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SEPTEMBER 2018 I PCB007 MAGAZINE 15 smooth. Both qualities are ideal for high-fre- quency circuitry to minimize crosstalk, shorts, and energy losses. Markets Utilizing Additive Fabrication The smartphone market is the most visible market to bring mSAP processes to high vol- ume production, with Apple leading the pack with the launch of the iPhone 8 and iPhone X in 2017 and other manufacturers quickly adopt- ing the technology. Current designs are blend- ing a combination of layers done with subtrac- tive etch and layers with the mSAP technology. mSAP technology allows for a thinner, small- er motherboard design. This was critical to the design to allow more room for the battery and extended battery life for consumers. The tech- nology in the iPhone X reveals 30-micron trace and space (Figure 1). Predictions for the com- ing years are for trace and space to be in the 10-micron range. The concept of blending the layers, utiliz- ing the mSAP process for layers with tight pin- outs and tough routing, and combining with other layers that are processed with subtrac - tive etch, was proven to be effective in the smartphone market and is spreading to oth- er markets: wearables, medical devices, med- ical implantables, automotive and aerospace and defense. It is hard to deny the advantag- es of moving from 10-layer HDI with four-lam- ination-cycles designs, to a 6-layer single- or double-lamination design. But, this does force us to look at both design and fabrication in a new way. As fabricators develop processes for this type of requirement, design rules need to be established and reliability testing needs to be completed. Real-World Applications What type of applications are discussing or adopting this new PCB technology? Appli- cations that need extremely thin copper, ap- plications that are concerned with space and weight, and applications that have complex pin-outs pushing the capabilities of traditional PCB manufacturing are all ones that could uti- lize SAP or mSAP technology. One example is medical implantables using 20-micron trace and space technology, with a double-sided design, on polyimide, with gold conductors. The combination of polyimide and gold is also compelling for biocompatibility reasons (Figure 2). Military/aerospace applications with high- density interconnect designs requiring tight pin-outs now have the option of finer lines and smaller vias. Following stack-up structures simi - lar to the work done in the smartphone designs, success is being found domestically by inte- grating layers with SAP technology and layers with subtr active etch technology, reducing lay- er count and reducing costly lamination cycles. Figure 1: Motherboard found in the iPhone X. (Source: IFIXIT and Creative Electron) Figure 2: Circuit fabricated with SAP technology. (Source: Averatek)