Molded differential PRT pressure sensor

• US 8,359,927 B2
• Filed: 08/12/2009
• Issued: 01/29/2013
• Est. Priority Date: 08/12/2009
• Status: Expired due to Fees

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Hooper, Stephen R., MacDonald, James D., McDonald, William G.
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): JENKINS, JERMAINE L
• Application Number:
  US12/539,853
• Publication Number:
  US 20110036174A1
• Time in Patent Office: 1,266 Days
• Field of Search: None
• US Class Current: 73/721
• CPC Class Codes: B81B 2201/0264 Pressure sensors
• CPC Class Codes: B81B 7/0061 suitable for fluid transfer from the MEMS out of the package or vice versa, e.g. transfer of liquid, gas, sound
• CPC Class Codes: B81C 2203/0154 Moulding a cap over the MEMS device
• CPC Class Codes: G01L 19/0084 to the outside of the housing other details about the housing see G01L19/14
• CPC Class Codes: G01L 19/141 Monolithic housings, e.g. molded or one-piece housings
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• 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 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• 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 2924/1461 MEMS
• CPC Class Codes: H01L 2924/15747 Copper [Cu] as principal constituent
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 2924/1815 Shape
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding

Abstract

A method and apparatus are described for fabricating an exposed differential pressure sensor (30) which protects interior electrical components (37) formed on a topside surface of a differential pressure sensor transducer die (31) from corrosive particles using a molding compound (39), but which vents both sides of a piezoresistive transducer sensor diaphragm (33) through a first vent hole (42) formed in an exposed die flag (36) and a second vent hole (38) formed in an exposed cap structure (33), enabling the sensor diaphragm (33) to sense differential pressure variations directly or indirectly through a protective gel.

Claims

1. A packaged differential pressure sensor, comprising:

an exposed die flag in which a first vent hole is formed;

a differential pressure sensor transducer die comprising a sensor diaphragm located between a backside and topside of the differential pressure sensor transducer die and sensor circuitry located on the topside of the differential pressure sensor transducer die, where the backside of the differential pressure sensor transducer is affixed to the exposed die flag so that a backside of the sensor diaphragm is directly vented to the environment through the first vent hole in the exposed die flag;

a cap structure in which a second vent hole is located, where the cap structure is attached to the topside of the differential pressure sensor transducer die and so that the topside of the sensor diaphragm is vented to the environment through the second vent hole in the cap structure;

one or more electrical connectors that are electrically coupled to the sensor circuitry located on the topside of the differential pressure sensor transducer die; and

a molded body formed at least partially around the electrical connectors and around the differential pressure sensor transducer die without covering the first vent hole in the exposed die flag or the second vent hole in the cap structure, where the molded body covers the sensor circuitry located on the topside of the differential pressure sensor transducer die.

2. The packaged differential pressure sensor of claim 1, where the cap structure is die bonded to the differential pressure sensor transducer die.

3. The packaged differential pressure sensor of claim 1, where the exposed die flag is in substantially the same plane as a plurality of lead frame elements forming at least part of the electrical connectors so that the exposed die flag and plurality of lead frame elements are exposed at a bottom surface of the molded body.

4. The packaged differential pressure sensor of claim 1, where the cap structure comprises a top surface in which the second vent hole is located, wherein the top surface of the cap structure and the second vent hole are exposed at a top surface of the molded body.

5. The packaged differential pressure sensor of claim 1, where the differential pressure sensor transducer die comprises a piezoresistive transducer die.

6. The packaged differential pressure sensor of claim 1, where the differential pressure sensor transducer die comprises a piezoresistive transducer die formed from a monocrystalline silicon substrate layer in which an opening is formed to define the sensor diaphragm.

7. The packaged differential pressure sensor of claim 1, where the one or more electrical connectors comprise:

one or more bond pads located on the topside of the differential pressure sensor transducer die;

a wire connector connected to each of the one or more bond pads; and

a lead frame element connected to each wire connector, where the lead frame element extends through the molded body.

8. The packaged differential pressure sensor of claim 1, where the molded body comprises a QFN (Quad Flat No leads), SOIC (Small-Outline Integrated Circuit), QFP (Quad Flat Package), or LGA (Land Grid Array) packaging body.

9. A method for packaging an exposed differential pressure sensor, comprising:

affixing a piezoresistive transducer die to a die flag so that a differential sensor diaphragm formed on the piezoresistive transducer die has a backside that is vented through a first vent hole formed in the die flag;

attaching a cap structure having a second vent hole to a topside of the piezoresistive transducer die so that the differential sensor diaphragm formed on the piezoresistive transducer die has a topside that is vented through the second vent hole in the cap structure;

electrically connecting circuitry located on the topside of the piezoresistive transducer die to one or more electrical connectors; and

forming a molded body at least partially around the one or more electrical connectors and around the piezoresistive transducer die to cover at least the circuitry on the topside of the piezoresistive transducer die without covering the first vent hole in the exposed die flag or the second vent hole in the cap structure.

10. The method of claim 9, where affixing the piezoresistive transducer die to the die flag comprises die bonding a backside of the piezoresistive transducer die to a lead frame so that the differential sensor diaphragm formed on the backside of the piezoresistive transducer die is aligned with the first vent hole formed in the die flag.

11. The method of claim 9, where affixing the piezoresistive transducer die to the die flag comprises attaching a backside of the piezoresistive transducer die to a lead frame comprising an exposed die flag that is in substantially the same plane as a plurality of lead frame elements forming at least part of the electrical connectors so that the exposed die flag and plurality of lead frame elements are exposed at a bottom surface of the molded body.

12. The method of claim 9, where the piezoresistive transducer die comprises a monocrystalline silicon substrate layer having a backside surface in which an opening is formed to define the backside of the differential sensor diaphragm.

13. The method of claim 9, where electrically connecting circuitry comprises wire coupling one or more bond pads located on the topside of the piezoresistive transducer die to one or more lead frame electrical connectors.

14. The method of claim 9, where electrically connecting circuitry comprises thermosonically bonding wire connectors to electrically connect one or more bond pads located on the topside of the piezoresistive transducer die to one or more lead frame electrical connectors.

15. The method of claim 9, where forming the molded body comprises overmolding or transfer molding a composite material to cover at least the circuitry on the topside of the piezoresistive transducer die without covering the first vent hole in the exposed die flag or the second vent hole in the cap structure.

16. The method of claim 9, where forming the molded body comprises forming a QFN (Quad Flat No leads), SOIC (Small-Outline Integrated Circuit), QFP (Quad Flat Package), or LGA (Land Grid Array) packaging body.

17. A packaged differential sensor, comprising:

a piezoresistive transducer die having a differential sensor diaphragm with first and second sensor surfaces;

an exposed pad attached to the piezoresistive transducer die having a first vent hole located in the exposed pad for venting the first sensor surface of the differential sensor diaphragm to a first external environment;

a cap structure attached to the piezoresistive transducer die having a second vent hole located in the cap structure for venting the second sensor surface of the differential sensor diaphragm to a second external environment;

a housing formed to surround and protect the piezoresistive transducer die without covering the first and second vent holes; and

at least a first electrical connector protruding through said housing that is electrically coupled to the piezoresistive transducer die.

18. The packaged differential pressure sensor of claim 17, where the first electrical connector comprises:

one or more bond pads located on the piezoresistive transducer die;

a wire connector connected to each of the one or more bond pads; and

a lead frame element connected to each wire connector, where the lead frame element extends through the housing.

19. The packaged differential pressure sensor of claim 17, where the housing comprises a QFN (Quad Flat No leads), SOIC (Small-Outline Integrated Circuit), QFP (Quad Flat Package), or LGA (Land Grid Array) packaging body.

20. The packaged differential pressure sensor of claim 17, where the cap structure comprises a silicon cap that is mounted to the piezoresistive transducer die with glass frit, direct bonding, epoxy, fusion bonding, or solvent bonding so that the second vent hole is aligned with the second sensor surface of the differential sensor diaphragm.