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Integrity Issues & Simulations and Measurements of Power Distribution Networks (PDN)
Keywords: power distribution networks, pdn, signal integrity
In this publication, signal integrity issues of Power Distribution Networks (PDNs) are addressed (to insure acceptable quality of signals within); Transmission line effects, Crosstalk, and Impedance mismatch. Power Integrity issues of PDNs are also addressed (to insure acceptable quality of power delivery within); Voltage drop, High impedance, Parasitic Via inductances, and Noise coupling. In this work, ANSYS™ HFSS 2013 FEM simulation techniques development, adaptive meshing, and convergence to S-parameters, Differential S-parameters, and Z-parameters to design and simulate PDNs under different conditions and the results are compared to measurements performed in our laboratories. There are several challenges in the practical design of PDNs. The Voltage Regulator is a Power Supply that keeps the voltage across a load constant as much as possible, by adjusting the amount of current supplied to the load. The challenge of designing a PDN is in accomplishing low voltage at load (0.8 V to 2.5 V) over a large varying current range (up to 100A). Bypass Capacitors work as charge storage and help to reduce the voltage drop at load points, capacitors increase the area and leakage power consumption of the chip Parasitic Via Inductances, parallel resonances can develop between de-caps and develop into very high impedance Noise Coupling. In the PDN design, the switching noise caused by a digital chip can be closely coupled to near signal traces, and the characteristics of the noise coupling depends on the clock frequency. As the layout density increases in extremely integrated structures, the noise in the power/ground networks becomes increasingly coupled to the signal traces. Differential signaling is a way of carrying electrical signals with two traces; one of the trace carries positive signal and another carries equal valued negative signal. Due to its high noise immunity, differential signaling can contain extremely high data rates (10 Gb/s) compared to single-ended signaling. Differential signaling induces current flow in a closed loop on the plane under the traces. This type of closed-loop current flow helps to reduce PDN inductance through opposing magnetic flux densities, which is very desirable for a PDN design. Therefore, Power Integrity issues including Voltage Drop, High Impedance, Parasitic Via Inductances, and Noise Coupling are included in the design. HFSS™ uses a numerical technique called the Finite Element Method (FEM). This is a procedure where a structure is subdivided into many smaller subsections called finite elements. The finite elements used by HFSS are tetrahedra, and the entire collection of tetrahedra is called a mesh. A solution is found for the fields within the finite elements, and these fields are interrelated so that Maxwell’s equations are satisfied across inter-element boundaries, yielding a field solution for the entire original structure. Once the field solution has been found, the generalized S-matrix solution is determined. In this work, ANSYS(TM) HFSS 2013 FEM simulation technique development, adaptive meshing, and convergence to S-parameters, Differential S-parameters, and Z-parameters to design and simulate PDNs under different conditions and the results are compared to measurements. These structures have been measured in Idaho Microelectronics Laboratories with the proper equipment (4 port N5225A PNA 10 MHz to 50 GHz, 4395A Impedance analyzer, coaxial calibration kits, Cascade Summit Probe Station located in a class 1000 clean room, Probes - GSG 150micron (x3), GS 150micron (x3), GS 500micron z-probe(x2) and GSG 500micron z-probe(x2), Gage kits – 1.85/2.4 mm and 3.5/2.92 mm, Calibration substrates – GS 150micron, GSG 150micron, and CSR-5, Probe contact substrates).
Aicha Elshabini, Professor Emeritus
University of Alaska Anchorage
Anchorage, AK

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