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June 2017 • The PCB Magazine 65 embedded resistors on the whole motherboard. Now, our process is a subtractive process, so all the area that's not being used as resistors is basi- cally etched off; essentially 95% of that layer is gone and only 5% is left for the resistors. Since they're all termination resistors, we decided to make a small interposer board and put all the termination resistors on it. Now in- stead of getting four motherboards on a pan- el, we'll get hundreds of these small interposer boards and that will be used to attach the IC; then that'll go on to the motherboards. What this does is essentially use a lot more of the re- sistive material. And the same idea is what we're seeing in the MEMS microphone market—the concept of making it a module. You have tens of thousands of these little PCBs on a panel and each one of those PCBs has two resistors; you're basically using 30% of the resistive material now. I'm just throwing those numbers out as an example but you're using a lot more of resis - tive material in that kind of design, a modular design. But you have these smaller PCBs and es- sentially you use more material and that's what you want to do. Holden: And that's clearly what Sandborn's software showed. The more you shrink things down and use the embedded capacitor resis- tive devices in the sensor or module, the more cost effective it is unless you're using an ad- ditive process. But since most of the materi- als are subtracted and not additive, the soft- ware allows you to choose both additive and subtractive or allow both to be plotted to see the difference. But I agree, the challenge is to take the applications that you've all talked about and step back and show the partitioning or the change in thinking that allows performance to go up and cost to go down by doing things differently than we've always done it. I haven't seen any articles that talk about the way we did it 20 or 30 years ago, where it's going to be like this, but if we partition it like you said and put the interposer in there, not only do we save costs but maybe now we don't have to buy fine pitch devices because the interposer can be 0.5 mm pitch, but the top of the interposer can be 1 mm. Now you're no longer forced to use very exotic HDI technologies on a whole board when the HDI is only used Figure 7: BioMed heater application—soft tissue expansion. A DEEP LOOK INTO EMBEDDED TECHNOLOGY