PCB007 Magazine

PCB007-June2021

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18 PCB007 MAGAZINE I JUNE 2021 e simple answer is a guarded yes. Cop- per is usually chosen for its superior all- round characteristics compared to oth- er metals: product designers appreciate qual- ities such as its low resistivity, easy formabil- ity, broad compatibility with other processes and materials, stability over time and temper- ature, low cost, and relatively easy availability, to name a few. In practice, alternatives are un- likely to deliver the advantages designers are usually looking for: better performance, small- er size, lower power, lower cost. If you want to design your PCB with 1- or 2-ounce copper instead of 4 ounces, the obvi- ous solution is to use wider conductors. e price is that a larger PCB area is required, which may not be an acceptable compromise. Obviously, copper is not the only conductor available to electronics designers. An alterna- tive may be sought to overcome various issues, either commercial or technical. ese may in- clude price and availability, or there may be a requirement for certain mechanical properties or corrosion resistance. In some cases, the ap- pearance of any visible conductors may be a consideration. Regarding the design of PCB traces, in par- ticular, the first aspect to consider is the resis- tivity, ρ (Greek, rho), of the chosen conductor. is is a constant for any given material and equivalent to the resistance of a sample having unit cross-sectional area and length. Mathe- matically, ρ = RA/l (R = resistance; A = cross- sectional area; l = length), expressed in MKS units as Ohm-meter (sometimes Ohm-centi- meter). e resistivity of copper is 1.77 × 10 -6 ohm-centimeter. From this, R = ρl/A, which suggests that you could replace a 4-ounce copper conductor with 1-ounce copper of four times the width. Clearly, this would occupy more space on the PCB. You could consider changing the con- ductive material. However, copper is difficult to beat when everything is considered, such as cost, environmental characteristics, and com- patibility with other electronic materials and manufacturing processes. Aluminum is sometimes used in applications such as large inverters and power converters in e-mobility and green energy applications. Alu- minum, at around half the price or less per kilo than copper, can be more economical when very large conductors are required. Howev- er, the resistivity is higher than that of cop- per, hence demanding a larger cross-section— effectively, thicker or wider traces—to achieve the same electrical performance. You also need to consider the effect of Is it possible to use another material as a substitute for heavy copper with different characteristics and the same performance? (For example: Instead of using FR-4 with 4-ounce base copper, use a material with other characteristics with 1- or 2-ounce copper.) A Q

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