Patent Description:
In certain prior art, an electronic assembly may have a restricted maximum operating power capacity because of limited thermal dissipation. If semiconductor devices in the electronic assembly are operated beyond their maximum operating power capacity, the electronic assembly may fail prematurely or be unreliable. For example, an electronics assembly with limited thermal dissipation might be applicable to a lesser power range of electric motors or generators than otherwise possible. Accordingly, there is need for an electronic assembly with improved thermal dissipation to increase or optimize the maximum operating power capacity.

<CIT> teaches a lead frame free packaged semiconductor device with an exposed heat sink formed by die bonding the semiconductor device directly to the heat sink and bonding package leads directly to the semiconductor die, and optionally to the heat sink. In an alternative embodiment, a lead frame free packaged semiconductor device with an exposed heat sink is formed by die bonding the semiconductor device directly to the heat sink and wire bonding package leads to the semiconductor die, and optionally to the heat sink.

<CIT> teaches the assembly of semiconductor components using a circuit board with a recess to take each component at least partially within it. A heat conductive and electrically insulating coupling takes heat from the component directly to a cooling element through surface contact. Before installation, the coupling has a curved shape in a material with a thermal conductivity of at least <NUM> W/(m*K), preferably at least <NUM> W/(m*K) using carbon, especially diamond, graphite foil, crystalline silicon, crystalline tin, gallium arsenide, conductive ceramic and especially beryllium oxide, aluminum nitrite, aluminum oxide.

The invention is defined in the independent claims to which reference should be made. Preferable features are set out in the dependent claims.

Like reference numbers indicate like elements throughout the drawings.

An electrical and mechanical connection between metal or alloy components or structures may be formed by soldering, brazing, fusing, welding, or applying conductive adhesive. Directly bonded refers to an electrical and mechanical connection, between the same or similar metals or alloys, or between compatible (but different) metals or alloys, that is formed by application of certain processes. Directly bonded refers to a bond, fusion, weld, or other electrical and mechanical connection between the same or similar metals or alloys, or between compatible metals or alloys from heat, pressure, ultrasound, reactive bonding, vapor-phase bonding, or other techniques.

Direct bonding may be accomplished by one or more of the following techniques that may be applied cumulatively or separately. Under a first technique of direct bonding, if the lead frame and the device pads are composed of copper or a copper alloy, the lead frame may be directly bonded to the device pads by direct copper-to-copper thermo-compression bonding or ultrasonic bonding. Thermo-compression bonding refers to the simultaneous application of pressure and heat to the materials to be joined.

Under a second technique of direct bonding, reactive bonding refers to an exothermic chemical reaction triggered by application of thermal energy from a reactive multilayer foil (e.g., of nickel and aluminum) to join the materials by creation of a new metallic material or alloy (e.g., nickel-aluminide). For example, the multilayer foil may be formed by sputtering thin alternating metal layers (e.g., nickel layers and aluminum layers), where each layer may be deposited to a thickness equal to or less than target thickness. At the time of preparing this document, suitable reactive multilayer foils (e.g., for direct bonding of a heat sink to a metallic region) were sold by the Indium Corporation under the trade name NanoFoil®.

Under a third technique of direct bonding, vapor-phase bonding methods may be used to bond a metal or alloy (e.g., copper) to silicon semiconductors using a vapor-deposition of a priming intermediate metal layer (e.g., tin) to form an intermetallic compound (e.g., copper-tin compound or alloy) at the joint, where the intermetallic compound may have lower thermal electrical and thermal resistance than a comparable solder joint. The vapor-phase bonding may require introducing an intermediate metallic material (e.g., tin) between the metal materials to be joined with application of heat or pressure, or both. The intermediate metallic material may have a lower melting point than metals or alloys to be electrically and mechanically connected.

For efficient thermal conduction, adjoining parts of the electronic assembly are joined to minimize thermal resistance and maximize heat transfer or thermal conductance between the adjoining parts. Thermal conductance may be enhanced by the manner in which parts of the electronic assembly <NUM> are connected or bonded. Direct bonding typically offers greater thermal conduction than a mere connection by soldering, conductive adhesive, or by contact between components with conductive grease. In general, "bonded " or "bonding" refers to parts of the electronic assembly <NUM> that are connected together or joined by adhesive (e.g., conductive adhesive or thermally conductive adhesive), soldered, brazed, or welded, whereas "direct bonding" results from the application of specific processes or techniques that reduce electrical and thermal resistance of the joint.

In accordance with one embodiment of the disclosure, <FIG>, inclusive, illustrate an electronic assembly <NUM>. In accordance with one embodiment of the disclosure, an electronic assembly <NUM> comprises a semiconductor device <NUM> (<FIG>, <FIG> and <FIG>) that has conductive pads <NUM> on a semiconductor first side <NUM> and a metallic region <NUM> on a semiconductor second side <NUM> opposite the first side <NUM>. The semiconductor device <NUM> may comprise one or more power semiconductor devices. A lead frame <NUM> provides separate terminals (e.g., supplemental terminals <NUM>, and terminals <NUM>, <NUM>, <NUM>) that are electrically and mechanically connected (e.g., directly bonded) to corresponding conductive pads <NUM>.

A first heat sink <NUM> comprises a first component <NUM> (e.g., heat exchanger or passive heat sink) having a mating side <NUM> (e.g., substantially planar side) and an opposite side opposite the mating side <NUM>. A portion of the mating side <NUM> is directly bonded with the metallic region <NUM> of the semiconductor device <NUM>. A circuit board <NUM> (in <FIG> or <FIG>) has an opening <NUM> for receiving the semiconductor device (<NUM> or <NUM> in <FIG>). The lead frame <NUM> extends outward toward the circuit board <NUM> or a board first side <NUM> of the circuit board <NUM>. A board second side <NUM> of the circuit board <NUM> is opposite the board first side <NUM>. Board conductive pads <NUM> or metallic terminations of conductive traces <NUM> are on the board first side <NUM> of the circuit board <NUM> to align with the corresponding terminals (<NUM>, <NUM>, <NUM>, <NUM>) of the lead frame <NUM> for electrical connection therewith. In one illustrative configuration, the lead frame may be constructed of copper base or core that is plated with a metal or alloy interface layer (e.g., silver, gold or nickel, or alloys of any of the foregoing metals).

A second heat sink <NUM> comprises a first member (<NUM> or <NUM>) having a mating side <NUM> (e.g., substantially planar side) and an opposite side opposite from the mating side <NUM>. In certain embodiments, the mating side <NUM> is in thermal communication (e.g., via a dielectric layer or thermal interface material <NUM>) with at least a portion of the semiconductor first side <NUM> or at least an interfacing surface of the terminals (<NUM>, <NUM>, <NUM>), where the conductive pads (<NUM>, <NUM>) may be directly bonded to corresponding different ones of the device conductive pads <NUM>. Further, in one embodiment, both the auxiliary metallic region <NUM> and one or more device conductive pads <NUM> associated with an alternating current output of a semiconductor device <NUM> are bonded (e.g., soldered) or directly bonded to output terminal <NUM>. The conductive pads <NUM> and auxiliary metallic regions (<NUM>, <NUM>) are show in phantom or dashed lines in <FIG> because they are located below the terminals (<NUM>, <NUM>, <NUM>).

The lead frame <NUM> may be directly bonded to the device pads <NUM> and one or more available auxiliary metallic regions (<NUM>, <NUM>, if present) of the semiconductor device <NUM>. If the internal circuitry of the semiconductor device <NUM> affords the opportunity, multiple respective device pads <NUM> can be interconnected to a same corresponding terminal (<NUM>, <NUM>, <NUM>) to increase the current capacity of the semiconductor device <NUM> as illustrated in <FIG>. For example, in <FIG> among the terminals the output terminal <NUM> is connected to an output phase of an inverter and is directly bonded to at least two conductive pads <NUM> an auxiliary metallic region <NUM> on the semiconductor first side <NUM>, and auxiliary metallic region <NUM>, where the output terminal <NUM> has a surface area that covers or overlies a majority of the first side <NUM> of the semiconductor device <NUM> where the output terminal <NUM> has a greater surface area than a lesser aggregate surface area of the direct current terminals (<NUM>, <NUM>).

In various embodiments, as best illustrated in <FIG>, inclusive, the electronic assembly <NUM> comprises one or more semiconductor devices (<NUM>, <NUM>) Each semiconductor device (<NUM>, <NUM>) may comprise one or more insulated-gate, bipolar transistors (IGBT's); power field- effect transistors (FET); power switching diodes, integrated circuits chips, transistors with diodes coupled to the collector, emitter or both; or field effect transistors with diodes coupled to the source, drain or both. For example, the semiconductor device <NUM> may comprise at least two power switching transistors, alone or with associated protective diodes, that are configured to provide one phase of an inverter for outputting an alternating current signal or pulse width modulated (PWM) signal for controlling a motor, supporting a generator, or supporting another electric machine.

Each semiconductor device (<NUM>, <NUM>) may comprise one or more semiconductor dies (<NUM>, <NUM>) and a lead frame <NUM> (or substrate <NUM>), where the semiconductor dies are semiconductor materials that are fabricated to form one or more transistors, diodes or circuits. The semiconductor device <NUM> may be formed of a semiconductor die (<NUM>, <NUM>) such as a silicon carbide semiconductor die. The lead frame <NUM> provides separate terminals (<NUM>, <NUM>, <NUM>, <NUM>) that are electrically and mechanically distinct from each other. The terminals are connected to appropriate corresponding device conductive pads <NUM> on the semiconductor device <NUM> to access its internal circuitry. The lead frame <NUM> provides a group of separate direct current terminals (<NUM>, <NUM>) for direct current supply to the semiconductor devices (<NUM>, <NUM>) and an output terminal (<NUM>) for an alternating current output. In one embodiment, the first terminal <NUM> and the second terminal <NUM> comprise terminals of the direct current bus and the third terminal <NUM> comprises an alternating current output phase (e.g., coupled to the source and drain node of field effect transistor pairs of an inverter phase circuit or the collector and emitter of bipolar transistor pairs of an inverter phase circuit) for an inverter. However, in other embodiments, the functions of the terminals (<NUM>, <NUM>, <NUM>) can be different.

In one configuration as shown in <FIG> and <FIG>, the output terminal or third terminal <NUM> may be mechanically and electrically connected to (e.g., directly bonded to) one or more auxiliary metallic regions (<NUM>, <NUM>), where each auxiliary metallic region (<NUM>, <NUM>) represents an oversized conductive pad (in comparison to conductive pads <NUM>) on the semiconductor die (<NUM>, <NUM>) or package. Similarly, the first terminal <NUM> and the second terminal <NUM> may be mechanically and electrically connected to (e.g., directly bonded to) other corresponding metallic regions or oversized conductive pads (in comparison to conductive pads <NUM>).

In one embodiment, the lead frame <NUM> has supplemental terminals <NUM> for one or more of the following signals: control, biasing circuitry, protection circuits (e.g., diodes), sensor support, data communications, or other functions. The supplemental terminals <NUM> of the lead frame <NUM> extend outward from the package <NUM> of the semiconductor device <NUM>; the supplemental terminals <NUM> may be connected to corresponding device conductive pads <NUM> (in <FIG>). As shown in <FIG>, the semiconductor device <NUM> has device pads <NUM> around a periphery of the semiconductor device <NUM> and one or more metallic regions (<NUM>, <NUM>) only occupy a central region of the semiconductor device <NUM>.

One or more lead frames <NUM> can eliminate requirements for wire-bonds to the semiconductor die (<NUM>, <NUM>); can provide optimized parameters for electrical characteristics such as minimized values of stray inductance and stray capacitance offered by circuitry (e.g., of a phase of the power inverter). Elimination of bond-wires and replacing them with the lead frame <NUM> can reduce overall cost of the semiconductor device <NUM> of the electronic assembly <NUM> and can reduce premature failures caused by wire-bond fatigue, for example.

In an alternate embodiment, the terminal <NUM> may have an optional notch <NUM> in its interfacing surface to provide stress relief (e.g., for differences in thermal expansion of various materials) or to provide access for insertion of potting material (e.g., polymer, elastomer or plastic). The optional nature of optional notch <NUM> is indicated by the dashed lines in <FIG>. The optional notch <NUM> may be generally V-shaped or U-shaped, for example. In one embodiment, the notch <NUM> provides savings of metallic material and amply supports the output current that flow outwards to an outer portion of the third conductive terminal <NUM> (e.g., alternating current terminal) that is connected to conductive pad <NUM>. Regardless of whether the optional notch <NUM> is present or absent, electrical current doesn't need to flow or concentrate in the triangular region defined by the notch <NUM> to supply an outer portion of terminal <NUM> with adequate current. Therefore, if the metallic material is taken out (or chopped out) to create optional notch <NUM>, the notch <NUM> doesn't disrupt or impede current flow in the electronic device or inverter.

In one embodiment, the presence of notch <NUM> helps mitigate any coefficient-of-thermal-expansion (CTE) mismatch between one or more primary semiconductor dies (<NUM>,<NUM>) on left-side of <FIG> and one or more secondary semiconductor dies on the right-side of <FIG>, where the primary semiconductor dies or secondary semiconductor dies are active at different times and may have different duty cycles. Either the primary semiconductor dies (e.g., low-side semiconductor switches) or the secondary semiconductor dies (e.g., high-side semiconductor switches) supply current (e.g., alternating current inverter phase output signal) to the outer portion of terminal <NUM> and the conductive pad <NUM>. Typically, the primary semiconductor dies and the secondary semiconductor dies do not provide current to terminal <NUM> simultaneously. Therefore, if a primary semiconductor die or dies heats the left-side of the electronics device <NUM> because of a greater duty cycle, activity or other reasons, the right-side semiconductor die or dies may be closer to internal ambient temperature, or vice versa. During operation of the electronic assembly or inverter, a differential temperature between the primary semiconductor dies and secondary semiconductor dies that could otherwise lead to CTE-related issues are mitigated by the presence of notch <NUM>.

<FIG> is top plan view of the semiconductor device <NUM> and circuit board <NUM> of the electronic assembly <NUM> along reference line <NUM>-<NUM> in <FIG>. In <FIG> and <FIG>, first conductive strip <NUM> on a board first side <NUM> of the board <NUM> is connected to the first terminal <NUM> at conductive pad <NUM> and has a sufficient size (e.g., width and thickness of metal, alloy or metallic material, such as a heavy copper pour) to carry the required direct current supply demanded by each semiconductor device <NUM> at the corresponding operating voltage and to promote secondary heat dissipation from the first terminal <NUM>. The second conductive strip <NUM> on a board second side <NUM> of the board <NUM> is connected to the second terminal <NUM> at conductive pad <NUM> (e.g., through a conductive via or blind via) and has a sufficient size (e.g., width and thickness of metal, alloy or metallic material) to carry the required direct current supply demanded by each semiconductor device <NUM> at the corresponding operating voltage and to promote secondary heat dissipation from the second terminal <NUM>. A third conductive strip <NUM> lies on the board second side <NUM> and is connected to the third terminal <NUM> at conductive pad <NUM> (e.g., through one or more conductive vias or blind vias). In one embodiment, the third conductive strip <NUM> has a sufficient size (e.g., width and thickness of metal, alloy or metallic material) to carry the required alternating current output or pulse-width modulation signal (e.g., to control one phase of an electric motor) and to promote secondary heat dissipation from the third terminal <NUM>.

The first conductive strip <NUM> on a board first side <NUM> of the board <NUM> and the second conductive strip <NUM> on a board second side <NUM> of the board <NUM> overlap spatially (but separated by the dielectric layer of the board) to minimize loop inductance. Minimization of loop inductance caused by power traces on board <NUM> allows power semiconductor devices (<NUM>, <NUM>) to switch faster and reduce energy loss to due reduction in switching time. Reduction in energy loss helps increase inverter efficiency and results in fuel savings for hybrid vehicles that use fuel for an internal combustion engine. Reduction in loop inductance tends to reduce over-voltage across DC terminals (<NUM> and <NUM>) and at output AC terminal (<NUM>), which can increase life of power semiconductor devices (<NUM>) and longevity of insulation system of electric motor drive by inverter or electronic assembly <NUM>. Therefore, the proposed packaging concept results in an electronic assembly <NUM> or inverter system that offers energy/fuel savings and increased reliability of the electric drive system because of potential or actual reductions in the electrical stress, thermal stress, or both.

In one alternate embodiment, the first conductive strip <NUM>, the second conductive strip <NUM> and the third conductive strip <NUM> may be thermally connected the first heat sink <NUM>, the second heat sink <NUM>, or an outer enclosure or cover of the electronic assembly by using high-voltage dielectric and high-thermal conductivity TIM (thermal interface material).

A current sensor <NUM> is located on the board first side <NUM> above the third conductive strip <NUM> to sense the alternating output current carried by the conductive strip <NUM> or outputted by the semiconductor device <NUM> (e.g., for a single inverter phase at output terminal <NUM>). The current sensor <NUM> may be associated with ferrite members <NUM> on each side of the current sensor <NUM>. The current sensor <NUM> and the ferrite members <NUM> are surrounded by a metallic shield <NUM> to shield the current sensor <NUM> from electromagnetic interference or noise that might otherwise degrade the sensitivity or performance of the current sensor <NUM>. The metallic shield <NUM> may conform to the size and shape of the current sensor <NUM>, alone or together with the ferrite members <NUM>, above circuit board <NUM> with a generally uniform spatial gap between the metallic shield <NUM> and the current sensor <NUM> for mechanical clearance. For example, the metallic shield <NUM> may conform to the size and shape of the current sensor <NUM>, alone or in combination with ferrite member <NUM>, that is substantially polygonal with an opening in its bottom above strip <NUM>. The metallic shield may be formed of one or more sections of metal screen, metallic material, or fabricated sheet metal. In one configuration, the metallic shield <NUM> may be integral with, secured to, or molded with an housing member of an enclosure cover that covers at least a top portion of the electronic assembly.

The current sensor <NUM> and shield <NUM>, which can be incorporated integrally into an upper case or housing cover, is capable of shielding a surface-mount current sensor <NUM> to sense alternating current power output at output terminal <NUM>. The shielding eliminates noise and interaction among sensors for different phases making inverter operation free from noise that occurs when non-core (magnetic core) based sensors are placed over alternating current strip or bus bar.

In an alternate embodiment, the first conductive strip <NUM>, the second conductive strip <NUM>, and the third conductive strip <NUM> can be replaced by metal bus bars or laminated metal members (e.g., metal bus bars) with an intermediate dielectric layer.

<FIG> is cross sectional view of a first embodiment of the electronic assembly along reference line <NUM>-<NUM> in <FIG> and further including passive heat sinks (<NUM>, <NUM>) or heat exchangers. In <FIG> and <FIG>, the first member <NUM> (e.g., heat exchanger or passive heat sink) of the second heat sink <NUM> is electrically isolated from the lead frame <NUM> by a thermal interface material <NUM>, a dielectric layer, or a dielectric adhesive. In some configurations, the second heat sink <NUM> may be connected to vehicle or chassis ground. A thermal interface material <NUM> (TIM) sheet or layer is placed between top surface of lead frame <NUM> and second heat sink <NUM>. In one embodiment, the TIM layer <NUM> is composed of a dielectric material or sheet that is adhesively bonded to the lead frame <NUM>, the second heat sink <NUM> or both. The first member <NUM> of the second heat sink <NUM> is electrically isolated or insulated from one or more terminals (<NUM>, <NUM> and <NUM>, or at least terminal <NUM>) by the thermal interface material <NUM>.

In the first heat sink <NUM>, first protrusions <NUM> extend from the first base portion <NUM>, such as a metallic plate. In the second heat sink <NUM>, second protrusions <NUM> extent from the second base portion <NUM>, such as metallic plate. The first protrusions <NUM> and the second protrusions <NUM> are arranged to dissipate thermal energy or heat from the semiconductor device <NUM> on both sides (<NUM>, <NUM>) of the semiconductor device <NUM>.

In <FIG>, <FIG> and <FIG>, the first component <NUM> (e.g., heat exchanger or passive heat sink) of the first heat sink <NUM> may be bonded or directly bonded to the a metallic region <NUM> on the device second side <NUM> (e.g., bonding surface or bottom surface) of the semiconductor device <NUM> or die (<NUM>, <NUM>). For example, the direct bonding supports a low resistance to thermal conductivity from the semiconductor device <NUM> to the first component <NUM> or first heat sink <NUM>. The metallic region <NUM> may be formed of copper, silver, gold, nickel or an alloy, for example. Alternately, the metallic region <NUM> may have a silver, gold or nickel layer that overlies a copper core. Similarly, the mating side <NUM> first component <NUM> and the mating side <NUM> of the first member (<NUM> or <NUM>) may be plated with silver, gold, nickel, or any alloy of the foregoing metals or a combination of the foregoing metals to facilitate bonding with the first component <NUM> and the first member (<NUM> or <NUM>).

The first component <NUM> or first heat sink <NUM> may be directly bonded to the metallic region <NUM> on the semiconductor device <NUM> by direct copper-to-copper, thermo-compressive bonding or ultrasonic bonding to bond a metallic layer <NUM> on the device second side <NUM> (e.g., bottom) of semiconductor package <NUM> to the first heat sink <NUM>, or its first component <NUM>, another suitable technique of direct bonding, such as reactive or vapor-phase bonding. The metallic region <NUM> (e.g., copper metallization region) on a device second side <NUM> (e.g., bottom) of semiconductor device <NUM> could be at ground or floating potential. The metallic region <NUM> can dissipate or transfer heat from the semiconductor device <NUM> to the first component <NUM> or the first heat sink <NUM>. Similarly, the auxiliary metallic region <NUM> and pads <NUM> can dissipate or transfer heat from the semiconductor device <NUM> to the second member <NUM> of the second heat sink <NUM> or its first member <NUM>. The presence of both auxiliary metallic region <NUM> and one or more pads <NUM> for any corresponding terminal provides potentially greater heat dissipation and current carrying capacity of the terminal than for a terminal of smaller size and dimensions.

In one embodiment, the first member (<NUM>, <NUM>) is formed of a metallic material, an alloy or metal, for example. However, in certain embodiments, the first member <NUM> may be formed of a dielectric material, such as ceramic. In certain configurations, the second member <NUM> may be formed of plastic, polymer, or a fiber-filled plastic or polymer material.

<FIG> is cross sectional view of a second embodiment of the electronic assembly along reference line <NUM>-<NUM> in <FIG> and further including passive heat sinks. The electronic assembly of <FIG> is similar to the electronic assembly of <FIG>, except first member <NUM> of <FIG> replaces first member <NUM> of <FIG> and TIM <NUM> has a greater size, shape and surface area commensurate with that of the first member <NUM>. The first member <NUM> may overlie the terminals (<NUM>, <NUM>, <NUM>). In contrast, the first member <NUM> of <FIG> may be narrower in width and may only overlie the third terminal <NUM> (output terminal). The first member <NUM> of the second heat sink <NUM> is electrically isolated or insulated from terminals (<NUM>, <NUM> and <NUM>) by the thermal interface material <NUM>. In <FIG>, the first heat sink <NUM> is bonded or directly bonded to the metallic region <NUM>.

The configuration of <FIG> is similar to the configuration of <FIG>, except a thermally conductive adhesive <NUM> is used between the metallic region <NUM> (or the second surface <NUM>) and the first component <NUM> of the first heat sink <NUM>. The semiconductor device <NUM> and the first heat sink <NUM> may be directly bonded, bonded or connected by thermally conductive adhesive <NUM>. If thermally conductive adhesive is used, it is possible to omit the metallic region on the bottom of the semiconductor device <NUM> of <FIG> and extend the package <NUM> around the bottom of the semiconductor device <NUM>.

<FIG> is cross sectional view of a fourth embodiment of the electronic assembly outside the scope of the invention along reference line <NUM>-<NUM> in <FIG> and further including passive heat sinks. The electronic assembly of <FIG> is similar to the electronic assembly of <FIG>, except the thermal interface material <NUM> and the lead frame <NUM> are replaced by the substrate <NUM> with its conductive trace terminals (<NUM>, <NUM>) and its dielectric layer <NUM> (e.g., ceramic, polymer or composite). The conductive traces (<NUM>, <NUM>) of the substrate comprise an output terminal <NUM> that is analogous to output terminal <NUM> on the electronic assembly of <FIG>. For example, the output terminal <NUM> may represent the alternating current output of one phase of the inverter. The output terminal <NUM>, or its interfacing surface, is bonded (or directly bonded) to one or more conductive pads <NUM> of the semiconductor device <NUM> and an auxiliary metallic region <NUM> on the device first side <NUM>; the mating surface <NUM> of the output terminal <NUM> is electrically and mechanically connected to one or more conductive pads <NUM> on the circuit board <NUM>. Similarly, the terminal <NUM> is bonded (or directly bonded) to one or more conductive pads <NUM> of the semiconductor device <NUM>; the mating surface <NUM> is electrically and mechanically connected to one or more conductive pads on the circuit board <NUM>. The output terminal <NUM> is connected to a corresponding conductive strip <NUM> (e.g., on the circuit board <NUM>), where the conductive strip <NUM> has sufficient size to promote secondary heat dissipation from the output terminal <NUM>. In certain configurations, the output terminal <NUM> is connected to a corresponding metal strip (e.g., conductive strip <NUM>) on the circuit board for heat transfer from the output terminal <NUM> to the metal strip.

As shown in <FIG>, inclusive, the bottom, sides, or air gaps below the lead frame of the semiconductor device are encapsulated with plastic, polymer, resin, or plastic or polymer with a suitable filler material, which may be referred to as package <NUM>. Encapsulation of the semiconductor device reduces assembly pollution, increases dimensional stability in response to thermal or mechanical stress, and avoids arcing or flash-over when the semiconductor device is operating at high operational voltage (e.g., <NUM> Volts plus nominal, plus transient voltage spikes). The semiconductor devices (<NUM>, <NUM>) in <FIG> may be used in a passively cooled mode without forming or providing the coolant passages, chambers or interiors for circulating coolant within the complete electronic assemblies <NUM> of <FIG>, <FIG>.

The electronic assembly <NUM> (or its semiconductor device <NUM>, <NUM>) of this disclosure allows thermal energy to be conducted efficiently away from the semiconductor device <NUM> to the first heat sink <NUM> (or its first component <NUM>), the second heat sink <NUM> (or its first member <NUM> or <NUM>), or both through one or more thermal pathways of the electronic assembly. In a first example, a first thermal pathway represents a thermally conductive path from the die (<NUM>, <NUM>) via a metallic region <NUM> that is bonded or directly bonded to the first heat sink <NUM>. In a second example, the first thermal pathway represents a thermally conductive path from the die (<NUM>, <NUM>) via a metallic region <NUM> (or package <NUM>) that thermally communicates with the first heat sink <NUM> through a thermal interface material <NUM> or thermally conductive adhesive. In a third example, a second thermal pathway represents a thermally conductive path from the die (<NUM>, <NUM>) via one or more device conductive pads <NUM> and one or more metallic regions (<NUM>, <NUM>) to the output terminal <NUM> (oversized alternating current terminal) that: (a) is connected (e.g., bonded or directly bonded) to conductive traces (e.g., strip <NUM> or heavy copper pours) of appropriate size for current and power of the output alternating current, and (b) thermally communicates to the second heat sink <NUM> (or its first member <NUM>, <NUM>) via a thermal interface material <NUM> or dielectric layer. For example, the thermal interface material <NUM> may be selected to have a certain minimum thermal conductivity or a target range of thermal conductivity. In one embodiment, the first thermal pathway and the second thermal pathway promote adequate heat dissipation for the semiconductor device <NUM> to work at a target power capacity rating at a desired duty cycle or continuous duty cycle.

Referring to <FIG>, <FIG>, the electronic assembly <NUM> comprises a first heat sink <NUM>, a second heat sink <NUM>, or both. A passively cooled heat sink may transfer, remove or conduct heat or thermal energy away from one or more semiconductor devices <NUM> to ambient air. An actively cooled heat sink may use a coolant or liquid to transfer heat or thermal energy from one or more semiconductor devices <NUM> by circulating coolant via a pump (e.g., pump <NUM> in <FIG>) to a radiator (e.g., radiator <NUM> in <FIG>) , or by circulating air via a fan, for example. In certain embodiments, as illustrated in <FIG>, the first heat sink <NUM> or the second heat sink <NUM> can comprise a passively cooled heat sink (e.g., cold plate). However, if the first heat sink <NUM> is used in conjunction with additional components of <FIG>, inclusive, and <FIG> and <FIG>, the first heat sink <NUM> may operate as an actively cooled heat sink. Similarly, if the second heat sink <NUM> is used in conjunction with additional components of <FIG>, inclusive, and <FIG> and <FIG>, the second heat sink <NUM> may operate as an actively cooled heat sink. If operated as an active heat sink, the second heat sink <NUM> and the first heat sink <NUM> may each comprise an enclosure for receiving a liquid coolant.

Throughout this document, a heat sink may refer to one or more of the following: a first heat sink <NUM>, the second heat sink <NUM>; a portion of the first heat sink <NUM>, such as the second component <NUM>; and a portion of the second heat sink <NUM>, such as the second member <NUM>. The heat sink may comprise a passive or active: first heat sink, second heat sink, or both. A passive heat sink may be cooled by ambient air, whereas the active heat sink may be cooled by coolant that is circulated or circulated air, for example.

In one embodiment, first heat sink <NUM> comprises a first component <NUM> and a second component <NUM> with a recess <NUM>. The first component <NUM> and the second component <NUM> mate to form an interior volume <NUM>, which is defined partially by the recess <NUM>. A seal <NUM> (e.g., gasket, sealant, or seal, such as illustrated in <FIG>) may intervene between the first component <NUM> and the second component <NUM> to provide a hermetic or liquid-tight seal such that coolant or liquid in the interior chamber <NUM> does not leak or escape into an outside or ambient environment. In one embodiment, a plate <NUM> with a slot or aperture <NUM> may be disposed between the first component <NUM> and the second component to reduce the hydraulic pressure or forces that would otherwise be exerted (e.g., upward against the first component <NUM> from the coolant to prevent the first base <NUM> from deforming, bulging or bending). In certain configurations, the second component <NUM> may be formed of plastic, polymer, or a fiber-filled plastic or polymer material.

In one embodiment, the first component <NUM> of the first heat sink <NUM> comprises a lid or first base <NUM> with first protrusions <NUM> (e.g., thermal dissipation members) extending from one end. First protrusions <NUM> may refer to fins, ridges, pins, elevated islands, or protrusions for heat dissipation. First protrusions <NUM> comprise thermal dissipation members that can populate the interior volume <NUM> and that are generally spaced apart from each other. The first protrusions <NUM> extend from the first base portion <NUM>, such as a metallic plate. In certain configurations, the base portion <NUM> may comprise a generally planar member of a generally uniform thickness. If coolant or liquid is circulated within the interior volume <NUM>, the first protrusions <NUM> facilitate heat transfer from the semiconductor devices <NUM> to the circulated coolant for removal via a radiator (e.g., <NUM> in <FIG>) or heat exchanger to ambient air or otherwise.

The first heat sink <NUM> features at least two ports <NUM>: an inlet and an outlet for a first heat sink <NUM>. The ports <NUM> are arranged for communication with the interior volume <NUM> to circulate a liquid coolant within the interior volume <NUM> of the first heat sink <NUM>. Each port <NUM> may be associated with a corresponding connector <NUM> to allow conduit or tubes to be attached thereto for connection to a pump, radiator, or both to circulate the coolant within the interior volume <NUM> and to remove thermal energy from the coolant to ambient air via the radiator.

In one embodiment, the second heat sink <NUM> further comprises a second member <NUM> that mates with the first member <NUM> to form an interior chamber <NUM>. For example, the second heat sink <NUM> may comprise a first member <NUM> (e.g., first housing member) that mates with a second member <NUM> (e.g., second housing member) to form the interior chamber <NUM>. A seal <NUM> (e.g., gasket, sealant, or seal, such as that illustrated in <FIG>) may intervene between the first member <NUM> and the second member <NUM> to provide a hermetic or liquid-tight seal such that coolant or liquid in the interior chamber <NUM> does not leak or escape into an outside or ambient environment.

One side of the first member <NUM> (e.g., heat sink or heat exchanger) comprises second protrusions <NUM> for heat dissipation. Second protrusions <NUM> may refer to fins, ridges, pins, elevated islands, or protrusions for heat dissipation. The first member <NUM> comprises the combination of the first base <NUM> and the second protrusions <NUM>. The first member <NUM> can be used as a passive heat sink in the absence of the second member <NUM>.

In one embodiment, in the second heat sink <NUM> second protrusions <NUM> or other thermal dissipation members populate the interior chamber <NUM> and are generally spaced apart from each other. The second protrusions <NUM> extend from a first base <NUM>. In certain configurations, the first base <NUM> may comprise a generally planar member of a generally uniform thickness. If coolant or liquid is circulated within the interior chamber <NUM>, the second protrusions <NUM> facilitate heat transfer from the semiconductor devices <NUM> to the circulated coolant for removal via a radiator (e.g., <NUM> in <FIG>) or heat exchanger to ambient air or otherwise. The second heat sink <NUM> features at least two ports <NUM>: an inlet and an outlet for a second heat sink <NUM>.

The ports <NUM> of the second heat sink <NUM> are arranged for communication with the interior chamber <NUM> to circulate a liquid coolant within the interior chamber <NUM> of the second heat sink <NUM>.

<FIG> is cross sectional view of the electronic assembly along reference line <NUM>-<NUM> in <FIG>. <FIG> is cross sectional view of the electronic assembly along reference line <NUM>-<NUM> in <FIG>. Like reference numbers in <FIG> and <FIG> indicate like elements. <FIG> illustrate the electronic assembly <NUM> after it is assembled. In one configuration, the electronic assembly <NUM> may be assembled as follows.

First, a semiconductor devices <NUM> is directly bonded to one or more cold plates or heat exchangers, such as first component <NUM> or the first heat sink <NUM> to form a chip assembly.

Second, the second sink <NUM> (or its first member <NUM> or <NUM>), or both through one or more thermal pathways of the electronic assembly. In a first example, a first thermal pathway represents a thermally conductive path from the die (<NUM>, <NUM>) via a metallic region <NUM> that is directly bonded to the first heat sink <NUM> or that is bonded with a thermally conductive adhesive.

Third, the chip assembly can be placed through an appropriately sized opening <NUM> in the circuit board <NUM>. A circuit board <NUM> has an opening <NUM> for receiving the semiconductor device <NUM>. The lead frame <NUM> extends at or outward toward a board first side <NUM> of the circuit board <NUM>. A board second side <NUM> of the circuit board <NUM> is opposite the first side <NUM>. Board conductive pads (<NUM>, <NUM>) are on the board first side <NUM> of the circuit board <NUM> to align with the corresponding terminals (<NUM>, <NUM>, <NUM>, <NUM>) of the lead frame <NUM> for electrical connection and mechanical connection with the corresponding terminals. In certain fabrication techniques, the opening <NUM> in the circuit board <NUM> allows after-treatment of power circuit to meet creepage, clearance and high voltage insulation requirements between semiconductor devices <NUM> and cold-plate. Exposure of chip assembly via the opening <NUM> in the circuit board <NUM> can lower manufacturing cost or simplify manufacturing processes because the washing and cleaning processes, which are needed to eliminate residue left-over from lead-frame application, are easier, simpler; in some circumstances can be eliminated.

Fourth, the second component <NUM> is joined or secured to the first component <NUM> to form the first heat sink <NUM> with an interior volume <NUM> for pumped fluid to circulate.

Fifth, the second member <NUM> is joined or secured to the first member (<NUM> or <NUM>) to form the second heat sink <NUM> with an interior chamber <NUM> for pumped fluid to circulate.

<FIG> provides an example of how the electronic assembly <NUM> is incorporated into a hybrid vehicle with an internal combination engine and one or more drive motors <NUM>. In <FIG>, the electronics assembly <NUM> uses active cooling. The electronic assembly <NUM> has an electrical transmission line <NUM> connected to the input of an motor <NUM>, such as electric drive motor <NUM> to propel a vehicle. In one example, the electronic assembly <NUM> receives direct current supply from a generator <NUM> or energy storage device (e.g., battery) via one or more electrical transmission lines <NUM>. The generator <NUM> may be mechanically driven or rotated by a shaft (e.g., directly or indirectly the crankshaft) of the internal combustion engine <NUM>.

The internal combustion engine <NUM> may also provide mechanical, rotational energy or electrical energy to a pump <NUM> that circulates coolant to one or more inlet ports <NUM> of the electronic assembly <NUM> and from one or more outlet ports <NUM> of the electronic assembly <NUM>. The coolant is also circulated between the inlet <NUM> and outlet <NUM> of the engine water jacket (e.g., block or head) of the internal combustion engine <NUM>. In one illustrative configuration, the output port <NUM> of the electronic assembly <NUM> and the outlet <NUM> of the engine water jacket are coupled via conduit <NUM> to a thermostatic valve <NUM> and cold temperature bypass line <NUM>. The thermostatic valve <NUM> opens at preset temperature or preset temperature range to bring the radiator <NUM> into the cooling circuit. Prior to opening of the thermostatic valve <NUM>, the coolant is routed through the cold temperature bypass line <NUM> back to the input <NUM> of the pump <NUM> to bypass the radiator <NUM>. After the thermostatic value opens at a preset temperature, one or more outlet ports <NUM> of the electronic assembly <NUM> are coupled (directly or indirectly) to a radiator inlet <NUM> of a radiator <NUM> via conduit <NUM>; similarly, the outlet <NUM> of the engine water jacket is coupled via conduit <NUM> to the radiator <NUM>. The radiator <NUM> has an outlet <NUM> that is coupled to the pump input <NUM> of the pump <NUM>. The radiator <NUM> may be cooled by fan <NUM> (e.g., electric fan <NUM>), where the fan <NUM> is powered by a direct current bus via one or more transmission lines <NUM>.

The electronic assembly supports either a separate coolant system from an internal combustion engine coolant loop or using the same coolant system of the internal combustion engine. For a separate coolant system, the maximum inlet temperature can be set to lesser maximum temperature (e.g., <NUM> degrees Celsius), whereas for the shared coolant system with the internal combustion engine the coolant temperature can be set to a greater maximum temperature (e.g., <NUM> degrees Celsius). The maximum temperature can be controlled via a thermostatic valve that opens to radiator and an associated fan, for example.

The electronic assembly of this disclosure does not require: (<NUM>) a direct bond copper (DBC) connection of a semiconductor device to a separate intervening copper base plate with an adjacent, distinct heat sink mounted to contact the separate base plate with thermally conductive grease, or (<NUM>) a direct bond copper connection of terminals of the semiconductor devices <NUM> to the conductive traces or pads of the circuit board. Here in one embodiment of this disclosure, the semiconductor devices <NUM> (e.g., semiconductor chipsets) are directly bonded on one or more cold-plates (heat-exchangers), including the first heat sink <NUM>, or its first component <NUM>, without any of use and inefficiency of thermally conductive grease; the terminals of the semiconductor device <NUM> can be connected to corresponding conductive pads or traces on the circuit board via direct bonding or via a conductive adhesive, soldering, brazing, or welding. Directly bonding of semiconductor devices <NUM> with one or more cold-plates without any need of DBC, base plate, and thermal grease can significantly reduce thermal resistance between silicon junctions within the semiconductor device <NUM> and coolant channels, interior, or chambers of the first heat sink <NUM>, for instance.

The electronic assembly of this disclosure is well-suited for double-sided thermal management of the electronic assembly, such as an inverter. Double-sided thermal management has the potential to significantly reduce the thermal resistance for semiconductor devices, capacitors, power devices and components. Further, the electronic assembly facilitates active, thermal management, such as active, single-sided thermal management or double-sided thermal management of the electronic assembly.

The electronic assembly of this disclosure supports a reduced size, weight and cost of inverter because it supports surface-mount manufacturing processes and a generally planar packaging configuration that make the circuit boards amenable to mass, cost effective production.

Claim 1:
An electronic assembly (<NUM>) comprising:
a semiconductor device (<NUM>) having conductive pads (<NUM>) on a device first side (<NUM>), a metallic region (<NUM>) on a device second side (<NUM>) opposite the first side (<NUM>), and a metallic region comprising a metallic central region (<NUM>) on the device first side. (<NUM>);
a lead frame (<NUM>) for providing separate terminals (<NUM>, <NUM>, <NUM>, <NUM>) that are electrically and mechanically connected to the conductive pads (<NUM>);
a first heat sink (<NUM>) comprising a first component (<NUM>) having a mating side (<NUM>), a portion of the mating side (<NUM>) directly bonded with the metallic region (<NUM>) of the semiconductor device (<NUM>) and having an opposite side opposite the mating side (<NUM>); and
a circuit board (<NUM>) having an opening (<NUM>), the semiconductor device (<NUM>) and the lead frame (<NUM>) extending at or outward toward a board first side (<NUM>) of the circuit board (<NUM>), a board second side (<NUM>) of the circuit board (<NUM>) opposite the first side (<NUM>), a plurality of board conductive pads (<NUM>) being on the board first side (<NUM>) of the circuit board (<NUM>) to align with the corresponding terminals (<NUM>, <NUM>, <NUM>, <NUM>) of the lead frame (<NUM>) for electrical connection therewith.