Patent Description:
Power modules employ transistors to output stable and reliable power for a variety of applications including use in aircraft and similar high-performance systems. Further, the operation of power modules can produce a sizable amount of heat that, if not properly managed, can damage the power module and/or produce unreliable operating conditions and power output. As such, control circuity is often employed to consider temperature when operating the power module.

<CIT> discloses a power module having a conductive layer for electrically connecting a plurality of power transistors. <CIT> discloses a power transistor comprising a temperature sensor which is mounted on a lead frame. <CIT> discloses a power transistor comprising a platinum RTD directly on the die.

Various needs are at least partially met through provision of the accurate and fast assessment or measurement of various properties of power modules described in the following detailed description, particularly when studied in conjunction with the drawings. A full and enabling disclosure of the aspects of the present description, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which refers to the appended figures, in which:.

For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present teachings. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present teachings. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required.

Typical power modules are constructed from a plurality of transistors with a plurality of surface wire bonds on a die surface for interconnecting the transistors and control circuitry together. As such, these modules do not provide an area for direct temperature sensing on the die surface. Rather, the modules employ alternative temperature sensing from printed circuit board (PCB) control circuitry, including indirect methods such as measuring a body diode, expensive optical method, or the like. The lack of a simple direct temperature measurement method increases operational costs and limits reliability and safety.

Generally speaking, the various aspects of the present disclosure can be employed with a power module comprising one or more power transistors and a conductive overlay for each of the one or more power transistors to provide a direct mounting surface for sensors such as a temperature sensor that can provide a direct temperature measurement for the one or more power transistors. The conductive overlay can include a well-defined metallic and stable surface that is directly connected to the power transistor die surface with short-distance metal connections. The additional surface of the conductive overlay makes it is possible to position a temperature sensor on top to provide fast and accurate sensing capability to improve reliability of module operation. This sensor can be easily wired to a PCB controller and data from the sensor can be provided to a gate board to provide for reliable module operation. The direct temperature measurement can result in increased reliability and safety when operating power modules.

The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein. The word "or" when used herein shall be interpreted as having a disjunctive construction rather than a conjunctive construction unless otherwise specifically indicated.

Accordingly, a value modified by a term or terms such as "about", "approximately", and "substantially", are not to be limited to the precise value specified.

The foregoing and other benefits may become clearer upon making a thorough review and study of the following detailed description. Referring now to the drawings, and in particular to <FIG>, a power module <NUM> is presented. The power module <NUM> includes conductive overlays <NUM> having temperature sensors <NUM> adhered or bonded to a top surface thereof. In some embodiments, the conductive overlays <NUM> can include a copper or other conductive material power overlay (POL) sufficient to provide a coupling surface for the temperature sensors <NUM>. Such a POL configuration can provide a planar interconnection region where various system inputs and outputs and external devices can interface with one or more power transistors <NUM> (see <FIG>). Examples of a POL that may form the conductive overlays <NUM> described herein are provided in <CIT>. However, it will be appreciated that the embodiments described herein are also applicable with respect to alternative planar interconnect technologies such as copper clips, multilayer organic PCB, etc. and also flip chip and chip-in-polymer technologies.

Turning now to <FIG>, a partial cross-section view of the power module <NUM> is shown. The power module <NUM> can further include heat conductive epoxy <NUM> for bonding the temperature sensors <NUM> to the conductive overlays <NUM>. The heat conductive epoxy <NUM> can serve as a heat transfer medium between the top surface of the conductive overlays <NUM> and the temperature sensors <NUM> so that the temperature sensors <NUM> get consistent and accurate readings therefrom. The temperature sensors <NUM> can be attached with the heat conductive epoxy <NUM> on the wide, well defined, metallic, and stable surface of the conductive overlays <NUM>. Further, the position of the temperature sensors <NUM> can correspond to the highest temperature locations on the conductive overlays <NUM>. In some embodiments, the highest temperature locations can be identified by modeling operation of the power module <NUM>. In some embodiments, the temperature sensors <NUM> can be attached to the conductive overlays <NUM> over a central one of the one or more power transistors <NUM>, which modeling and testing indicates as the hottest location for the power module <NUM>. However, it will be appreciated that other locations are also contemplated and in some embodiments multiple temperature sensors may be positioned in close proximity to the same general location.

The temperature sensors <NUM> can include thermocouples and/or a resistance temperature detector having a non-conductive housing.

The one or more power transistors <NUM> have respective die surfaces over which the conductive overlays <NUM> are positioned. The power transistors <NUM> can include Silicon-carbide (SiC) MOSFETs or similar power transistors known in the art.

A non-conductive layer <NUM> and an adhesive layer <NUM> can be positioned between the conductive overlays <NUM> and the one or more power transistors <NUM>. The non-conductive layer <NUM> can act as a dielectric layer between the respective die surfaces of the power transistors <NUM> and the conductive overlays <NUM>. The non-conductive layer <NUM> can include Kapton or other similar material.

Further, the conductive overlays <NUM> can include vias <NUM> that electrically couple the conductive overlays <NUM> to the one or more power transistors <NUM>. In these embodiments, the vias <NUM> can pass through the non-conductive layer <NUM> and the adhesive layer <NUM> to provide a direct metallic connection between the conductive overlays <NUM> and the one or more power transistors <NUM>. Additionally or alternatively, in some embodiments, one or more sintered layers can be utilized to interconnect the conductive overlays <NUM> to the surfaces of the one or more power transistors.

Turning now to <FIG>, another schematic view of the power module <NUM> is shown. As seen in <FIG>, in some embodiments, the power module <NUM> can include additional sensors coupled to the conductive overlays <NUM>. The additional sensors can include a plurality of current sensors <NUM> that are physically bonded and electrically coupled to the conductive overlays <NUM> to measure current flow between two of the one or more power transistors <NUM> or other elements of the power module <NUM>.

As seen in the additional partial cross-section view of the power module <NUM> of <FIG>, the current sensors <NUM> can be bonded to the conductive overlays <NUM> with solder <NUM> and can bridge over gaps between sections of the conductive overlays <NUM>. The current sensors <NUM> can include current sensing shunts that are attached to the conductive overlays <NUM> during an assembly process for the power module <NUM>. The current sensors <NUM> can be positioned between other current or temperature sensors or between top copper sections of the conductive overlays <NUM> to provide for a local current value.

In some embodiments, the conductive overlays <NUM> are displaced a distance from the respective die surface of each of the plurality of transistors <NUM> such that the temperature sensors <NUM> and/or the plurality of current sensors <NUM> coupled to the top surface of the conductive overlays <NUM> are also displaced from the respective die surface of each of the plurality of transistors <NUM> by the distance. The vias <NUM> can bridge the distance to electrically couple the conductive overlay <NUM> to each of the one or more power transistors <NUM>.

The distance between the top surface of the conductive overlays <NUM> to which the temperature sensors <NUM> and solder current sensors <NUM> are coupled and the top surface of the power transistors <NUM> can be approximately <NUM>, where <NUM> of the distance results from a thickness of the conductive overlays <NUM> and <NUM> of the distance results from a thickness of the vias <NUM>. The short distance between the top surface of the power transistors <NUM> and the top surface of the conductive overlays <NUM> to which the temperature sensors <NUM> are coupled can increase the accuracy of temperature measurement as compared to other indirect temperature measurement methods. In particular the close distance helps to ensure that the temperature reading closely corresponds to the actual temperature of the top surface of the power transistors <NUM> because the distance limits dissipation of heat before it is read by the temperature sensors <NUM> and/or limits the influence of other heat sources on the temperature value read by the temperature sensors <NUM>.

Turning now to <FIG> another schematic of the power module <NUM> is shown. As seen in <FIG>, the temperature sensors <NUM> and the plurality of current sensors <NUM> can be electrically coupled to control circuit <NUM> via wires and solder <NUM> and <NUM> respectively.

As seen in <FIG>, the control circuit <NUM> can include a printed circuit board that can rest within a housing that contains the rest of the power module <NUM>. The control circuit <NUM> can pass signals to a gate board that is connected to the control circuit <NUM> to assist in controlling operation of the one or more power transistors <NUM>.

It will be appreciated that although the embodiments of the power module <NUM> shown in <FIG> depict two conductive overlays <NUM> coupled to two groups or sets of the one or more power transistors <NUM>, embodiments with more and fewer conductive overlays <NUM> are contemplated.

Turning now to <FIG>, the embodiments described herein are also directed to a method <NUM> of controlling the power module <NUM> using the control circuit <NUM>. According to a step <NUM> of the method <NUM>, the temperature sensors <NUM> directly measure a surface temperature of the conductive overlays <NUM> and/or the current sensors <NUM> measure current flow. According to a step <NUM> of the method <NUM>, the control circuit <NUM> modulates operation of the one or more power transistors <NUM>, which are electrically coupled to the control circuit <NUM>.

Modulating the operation of the power transistors <NUM> can be based on one or more of the direct measurement of the surface temperature with the temperature sensors <NUM> and the measurement of current flow from the plurality of current sensors <NUM>. Further, modulating the operation of the power transistors <NUM> can include stopping operation of one, more, or all of the one or more power transistors <NUM> when the direct temperature measurement and or the current measurements exceed preconfigured threshold values. Further, modulating the operation of the power transistors <NUM> can include limiting operation of one, more, or all of the one or more power transistors <NUM> when the direct temperature measurement and or the current measurements exceed additionally preconfigured threshold values. Limiting the operation can include shutting down only some of the one or more power transistors <NUM> and/or changing operating parameters such as switching frequency, power input or the like such that the temperature and or current measurement values will be reduced to levels consistent with normal safe operation of the power module <NUM>.

Claim 1:
A power module (<NUM>) comprising:
one or more power transistors (<NUM>) each having a respective die surface;
a conductive overlay (<NUM>) electrically coupled to each of the one or more power transistors (<NUM>) over the respective die surface thereof; and characterised in that the power module further comprises
a temperature sensor physically bonded to a top surface of the conductive overlay (<NUM>) to provide a direct temperature measurement for the one or more power transistors (<NUM>).