Exposed pad backside pressure sensor package
View Patent ↗A method and apparatus are described for fabricating an exposed backside pressure sensor ( 30 ) which protects interior electrical components ( 37 ) formed on a topside surface of a pressure sensor transducer die ( 31 ) from corrosive particles using a protective gel layer ( 38 ) and molding compound ( 39 ), but which vents a piezoresistive transducer sensor diaphragm ( 33 ) formed on a backside of the pressure sensor transducer die ( 31 ) through a vent hole ( 42 ) formed in an exposed die flag ( 36 ), enabling the sensor diaphragm ( 33 ) to directly sense pressure variations without the influence of a protective gel.
1. A packaged pressure sensor, comprising:
an exposed die flag in which a vent hole is formed;
a pressure sensor transducer die comprising a sensor diaphragm formed on a backside of the pressure sensor transducer die and sensor circuitry formed on a topside of the pressure sensor transducer die, where the backside of the pressure sensor transducer is affixed to the exposed die flag so that the sensor diaphragm is directly vented to the environment through the vent hole in the exposed die flag;
one or more electrical connectors that are electrically coupled to the sensor circuitry formed on the topside of the pressure sensor transducer die; and
a molded body formed at least partially around the electrical connectors and around the pressure sensor transducer die without covering the exposed die flag, where the molded body protects the sensor circuitry formed on the topside of the pressure sensor transducer die from corrosive external environmental conditions.
2. The packaged pressure sensor of claim 1 , further comprising a protective gel covering at least part of the topside of the pressure sensor transducer die without covering the sensor diaphragm on the backside.
3. The packaged pressure sensor of claim 1 , where the exposed die flag is recessed with respect to a plurality of lead frame elements forming at least part of the electrical connectors so that the plurality of lead frame elements extend through a side surface of the molded body, while a bottom surface of the molded body is formed to be flush with the exposed die flag.
4. The packaged pressure sensor of claim 1 , where the pressure sensor transducer die comprises a piezoresistive transducer die.
5. The packaged pressure sensor of claim 1 , where the 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.
6. The packaged pressure sensor of claim 1 , where the one or more electrical connectors comprise:
one or more bond pads formed on the topside of the 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.
7. The packaged 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.
8. A method for packaging an exposed pressure sensor, comprising:
affixing a piezoresistive transducer die to a die flag so that a sensor diaphragm formed on a backside of the piezoresistive transducer die is vented through a vent hole formed in the die flag;
electrically connecting circuitry formed on a 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 and to leave exposed the die flag, where the molded body protects the circuitry formed on the topside of the piezoresistive transducer die from external environmental conditions.
9. The method of claim 8 , where affixing the piezoresistive transducer die to the die flag comprises die bonding the backside of the piezoresistive transducer die to a lead frame so that the sensor diaphragm formed on the backside of the piezoresistive transducer die is aligned with the vent hole formed in the die flag.
10. The method of claim 8 , where affixing the piezoresistive transducer die to the die flag comprises attaching the backside of the piezoresistive transducer die to a lead frame comprising a recessed die flag that is recessed with respect to a plurality of lead frame elements so that a bottom surface of the molded body is flush with the recessed die flag in which the vent hold is formed.
11. The method of claim 8 , where the piezoresistive transducer die comprises a monocrystalline silicon substrate layer having a backside surface in which an opening is formed to define the sensor diaphragm.
12. The method of claim 8 , where electrically connecting circuitry comprises wire coupling one or more bond pads formed on the topside of the piezoresistive transducer die to one or more lead frame electrical connectors.
13. The method of claim 8 , where electrically connecting circuitry comprises thermosonically bonding wire connectors to electrically connect one or more bond pads formed on the topside of the piezoresistive transducer die to one or more lead frame electrical connectors.
14. The method of claim 8 , further comprising dispensing a protective gel over the circuitry formed on the topside of the piezoresistive transducer die prior to forming the molded body and without covering the sensor diaphragm on the backside of the piezoresistive transducer die.
15. The method of claim 8 , 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 vent hole formed in the die flag.
16. The method of claim 8 , 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 pressure sensor, comprising:
a molded body housing with an opening formed in a bottom surface of the molded body housing;
an exposed pad attached to the bottom surface of the molded body housing to enclose the opening except for a vent hole that is formed in the exposed pad;
a backside piezoresistive transducer die having a diaphragm which is placed in the enclosed opening and attached to the exposed pad so that the diaphragm is vented through the vent hole; and
at least a first electrical connector protruding through said molded body housing that is electrically coupled to the backside piezoresistive transducer die.
18. The packaged pressure sensor of claim 17 , where the first electrical connector comprises:
one or more bond pads formed on the backside 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 molded body housing.
19. The packaged pressure sensor of claim 17 , where the molded body 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 pressure sensor of claim 17 , comprising a protective gel covering one or more circuits or conductors formed on a topside of the backside piezoresistive transducer die without covering the diaphragm on a backside of the backside piezoresistive transducer die.