards have been constantly developed and improved in the past years. In particular, their form factor was adapted to the new market requirements so that the overall dimensions of an electronic card in use today could be reduced, for instance, down to 12 mm×15 mm for a mini UICC (Universal Integrated Circuit Card), which generally have dimensions of 5 mm×6 mm×0.85 mm. These cards can include memory circuits and control circuits and can be easily integrated in small size devices or electronic circuitry, such as the onboard system of a car or a machine for performing dedicated tasks. 
     A possible application for electronic cards is the automatic exchange of information between two or more end devices in order to allow remote monitoring, control or maintenance of machines or systems. In general, electronic cards with reduced dimensions are widely used in all kinds of so called machine to machine applications. Furthermore, it is known to use cards in mobile telephones, personal digital assistants, radio modems, and radio modules according to the GSM mobile standard (global system for mobile communication) or the UMTS mobile standard (universal mobile telecommunications system) in order to identify the user of the mobile terminal within the mobile network. These chip cards are plugged into the user equipment in order to read out the data stored thereon. 
       FIG. 16  shows a slide-in connecting device for connecting a known UICC  200 , manufactured by a conventional laminate frame (lamframe) process, to internal device contacts  142  of the user equipment. As shown schematically in  FIG. 16 , electric contacts  204  of the UICC  200  are positioned on a base surface  202  of the card housing, and contact sharp edges  201  of the internal device contact  142 . These sharp edges  201  in current lamframe layouts are prepared by a cutting step on the outside of the separated chip cards, and may lead to connector contact wear and also to corrosion. This causes connection reliability problems. 
     Furthermore, the package of the conventional chip card  200  is fabricated by overmolding a plated metal strip and then separating these contacts by cutting same. In a next fabrication step, the integrated circuit die is placed and wired bonded and, finally, a second overmold closes the package, but leaves open the contacts  204 . As can be seen from  FIG. 16 , at the edge  201 , the contact  204  is not only very sharp, but also is not covered by the gold plating step, because the cutting is performed after plating the contacts; therefore corrosion may occur in the region  201 . 
     Generally, chip cards are required to comply with a number of different requirements depending on the particular field of application. For instance, with respect to modem applications, chip cards comply with industrial and environment standards (i.e. requires IP20 dust protection), higher operating temperatures, and automatic pick and place. With respect to a localization application, the size of chip cards is an important criteria, as well as alternative connector application style. In automotive applications, reliability is a significant requirement, especially within a harsh environment (vibration and shock). 
     Consequently, a semiconductor device, in particular, a chip card and a belonging method of fabrication is needed, which improves the quality, stability and reliability of electrical connection to counter contacts of an electronic device. 
     SUMMARY 
     Therefore, the invention has been made in view of the above problems, and it is an object of the invention to provide a semiconductor device based on an overmolding a stamped strip instead of the known laminated strips, the so-called lamframes. 
     In particular, the semiconductor device includes a housing, an integrated circuit die, and a contact. The housing has a base surface and a lateral surface which extends to the base surface. The integrated circuit die is positioned on an inside of the housing. While the contact includes a first mating section, a second mating section, and a bent section. The first and second mating sections are arranged on the base surface and lateral surface, respectively, and are connected to each other via the bent section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the invention will now be described with reference to the accompanying drawings. In the drawings, the same components have the same reference numerals. The drawings are incorporated into and form a part of the specification for the purpose of explaining the principles of the invention. However, the drawings are not to be construed as limiting the invention to only the illustrated and described examples of how the invention can be used and made. Moreover, different aspects and details of the embodiments explained in the following may form inventive solutions in alternative combinations or arrangements. Further features and advantages will become apparent from the following and more detailed description of the invention which is illustrated in the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a base surface of a semiconductor device according to the invention, having been fully assembled; 
         FIG. 2  is a perspective view of a top surface of the semiconductor device of  FIG. 1 ; 
         FIG. 3  is a perspective of the chip card of  FIG. 2 , showing an inside view of the semiconductor device; 
         FIG. 4  is a perspective view of a lead frame according to the invention in a first manufacturing step; 
         FIG. 5  is a perspective view of the lead frame of  FIG. 4  after bending contacts of the semiconductor device according to the invention; 
         FIG. 6  is a perspective of the lead frame of  FIG. 5  after providing insulation elements to support and insulate the contacts; 
         FIG. 7  is perspective view of the lead frame of  FIG. 6  after punching slots that separate the contacts from each other and from a die attach pad; 
         FIG. 8  is a perspective view of the lead frame of  FIG. 7  after attaching a integrated circuit die; 
         FIG. 9  is a perspective view of the lead frame of  FIG. 8  after providing wire bond connections between the integrated circuit die and the contacts; 
         FIG. 10  is a perspective view of another lead frame according to the invention; 
         FIG. 11  is a perspective view of base surface of another semiconductor device according to the invention; 
         FIG. 12  is a perspective view of a top surface of the semiconductor device of  FIG. 11 ; 
         FIG. 13  is a perspective view of the semiconductor device of  FIG. 12 , showing an inside view of the semiconductor device; 
         FIG. 14  is a sectional view of a connecting device for the a semiconductor device according to the invention; 
         FIG. 15  is a sectional view of another connecting device for the a semiconductor device according to the invention; and 
         FIG. 16  is a sectional view of a slide-in connecting device for connecting a conventional chip card. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
       FIG. 1  shows in a perspective view a semiconductor device, such as a micro universal integrated circuit card (UICC)  100 , according to the invention. Of course, the inventive concept can be used with any other integrated circuit package which is intended to be brought into contact with belonging contacts or to be soldered to a substrate. The micro UICC  100  is shown in  FIG. 1 , with the contact carrying base surface  102  facing upward in order to illustrate more clearly the contacts  104 . According to the invention, each contact  104  includes a first mating section  108  in plane with the base surface  102 , and a second mating section  110  that extend across to the first mating sections  108  and are arranged along a lateral surface  106 . 
     A bent section  112  connects the first and second mating sections  108 ,  110  to each other. According to the shown embodiment, this bent section  112  is prepared as a curved section. The design of such a contact  104  allows for slide-in application contacting with minimal wear. However, the bent section  112  can also have other suitable shapes, such as a combination of two 45° bends with a short straight portion there between. Further, the bent region here results in an essentially perpendicular arrangement of the first and second mating surfaces  108 ,  110  with respect to each other, but any other angle between the first and second mating surfaces  108 ,  110  can also be formed according to the invention. As is clear from  FIG. 1 , the bent section  112  is a smooth bent section with no discontinuous formations, thereby forming a cross-over between the first and second mating surfaces  108 ,  110 , being free of any sharp edges. In particular, the bent section  112  is configured as a continuous region, such that the cross-over between the first and second mating sections  108 ,  110  is a smooth cross-over with no discontinuous formations. Accordingly, by providing a continuous cross-over the formation of a sharp-edge between said first and second mating sections  108 ,  110  is avoided. The advantage thereof is among others an increased reliability, since the wear of a chip or counter contact can be reduced. 
     As will become more apparent from  FIG. 3 , the contacts  104  are electrically insulated from each other and mechanically supported by an insulating element  114 . The insulating element  114  can for instance be manufactured by an injection molding step. 
     A cooling surface  116  of a die attach pad  118  extends to the outside of the semiconductor device, micro UICC  100 , in order to operate as a heat sink. When the micro UICC  100  is directly soldered, for instance, to a printed circuit board (PCB), the cooling surface  116  can be soldered to a belonging copper surface of the printed circuit board to provide a heat sink function and quickly dissipate heat generated by the integrated circuit die  124 . 
     As shown in  FIG. 2 , a cover  120  closes the housing  122 . This cover  120  is for instance formed by a plastic material that is overmolded in order to tightly close the housing  122 . As the surface of the cover  120  is completely smooth, it offers the advantage of representing a relatively large and well-defined pick-and-place area for an automatic placement machine. 
     In  FIG. 3 , the micro UICC  100  is shown without the material of the cover  120  in order to explain the inner structure of the micro UICC  100 . On the inside of the housing  122 , the integrated circuit die  124  is attached to the die attach pad  118 . The integrated circuit die  124  can be fixed to the die attach pad  118  by many known techniques, such as gluing, soldering or the like. The electrical connections between the integrated circuit die  124  and bond pads  136  of the contacts  104  can, for instance, be established by wire bonding. As will be apparent from the description of the manufacturing steps, small, sharp edges resulting from cutting and stamping a metal lead frame are either completely covered by the cover material  120  along a insulating sections  126  between the contacts  104  and the die attach pad  118 . Alternatively, sharp edges are only to be found on surfaces which are not critical for electrical connections, such as the second lateral surfaces  128 . 
     With reference to  FIGS. 4 to 9 , the manufacturing process of semiconductor devices according to the invention, such as a micro UICC  100 , from a lead frame  130  will be explained in detail. The lead frame  130  is part of a carrier strip in a reel-to-reel process suitable for fully automated manufacturing. As shown in  FIG. 4 , a first stamping process is performed to provide the contacts  104  and further provide webs  134  for fixing the lead frame on the carrier  131  of the strip. Sprocket holes  132  are provided for the processing in a reel-to-reel process. 
     Next, a bending step follows, which provides the bent section  112  and forms the contacts  104  to have the first and second mating sections  108 ,  110  that extend across to each other. However, any other profiles of the bent section  112  can also be fabricated during this step. 
     After the forming step, the first and second mating sections  108 ,  110  of the contacts  104  can be plated with an electrically conductive and/or corrosion stable film, such as gold. Of course, all usual deposition techniques and materials for forming such a plating layer can be applied. The bending process also has the advantage that a selective galvanic plating process can be performed. 
       FIG. 6  shows the lead frame  130  after a first overmolding step wherein the insulating elements  114  are formed. The contacts  104  together with their radius are embedded and supported in the material of the insulating element  114  during this overmolding step. 
     Subsequently, a further punching step can be performed in order to separate the contacts  104  from each other, which are mechanically fixed within the insulating element  114 . The stamped slots form the insulating section  126  between the die attach pad  118  and the contacts  104  in the finally mounted state (see  FIG. 7 ). 
     By conventional die attaching techniques, the integrated circuit die  124  is attached to the die attach pad  118 , as can be seen from  FIG. 8 . However, carrier strips, not having an installed integrated circuit die  124 , can also be kept on stock and transferred to a customer in the form they have in  FIG. 7 . 
     As shown in  FIG. 9 , a wire bonding step is performed to provide electrical connection between the integrated circuit die  124  and bond pads  136  of the contacts. 
     Before the webs  134  are cut and the semiconductor devices are separated, thereby forming the individual micro UICCs  100 , the cover  120  is added, which is shown in  FIGS. 1 and 2 . The cover  120  can be produced by a second overmolding step or by potting, filling or encapsulation steps, or by mounting a cover  120 . This assembly step can also be performed by a customer. 
       FIG. 10  shows another embodiment of a lead frame  130  structure used to manufacture a semiconductor device according to the invention, where, instead of the metallic webs  134  that establish an electrical contact between the outside carrier  131  and the contacts  104 , a non-conductive link  115  to the strip is provided by mounting the contacts  104  as a separate part embedded within the insulating element  114 . This embodiment can replace the embodiment of  FIG. 7 . Due to the non-conductive fixing means  115 , a test of the electrical connections between the bond pads and the integrated circuit die  124  can be performed on the strip without the necessity of isolating the individual semiconductor devices by cutting them apart, even after attaching the integrated circuit die  124  and performing the wire bonding process. 
     Another embodiment of a semiconductor device according to the invention is shown in  FIGS. 11 to 13 , where the insulating elements  114  are formed as a frame  138  which encompasses the integrated circuit die  124 . Accordingly, the circumferentially closed insulating frame  138  has the advantage that the potting or overmolding process for providing the cover  120  is facilitated. 
       FIGS. 14 and 15  show two possible electrical contacting schemes for the semiconductor device according to the invention, such as a micro UICC  100 . 
     As can be seen from  FIG. 14 , the second mating section  110  on the lateral surface  106  allows for a contacting by means of a slide-in motion without the necessity of applying a residual pressure in a contacting direction  140 . The micro UICC  100  is kept in position by the friction force on the contacts  104 . When forming the bent section  112  in a way that the second mating section  110  is bent by more than 90° or includes a recess (not shown) allowing engagement of the counter contact  142 , a form fit can be achieved. 
     The tolerance chain of this arrangement is very short because only the sum of the tolerance of the semiconductor device and of the distance between the counter contacts  142  has to be considered, whereby the reliability can be enhanced. Furthermore, this sort of contacting leads to a larger wipe area between the contact  104  and the counter contact  142 . A large wipe distance, however, is favourable because it cleans the contact point of any pollution. Furthermore, side contacts according to the invention allow for an ultra low height socket and enhance the reliability of the electric contact. Side contacting schemes moreover allow a fully automated pick and place assembly of the semiconductor device. 
     Also with a press-in contact, as shown in  FIG. 15 , a micro UICC  100  according to the invention can easily be used. This arrangement has the advantage that it allows for a very small printed circuit board area. In any case, the inventive side and bottom contacts enhance the design flexibility for a module designer. 
     By providing a connection surface on the bottom as well as on the side of the housing  122 , and by providing a full radius there between, in the case of slide-in contacting, minimal wear can be achieved. Furthermore, the contact  104  edges can also be covered with a metal plating and therefore the reliability of the electric contact  104  is enhanced considerably. Additionally, many different mating directions and contacting schemes are possible. Finally, a higher reliability of the connection due to reduced tolerance chains can be achieved, when using the inventive chip card in sockets with contacts mating on the side contacts of the chip card&#39;s package. 
     A semiconductor device according to the invention which can be used for memory cards, smart cards, ID cards and socketable ICs offers several advantages. Firstly, the semiconductor device according to the invention allows for fully plated contact areas and makes sure that no bare base material of the lead frame  130  is exposed. Further, many different mating directions and principles for the electrical contact  104  to a counter contact  142  are possible. In particular, electrical contact  104  can be established through the two mating surfaces at the bottom and the side surface as well as via the radius of the contact  104 . 
     Slide-in mating motions can be performed with minimal wear to the connector device because sharp edges can be avoided. Finally, high reliability of the connections can be achieved due to reduced tolerance chain in sockets when using the contacts  104  mating on the side contact  104  of the semiconductor package. 
     According to an advantageous embodiment of the present invention, the housing  122  comprises an electrically insulating cover  120  for protecting and electrically insulating the integrated circuit die  124 . This cover  120  can for instance be formed by a further overmolding process. In case that the semiconductor device is directly soldered to a printed circuit board (PCB), the cooling surface  116  can also be soldered to copper surfaces on the PCB which provide heat sink function. 
     The configurations described in the above-described embodiment can be selected or changed to other configurations as appropriate. Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.