Package for sealing an integrated circuit die

• US 6,323,550 B1
• Filed: 06/06/1995
• Issued: 11/27/2001
• Est. Priority Date: 06/06/1995
• Status: Expired due to Term

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Martin, John R., Roberts, Carl M. Jr.
• Primary Examiner(s): Chaudhuri, Olik
• Assistant Examiner(s): HA, NATHAN W
• Application Number:
  US08/471,748
• Time in Patent Office: 2,366 Days
• Field of Search: 257/254, 257/417, 257/659, 257/704
• US Class Current: 257/704
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: H01L 2224/32245 the item being metallic
• 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 2224/48465 the other connecting portion not on the bonding area being a wedge bond, i.e. ball-to-wedge, regular stitch
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• 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 2924/01019 Potassium [K]
• CPC Class Codes: H01L 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/10253 Silicon [Si]
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding

Abstract

A die has a part that is sealed with a cap. The seal can be hermetic or non-hermetic. If hermetic, a layer of glass or metal is formed in the surface of the die, and the cap has a layer of glass or metal at a peripheral area so that, when heated, the layers form a hermetic seal. A non-hermetic seal can be formed by bonding a cap with a patterned adhesive. The cap, which can be silicon or can be a metal paddle, is electrically coupled to a fixed voltage to shield the part of the die.

Claims

1. A semiconductor assembly comprising:

a die having a substrate and a movable member suspended over the substrate;

a cap bonded over the face of the die, the cap having an outer perimeter that surrounds and seals the member, the member and the cap defining a space therebetween so that the cap does not contact the member; and

a plastic package encapsulating the die and the cap, the plastic contacting the cap and not the member, the seal being sufficient to prevent plastic from contacting the member when the die is packaged.

2. The assembly of claim 1, wherein the die includes an accelerometer and the member includes a mass with a plurality of finders extending perendicular to a direction of movement, the mass being suspended over a surface of the die.

3. The assembly of claim 1, wherein the cap is bonded with an adhesive.

4. The assembly of claim 1, further including a leadframe, wirebonds extending from the leadframe to the die, and a saddle, wherein a bottom surface of the die is mounted to the paddle, and the mass is suspended over a top surface of the die.

5. The assembly of claim 1, wherein the cap includes silicon.

6. The assembly of claim 1, wherein the cap includes a metal paddle.

7. The assembly of claim 1, wherein the die has a layer of one of a glass and metal and the cap has a layer of one of a glass and a metal, the layer on the die and the layer on the cap being bonded together so that a seal between the layers is hermetic.

8. The assembly of claim 1, wherein the cap is coupled to a fixed voltage.

36. The assembly of claim 1, wherein the movable member has a body with a plurality of fingers extending away from the body.

38. The assembly of claim 6, further comprising a voltage source, wherein the metal cap is electrically coupled to the voltage source.

9. A method comprising the steps of:

positioning a cap over a semiconductor die having a part formed in a face of the die so that an outer periphery of the cap surrounds the part of the die;

providing an organic adhesive over one of the cap and a periphery of the die; and

bonding the cap over a face of a semiconductor die with the organic adhesive so that the cap surrounds and seals the part and so that the cap and the face of the die define a gap that prevents the cap from contacting the part.

10. The method of claim 9, further comprising the step of flowing plastic over the die and the cap to package the die, wherein the cap prevents the plastic from contacting the part of the die.

11. The method of claim 10, wherein the bonding step includes bonding a cap over an accelerometer.

12. The method of claim 11, wherein the part includes a suspended, movable mass, the outer perimeter of the cap surrounding and sealing the suspended, movable mass.

13. The method of claim 9, wherein the providing step includes patterning the organic adhesive around a periphery of the cap.

14. The method of claim 9, wherein the patterning step includes patterning the organic adhesive on the die.

16. The method of claim 9, wherein the cap includes a conductive material, the method further comprising a step of coupling the cap to a source of a fixed voltage.

17. The method of claim 9, further comprising, prior to the bonding step, a step of etching a central portion of the cap.

18. The method of claim 17, wherein the etching step includes forming porous silicon that getters moisture.

19. The method of claim 9, wherein the bonding step includes providing a non-conductive adhesive on one of the cap and the die.

20. The method of claim 9, wherein the bonding step includes providing a conductive adhesive between the cap and a section of the die adapted for being coupled to a fixed voltage.

15. A method comprising the steps of:

positioning a cap over a semiconductor die having a part formed in a face of the die so that an outer periphery of the cap surrounds the part of the die;

providing a first layer made of one of glass and metal on the cap;

providing a second layer made of one of glass and metal on the substrate; and

heating the first and second layers so that the layers fuse together to form a hermetic seal.

23. The method of claim 15, wherein the at least one forming step includes forming a layer of aluminum.

39. The method of claim 15, wherein at least one of the providing steps includes includes forming a layer of metal.

40. The method of claim 15, wherein the at least one forming step includes forming a layer of gold.

21. An apparatus comprising:

a metal paddle;

a semiconductor die having a suspended, movable mass in a top face of the die, and a bottom face bonded to the paddle; and

a cap bonded over the first face so that a void region is defined between the cap and the part, an outer periphery of the cap surrounding and sealing the part.

22. The apparatus of claim 21, further comprising a plastic package encapsulating the die and the cap, the plastic contacting the cap and not the part.

24. The apparatus of claim 21, wherein the cap includes silicon.

27. The apparatus of claim 21, wherein the cap is bonded with an adhesive that is thick enough to serve as a standoff to prevent contact between the mass and the cap.

28. The apparatus of claim 21, wherein the cap has a peripheral bond ring and a recessed portion.

29. The apparatus of claim 21, wherein the die is a micromachined pressure sensor and the part is a diaphragm.

30. The apparatus of claim 21, further comprising a leadframe, wherein the cap has a member extending from over the part to the leadframe.

31. The apparatus of claim 21, further including wirebonds coupling the die to the leadframe, the wirebonds being arched to a height over the die, wherein the cap has a thickness less than the height.

32. The apparatus of claim 21, wherein the cap has a silicon body and a peripheral area including one of a glass and a metal, and wherein the die has a layer of one of a glass and a metal surrounding the part, the peripheral area of the cap and the layer in the die forming a hermetic seal around the part.

33. The apparatus of claim 32, wherein the peripheral area includes gold.

34. The apparatus of claim 32, wherein the layer in the die includes aluminum.

35. The apparatus of claim 28, wherein, in the recessed portion, the cap has porous silicon for gettering moisture.

25. An apparatus comprising:

a semiconductor die having a movable part in a top face of the die; and

a can bonded over the first face so that a void region is defined between the cap and the part, an outer periphery of the cap surrounding and sealing the part, wherein the cap is made of metal.

26. The apparatus of claim 25, wherein the cap is electrically coupled to a section of the die for coupling to a fixed voltage source.

37. The apparatus of claim 25, further comprising a voltage source, wherein the metal cap is electrically coupled to the voltage source.