Magnetic field sensors and methods for fabricating the magnetic field sensors

• US 8,486,755 B2
• Filed: 12/05/2008
• Issued: 07/16/2013
• 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:
  US12/328,798
• Publication Number:
  US 20100141249A1
• Time in Patent Office: 1,684 Days
• Field of Search: 438/106, 438/3, 438/126, 257/678, 257/702
• US Class Current: 438/106
• 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 method of fabricating a magnetic field sensor, comprising:

attaching a magnetic field sensor circuit die to a first surface of a die attach pad of a lead frame, the die attach pad having the first surface and a second opposing surface;

molding a molded capsule upon the die attach pad to enclose 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;

placing a magnet into the cavity and proximate to the second opposing surface of the die attach pad;

placing a liquid encapsulant into the cavity proximate to the magnet; and

curing the liquid encapsulant to a solid condition to encapsulate the magnet.

2. The method 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 with the mold compound, 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 method of claim 1, wherein the molded capsule is formed in a one step molding process.

4. The method of claim 1, further comprising placing a glass filled epoxy onto the second surface of the die attach pad.

5. The method of claim 1, further comprising attaching a capacitor 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 method 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 method 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 method of fabricating a magnetic field sensor, comprising:

attaching a magnetic field sensor circuit die to a first surface of a die attach pad of a lead frame, the die attach pad having the first surface and a second opposing surface;

forming 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;

placing a liquid material into the cavity and proximate to the second opposing surface of the die attach pad, wherein the liquid material is filled with ferromagnetic particles to either generate a magnetic field or to concentrate a magnetic field; and

curing the liquid material.

9. The method 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 method 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.