Method of forming fine pitch interconnections employing magnetic masks

• US 6,406,988 B1
• Filed: 11/12/1998
• Issued: 06/18/2002
• Est. Priority Date: 04/24/1998
• Status: Expired due to Fees

• Current Assignee: Amerasia International Technology, Inc.
• Original Assignee: Amerasia International Technology, Inc.
• Inventors: Chung, Kevin Kwong-Tai
• Primary Examiner(s): Whitehead, Jr., Carl
• Assistant Examiner(s): NOVACEK, CHRISTY L
• Application Number:
  US09/190,837
• Time in Patent Office: 1,314 Days
• Field of Search: 438/3, 438/108, 438/119, 438/612, 438/613, 438/942, 438/943, 438/945, 438/975
• US Class Current: 438/612
• CPC Class Codes: B41M 3/00 Printing processes to produce particular kinds of printed work, e.g. patterns printing apparatus or machines of special type or for particular purposes B41F17/00; special designs or pictures per se B44F; manufacturing printed circuits using printing techniques H05K3/12 ; manufacturing organic semiconductor devices using printing techniques H10K71/13
• CPC Class Codes: H01L 21/4867 Applying pastes or inks, e.g. screen printing H01L21/486 takes precedence
• CPC Class Codes: H01L 2224/05568 the whole external layer protruding from the surface
• CPC Class Codes: H01L 2224/05573 Single external layer
• CPC Class Codes: H01L 2224/05624 Aluminium [Al] as principal constituent
• CPC Class Codes: H01L 2224/11003 for holding or transferring the bump preform
• CPC Class Codes: H01L 2224/2919 with a principal constituent of the material being a polymer, e.g. polyester, phenolic based polymer, epoxy
• CPC Class Codes: H01L 2224/81192 wherein the bump connectors are disposed only on another item or body to be connected to the semiconductor or solid-state body
• CPC Class Codes: H01L 2224/83851 being an anisotropic conductive adhesive
• CPC Class Codes: H01L 24/83 using a layer connector
• 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 2924/00014 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 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/14 Integrated circuits
• CPC Class Codes: H05K 3/1225 Screens or stencils; Holders therefor
• CPC Class Codes: Y10S 438/942 Masking
• CPC Class Codes: Y10S 438/943 Movable
• CPC Class Codes: Y10S 438/945 Special, e.g. metal
• CPC Class Codes: Y10S 438/975 Substrate or mask aligning feature

Abstract

In the construction of electronic devices with one or more flip chips and, in some cases, one or more leadless components, mounted on a substrate, the interconnections are made with conductive adhesive deposited using specialized masks. A magnetic metal mask fabricated of a membrane of magnetic material is placed temporarily onto the face of a semiconductor wafer or of a circuit or other substrate. When properly positioned with respect to the wafer or substrate, such as by relational guide holes, the mask is held in place by the magnetic forces produced by a controllable electromagnet. Contact pad openings in the magnetic metal mask are formed by suitable means such as laser cutting or photo-etching. The magnetic metal mask may include a flexible interface layer on the side facing the wafer or substrate to assure tight sealing thereto, so as to reduce smearing and bridging of the conductive adhesive paste and avoid bridging between contact pads that might otherwise occur during deposition of the paste. Magnetic metal masks may be utilized for depositing various types of adhesives including both solder pastes and conductive and non-conductive polymer adhesives, on semiconductor devices, other electronic components, substrates for electronic devices and printed wiring circuit boards.

Claims

1. A method for forming a pattern of adhesive on a substrate comprising:

obtaining a substrate having a pattern of sites thereon on which adhesive is to be deposited;

obtaining a magnetic mask having a pattern of apertures therethrough corresponding to the pattern of sites, wherein the magnetic mask includes a thin metal membrane and a layer of compressible material having a surface energy less than about 50 dyne/cm formed on at least one side of the thin metal membrane, one of the thin metal membrane and the compressible material having ferromagnetic properties, and wherein ones of the apertures in the layer of compressible material are substantially larger than corresponding ones of the apertures in the thin metal membrane;

positioning the substrate and the magnetic mask proximate each other with the compressible layer against the substrate so that the pattern of sites and the pattern of apertures correspond;

controllably energizing an electromagnet to generate a magnetic field to hold the substrate and the compressible layer of the magnetic mask in close contact;

applying adhesive onto the pattern of sites of the substrate through the apertures of the magnetic mask;

controllably de-energizing the electromagnet; and

removing the magnetic mask to leave the adhesive on the pattern of sites on the substrate.

2. The method of claim 1 wherein said obtaining a magnetic mask includes obtaining a thin metal membrane of ferromagnetic material,

wherein the ferromagnetic material is selected from the group consisting of steel, carbon steel, magnetic stainless steel, nickel alloy, iron alloy, polymeric film loaded with fine ferromagnetic particles, and combinations and laminations thereof.

3. The method of claim 1 wherein said obtaining a magnetic mask includes obtaining a thin metal membrane and forming a layer of compressible polymer filled with fine ferromagnetic particles on at least one surface of the thin metal membrane.

4. The method of claim 1 wherein said obtaining a magnetic mask includes forming the pattern of apertures by at least one of photo-etching, laser machining, electroforming, die cutting and screen emulsion.

5. The method of claim 1 wherein said obtaining a substrate includes one of:

(a) obtaining a semiconductor wafer having a plurality of electrical circuits formed therein, each of the electrical circuits having contact pads that are included in the pattern of sites; and

(b) obtaining a printed wiring circuit board having an electrical circuit wiring pattern thereon, wherein the electrical circuit wiring pattern has contact pads that are included in the pattern of sites.

6. The method of claim 1,

wherein the magnetic mask has relational alignment holes in known predetermined position with respect to the pattern of apertures,

wherein the substrate has corresponding relational alignment holes in the same known predetermined position with respect to the pattern of sites, and

wherein positioning the substrate and the magnetic mask includes aligning at least two relational alignment holes on the magnetic mask with two corresponding relational alignment holes on the substrate.

7. The method of claim 6 wherein said aligning at least two relational alignment holes includes inserting respective alignment pins through each respective aligned pair of corresponding relational alignment holes of the magnetic mask and the substrate.

8. The method of claim 1 wherein said controllably energizing the electromagnet includes gradually increasing an electrical current applied to an electrical coil of the electromagnet to a first value prior to said positioning the substrate and the magnetic mask, and then gradually increasing the electrical current to a second substantially greater value.

9. The method of claim 8 wherein the second substantially greater value is sufficient to generate about 10 psi of pressure between the substrate and the magnetic mask.

10. The method of claim 1 wherein said applying adhesive includes one of:

applying a solder paste,

applying a flexible polymer adhesive, and

applying a flexible polymer adhesive filled with sufficient electrically-conductive particles to render the flexible polymer adhesive conductive.

11. The method of claim 10 wherein the flexible polymer adhesive is selected from the group consisting of thermoplastic resins and thermosetting resins.

12. The method of claim 10 wherein the electrically-conductive particles are selected from the group consisting of gold, silver, platinum, palladium, alloys thereof, and coatings thereof on a base material.

13. The method of claim 1 further comprising attaching the substrate to a device substrate having a pattern of sites thereon corresponding to the pattern of sites on the substrate, wherein the corresponding sites of the respective patterns of sites are aligned and are joined by the adhesive.

14. The method of claim 13 wherein said attaching the substrate includes at least one of:

heating the substrate and the device substrate, and

pressing the substrate and the device substrate together.

15. The method of claim 1 wherein the pattern of sites have a pitch of less than 300 microns.

16. The method of claim 1 wherein the pattern of sites have a pitch of less than 100 microns.

17. The method of claim 1 wherein at least one of the apertures has a width dimension of less than 300 microns.

18. The method of claim 1 wherein at least one of the apertures has a width dimension of less than 100 microns.

19. A method for forming a pattern of adhesive on a substrate comprising:

obtaining a substrate having a pattern of sites thereon on which adhesive is to be deposited;

obtaining a magnetic mask having a pattern of apertures therethrough corresponding to the pattern of sites, wherein the magnetic mask includes a thin metal membrane and a layer of compressible material having a surface energy less than about 50 dyne/cm formed on at least one side of the thin metal membrane, one of the thin metal membrane and the compressible material having ferromagnetic properties, wherein said obtaining a magnetic mask includes;

obtaining the thin metal membrane having the pattern of apertures therein, and

forming the layer of compressible material on at least one surface of the thin sheet of metal material,

wherein the apertures in the layer of compressible material are substantially larger than corresponding ones of the apertures in the thin metal membrane;

positioning the substrate and the magnetic mask proximate each other with the compressible layer against the substrate so that the pattern of sites and the pattern of apertures correspond;

controllably energizing an electromagnet to generate a magnetic field to hold the substrate and the compressible layer of the magnetic mask in close contact;

applying adhesive onto the pattern of sites of the substrate through the apertures of the magnetic mask;

controllably de-energizing the electromagnet; and

removing the magnetic mask to leave the adhesive on the pattern of sites on the substrate.

20. A method for forming a pattern of adhesive on a substrate comprising:

obtaining a substrate having a pattern of sites thereon on which adhesive is to be deposited;

obtaining a magnetic mask having a pattern of apertures therethrough corresponding to the pattern of sites, wherein the magnetic mask includes a thin metal membrane and a layer of compressible material having a surface energy less than about 50 dyne/cm formed on at least one side of the thin metal membrane, one of the thin metal membrane and the compressible material having ferromagnetic properties;

wherein at least one of the apertures in the layer of compressible material encompasses a plurality of ones of the apertures in the thin sheet of metal material;

positioning the substrate and the magnetic mask proximate each other with the compressible layer against the substrate so that the pattern of sites and the pattern of apertures correspond;

controllably energizing an electromagnet to generate a magnetic field to hold the substrate and the compressible layer of the magnetic mask in close contact;

applying adhesive onto the pattern of sites of the substrate through the apertures of the magnetic mask;

controllably de-energizing the electromagnet; and

removing the magnetic mask to leave the adhesive on the pattern of sites on the substrate.

21. A method for forming a pattern of adhesive on a substrate comprising:

obtaining a substrate having a pattern of sites thereon on which adhesive is to be deposited;

obtaining a magnetic mask having a pattern of apertures therethrough corresponding to the pattern of sites, wherein ones of the apertures of the magnetic mask are substantially larger at a first end than at an other end thereof;

placing the substrate and the magnetic mask proximate each other with the larger first end of the ones of the apertures near the substrate so that the pattern of sites and the pattern of apertures correspond;

after said placing, applying a controlled electrical current to controllably energize an electromagnet to provide a first magnetic field strength sufficient to conform the magnetic mask to the substrate,

wherein said applying a controlled electrical current includes gradually increasing the electrical current to a first value corresponding to the first magnetic field strength;

then aligning the substrate and the magnetic mask so that the pattern of sites and the pattern of apertures correspond;

then gradually increasing the electrical current applied to the electromagnet to a second substantially greater value to provide a second magnetic field strength substantially greater than the first magnetic field strength and sufficient to hold the magnetic mask and the substrate in close contact;

then, applying adhesive onto the pattern of sites of the substrate through the apertures of the magnetic mask;

controllably de-energizing the electromagnet by gradually decreasing the electrical current applied to the electromagnet; and

removing the magnetic mask from the substrate to leave the adhesive on the pattern of sites on the substrate.

22. The method of claim 21 wherein the magnetic mask includes a thin metal membrane and a layer of compressible material having a surface energy less than about 50 dyne/cm formed on at least one side of the thin metal membrane, one of the thin metal membrane and the compressible material having ferromagnetic properties.

23. The method of claim 21 wherein said obtaining a magnetic mask includes obtaining a thin metal membrane of ferromagnetic material,

wherein the ferromagnetic material is selected from the group consisting of steel, carbon steel, magnetic stainless steel, nickel alloy, iron alloy, polymeric film loaded with fine ferromagnetic particles, and combinations and laminations thereof.

24. The method of claim 21 wherein said obtaining a magnetic mask includes obtaining a thin metal membrane and forming a layer of compressible polymer filled with fine ferromagnetic particles on at least one surface of the thin metal membrane.

25. The method of claim 21 wherein said obtaining a magnetic mask includes forming the pattern of apertures by at least one of photo-etching, laser machining, electroforming, die cutting and screen emulsion.

26. The method of claim 21 wherein said obtaining a substrate includes one of:

(a) obtaining a semiconductor wafer having a plurality of electrical circuits formed therein, each of the electrical circuits having contact pads that are included in the pattern of sites; and

(b) obtaining a printed wiring circuit board having an electrical circuit wiring pattern thereon, wherein the electrical circuit wiring pattern has contact pads that are included in the pattern of sites.

27. The method of claim 21,

wherein the magnetic mask has relational alignment holes in known predetermined position with respect to the pattern of apertures,

wherein the substrate has corresponding relational alignment holes in the same known predetermined position with respect to the pattern of sites, and

wherein placing the substrate and the magnetic mask includes aligning at least two relational alignment holes on the magnetic mask with two corresponding relational alignment holes on the substrate.

28. The method of claim 27 wherein said aligning at least two relational alignment holes includes inserting respective alignment pins through each respective aligned pair of corresponding relational alignment holes of the magnetic mask and the substrate.

29. The method of claim 21 wherein the second substantially greater value is sufficient to generate about 10 psi of pressure between the substrate and the magnetic mask.

30. The method of claim 21 wherein said applying adhesive includes one of:

applying a solder paste,

applying a flexible polymer adhesive, and

applying a flexible polymer adhesive filled with sufficient electrically-conductive particles to render the flexible polymer adhesive conductive.

31. The method of claim 30 wherein the flexible polymer adhesive is selected from the group consisting of thermoplastic resins and thermosetting resins.

32. The method of claim 30 wherein the electrically-conductive particles are selected from the group consisting of gold, silver, platinum, palladium, alloys thereof, and coatings thereof on a base material.

33. The method of claim 21 further comprising attaching the substrate to a device substrate having a pattern of sites thereon corresponding to the pattern of sites on the substrate, wherein the corresponding sites of the respective patterns of sites are aligned and are joined by the adhesive.

34. The method of claim 33 wherein said attaching the substrate includes at least one of:

heating the substrate and the device substrate, and

pressing the substrate and the device substrate together.

35. A method for forming a pattern of adhesive on a substrate comprising:

obtaining a substrate having a pattern of sites thereon on which adhesive is to be deposited;

obtaining a magnetic mask having a pattern of apertures therethrough corresponding to the pattern of sites, wherein said obtaining a magnetic mask includes;

obtaining a thin metal membrane having the pattern of apertures therein, and

forming a layer of compressible material on at least one surface of the thin sheet of metal material,

wherein the apertures in the layer of compressible material are substantially larger than corresponding ones of the apertures in the thin metal membrane;

placing the substrate and the magnetic mask proximate each other with the larger end of the apertures near the substrate so that the pattern of sites and the pattern of apertures correspond;

after said placing, applying a controlled electrical current to controllably energize an electromagnet to provide a first magnetic field strength sufficient to conform the magnetic mask to the substrate,

wherein said applying a controlled electrical current includes gradually increasing the electrical current to a first value corresponding to the first magnetic field strength;

then aligning the substrate and the magnetic mask so that the pattern of sites and the pattern of apertures correspond;

then gradually increasing the electrical current applied to the electromagnet to a second substantially greater value to provide a second magnetic field strength substantially greater than the first magnetic field strength and sufficient to hold the magnetic mask and the substrate in close contact;

then, applying adhesive onto the pattern of sites of the substrate through the apertures of the magnetic mask;

controllably de-energizing the electromagnet by gradually decreasing the electrical current applied to the electromagnet; and

removing the magnetic mask from the substrate to leave the adhesive on the pattern of sites on the substrate.

36. A method for forming a pattern of adhesive on a substrate comprising:

obtaining a substrate having a pattern of sites thereon on which adhesive is to be deposited;

obtaining a magnetic mask having a pattern of apertures therethrough corresponding to the pattern of sites, the magnetic mask including a thin metal membrane and a layer of compressible material on at least one layer thereof,

wherein apertures in the layer of compressible material are substantially larger than corresponding ones of apertures in the thin metal membrane, and

wherein at least one of the apertures in the layer of compressible material encompasses a plurality of ones of the apertures in the thin metal membrane;

placing the substrate and the magnetic mask proximate each other so that the pattern of sites and the pattern of apertures correspond;

after said placing, applying a controlled electrical current to controllably energize an electromagnet to provide a first magnetic field strength sufficient to conform the magnetic mask to the substrate,

wherein said applying a controlled electrical current includes gradually increasing the electrical current to a first value corresponding to the first magnetic field strength;

then aligning the substrate and the magnetic mask so that the pattern of sites and the pattern of apertures correspond;

then gradually increasing the electrical current applied to the electromagnet to a second substantially greater value to provide a second magnetic field strength substantially greater than the first magnetic field strength and sufficient to hold the magnetic mask and the substrate in close contact;

then, applying adhesive onto the pattern of sites of the substrate through the apertures of the magnetic mask;

controllably de-energizing the electromagnet by gradually decreasing the electrical current applied to the electromagnet; and

removing the magnetic mask from the substrate to leave the adhesive on the pattern of sites on the substrate.