Patent Application
20070297151
In accordance with some embodiments of the present invention, a conductive polymer may be used as part of the interconnect to attach a die to a package. The conductive polymer can be used on either the package or the die. The conductive polymer may be sufficiently flexible to reduce stress in interlayer dielectric layers within the die.
As used herein, a conductive polymer is a polymer that has a conductivity of at least above 1E6 Siemens per meter (S/m) or no more than one to two orders of magnitude more resistive than copper. Examples of conductive polymers include organic polymers, copolymers, and conjugated polymers. Specific examples includes polyaniline, polypyrrole, polythiophenes (polyethylenedioxythiophene, and poly(3 hexylthiophene)), poly (p-phenylene vinylene), polyacetylene, poly(fluorene) polynaphthalene and poly(p-phenylenesulfide).
In some embodiments, conductive or nonconductive polymers may be made conductive or more conductive by inserting conductive additives such as carbon particles or metallic fibers, such as copper or silver fibers. In many cases, organic conductive polymers have delocalized conduction bands, often including aromatic units that create a band structure without localized state. Charge carriers having been introduced into conduction or valence bands dramatically increase conductivity.
In accordance with some embodiments of the present invention, desirable conductive polymers may have a deflection greater than 7 mm./N normal to their surface and greater than 10 mm./N in a tangential direction.
Referring to
The substrate 14 may include a lower metallic or copper trace 16 coupled by a vertical electrical connection or via 30 through a dielectric layer 18. The dielectric layer 18, in the vicinity of an electrical path, may be covered with a solder resist 20. An opening through the solder resist provides room for an electrical connection between the trace 16 and the solder ball 22.
In one embodiment of the present invention, a pair of metallic pads 26 and 24 may sandwich an intervening conductive polymer 28. The pads 26 and 24 may be copper in one embodiment of the present invention. In such an embodiment, the via 30 may also be formed of copper, although other materials may also be utilized. The thickness of the conductive polymer 28 may be from about 10 to 50 microns in one embodiment. In some embodiments, the combined resistance of the pads 26, 24 and polymer 28 may be about five milliOhms or less.
As a result of the arrangement shown in
Referring to
By using the conductive polymer as part of the interconnect, stress may be reduced in the interlayer dielectric within the integrated circuit. In some embodiments, the conductive polymer does not replace the solder bump, but is merely an additional layer used to reduce stress.
The formation of the polymer 28 or 28a may be done in a variety of different ways. In one embodiment, the polymer may be screen printed. Another alternative is to spin the polymer on and then, using photoresist, remove the polymer from areas where the polymer is not desired. Also, a mask may be used so that the polymer may be deposited and the mask thereafter removed. Other possible techniques include sputtering, dipping, electrophoretic coating, electron beam deposition, spraying, and vacuum deposition.
As another alternative, a monomer that will form the conductor polymer may be mixed with a polymerization catalyst to form a dispersion. One suitable polymerization catalyst is Baytron C catalyst, which is iron III toluene-sulfonate and n-butynol sold by H. C. Starck GmbH, Gostar, Germany. Baytron C catalyst is a commercially available catalyst for Baytron M polymer which is 3, 4-ethylenedioxythiophene, a monomer sold by H. C. Starck GmbH, Gostar, Germany.
Once the catalyst dispersion is formed, various techniques may be utilized to apply the polymer, including any of the techniques described above. In some embodiments, the conductive polymer may be healed or cured. Curing may occur after each application of a conductive polymer layer or may occur after the application of the entire conductive polymer coating. In some embodiments, the conductive polymer may be cured by dipping into an electrolyte solution, such as a solution of phosphoric acid and/or sulfuric acid and thereafter applying a constant voltage to the solution until the current is reduced to a pre-selected level.
Referring to
Referring to
Thus, the board 30 may correspond to the substrate 14 in some embodiments. In other embodiments, the die may be a processor secured to a substrate through a conductive polymer and the die and substrate may be packaged as an integrated circuit package that is thereafter mounted on a board such as a printed circuit board. However, generally, the substrate 14 may be coupled to the board 30. Other arrangements are also possible. Of course, the configuration of a processor-based system and its application is highly variable. For example, in addition to forming integrated circuits on motherboards or other components, the present invention may be utilized in a variety of integrated circuits, including memory integrated circuits, logic integrated circuits, and communication circuits, to mention a few examples.
Generally, embodiments will have application in situations where surface mounting of an integrated circuit to a board or other substrate is achieved while using relatively low dielectric constant materials that may be prone to cracking due to the coefficient of thermal expansion mismatching, jostling, and application of heat in processing the integrated circuit and the board.
References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application.
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
