Abstract:
A method of fabricating a memory card. The method comprises the initial step of providing a leadframe which has a dambar and a plurality of contacts, each of the contacts being attached to the dambar by at least one tie bar. A molded first body section is formed on the leadframe subsequent to the electrical connection of a semiconductor die thereto such that portions of the leadframe other than for the contacts thereof are covered by the first body section. After the tie bars and dambar have been removed from the leadframe, a second body section is formed on the contacts of the leadframe such that portions of the contacts are exposed in a common exterior surface of the second body section. The second body section defines the leading edge of the memory card which has no metal of the leadframe exposed therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates generally to memory cards, and more particularly, to a memory card (e.g., a multi-media card (MMC)) wherein a two-step transfer mold procedure is used to form the memory card body which partially encapsulates the memory card leadframe structure so that the tie bars used to connect the external signal contacts to the outer frame of the leadframe can be removed prior to the complete formation of the body.  
         [0004]     As is well known in the electronics industry, memory cards are being used in increasing numbers to provide memory storage and other electronic functions for devices such as digital cameras, MP3 players, cellular phones, and Personal Digital Assistants. In this regard, memory cards are provided in various formats, including multi-media cards and secure digital cards.  
         [0005]     Typically, memory cards comprise multiple integrated circuit devices or semiconductor dies. The dies are interconnected using a circuit board substrate which adds to the weight, thickness, stiffness and complexity of the card. Memory cards also include electrical contacts for providing an external interface to an insertion point or socket. These electrical contacts are typically disposed on the backside of the circuit board substrate, with the electrical connection to the dies being provided by vias which extend through the circuit board substrate.  
         [0006]     In an effort to simplify the process steps needed to fabricate the memory card, there has been developed by Applicant a memory card wherein a leadframe assembly is used as an alternative to the circuit board substrate, as described in Applicant&#39;s co-pending U.S. application Ser. No. 09/956,190 entitled LEAD-FRAME METHOD AND ASSEMBLY FOR INTERCONNECTING CIRCUITS WITHIN A CIRCUIT MODULE filed Sep. 19, 2001, the disclosure of which is incorporated herein by reference. As is described in Ser. No. 09/956,190, the leadframe and semiconductor die of the memory card are covered with an encapsulant which hardens into a cover or body of the memory card. The body is sized and configured to meet or achieve a “form factor” for the memory card. In the completed memory card, the contacts of the leadframe are exposed within a common surface of the body, with the die pad of the leadframe and the semiconductor die mounted thereto being disposed within or covered by the body.  
         [0007]     Memory cards, such as multi-media cards, are used by advancing the same into a host socket which includes a plurality of connector pins. Many host sockets include nine connector pins to accommodate the seven contacts included in many memory card formats such as multi-media cards, and the nine contacts included in the secure digital card memory card format. Applicant has previously determined that one of the drawbacks associated with leadframe based memory cards is that portions of the tie bars which are used to connect the contacts to the outer frame of the leadframe are typically exposed in the leading edge of the memory card which is initially advanced into the host socket. More particularly, exposed within this leading edge are the severed ends of the tie bars created as a result of the cutting or singulation process typically used to separate the outer frame of the leadframe from the remainder thereof subsequent to the formation of the body of the memory card. These exposed portions of the tie bars give rise to a potential to short against the metal features of the host socket, and are thus highly undesirable.  
         [0008]     The present invention addresses and overcomes the above-described deficiencies of currently known leadframe based memory cards by providing a memory card wherein a two-step transfer mold procedure is used to form the memory card body which partially encapsulates the memory card leadframe structure so that the tie bars used to secure the contacts to the outer frame can be removed prior to the complete formation of the body. More particularly, in an initial step of the fabrication process, a first body section is molded to portions of the leadframe other than for the contacts thereof. This initial molding step is followed by a trimming procedure wherein the outer frame and tie bars used to connect the contacts thereto are removed from the leadframe. Thereafter, a second molding procedure is completed wherein a second body section is molded to the leadframe in a manner partially encapsulating the contacts thereof. Though a portion of each of the contacts is exposed in a common surface of the second body section, no metal is exposed in that surface of the second body section which defines the leading edge of the memory card. These and other attributes of the present invention will be described in more detail below.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     In accordance with the present invention, there is provided a method for manufacturing a memory card such as a multi-media card which involves a two-step molding process. The initial molding step facilitates the formation of a first body section of the memory card which effectively supports the contacts of the leadframe in a manner allowing for the removal of the tie bars of the leadframe used to support the contacts within the outer frame or dambar thereof. Subsequent to the formation of the first body section, a trimming procedure is completed which removes the dambar and the contact supporting tie bars from the remainder of the leadframe. Thereafter, a second, follow-up molding step is completed to facilitate the formation of a second body section of the memory card which partially encapsulates the contacts such that portions of the contacts are exposed in a common surface of the second body section. However, no metal is exposed in that surface of the second body section which defines the leading edge of the memory card.  
         [0010]     As a result of the complete removal of the tie bars attaching the contacts of the leadframe to the dambar thereof, the completely formed memory card does not include any tie bar ends exposed in the leading edge thereof. In this regard, the absence of the exposed ends of the tie bars in the leading edge of the memory card eliminates the potential for the tie bars shorting against the metal features of the host socket into which the memory card is to be inserted.  
         [0011]     The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein:  
         [0013]      FIG. 1  is a bottom plan view of a memory card fabricated through the use of the molding method of the present invention;  
         [0014]      FIG. 2  is a top plan view of the leadframe of the memory card shown in  FIG. 1  prior to the formation of the molded body sections thereon; and  
         [0015]      FIGS. 3-5  illustrate an exemplary sequence of steps which may be used to facilitate the fabrication of the memory card in accordance with the present invention 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same,  FIG. 1  depicts a memory card  10  which includes a leadframe  12  best shown in  FIG. 2 . As shown in  FIG. 1 , the memory card  10  has a form factor particularly suited for use in a multi-media card memory application. However, those of ordinary skill in the art will recognize that the memory card  10  may have alternative memory card formats, including those of secure digital cards (SDC), compact flash (CF), smart media, memory stick, and other small form factor memory cards.  
         [0017]     The leadframe  12  of the memory card  10  comprises an outer frame or dambar  14  which is eventually removed from the leadframe  12  as described below, and thus does not constitute part of the completed memory card  10 . Dambar  14  has a generally rectangular configuration defining an opposed pair of longitudinal sides or segments  16  and an opposed pair of lateral sides or segments  18 . In addition to the dambar  14 , the leadframe  12  includes a die attach area or die pad  20  which is disposed within the interior of the dambar  14 . Die pad  20  defines opposed, generally planar top and bottom surfaces. Integrally connected to and extending from one lateral side  18  of the dambar  14  is a plurality of contacts  22  of the leadframe  12 . Each of the contacts  22  also defines opposed, generally planar top and bottom surfaces. Integrally connected to and extending from each of the contacts  22  is a conductive trace  24 . The traces  24  terminate in close proximity to the die pad  20 . Tie bars  26  are used to integrally connect the die pad  20  to the longitudinal sides  16  of the dambar  14 . Similarly, one or more tie bars  27  are used to integrally connect the contacts  22  to one lateral side  18  of the dambar  14 . In particular, as is seen in  FIG. 2 , two tie bars  27  are integrally connected to and extend between each contact  22  and the corresponding lateral side  18 , though one or more than two tie bars  27  may be used to facilitate such connection.  
         [0018]     In the memory card  10 , attached to the top surface of the die pad  20  is a semiconductor die  30 . The semiconductor die  30  is electrically connected to the leadframe  12 , and more particularly to one or more traces  24  alone or in combination with the die pad  20  through the use of conductive wires  32 . In this regard, the conductive wires  32  effectively place the semiconductor die  30  into electrical communication with the leadframe  12  and, more particularly, to one or more of the contacts  22  thereof.  
         [0019]     The leadframe  12  is preferably fabricated from a conductive metal material (e.g., copper) through either a chemical etching or mechanical stamping process. Those of ordinary skill in the art will recognize that the leadframe  12  may be formed to include any number of contacts  22  depending on the desired application for the memory card  10 . As shown in  FIG. 1 , the memory card  10  includes seven contacts  22  which is the typical number included for a multi-media card application. In the memory card  10 , more than one semiconductor die  30  may be attached to the die pad  20 . In addition to the semiconductor die(s)  30 , the die pad  20  may also accommodate one or more other devices such as passive devices. The semiconductor die(s)  30  alone or in combination with the other devices may, rather than being attached directly to the die pad  20 , be attached to an intervening substrate. Further, the leadframe  12  may be configured to define more than one die pad  20 , with such multiple die pad(s) each accommodating one or more semiconductor dies alone or in combination with other devices such as passive devices. The pattern of conductive traces  24  may also be varied depending upon the number and arrangement of die pads and the number of semiconductor dies and/or other passive devices included in the memory card  10 . Thus, the configuration of the leadframe  12  of the memory card  10  is variable, in that the number and arrangement of semiconductor dies, die pads, contacts, and conductive traces may be varied as needed to satisfy the requirements of a particular application.  
         [0020]     Subsequent to the electrical connection of the semiconductor die  30  to the leadframe  12  in the above-described manner, the leadframe  12  is preferably subjected to a bending operation wherein each of the traces  24  is bent so as to facilitate the creation of an angled or sloped portion therein (as seen in  FIGS. 3-5 ) which is located between the contacts  22  and the die pad  20 . The bending of the traces  24  removes the contacts  22  from their original co-planar relationship to the die pad  20 . Thus, the contacts  22  and the die pad  20  extend along respective ones of spaced, generally parallel planes. The bending of the leadframe  12  in the above-described manner may occur either prior to the attachment of the semiconductor die  30  to the top surface of the die pad  20 , or subsequent to the extension of the conductive wires  32  between the terminals of the semiconductor die  30  and the traces  24 .  
         [0021]     It is further contemplated that the leadframe  12  will be subjected to a etching process wherein the thicknesses of the traces  24  are reduced in comparison to the remainder of the leadframe  12 . As shown in  FIGS. 3-5 , the traces  24  are subjected to a half-etching process such that the thicknesses thereof is approximately half that of the contacts  22  and die pad  20  of the leadframe  12 . Thus, those portions of the traces  24  which are integrally connected to the contacts  22  and are not up-set as a result of the completion of the aforementioned bending operation are still perpendicularly recessed inwardly relative to the bottom surfaces of the contacts  22 .  
         [0022]     Referring now to  FIGS. 3-5 , in accordance with the present invention, the memory card  10  is fabricated by initially forming the leadframe  12  to have the above-described structural attributes. Thereafter, the semiconductor die(s)  30  and/or other devices are secured to the top surface of the die pad  20  and electrically connected thereto and/or to the traces  24  through the use of the conductive wires  32 . Thereafter, the leadframe  12  is optionally bent in the above-described manner to facilitate the formation of the angled or sloped portion within each of the traces  24 .  
         [0023]     The leadframe  12  next is placed into a mold cavity collectively defined by a top mold section  34  and a bottom mold section  36  ( FIG. 3 ). The leadframe  12  is preferably captured between the top and bottom mold sections  34 ,  36  such that the top surfaces of the contacts  22  are completely or substantially covered by a portion of the top mold section  34 , with the bottom surfaces of the contacts  22  being completely covered by a portion of the bottom mold section  36 . Thus, with the contacts  22  of the leadframe being captured between the top and bottom mold sections  34 ,  36 , the traces  24  and die pad  30  of the leadframe reside in an open area of the mold cavity in spaced relation to the top and bottom mold sections  34 ,  36 , as do the semiconductor die  30  and conductive wires  32  interfaced to the leadframe  12 .  
         [0024]     Subsequent to the placement of the leadframe  12  between the top and bottom mold sections  34 ,  36  in the above-described manner, a first molding step is conducted wherein an encapsulant material is injected into the open area of the mold cavity defined between the top and bottom mold sections  34 ,  36 . The encapsulant material flows about and completely encapsulates the die pad  20  and traces  24  of the leadframe  12 , as well as the semiconductor die  30  and conductive wires  32 . The encapsulant material is preferably a plastic (e.g., thermoset, thermoplastic) which, upon hardening, forms a molded first body section  38  of the memory card  10  ( FIG. 4 ). The first body section  38  defines a generally planar top surface  40 , an opposed, generally planar bottom surface  42 , an opposed pair of longitudinal side surfaces  44 , and a lateral side surface  46 . The first body section  38  further defines a sloped lateral side surface  48 . While the longitudinal side surfaces  44  and lateral side surface  46  extend generally perpendicularly between the top and bottom surfaces  40 ,  42 , the sloped lateral side surface  48  extends non-perpendicularly between the top and bottom surfaces  40 ,  42  and is disposed adjacent to the contacts  22  of the leadframe  12 . Thus, as is further seen in  FIG. 4 , the contacts  22  protrude from the sloped lateral side surface  48  of the first body section  38 . It is contemplated that the die pad  20  of the leadframe  12  may be formed to be of sufficient thickness such that the bottom surface thereof is exposed in and substantially flush with the bottom surface  42  of the first body section  38 .  
         [0025]     The bending of the leadframe  12  and resultant formation of the angled portions within the traces  24  in the aforementioned manner allows the up-set die pad  20  and up-set portions of the traces  24  (as well as the semiconductor die  30  and conductive wires  32  interfaced thereto) to be completely encovered or encapsulated by the encapsulant material, and hence the first body section  38 . Even those portions of the traces  24  which are not up-set are completely covered or encapsulated by the first body section  38  due to the same being of reduced thickness in comparison to the contacts  22  as a result of the completion of the above-described partial etching process. Thus, no portion of any of the traces  24  is exposed in the first body section  38  of the memory card  10 .  
         [0026]     Subsequent to the formation of the first body section  38 , the leadframe  12  is subjected to a singulation process wherein the dambar  14  is removed from the remainder of the leadframe  12 . Such removal typically entails cutting portions of the tie bars  26  which protrude from the first body section  38 , in addition to trimming or removing the tie bars  27  from the contacts  22 . It is contemplated that the singulation process may be completed through a sawing or punching operation. The complete formation of the first body section  38  allows for the removal of the tie bars  27  since the contacts  22  are supported and maintained in prescribed orientations relative to each other as a result of the traces  24  integrally connected thereto being embedded within the first body section  38 .  
         [0027]     Subsequent to the formation of the first body section  38  and removal of the dambar  14  in the above-described manner, the partially fabricated memory card  10  is placed into another suitably shaped mold cavity which, upon the injection of additional encapsulant material thereinto, facilitates the formation of a molded second body section  50  of the memory card  10  ( FIG. 5 ). The second body section  50  itself defines a generally planar top surface  52 , an opposed, generally planar bottom surface  54 , an opposed pair of lateral side surfaces  56 , and a longitudinal side surface  58 . Extending angularly between the longitudinal side surface  58  and one of the lateral side surfaces  56  is a sloped side surface  60 . The second body section  50  further defines a sloped longitudinal side surface  62  which is complimentary to and abutted against the sloped lateral side surface  48  of the first body section  38 . In addition to the side surfaces  48 ,  62  being engaged to each other, the top surface  52  of the second body section  50  extends in generally co-planar, continuous relation to the top surface  40  of the first body section  38 . Similarly, the bottom surface  54  of the second body section  58  extends in generally co-planar, continuous relation to the bottom surface  42  of the first body section  38 , with the lateral side surfaces  56  of the first body section  58  extending in generally co-planar, continuous relation to respective ones of the longitudinal side surfaces  44  of the first body section  38 . The bottom surfaces of the contacts  22  of the leadframe  12  are exposed in and substantially flush with the bottom surface  54  of the second body section  50 .  
         [0028]     The formation of the second body section  50  completes the fabrication of the memory card  10 . This fabrication technique wherein the tie bars  27  are completely removed prior to the formation of the second body section  50  allows the distal ends of the contacts  22  (i.e., those ends opposite the ends having the traces  24  protruding therefrom) to be completely covered by the second body section  50 . As a result, no severed distal ends of the tie bars  27  remain exposed in the longitudinal side  58  of the second body section  50  which itself defines the leading edge of the memory card  10 . The absence of any exposed metal in the leading edge of the memory card  10  eliminates potential occurances of shorting against the metal features of the host socket. As indicated above, this represents a departure from and provides a significant advantage over currently known fabrication techniques wherein the severed distal ends of the tie bars used to support the contacts of the leadframe within the dambar thereof remain exposed in the leading edge of the memory card subsequent to the complete fabrication thereof.  
         [0029]     This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure