Patent Publication Number: US-2021166998-A1

Title: Semiconductor package having a lead frame and a clip frame

Description:
BACKGROUND 
     Power semiconductor packages include a power semiconductor die embedded in a mold compound. Electrical connections within the mold compound are formed between terminals of the power semiconductor die and leads of the package. The leads are part of a lead frame to which the power semiconductor die is attached. Some types of power semiconductor packages use a metal clip to connect the source terminal at the top side of the power semiconductor die to a lead post of the lead frame. The clip assembly typically includes two parts: the metal clip itself and the lead post. Both parts are typically soldered together, which requires a landing zone for attaching the clip on the lead frame. The clip landing zone consumes space on the lead frame, since attachment of the clip to the lead frame is done by soldering, diffusion soldering or a similar process. The contact area required for the clip cannot be used for additional die area in the package. Also, the clip attachment process is done in a serial manner and therefore is slow and costly. Furthermore, the gate terminal of the power semiconductor is typically contacted by a bond wire which requires an additional process step with extra equipment investment and has different requirements regarding surfaces on the die and the lead frame. 
     Thus, there is a need for an improved contact structure for power semiconductor packages. 
     SUMMARY 
     According to an embodiment of a method of manufacturing a molded semiconductor package, the method comprises: providing a lead frame comprising a die pad and one or more first leads monolithically formed with the die pad and extending outward from the die pad in a first direction, the die pad and the one or more first leads being attached to a periphery of the lead frame; attaching a first side of a semiconductor die to the die pad; aligning a clip frame with the lead frame so that a first pre-bent metal clip of the clip frame is vertically aligned with a power terminal at a second side of the semiconductor die opposite the first side, the clip frame further comprising one or more second leads monolithically formed with the first pre-bent metal clip and extending outward from the first pre-bent metal clip in a second direction different than the first direction and attached to a periphery of the clip frame; attaching the first pre-bent metal clip to the power terminal at the second side of the semiconductor die; embedding the semiconductor die in a mold compound so that the one or more first leads and the one or more second protrude from the mold compound in generally planar directions and do not vertically overlap with one another; and separating the one or more first leads from the periphery of the lead frame and the one or more second leads from the periphery of the clip frame outside the mold compound. 
     Separating the one or more first leads from the periphery of the lead frame and the one or more second leads from the periphery of the clip frame outside the mold compound may comprise stamping the one or more first leads and the one or more second leads outside the mold compound, or cutting the one or more first leads and the one or more second leads outside the mold compound. 
     Separately or in combination, the method may further comprise: attaching a second pre-bent metal clip of the clip frame to a control terminal at the second side of the semiconductor die, wherein the clip frame further comprises a third lead extending outward from the second pre-bent metal clip and attached to the periphery of the clip frame, wherein after embedding the semiconductor die in the mold compound, the third lead protrudes from the mold and does not vertically overlap with the one or more first leads. 
     Separately or in combination, the method may further comprise: separating the third lead from the periphery of the clip frame outside the mold compound via a same stamping process used to separate the one or more first leads from the periphery of the lead frame and the one or more second leads from the periphery of the clip frame. 
     Separately or in combination, the one or more first leads may protrude from a first side face of the mold compound after separation from the periphery of the lead frame and the one or more second leads may protrude from a second side face of the mold compound different than the first side face after separation from the periphery of the clip frame. 
     Separately or in combination, the method may further comprise: plating the part of the one or more first leads which protrudes from the first side face of the mold compound and the part of the one or more second leads which protrudes from the second side face of the mold compound, to form wettable lead surfaces at different side faces of the mold compound. 
     Separately or in combination, the lead frame may be unbent. 
     Separately or in combination, the clip frame may comprise alignment features to aid in the aligning of the clip frame with the lead frame. 
     Separately or in combination, the clip frame may be stacked on top of the lead frame in an area of a mold runner used during the embedding of the semiconductor die in the mold compound. 
     Separately or in combination, the method may further comprise: pressing the clip frame against the lead frame to provide tight sealing during the embedding of the semiconductor die in the mold compound. 
     According to an embodiment of a molded semiconductor package, the molded semiconductor package may comprise: a lead frame comprising a die pad and one or more first leads monolithically formed with the die pad and extending outward from the die pad in a first direction; a semiconductor die attached to the die pad at a first side of the semiconductor die; a clip frame comprising a first metal clip attached to a power terminal at a second side of the semiconductor die opposite the first side, and one or more second leads monolithically formed with the first metal clip and extending outward from the first metal clip in a second direction different than the first direction; and a mold compound embedding the semiconductor die, wherein the one or more first leads and the one or more second leads are exposed at different sides of the mold compound and do not vertically overlap with one another, wherein within the mold compound, the first metal clip transitions from a first level above the power terminal at the second side of the semiconductor die to a second level in a same plane as the one or more first leads and the one or more second leads. 
     The clip frame may further comprise a second metal clip attached to a control terminal at the second side of the semiconductor die and a third lead extending outward from the second metal clip, and the third lead may be exposed at a side of the mold compound and may not vertically overlap with the one or more first leads. 
     Separately or in combination, the one or more first leads may protrude from a first side face of the mold compound and the one or more second leads may protrude from a second side face of the mold compound different than the first side face. 
     Separately or in combination, the part of the one or more first leads which protrudes from the first side face of the mold compound and the part of the one or more second leads which protrudes from the second side face of the mold compound may be at least partially plated to form wettable lead surfaces at different side faces of the mold compound. 
     Separately or in combination, the first metal clip maybe bent in at least two different places within the mold compound. 
     Separately or in combination, the semiconductor die may be a power transistor die, a power terminal at the first side of the power semiconductor die may be a drain or collector terminal, the power terminal at the second side of the power semiconductor die may be a source or emitter terminal, and the power semiconductor die maybe attached to the die pad in a drain-down or collector-down configuration. 
     Separately or in combination, the semiconductor die may be a power transistor die, a power terminal at the first side of the power semiconductor die may be a source or emitter terminal, the power terminal at the second side of the power semiconductor die may be a drain or collector terminal, and the power semiconductor die may be attached to the die pad in a source-down or emitter-down configuration. 
     Separately or in combination, the lead frame may comprise an additional lead attached to a control terminal at the first side of the power semiconductor die and the additional lead may be exposed at the same side of the mold compound as the one or more first leads. 
     According to an embodiment of a method of manufacturing molded semiconductor packages, the method comprises: providing a lead frame panel which includes a plurality of unit lead frames connected to one another, each unit lead frame comprising a die pad and one or more first leads monolithically formed with the die pad and extending outward from the die pad in a first direction, the die pad and the one or more first leads being attached to a periphery of the unit lead frame; attaching a separate semiconductor die at a first side to each of the die pads, each semiconductor die comprising a power terminal at a second side opposite the first side; aligning a clip frame panel with the lead frame panel, the clip frame panel including a plurality of unit clip frames connected to one another, each unit clip frame comprising a first pre-bent metal clip vertically aligned with a corresponding power terminal at the second side of one of the semiconductor dies, and one or more second leads monolithically formed with the first pre-bent metal clip and extending outward from the first pre-bent metal clip in a second direction different than the first direction and attached to a periphery of the unit clip frame; attaching each first pre-bent metal clip to the power terminal at the second side of the corresponding semiconductor die; embedding the semiconductor dies in a mold compound so that each one or more first leads and each one or more second leads protrude from the mold compound in generally planar directions and do not vertically overlap with one another; and separating each one or more first leads from the periphery of the corresponding unit lead frame and each one or more second leads from the periphery of the corresponding unit clip frame outside the mold compound. 
     Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. The features of the various illustrated embodiments can be combined unless they exclude each other. Embodiments are depicted in the drawings and are detailed in the description which follows. 
         FIGS. 1A through 1C  illustrate an embodiment of a molded semiconductor package having a lead frame to which a semiconductor die is attached and a separate clip frame for contacting one or more terminals at the top side of the semiconductor die.  FIG. 1A  shows the semiconductor package after molding, but prior to singulation.  FIG. 1B  shows the semiconductor package after die attach, but prior to clip frame placement.  FIG. 1C  shows the semiconductor package after clip frame placement, but prior to molding. 
         FIG. 2  illustrates an embodiment of a method of manufacturing molded semiconductor packages each having a lead frame to which a semiconductor die is attached and a separate clip frame for contacting one or more terminals at the top side of the semiconductor die. 
         FIGS. 3A through 3D  illustrate a lead frame panel and a clip frame panel during different stages of the manufacturing method illustrated in  FIG. 2 , with  FIGS. 3A and 3C  being enlarged partial views. 
         FIGS. 4A and 4B  illustrate respective partial views of the clip frame panel, according to further embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments described herein provide a molded semiconductor package that includes a lead frame to which a semiconductor die is attached and a separate clip frame for contacting one or more terminals at the top side of the semiconductor die. Each clip used to contact a terminal at the top side of the semiconductor die is disposed in a frame separate from the lead frame to which the semiconductor die is attached. Hence, the lead frame contains the leads and contacts for some but not all of the die terminals. The separate clip frame provides the leads and contacts for the remaining die terminal(s). 
       FIGS. 1A through 1C  illustrate an embodiment of a molded semiconductor package  100  prior to singulation, i.e., physical separation from other molded semiconductor packages formed at the same time.  FIG. 1A  shows the semiconductor package  100  after molding, but prior to singulation.  FIG. 1B  shows the semiconductor package  100  after die attach, but prior to clip frame placement.  FIG. 1C  shows the semiconductor package  100  after clip frame placement, but prior to molding. 
     The molded semiconductor package  100  includes a lead frame  102  and a separate clip frame  104 . The lead frame  102  includes a die pad  106  and one or more first leads  108  monolithically formed with the die pad  106  and extending outward from the die pad  106  in a first direction x 1 . That is, the die pad  106  and the one or more first leads  108  are formed or composed of the same material without joints and are at the same potential (e.g. power, ground, etc.). In some cases, only a single first lead  108  may be monolithically formed with the die pad  106  and extend outward from the die pad  106  in the first direction x 1 . For example, the lead frame  102  may be cut along the dashed line labelled A 1  or along the dashed line labelled A 2  in  FIG. 1B . In other cases, more than one first lead  108  may be monolithically formed with the die pad  106  and extend outward from the die pad  106  in the first direction x 1 . For example, the lead frame  102  may be cut along the dashed line labelled A 3  in  FIG. 1B . Hence, the use of the term ‘first lead(s)’ herein to indicate that one or more first leads  108  may be monolithically formed with the die pad  106  and extend outward from the die pad  106  in a first direction x 1 . 
     In each case, the die pad  106  is the region of the lead frame  102  to which one or more semiconductor dies  110  are attached. At least one semiconductor die  110  is attached to the die pad  106  of the lead frame  102 , and each semiconductor die  110  attached to the die pad  106  is embedded in a plastic mold compound  112  such as an epoxy mold compound. 
     The semiconductor die  110  attached to the lead frame  102  may be a vertical device in that the main current path is between the top and bottom sides of the die  110 . In this case, a power terminal (out of view) of the semiconductor die  110  is attached to the die pad  106  of the lead frame  102 . The semiconductor die  110  may instead be a lateral device in that the main current path is along the top side of the die  110 . In this case, all power terminals of the semiconductor die  110  are disposed at the top side of the die  110  which faces away from the die pad  106  of the lead frame  102 . More than one semiconductor die  110  may be attached to the lead frame  102  and/or the molded semiconductor package  100  may include more than one lead frame  102  with one or more semiconductor dies  110  attached to each lead frame  102 . 
     The separate clip frame  104  of the molded semiconductor package  100  includes at least a first metal clip  114  and one or more second leads  116  monolithically formed with the first metal clip  114  and extending outward from the first metal clip  114  in a second direction x 2  different than the first direction x 1 . In some cases, only a single second lead  116  may be monolithically formed with the first metal clip  114  and extend outward from the first metal clip  114  in the second direction x 2 . For example, the clip frame  104  may be cut along the dashed line labelled B 1  in  FIG. 1C . In other cases, more than one second lead  116  may be monolithically formed with the first metal clip  114  and extend outward from the first metal clip  114  in the second direction x 2 . For example, the clip frame  104  may be cut along the dashed line labelled B 2  in  FIG. 1C . Hence, the use of the term ‘second lead(s)’ herein to indicate that one or more second leads  116  may be monolithically formed with the first metal clip  114  of the clip frame  104  and extend outward from the first metal clip  114  in a second direction x 2 . 
     In each case, the different directions x 1 , x 2  in which the first and second leads  108 ,  116  extend depends on the type of molded semiconductor package  100 . For example, in the case of SSO8 (shrink small-outline package), TSOP (thin small-outline package), TSON (thin small outline non-leaded), TOLL (transistor outline-leadless), or other type of dual row flat package, the first lead(s)  108  of the lead frame  102  and the second lead(s)  116  of the clip frame  104  extend in opposite directions x 1 , x 2  and are disposed at opposite sides of the molded semiconductor package  100 . In the case of QFP (quad flat package), QFN (quad flat no-leads package), or other type of quad row flat package, the first lead(s)  108  of the lead frame  102  and the second lead(s)  116  of the clip frame  104  extend in different but not necessarily opposite directions x 1 , x 2  and are disposed at different but not necessarily opposite sides of the molded semiconductor package  100 . In the case of multiple first leads  108  and/or multiple second leads  118 , all leads  108 / 116  of the same kind (e.g. power, ground, etc.) need not necessarily extend in the same direction. For example, in the case of a QFN package, one first lead  108  may be disposed on each side on the lead frame  102  and all the second leads  116  may be disposed on the clip frame  104 , e.g., also on four sides. Even in this case, none of the first leads  108  of the lead frame  102  would vertically overlap with any of the second leads  116  of the clip frame  104 . 
     The molded semiconductor package  100  illustrated in  FIGS. 1A through 1C  is shown as a dual row leadless flat package. In general, the molded semiconductor package embodiments described herein may be implemented in any type of dual row or quad row flat package. For some types of packages, part of each first lead  108  of the lead frame  102  and part of each second lead  116  of the clip frame  104  are not covered by the mold compound  112 . The uncovered part of the leads  108 ,  116  may be flush, recessed, or protrude slightly from the mold compound  112 . For other types of packages, the first lead(s)  108  of the lead frame  102  and the second lead(s)  116  of the clip frame  104  protrude outward from different but not necessarily opposite side faces  120  of the mold compound  112 . 
     In each case, the first lead(s)  108  of the lead frame  102  and the second lead(s)  116  of the clip frame  104  are exposed at different side faces  120  of the mold compound  112  and do not vertically overlap with one another.  FIG. 1A  shows each first lead  108  of the lead frame  102  and each second lead  116  of the clip frame  106  exposed at different side faces  120  of the mold compound  120 .  FIG. 1C  shows each first lead  108  of the lead frame  102  and each second lead  116  of the clip frame  104  not vertically overlapping with one another. One or more tie bars  122  may be provided to further stabilize the die pad  106  during the die attach and molding processes. The tie bars  122  are severed during the singulation process, as are each first lead  108  of the lead frame  102  and each second lead  116  of the clip frame  104 , to physically separate the molded semiconductor package  100  from other molded semiconductor packages manufactured at the same time. 
     Within the mold compound  112 , the metal clip  114  of the clip frame  104  transitions from a first level above a power terminal  124  at the top side of the semiconductor die  110  to a second level in the same plane as the first lead(s)  108  of the lead frame  102  and the second lead(s)  116  of the clip frame  104 . That is, the metal clip  114  of the clip frame  104  may be pre-bent in a way such that the clip  114  can be attached, e.g. by soldering, to the power terminal  124  at the top side of the semiconductor die  110  and such that each clip frame lead  116  monolithically formed with the metal clip  114  and extending outward from the clip  114  may reach the same level as the first lead(s)  108  of the lead frame  102 . In one embodiment, the metal clip  114  of the clip frame  104  is bent in at least two different places  126 ,  128  within the mold compound  112  to provide the transition from the first level to the second level. The lead frame  102  may be unbent, allowing for easy application of die attach material (out of view) such as solder paste, sinter paste, glue, etc. to the die pad  106  of the lead frame  102  using a printing process such as stencil or screen printing or a dispensing or jetting process, etc. Even if the lead frame  102  is unbent, the lead frame  102  may still include coined areas, dimples, grooves, etc. 
     By using a separate clip frame  104  to implement some of the package leads, the size of the die pad  106  to which the semiconductor die  110  is attached can be increased, e.g., by approximately 20% or more, since the metal clip  116  is not attached to a separate lead post of the lead frame  102 . Instead, each lead  116  provided by the clip frame  104  is monolithically formed with the metal clip  116  and terminates at the same level as the first lead(s)  108  of the lead frame  102 . Hence, no separate lead post is needed to accommodate the metal clip  116 . By using the clip frame  104  described herein, the area allocated for contacting a conventional metal clip to a separate lead post may instead be used to accommodate a larger semiconductor die without increasing the overall size of the molded semiconductor package  100 . 
     In one embodiment, the semiconductor die  110  is a vertical power transistor die such as a power MOSFET (metal-oxide-semiconductor field effect transistor) die, IGBT (insulated gate bipolar transistor) die, etc. and a power terminal (out of view) at the bottom side of the power semiconductor die  110  is a drain or collector terminal. According to this embodiment, the power terminal  124  at the top side of the power semiconductor die  110  is a source or emitter terminal and the power semiconductor die  110  is attached to the die pad  106  of the lead frame  102  in a drain-down configuration in the case of a MOSFET or in an collector-down configuration in the case of an IGBT. Further according to this embodiment, the control (gate) terminal  130  of the semiconductor die  110  is located at the top side of the die  110  with the source terminal  124 . The clip frame  104  may further include an additional metal clip  132  attached to the control terminal  130  at the top side of the semiconductor die  110  and an additional lead  134  extending outward from the additional metal clip  132  and monolithically formed with the additional metal clip  132 . The additional lead  134  of the clip frame  104  is exposed at a side of the mold compound  112  and does not vertically overlap with the first lead(s)  108  of the lead frame  102 . The additional metal clip  132  of the clip frame  104  may transition from the first level above the power terminal  124  at the top side of the semiconductor die  110  to the second level in the same plane as the lead(s)  108  of the lead frame  102  and the lead(s)  116 ,  134  of the clip frame  104 .  FIG. 1C  shows such the additional metal clip  132  provided as part of the clip frame  104 . 
     By providing the additional metal clip  132  as part of the clip frame  104 , a wire bond for contacting the control terminal  130  at the top side of the semiconductor die  110  is not required, since the clip frame  104  also provides the gate contact. However, a wire bond may be used for contacting the control terminal  130  at the top side of the semiconductor die  110  instead of the clip frame  104 . In this case, the bond wire connection would extend from the control terminal  130  at the top side of the semiconductor die  110  to one an additional lead (not shown) of the lead frame  102  or to one additional lead (also not shown) of the clip frame  104 . 
     In another embodiment, the semiconductor die  110  is a vertical power transistor die and the power terminal at the bottom side of the power semiconductor die  110  is a source or emitter terminal. According to this embodiment, the power terminal  124  at the top side of the power semiconductor die  110  is a drain or collector terminal and the die  110  is attached to the die pad  106  of the lead frame  120  in a source-down configuration in the case of a MOSFET or in an emitter-down configuration in the case of an IGBT. Further according to this embodiment, the control (gate) terminal  130  of the semiconductor die is located at the bottom side of the die  110  with the source or emitter terminal. The lead frame  102  may include an additional lead (not shown) attached to the control terminal  130  at the bottom side of the power semiconductor die  110 . The additional lead of the lead frame  102  may be exposed at the same side of the mold compound  112  as the first lead(s)  108  of the lead frame  102 . 
     In yet another embodiment, the semiconductor die  110  is a lateral power transistor die such as a HEMT (high-electron mobility transistor) die, a driver die for a power transistor die, a controller die, etc. According to this embodiment, all power terminals are disposed at the top side of the power semiconductor die  110  and a thermal connection is provided between the backside of the die  110  and the die pad  106  of the lead frame  102 . 
     The molded semiconductor package  100  can use different interconnect technologies for contacting the semiconductor die  110  and the metal clip  114  of the clip frame  104 . Separately or in combination, more than one semiconductor die can be embedded in the mold compound  112 , and the clip frame  104  may include more than one metal clip to accommodate the different dies. If more than one terminal is provided at the top side of the semiconductor die  110 , the clip frame  104  may be used as the exclusive interconnect for all terminals at the top side of each semiconductor die. Alternatively, the clip frame  104  may be used in conjunction with other interconnect types such as wire bonds, metal ribbons, etc. to form the connections to the terminals at the top side of each semiconductor die, if more than one terminal is provided at the top side of the semiconductor die  110 . Separately or in combination, the clip frame  104  may provide one or more interconnections between multiple dies in the case of more than one semiconductor die  110  being included in the same molded semiconductor package  100 . For example, the clip frame  104  may provide an interconnection between an IGBT power transistor die and a freewheeling diode die include in the same molded semiconductor package  100 . In another example, the clip frame  104  may connect two power transistor dies (e.g. MOSFETs) included in the same molded semiconductor package  100  in a half bridge configuration. One power transistor die may be mounted in a drain-down configuration and the other power transistor die in a source-down configuration. In another case, both power transistor dies may be mounted in the same drain-down or source-down configuration. In each case, the clip frame  104  can be used to connect two or more semiconductor dies included in the same molded semiconductor package  100  at the respective top sides of the dies. 
       FIG. 2  illustrates an embodiment of a method of manufacturing molded semiconductor packages each having a lead frame to which a semiconductor die is attached and a separate clip frame for contacting one or more terminals at the top side of the semiconductor die. The method may be used to manufacture the molded semiconductor package  100  illustrated in  FIGS. 1A through 1C  and described above.  FIGS. 3A through 3D  illustrate a lead frame panel  300  and a clip frame panel  302  during different stages of the manufacturing method illustrated in  FIG. 2 , with  FIGS. 3A and 3C  being enlarged partial views. 
     The manufacturing method illustrated in  FIG. 2  includes providing a lead frame panel  300  which includes a plurality of unit lead frames  304  connected to one another (Block  200 ). Each unit lead frame  304  includes a die pad  306  and one or more first leads  308  monolithically formed with the die pad  306  and extending outward from the die pad  306  in a first direction x 1 . The die pad  306  and the one or more first leads  308  are attached to a periphery  310  of the corresponding unit lead frame  304 . One or more tie bars  312  may be provided to further secure each respective die pad  306  to the periphery  310  of the corresponding unit lead frame  304 . The lead frame panel  300  may be formed from a metal sheet, and the lead frame features described herein may be formed using typical techniques such as stamping, punching, etching, etc. Exemplary materials for the lead frame panel  300  include metals such as copper, aluminum, nickel, iron, zinc, etc., and alloys thereof. 
     The manufacturing method illustrated in  FIG. 2  further includes attaching a separate semiconductor die  314  at the bottom side to each of the die pads  306  of the lead frame panel  300  (Block  210 ).  FIG. 3A  shows several lead frame units  304  of the lead frame panel  300  after the die attach process. Each semiconductor die  314  includes a power terminal  316  at the die top side. Depending on the type of semiconductor dies  314 , each die  314  may also have a power terminal (out of view) at the die bottom side. The lead frame panel  300  may be unbent, allowing for easy application of a die attach material such as solder paste, sinter paste, glue, etc. to the die pad  306  of each unit lead frame  304 . Even if the lead frame panel  300  is unbent, the lead frame panel  300  may still include coined areas, dimples, grooves, etc. The die attach material may be applied to the die pads  306  using a typical process such as a printing process (e.g. stencil, screen printing, etc.), a dispensing process, a jetting process, etc. Each semiconductor die  314  may also include, e.g., in the case of a power transistor die, a control (gate) terminal  318  at the die top side or at the die bottom side. 
     The manufacturing method illustrated in  FIG. 2  further includes vertically aligning a clip frame panel  302  with the lead frame panel  300  (Block  220 ).  FIG. 3B  shows the clip frame panel  302  vertically aligned with the lead frame panel  300 , and  FIG. 3C  shows an enlarged region of the overlapping structure. The clip frame panel  302  may be pressed against the lead frame panel  300  to provide tight sealing during molding of the semiconductor dies  314 . The unit clip frames  304  may be stacked on top of respective unit lead frames  320  of the clip frame panel  302  in an area of a mold runner  322  used during the molding process. In general, the clip frame panel  302  includes a plurality of unit clip frames  320  connected to one another. Each unit clip frame  320  includes a first pre-bent metal clip  324  vertically aligned with the corresponding power terminal  316  at the top side of one of the semiconductor dies  314 , and one or more second leads  326  monolithically formed with the first pre-bent metal clip  324 . The metal clips  324  are pre-bent before the package assembly process, and the metal clips  324  are formed in such a way that after assembly the clips  324  connect to the front side of the semiconductor dies  314  while each second lead  326  of the unit clip frames  320  is on the same level as each first leads  308  of the unit lead frames  304 . 
     The second lead(s)  326  of each unit clip frame  320  extend outward from the first pre-bent metal clip  324  in a second direction x 2  different than the extension direction x 1  for the first lead(s)  308  of the corresponding unit lead frame  304 , and are attached to a periphery  328  of the unit clip frame  320 . The first pre-bent metal clip  324  of the unit clip frames  320  may transition from a first level above the power terminal  316  at the top side of the corresponding semiconductor die  314  to a second level in the same plane as the first lead(s)  308  of the unit lead frames  304  and the second lead(s)  326  of the unit clip frames  320 , as previously described herein. For example, the first metal clip  324  of the unit clip frames  320  may be bent in at least two different places to provide the transition from the first level to the second level. 
     The manufacturing method illustrated in  FIG. 2  further includes attaching each first pre-bent metal clip  324  of the unit clip frames  320  to the power terminal  316  at the top side of the corresponding semiconductor die  314  (Block  230 ). A force/weight may be applied during the clip attach process to achieve the correct height of the unit clip frames  320 . The same or different type of die attach material used to attach the semiconductor dies  314  to the die pads  306  of the unit lead frames  304  may be used to attach each first pre-bent metal clip  324  of the unit clip frames  320  to the second power terminal  316  at the top side of the corresponding semiconductor die  314 . One or both joints, between the die pads  306  and dies  314  and/or between the metal clips  324  and the top-side power terminal  316  of the dies  314 , may be realized by, e.g., diffusion soldering so that no additional application of a joining material is done. Each first pre-bent metal clip  324  of the unit clip frames  320  instead may be attached to the power terminal  316  at the top side of the corresponding semiconductor die  314  before the semiconductor dies  314  are attached to the respective unit lead frames  304 . That is, Block  230  in  FIG. 2  may be performed before Block  210 . In general, a particular sequence of steps is not required unless explicitly stated. In either case, after the chip assembly process, soldering, sintering, etc. of the die attach regions may be finished by, e.g., reflow. 
     The unit clip frames  320  may each further include a second pre-bent metal clip  330  in the case of the semiconductor dies  314  having a control (gate) terminal  318  at the top side of the dies  314 . The second metal clip  330  of the unit clip frames  320  may be pre-bent in the same way as the first metal clip  324  of the unit clip frames  320 , so as to transition from the same first level above the power terminal  316  at the top side of the semiconductor dies  314  to the second level in the same plane as the first lead(s)  308  of the unit lead frames  304  and the second lead(s)  326  of the unit clip frames  320 . Each unit clip frame  320  may also include an additional lead  332  extending outward from the second pre-bent metal clip  330  and attached to the periphery  328  of the unit clip frame  320 . 
     In the case of the unit clip frames  320  including a second pre-bent clip  330  for contacting the control terminal  318  of the semiconductor dies  314 , the manufacturing method may further include attaching the second pre-bent metal clip  330  of each unit clip frame  320  to the control terminal  318  at the top side of the corresponding semiconductor die  314 , thereby providing a gate contact by a metal clip  330  instead of a wire bond. As previously described herein, a wire bond connection may be used instead or the control terminal  318  may be disposed at the bottom side of the semiconductor dies  314  instead of the top side, in which case each unit lead frame  304  includes an additional lead (not shown) for contacting the gate terminal  318  at the bottom side of the semiconductor dies  314 . 
     The manufacturing method illustrated in  FIG. 2  further includes embedding the semiconductor dies  314  in a mold compound  334  so that each first lead  308  of the unit lead frames  304  and each second lead  326  of the unit clip frames  320  protrude from the mold compound  334  in generally planar directions, e.g. x 1  and x 2  in  FIGS. 3A through 3D , and do not vertically overlap with one another (Block  240 ).  FIG. 3D  shows the semiconductor dies  314  embedded in the mold compound  334 . The unit clip frames  320  may be pressed against the respective unit lead frames  304  to provide tight sealing during the embedding of the semiconductor dies  314  in the mold compound  334 . The unit lead frames  304  may be partially etched or coined from the bottom side, to allow a larger die pad at a given insulation distance and/or to improve locking with the mold compound  334 . 
     For each molded semiconductor package  336 , the lead(s)  308  of the unit lead frame  304  and the leads  326 ,  332  of the clip frame  320  extend in different but not necessarily opposite directions, e.g. x 1  and x 2  in  FIGS. 3A through 3D , and are disposed at different but not necessarily opposite sides of the molded semiconductor package  336 . Any typical molding process such as injection molding, compression molding, film-assisted molding (FAM), reaction injection molding (RIM), resin transfer molding (RTM), map molding, blow molding, etc. may be used to embed the semiconductor dies  314  in the mold compound  334 . Common mold compounds and resins include, but are not limited to, thermoset resins, gel elastomers, encapsulants, potting compounds, composites, optical grade materials, etc. 
     The manufacturing method illustrated in  FIG. 2  further includes separating each lead  308  from the periphery  310  of the corresponding unit lead frame  304  and each lead  326 ,  332  from the periphery  328  of the corresponding unit clip frame  320  outside the mold compound  334  (Block  250 ). In one embodiment, each lead  308  of the unit lead frames  304  is separated from the periphery  310  of the corresponding unit lead frame  304  and each lead  326 ,  332  of the unit clip frames  320  is separated from the periphery  328  of the corresponding unit clip frame  320  outside the mold compound  334  by stamping the leads  308 ,  326 ,  332  outside the mold compound  334 . In another embodiment, each lead  308  of the unit lead frames  304  is separated from the periphery  310  of the corresponding unit lead frame  304  and each lead  326 ,  332  of the unit clip frames  320  is separated from the periphery  328  of the corresponding unit clip frame  320  outside the mold compound  334  by cutting the leads  308 ,  326 ,  332  outside the mold compound  334 . 
     Since the leads  308 ,  326 ,  332  lay open and are free from the mold compound  334 , lead cutting is simpler and no (metal) smearing effects should occur, particularly since the leads  326 ,  332  of the clip frames  320  do not vertically overlap with the lead(s)  308  of the lead frames  304 . The overall complexity of the manufacturing process also is reduced, by using only a single clip frame panel  302  which eases the assembly process because independent of whether a human or a machine provides the frames  300 ,  302  on top of each other, there is only a single action needed instead of attaching several metal clips (or rows of metal clips) to a single lead frame panel. Furthermore, the use of a single clip frame panel  302  also eliminates clip tilt/rotation issues in comparison with attaching several metal clips (or rows of metal clips) to a single lead frame panel since all of the unit clip frames  320  are secured to the same clip frame panel  302 . 
     In the case of each unit clip frame  320  including a second pre-bent clip  330  for contacting a control terminal  316  at the top side of the corresponding semiconductor die  314 , the manufacturing method may further include separating the lead  332  monolithically formed with the second pre-bent metal clip  330  from the periphery  328  of the corresponding unit clip frame  320  outside the mold compound  334  via the same singulation process such as stamping or cutting used to separate each lead  308  from the periphery  310  of the corresponding unit lead frame  304  and each lead  326 ,  332  from the periphery  328  of the corresponding unit clip frame  320 . For some types of packages, part of each lead  308  of the unit lead frame  304  and part of each lead  326 ,  332  of the unit clip frame  320  of each molded package  336  may not be covered by the mold compound  334 . The uncovered part of the leads  308 ,  326 ,  332  may be flush, recessed, or protrude slightly from the mold compound  334 . For some types of packages, each lead  308  of the unit lead frame  304  and each lead  326 ,  332  of the unit clip frame  320  of each molded package  336  may protrude outward from different but not necessarily opposite side faces  338  of the mold compound  334 . 
     The manufacturing method may also include galvanic or electroless plating the part of each lead  308  of the unit lead frames  304  and the part of each lead  326 ,  332  of the unit clip frames  320  which protrude from different side faces  338  of the mold compound  334 , to form wettable lead surfaces at different side faces  338  of the mold compound  334  of each molded semiconductor package  336 , allowing for an easier inspection of subsequent solder connections between the leads  308 ,  326 ,  332  of the molded semiconductor package  336  to a board since wetting/solder joints are readily visible. 
     The assembly shown in  FIGS. 3A through 3D  may instead be manufactured upside down, with the clip attach process (Block  230 ) being performed before the die attach process (Block  210 ), and/or a printing process such as stencil or screen printing may be used separately on the lead frame panel  300  and clip frame panel  302 . In the case of power transistor dies, the semiconductor dies  314  may instead be placed source-down (or emitter-down) and each unit lead frame  304  may provide the source and gate contacts whereas the metal clip  334  of the corresponding unit clip frame  320  forms a single pad only for the drain. Each unit clip frame panel  302  and/or lead frame panel  300  may have alignment features  340  such as dimples, holes, etc. to aid in the aligning of the clip frame panel  302  with the respective lead frame panel  300 . For example, an optical alignment process or a pin alignment process may be used to align the clip frame panel  302  with the lead frame panel  300 . 
       FIGS. 4A and 4B  illustrate respective partial views of the clip frame panel  302 , according to further embodiments. There may be crossings between the unit clip frames  320  and the respective unit lead frames  304 . 
     To reduce insulation distance and avoid shorts, the edge of the first metal clips  324  may include wave-like features  400  which extend upward in a wave-like manner at the edge of the respective semiconductor chips  314 . To accommodate more than one die size per clip  324 , additional wave-like features  402  may be added inward from the clip edge. For example, each first metal clip  324  may have two intersecting (transverse) wave-like features  402  so as to accommodate four different chip sizes. The regions labelled  404 ,  406  in  FIG. 4A  and the regions labelled  408 ,  410  in  FIG. 4B  indicate different chip size areas which can be accommodated by the same first metal clip  324  by providing the wave-like features  400 ,  402 . The wave-like features  400 ,  402  may also be formed as slots or as a coined bottom side or some combination of both. Features such as dimples, slots, crosses, etc. may be applied to the first metal clips  324 , e.g., to mitigate against die tilting/rotation and/or to improve mold locking. 
     Terms such as “first”, “second”, and the like, are used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
     As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
     It is to be understood that the features of the various embodiments described herein may be combined with each other, unless specifically noted otherwise. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.