Abstract:
A method of fabricating a packaged semiconductor includes forming a conductive frame as an integral piece of conductive material. The frame includes an inner portion and a ring portion encircling the inner portion. The ring portion includes a first ring portion encircling first and second sides of the inner portion, and a first bar portion located on a third side of the inner portion. The method includes mounting a semiconductor die to a first surface of the inner portion of the frame. The die is configured to receive power via the first ring portion. The method includes applying a casing, which covers the die, to the frame. The method includes, after the casing is applied to the frame, removing (i) sections of the frame that connect the inner portion to the ring portion, and (ii) sections of the frame that connect the first ring portion to the first bar portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. patent application Ser. No. 12/731,782 (now U.S. Pat. No. 8,383,962), filed on Mar. 25, 2010, which claims the benefit of U.S. Provisional Application No. 61/167,726, filed on Apr. 8, 2009. The entire disclosures of the above referenced applications are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to semiconductor packaging and more particularly to exposed die pad packages including a power ring. 
       BACKGROUND 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    Semiconductor devices are generally manufactured on a silicon wafer. Each silicon wafer undergoes various processing steps to create multiple individual devices on the wafer. Each device on the wafer is referred to as a die. When the wafer is complete, the wafer is divided into the individual dies (or, dice). For example only, this dividing may be performed by sawing or by scoring and snapping. 
         [0005]    The dice are generally vulnerable to their environment. For example only, the dice are physically fragile and prone to cracking and breaking when being handled. In addition, the dice are prone to contamination, both by physical contact as well as by airborne particles. The dice are also very sensitive to electrostatic discharge. For these and other reasons, the dice are often packaged. The packaged dice, or chips, are much easier to handle and may be easier to use in applications such as printed circuit boards. 
         [0006]    A package may include one die or may include multiple dice. For ease of explanation, the following description will refer to a single die, although the present application applies to the packaging of multiple dice into a single package. 
         [0007]    An exemplary package includes a first package piece to which the die is mounted. The first package piece includes a first face and a second face. The first face includes a die attach area where the die is placed. The second face may include features for electrically and mechanically connecting the package to a printed circuit board. Leads carry electrical signals from the die to the printed circuit board. Portions of the leads may be located on the first face of the first package piece. 
         [0008]    When the die is secured to the die attach area of the first package piece, wire bonds may be formed between bond pads of the die and the leads. The leads may be bent so that they wrap around the edges of the first face and protrude past the second face. The leads can therefore be inserted into through-holes of a circuit board. Often, leads are attached to two opposing edges of the first face. This creates two rows of protruding leads, and the package is called a dual inline pin (DIP) package. 
         [0009]    Through-holes may make circuit board layout more difficult and may prevent components from being placed on both sides of the circuit board. Surface mounting technology, where leads do not protrude through the circuit board, avoids these problems. The leads of a surface-mount package are generally bent to be parallel to the second face, and therefore present flat contacting surfaces to corresponding receiving pads on the circuit board. 
         [0010]    Traditionally, leads have been located around the perimeter of the package. This is because the die occupies the center of the package and the bond wires connect outward from the die to the perimeter of the package. A surface-mounted version of the DIP package is a small-outline integrated circuit (SOIC), where the leads are bent outward when they reach the second face to form a gull-wing shape. 
         [0011]    When the package has leads on all four edges, the package may be referred to as a quad flat package (QFP). When the leads do not extend beyond the edges of the package, the package may be referred to as a quad flat no-leads package (QFN). Some QFN packages include a central pad on the second face that dissipates thermal energy from the package to the circuit board. 
         [0012]    To allow for greater connection density, leads may be formed in the interior area of the second face of the package. Internal wiring of the package may route signals from where bond wires connect at the perimeter of the package on the first surface to interior leads on the second surface of the package. 
         [0013]    As described above, the face of the die has traditionally been exposed and bond wires connect the exposed bond pads of the die to leads of the package. In flip-chip packaging, the die is inverted onto the package, causing the bond pads of the die to contact the first face of the package. Then, the die can be designed to include bond pads in the center of the die, which will be located above the center of the package. This decreases the need for special conductors within the package that route signals from the perimeter of the first face to the center of the second face. 
         [0014]    In one example, package leads are in the form of pins; such a package is called a pin grid array (PGA). Pin grid array packages may mount to a socket that is surface-mounted to the circuit board. In another example, the package includes an array of pads that connects to an array of pads on the circuit board. A ball of solder may be placed on each of the package pads; such a package is called a ball grid array (BGA). 
         [0015]    A land grid array package includes pads that interface with pads on the circuit board. However, the land grid array package does not include balls of solder on the package pads. Instead, the circuit board may have a layer of solder on the pads. The solder may be restricted to the pad locations by using a mask when applying the solder. Once the package is positioned on the circuit board, the solder can be reflowed to secure each of the package pads to each of the receiving pads of the circuit board. 
         [0016]    Alternatively, a socket may be connected to the circuit board. The socket applies clamping force to the package. This clamping force can either force the package pads to contact pads of the circuit board or cause the package pads to contact pads of the socket. A socket may allow for easy replacement of the package. 
         [0017]    Once the die is mechanically and electrically connected to the first piece of the package, the die is covered. This isolates the die and any other components, such as bond wires, from the environment. The die may be covered by attaching a second package piece, such as a lid, to the first piece of the package. The first and second pieces may be sealed to prevent any contaminants from entering the space where the die is located. 
       SUMMARY 
       [0018]    A packaged semiconductor is disclosed. The packaged semiconductor comprises a conductive integral frame that includes an inner portion and a ring portion encircling the inner portion, a semiconductor die that is mounted to a first surface of the inner portion of the conductive frame, and a casing that supports the conductive frame and covers the semiconductor die. Sections of the conductive frame that connect the inner portion to the ring portion are removed after the casing is applied to the conductive frame. 
         [0019]    The ring portion includes a continuous first ring portion that encircles at least three sides of the inner portion. In one embodiment, the continuous first ring portion completely encircles the inner portion. 
         [0020]    In one embodiment, the ring portion includes a first bar portion on a fourth side of the semiconductor die. The first bar portion is insulated from the first ring portion. In another embodiment, the ring portion further includes a second bar portion on the fourth side of the semiconductor die. The first bar portion, the second bar portion and the first ring portion are insulated from each other. 
         [0021]    In one embodiment, the first surface of the inner portion defines a first plane. The ring portion is formed co-planar with the first plane. In another embodiment, the inner portion includes an elevated ring that is formed in a second plane. The second plane is parallel to and spaced apart from the first plane. 
         [0022]    Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0023]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0024]      FIGS. 1-2  are partial top views of an exemplary packaged die according to the principles of the present disclosure; 
           [0025]      FIG. 3A  is an exemplary partial top view of the packaged die of  FIG. 1  at a later stage of manufacturing; 
           [0026]      FIG. 3B  is an exemplary top view of a printed circuit board contact pattern corresponding to the packaged die of  FIG. 3A ; 
           [0027]      FIG. 4A  is a cross-sectional view of an exemplary implementation of the packaged die of  FIG. 3 ; 
           [0028]      FIGS. 4B-4D  are cross-sectional views of additional exemplary implementations of packaged dies; 
           [0029]      FIGS. 5-10  are partial top views of exemplary packaged dies; 
           [0030]      FIG. 11  is a cross-sectional view of an exemplary implementation of the packaged die of  FIG. 10 ; 
           [0031]      FIGS. 12-13  are partial top views of exemplary packaged dies; 
           [0032]      FIG. 14  is a cross-sectional view of an exemplary implementation of the packaged die of  FIG. 13 , which includes an elevated ring; and 
           [0033]      FIGS. 15-22  are partial top views of exemplary packaged dies. 
       
    
    
     DESCRIPTION 
       [0034]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0035]    Referring now to  FIG. 1 , a partial top view of a package is shown. The package includes a conductive lead frame  100 . For example, the frame  100  may be made of metal, and may be formed by stamping a sheet of metal. Once the frame  100  is formed, a die  104  is mounted to the frame  100 . The die  104  may be mounted directly to the frame  100  or to an intermediary layer (not shown). For example only, the intermediary layer may be an insulator to prevent shorts between the die  104  and the frame  100 . 
         [0036]    In various implementations, it may be desirable for a face of the die  104  that contacts the frame  100  to be electrically continuous. For example only, the face of the die  104  may include ground connections, and the conductive frame  100  can therefore decrease the resistance between the ground connections. 
         [0037]    The die  104  may also be connected to the frame  100  via bond wires  116 , such as bond wires  108  and  112 . In addition, bond wires  116  may electrically connect the die  104  to bond fingers  120  of the package. For ease of illustration, only some of the bond fingers  120  are shown. The bond fingers  120  may be present on all four sides of the frame  100 , or may be limited to one or more sides. 
         [0038]    Once bond wires are connected, the die  104  is enclosed in a casing (shown in  FIG. 4A ) that secures the frame  100 . The casing may include an encapsulating material, such as epoxy, plastic, or resin, and may be applied using an injection molding process. 
         [0039]    Referring now to  FIG. 2 , it may be desirable to split the frame  100  into two pieces to, for example, create a ground plane  124  and a power ring  128 . The ground plane  124  can provide ground connections to the die  104  via bond wires such as the bond wires  108  and/or through direction connection to the die  104 . The power ring  128  may provide operating power to the die  104 , such as via the bond wires  112 . 
         [0040]    In order to electrically separate the power ring  128  from the ground plane  124 , connecting sections  132  indicated by circles may be removed. Removal of the connecting sections  132  is performed after the frame  100  and the die  104  have been encased. In this way, disconnected sections of the frame  100  are fixed in place by the casing. Removal of the connecting sections  132  may be effected using any of a number of appropriate milling techniques and/or equipment including, for example, lasers, router bits, saw blades, etc. For example, where higher cutting precision is desired (such as, in the case of a localized trench or cut), lasers, router bits or small-diameter saw blades may be used; on the other hand, where lower cutting precision is sufficient (such as, in the case where one side of the frame  100  is cut), large-diameter saw blades may be used. 
         [0041]    Referring now to  FIG. 3A , the power ring  128  is shown separated from the ground plane  124 . For example, a cavity  140  is present where one of the connecting sections  132  of the frame  100  was previously located. Removing the connecting sections  132  means that the connecting sections  132  no longer conduct electricity between different portions of the frame  100 . For example only, the connecting sections  132  may be completely removed. Alternatively, vestigial pieces of the connecting sections  132  may remain, such as is shown in  FIG. 3A . It should be further noted that while the edges of the cavity  140  shown in  FIG. 3A  are straight, such edges may also be round or curved, depending on the type of technique and/or equipment that is used to perform the removal. 
         [0042]    Material from the frame  100  may be removed by any suitable process. For example only, mechanical removal, chemical etching, or laser removal may be performed. Mechanical removal may be performed using, for example only, a router, a saw, a drill, or a high pressure stream of fluid. Chemical etching may include using photolithography to define the portions of the frame  100  that will be removed. 
         [0043]    Referring now to  FIG. 3B , a contact pattern  150  may be formed on a printed circuit board to receive the packaged die of  FIG. 3A . The contact pattern  150  includes lead contact areas  154 , ring contact area  158 , and plane contact area  162 . Each of the lead contact areas  154  allows an electrical connection with one of the bond fingers  120 . The ring contact area  158  allows an electrical connection with the power ring  128 , and the plane contact area  162  similarly allows an electrical connection with the ground plane  124 . 
         [0044]    The contact pattern  150  may be modified based on the arrangement of the packaged die that will be mounted to the printed circuit board. In various implementations, the contact pattern  150  may accommodate multiple types of packaged dies. For example only, some packaged dies may not include a bond finger corresponding to each of the lead contact areas  154 . In another example, the ground plane  124  of some packaged dies may be smaller than the plane contact area  162 . 
         [0045]    Solder may provide an electrical and a physical connection between the contact pattern  150  and the packaged die. Each contact area of the contact pattern  150  may be connected to a trace on the printed circuit board. For example only, a multi-layer printed circuit board may include a ground plane. The ground plane may be connected to the plane contact area  162 , such as through an array of vias. 
         [0046]    Referring now to  FIG. 4A , a cross-sectional side view of the packaged die of  FIG. 3A  is shown. The die  104  is shown surrounded by a casing  200 . As described above, the casing  200  may include one or more pieces, or may be a coating applied to the die  104 . In  FIG. 4A , the bond fingers  120  are part of leads  204 . The lead  204  may be formed from a continuous piece of material, such as metal, or may be formed from a joining of multiple pieces. The lead  204  may be formed in the shape shown in  FIG. 4A  by bending, which may be performed before or after mounting the die  104  to the frame  100 . 
         [0047]    In the example of  FIG. 4A , the lead  204  extends from the edge of the casing  200 . Various other lead structures are possible. Three further examples are given in  FIGS. 4B ,  4 C, and  4 D. In  FIG. 4B , lead  220  is bent so that the bottom portion of the lead  220  remains within the confines of the casing  200 , as viewed from a top view. This may reduce the amount of space required for the packaged chip on the circuit board. 
         [0048]    In  FIG. 4C , lead  230  is enclosed by the casing  200 . The bond finger  120  portion of the lead  230  may be connected to a bottom portion of the lead  230  using a through-hole, or via. In  FIG. 4D , a lead  240  is located on the bottom of the casing  200 . The bond finger  120  may serve as not only the seat of the bond wire, but also as the portion of the lead  240  that will contact the circuit board. 
         [0049]    Returning now to  FIG. 4A , the ground plane  124  and the power ring  128  are exposed at the bottom of the casing  200 . The ground plane  124  and the power ring  128  may be flush with the bottom surface of the casing  200  or may protrude beyond the bottom surface of the casing  200 . This may allow for more reliable seating against a circuit board that is not perfectly flat. 
         [0050]    Although a true cross-section may show only a single one of the bond wires, for purposes of illustration, bond wire  108 , bond wire  112 , and bond wire  116  are all shown in  FIG. 4A . The cavity  140  between the ground plane  124  and the power ring  128  is created to separate the power ring  128  from the ground plane  124 . This cavity may be filled with additional encapsulating material. For example only, the cavity  140  may be filled with the same compound of which the casing  200  is made. 
         [0051]    A further packaging process step may include trimming the leads  204  to reduce their protrusion beyond the edges of the casing  200 . In addition, the leads  204  may be plated for corrosion resistance and more reliable electrical connection. The leads  204  may be flexible to increase the reliability of connections to a circuit board that is less than perfectly flat. 
         [0052]    Although labeled as ground and power for ease of explanation, the ground plane  124  and the power ring  128  may carry other signals between the die  104  and the circuit board. For example only, the roles may be reversed, with power being provided to the die  104  via the ground plane  124  and a ground connection being provided by the power ring  128 . 
         [0053]    In another example, negative and positive power supplies, or vice versa, may be provided by the ground plane  124  and the power ring  128 , respectively. Ground connections may then be provided by one or more of the leads  204 . In yet another example, one of the ground plane  124  and the power ring  128  may provide input power to the die  104 , while the other carries output power. For example, such an arrangement may be used when the die  104  is a voltage regulator or converter. 
         [0054]    Referring now to  FIG. 5 , a die  304  is connected to a frame  308 . When connecting portions of the frame  308  are removed, the resulting structure is shown in  FIG. 6 . The frame  308  is seen to be split into a plane  312 , a partial ring  316 , and a bar  320 . For clarity of illustration, bond wires connecting the die  304  to the bar  320  are not shown. In addition, additional bond wires may connect the die  304  to additional portions of the partial ring  316 . For example only, bond wires may radiate from the die  304  in all directions. 
         [0055]    The plane  312 , the partial ring  316 , and the bar  320  can be used to carry any signals to and from the die  304 . In one example, the plane  312  provides ground connections to the die  304 . The partial ring  316  provides analog power to the die  304 , and the bar  320  provides digital power to the die  304 . This may reduce the amount of power supply noise introduced from the digital componentry of the die  304  into the analog componentry of the die  304  and vice versa. 
         [0056]    Referring now to  FIG. 7 , another frame  350  is shown. When connecting sections are removed, a plane  354 , a partial ring  358 , a bar  362 , and two sub-bars  366  and  370  are formed. Although shown as separately formed in  FIG. 7 , sub-bars  366  and  370  may initially be connected together. The connecting portion can be removed as part of the packaging process. 
         [0057]    For example only, the plane  354  may provide a ground connection to the die  304 . As used in this application, ground means a common potential that may or may not be the same as earth ground. The common potential may be connected to a system ground of a system in which the die  304  is used. The partial ring  358  may provide analog power to the die  304 , while the bar  362  provides digital power to the die  304 . 
         [0058]    The sub-bars  366  and  370  may provide additional power supplies to the die  304 . For example only, the sub-bars  366  and  370  may provide power at different voltages than that provided by the bar  362  or the partial ring  358 . For example only, the power supplied by the sub-bars  366  and  370  may be for input/output circuitry operating at two different voltage levels. This may allow the die  304  to interface with components that each operate at different voltages than the internal circuitry of the die  304 . 
         [0059]    Referring now to  FIG. 9 , a frame  400  is shown. When connecting portions of the frame  400  are removed, the resulting structure is shown in  FIG. 10 . In  FIG. 10 , a plane  408  and concentric inner and outer rings  412  and  416  are created. The die  304  may connect directly to the plane  408  or may connect via bonding wires (not shown). 
         [0060]    Referring now to  FIG. 11 , a cross-sectional view of the package of  FIG. 10  is shown. Gaps  420  and  422  result from separating the inner ring  412  from the plane  408  and the outer ring  416 . 
         [0061]    Referring now to  FIG. 12 , a frame  500  is shown. The frame  500  appears similar to the frame  400  of  FIG. 9  in this top view. As shown in  FIG. 13 , only some interconnecting portions are removed from the frame  500 . The resulting portions of the frame  500  form a plane/ring  508  and a ring  512 . 
         [0062]    Referring now to  FIG. 14 , differences between the frame  500  of  FIG. 12  and the frame  400  of  FIG. 9  can be seen. The plane/ring  508  includes an elevated ring, as seen at  520  and  522 . Bond wires  530  connect the die  504  to the elevated ring portion of the plane/ring  508 . Elevating the ring may make the wire-bonding faster, cheaper, or less error-prone, and may result in more reliable wire bonds. 
         [0063]    Referring now to  FIG. 15 , a frame  600  is shown with a die  604 . In  FIG. 16 , some interconnecting portions of the frame  600  have been removed to create a plane/ring  608 , a partial ring  612 , and a bar  616 . The ring portion of the plane/ring  608  may be elevated, as shown in  FIG. 14 . 
         [0064]    Referring now to  FIG. 17 , a frame  700  is shown with a die  704 . In  FIG. 18 , interconnecting portions of the frame  700  have been removed. A plane/ring  708  may include an elevated ring, similar to  FIG. 16 . A partial ring  712 , a bar  716 , and sub-bars  720  and  724  are also formed from the frame  700 . 
         [0065]    Frames may be created for which part or all of one or more bars are missing. For example only, referring now to  FIG. 19 , a frame  800  is shown with a die  804 . In  FIG. 20 , interconnecting portions of the frame  800  have been removed. The die  804  is mounted to a plane  808 . A partial ring  812  encircles two sides of the plane  808 . A bar  816  is formed on a third side of the plane  808 . 
         [0066]    Together, the partial ring  812  and the bar  816  partially encircle the plane  808 , leaving the fourth side of the plane  808  open. By omitting material on the fourth side of the plane  808 , the amount of metal required for the frame  800  may be reduced, which may decrease the unit cost of the frame  800 . One or more additional rings (not shown) may completely or partially encircle the plane  808 . The additional rings may be concentric, and may partially encircle different sides of the plane  808 . 
         [0067]    In another example, referring now to  FIG. 21 , a frame  900  is shown with a die  904 . In  FIG. 22 , interconnecting portions of the frame  900  have been removed. The die  904  is mounted to a plane  908 . A bar  912  is located on one side of the plane  908 . In this example, the remaining three sides of the plane  908  are open, with no associated bar or ring. 
         [0068]    Although various examples have been shown in the preceding figures, additional partial and/or full rings may be included. In addition, any ring may be split into partial rings, bars, or sub-bars. In addition, part or all of any ring may be formed in the same plane as any other ring, or may be elevated or lowered with respect to any other ring. 
         [0069]    In addition, although various examples of uses for connections have been given above, additional uses for each section of a frame are possible. In various implementations, a single package may be used with different types of dice. Depending on the particular die, a portion of the frame may perform different functions. For example only, a portion of the frame may be used for analog power if one type of die is attached, while being used for digital power if another type of die is attached. In addition, based on the particular die placed in the package, certain connecting sections may be left in place instead of being removed. This may allow a single frame structure to accommodate multiple configurations of rings and bars. 
         [0070]    The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims.