Patent Description:
Sensors are widely used in electronic devices to measure attributes of the environment and report a measured sensor value. Magnetic sensors more in particular are used to measure magnetic fields, for example in transportation systems such as automobiles. Magnetic sensors can incorporate Hall effect sensors that generate an output voltage proportional to an applied magnetic field associated with a current passing through a conductor or magneto-resistive materials whose electrical resistance changes in response to an external magnetic field.

Conventional current sensors based on Hall effect elements are well known in the art. The Hall effect is the production of a voltage difference (the Hall voltage) across an electrically conductive material (such as a wire), transverse to the electric current in the material and to an applied magnetic field perpendicular to the current. The voltage difference can be measured and, if the applied magnetic field is known, the current in the electrically conductive material can be deduced. Such a current sensor can be called a magnetic current sensor.

Magnetic current sensors that detect a magnetic field generated by a current are conventionally packaged in an integrated circuit (IC) housing. ICs are formed on a single die ('chip') cut from a semiconductor wafer containing a large number of identical dies. The dies are relatively small and fragile, are susceptible to harmful environmental elements, particularly moisture, and generate a relatively large amount of heat in a relatively small volume during operation. Accordingly, ICs must be packaged in an affordable, yet robust housing that protect them from the environment, enable them to be reliably mounted to and interconnected with, for example, a printed circuit board (PCB) populated with associated electronic components, and to effectively dissipate the heat they generate during operation.

<FIG> illustrates a cross-sectional view of a typical case. A die (<NUM>), e.g. a silicon die, contains a front side being an active side (<NUM>) and a back side (<NUM>). This back side is disposed on a die attach pad (<NUM>) (also called a paddle). On the active side is disposed an integrated circuit. Via fine conductive wire bonds (<NUM>) electrical interconnections are made between the integrated circuit and at least two leads (<NUM>) of a lead frame, e.g. a metallic lead frame. The leads extend from a first end integral with the frame to an opposite second end adjacent to, but spaced apart from, the die pad. The leads are arranged to carry signals outside of the package (<NUM>). In general, the die and inner portions of the lead frame are encapsulated with a molding material to protect the electrical connections and the delicate electrical components on the active side of the die.

Another type of prior art solution is depicted in <FIG>. In this so-called flip-chip arrangement the active side (<NUM>) of the die (<NUM>) is oriented in the opposite direction compared to <FIG>. Solder balls (<NUM>) are used to establish connection between the inner portions of the leads and the substrate. The arrangement of <FIG> offers the advantage over that of <FIG> that the active side of the die is now closer to a conductor that may be provided below the packaged die.

In <CIT> magnetic field current sensors are disclosed including a semiconductor die having first and second opposing surfaces, at least one magnetic field sensing element and a conductor. This conductor is inside the sensor package.

Application <CIT> relates to a packaged multichip isolation device comprising a leadframe having a two different die pads, each with an integrated circuit thereon having a bond pad connected to a different lead. Current sensing is not discussed.

In <CIT> is presented a die attach package for connecting a die or chip of die-down orientation to a printed circuit board in a die-up orientation. The package includes a substrate with leads which are modified to pass under the die when the die is attached. A flattened ball is attached to die contacts and a gold wire runs parallel to the die and then to a via on the substrate. The die is attached to the substrate using a non-electrically-conductive material. Current sensing is not discussed.

<CIT> presents a die attach package for connecting a die or chip of die-down orientation to a printed circuit board in a die-up orientation.

Patent <CIT> relates to a test socket assembly including a test and failure-analysis socket and an adapter board.

In <CIT> an integrated circuit chip is proposed with its interconnecting pads re-arranged in substantially a straight line.

<CIT> is concerned with a current sensing device comprising a substrate mounted relative to an electrical conductor having a symmetry plane, a first magnetic sensor located at a first location outside the symmetry plane and a second magnetic sensor located at a second location in the symmetry plane and a processing circuit.

<CIT> discloses a magnetic sensor package with a plurality of sensors, a signal processing circuit, and a metal plate. The magnetic sensors and the signal processing circuit are mounted on the metal plate.

<CIT> relates to current measurements over a wide frequency range with an AMR-based sensing circuit by folding the current carrying trace around the AMR sensor to concentrate and normalize the magnetic field generated by the current over a wide frequency range.

<CIT> is concerned with wideband contactless magnetoresistive-Rogowski current sensing to provide current sensing from DC to <NUM> or more.

In <CIT> current sensor package is presented, comprising a current path and a sensing device. The sensing device is spaced from the current path. The sensing device comprising a sensor element is configured for sensing a magnetic field generated by a current flowing through the current path. The sensing device is electrically connected to a conductive trace. An encapsulant extends continuously between the current path and the sensing device.

There remains, however, a need for integrated circuits for current sensing wherein the distance between the active surface of the substrate and the package is kept as small as possible, so that a magnetic field created by a current flowing in an electrical conductor can be sensed by the integrated circuit as good as possible.

It is an object of embodiments of the present invention to provide for a system comprising an integrated circuit for current sensing having an active side so positioned that the sensitivity to sense a current in the conductor is improved.

The above objective is accomplished by the solution according to the present invention.

In a first aspect the invention relates to a current sensor system comprising a conductor and a packaged integrated circuit for sensing a current in the conductor. The conductor is fully external to the packaged integrated circuit. The packaged integrated circuit comprises :.

wherein the back surface of the substrate is disposed on a support formed by at least two inner lead portions of the plurality of leads and the active side of the substrate is oriented towards the outer ends of the outer lead portions of the leads in a direction perpendicular to a plane defined by the support.

The proposed solution indeed allows for increasing the sensitivity when a current in the conductor is to be measured. This is achieved by having the active surface so positioned that it faces towards the outer lead portions. In some embodiments the increased sensitivity can be obtained by shortening the distance between the active surface and the conductor. In other embodiments an increase of sensitivity is achieved by using the inner lead portions as an electrostatic shield. In some embodiments the effects of shortening the distance and shielding are combined. Details are provided later in this description.

The at least two inner lead portions preferably do not overlap with the one or more magnetic sensing elements.

In one embodiment the one or more magnetic sensing elements are Hall effect plates disposed in the active surface of the substrate.

In one embodiment the one or more magnetic sensing elements are magnetoresistance elements.

In another embodiment the one or more magnetic sensing elements are compound semiconductors disposed on or stacked on the active surface of the substrate.

In embodiments of the invention two or more inner lead portions of the plurality of leads are bent. The bending can be in some embodiments with an offset in the direction away from the outer extremities of the outer lead portions. In other embodiments the bending is with an offset in the direction towards the outer extremities of the outer lead portions.

In advantageous embodiments the conductor is so positioned that the active surface of the substrate faces the conductor. In other advantageous embodiments the conductor is so positioned that the active surface of the substrate faces away from the conductor.

In some embodiments the outer ends of the outer lead portions are mounted on a printed circuit board or on a plastic support. In certain embodiments the printed circuit board comprises a ground layer.

In advantageous embodiments there is no magnetic material present in the integrated circuit to concentrate a magnetic field to be sensed by the one or more magnetic sensing elements. In other words, the integrated circuit of the system is then coreless.

In a more specific embodiment the conductor is a trace in a printed circuit board circuit.

In an embodiment the conductor is a bus bar.

In another aspect the invention relates to a current sensor system comprising a conductor and a packaged integrated circuit for sensing a current in said conductor, said conductor being fully external to the packaged integrated circuit, said packaged integrated circuit comprising :.

wherein the back surface of the substrate is disposed on a conductive support and the active side of the substrate is oriented towards the outer ends of the outer lead portions of the leads in a direction perpendicular to a plane defined by the support and wherein the conductor is so positioned that the active surface of the substrate faces away from the conductor.

The conductive support then shields the substrate from the conductor.

In some embodiments the support is a die paddle. The support may have at least one opening. In other embodiments the support does not have any opening.

Advantageously, the support is formed by at least two inner lead portions of the plurality of leads.

In this respect, the invention is defined and limited by the appended claims.

In one aspect the invention relates to a current sensing system comprising a conductor and a packaged integrated circuit as described in various embodiments hereafter. The integrated circuit is flip-chip arranged. In preferred embodiments the integrated circuit is positioned on top of the conductor that conducts electrical current. In other embodiments the conductor is on the other side with respect to the integrated circuit.

<FIG> illustrates an embodiment of a packaged integrated circuit for current sensing comprised in a current sensor system according to this invention. The conductor itself is not shown in the figure. The circuit comprises a substrate (<NUM>) with an active surface (<NUM>) and a back surface (<NUM>). With active surface is meant the side that comprises the active circuitry. On or in the active side are disposed one or more magnetic sensing elements (<NUM>). The integrated circuit further comprises a processing circuit (not shown in the figure) disposed in or on the active surface, wherein signals received from the one or more magnetic sensing elements are further processed to determine a signal indicative of the sensed current. Electrical connections (<NUM>), for example wire bonds, interconnect the substrate with leads (<NUM>) of a lead frame, via which signals can be brought outside the package. The leads typically comprise an inner lead portion inside the housing (<NUM>) and an outer lead portion extending outside the housing and having an outer end that is arranged to be placed on a printed circuit board or other wiring substrate. The electrical connections (<NUM>), e.g. the wire bonds, connect the lower surface of the inner lead portions with the active surface of the integrated circuit. The back surface of the substrate is disposed on the inner portions (or on at least part thereof) of the leads which serve as a support. This support forms a plane, for example in the embodiment of <FIG> a horizontal plane. The inner lead portions and the back side of the substrate are fixed to one another by means of for example a die attach adhesive or glue. It is not needed that all of the leads are used to form the support. In some embodiments only a subset of the leads serve as support, whereas other leads do not at all have any supporting function. The integrated circuit is arranged in a flipped configuration, whereby the active side is oriented in a direction away from the support (i.e. away from the inner portions of the lead) and towards the side where the outer lead portions are connectable to the printed circuit board. The arrow in <FIG> indicates this direction perpendicular to the support formed by the inner lead portions and towards the outer ends of the outer lead portions of the leads.

In embodiments of the invention the one or more magnetic sensing elements are silicon Hall effect sensors integrated in the active surface. In other embodiments TMR, GMR, or more generally magnetoresistance (MR) elements are used. In these embodiments the axis of sensitivity is parallel to the active surface. Additionally or alternatively magnetic sensing elements may be stacked on top of the active surface, or assembled by transfer printing, as will be illustrated later in this description. In this case the semiconductor compounds can binary or ternary alloys.

Common elements for compound semiconductors comprise for example binary III-V materials like e.g. GaAs, InP, InSb, or ternary alloys, e.g. AlGaAs or InGaAs. In some embodiments the compound semiconductor material is a non-magnetic semiconductor material.

In some embodiments the one or more magnetic sensing elements is/are so positioned that there is no overlap with the leads of the lead frame.

In advantageous embodiments at least two magnetic sensing elements are provided in or on the active side of the substrate. Such a configuration with at least two magnetic sensing elements is advantageous, for example for performing offset cancellation and/or stray field rejection.

In preferred embodiments of the invention the one or more magnetic sensing elements are Hall effect elements. The magnetic sensing element then has an axis of sensitivity perpendicular to the active surface. In case at least two Hall effect elements are present, they are preferably orthogonally biased. As well known in the art, this means that the operation of the magnetic sensing elements is based on pairing an even number of sensing elements and biasing them orthogonally so that orthogonal current directions are obtained.

In embodiments the integrated circuit is disposed on, directly on, over, in contact with, for example in direct contact with, above, below or adjacent to a conductor surface of the system's conductor through which the current to be measured flows. In some embodiments the active surface of the substrate faces the conductor, as for example in <FIG>. Given that the integrated circuit of the system according to these embodiments of the invention may be primarily designed to reduce the distance to the conductor, it is clear that embodiments wherein this objective is best met, are also most preferred.

In some embodiments the packaged integrated circuit of the system according to the invention is coreless, meaning that there is no magnetic core present, i.e. no magnetic material to concentrate the field. This is sometimes also referred to as a coreless sensor. Due to the flipped arrangement the sensitivity of the sensing circuit is increased so that there is no strict need for a magnetic core or concentrator. Further such a coreless sensor is also beneficial with respect to the linear behaviour, as non-linear effects due to the magnetic core or concentrator are avoided.

Some more embodiments of the system of the invention are now presented in detail.

In <FIG> an embodiment is shown wherein the inner portions of the leads display a small downset so that the parts containing the inner extremities of the leads (which serve as the support) form a horizontal plane slightly offset from the horizontal plane formed by the inner lead portions where they come out of the package. Note that, as in <FIG>, the conductor is not shown. In <FIG> the offset is in the direction opposite to the location of the outer extremities of the outer lead portions, i.e. farther away from the outer ends of the outer lead portions. This offers the advantage that additional space is created between the active surface of the substrate (<NUM>) and the housing (<NUM>). The embodiment of <FIG> also shows a further optional sensing element. In a preferred embodiment these two magnetic sensing elements are orthogonally biased.

In a variant embodiment the small downset of the inner portions of the leads is in the opposite direction of the direction shown in <FIG>. In other words, the parts containing the inner extremities of the leads form a horizontal plane slightly offset from the horizontal plane formed by the inner lead portions where they come out of the package, in the direction towards the lower surface of the housing. In this way the components of the active surface can be brought even closer to the conductor where the current is to be sensed.

The extra space that may be gained is in the embodiment illustrated in <FIG> exploited to place a stacked magnetic sensor on the active surface (<NUM>). In other embodiments there may be more than one stacked magnetic sensor. Wire bonds <NUM> establish the connection between the active surface and the inner portions of the leads. The electrical connection between the stacked sensor and the substrate can be ascertained for example by means of wire bonding (as shown in <FIG>) or via a redistribution layer. Alternatively the stacked GaAs die can be flipped on the substrate and connected by means of solder balls to the substrate.

The stacked magnetic sensor(s) as in <FIG> may comprise at least one magnetic sensing element in a semiconductor compound material, e.g. an III-V semiconductor. Common elements for compound semiconductors comprise for example binary III-V materials like e.g. GaAs, InP, InSb, or ternary alloys, e.g. AlGaAs or InGaAs. If there is more than one magnetic sensing element, the various sensing elements may be made of the same semiconductor material or not. In some embodiments the compound semiconductor material is a non-magnetic semiconductor material.

In <FIG> a combination is made of the embodiment of <FIG> with a stacked magnetic sensor and the embodiments of the preceding figures with a sensing element in the die.

The processing circuit disposed in the silicon substrate is not shown in any figure, but is now briefly described, even though this component is well known in the art. The processing circuit may comprise analog and/or digital electronics and is arranged to receive signals from the sensing elements. The processing circuit comprises computation means to derive an output signal indicative of the sensed signal, i.e. of the measured current in the conductor. In some embodiments information from a temperature sensor that may be part of the processing circuit can thereby be taken into account.

The conductor is in some embodiments so positioned that the active surface of the substrate faces the conductor. The conductor can have a plurality of conductor surfaces and can be a laminated structure with different electrically isolated layers of materials, for example electrically conductive materials. The sensing device can be disposed on, directly on, over, in contact with, for example in direct contact with or above a conductor surface of the conductor.

In the embodiment shown in <FIG> the active surface of the substrate faces away from the conductor. Hence, the conductor is now on the other side of the integrated circuit compared to the previously discussed embodiments. <FIG> illustrates an example wherein stacked magnetic sensors are applied. Similarly as mentioned before, compound semiconductors comprising e.g. binary III-V materials can be used. Obviously, in other embodiments instead of stacked magnetic sensors, magnetic sensors in or on the active side of the substrate can be used. As the conductor is now located at the opposite side of the packaged integrated circuit, the inner lead portions do not only act as a support but also as an electrostatic shield for the capacitive coupling from the conductor to the integrated circuit. Advantageously, a ground layer (<NUM>) is provided, e.g. in the printed circuit board (<NUM>). Coupled with that ground layer the leads then can act as a Faraday cage. The set-up of <FIG> may be advantageous in that the printed circuit board is further away from the conductor and thus less subject to temperature increase. Another advantage may be an increased magnetic gain as there is no printed circuit board between the sensor and the conductor.

As set out above the integrated circuit is in some embodiments coreless, meaning that there is no magnetic material to concentrate the field. In such cases a coreless current sensor system is obtained.

The skilled person will readily appreciate that features described in relation to any of <FIG>, can readily be combined with the embodiment of <FIG>.

In the system of this invention the conductor is located outside the housing. In some embodiments the conductor is a bus bar. In some embodiments the outer ends of the outer lead portions can be mounted on a printed circuit board or on a plastic support. <FIG> provides an illustration. The bus bar (<NUM>) is in this example positioned below the printed circuit board (<NUM>) and faces the active surface of the integrated circuit. The distance between the conductor and the active surface of the integrated circuit is so made as short as possible. In the embodiment of <FIG> there are two stacked magnetic sensors provided on top of the die (<NUM>). Having two such stacked magnetic sensors is advantageous in that it allows deriving a differential signal, which is immune to stray fields. The processing circuit is then adapted to deal with differential signals.

In one embodiment the conductor has a cross section having a dimension (width and/or thickness) larger than the integrated circuit. The width and/or thickness may even be larger than the package, or larger than the sensor. An advantage is that high currents can be carried and measured. For example, the conductor can be larger than <NUM>% the size of the chip, or larger than <NUM>% the size of the chip. In one embodiment both the thickness and width are larger than <NUM>% the size of the chip.

In some embodiments the conductor may be a trace in a printed circuit board circuit whereon the integrated circuit is assembled. This is depicted in <FIG>. The conductor in the printed circuit board may comprise one metal layer or two metal layers (as in <FIG>) or multiple metal layers. In some embodiments, the current conductor width and/or thickness is smaller in the vicinity of the current sensor, such as to locally increase the current density and increase the sensed magnetic field at the sensor location.

In another aspect the invention also relates to an integrated circuit as depicted in <FIG> and to a system for current sensing comprising a conductor and such an integrated circuit. The integrated circuit comprises a substrate (<NUM>) with an active surface (<NUM>) and a back surface (<NUM>). With active surface is meant the side that comprises the active circuitry. On or in the active side are disposed one or more magnetic sensing elements (<NUM>). The integrated circuit further comprises a processing circuit (not shown in the figure) disposed in or on the active surface and similar to the one already discussed before, wherein signals received from the one or more magnetic sensing elements are further processed. Electrical connections (<NUM>), for example wire bonds, interconnect the substrate with leads (<NUM>) of a lead frame, via which signals can be brought outside the package. Techniques like heat staking may be optionally applied. The leads typically comprise an outer lead portion extending outside the housing (<NUM>) and arranged to be placed on a printed circuit board or other wiring substrate, and an inner lead portion inside the housing. The electrical connections (<NUM>), e.g. the wire bonds, connect the lower surface of the inner lead portions with the active surface of the integrated circuit. The back surface of the substrate is disposed on a support (<NUM>). The support is not necessarily aligned with the leads. In some embodiments the support is a non-conductive die paddle. This support forms a plane, for example in the embodiment of <FIG> a horizontal plane. The integrated circuit is arranged in a flipped configuration, whereby the active side is oriented in a direction away from the support (and from the inner portions of the lead) and towards the side where the outer lead portion are connectable to the printed circuit board. The arrow in <FIG> indicates this direction perpendicular to the support (<NUM>) and towards the outer lead portions of the leads.

As already discussed previously, the one or more magnetic sensing elements are silicon Hall effect sensors integrated in the active surface. In other implementations TMR, GMR, or more generally magnetoresistance (MR) elements are used. The axis of sensitivity is then parallel to the active surface. Additionally or alternatively magnetic sensing elements may be stacked on top of the active surface, or assembled by transfer printing, as already mentioned earlier in this description. In this case the semiconductor compounds can binary or ternary alloys.

Also here common elements for compound semiconductors comprise for example binary III-V materials like e.g. GaAs, InP, InSb, or ternary alloys, e.g. AlGaAs or InGaAs. In some embodiments the compound semiconductor material is a non-magnetic semiconductor material.

The one or more magnetic sensing elements may be so positioned that there is no overlap with the leads of the lead frame.

Providing at least two magnetic sensing elements in or on the active side of the substrate may yield an advantageous configuration, for example for performing offset cancellation and/or stray field rejection.

The one or more magnetic sensing elements are preferably Hall effect elements. The magnetic sensing element then has an axis of sensitivity perpendicular to the active surface. In case at least two Hall effect elements are present, they are preferably orthogonally biased.

The integrated circuit in <FIG> is disposed on, directly on, over, in contact with, for example in direct contact with, above, below or adjacent to a conductor surface of the conductor through which the current to be measured flows. The active surface of the substrate faces the conductor in <FIG>. As the integrated circuit may be primarily designed to reduce the distance to the conductor, it is clear that implementations wherein this objective is best met, are also most preferred.

Also here the packaged integrated circuit may be coreless. Due to the flipped arrangement the sensitivity of the sensing circuit is increased so that there is no strict need for a magnetic core or concentrator. Further such a coreless sensor is also beneficial with respect to the linear behaviour, as non-linear effects due to the magnetic core or concentrator are avoided.

An alternative to <FIG> is presented in <FIG>. The die paddle is made of conductive material. In that case the die paddle in the support is optionally provided with an opening. There may also be more than one opening. This is particularly advantageous in that the occurrence of eddy currents is reduced. The use of a conductive die paddle yields a cost effective solution.

In a configuration as in <FIG> the conductor can be positioned as in <FIG>, i.e. with the active surface of the substrate facing away from the conductor, provided that the die paddle is conductive. This also yields a shielding effect as in <FIG>. Optionally, the die paddle may be connected to ground.

The configuration of <FIG> (i.e. with conductive die paddle with possibly one or more openings and/or partial cut-out) can be used as in <FIG>. The die paddle does not need to be continuous to act as an electrostatic shield. In particular, the one or more openings may be designed to be small enough such as to block electrostatic perturbation at or below a desired range of frequencies. Optionally, the magnetic sensing element can be disposed near the opening in the die paddle. In such a configuration, the integrated circuit is protected from electrostatic perturbation (capacitive coupling from the bus bar) and the sensing element is less affected by eddy currents flowing in the die paddle.

Claim 1:
Current sensor system comprising a conductor and a packaged integrated circuit for sensing a current in said conductor, said conductor being fully external to said packaged integrated circuit, said packaged integrated circuit comprising :
- a substrate (<NUM>) having an active surface (<NUM>) and a back surface (<NUM>),
- one or more magnetic sensing elements (<NUM>) disposed in or on said active surface of said substrate,
- a processing circuit disposed in or on said active surface of said substrate and arranged to process signals received from said one or more magnetic sensing elements to derive an output signal indicative of a sensed current in said conductor,
- a housing (<NUM>),
- a plurality of leads (<NUM>) having an outer lead portion extending outside said housing and an inner lead portion,
- electrical connections (<NUM>) between said leads and said active surface of said substrate,
characterised in that said back surface of said substrate is disposed on a support (<NUM>) formed by at least two inner lead portions of said plurality of leads and said active side of said substrate is oriented towards the outer ends of said outer lead portions of said leads in a direction perpendicular to a plane defined by said support.