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JUNE 2021 I PCB007 MAGAZINE 51 native to conventional fabrication techniques. Core-to-core joining is the most common im- plementation and most closely resembles the generic process flow. is method could be used to form alternating layers of copper and TLPS vias, but most commonly PCB subas- semblies with multiple layers interconnected by PTH are joined as large "chunks" of the over- all PCB structure. is method is also popularly used to interconnect cores of dissimilar types, whether in dielectric material, circuit density or analog/digital design rules. e core-to-core process flow is depicted in Figure 6. Figure 7 depicts a variant in which TLPS vias are mixed with conventional PTH cores and se- quential-build-up HDI with plated microvias. is process flow takes advantage of the abili- ty to fabricate the interior cores cost effective- ly and limit the expensive plated-HDI process just to high density outer layers. TLPS paste is more resistive than copper so this type of mix- and-match can provide a means to maximize signal performance in the sensitive outer layers. A third popular variant is to go full-Z with TLPS vias and no PTH or plated microvias. In this process flow, each layer undergoes just two lamination cycles no matter how many layers are in the final PCB construction. e first lam- ination cycle is used to create the double-sid- ed 2-layer core with sintered TLPS connecting the opposing faces. e standard process flow is then used to interconnect the TLPS-based cores together in a single lamination cycle. is concept is depicted in Figure 8. As with all the other process flows depicted, there are many possible variations on this theme. Figure 8: Implementation method for anywhere TLPS paste vias as exclusive Z-axis interconnect method. Figure 7: Mixed mode implementation method for installing TLPS paste vias in high-layer-count PCBs.