Multiple-layer signal conductor
View Patent ↗A multiple-layer signal conductor has increased surface area for mitigation of skin effect. Parallel extending elongated strips of conductive material are placed in parallel layers and are separated by a thin layer of dielectric. The elongated strips are conductively connected to one another by regularly spaced vias such that a single signal conductor with multiple conductive layers is formed. During high-speed signaling, the skin effect causes current to concentrate near the surfaces of conductors. The multiple-layer signal conductor, however, has increased surface area with respect to its total cross-sectional area. The effective cross-sectional area which is conductive during high-speed signaling is therefore increased, leading to positive effects on transmission line resistance, heating, signal integrity and signal propagation delay. The multiple-layer signal conductor sees special use on silicon circuit boards and can conduct signals at ten gigahertz or greater for distances of up to five inches without rebuffering or termination.
1. An apparatus comprising:
a first elongated strip of conductive material, wherein a first point on the first elongated strip is separated from a second point on the first elongated strip by a length of at least two inches, wherein the first elongated strip has an average width of less than approximately fifteen microns;
a second elongated strip of conductive material, wherein a first point on the second elongated strip is separated from a second point on the second elongated strip by a length of at least two inches, wherein the second elongated strip is disposed over the first elongated strip, and wherein the second elongated strip extends parallel to the first elongated strip, wherein the second elongated strip has an average width of less than approximately fifteen microns;
a layer of dielectric material disposed between the first elongated strip and the second elongated strip;
a first conductive via connecting the first point on the first elongated strip to the first point on the second elongated strip;
a second conductive via connecting the second point on the first elongated strip to the second point on the second elongated strip; and
a substrate that supports the first and second elongated strips, and wherein the substrate is taken from the group consisting of: a substrate that includes fiberglass, a semiconductor substrate, a flexible insulative substrate material, and a ceramic substrate.
2. The apparatus of claim 1 , wherein the second elongated strip includes a conductive land portion.
3. The apparatus of claim 1 , wherein the first and second elongated strips are metal conductors.
4. The apparatus of claim 1 , wherein the first elongated strip has a thickness of less than two microns, and wherein the second elongated strip has a thickness of less than two microns.
5. The apparatus of claim 1 , wherein the distance between the first conductive via and the second conductive via is at least two inches.
6. The apparatus of claim 1 , wherein the first elongated strip is unterminated, and wherein the second elongated strip is unterminated.
7. The apparatus of claim 1 , wherein the layer of dielectric has a thickness of at least five hundred nanometers.
8. The apparatus of claim 1 , wherein the first elongated strip and the second elongated strip form a signal conductor, wherein the signal conductor is part of a high-speed serial bus coupled to a Field Programmable Gate Array (FPGA).
9. The apparatus of claim 1 , wherein the first elongated strip and the second elongated strip together form a signal conductor, and wherein an output lead of a signal driver is coupled to drive a signal onto the signal conductor.
10. The apparatus of claim 1 , wherein the first elongated strip and the second elongated strip conduct a signal having a rise time of less than two hundred picoseconds.
11. The apparatus of claim 10 , wherein the first elongated strip and the second elongated strip together form a signal conductor, wherein the signal conductor has a resistance of greater than ten ohms at zero hertz, and wherein the signal conductor has an effective resistance of less than fifty ohms at ten gigahertz.
12. An apparatus comprising:
a substrate taken from the group consisting of: a substrate that includes fiberglass, a semiconductor substrate, a flexible insulative substrate material, and a ceramic substrate; and
means disposed on the substrate for communicating a signal a distance of at least two inches, wherein the means has a characteristic resistance of greater than ten ohms at zero hertz, and wherein the means has an effective resistance of less than fifty ohms at ten gigahertz.
13. The apparatus of claim 12 , wherein the apparatus is a silicon circuit board.
14. A method comprising:
providing a substrate; and
providing a multi-layer signal conductor on the substrate, wherein the multi-layer signal conductor includes a first elongated strip of conductive material that has an average width of less than approximately fifteen microns and a length of at least two inches, a second elongated strip of conductive material that has an average width of less than approximately fifteen microns and a length of at least two inches, and a plurality of conductive vias that conductively connect the first and second elongated strips at substantially regular intervals.
15. The method of claim 14 , wherein the substrate is a semiconductor substrate.
16. The method of claim 14 , wherein the second elongated strip extends over and parallel to the first elongated strip.
17. The method of claim 14 , wherein the first elongated strip has a thickness of less than two microns, and wherein the second elongated strip has thickness of less than two microns.
18. The method of claim 14 , wherein the vias of the plurality of conductive vias are distributed along the first and second elongated strips such that there is at least one via in each six millimeter section of the multi-layer signal conductor.
19. The method of claim 14 , wherein the multi-layer signal conductor is unterminated.
20. The method of claim 14 , wherein the multi-layer signal conductor and substrate are parts of a silicon circuit board.