Not long ago, a very creative engineer in Europe proposed a novel concept for layer-to-layer connections that has higher density than the conventional through-hole. That engineer is Joan Torne’ of NEXTGin Technologies BV  and his technology is called, “Vertical Conductive Structures-VeCS”. It employs the conventional PCB TH fab equipment, increases densities to that of HDI, with capabilities down to 0.4 mm pitch BGAs.
The concept is to peck-drill or route a slot or cavity into the board (for blind connections) or through the board, then metallize and plate. In the final fabrication step, slightly larger holes are drilled that creates a vertical connection between layers, as seen in Figure 1 a. As you can see from the illustration in Figure 1b, these smaller vertical connections take up less room than a conventional drilled through-hole, thus allowing more space for routing. In the example I created in Figure 1c, I compared TH, microvias and VeCS for a 1.0 mm pitch BGA. For the TH, you can squeeze 2-tracks under the dog-bone breakouts, while using swing-microvias, you can achieve 7-tracks. Equally as dense is the VeCS breakouts with 7-tracks. When dropping to 0.5 mm pitch BGAs, for TH, there is no room to route more than one-track through, if using via-in-pad, but for HDI, you can route 7 tracks between the blind-vias. VeCS is almost as dense with the ability to route 5-tracks between the vertical connections. For the larger pitches, there is some flexibility with VeCS breakout, as seen in the 1.0 mm with two different routing into the cavity.
FIGURE 1. a. The VeCS technology creates vertical traces to connect layers together rather than employing an entire hole; b. A 3D view shows the advantage of additional routing space created by using only the vertical wall; c. A comparison of the two common technologies, TH and HDI versus VeCS for two BGA breakouts-1.0 mm and 0.5 mm BGAs.
The routing rules for Figure 1c are shown in Table 1:
TABLE 1. Design and routing rules for the two BGA breakouts and routings for through-hole, HDI-microvias and VeCS technology
The VeCS manufacturing process hasn’t changed the conventional multilayer manufacturing process, just a few additional steps have been added:
1. Drill or route a slot between BGA lands
2. Metallize as normal
3. Image with VeCS breakouts adjacent to the metallized slot
4. Plate as normal
5. Strip and etch as normal
6. At final fabrication, drill out the metallization for vertical traces
The process (seen in Figure 2) does not require the use of a laser drill and is compatible with a panel plate process.
FIGURE 2. The VeCS fabrication process is very conventional
The only article published on the technology, The PCB magazine-February 2017 , indicated Joan had created test vehicles to test reliability and used Altium Designer® to create the artwork. The fabrication and testing were done by WUS. After multiple lead-free reflow cycles and thermal cycling to failure-results were comparable with through-holes. Signal integrity appears to be slightly better as the vertical trace has less inductance than a hole, but the slots or cavities may interfere with ground pours.
For the cost trade-offs, the increase routing density will hopefully allow fewer signal and reference layers or a smaller board with more-up per panel. Thus, saving money and paying for the one-up drilling or routing process to create the cavities or slots in the board.
If this is a concept that you might use, contact your favorite PCB fabricator to try a test board. If you want to use it in a design, contact NEXTGin  to see about the patent status of the technology. NEXTGin report two PCB fabricators are currently using the technology.