Magnetic field sensors and methods for fabricating the magnetic field sensors

• US 8,461,677 B2
• Filed: 09/23/2011
• Issued: 06/11/2013
• Est. Priority Date: 12/05/2008
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Ararao, Virgil, Sharma, Nirmal, Engel, Raymond W., Gagnon, Jay, Sauber, John, Taylor, William P., Kam-Lum, Elsa
• Primary Examiner(s): Smith, Zandra
• Assistant Examiner(s): Niesz, Jamie C
• Application Number:
  US13/241,380
• Publication Number:
  US 20120013333A1
• Time in Patent Office: 627 Days
• Field of Search: 257/678, 257/690, 257/730, 257/E23.124, 257/E23.126
• US Class Current: 257/730
• CPC Class Codes: G01R 33/0047 Housings or packaging of magnetic sensors packaging of semiconductor devices H01L23/00; Holders
• CPC Class Codes: G01R 33/02 Measuring direction or magnitude of magnetic fields or magnetic flux G01R33/20 takes precedence
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/10156 at the periphery
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 2924/1815 Shape
• CPC Class Codes: H10N 50/01 Manufacture or treatment
• CPC Class Codes: H10N 50/80 Constructional details

Abstract

Magnetic field sensors and associated methods of manufacturing the magnetic field sensors include molded structures to encapsulate a magnetic field sensing element and an associated die attach pad of a lead frame and to also encapsulate or form a magnet or a flux concentrator.

Claims

1. A magnetic field sensor, comprising:

a lead frame comprising a die attach pad, wherein the die attach pad comprises first and second opposing surfaces;

a magnetic field sensor circuit die proximate to the first surface of the die attach pad;

a molded capsule molded upon the die attach pad and enclosing the magnetic field sensor circuit die, wherein the molded capsule includes a cavity having an inner cavity surface, wherein a portion of the inner cavity surface is proximate to the second surface of the die attach pad, and wherein the cavity has a shape capable of retaining a liquid;

a magnet proximate to the second surface of the die attach pad and disposed within the cavity; and

a cured liquid encapsulant disposed within the cavity and configured to encapsulate the magnet within the cavity.

2. The magnetic field sensor of claim 1, wherein the molded capsule is comprised of a mold compound, wherein the molded capsule covers the second opposing surface of the die attach pad, wherein the mold compound of the molded capsule forms an insulating layer over the second opposing surface of the die attach pad between the magnet and the second opposing surface of the die attach pad.

3. The magnetic field sensor of claim 1, wherein the molded capsule consists of one uniform material.

4. The magnetic field sensor of claim 1, further comprising a glass filled epoxy disposed on the second surface of the die attach pad.

5. The magnetic field sensor of claim 1, further comprising a capacitor coupled across at least two leads of the lead frame at a position that results in the capacitor being encased within the molded capsule.

6. The magnetic field sensor of claim 1, wherein the magnet has a magnetic field oriented approximately perpendicular to the first and second surfaces of the die attach pad, and wherein the magnetic field sensor circuit die comprises a magnetic field sensing element having a maximum response axis approximately perpendicular to the first and second surfaces of the die attach pad.

7. The magnetic field sensor of claim 1, wherein the magnet has a magnetic field oriented approximately parallel to the first and second surfaces of the die attach pad, and wherein the magnetic field sensor circuit die comprises a magnetic field sensing element having a maximum response axis approximately parallel to the first and second surfaces of the die attach pad.

8. A magnetic field sensor, comprising:

a lead frame comprising a die attach pad, wherein the die attach pad comprises first and second opposing surfaces;

a magnetic field sensor circuit die proximate to the first surface of the die attach pad;

a molded capsule enclosing the magnetic field sensor circuit die, wherein the molded capsule includes a cavity having an inner cavity surface, wherein a bottom of the inner cavity surface is proximate to the second surface of the die attach pad, and wherein the cavity has a continuous side wall extending from the bottom to form the cavity with a shape capable of retaining a liquid; and

a cured liquid material disposed within the cavity, wherein the cured liquid material is filled with ferromagnetic particles to either generate a magnetic field or to concentrate a magnetic field.

9. The magnetic field sensor of claim 8, wherein the cavity comprises a rim distal from the bottom of the cavity, the rim having an opening in a plane parallel to the die attach pad.

10. The magnetic field sensor of claim 8, wherein the cavity has the shape capable of retaining a liquid when the liquid is not otherwise retained in relation to the cavity.