Magnetic field gradient sensor and current sensor having same

Abstract

A magnetic field gradient transducer (1) for surface mounting on a circuit board (21), comprising:-an integrated circuit (IC) chip (2) comprising an active first side (9a), a second side (9b), at least two magnetic field sensing portions (20) on the active side, and connection terminals (11) on the active side, the at least two magnetic field sensing portions (20) are separated by a gap (G) configured for magnetic field gradient measurement; a leadframe structure (3) comprising a plurality of secondary conductors (5) and a shielding conductor (6), the shielding conductor being in overlapping relationship with the IC chip; -a plurality of secondary conductor bonding wires (14) interconnecting two or more of the secondary conductors (5) to the connection terminals (11) of the IC chip; and-an insulating housing (7) overmolded on the IC chip, the secondary conductor bonding wires and a portion of the lead frame structure (3), whereby the circuit board contact portions of the secondary conductor and the shielding conductor are exposed and configured for surface-mounted connection with the external circuit board. The shielding conductor has a non-recessed portion (12) and a recessed portion (13) on which the IC chip is mounted, the thickness H2 of the recessed portion being smaller than the thickness H1 of the non-recessed portion and the secondary conductor.

Description

[0001] The present invention relates to a surface mounted on a circuit board integrated circuit magnetic field gradient transducer for current sensing applications. The present invention further relates to an open loop coreless current transducer with an integrated circuit magnetic field gradient transducer.

[0002] It is known to provide an integrated circuit magnetic field gradient transducer for current sensing applications with surface mount electrical connections for mounting on a circuit board. In many applications it is advantageous to have a magnetic field transducer with a very compact and low height for measuring the current in a primary conductor on a circuit board, or the current in a primary conductor integrated with the magnetic field transducer, or the current in a primary conductor to which the magnetic field transducer is assembled.

[0003] Such a coreless magnetic field transducer can comprise an integrated circuit (IC) chip with an active sensing layer thereon that detects a magnetic field induced by a current to be measured flowing in a primary conductor in the vicinity of the magnetic field transducer, the integrated circuit chip being electrically connected to secondary contacts that supply power and allow transmission of a measurement signal to an external circuit board.

[0004] The active part and the connection interface on a semiconductor substrate, for example a CMOS IC, are usually provided on the same side of the IC. It is known to connect the IC chip interconnects to a secondary conductor formed by a lead frame with wirebonds. The lead frame is a strip of sheet metal that is punched and shaped to cut out the auxiliary contacts from the metal sheet, the contacts and the integrated circuit being overmoulded by an insulating polymer, the connection ends of the contacts being exposed and configured for solder or fusion connection to circuit traces on a circuit board.

[0005] The magnetic field gradient sensor has two magnetic field active sensing parts separated by a gap, which are configured to measure the difference of the magnetic field between the two separated parts. The magnetic field gradient sensor is very compact and sensitive and very suitable for a coreless transducer, however, it is sensitive to external electric fields. Furthermore, the strength of the measurement signal of a magnetic field gradient sensor for current sensing applications strongly depends on the distance to the primary conductor.

[0006] In view of the above, it is an object of the present invention to provide a surface mounted on a circuit board magnetic field gradient transducer for current sensing applications with a high measurement sensitivity.

[0007] It is advantageous to provide a surface mounted on a circuit board magnetic field gradient transducer for current sensing applications that is compact and cost-effective to manufacture.

[0008] It is another object of the present invention to provide an open loop coreless current transducer on a circuit board which is accurate, compact and cost-effective to manufacture.

[0009] The object of the present invention is achieved by providing a magnetic field gradient transducer according to claim 1.

[0010] The object of the present invention is achieved by providing a current transducer according to claim 8.

[0011] The object of the present invention is achieved by providing a method of manufacturing a magnetic field gradient transducer according to claim 9.

[0012] A magnetic field gradient transducer for surface mounting on a circuit board, comprising - an integrated circuit (IC) chip comprising an active first side, a second side, at least two magnetic field sensing portions on the active side and connection terminals on the active side, the at least two magnetic field sensing portions being separated by a gap configured for magnetic field gradient measurements,

[0013] - a leadframe structure comprising a plurality of secondary conductors and a shielding conductor, the shielding conductor being in an overlapping relationship with the IC chip,

[0014] - a plurality of secondary conductor bonds interconnecting two or more of the secondary conductors to the connection terminals of the IC chip, and

[0015] - an insulating housing overmolded on the IC chip, the secondary conductor bonds and a part of the leadframe structure, whereby circuit board contact portions of the secondary conductors and the shielding conductor are exposed and configured for surface mounting connection to the external circuit board.

[0016] The shielding conductor has a non-indented portion and an indented portion, on which the IC chip is mounted, the thickness H2 of the indented portion being smaller than the thickness H1 of the non-indented portion and the secondary conductors.

[0017] In an advantageous embodiment, the indented portion is bounded on at least two edges by the non-indented portion.

[0018] In an advantageous embodiment, the IC chip has a rectangular shape, the long sides of the rectangular shaped IC chip being parallel to the at least two edges of the indented portion.

[0019] In an advantageous embodiment, the indented portion is substantially linear.

[0020] In an advantageous embodiment, the shielded conductor recessed portion extends from a first outer side of the transducer to a second, opposite outer side of the transducer.

[0021] In an advantageous embodiment, the recessed portion extends from the first outer side of the transducer to the second, opposite outer side of the transducer.

[0022] In an advantageous embodiment, an insulating layer is located between the second side of the IC chip and the recessed portion of the leadframe structure.

[0023] Also disclosed herein is an open loop coreless current transducer comprising a circuit board, a primary conductor formed on or in the circuit board for carrying a current to be measured, and a magnetic field gradient sensor according to any preceding embodiment mounted on the circuit board over the primary conductor.

[0024] The present invention also discloses a method of manufacturing a magnetic field gradient transducer according to any preceding embodiment, comprising forming the shielded conductor as a continuous strip extending along the length of a plurality of magnetic field gradient transducers, mounting a plurality of the IC chips in the recessed portion at a defined spacing, wire bonding the secondary conductor leads to the connection terminals on the IC chips, overmolding the overmolding housing over the length of a plurality of magnetic field gradient transducers while the shielded conductor remains in the form of the continuous strip, and then separating individual transducers by cutting the shielded conductor strip and overmolding housing at a defined spacing corresponding to the outer side of the transducer.

[0025] Other objects and advantageous features of the present invention will appear from the claims, the detailed description and the drawings, in which:

[0026] Figure 1 is a perspective view of a surface mount magnetic field gradient transducer according to an embodiment of the present invention, with the overmolding housing portion shown transparent.

[0027] With reference to the drawings, a magnetic field gradient transducer 1 for surface mount connection on an external circuit board comprises an integrated circuit (IC) chip 2 mounted on a leadframe structure 3 housed within an insulating overmolding housing 7.

[0028] The integrated circuit (IC) chip 2 has a first active side 9a and a second side 9b, at least the first active side 9a having an active portion comprising electrical connection terminals 11 for connection to power and signal transmission conductors, and a pair of magnetic field sensor portions 20 arranged at or near the surface of the first active side 9a. The pair of magnetic field active sensing portions are separated by a gap, configured to measure the difference or gradient of the magnetic field between the two separated magnetic field sensing portions.

[0029] If the primary conductor 4 carrying the primary current to be measured passes substantially centrally through the gap G separating the magnetic field sensing portions, the magnetic field at the location of the magnetic field sensing portions has opposite polarity.

[0030] The primary conductor 4 can be in the form of a circuit trace in or on a circuit board 21, or in the form of a separate busbar assembled to the circuit board.

[0031] Each magnetic field sensing portion can comprise a Hall effect sensor, or a giant magnetoresistive sensor, or other form of magnetic field sensor known in the art. The IC chip 2 can be in the form of a CMOS chip, for example, although other types of semiconductor integrated circuit chip with magnetic field sensing portions known in the art can be used. No further description of the semiconductor chip is required, such semiconductor chips with magnetic field sensing portions and connection terminals are known per se in the art.

[0032] The leadframe structure 3 comprises a shield conductor 6 and a plurality of secondary conductors 5. The leadframe structure is formed from a conductive metal sheet, more specifically in the form of a band or strip, which is punched and shaped in a punching and shaping process so as to cut, bend and / or stamp the metal sheet, thereby forming the shield conductor and the secondary conductors. Punching and shaping a leadframe structure from a metal sheet is a technique known per se.

[0033] The secondary conductors 5 for power supply and signal connections for interconnecting the IC chip 2 to an external circuit to which the current transducer is to be connected comprise a plurality of conductors formed from the leadframe structure, each secondary conductor comprising a connection portion 15 on one side and a surface mount connection terminal 16 on the other side. The surface mount connection terminals 16 can for example be arranged in a row, presenting contact pads intended for surface mount soldering or welding connection to circuit traces of an external circuit board, as known per se in the art. The surface mount connection terminals 16 are thus located near the outer edge of the transducer overmold housing 7, the IC connection side 15 being located near the IC chip 2, allowing wire bonding connection between the IC chip 2 and the IC connection side 15 of the secondary conductors. In variants, the secondary conductor terminals can have punched and shaped contact portions of various shapes and configurations, for example contact portions protruding downward and outward from the IC chip housing lower surface 10, adapted for surface mount connection to circuit board conductive traces, as known per se in the art.

[0034] The wirebonds 14 are connected between the IC connection side 15 of each secondary conductor 5 and the connection terminals 11 on the active first side 9a of the IC chip 2. It can be noted that some secondary conductors can have no connection to the IC chip, forming redundant secondary conductors for semiconductor chips with more connection portions. In other words, the number of connections depends on the functionality contained in the integrated circuit chip. The leadframe conductor structure 3 can have a constant structure, while the number of wirebond interconnections between the secondary conductors and the IC chip can depend on the configuration of the IC chip and the required functionality to be incorporated in the transducer.

[0035] According to the wirebonds for the primary and secondary conductors, any suitable wirebondable layer can be plated.

[0036] The shield conductor 6 is located underneath and overlapping the IC chip 2, such that the IC chip is mounted on the shield conductor 6. The shield conductor 6 serves as a shield conductor for electrical shielding of the IC chip 2, and can also serve as a heat conductor for heat dissipation from the IC chip 2.

[0037] Similar to the secondary conductors, the shield conductor 6 comprises one or more surface mount connection terminals 17 on the bottom side. The surface mount connection terminals 17 can for example be arranged in a row, presenting contact pads as known per se in the art, intended for surface mount soldering or welding connection to circuit traces of an external circuit board. The surface mount connection terminals 17 are thus positioned in the vicinity of the outer edge of the transducer overmold housing 7. In variants, the secondary conductor terminals can have stamped and shaped contact portions with various shapes and configurations, for example protruding downward and outward from the IC chip housing lower surface 10, adapted for surface mount connection to circuit board conductive traces, as known per se in the art.

[0038] The metal sheet from which the leadframe is cut out has a thickness H1, which is also the thickness of the non-recessed portions 12 of the secondary conductors 5 and the shield conductor 6. The shield conductor comprises recessed portions 13, which have a thickness H2 that is smaller than the thickness H1 of the non-recessed portions 12. The recessed portion thickness H2 is preferably less than 60% of the non-recessed portion thickness H1, for example about 50% (H2 < 0.6 x H1, for example H2 = 0.5 x H1).

[0039] The recessed portions 13 can be formed by etching or other subtractive manufacturing techniques known per se, for example mechanical machining, grinding, electrospark erosion, ablation processes, or can be formed by stamping or rolling with a die that compresses and plastically deforms the material of the leadframe structure.

[0040] The recess advantageously reduces the distance between the magnetic field sensing portion 20 and the mounting side 10 of the transducer, and thus the distance between the magnetic field sensing portion 20 and the primary conductor 4 formed in or on the circuit board 21 or assembled to the circuit board. The recess allows the shielding quality of the IC chip 2 to be maintained while ensuring greater measurement sensitivity due to the reduced distance between the magnetic field sensing portion and the magnetic field source, in this case the primary conductor. The recess also provides the advantage of reducing the overall thickness of the transducer, making it more compact than in a configuration without a recess in the shielding conductor.

[0041] A slot 19 can be cut from the shielding conductor to reduce eddy currents.

[0042] In an embodiment, the recess portion can be a continuous linear recess formed in the lead frame structure to simplify the process of forming the recess, with the IC chip having a rectangular shape and the long side of the IC chip being parallel to the linear edge of the recess. The recess portion is preferably formed within the non-recessed portion defined by the non-recessed portions on at least two edges 23. The recess can also be used to position and secure the mounting of the IC chip during assembly.

[0043] The ends of the shielding conductor and recess portion can extend from one outer side 22 of the housing 7 to the opposite second outer side 22.

[0044] An insulating layer 8 is located between the second side 9b of the IC chip and the recess portion 13 of the lead frame structure 3. The insulating layer 8 can consist of an adhesive material in order to be adhered to the second side of the IC chip and the surface portion of the lead frame covered by the insulating layer during assembly of the transducer, or can comprise an insulating foil with an adhesive coating adhered to the material of the lead frame and / or the IC chip. The insulating layer can also be soldered to the lead frame or held in the assembled position between the lead frame and the IC chip by other means before overmolding of the insulating housing 7.

[0045] In an advantageous manufacturing process of the magnetic field gradient transducer, the shielding conductor can be formed as a continuous strip extending along the length of a plurality of transducers, with the IC chips mounted in the recess at defined intervals, the lead bonding of the secondary conductor and the overmolding of the overmolding housing 7 being performed while the shielding conductor 6 remains in the form of a continuous strip. The individual transducers can then be separated by cutting the shielding conductor strip and the overmolding housing at defined intervals corresponding to the side edges 22 of the transducers.

[0046] By this method, the IC chip assembly process, the lead bonding process and the overmolding process on the lead frame structure are very economical.

[0047] List of reference signs used

[0048] Current transducer 100

[0049] Circuit board 21

[0050] Primary conductor 4

[0051] Magnetic field gradient transducer 1

[0052] Integrated circuit (IC) chip 2

[0053] First side (active side) 9a

[0054] Magnetic field sensing portion 20

[0055] Connection terminal 11

[0056] Second side 9b

[0057] Insulating layer 8 (between IC chip and lead frame) Lead frame structure 3

[0058] Secondary conductor 5

[0059] Shielding conductor 6

[0060] Secondary conductor 5

[0061] IC connection side 15

[0062] Surface mount connection terminal 16

[0063] Secondary conductor bond wire 14

[0064] Shielding conductor 6

[0065] IC mounting side 18

[0066] Non-recessed portion 12

[0067] Height H1

[0068] Recessed portion 13

[0069] Height H2

[0070] Recessed edge 23

[0071] Slot 19

[0072] Surface mount connection terminal 17

[0073] Overmolded housing 7

[0074] Mounting side 10

[0075] Outer side 22

Claims

1. A magnetic field gradient transducer (1) for surface mounting on a circuit board (21), comprising - an integrated circuit (IC) chip (2) comprising an active first side (9a), a second side (9b), at least two magnetic field sensing portions (20) on the active side, and connection terminals (11) on the active side, the at least two magnetic field sensing portions (20) being separated by a gap (G) configured for magnetic field gradient measurement, - a lead frame structure (3) comprising a plurality of secondary conductors (5) and a shield conductor (6), said shield conductor being in overlapping relationship with said IC chip, - a plurality of secondary conductor bonding wires (14) interconnecting two or more of the secondary conductors (5) to the connection terminals (11) of the IC chip, and an insulating housing (7) overmolded over the IC chip, the secondary conductor bond wires, and a portion of the leadframe structure (3), whereby the circuit board contacting portions of the secondary conductor and the shield conductor are exposed and configured for surface mount connection to the external circuit board, It is characterized by: The shield conductor has a non-recessed portion (12) and a recessed portion (13) on which the IC chip is mounted, the recessed portion having a thickness H2 smaller than a thickness H1 of the non-recessed portion and the secondary conductor.

2. The magnetic field gradient transducer according to claim 1, wherein The recessed portion is delimited on at least two edges (23) by the non-recessed portion.

3. The magnetic field gradient transducer according to any one of the preceding claims, wherein: The IC chip has a rectangular shape, and long sides of the rectangular IC chip are parallel to the at least two edges of the recessed portion.

4. A magnetic field gradient transducer according to any one of the preceding claims, wherein: The recessed portion is substantially linear.

5. The magnetic field gradient transducer according to any one of the preceding claims, wherein: The shield conductor recess extends from a first side (22) of the transducer to a second, opposing side (22) of the transducer.

6. A magnetic field gradient transducer according to any one of the preceding claims, wherein: The recessed portion extends from the first side (22) of the transducer to the second opposing side (22) of the transducer.

7. A magnetic field gradient transducer according to any one of the preceding claims, wherein: An insulating layer (8) is positioned between the second side (9b) of the IC chip and the recessed portion (13) of the leadframe structure (3).

8. An open-loop current transducer (100) comprising a circuit board (21), a primary conductor (4) formed on or in the circuit board for carrying a current to be measured, and a magnetic field gradient transducer (1) according to any preceding claim mounted on the circuit board above the primary conductor.

9. A method for manufacturing a magnetic field gradient transducer according to any one of claims 1 to 7, comprising: The shield conductor is formed into a continuous strip extending along the length of the plurality of magnetic field gradient transducers, a plurality of the IC chips are mounted in the recessed portion at defined intervals, the secondary conductor leads are bonded to the connection terminals on the IC chips, the overmolded housing (7) is overmolded over the length of the plurality of magnetic field gradient transducers while the shield conductor remains in the form of a continuous strip, and the individual transducers are then separated by cutting the shield conductor strip and the overmolded housing at defined intervals corresponding to the outer sides (22) of the transducers.

Images