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Design007-June2021

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72 DESIGN007 MAGAZINE I JUNE 2021 e decision to embed passive compo- nents within the PCB structure is commonly prompted by two key barriers: restricted sur- face area and interconnect complexity. e PCB's functionality may also require a signifi- cant number of semiconductor packages, oen requiring very close coupling to meet their target performance potential. Regarding sur- face area challenges, many companies are con- fronted with the need to reduce end-product size to maintain a competitive edge in a partic- ular market, or to satisfy the anticipated needs of their customer base. Over 70% of the components occupying space on a typical printed circuit board are passive (resistors, capacitors, inductors). Although most passive components are mini- mal in size, they can occupy up to 50% of the board's surface area. Transferring most of the resistor elements onto the subsurface layers of the PCB will enable the designer the oppor- tunity to optimize semiconductor placement, reduce circuit board size (typical of that illus- trated in Figure 1), and ultimately achieve the most efficient interconnect between principal functions. As an alternative to the thick-film resis- tor process detailed in Part 1 of this topic, a significant number of PCB fabricators are offering embedded thin-film resistor capa- bility. In comparing the thick-film resistor forming process, photo-lithography has replaced the printing and dispensing of paste-like resist materials to define the embed- ded resistors' geometry. Many circuit board fabricators prefer the coated copper foil technology because the composite materi- al's base value range is more precise than the deposited thick-film alternative, ensuring that the value and tolerance of the formed resis- tor element is more likely to meet customer expectation. Embedding Resistor Elements, Part 2 Designers Notebook by Vern Solberg, CONSULTANT Figure 1: Comparing PCB area utilization of discrete surface-mounted resistors to that employing embedded thin-film resistors.

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