Abstract:
A semiconductor package comprises a die attach pad and a support member at least partially circumscribing it. Several sets of contact pads are attached to the support member. The support member is able to be etched away thereby electrically isolating the contact pads. A method for making a leadframe and subsequently a semiconductor package comprises partially etching desired features into a copper substrate, and then through etching the substrate to form the support member and several sets of contact pads. Die attach, wirebonding and molding follow. The support member is etched away, electrically isolating the contact pads and leaving a groove in the bottom of the package. The groove is able to be filled with epoxy or mold compound.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional application of co-pending U.S. patent application Ser. No. 13/045,253, filed Mar. 10, 2011, and entitled “Leadframe Based Multi Terminal IC Package,” which claims benefit of priority under 35 U.S.C. section 119(e) of the co-pending U.S. Provisional Patent Application Ser. No. 61/313,009 filed Mar. 11, 2010, entitled “LEADFRAME MULTI TERMINAL IC PACKAGE,” which are both hereby incorporated by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is related to the field of semiconductor device manufacturing. More specifically, the present invention relates to leadframes for stabilizing wire bond placement and avoiding bent leads. 
       BACKGROUND 
       [0003]    In general, multiterminal integrated circuit (IC) packages are formed from a copper substrate.  FIG. 1  shows such a prior art process. A bare copper substrate  100  is partially etched to pattern the contact pads  103  and the die attach pad  102 . The partial etching is able to be done in any number of ways known by the person of ordinary skill. The substrate  100  is seen in cross section. The contact pads  103  are in several rows surrounding the die attach pad  102 . Each row of contact pads is still an integral piece of the leadframe  100 . For each row of contacts, there is one section of half etched copper in an inside perimeter and an outside perimeter. In the example provided, there are two rows of contact pads  103 . There is a first etched portion  103 A, a second etched portion  103 B, and a third etched portion  103 C. These portions must be removed before the semiconductor device can be put to use since all contacts pads  103  are electrically coupled before removal of the portions  103 A,  103 B, and  103 C. A semiconductor die  106  is placed on the die attach pad  102 . Then, wire bonds  105  are selectively mounted from the semiconductor die  106  to the contact pads  103  and die attach pad  102 . Also, all of the substrate  100  but the portions  103 A,  103 B and  103 C are coated on a bottom side with an etch resist material. The substrate  100 , semiconductor device  106  and wire bonds  105  are encased in a mold compound  107 . Then, the assembly is submerged in an etching solution until the portions  103 A,  103 B, and  103 C are sacrificed, electrically isolating the contacts  103 . It should be noted that two partial etching steps were required in this prior art: once to form the partial etched areas  103 A,  103 B, and  103 C and once to sacrifice the substrate  100 . In this example given, the contact pads, die attach pad and other features are substantially planar on all surfaces. If any features, such as stand offs, or the like are to be incorporated, further half etching steps are required. A staggered or stepped form factor will require an etching step for every step. As a result, thicker copper substrates are necessary. Furthermore, accuracy is sacrificed. For example, if a standoff is needed on one of the rows of contact pads  103 , they must first be partially etched into the locations where the contact pads  203  will be formed. Then, the portions  103 A,  103 B, and  103 C must be partially etched deeper. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    In a first aspect of the invention, a semiconductor package comprises a die attach pad, a first set of contact pads surrounding the die attach pad, a groove at least partially circumscribing the first row of contact pads, and a second set of contact pads surrounding the groove. Generally, the semiconductor package further comprises at least one semiconductor die mounted on the die attach pad and a plurality of bondwires for electrically coupling the at least one semiconductor die to at least one contact pad. Preferably, the bottom surface of the semiconductor package is substantially planar except for the groove. The groove defines a channel that substantially encompasses the first row of contact pads. The first set of contact pads generally surrounds the die attach pad and is bounded by the groove. In some embodiments, the second set of contact pads surrounds the groove and is bounded by the perimeter of the semiconductor package. In some embodiments, the bottom surface of the die attach pad and bottom surfaces of the contact pads define the substantially planar bottom surface of the package. The first and second set of contact pads are able to be offset from the groove or exposed by the groove. In some embodiments, the groove comprises an epoxy filler. 
         [0005]    In some embodiments, the package further comprises a third set of contact pads between the first set of contact pads and the die attach pad. The third set of contact pads surrounds the die attach pad and is bounded by the first set of contact pads, the groove, and the second set of contact pads. Also, the package is able to have a fourth set of contact pads around the second set of contact pads. The fourth set of contact pads surrounds the die attach pad, the first set of contact pads, the groove, and the second set of contact pads and is bounded by the perimeter of the semiconductor package. 
         [0006]    In another aspect of the invention, a method of making a semiconductor package comprises etching a through pattern in a metal substrate, thereby forming a die attach pad, a first set of contact pads surrounding the die attach pad and a second set of contact pads surrounding the first set of contact pads, wherein the first and the second set of contact pads are coupled with a support member. Then at least one semiconductor die is mounted on the die attach pad and bondwires electrically couple the at least one semiconductor die to at least one contact pad. Then, the semiconductor die, bondwires and contact pads are at least partially encased in a mold compound while leaving one surface of the metal substrate exposed. After, the support member is etched away, thereby electrically isolating the first and second set of contact pads with respect to each other. The groove formed by etching away the support member is able to be filled with an epoxy. In some embodiments, etching a through pattern in a metal substrate further comprises forming a third set of contact pads, the third set of contact pads surrounding the die attach pad. The third set of contact pads is able to be bounded by the first set of contact pads, the groove, the second set of contact pads and the perimeter of the package. 
         [0007]    In another aspect of the device, a leadframe for supporting a semiconductor device, comprises a die attach pad a first set of contact pads surrounding the die attach pad, a support member at least partially circumscribing the first set of contact pads, a second set of contact pads around he support member, and an outer perimeter. At least one of the first set of contacts and the second set of contacts is anchored to the support member. Preferably, the bottom surface of the leadframe is coated with an etch resist material except for the support member to allow for the support member to be etched away thereby electrically isolating the sets of contacts with respect to each other. In some embodiments, the leadframe further comprises a third set of contacts around the die attach pad. The third set of contacts is able to be anchored to the die attach pad or the support member. The third set of contacts is bounded by the first set of contacts, the support member, and the perimeter. The leadframe is also able to comprise a fourth set of contacts around the second set of contacts. The fourth set of contacts surrounds the first, second, and third set of contacts as well as the support member. The fourth set of contacts are able to be anchored to the support member or the perimeter. As a result, when the support member is etched away, any sets of contacts anchored to it are electrically isolated with respect to each other. In embodiments where the fourth set of contacts is anchored to the perimeter, the fourth set of contacts is electrically isolated during singulation. 
         [0008]    Advantageously, the semiconductor package described above, utilizing the method and leadframe disclosed is able to be manufactured in fewer etching steps than what is disclosed by the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The novel features of the invention are set forth in the appended claims. However, for purpose of explanation, several embodiments of the invention are set forth in the following figures. 
           [0010]      FIG. 1  is a prior art leadframe. 
           [0011]      FIG. 2  is a leadframe per an embodiment of this invention shown from a front and back view. 
           [0012]      FIG. 3A  shows the leadframe of  FIG. 2  having die and wirebonds mounted thereon. 
           [0013]      FIG. 3B  shows the leadframe of  FIG. 2  encapsulated in molding compound. 
           [0014]      FIG. 3C  shows the leadframe of  FIG. 2  in an etching process. 
           [0015]      FIG. 3D  shows the leadframe of  FIG. 2  in an epoxy process. 
           [0016]      FIG. 3E  shows the leadframe of  FIG. 2  in a singulation process. 
           [0017]      FIG. 4A  shows semiconductor packages per embodiments of this invention. 
           [0018]      FIG. 4B  shows semiconductor packages per embodiments of this invention. 
           [0019]      FIG. 5A  shows an embodiment of the leadframe of  FIG. 2  before and after an etching process. 
           [0020]      FIG. 5B  shows an embodiment of the leadframe of  FIG. 2  before and after an etching process. 
           [0021]      FIG. 6A  shows a flowchart of method steps per an embodiment of the invention. 
           [0022]      FIG. 6B  shows a flowchart of method steps per an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    In the following description, numerous details are set forth for purposes of explanation. However, one of ordinary skill in the art will realize that the invention can be practiced without the use of these specific details. Thus, the present invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and features described herein or with equivalent alternatives. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. The person of ordinary skill having the benefit of this disclosure will readily appreciate that elements from the several drawings are interchangeable between the embodiments shown and described. 
         [0024]    In general, the invention described below effectuates the manufacture of high density, multi row leadframes and semiconductor packages in fewer process steps; specifically using fewer etching steps. It is well known that the semiconductor industry is extremely cost driven and fewer processing steps leads to higher throughput and lower cost.  FIG. 2  shows a leadframe  200  per one embodiment of this invention from a top view and a bottom view. In this exemplary embodiment, the leadframe  200  is a matrix of four individual units  200 A,  200 B,  200 C, and  200 D supported by a frame  201 . The top view shows the top surface. The top surface is the surface on which at least one semiconductor die (not shown) will eventually be mounted. The bottom view shows the bottom surface. The bottom surface will eventually be the surface mounted to an end application such as a circuit board. 
         [0025]    Preferably, the leadframe  200  has been through-etched to reveal several structures thereon, and leave behind a completely etched away portion  208 . Each individual unit  200 A,  200 B,  200 C, and  200 D comprises a die attach pad  206 . The die attach pad  206  is configured to support an eventual semiconductor die that will be mounted thereto. On a top surface, the die attach pad  206  is exposed copper. On a bottom side, the die attach pad is preferably coated with an etch resist material. Surrounding each die attach pad  206  is a first set of contact pads  202 . The first set of contact pads  202  are preferably anchored to a support member  209  that at least partially circumscribes the die attach pad  206 . The support member  209  is anchored to the die attach pad  206  by cross members  209 A- 209 D. In some embodiments, the cross members  209 A- 209 D are substantially co-planar with the support member  209 . Alternatively, the cross members  209 A- 209 D are raised with respect to the support member  209 . Preferably, the first set of contact pads  202  are anchored to the support member  209 . The first set of contact pads  202  surrounds the die attach pad  206  and is bounded by the support member  209 . The leadframe  200  further comprises a second set of contact pads  203 . The second set of contact pads  203  is preferably anchored to the support member  209 . The second set of contact pads  203  surrounds the support member  209  and is bounded by the frame  201  or another individual unit  200 A- 200 D. Preferably, the second set of contact pads  203  is anchored to the support member  209 . 
         [0026]    In some embodiments, the leadframe  200  further comprises a third set of contacts  204 . The third set of contacts  204  surrounds the die attach pad  206  and is bounded by the first set of contact pads  202 , support member  209 , second set of contacts  203  and the frame  201 . The third set of contacts  204  is able to be anchored to the support member  209 . In order to offset the third set of contacts  204  from the first set of contacts  202  while maintaining their position between the die attach pad  206  and the first set of contacts  202 , the third set of contacts  204  are anchored to the support member  209  by anchor bars  204 A. Preferably, the anchor bars  204 A are elevated with respect to the support member  209 . Advantageously, in a later processing step when the support member  209  is sacrificed, the anchor bars  204 A will be elevated with respect to the bottom surface of a resulting semiconductor package. 
         [0027]    In some embodiments, the leadframe  200  further comprises a fourth set of contacts  205 . The fourth set of contacts  205  surrounds the die attach pad  206 , first set of contacts  202 , third set of contacts  204 , the support member  209 , and the second set of contact  203 . The fourth set of contacts  205  is bounded by the frame  201 . In the example shown in  FIG. 2 , the fourth set of contacts  205  is anchored to the frame  201 . Alternatively, the fourth set of contacts  205  is able to be anchored to the support member  209  via anchor bars (not shown). On the bottom side, the leadframe  200  is substantially coated in an etch resist material as indicated by the striped area. Preferably, the support member  209  is not coated with an etch resist material. Advantageously, during a later etch process, the support member  209  will be sacrificed. Upon etching away of the support member  209 , the sets of contacts  202 - 205  that are anchored to the support member  209  are electrically isolated from one another. The individual units  200 A,  200 B,  200 C, and  200 D have square arrays of contact pads, wherein every side of each individual unit has the same number of contact pads. Alternatively, each side can have a different number of contact pads. In general, each side can have the same or different number of contact pads. However, rectangular individual units  200 A,  200 B,  200 C, and  200 D are also able to be realized. 
         [0028]      FIG. 3A  shows the leadframe  200  of  FIG. 2  in later processing steps for forming a semiconductor package. The leadframe  200  has semiconductor die  215  mounted on the die attach pads  206 . In the example shown, there is one semiconductor die  215  per die attach pad  206 . As applications require, multiple semiconductor die may be mounted on the die attach pads  206 . The semiconductor die  215  are electrically coupled to the multiple contact pads of the several sets described so far by bondwires  217 . In some embodiments, the bondwires  217  are gold.  FIG. 3B  shows the leadframe  200  encased in a mold compound  230  from a top view and a bottom view. Preferably, the mold compound  230  encases the semiconductor die  215  and bondwires  217  of  FIG. 3A . In the exploded box of the bottom view, the etched away portion  208  first shown in  FIG. 2  is depicted filled in with mold compound  230 . The first set of contacts  202  and second set of contacts  203  are adjacent to the support member  209 . The support member  209  is not coated in a etch resistant material indicated by the shaded regions. The third set of contacts  204  and fourth set of contacts  205  are exposed in order to make contact with a circuit board in a final application. The anchor bars  204 A of  FIG. 2  that anchored the third set of contacts  204  to the support member  209  are encased within the mold compound  230 . In embodiments where the fourth set of contacts  205  are anchored to the support member  209 , the anchor bars used to anchor them are also embedded within the mold compound as well. Preferably, the bottom surfaces of the die attach pad  206 , the mold compound  230  that has filled the etched away portion  208 , and the first, second, third and fourth set of contacts  202 - 205  define a substantially planar surface. Alternatively, the mold compound  230  filled into the etched away portion  208  is able to be recessed with respect to a substantially planar portion defined by the bottom surfaces of the several sets of contacts  202 - 205  and die attach pad  206 . 
         [0029]      FIG. 3C  shows the leadframe  200  before and after being dipped in an etching solution  241  in a vat  242 . As described above, the bottom surfaces of the leadframe  200  are substantially covered in an etch resist depicted by the shaded regions, except for the support member  209 . On the top surface, any previously exposed copper is encased in the mold compound  230  in  FIG. 3B  and is therefore etch-resistant. Preferably, the frame  201  shown in  FIG. 2  is coated in an etch resist on both the top and bottom sides in order to preserve the perimeter for convenience in later processing steps. As a result of dipping the leadframe in the etching solution  241 , the support member  209  is sacrificed. Advantageously, the several sets of contacts  202 - 205  are electrically isolated with respect to each other. When the support member  209  is etched away, what is left behind is a groove  240  that substantially circumscribes at least the first row of contact pads  202  on each of the individual units  200 A- 200 D.  FIG. 3D  shows an optional step of filling the groove  240  with an epoxy  250 . The epoxy  250  is able to be injected into the groove  240  by a nozzle  255 . Alternatively, the epoxy  250  is able to be pressed into the groove  240  by a mold. In other embodiments, a second molding step may be used to fill the groove with mold compound.  FIG. 3E  shows the leadframe  200  being singulated into individual semiconductor packages  200 A- 200 D. Preferably, a saw  260  cuts along the lines  260 A and  260 B to singulate the devices. The saw lines  260 C- 260 F separate the frame  201  from the devices  200 A- 200 D. In embodiments wherein the fourth set of contact pads  205  in  FIG. 2  are anchored to the frame  201 , the singulation step also serves to electrically isolate the contact pads in the fourth set of contact pads  205  with respect to each other. 
         [0030]      FIGS. 4A and 4B  show exemplary configurations for the first set of contacts  202  and the second set of contacts  203  with respect to the groove  240  that was formed when the support member  209  was etched away as shown in  FIG. 3C .  FIG. 4A  shows the first row of contacts  202  and second row of contacts  203  exposed by the groove  240  and an embodiment wherein the groove  240  has been filled in with epoxy  250 . In the embodiment wherein the groove is exposed, the portion of the anchor bar  204 A that has not been sacrificed by the etching process can be seen within the groove  240 . In embodiments wherein the optional epoxy filler  250  has been filled into the groove  240 , the first and second set of contacts  202  and  203  are adjacent to the epoxy filler  250 .  FIG. 4B  shows an alternative embodiment wherein the first set of contacts  202  and second set of contacts  203  are offset from the groove  240 . In such embodiments, the first set of contacts  202  and second set of contacts  203  are anchored to the support member  209  of  FIG. 2  by standoff members (not shown). Although this exemplary embodiment shows both the first set  202  and second set  203  of contacts offset from the groove  240 , any combination of the sets of contacts are able to be offset from the groove  240 . 
         [0031]      FIGS. 5A and 5B  show exemplary arrangements of the several rows of contact pads  202 - 205  and the support member according to various embodiments of the present invention.  FIG. 5A  shows the leadframe  200  on a top and a bottom side both before and after removal of the support member  209  and frame  201 . In this depiction, the mold compound, wirebonds and semiconductor die are not shown for the sake of clarity. However, it will be understood by the person of ordinary skill having the benefit of this disclosure that the “after” representations would include those elements. Before etching and singulation, the first set of contacts  202 , second set of contacts  203  and third set of contacts  204  are anchored to the support member  209 . The third set of contacts  204  is anchored to the support member  209  by anchor bars  204 A. In this embodiment, the anchor bars  204 A are elevated with respect to the support member  209 . Advantageously, when the support member  209  is removed in a later processing step, the anchor bars  204 A are encased in a mold compound and therefore not exposed to the exterior of the resultant semiconductor package. The first row of contacts  202  is anchored to the support member  209  by standoffs  202 A. In the example of  FIG. 5A , the top surfaces of the contacts pads in the first set  202  are offset from the support member  209 . Similarly, the second set of contact pads  203  are anchored to the support member  209  standoffs  203 A. Alternatively, the set of contacts  202  or  203  are able to be anchored directly to the support member  209 . In the embodiment of  FIG. 5A , the fourth set of contacts  205  is anchored to the frame  201 . The fourth set of contacts  205  is flush on a top and bottom surface with the frame  201 . Alternatively, the fourth set of contacts  205  is able to be offset from the frame  201  by standoffs. In such embodiments, the fourth set of contacts  205  will not be exposed to a side surface of the resultant semiconductor package. In the embodiment shown in  FIG. 5A , when the frame  201  is sawn away during singulation, the fourth set of contacts  205  will be exposed to a side of the resultant semiconductor package. In such embodiments, an end user of the semiconductor package will be able to probe the individual contact pads in the fourth set of contact pads  205  even after the semiconductor package has been mounted to an end application, such as a circuit board. In the embodiment shown in  FIG. 5B , the fourth set of contacts  205  is anchored to the frame  201  and to the support member  209 . The fourth set of contacts  205  is anchored to the support member via anchor bars  205 A. Alternatively, the fourth set of contacts is able to be anchored only to the support member  209 . The anchor bars  205 A are preferably elevated with respect to the support member  209 . Advantageously, the anchor bars  205 A will be encased in mold compound and will not be exposed to any outer surface of the resultant semiconductor package. Furthermore, the cross members  209 A are also elevated with respect to the support member  209 . Persons of ordinary skill with the benefit of this disclosure will appreciate that forming the various elements such as the offset standoffs  202 A and  203 A, the cross member  209 A, or any other element having faceted characteristics is able to be achieved during a partial etching process. 
         [0032]      FIGS. 6A and 6B  are a flowchart showing the process steps for making the leadframe and the semiconductor device described above. Each step is shown in a top view and a side cutaway view for clarity. In a step  600 , a substantially planar copper leadframe  200  is provided. In a step  610 , patterns  615  are partially etched on a top and a bottom side of the leadframe  200 . These patterns are able to later form the raised anchor bars  204 A and  205 A, the standoffs  202 A and  203 A, the elevated cross member  209 A- 209 D, or any other structure discussed above or advantageous to the semiconductor package. In a step  620 , a pattern is through etched thereby forming the first set of contacts  202 , the second set of contacts  203 , the support member  209 , die attach pad  206 , and cross members  209 A- 209 D. In the example of  FIG. 6 , only two sets of contact pads are formed. However, as discussed above, any number of contact pads may be added. Thereafter, a die  215  is mounted on the die attach pad  206  and wirebonds electrically couple the semiconductor die  215  to the several contact pads. In a step  630 , the leadframe  200  is encased in a mold compound  230 . In a step  640 , the support member is etched away, leaving a groove  240 . Advantageously, the first set  202  and second set  203  of contact pads are electrically isolated with respect to each other. Optionally, the groove  240  is able to be filled with epoxy or mold compound. Finally, in a step  650 , the device is singulated, forming a complete semiconductor package. 
         [0033]    While the invention has been described with reference to numerous specific details, one of ordinary skill in the art will recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention. Thus, one of ordinary skill in the art will understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.