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46 DESIGN007 MAGAZINE I AUGUST 2018 tunately, standard decoupling capacitors have little impact over 1GHz and the only way to reduce the AC impedance of the power distri- bution network (PDN), above this frequency, is to use ECM or alternatively on-die capaci- tance. These ultra-thin laminates replace the conventional power and ground planes and have excellent stability of dielectric constant and loss up to 15GHz. As the supply chain grows and becomes more competitive, the costs associated with the use of these materi- als will continue to decrease which will make system cost reductions possible in a greater number and variety of applications. Figure 3 outlines the relative dielectric con- stant of low loss materials. 3M, embedded capacitor material (top left) is the standout. It is a copper clad laminate that utilizes an ultra-thin, high Dk-value dielectric material, between the copper planes, to deliver a capaci- tance density of up to 20nF/in 2 . Whereas, typi- cal values of Dk, for low-loss materials, vary between 3.2 and 4.0. But, keep in mind that these low loss dielectrics are placed adjacent to signal traces in which case a low Dk is required Matching material performance numbers of the dielectric constant is also important. A small difference in this value between materials can impact impedance, line widths/clearances, and thus losses significantly. Also the dielectric constant, of a material, determines the propa- gation speed of the signal in the medium. So, if Dk values vary, on different layers of the sub- strate, then bus timing may also be an issue. One should consider construction options that allow a drop-in material that matches the impedance for each layer of the stackup. With the continuous trend to smaller feature sizes and faster signal speeds, planar capaci- tor laminate or embedded capacitor materials (ECMs) are becoming a cost-effective solution for improved power integrity. This technology provides an effective approach for decoupling high-performance ICs whilst also reducing electromagnetic interference. Embedded Capacitance technology allows for a very thin dielectric layer (0.24 - 2.0 mil) that provides distributive decoupling capaci- tance and takes the place of conventional dis- crete decoupling capacitors over 1GHz. Unfor- Figure 3: Dielectric constant vs. frequency of low-loss materials.