Semiconductor assembly, electric power device and method of manufacturing

The present disclosure relates to assemblies allowing load current sensing, e.g. for chip-scale packages, e.g. for chip- scale packages including power semiconductors, and to corresponding electric devices.

It is desired to know a load current or phase current of an electric device, e.g. of a power converter, e.g. to realize a closed loop control of the power conversion functionality.

In conventional inverters, e.g. for automotive use, and other applications, Hall-effect-sensors are used. The sensors are mounted around the phase outputs and are a limiting factor in cost and construction volume.

It is further possible to replace Hall sensors with power module on-board shunt resistors. However, shunt resistors have high ohmic losses involved when generating a sensor output in the Volt range required for further signal processing .

Another approach is based on integrating a current mirror on- chip. However, sacrificing a fraction of the active area for installing a parallel path for current sensing increases on- state resistance and reduces bond pad area on the topside. In addition, when considering SiC (silicon carbide) devices with very expensive chip area, the on-chip solution becomes expensive . From EP 3012846 A1 printed circuit boards with an inductance element are known. From US 2017/271260 A1 semiconductor assemblies including a semiconductor chip and a passive circuit element are known. From US 2001/023530 A1 inductive elements consisting of a plurality of interconnected conducted segments integrated in a substrate are known. From US 2003/013264 A1 inductors for sensing a magnetic flux are known. From US 2015/028487 A1 semiconductor elements and sensing coils are known.

Thus, embodiments of the disclosure relate to the possibility to sense a load current or phase current of an electric device, e.g. of a power converter. It would be beneficial if a closed loop control of a power conversion functionality could be realized in a simple and efficient manner with such a sensing. Further, the solution may be compatible with power modules. Further, the solution may require minimum costs and space. Also, the solution may be with a small capacitive coupling and allow low or no common-mode distortions, e.g. when sensing fast switching devices.

To that end, a semiconductor assembly and an electric device according to the independent claims are provided. Dependent claims provide preferred embodiments.

The semiconductor assembly comprises a body with a bottom side and a top side and a vertical extension from the bottom side and the top side. Further, the semiconductor assembly comprises a semiconductor element arranged in the body and a sensing coil arranged in the body. The sensing coil has at least one winding. The sensing coil is provided and adapted such that a magnetic flux associated with an electric current propagating along a current path in a vertical direction causes a detectable voltage in the sensing coil.

Such a semiconductor assembly allows - via its sensing coil, e.g. when directly integrated in the body, via and surrounding the current path associated with the semiconductor element - sensing a load current or phase current of the semiconductor element, e.g. to realize a closed loop control without the need for cost intensive and area and volume consuming further elements such as hall sensors or other external circuitry. Such a semiconductor assembly allows generating a sensor output in the Volt range required for further signal processing. Further, the semiconductor assembly can be realized in a simple and efficient manner involving essentially no further costs or space consumption. Further, the semiconductor assembly is compatible with power applications. Further, the semiconductor assembly allows for a small capacitive coupling and a substantial reduction of common-mode distortions making it a suitable for fast switching devices.

In the semiconductor assembly the at least one winding can be arranged in a plane parallel to the vertical direction.

The semiconductor assembly according can be a chip-scale package or a chip-scale-like package.

In this respect, a chip-scale package is a package with a single semiconductor chip and where the footprint or volume of the package may not be larger than 200 percent of the footprint or volume of the chip. It is also possible that the package may not be larger than 150% or even 120% of the footprint or volume of the chip. Correspondingly, the semiconductor assembly can further comprise one or more additional semiconductor elements in the form of the semiconductor element such that the semiconductor assembly is a multi-chip chip-scale-like package or a multi chip module.

In this respect, a multi-chip module is a module comprising the semiconductor element and one or more additional chips or elements such as an additional semiconductor element. The one or more additional chips or elements can be directly or monolithically integrated in the body of the semiconductor assembly.

Correspondingly, a multi-chip chip-scale-like package is a multi-chip module where the footprint or volume of the package may not be larger than 200 percent of sum of the footprints or volumes of the individual chips or elements. It is also possible that the package may not be larger than 150% or even 120% of the footprint or volume of the chip.

In the semiconductor assembly the semiconductor element and the at least one winding can be directly integrated in a dielectric material.

In the semiconductor assembly the dielectric material can comprise one or two or more segments or layers, each segment or layer comprising or consisting of a material or a combination of materials selected from a PCB material, a mold material, a thermoplastic material, epoxy resin, FR-2, phenolic paper, phenolic cotton paper, paper impregnated with a phenol formaldehyde resin, FR-4, a woven fiberglass cloth impregnated with an epoxy resin, a polyimide, a polyimide- fluoropolymer, a polyimide-fluoropolymer composite, FR-1, FR- 3, FR-5, woven fiberglass, high strength at higher temperatures, FR-6, G-10, G-ll, CEM-1, CEM-2, CEM-3, CEM-4, CEM-5, PTFE, RF-35, a ceramic, Alumina.

In this respect, a layer has - except structured metallizations, vias and circuit elements - body material essentially homogeneous over the lateral area of the semiconductor assembly. Segments of different body material can be arranged one next to another in a given vertical height of the body. Thus, the body can comprise different layers to fully enclose and directly integrate the semiconductor chip in the body. Between different layers structured metallizations for redistributing power or signals can be arranged. Within the layers vias can be arranged to electrically connect the semiconductor element, the structured metallizations and contacts for connecting the semiconductor assembly to an external circuit environment.

The semiconductor assembly can comprise one or more further sensing coils in form of the sensing coil. The one or more further sensing coils can be provided and adapted such that a magnetic flux associated with a time varying electric current propagating in the vertical direction causes a detectable voltage in the one or more further sensing coils.

When more than one sensing coil is present then the one or more sensing coils can be electrically connected in series to increase the induced voltage to improve the signal-to-noise ratio.

In the body of the semiconductor assembly the sensing coil can comprise lateral metallization structures and vertical vias. In the semiconductor assembly the vertical vias can electrically connect lateral metallization structures such that one, two or more segments or layers of the dielectric material are arranged between the lateral metallization structures .

In the semiconductor assembly the sensing coil can be a helical coil arranged along a path laterally surrounding the current path.

The semiconductor assembly can further comprise a compensation coil with a compensating winding for each winding of the sensing coil. The compensating coil can be provided and adapted to compensate a common mode distortion of the sensing coil.

The sensing coil and the compensation coil can establish a differential sensing structure.

The semiconductor assembly can further comprise a second current path in the negative vertical direction -z and an auxiliary coil adapted and provided such that a magnetic flux associated with an electric current propagating along the second current path in the negative vertical direction causes a detectable voltage in the auxiliary coil.

In the semiconductor assembly the current path in the vertical direction can comprise sections electrically connected in parallel.

In the semiconductor assembly the semiconductor element can be a semiconductor for power electronics applications. In the semiconductor assembly the semiconductor element can be a bipolar transistor, e.g., an IGBT (insulated gate bipolar transistor), or a field-effect transistor (FET) such as a low on-resistance silicon carbide MOSFET (Metal Oxide Semiconductor-FET ) or a MISFET (Metal Insulating Semiconductor-FET), exemplarily with low on-resistance.

The semiconductor assembly can further comprise contacts provided and adapted for a connection to an external circuit environment. The contacts can be distributed over the top side and the bottom side of the semiconductor assembly. Or the contacts can be arranged at the top side of the semiconductor assembly. Or the contacts arranged at the bottom side of the semiconductor assembly.

A corresponding electric power device can comprise such a semiconductor assembly as described above. The device can be applied in power electronics converters. An example may be an automotive traction inverter.

The electric power device can further comprise an integrating circuit coupled to the sensing coil. The voltage sensed by the sensing coil can be proportional to the temporal derivation of the current propagating along the current path. Thus, an integration of the sensed voltage over time can yield a signal proportional to the load current.

The electric power device or its semiconductor assembly can exemplarily be used for phase current sensing, fault current detection, static current imbalance assessment, dynamic current imbalance assessment, current control and/or current monitoring . The sensing coil can surround the current propagation path in the horizontal x-y-plane.

Then, the induced voltage can be calculated according to equation (1):

(t)=- (ANm ₀ /\)*dl(t)/dt, (1)

V(t) is the sensed voltage signal of the sensing coil, A is the winding area, N is the number of windings, 1 is the length of the coil, and dl/dt(t) is the current transient inside the coil.

As an example, an output voltage of 1.26 V can be obtained for 40 loops of a rectangular cross section of 1.0 x 0.1 mm ² with 1 mm distance with a coil length of 4 cm and a switching transient of dl/dt = 10 A/ns. Reducing the distance between windings to 0.1 mm (i.e. stacking the windings with a higher density) would result into 400 loops and an output voltage of 12.6 V.

A method of manufacturing a corresponding semiconductor assembly can comprise the steps of

- providing a semiconductor element,

- embedding the semiconductor element in one or more layers of dielectric material.

The method can further comprise steps for creating first lateral and vertical structured metallizations, e.g. for redistributing power and/or signals. And the method can comprise creating lateral and vertical structured metallizations to establish windings of a sensing coil. For the creation of the structured metallizations of the sensing coil and for the creation of other structured metallizations the same steps, processes and materials can be used.

The accompanying figures are included to provide a further understanding. In the figures, elements of the same structure and/or functionality may be referenced by the same reference signs. It is to be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

In the figures:

Fig. 1 shows elements of the semiconductor assembly illustrating details of the working principle.

Fig. 2 shows details of a cross section of a semiconductor assembly .

Fig. 3 shows details of a top side of a semiconductor assembly .

Fig. 4 shows a segment of an isolated sensing coil in an enlarged perspective view.

Fig. 5 shows the principle of compensating common mode distortions . Fig. 6 shows details of a semiconductor assembly wherein the vertical height of the sensing coils essentially equals the vertical height of the semiconductor assembly.

Fig. 7 shows details of a semiconductor assembly wherein external contacts are arranged on a common side.

Fig. 8 shows a cross section corresponding to fig. 7.

Fig. 9 shows a top view onto a semiconductor assembly with three nested sensing coils.

Fig. 10 shows a top view onto a multi-chip-module.

Fig. 11 shows the use of an integrating circuit.

Fig. 12 shows the possibility of the provision of a return line of the coil that minimizes spurious coupling from non- wanted magnetic fields.

Figure 1 shows a semiconductor assembly 16 with a semiconductor element 19 directly integrated in a dielectric material 5. The semiconductor element has a direction of the current through the semiconductor element in a vertical direction z. A current in the vertical direction z generates a magnetic field surrounding the current propagation path. To obtain information regarding the current a winding 22 of the sensing coil 18 is arranged such that the magnetic flux associated with the current is captured. Thus, the winding has a normal essentially parallel the direction of the magnetic at the position of the winding. A change of current corresponds to a change of magnetic flux through the coil and a change of magnetic flux corresponds to a voltage induction in the coil. By evaluating the voltage, e.g. via integration, sensing information can be obtained to precisely monitor the current associated with the current path, i.e. with the semiconductor element.

Of course, the number on windings of the coil is not limited to one. The number of windings can be between 1 and 1000, e.g. between 200 and 500.

The voltage induced is proportional to the flux for each winding. The total sensed voltage is the sum of the voltage contribution provided by each winding of the coil. Thus, by appropriately selecting the number of windings and by appropriately locating each winding at a corresponding position of magnetic field strength, the total sensing voltage for a given current-changing rate can be adjusted to match a given specification.

The semiconductor element can be an IGBT having an emitter 6 and a collector 3 or a MOSFET with a source and a drain contact or a MISFET. Thus, the current-changes between emitter and collector can be precisely determined even for high frequency applications.

The windings of the coil can be realized as structured metallizations. The windings can be comprised of vertical and horizontal sections. Vertical sections have an extensions along the vertical direction z. Horizontal sections can have extensions in the horizontal x-y plane. Vertical sections can be realized as vias vertically penetrating through a layer 13 or a section of the dielectric material of the body.

Horizontal sections can be realized as structured metallizations vertically arranged between different layers or sections of the dielectric material or at the top side 20 or bottom side 1 of the body.

As the structuring of such horizontal or vertical connection structures may be necessary for electrical connections to and from the semiconductor element, e.g. for establishing a redistribution layer 13 or the like, the creation of the coil does not need any further steps during manufacturing and the direct integration can be performed essentially without the need for additional volume or footprint.

Figure 2 shows a semiconductor assembly design where the semiconductor assembly establishes a chip-scale-package. The sensing coil is simultaneously created during manufacturing by embedding processes of lamination, via drilling, and metallization by via filling and formation of redistribution layers.

The electronic device is bonded with its collector 3 contact to a lead frame 14, embedded in a PCB laminate or mold compound and contacted by Copper (Cu) vias. In a second laminate or mold compound layer 13, the semiconductor element interconnect vias are prolonged to the top side and redistributed to Gate 9 and Emitter 6 contact pads. In addition, the sensing coil realized as a helical coil is added around the Emitter load current vias by further vias and redistribution lines as structured metallizations that are terminated by two current sense contact pads 10 and 11 on the top side. All vias and redistribution s are manufactured in an automated PCB manufacturing equipment via drilling, sputtering and electroplating.

Figure 3 illustrates a top view onto the semiconductor assembly of figure 2. The sensing coil has a plurality of windings 22 and the sensing coil horizontally surrounds - in the x-y-plane - the vertical current path.

On the top side of the semiconductor assembly the emitter side contact 6 and the gate 9 contact are arranged. Further, the two connections to the coil 10 and 11 are arranged on the top side of the semiconductor assembly.

Figure 4 shows an enlarged perspective view of three windings 22 of the sensing coil 18 isolated for better illustration. The sensing coil's structured metallizations are created during manufacturing simultaneously with other structured metallizations created in the embedding processes.

In addition, fig. 4 shows the sensing coil realized as helical coil comprising vertical vias 21 and lateral metallization structures 15.

It is possible that each winding 22 of the coil has the structured metallizations essentially arranged is a plane parallel to the vertical direction z, except small sections dedicated to electrically connect a neighboring winding needed to prevent a short circuit of the winding 22.

Figure 5 illustrates the principle of reducing or eliminating common-mode distortion utilizing a compensation coil 2 in addition to the sensing coil 18. The compensating coil 2 and the sensing coil are arranged such that for each winding of the sensing coil there is a winding of the compensating coil essentially overlapping with the winding of the sensing coil The sensing coil and the compensating coil are electrically connected to one another such that their induced sensing voltages are with a phase shift of 180 degrees added and common-mode distortions are compensated. Thus, a balanced signal conduction is obtained and the unbalanced common-mode distortions are essentially eliminated.

This configuration of a compensating coil 2 in addition to the sensing coil 2 can also reduce the capacitive coupling, e.g. when sensing fast switching devices, a differential Rogowski coil as depicted in Fig. 3 can be used.

Figure 12 shows the possibility of the provision of a return line of the coil that minimizes spurious coupling from non- wanted magnetic fields in a perspective view (top portion of fig. 12) and in a view onto the x-z plane (bottom portion of fig. 12).

Figure 6 shows a variant of figure 2. In the semiconductor assembly according to figure 6 the windings of the sensing coil 18 has a vertical extension reaching from the top side of the semiconductor assembly 16 to the bottom side of the semiconductor assembly. Thus, the area of each winding is increased. Thus, the flux is increased. Thus, the sensed voltage is increased. Thus, the signal-to-noise ratio is improved.

Figure 7 shows the possibility of arranging the connections of the semiconductor assembly 16 to an external circuit environment on the top side. To that end, vias arranged next to the semiconductor element 19 electrically connecting the collector-side connection 3 at the bottom side of the semiconductor assembly to corresponding top side connections are provided.

Thus, there is provided another vertical current path with the current direction opposed to the current direction directly via the semiconductor element. Thus, there is another possibility to utilize the sensing principle with a directly integrated sensing coil.

Correspondingly, the semiconductor assembly shown in figure 7 has a further sensing coil 18b surrounding - in the lateral x-y plane - the opposed direction current path.

Hereby it is important that the further sensing coil 18b is insulated from the collector potential. This can be obtained by providing a structured lead frame (not shown), e.g. by a pick & place process of Cu lead frames on a release film during manufacturing.

Compared to the sensing coil 18 arranged above the semiconductor element, the loop height of the further sensing coil 18b can be increased, e.g., from 0.1 to 0.3 mm, leading to a 3 times higher voltage signal.

Figure 8 shows the possibility of electrically connecting the sensing coil 18 of figure 7 in series to the further sensing coil 18b in order to obtain a higher (i.e. added) sensing voltage. Similarly, figure 9 shows the possibility of providing more than one (e.g. three) sensing coil 18 surrounding the same vertical current path. This allows increased signal quality and the redundancy allows increased reliability.

Figure 10 shows the possibility - in a multi-chip module - to evaluate the current through a plurality of semiconducting elements in an element specific manner. Individually monitoring the trend of each semiconductor element allows identification of failing elements and the prediction of expected failures of each individual semiconductor element.

Figure 11 shows the possibility of providing an integrating circuit 23 to evaluate the derivative related sensed voltage (compare equation (1)).

The integrating circuit 12 can be directly integrated in the body of the semiconductor assembly. However, it is also possible that the integrating circuit is an element of an associated electric device comprising the semiconductor assembly and the integrating circuit as separate items, e.g. as shown in figure 11. Then the semiconductor assembly and the integrating circuit 12 can be arranged on a common carrier, e.g. a common printed circuit board.

Further, figure 11 shows the possibility of having an additional semiconductor element 19 arranged in the assembly.

While the semiconductor assembly or electric power device is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the figures. It should be understood, however, that the intention is not to limit the semiconductor assembly or device to the particular details described. On the contrary, the semiconductor assembly or device is to cover all possible modifications, equivalents, and alternatives.

List of reference signs

1: bottom side

2: compensating coil

3: collector side contact

4: current path

4b: second current path

5: dielectric material

6: emitter side contact

7: electric power device

9: gate connection

10, 11: current sense contact pad 12: integrating circuit

13: layer

14: lead frame

15: lateral metallization structure

16: Semiconductor assembly

17: multi-chip module

18: sensing coil

18b: further sensing coil

19: semiconductor element

19b: additional semiconductor element

20: top side

21: vertical via

22: winding

23: integrating circuit x, y: lateral directions z: vertical direction