Printed circuit board with integral heat sink for semiconductor package

• US 20020043402A1
• Filed: 12/05/2001
• Published: 04/18/2002
• Est. Priority Date: 05/12/1999
• Status: Active Grant

• Current Assignee: Amkor Technology Singapore Holding Pte., Ltd. (Amkor Technology Incorporated)
• Original Assignee: Frank J. Juskey, John R. Mcmillan, Ronald P. Huemoeller
• Inventors: Juskey, Frank J., McMillan, John R., Huemoeller, Ronald P.
• Granted Patent: US 6,507,102 B2
• Time in Patent Office: Days
• US Class Current: 174/260
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48464 the other connecting portion not on the bonding area also being a ball bond, i.e. ball-to-ball
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 23/3128 the substrate having spherical bumps for external connection
• CPC Class Codes: H01L 23/3677 Wire-like or pin-like cooling fins or heat sinks
• CPC Class Codes: H01L 24/45 of an individual wire connector
• CPC Class Codes: H01L 24/48 of an individual wire 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 2924/01004 Beryllium [Be]
• CPC Class Codes: H01L 2924/01019 Potassium [K]
• CPC Class Codes: H01L 2924/01078 Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/15311 being a ball array, e.g. BGA
• CPC Class Codes: H05K 1/0204 using means for thermal conduction connection in the thickness direction of the substrate H05K1/0207 takes precedence
• CPC Class Codes: H05K 2201/0355 Metal foils
• CPC Class Codes: H05K 2201/10416 : Metallic blocks or heatsinks completely inserted in a PCB metallic supports H05K3/0061
• CPC Class Codes: H05K 3/4046 : using auxiliary conductive elements, e.g. metallic spheres, eyelets, pieces of wire
• CPC Class Codes: Y10T 29/49128 : Assembling formed circuit to base
• CPC Class Codes: Y10T 29/49155 : Manufacturing circuit on or in base

Abstract

A low-cost printed circuit board for a semiconductor package having the footprint of a ball grid array package has an integral heat sink, or “slug,” for the mounting of one or more semiconductor chips, capable of efficiently conducting away at least five watts from the package in typical applications. It is made by forming an opening through a sheet, or substrate, of B-stage epoxy/fiberglass composite, or “pre-preg,” then inserting a slug of a thermally conductive material having the same size and shape as the opening into the opening. The slug-containing composite is sandwiched between two thin layers of a conductive metal, preferably copper, and the resulting sandwich is simultaneously pressed and heated between the platen of a heated press. The heat and pressure forces the resin to the surface of the composite and into the space between the slug and the walls of the composite, where it solidifies, bonding the edges of the slug to the substrate within the opening and adhering the conductive layers to the upper and lower surfaces of the substrate. The resulting laminate can thereafter be processed as a convention printed circuit board to incorporate conventional circuit board features, e.g., circuit traces, wire bonding pads, solder ball mounting lands, and via holes.

Claims

1. A method for fabricating a low-cost printed circuit board having an integral heat sink for use in a semiconductor package, comprising:

selecting a sheet of composite material having a predetermined thickness and generally parallel top and bottom surfaces;

forming an opening through the sheet, the opening having a periphery and defining interior sidewalls on the sheet inside of the opening that are generally perpendicular to the top and bottom surfaces of the sheet;

forming a heat sink of a thermally conductive material, the heat sink having a thickness that is the about the same as the thickness of the dielectric sheet, generally parallel top and bottom surfaces, a periphery that is about the same size and shape as the periphery of the opening in the sheet, and exterior sidewalls that are generally perpendicular to the top and bottom surfaces of the heat sink;

inserting the heat sink in the opening in the dielectric sheet such that the respective top and bottom surfaces of the heat sink and the dielectric sheet are generally coplanar, with the respective exterior sidewalls of the heat sink and the interior sidewalls of the dielectric sheet in spaced opposition to each other; and

,

adhering the opposing sidewalls of the heat sink and the dielectric sheet to each other such that the heat sink is retained within the opening in the dielectric sheet, with the respective top and bottom surfaces of the heat sink and the dielectric sheet generally coplanar with each other.

2. The method of claim 1, wherein the dielectric sheet comprises a composite of a fibrous dielectric material impregnated with a thermosetting resin, and wherein adhering the spaced, opposing sidewalls of the heat sink and the dielectric sheet to each other comprises:

placing the heat sink and the dielectric sheet between the platen of a heated press;

applying heat and pressure to the top and bottom surfaces the dielectric sheet and heat sink with the press until molten resin flows from the dielectric sheet into the space between the exterior sidewalls of the heat sink and the interior sidewalls of the dielectric sheet and solidifies therein.

3. The method of claim 2, further comprising placing a layer of an electrically conductive material between a platen of the press and at least one of the top and bottom surfaces of the dielectric sheet so that molten resin flows from the dielectric sheet into contact with a facing surface of the conductive layer and adheres the conductive layer to the at least one surface of the dielectric sheet.

4. The method of claim 3, further comprising oxidizing the facing surface of the conductive layer before adhering it to the at least one surface of the dielectric sheet.

5. The method of claim 3, further comprising removing a portion of the conductive layer overlying the heat sink to expose an underlying surface of the heat sink through the layer.

6. The method of claim 5, further comprising etching the exposed surface of the heat sink to remove excess resin present thereon.

7. The method of claim 1, further comprising forming a via hole through the dielectric sheet that extends from the top surface of the sheet to the bottom surface thereof, the via hole defining interior sidewalls on the dielectric sheet inside of the via hole.

8. The method of claim 7, further comprising plating the sidewalls of the dielectric sheet inside of the via holes with an electrically conductive material.

9. The method of claim 3, further comprising forming a circuit trace in the electrically conductive layer.

10. The method of claim 9, wherein forming a circuit trace in the electrically conductive layer comprises:

printing a portion of the layer with an etch-resistant material; and

,

etching away a portion of the layer not printed with the etch-resistant material.

11. The method of claim 3, wherein the layer of electrically conductive material is adhered to the bottom surface of the dielectric sheet, and further comprising forming a land in the layer for the attachment thereto of a ball of solder.

12. The method of claim 1, wherein the heat sink comprises copper.

13. The method of claim 3, wherein the electrically conductive layer comprises copper.

14. The method of claim 2, wherein the fibrous dielectric material comprises fiberglass.

15. The method of claim 2, wherein the thermosetting resin comprises a polyimide resin, a epichloridehydrin bisphenol-A resin, or a bismaleimidetriazine resin.

17. The method of claim 16, further comprising removing portions of the electrically conductive sheets on the opposite surfaces of the substrate in regions overlying the slug.

18. The method of claim 16, further comprising drilling a via hole through the substrate and the two electrically conductive sheets.

19. The method of claim 16, further comprising forming a conductive trace, a wire bonding pad, or a solder ball mounting land in the electrically conductive sheets.

20. The method of claim 16, wherein the electrically conductive sheets comprise copper foil, the thermally conductive slug comprises copper or a beryllium-copper alloy, the substrate comprises fiberglass, and the epoxy comprises a polyimide resin, an epichloridehydrin bisphenol-A resin, or a bismaleimidetfiazine resin.

16. A method of making a low-cost printed circuit board having an integral heat sink for use in a semiconductor package, comprising:

punching an opening of a given size and shape through a porous, insulative substrate impregnated with a stage B epoxy, the substrate having a predetermined thickness and opposite surfaces;

pressing a slug of a thermally conductive metal into the opening, the slug having about the same size and shape as the opening and about the same thickness as the substrate;

positioning the substrate between two sheets of an electrically conductive metal to form a sandwich; and

,

applying heat and pressure to opposite faces of the sandwich to laminate the electrically conductive sheets to the respective opposite surfaces of the substrate and bond the slug in the opening.