Power semiconductor module for PCB embedding, power electronic assembly having a power module embedded in a PCB, and corresponding methods of production

A power module for PCB embedding includes: a leadframe; a power semiconductor die with a first load terminal and control terminal at a first side of the die and a second load terminal at the opposite side, the second load terminal soldered to the leadframe; a first metal clip soldered to the first load terminal and forming a first terminal of the power module at a first side of the power module; and a second metal clip soldered to the control terminal and forming a second terminal of the power module at the first side of the power module. The leadframe forms a third terminal of the power module at the first side of the power module, or a third metal clip is soldered to the leadframe and forms the third terminal. The power module terminals are coplanar within +/−30 μm at the first side of the power module.

BACKGROUND

Power semiconductor modules for embedding in a PCB (printed circuit board) typically include a large metal block with a power semiconductor die attached to the metal block. The metal block and power semiconductor die are embedded in a PCB insulator material such as FR4. Holes are then formed in the insulator material to access electrical contact pads of the power semiconductor die, and the holes are filled with an electrically conductive material such as copper. Additional semiconductor dies and other components such as passives (capacitors, inductors, resistors, etc.) are typically attached to the top side of the PCB.

The process described above suffers from die placement accuracy issues and requires tight control for interfaces that are later connected by vias. Accurate gate pad contacting is particularly problematic, since the gate pad of a power semiconductor die is relatively small compare to the power/load pads. Furthermore, semiconductor material such as silicon is highly sensitive to laser drilling used to form the openings in the PCB insulator material, contamination from the PCB process, and ions present in FR4 and other types of glass-reinforced epoxy laminate materials used in PCB processing.

Accordingly, there is a need for an embedded power semiconductor module that does not suffer from the problems described above and related methods of production.

SUMMARY

According to an embodiment of a method of batch producing power modules, the method comprises: applying a first solder paste to substrate sections of a leadframe structure; placing a plurality of power semiconductor dies on the first solder paste, each power semiconductor die having a first load terminal and a control terminal at a first side that faces away from the leadframe structure and a second load terminal contacting the first solder paste at a second side opposite the first side; applying a second solder paste to the first load terminal and the control terminal of each power semiconductor die; vertically aligning a metal clip frame with the leadframe structure, the metal clip frame comprising a first metal clip vertically aligned with the first load terminal of each power semiconductor die and a second metal clip vertically aligned with the control terminal of each power semiconductor die; pressing the metal clip frame toward the leadframe structure in a pressing direction, wherein a hard stop feature prevents further pressing when the hard stop feature is engaged; reflowing the first solder paste and the second solder paste to form a first soldered joint between each first metal clip and the corresponding first load terminal of each power semiconductor die, a second soldered joint between each second metal clip and the corresponding control terminal of each power semiconductor die, and a third soldered joint between the second load terminal of each power semiconductor die and the corresponding substrate section of the leadframe structure; and severing connections to the leadframe structure and to the metal clip frame, to form individual power modules.

According to an embodiment of a method of producing an electronic assembly, the method comprises: embedding a power module in an electrically insulating body of a printed circuit board, the power module comprising: a leadframe; a power semiconductor die having a first load terminal and a control terminal at a first side of the power semiconductor die and a second load terminal at a second side opposite the first side, the second load terminal being soldered to the leadframe; a first metal clip soldered to the first load terminal and forming a first terminal of the power module at a first side of the power module; and a second metal clip soldered to the control terminal and forming a second terminal of the power module at the first side of the power module, wherein the leadframe extends to the first side of the power module and forms a third terminal of the power module at the first side of the power module, or a third metal clip is soldered to the leadframe and forms the third terminal of the power module; forming a plurality of openings in the electrically insulating body of the printed circuit board that expose the first terminal, the second terminal and the third terminal of the power module at the first side of the power module; and filling the plurality of openings with an electrically conductive material.

According to an embodiment of a power electronic assembly, the power electronic assembly comprises: a printed circuit board (PCB); and a power module embedded in the PCB, wherein the power module comprises: a leadframe; a power semiconductor die having a first load terminal and a control terminal at a first side of the power semiconductor die and a second load terminal at a second side opposite the first side, the second load terminal being soldered to the leadframe; a first metal clip soldered to the first load terminal and forming a first terminal of the power module at a first side of the power module; and a second metal clip soldered to the control terminal and forming a second terminal of the power module at the first side of the power module, wherein the leadframe extends to the first side of the power module and forms a third terminal of the power module at the first side of the power module, or a third metal clip is soldered to the leadframe and forms the third terminal of the power module, wherein the PCB includes electrically conductive vias that extend through one or more insulating layers of the PCB and contact the first terminal, the second terminal and the third terminal of the power module at the first side of the power module.

According to an embodiment of a power module for embedding in a printed circuit board (PCB), the power module comprises: a leadframe; a power semiconductor die having a first load terminal and a control terminal at a first side of the power semiconductor die and a second load terminal at a second side opposite the first side, the second load terminal being soldered to the leadframe; a first metal clip soldered to the first load terminal and forming a first terminal of the power module at a first side of the power module; and a second metal clip soldered to the control terminal and forming a second terminal of the power module at the first side of the power module, wherein the leadframe extends to the first side of the power module and forms a third terminal of the power module at the first side of the power module, or a third metal clip is soldered to the leadframe and forms the third terminal of the power module, wherein the first terminal, the second terminal and the third terminal of the power module are coplanar within +/−30 μm at the first side of the power module.

DETAILED DESCRIPTION

The embodiments described herein provide a power semiconductor module for PCB embedding, a power electronic assembly that includes the power module embedded in a PCB, and corresponding methods of production. The power module production process uses solder paste instead of diffusion soldering for attaching a power semiconductor die to a leadframe and for attaching metal clips to terminals at the opposite side of the power semiconductor die as the leadframe, but with improved tolerance control. The metal clips soldered to the terminals of the power semiconductor die at the opposite side as the leadframe form terminals of the power module at the front side of the power module. Improved tolerance control results by using the leadframe or an additional metal clip soldered to the leadframe as an additional terminal of the power module at the front side of the power module.

The power module terminals may be coplanar within +/−30 μm at the front side of the power module. The solder layers on the front and back sides of the power semiconductor die balance the tolerances associated with the solder process and also die warpage. Accordingly, relatively thin dies (e.g., 100 μm thickness or less in the case of Si) with standard front side metallization may be used instead of a diffusion solder process. Diffusion soldering relies on a reaction between a thin layer of molten solder and metal on the components to form one or more intermetallic phases that are solid at the joining temperature. The resulting diffusion soldered joint will not remelt unless heated to a higher temperature at which one of the intermetallic phases melts. The embodiments described herein yield a power semiconductor module with similar tolerances provided by diffusion solder-based processes but without the added complexity, while not requiring the use of a thick front side metallization (e.g., 10 μm thick Cu). Also, standard solder processes are 100° C. lower than diffusion soldering, thus avoiding bimetallic bending of the die-to-metallization (e.g., Cu) interface.

Described next, with reference to the figures, are exemplary embodiments of the power semiconductor module for PCB embedding, a power electronic assembly that includes the power module embedded in a PCB, and corresponding methods of production.

FIG.1illustrate a cross-sectional view of a power module100for embedding in a printed circuit board (PCB). In one embodiment, the power module100has a rated voltage in a range of 600V to 1200V. The power module100may instead have a lower (<600V) rated voltage or a higher (>1200V) rated voltage.

The power module100includes at least one leadframe102and at least one power semiconductor die104attached to the leadframe102. The leadframe102may be made of copper (Cu), nickel (Ni), nickel phosphorous (NiP), silver (Ag), palladium (Pd), gold (Au), etc., alloys or combinations thereof, or any other electrically conductive material suitable for leadframe applications. The power semiconductor die104may comprise any type of semiconductor material such as Si, SiC, GaN, etc. and have a rated voltage in a range of 600V to 1200V. The power semiconductor die104may instead have a lower (<600V) rated voltage or a higher (>1200V) rated voltage.

FIG.1illustrates the power semiconductor die104as a vertical power device. In the case of a vertical power device, some load and possibly signal connections to the power semiconductor die104are made at the back side106of the die104which is attached to the leadframe102. For example, in the case of a vertical power MOSFET (metal-oxide-semiconductor field-effect transistor) or vertical IGBT (insulated gate bipolar transistor), source/emitter and gate connections may be made at the front side108of the power semiconductor die104and a drain/collector connection may be made at the back side106of the die104.

More generally, and in the case of a vertical power transistor, the power semiconductor die104has a first load terminal110and a control terminal112at the front side108of the die104and a second load terminal114at the back side106of the die104. For a vertical power MOSFET, the first load terminal110may be a source terminal, the second load terminal114may be a drain terminal, and the control terminal112may be a gate terminal. For a vertical IGBT, the first load terminal110may be an emitter terminal, the second load terminal114may be a collector terminal, and the control terminal112may be a gate terminal. Depending on how the gate connections are routed, the first load terminal110may be implemented as a contiguous (uninterrupted) metal pad or as a segmented metal pad having two or more spaced apart sections. The second load terminal114at the back side106of the power semiconductor die104similarly may be implemented as a contiguous metal pad or as a segmented metal pad, e.g., to account for CTE (coefficient of thermal expansion) mismatch.

In each case, the second load terminal114of the power semiconductor die104is soldered to the leadframe102. At the opposite (front) side108of the power semiconductor die104, a first metal clip116is soldered to the first load terminal110of the die104and forms a first terminal118of the power module100at the front side120of the power module100. A second metal clip122is soldered to the control terminal112of the power semiconductor die104and forms a second terminal124of the power module100at the first side122of the power module100.

The first metal clip116is soldered to the first load terminal110of the power semiconductor die104via a first soldered joint126, the second metal clip122is soldered to the control terminal112of the die104via a second soldered joint128, and the second load terminal114of the die104is soldered to the leadframe102via a third soldered joint130. The soldered joints126,128,130are each formed from a solder paste. Hence, the soldered joints126,128,130are not diffusion soldered joints. That is, the soldered joints126,128,130are not formed by a diffusion soldering process that involves reacting a thin layer of molten solder with metal of the leadframe102and die terminals110,112to form one or more intermetallic phases that becomes solid at the joining temperature. Instead, solder paste is used to form the soldered joints126,128,130between the terminals110,112,114of the power semiconductor die104and the metal clips116,122and leadframe102, respectively.

Further according to the embodiment illustrated inFIG.1, a section132of the leadframe102extends to the first side120of the power module100and forms a third terminal134of the power module100at the first side120of the module100. The leadframe102may be coined, stamped, etched, etc. to yield the dual-gauge (dual-thickness) configuration shown inFIG.1and according to which the extended section132of the leadframe102forms a terminal134of the power module100.

The first terminal118, the second terminal124and the third terminal134of the power module100provide respective points of external electrical contact for the power module100and are coplanar within +/−30 μm at the first side120of the power module100as indicated by ‘CP’ inFIG.1. That is, the first terminal118, the second terminal124and the third terminal134of the power module100may lie in the same horizontal plane (e.g., HP1or HP2inFIG.1) relative to the first side120of the power module100or may lie in different horizontal planes (e.g., HP1and HP2inFIG.1) with a vertical offset of no more than +/−30 μm between the horizontal planes.

The soldered joints126,128,130at the back and front sides106,108of the power semiconductor die104balance the tolerances associated with the solder process and also die warpage, enabling a module terminal coplanarity of +/−30 μm at the first side120of the power module100. Accordingly, relatively thin dies (e.g., 100 μm thickness or less) with solderable front side metallization (e.g., 5 μm thick Cu, Ni, AlCu, AlSiCu, etc.) may be used to realize the first load terminal110and the control terminal112at the front side108of the power semiconductor die104. Solderable back side metallization (e.g., NiAg, NiV, etc.) may be used to realize the second load terminal114at the back side106of the power semiconductor die104. Accordingly, a thicker front side metallization (e.g., 10 μm thick Cu) is not required. For example, the first load terminal110, the second load terminal114and the control terminal112of the power semiconductor die104may comprise Cu and have a thickness less than 10 μm.

The power module100will be subsequently embedded in a PCB laminate material such as FR4. Conductive vias to the power module terminals118,124,134will be formed by laser drilling through the PCB laminate material and subsequent via filling or lining with Cu. Via length is a critical parameter of the OPCB embedding process. A poorly controlled module terminal coplanarity (outside +/−30 μm) results in overly long or overly short vias. Typically, a via aspect ratio (vertical height to horizontal width) of 1 is preferred. If a via is too tall, the risk of an incomplete via increases. That is, some PCB laminate material may remain in the via and the corresponding electrical connection is not formed. If a via is too wide, the risk of a partially filled via increases. That is, the via may not be adequately filled or lined with Cu and the corresponding electrical connection is insufficient or incomplete. Via length is a function of the power module terminal coplanarity. A terminal coplanarity of +/−30 μm at the first side120of the power module100ensures proper formation of the vias during the PCB embedding process.

One or more additional metal clips (not shown) may be attached to corresponding terminal(s) at the front side108of the power semiconductor die104, e.g., in case the power semiconductor die104includes more than the first load terminal110and the control terminal112at the front side108of the die104. For example, the power semiconductor die104may include one or more sense terminals (not shown) such as a current sense and/or temperature sense terminal at the front side108of the power semiconductor die104. In these cases, each additional metal clip attached to a corresponding terminal at the front side108of the power semiconductor die104forms a terminal of the power module100and is coplanar with the other power module terminals118,124,134within +/−30 μm at the first side120of the power module100.

FIG.2illustrate a cross-sectional view of another embodiment of a power module200for embedding in a PCB. The embodiment shown inFIG.2is similar to the embodiment shown inFIG.1. Different, however, the power module200ofFIG.2is a molded power module. That is, the power semiconductor die104and part of the leadframe102are embedded in a molding compound202. The molding compound202may be formed by a molding process such as injection molding, compression molding, transfer molding, etc. The terminals118,124,134of the power module200are exposed from the molding compound202and therefore accessible for external connection. The back side204of the leadframe102also may be exposed from the molding compound202to enhance heat dissipation at the back side206of the power module200.

FIG.3illustrate a cross-sectional view of another embodiment of a power module300for embedding in a PCB. The embodiment shown inFIG.3is similar to the embodiment shown inFIG.1. Different, however, a third metal clip302is soldered to the leadframe102and forms the third terminal134of the power module300. For example, the third metal clip302may be soldered to the extended section132of the leadframe102. More generally, the third metal clip302is soldered to the leadframe102via a corresponding soldered joint304. The soldered joint304is formed from a solder paste and therefore is not a diffusion soldered joint. As with the embodiments illustrated inFIGS.1and2, the terminals118,124,134of the power module300shown inFIG.3are coplanar within +/−30 μm at the first side124of the power module300.

FIG.4illustrate a cross-sectional view of another embodiment of a power module400for embedding in a PCB. The embodiment shown inFIG.4is similar to the embodiment shown inFIG.3. Different, however, the power module400ofFIG.4is a molded power module. Similar toFIG.2, the power semiconductor die104and part of the leadframe102are embedded in a molding compound202. The terminals118,124,134of the power module200are exposed from the molding compound202and therefore accessible for external connection. The back side204of the leadframe102also may be exposed from the molding compound202to enhance heat dissipation at the back side206of the power module200.

FIGS.5A through5Eillustrate partial top plan views during different stages of batch producing power modules, e.g., of the kinds shown inFIGS.1through4.

FIG.5Ashows a leadframe structure500such as a leadframe strip or sheet formed from an electrically conductive material such as Cu, Ni, NiP, Ag, Pd, Au, etc., alloys or combinations thereof, or any other electrically conductive material suitable for leadframe applications. According to one technique, the leadframe structure500is provided by a sheet of metal and the various features of the leadframe structure500are formed by performing techniques such as stamping, punching, etching, bending, coining, etc. to form substrate sections502which are temporality secured to the periphery504of the leadframe structure500and/or to adjacent substrate sections502by connecting structures506such as tie bars. The substrate sections502are subsequently separated from one another and from the periphery504of the leadframe structure500by severing the connecting structures506. The leadframes102shown inFIGS.1through4may correspond to any of the substrate sections502of the leadframe structure500. For example, an extended leadframe section132is identified inFIG.5Afor one of the substrate sections502.

FIG.5Bshows a first solder paste508applied to the substrate sections502of the leadframe structure500. The first solder paste508may be applied to the substrate sections502using a printing process such as stencil or screen printing or a dispensing or jetting process, etc.

FIG.5Cshows a power semiconductor die104placed on the first solder paste508applied to the substrate sections502of the leadframe structure500. Each power semiconductor die104has a first load terminal110and a control terminal112at a first side that faces away from the leadframe structure500and a second load terminal (out of view; terminal114inFIGS.1through4) contacting the first solder paste508at a second side opposite the first side. The first load terminal110of each power semiconductor die104may be a contiguous metal pad as shown inFIG.5Cor a segmented metal pad having two or more spaced apart sections. The second load terminal at the opposite side of each power semiconductor die also may be implemented as a contiguous metal pad or as a segmented metal pad, e.g., as previously described herein. In one embodiment, each power semiconductor die104has a thickness less than 100 μm and the first load terminal110, the second load terminal114and the control terminal112of each power semiconductor die104comprise Cu and have a thickness less than 10 μm.

FIG.5Dshows a second solder paste510applied to the first load terminal110and the control terminal112of each power semiconductor die104. The second solder paste510may be applied to the die terminals110,112using a printing process such as stencil or screen printing or a dispensing or jetting process, etc.

FIG.5Eshows a metal clip frame512vertically aligned with the leadframe structure500. The metal clip frame512includes a first metal clip116vertically aligned with the first load terminal110of each power semiconductor die104and a second metal clip122vertically aligned with the control terminal112of each power semiconductor die104. The first and second metal clips116,122shown inFIG.5Ecorrespond to the first and second metal clips116,122shown inFIGS.1through4.

In one embodiment, each first metal clip116has a plurality of slots514configured as a reservoir for accommodating the second solder paste510used to solder the first metal clip116to the first load terminal110of the corresponding power semiconductor die104. Similarly, each second metal clip112may have one or more slots516configured as a reservoir for accommodating the second solder paste510used to solder the second metal clip122to the control terminal112of the corresponding power semiconductor die104.

The metal clips116,122are temporality secured to the periphery518of the metal clip frame512and/or to adjacent metal clips116/122by connecting structures520such as tie bars. The metal clip frame512is pressed toward the leadframe structure500in a pressing direction which is perpendicular to the view provided inFIG.5E. A hard stop feature522prevents further pressing when the hard stop feature522is engaged. The hard stop feature522is out of view inFIG.5Eand therefore illustrated by dashed ovals. The hard stop feature522may be part of the metal clip frame512, part of the leadframe structure500, partly formed on the metal clip frame512and partly formed on the leadframe structure500, or a separate component interposed between the metal clip frame512and the leadframe structure500.

The first solder paste508and the second solder paste510are then reflowed to form the first soldered joint126between each first metal clip116and the corresponding first load terminal110of each power semiconductor die104, the second soldered joint128between each second metal clip122and the corresponding control terminal112of each power semiconductor die104, and the third soldered joint130between the second load terminal114of each power semiconductor die104and the corresponding substrate section502of the leadframe structure500.

The connections506,520to the leadframe structure500and to the metal clip frame512are then severed to form individual power modules, e.g., of the kind illustrated in any ofFIGS.1through4. The connections506,520may be severed by stamping, punching, laser cutting, saw blade cutting, etching, etc. Prior to severing the connections506,520to the leadframe structure500and to the metal clip frame512, the power modules may be molded to yield molded power modules, e.g., as shown inFIGS.2and4.

The hard stop feature522may be used to determine the bond line thickness for each first soldered joint126, each second soldered joint128, and each third soldered joint130and thus helps to ensure a terminal coplanarity of +/−30 μm at the first side of each power module. The hard stop feature522may include a plurality of protrusions at a side of the metal clip frame512that faces the leadframe structure500when the metal clip frame512is vertically aligned with the leadframe structure500. Separately or in combination, the hard stop feature522may include a plurality of protrusions at a side of the leadframe structure500that faces the metal clip frame512when the metal clip frame512is vertically aligned with the leadframe structure500. Separately or in combination, the hard stop feature522may include a plurality of tabs, bumps or similar structures that protrude downward from the periphery518of the metal clip frame512in a direction toward the leadframe structure500when the metal clip frame512is vertically aligned with the leadframe structure500. Separately or in combination, the hard stop feature522may be designed to limit movement of the metal clip frame512in at least one lateral direction (x and/or y direction inFIG.5E) that is orthogonal to the pressing direction, when the metal clip frame512is pressed onto the leadframe structure500. For example, the hard stop feature522may be designed as a locking mechanism such as a protrusion, tab, bump, etc. formed on the metal clip frame512or leadframe structure500and a correspondingly mated recess on the other structure504/512that prevents movement in the x and/or y direction when the metal clip frame512is pressed onto the leadframe structure500.

FIG.6illustrates an embodiment of the hard stop feature522.FIG.6shows part of the metal clip frame512vertically aligned with and pressed onto the leadframe structure500. According to this embodiment, the metal clip frame512has been punched, stamped, coined, etc. to form a recess or dimple600at the side602of the metal clip frame512facing away from the leadframe structure500. A corresponding protrusion604extends from the opposite side of the metal clip frame512in the region of the recess/dimple600. Implementing the hard stop feature522as a protrusion604at the side of the metal clip frame512facing the leadframe structure500prevents further pressing of the metal clip frame512towards the leadframe structure500once the protrusion604engages the leadframe structure500.

The leadframe structure500instead may include the protrusion604, or both the metal clip frame512and the leadframe structure500may include the protrusion604. More than one protrusion604may be formed on the metal clip frame512and/or the leadframe structure500, and the protrusion604may have any dimensions and shape suitable for functioning as a hard stop against further oppressing of the metal clip frame512towards the leadframe structure500once engaged. A mating structure, e.g., such as a recess may be formed in the opposite metal structure500/512and dimensioned to receive the protrusion to limit movement of the metal clip frame512in at least one lateral direction that is orthogonal to the pressing direction when the metal clip frame512is pressed onto the leadframe structure500.

FIG.7illustrates another embodiment of the hard stop feature522.FIG.7shows the metal clip frame512vertically aligned with the leadframe structure500and a corresponding enlarged view. According to this embodiment, the metal clip frame512is implemented as separate dual-clip frames700. Each dual-clip frame700includes two pairs of first and second metal clips116,122connected by a bridging region702that is removed by cutting, etching, stamping, etc. after all soldered joints126,128,130are formed. Each dual-clip frame700is aligned with an adjacent pair of power semiconductor dies104attached to the leadframe structure500, with one pair of the first and second metal clips116,122aligned with the first load terminal110and control terminal112, respectively, of one power semiconductor die104and the other pair of the first and second metal clips116,122aligned with the first load terminal110and control terminal112, respectively, of the adjacent power semiconductor die104.

Further according to the embodiment inFIG.7, a pair of tabs or protrusions704on each dual-clip frame700that are bent downward in a direction towards the leadframe structure500enable the hard stop function. During vertical alignment and pressing of the dual-clip frames700onto the leadframe structure500, the tabs/protrusions704engage the leadframe structure500and prevent further pressing of the dual-clip frames700. The leadframe structure500instead may include the tabs/protrusions704, or both the dual-clip frames700and the leadframe structure500may include the tabs/protrusions704.

FIGS.8A through8Gillustrate respective partial cross-sectional views of an embodiment of producing an electronic assembly using the power modules described herein. The illustrated PCB embedding process uses the molded power module400shown inFIG.4. However, any of the power modules described herein may be used instead.

FIG.8Ashows a first PCB laminate800that includes a Cu foil802and one or more layers of prepreg (pre-impregnated) material804. Each prepreg layer804comprises a PCB dielectric such as FR4.

FIG.8Bshows another prepreg layer806on the first PCB laminate800and having an opening808for receiving the molded power module400. The additional prepreg layer806comprises a PCB dielectric such as FR4.

FIG.8Cshows the molded power module400seated in the opening808of the additional prepreg layer806. The molded power module400may be seated in the opening808of the additional prepreg layer806after being tested.

FIG.8Dshows a second PCB laminate810covering the molded power module400and the additional prepreg layer806with the opening808. The second PCB laminate810that includes a Cu foil812and one or more prepreg layers814each of which comprises a PCB dielectric such as FR4. The Cu foil812of the second PCB laminate810may be patterned to provide adequate isolation between the different electric potentials and control signalling of the molded power module400.

FIG.8Eshows the stacked structure after a lamination process which may include elevated temperature, e.g., 130-150° C., elevated pressure, e.g., 3 MPa, and vacuum. The lamination process cures the PCB dielectrics of the prepreg layers804,806,814to form an electrically insulating body816of the PCB and in which the molded power module400is embedded. More than one molded power module may be embedded in the electrically insulating body816.

FIG.8Fshows openings818formed in the Cu foils802,812and the electrically insulating body816of the PCB. The openings818may be formed by laser drilling, mechanical drilling, etc. The openings818at the bottom side820of the PCB may be formed at the same time or at a different time as the openings818at the top side822of the PCB. The openings818at the bottom side820of the PCB expose the unmolded back side204of the molded power module400.

The openings818at the top side822of the PCB expose contact regions of the respective module terminals118,124,134at the front side120of the power module400. Three exposed terminals118,124,134are shown at the front side120of the power module400inFIG.8F. The molded power module400may have more terminals that can be exposed through the openings818, as previously explained herein.

The molded power module400may have a terminal coplanarity of +/−30 μm at the module front side120, as previously described herein. Accordingly, the openings814at the top side822of the PCB have a relatively uniform depth (e.g., 50 microns). The module terminals118,124,134protect the underlying metal contact pads110,112of the power semiconductor die104from being damaged by the laser/mechanical via drilling process used to form the openings818.

FIG.8Gshows the openings818filled with an electrically conductive material826such as Cu, e.g., using an electroless Cu plating process. The electrically conductive material826at the top side of the PCB may form vias that connect the different sections of the patterned Cu foil812to the contact regions of the respective module terminals118,124,134. That is, the vias formed by the electrically conductive material826extend through the upper part of the electrically insulating body816of the PCB and contact the first terminal118, the second terminal124and the third terminal134of the molded power module400. The electrically conductive material826at the bottom side of the PCB may similar form vias that connect the bottom Cu foil802to the unmolded back side204of the molded power module400.

The PCB lamination process may be continued to form one or more additional PCB layers above and/or below the electrically insulating body816of the PCB in which the molded power module400is embedded. Each additional PCB layer may be used to provide additional levels of electrical interconnection and/or redistribution. Components such as drivers, controllers, passives (inductors, capacitors, etc.), coolers, etc. may be attached to the uppermost layer of the PCB and electrically connected to the molded power module400embedded therein to form an electronic circuit such as a multi-phase phase drive for power steering, climate compressors, power converters, power inverters, etc.

As explained above, the power semiconductor dies included in the power modules may have a thickness less than 100 μm and the first load terminal, the second load terminal and the control terminal of the power semiconductor dies may each comprise Cu and have a thickness less than 10 μm. The power modules embedded in the PCB may be molded or unmolded power modules, e.g., as shown inFIGS.1through4. The first metal clip of the power modules may have a plurality of slots configured as a reservoir for accommodating solder paste used to solder the first metal clip to the first load terminal of the respective power semiconductor die, e.g., as shown inFIG.5E. Separately or in combination, the second metal clip of the power modules may have one or more slots configured as a reservoir for accommodating solder paste used to solder the second metal clip to the control terminal of the power semiconductor die, e.g., as shown inFIG.5E.

Example 1. A method of batch producing power modules, the method comprising: applying a first solder paste to substrate sections of a leadframe structure; placing a plurality of power semiconductor dies on the first solder paste, each power semiconductor die having a first load terminal and a control terminal at a first side that faces away from the leadframe structure and a second load terminal contacting the first solder paste at a second side opposite the first side; applying a second solder paste to the first load terminal and the control terminal of each power semiconductor die; vertically aligning a metal clip frame with the leadframe structure, the metal clip frame comprising a first metal clip vertically aligned with the first load terminal of each power semiconductor die and a second metal clip vertically aligned with the control terminal of each power semiconductor die; pressing the metal clip frame toward the leadframe structure in a pressing direction, wherein a hard stop feature prevents further pressing when the hard stop feature is engaged; reflowing the first solder paste and the second solder paste to form a first soldered joint between each first metal clip and the corresponding first load terminal of each power semiconductor die, a second soldered joint between each second metal clip and the corresponding control terminal of each power semiconductor die, and a third soldered joint between the second load terminal of each power semiconductor die and the corresponding substrate section of the leadframe structure; and severing connections to the leadframe structure and to the metal clip frame, to form individual power modules.

Example 2. The method of example 1, wherein each power semiconductor die has a thickness less than 100 μm, and wherein the first load terminal, the second load terminal and the control terminal of each power semiconductor die comprise Cu and have a thickness less than 10 μm.

Example 3. The method of example 1 or 2, wherein the first terminal, the second terminal and the third terminal of each power module are coplanar within +/−30 μm at the first side of the power module.

Example 4. The method of any of examples 1 through 3, wherein the hard stop feature determines a bond line thickness for each first soldered joint, each second soldered joint, and each third soldered joint.

Example 5. The method of any of examples 1 through 5, wherein the hard stop feature comprises a plurality of protrusions at a side of the metal clip frame that faces the leadframe structure when the metal clip frame is vertically aligned with the leadframe structure.

Example 6. The method of any of examples 1 through 5, wherein the hard stop feature comprises a plurality of protrusions at a side of the leadframe structure that faces the metal clip frame when the metal clip frame is vertically aligned with the leadframe structure.

Example 7. The method of any of examples 1 through 6, wherein the hard stop feature comprises a plurality of tabs that protrude downward from a periphery of the metal clip frame in a direction toward the leadframe structure when the metal clip frame is vertically aligned with the leadframe structure.

Example 8. The method of any of examples 1 through 7, wherein the hard stop feature limits movement of the metal clip frame in at least one lateral direction that is orthogonal to the pressing direction, when the metal clip frame is pressed onto the leadframe structure.

Example 9. The method of any of examples 1 through 8, wherein each first metal clip of the metal clip frame has a plurality of slots configured as a reservoir for accommodating the second solder paste during the pressing and the reflowing.

Example 10. The method of any of examples 1 through 9, wherein each second metal clip of the metal clip frame has one or more slots configured as a reservoir for accommodating the second solder paste during the pressing and the reflowing.

Example 11. The method of any of examples 1 through 10, further comprising: prior to severing the connections to the leadframe structure and to the metal clip frame, molding the power modules.

Example 12. A method of producing an electronic assembly, the method comprising: embedding a power module in an electrically insulating body of a printed circuit board, the power module comprising: a leadframe; a power semiconductor die having a first load terminal and a control terminal at a first side of the power semiconductor die and a second load terminal at a second side opposite the first side, the second load terminal being soldered to the leadframe; a first metal clip soldered to the first load terminal and forming a first terminal of the power module at a first side of the power module; and a second metal clip soldered to the control terminal and forming a second terminal of the power module at the first side of the power module, wherein the leadframe extends to the first side of the power module and forms a third terminal of the power module at the first side of the power module, or a third metal clip is soldered to the leadframe and forms the third terminal of the power module; forming a plurality of openings in the electrically insulating body of the printed circuit board that expose the first terminal, the second terminal and the third terminal of the power module at the first side of the power module; and filling the plurality of openings with an electrically conductive material.

Example 13. The method of example 12, wherein the openings are formed in the electrically insulating body of the printed circuit board by laser drilling, wherein the power semiconductor die has a thickness less than 100 μm, and wherein the first load terminal, the second load terminal and the control terminal of the power semiconductor die each comprise Cu and have a thickness less than 10 μm.

Example 14. The method of example 12 or 13, wherein the first terminal, the second terminal and the third terminal of the power module are coplanar within +/−30 μm at the first side of the power module.

Example 15. The method of any of examples 12 through 14, wherein the power module is a molded module.

Example 16. The method of any of examples 12 through 15, wherein the first metal clip of the power module has a plurality of slots configured as a reservoir for accommodating solder paste used to solder the first metal clip to the first load terminal of the power semiconductor die.

Example 17. The method of any of examples 12 through 16, wherein the second metal clip of the power module has one or more slots configured as a reservoir for accommodating solder paste used to solder the second metal clip to the control terminal of the power semiconductor die.

Example 18. A power electronic assembly, comprising: a printed circuit board (PCB); and a power module embedded in the PCB, wherein the power module comprises: a leadframe; a power semiconductor die having a first load terminal and a control terminal at a first side of the power semiconductor die and a second load terminal at a second side opposite the first side, the second load terminal being soldered to the leadframe; a first metal clip soldered to the first load terminal and forming a first terminal of the power module at a first side of the power module; and a second metal clip soldered to the control terminal and forming a second terminal of the power module at the first side of the power module, wherein the leadframe extends to the first side of the power module and forms a third terminal of the power module at the first side of the power module, or a third metal clip is soldered to the leadframe and forms the third terminal of the power module, wherein the PCB includes electrically conductive vias that extend through one or more insulating layers of the PCB and contact the first terminal, the second terminal and the third terminal of the power module at the first side of the power module.

Example 19. The power electronic assembly of example 18, wherein the first terminal, the second terminal and the third terminal of the power module are coplanar within +/−30 μm at the first side of the power module.

Example 20. The power electronic assembly of example 18 or 19, wherein the power module is a molded module.

Example 21. The power electronic assembly of any of examples 18 through 20, wherein the first metal clip of the power module has a plurality of slots configured as a reservoir for accommodating solder paste used to solder the first metal clip to the first load terminal of the power semiconductor die.

Example 22. The power electronic assembly of any of examples 18 through 21, wherein the second metal clip of the power module has one or more slots configured as a reservoir for accommodating solder paste used to solder the second metal clip to the control terminal of the power semiconductor die.

Example 23. A power module for embedding in a printed circuit board (PCB), the power module comprising: a leadframe; a power semiconductor die having a first load terminal and a control terminal at a first side of the power semiconductor die and a second load terminal at a second side opposite the first side, the second load terminal being soldered to the leadframe; a first metal clip soldered to the first load terminal and forming a first terminal of the power module at a first side of the power module; and a second metal clip soldered to the control terminal and forming a second terminal of the power module at the first side of the power module, wherein the leadframe extends to the first side of the power module and forms a third terminal of the power module at the first side of the power module, or a third metal clip is soldered to the leadframe and forms the third terminal of the power module, wherein the first terminal, the second terminal and the third terminal of the power module are coplanar within +/−30 μm at the first side of the power module.

Example 24. The power module of example 23, wherein the first metal clip has a plurality of slots configured as a reservoir for accommodating solder paste used to solder the first metal clip to the first load terminal of the power semiconductor die.

Example 25. The power module of example 23 or 24, wherein the second metal clip has one or more slots configured as a reservoir for accommodating solder paste used to solder the second metal clip to the control terminal of the power semiconductor die.