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October 2014 • The PCB Magazine 57 All of these applications share the same objec- tive—the efficient and economical manage- ment of power. Heavy, bulky electromechanical relays are being replaced by IGBT or MOSFET switches, and these same devices are also used for power control through pulse width modula- tion of IGBT or MOSFET power stages. The problems faced by peripheral RTUs in smart grid systems are identical to those involv- ing digital power—the need to carry and con- trol loads up through 24KVA. The MiB types generating the most interest are the thick cop- per multilayer and discrete wire types and their variants, providing current management capa- bilities well in excess of the ranges needed for domestic appliances and utilities such as air conditioning and hot water heating. One of these, Schweizer's combi board, is shown in Figure 4. This structure combines thick and thin copper on the same layer, addressing the limitation of conventional thick copper MiB types where all the copper on either external or internal layers is the same thickness. The result is a "selective" technology, where heavy copper is used only where needed. Therefore, in addi- tion to the cost benefits of selectivity, the combi board enables integration of logic/control and current sensing into the same board. This level of integration is also achievable with discrete wire technologies. Häusermann's HSMtec © and Jumatech's WireLaid © provide the ability to embed 0.5 mm thick copper strips (profiles) and copper wires within the board as shown in Figure 5. The profiles and wires which make up the MiB components in a discrete wire board are bonded to tracks etched on innerlayer cores, basically forming a sandwich consisting of the etched track and the bonded elements. This patented process ensures a consistent bond line between the track and the wire/profile which is essential for uniform heat spreading and consis- tent conductor cross-sectional area. It also sim- plifies the layout task and/or conversion from conventional designs, as placement of the high current MiB components: The wires and profiles THE SMART GRID OPPORTUNITY continues figure 5: hsmtec layup. (source: häusermann gmbh)