Magnetic Field Sensor Integrated Circuit with Integral Ferromagnetic Material

• US 20130249544A1
• Filed: 03/20/2012
• Published: 09/26/2013
• Est. Priority Date: 03/20/2012
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Vig, Ravi, Taylor, William P., Friedrich, Andreas P., David, Paul, Burdette, Eric, Shoemaker, Eric, Doogue, Michael C., Lo, Marie-Adelaide
• Granted Patent: US 10,234,513 B2
• Time in Patent Office: Days
• US Class Current: 324/252
• CPC Class Codes: G01B 7/30 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01R 15/202 using Hall-effect devices Hall elements in arrangements for measuring electrical power G01R21/08
• CPC Class Codes: G01R 33/0011 comprising means, e.g. flux concentrators, flux guides, for guiding or concentrating the magnetic flux, e.g. to the magnetic sensor
• CPC Class Codes: G01R 33/0047 Housings or packaging of magnetic sensors packaging of semiconductor devices H01L23/00; Holders
• CPC Class Codes: G01R 33/072 Constructional adaptation of the sensor to specific applications
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/4826 Connecting between the body and an opposite side of the item with respect to the body
• CPC Class Codes: H01L 2224/73215 Layer and wire connectors
• CPC Class Codes: H01L 2924/19105 in a side-by-side arrangement on a common die mounting substrate

Abstract

A magnetic field sensor includes a lead frame, a semiconductor die supporting a magnetic field sensing element, a non-conductive mold material enclosing the die and a portion of the lead frame, a ferromagnetic mold material secured to the non-conductive mold material and a securing mechanism to securely engage the mold materials. The ferromagnetic mold material may comprise a soft ferromagnetic material to form a concentrator or a hard ferromagnetic material to form a bias magnet. The ferromagnetic mold material may be tapered and includes a non-contiguous central region, as may be an aperture or may contain the non-conductive mold material or an overmold material. Further embodiments include die up, lead on chip, and flip-chip arrangements, wafer level techniques to form the concentrator or bias magnet, integrated components, such as capacitors, on the lead frame, and a bias magnet with one or more channels to facilitate overmolding.

Claims

1. A magnetic field sensor, comprising:

a lead frame having a first surface and a second opposing surface;

a semiconductor die having a first surface in which a magnetic field sensing element is disposed and a second opposing surface attached to the first surface of the lead frame;

a non-conductive mold material enclosing the die and at least a portion of the lead frame; and

a ferromagnetic mold material secured to a portion of the non-conductive mold material, wherein the ferromagnetic mold material is tapered from a first end proximate to the lead frame to a second end distal from the lead frame and wherein at least one of the non-conductive mold material and the ferromagnetic mold material comprises a securing mechanism for engaging the other one of the non-conductive mold material and the ferromagnetic mold material.

2. The magnetic field sensor of claim 1 wherein the ferromagnetic mold material comprises a hard ferromagnetic material to form a bias magnet.

3. The magnetic field sensor of claim 2 wherein the hard ferromagnetic material comprises at least one of a ferrite, a SmCo alloy, a NdFeB alloy, a thermoplastic polymer with hard magnetic particles, or a thermoset polymer with hard magnetic particles.

4. The magnetic field sensor of claim 1 wherein the ferromagnetic mold material comprises a soft ferromagnetic material to form a concentrator.

5. The magnetic field sensor of claim 4 wherein the soft ferromagnetic material comprises at least one of NiFe, Ni, a Ni alloy, steel, or ferrite.

6. The magnetic field sensor of claim 1 wherein the ferromagnetic mold material has a non-contiguous central region extending from adjacent to the first end of the ferromagnetic mold material to the second end of the ferromagnetic mold material.

7. The magnetic field sensor of claim 6 wherein the ferromagnetic mold material forms a substantially D-shaped, O-shaped, U-shaped, or C-shaped structure.

8. The magnetic field sensor of claim 6 wherein the non-conductive mold material comprises a protrusion extending into the central region of the ferromagnetic mold material.

9. The magnetic field sensor of claim 8 wherein the protrusion extends from adjacent to the first end of the ferromagnetic mold material to the second end of the ferromagnetic mold material.

10. The magnetic field sensor of claim 9 wherein the protrusion extends from adjacent to the first end of the ferromagnetic mold material to terminate before the second end of the ferromagnetic mold material, and wherein the ferromagnetic mold material covers the protrusion.

11. The magnetic field sensor of claim 6 further comprising a third mold material disposed in and secured to the central region of the ferromagnetic mold material, wherein the third mold material is comprised of a soft ferromagnetic material.

12. The magnetic field sensor of claim 1 further comprising a thermoset adhesive, wherein the ferromagnetic mold material is secured to a portion of the non-conductive mold material with the thermoset adhesive.

13. A magnetic field sensor comprising:

a lead frame having a first surface and a second opposing surface;

a semiconductor die having a first surface in which a magnetic field sensing element is disposed and a second opposing surface attached to the first surface of the lead frame;

a non-conductive mold material enclosing the die and at least a portion of the lead frame; and

a ferromagnetic mold material secured to a portion of the non-conductive mold material, wherein the ferromagnetic mold material comprises a non-contiguous central region extending from a first end proximate to the lead frame to a second end distal from the lead frame.

14. The magnetic field sensor of claim 13 wherein the ferromagnetic mold material is secured to a portion of the non-conductive mold material and a second portion of the lead frame that extends beyond the non-conductive mold material.

15. The magnetic field sensor of claim 13 wherein the ferromagnetic mold material is a hard ferromagnetic material.

16. The magnetic field sensor of claim 15 wherein the hard ferromagnetic material comprises at least one of a ferrite, a SmCo alloy, a NdFeB alloy, a thermoplastic polymer with hard magnetic particles, or a thermoset polymer with hard magnetic particles.

17. The magnetic field sensor of claim 13 wherein the non-conductive mold material comprises a protrusion extending into the non-contiguous central region of the ferromagnetic mold material.

18. The magnetic field sensor of claim 17 wherein the protrusion extends from adjacent to the first end of the ferromagnetic mold material to the second end of the ferromagnetic mold material.

19. The magnetic field sensor of claim 15 further comprising a third mold material disposed in and secured to the central region of the ferromagnetic mold material, wherein the third mold material is comprised of a soft ferromagnetic material.

20. A magnetic field sensor, comprising:

a lead frame having a first surface, a second opposing surface, and a plurality of leads;

at least one capacitor coupled to at least one of said plurality of leads;

a semiconductor die having a first surface in which a magnetic field sensing element is disposed and a second opposing surface;

a non-conductive mold material enclosing the die, at least a portion of the lead frame, and said at least one capacitor; and

a ferromagnetic mold material secured to a portion of the non-conductive mold material.

21. The magnetic field sensor of claim 20 wherein the ferromagnetic mold material comprises a hard ferromagnetic material.

22. The magnetic field sensor of claim 20 wherein the ferromagnetic mold material comprises a soft ferromagnetic material.

23. The magnetic field sensor of claim 20 wherein the at least one capacitor is adjacent to the first surface of the lead frame.

24. The magnetic field sensor of claim 20 wherein the at least one capacitor is adjacent to the second surface of the lead frame.

25. The magnetic field sensor of claim 20 wherein the first surface of the die is attached to the first surface of the lead frame.

26. The magnetic field sensor of claim 20 wherein the second surface of the die is attached to the first surface of the lead frame.

27. The magnetic field sensor of claim 20 wherein the lead frame has a recessed region and the at least one capacitor is positioned in the recessed region.

28. A magnetic field sensor, comprising:

a lead frame having a first surface comprising a die attach area and a second opposing surface;

a semiconductor die having a first surface attached to said die attach area and in which a magnetic field sensing element is disposed;

a non-conductive mold material enclosing the die and at least a portion of the lead frame; and

a ferromagnetic mold material secured to a portion of the non-conductive mold material.

29. The magnetic field sensor of claim 28 wherein the lead frame comprises a plurality of leads and wherein the sensor further comprises at least one capacitor coupled to at least one of the plurality of leads.

30. The magnetic field sensor of claim 29 wherein the at least one capacitor is adjacent to the first surface of the lead frame.

31. The magnetic field sensor of claim 29 wherein the at least one capacitor is adjacent to the second surface of the lead frame.

32. The magnetic field sensor of claim 28 wherein the ferromagnetic mold material comprises a hard ferromagnetic material.

33. The magnetic field sensor of claim 28 wherein the ferromagnetic mold material comprises a soft ferromagnetic material.

34. A magnetic field sensor comprising:

a lead frame;

a semiconductor die attached to the lead frame and having a first surface and a second opposing surface wherein a magnetic field sensing element is disposed in one of the first and second opposing surfaces; and

a layer of ferromagnetic material applied to the second surface of the semiconductor die by a wafer level technique.

35. The magnetic field sensor of claim 34 wherein the magnetic field sensing element is disposed in the first surface of the die and is coupled to the lead frame from the first surface of the die.

36. The magnetic field sensor of claim 34 wherein the magnetic field sensing element is disposed in the first surface of the die and is coupled to lead frame from the second surface of the die.

37. The magnetic field sensor of claim 34 wherein the magnetic field sensing element is disposed in the second surface of the die.

38. A magnetic field sensor comprising:

a lead frame having a first surface and a second opposing surface;

a semiconductor die having a first surface in which a magnetic field sensing element is disposed and a second opposing surface attached to the first surface of the lead frame;

a magnet attached to the second surface of the lead frame and having a non-contiguous central region and at least one channel extending laterally from the central region; and

an overmold material forming an enclosure surrounding the magnet, semiconductor die, and a portion of the lead frame.

39. The magnetic field sensor of claim 38 wherein the magnet comprises a mold material.

40. The magnetic field sensor of claim 38 wherein the magnet comprises a plurality of channels extending laterally from the central aperture.