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ECE 546 – Jose Schutt-Aine 1 ECE 546 Lecture - 07 Nonideal Conductors and Dielectrics Spring 2014 Jose E. Schutt-Aine Electrical & Computer Engineering University of Illinois

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ECE 546 – Jose Schutt-Aine 2 : conductivity of material medium ( -1 m -1 ) Material Medium or sincethen

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ECE 546 – Jose Schutt-Aine 3 Wave in Material Medium is complex propagation constant associated with attenuation of wave associated with propagation of wave

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ECE 546 – Jose Schutt-Aine 4 Wave in Material Medium decaying exponential Solution: Magnetic field Complex intrinsic impedance

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ECE 546 – Jose Schutt-Aine 5 Skin Depth The decay of electromagnetic wave propagating into a conductor is measured in terms of the skin depth For good conductors: Wave decay Definition: skin depth is distance over which amplitude of wave drops by 1/e.

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ECE 546 – Jose Schutt-Aine 6 Skin Depth e -1 Wave motion For perfect conductor, = 0 and current only flows on the surface

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ECE 546 – Jose Schutt-Aine 7 DC Resistance l: conductor length : conductivity

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ECE 546 – Jose Schutt-Aine 8 AC Resistance l: conductor length : conductivity f: frequency

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ECE 546 – Jose Schutt-Aine 9 Frequency-Dependent Resistance Approximation is to assume that all the current is flowing uniformly within a skin depth

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ECE 546 – Jose Schutt-Aine 10 Resistance is ~ constant when >t Resistance changes with Frequency-Dependent Resistance

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ECE 546 – Jose Schutt-Aine 11 Reference Plane Current

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ECE 546 – Jose Schutt-Aine 12 r H. A. Wheeler, "Formulas for the skin effect," Proc. IRE, vol. 30, pp ,1942 Skin Effect in Microstrip

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ECE 546 – Jose Schutt-Aine 13 Current density varies as Note that the phase of the current density varies as a function of y The voltage measured over a section of conductor of length D is: Skin Effect in Microstrip

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ECE 546 – Jose Schutt-Aine 14 The skin effect impedance is where Skin Effect in Microstrip is the bulk resistivity of the conductor with Skin effect has reactive (inductive) component

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ECE 546 – Jose Schutt-Aine 15 The internal inductance can be calculated directly from the ac resistance Internal Inductance Skin effect resistance goes up with frequency Skin effect inductance goes down with frequency

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ECE 546 – Jose Schutt-Aine 16 When the tooth height is comparable to the skin depth, roughness effects cannot be ignored Surface Roughness Copper surfaces are rough to facilitate adhesion to dielectric during PCB manufacturing Surface roughness will increase ohmic losses

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ECE 546 – Jose Schutt-Aine 17 Hammerstad Model

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ECE 546 – Jose Schutt-Aine 18 Hammerstad Model h RMS : root mean square value of surface roughness height : skin depth f =t : frequency where the skin depth is equal to the thickness of the conductor

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ECE 546 – Jose Schutt-Aine 19 Hemispherical Model

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ECE 546 – Jose Schutt-Aine 20 Hemispherical Model

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ECE 546 – Jose Schutt-Aine 21 Huray Model

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ECE 546 – Jose Schutt-Aine 22 Huray Model H o : magnitude of applied H field.

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ECE 546 – Jose Schutt-Aine 23 Dielectrics and Polarization Field causes the formation of dipoles polarization No field Applied field Bound surface charge density –q sp on upper surface and +q sp on lower surface of the slab.

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ECE 546 – Jose Schutt-Aine 24 : electric flux density : applied electric field : electric susceptibility : free-space permittivity : static permittivity Dielectrics and Polarization : polarization vector

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ECE 546 – Jose Schutt-Aine 25 Material r Air Styrofoam Paraffin Teflon Plywood RT/duroid 5880 Polyethylene RT/duroid 5870 Glass-reinforced teflon (microfiber) Teflon quartz (woven) Glass-reinforced teflon (woven) Cross-linked polystyrene (unreinforced) Polyphenelene oxide (PPO) Glass-reinf orced polystyrene Amber Rubber Plexiglas Dielectric Constant

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ECE 546 – Jose Schutt-Aine 26 Material r Lucite Fused silica Nylon (solid) Quartz Bakelite Formica Lead glass Mica Beryllium oxide (BeO) Marble Flint glass Ferrite (FqO,) Silicon (Si) Gallium arsenide (GaAs) Ammonia (liquid) Glycerin Water Dielectric Constants

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ECE 546 – Jose Schutt-Aine 27 When a material is subjected to an applied electric field, the centroids of the positive and negative charges are displaced relative to each other forming a linear dipole. When the applied fields begin to alternate in polarity, the permittivities are affected and become functions of the frequency of the alternating fields. AC Variations

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ECE 546 – Jose Schutt-Aine 28 Reverses in polarity cause incremental changes in the static conductivity s heating of materials using microwaves (e.g. food cooking) When an electric field is applied, it is assumed that the positive charge remains stationary and the negative charge moves relative to the positive along a platform that exhibits a friction (damping) coefficient d. AC Variations

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ECE 546 – Jose Schutt-Aine 29 Complex Permittivity : damping coefficient : mass : free space permittivity : dipole charge : dipole density : natural frequency : applied frequency : spring (tension) factor

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ECE 546 – Jose Schutt-Aine 30 Complex Permittivity e : total conductivity composed of the static portion s and the alternative part a caused by the rotation of the dipoles

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ECE 546 – Jose Schutt-Aine 31 Complex Permittivity : total electric current density : impressed (source) electric current density : effective electric conduction current density : effective displacement electric current density

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ECE 546 – Jose Schutt-Aine 32 Complex Permittivity

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ECE 546 – Jose Schutt-Aine 33 Dielectric Properties Good Dielectrics: Good Conductors:

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ECE 546 – Jose Schutt-Aine 34 Dielectric Properties Good Dielectrics: Good Conductors:

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ECE 546 – Jose Schutt-Aine 35 Kramers-Kronig Relations There is a relation between the real and imaginary parts of the complex permittivity: Debye Equation

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ECE 546 – Jose Schutt-Aine 36 Kramers-Kronig Relations e is a relaxation time constant:

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ECE 546 – Jose Schutt-Aine 37 Material rtan Air Alcohol (ethyl) Aluminum oxide Bakelite Carbon dioxide Germanium Glass Ice Mica Nylon Paper Plexiglas Polystyrene Porcelain * x x x x x x x x x10 -3 Dielectric Materials

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ECE 546 – Jose Schutt-Aine 38 Material rtan Pyrex glass Quartz (fused) Rubber Silica (fused) Silicon Snow Sodium chloride Soil (dry) Styrofoam Teflon Titanium dioxide Water (distilled) Water (sea) Water (dehydrated) Wood (dry) x x x x x x x x x x x10 -2 Dielectric Materials

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ECE 546 – Jose Schutt-Aine 39 Source: H. Barnes et al, "ATE Interconnect Performance to 43 Gps Using Advanced PCB Materials", DesignCon 2008 PCB Stackup

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ECE 546 – Jose Schutt-Aine 40 The skew (time delay) between the two traces of the differential pair should be zero. Any skew between the two traces causes the differential signal to convert into a common signal. Differential signaling is widely used in the industry today. High-speed serial interfaces such as PCI-E, XAUI, OC768, and CEI use differential signaling for transmitting and receiving data in point-to-point topology between a driver (TX) and receiver (RX) connected by a differential pair. Differential Signaling

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ECE 546 – Jose Schutt-Aine 41 Fiber Weave Effect Source: S. McMorrow, C. Heard, "The Impact of PCB Laminate Weave on the Electrical Performance of Differential Signaling at Multi-Gigabit Data Rates", DesignCon Fiberglass weave pattern causes signals to propagate at different speeds in differential pairs

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ECE 546 – Jose Schutt-Aine 42 Source: Lambert Simonovich, "Practical Fiber Weave Effect Modeling", White Paper-Issue 3, March 2, Fiber Weave Effect

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ECE 546 – Jose Schutt-Aine 43 Source: S. Hall and H. Heck, Advanced Signal Integrity for High-Speed Digital Designs, J. Wiley, IEEE, Fiber Weave Effect

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ECE 546 – Jose Schutt-Aine 44 Source: S. McMorrow, C. Heard, "The Impact of PCB Laminate Weave on the Electrical Performance of Differential Signaling at Multi-Gigabit Data Rates", DesignCon Fiber Weave Effect Group delay variation

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ECE 546 – Jose Schutt-Aine 45 Source: S. McMorrow, C. Heard, "The Impact of PCB Laminate Weave on the Electrical Performance of Differential Signaling at Multi-Gigabit Data Rates", DesignCon Fiber Weave Effect Group delay variation: effect of angle

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ECE 546 – Jose Schutt-Aine 46 Source: S. Hall and H. Heck, Advanced Signal Integrity for High-Speed Digital Designs, J. Wiley, IEEE, Fiber Weave Effect Straight traces

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ECE 546 – Jose Schutt-Aine 47 Source: S. Hall and H. Heck, Advanced Signal Integrity for High-Speed Digital Designs, J. Wiley, IEEE, Fiber Weave Effect 45 o traces

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ECE 546 – Jose Schutt-Aine 48 Source: PCB Dielectric Material Selection and Fiber Weave Effect on High-Speed Channel Routing, Altera Application Note AN , January Fiber Weave Effect straight traces zig-zag traces

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ECE 546 – Jose Schutt-Aine 49 Source: PCB Dielectric Material Selection and Fiber Weave Effect on High-Speed Channel Routing, Altera Application Note AN , January Fiber Weave Effect Skew on straight traces

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ECE 546 – Jose Schutt-Aine 50 Source: PCB Dielectric Material Selection and Fiber Weave Effect on High-Speed Channel Routing, Altera Application Note AN , January Fiber Weave Effect Skew on zig-zag traces

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ECE 546 – Jose Schutt-Aine 51 Mitigation Techniques Use wider widths to achieve impedance targets. Specify a denser weave (2116, 2113, 7268, 1652) compared to a sparse weave (106, 1080). Move to a better substrate such as Nelco Perform floor planning such that routing is at an angle rather than orthogonal. Make use of zig-zag routing Fiber Weave Effect

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