Leadframeless package structure and method
A method for providing a leadframeless package structure is provided. The method includes providing a temporary carrier. The temporary carrier is coupled to a metal foil layer with a temporary adhesive layer. An integrated circuit chip is coupled to the metal foil layer. The temporary adhesive layer and the temporary carrier are removed to form the leadframeless package structure after molding.
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The present invention is directed in general to integrated circuits and, more specifically, to a leadframeless package structure and method.
BACKGROUND OF THE INVENTIONA conventional integrated circuit package generally comprises a leadframe made from 0.005-inch thick metal, an integrated circuit made of silicon, and a protective material to protect the electrical connections between the integrated circuit and the leadframe. The leadframe acts as an electrical and mechanical interface between the integrated circuit and the printed circuit board (PCB) on which the integrated circuit package is soldered. These packages are generally known as Dual-In-Line Package (DIP), Small Outline package (SO), or Quad Flat Package. (QFP). In the manufacturing of these packages with leadframes, heavy industrial tools such as stamping and forming are required. These tools are expansive and dedicated to one package size and pin count. A leadframeless package is highly desirable because it requires a minimum of dedicated tooling such as, for example, one photomask and one solder ball fixture.
Recent development of higher pin count packages has substituted the leadframe with a fiberglass material. These packages are generally known as Ball Grid Array (BGA). The fiberglass material has metal foils (0.0015-inch thick) on the top and bottom sides and conductor patterns are etched on both sides to connect the die to the PCB.
Conventional packaging options for high performance integrated circuit dice include the use of a substrate or leadframe as a carrier. These are normally incorporated D permanently in the final package structure. Disadvantages associated with these package structures include a limited ability to re-use the leadframe or substrate for another die. The leadframe or substrate becomes a fixed material cost for every package manufactured. The tooling for stamping the leadframe and the artwork for etching new substrates are quite substantial when there is a change in die size as the feature size of the integrated circuit is shrunk. In addition, the substrate or leadframe contributes to the thickness of the package structure, which is generally desired to be minimized. Also, when solder balls are used with the integrated circuit die, as in BGA packages, the width and depth of the package structure may be greater than desired due to the inclusion of the connections to the solder balls that are exterior to the area encompassed by the die.
SUMMARY OF THE INVENTIONIn accordance with the present invention, a leadframeless package structure and method are provided that substantially eliminate or reduce disadvantages and problems associated with conventional systems and methods. In particular, a temporary carrier that is coupled to the structure during formation is removed after formation is complete, resulting in a structure without a leadframe.
According to one embodiment of the present invention, a leadframeless package structure is provided that includes a temporary carrier, a metal foil layer, an integrated circuit chip, a plurality of bonding wires, and a molding compound. After attaching the metal foil layer to the temporary adhesive/carrier system, the metal foil is patterned and etched (using conventional techniques commonly known in the PCB industry) to produce a set of planar electrical traces, die attach pads and bonding pads. The die is then attached (using conventional semiconductor assembly techniques) to the special die attach pad formed in the metal foil. Subsequently, conventional wirebond techniques are used to form electrical interconnects between the die and the electrical traces in the metal foil. Special pads are also provided in the metal foil for this purpose. Following a molding step, which encases the delicate wirebonds and die with a plastic which provides rigidity and protection, the temporary carrier portion is removed.
Technical advantages of one or more embodiments of the present invention include providing an improved leadframeless package structure. In a particular embodiment, a temporary carrier is coupled to the structure with a suitable adhesive layer during formation. The adhesive and carrier system are removed after molding. As a result, the chips attached to the structure have no leadframes or substrates. Accordingly, the leadframeless package structure has a reduced fixed cost of materials, is capable of accommodating large and small dice at minimum tooling cost, has a reduced thickness due to the absence of a carrier, and can provide a chip-scale package when second level interconnects (e.g., solder pads) are located within the approximate footprint of the die.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, description, and claims.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.
BRIEF DESCRIPTION OF THE DRAWINGSFor a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals represent like parts, in which:
FIGS. 1A-E are a series of schematic cross-sectional diagrams illustrating a method for forming a leadframeless package structure in accordance with one embodiment of the present invention;
FIGS. 2A-B are schematic cross-sectional diagrams illustrating an alternate embodiment for the steps illustrated in FIGS. 1D-E; and
FIGS. 4A-D are schematic top-view diagrams illustrating the leadframeless package structure of
Referring to
The temporary adhesive layer 30 is formed over the temporary carrier 20. The temporary adhesive layer 30 may be formed by any suitable means. The temporary adhesive layer 30 comprises a material that may be removed from a metal layer without damage to the metal layer. For example, the temporary adhesive layer 30 may comprise silicone or other suitable adhesive material.
Referring to
A mask (not illustrated in
Referring to
The permanent adhesive 60 comprises a non-conductive material that will adhere to the metal foil layer 40 and to the chips 50 indefinitely. For example, the permanent adhesive 60 may comprise an epoxy, such as QMI 536, manufactured by Quantum Materials, Inc., or other suitable adhesive material.
Referring to
A molding compound 80 is conventionally formed outwardly of the metal foil layer 40 and the chips 50. The molding compound 80 forms a rigid encasement that covers the metal foil layer 40, the chips 50, and the bonding wires 70, thereby protecting the electrical connections between the chips 50 and the metal foil layer 40. The molding compound 80 may comprise any suitable insulative material, such as epoxy novolac thermoset plastic_EME 6600, manufactured by Sumitomo Bakelite Co., Ltd., or the like. The chips 50 may be arrayed in a matrix of groups of related dice or in a matrix array of individual dice. It is possible to overmold the entire array of dice or array of groups of dice at once using a single cavity or alternatively to overmold individual dice or individual groups of dice using a cavity for each group or unit. If the former method is used, the individual components will need to be singulated from the bulk group using conventional semiconductor assembly manufacturing techniques.
Referring to
The resulting structure 10 may then be coupled to a printed circuit board (not illustrated in
Thus, the structure 10 provides a set of chips 50 without leadframes or carriers. Thus, this leadframeless package structure 10 has a minimum material cost, is capable of more easily accommodating die size changes with minimum tooling cost for the patterning of one layer instead of multiple layers in a BGA substrate, has a reduced thickness due to the lack of leadframes or substrates, and provides a chip-scale package when the solder pads are arrayed approximately underneath the chip 50.
FIGS. 2A-B are schematic cross-sectional diagrams illustrating an alternate embodiment for the steps illustrated in FIGS. 1D-E. Thus, referring to
As described in connection with
Thus, the molding compound 80 is operable to cover the metal foil layer 40, the areas of the chip 50 other than the exposed surface 90, and the bonding wires 70, thereby protecting the electrical connections between the chips 50 and the metal foil layer 40.
Referring to
FIGS. 4A-D are schematic top-view diagrams illustrating the leadframeless package structure 10 in accordance with multiple embodiments of the present invention. For each of the embodiments illustrated in FIGS. 4A-D, the chips 50 may comprise the chips 50 illustrated in
For the embodiment illustrated in
For the embodiment illustrated in
For the embodiment illustrated in
Although the illustrated embodiment comprises four chips 50 in each multi-chip module, it will be understood that each multi-chip module may comprise any suitable number of chips 50 without departing from the scope of the present invention. In addition, although the illustrated embodiment comprises four multi-chip modules for the molded section 150, it will be understood that each molded section 150 may comprise any suitable number of multi-chip modules without departing from the scope of the present invention.
Although the present invention has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.
Claims
1-14. (canceled)
15. A leadframeless package structure, comprising:
- a temporary carrier:
- a metal foil layer;
- a temporary adhesive coupling the temporary carrier and the metal foil layer;
- an integrated circuit chip coupled to the metal foil layer;
- a plurality of bonding wires, each bonding wire coupling a specified area of the chip to the metal foil layer; and
- a molding compound formed outwardly of the metal foil layer, the bonding wires and the chip;
- wherein the temporary adhesive when thermally softened allows the temporary carrier to be uncoupled from the metal foil layer, the temporary adhesive when thermally softened having an adhesion to the temporary carrier that is greater than an adhesion to at least one of: the metal foil layer and the molding compound.
16. (canceled)
17. The leadframeless package structure of claim 15, the temporary carrier comprising at least one of aluminum, stainless steel, and laminate epoxy fiberglass, and the temporary adhesive layer comprising silicone.
18. The leadframeless package structure of claim 15, further comprising a permanent adhesive coupling the chip to the metal foil layer.
19. The leadframeless package structure of claim 15, the metal foil layer comprising at least one of copper and gold-plated copper.
20. A leadframeless package structure comprising a multi-chip module, the multi-chip module comprising:
- at least one temporary carrier:
- at least one metal foil layer;
- a temporary adhesive coupling the at least one temporary carrier and the at least one metal foil layer:
- a plurality of integrated circuit chips:
- a permanent adhesive coupling the integrated circuit chips to the at least one metal foil layer;
- a plurality of bonding wires, each bonding wire coupling a specified area of one of the chips to one of the metal foil layers; and
- a molding compound formed outwardly of the metal foil layers, the bonding wires and the chips;
- wherein the temporary adhesive when thermally softened allows the at least one temporary carrier to be uncoupled from the at least one metal foil layer, the temporary adhesive when thermally softened having an adhesion to the at least one temporary carrier that is greater than an adhesion to at least one of: the at least one metal foil layer and the molding compound.
21. The leadframeless package structure of claim 18, wherein the permanent adhesive comprises an epoxy resin.
22. The leadframeless package structure of claim 15, wherein the temporary carrier comprises a rigid temporary carrier.
23. The leadframeless package structure of claim 15, wherein the metal foil layer is patterned and etched to form circuit patterns.
24. The leadframeless package structure of claim 15, wherein the plurality of bonding wires couple bond pads on the chip to the metal foil layer.
25. The leadframeless package structure of claim 15, wherein the molding compound is selectively formed over and around portions of the chip to expose a surface of the chip.
26. The leadframeless package structure of claim 20, wherein the at least one temporary carrier comprises at least one rigid temporary carrier.
27. The leadframeless package structure of claim 20, wherein the at least one temporary carrier comprises at least one of aluminum, stainless steel, and laminate epoxy fiberglass, and the temporary adhesive layer comprises silicone.
28. The leadframeless package structure of claim 20, wherein the at least one metal foil layer comprises at least one of copper and gold-plated copper.
29. The leadframeless package structure of claim 20, wherein the permanent adhesive comprises an epoxy resin.
30. The leadframeless package structure of claim 20, wherein the at least one metal foil layer is patterned and etched to form circuit patterns.
31. The leadframeless package structure of claim 20, wherein the plurality of bonding wires couple bond pads on the chips to the at least one metal foil layer.
32. The leadframeless package structure of claim 20, wherein the molding compound is selectively formed over and around portions of at least one of the chips to expose a surface of at least one of the chips.
33. A leadframeless package structure, comprising:
- a rigid temporary carrier;
- a metal foil layer coupled to the rigid temporary carrier by a temporary adhesive;
- an integrated circuit chip coupled to the metal foil layer;
- a plurality of bonding wires each coupling the chip to the metal foil layer; and
- a molding compound formed outwardly of the metal foil layer, the bonding wires and the chip;
- wherein the temporary adhesive is capable of allowing the rigid temporary carrier to be uncoupled from the metal foil layer, the temporary adhesive further capable of adhering more to the rigid temporary carrier than to the metal foil layer and the molding compound when the rigid temporary carrier is uncoupled from the metal foil layer.
34. The leadframeless package structure of claim 33, wherein the temporary adhesive when thermally softened has an adhesion to the temporary carrier that is greater than an adhesion to at least one of: the metal foil layer and the molding compound.
35. The leadframeless package structure of claim 33, wherein the molding compound is selectively formed over and around portions of the chip to expose a surface of the chip.
Type: Application
Filed: Apr 25, 2006
Publication Date: Nov 23, 2006
Applicant: STMicroelectronics, Inc. (Carrollton, TX)
Inventors: Harry Siegel (Hurst, TX), Anthony Chiu (Richardson, TX)
Application Number: 11/410,501
International Classification: H01L 23/495 (20060101);