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76 PCB007 MAGAZINE I APRIL 2019 dustry has been leaning towards the complete- ly copper filled blind microvia rather than a plugged microvia as the leading edge solution. Today, copper-filled microvias are the standard for almost all HDI PCB manufacturers. The second driver is the thermal management on a substrate. One source [1] said it this way: "As the power and packing density of elec- tronic components increase, the amount of waste heat generated in a small space also rises greatly. This results in dangerously high tem- peratures, and thus increases the failure risk of electronic devices. Today, 55% of electronic component failures are caused by increased temperatures alone." Solutions were needed to integrate features with high thermal conductivity to manage the heat transfer on the substrates from one side to the other to minimize hot spots on the electron - ic devices over a lifetime. Higher-performing chips tend to generate local hot spots, result- ing in material degradation and premature field failure. Integration of thermal vias in high-per- formance electronics can minimize the occur- rence of hot spots; therefore, their utilization in the industry has become more widespread. In the beginning, thermal vias were noth- ing more than standard conformal vias, but the thermal conductivity was not good enough. Fol- lowing that, plugging pastes were introduced to enhance the thermal conductivity of a standard through-hole. But in this case, similar disadvan- tages of plugging appeared. Meanwhile, com- plete copper-filled through-holes were realized in 2006 by bridge plating or X-plating technolo- gy. Today, completely copper-filled through-hole structures are at the leading edge of technology for thermal via structures because copper has almost the best thermal conductivity—and it has to be plated, nonetheless. The third driver is signal frequency. Elec- tronic signal frequencies in an electronic pack- age or inside of a PCB are increasing over time and continue to do so. Stacked microvias and fan-out vias are becoming more and more of a disadvantage for the transmission of high- frequency signals due to creating resistances at high frequencies. Thus, the push of high- frequency applications further increased the demand for technologies like copper-filled through holes. Right now, 5G infrastructure is already using the copper-filled through-hole technology in the field of smartphones. The fourth driver, especially for through- hole filling, is the quality-and-yield aspect. The alternatives for electroplated copper-filled through-holes require many additional process steps or new materials, such as plugging paste (explained in Figure 6 later in this article). Each of these additional process steps or materials introduces a variety of risks and manufacturing problems, resulting in a lower yield. Therefore, the "one-step" solution to fill through-holes with copper is the preferred solution without introducing new materials into the PCB. Microvia Filling With Copper The filling of microvias with copper was es- tablished as a standard in PCB HDI production more than 20 years ago. For example, there was the introduction of supervia filling tech- nology with very low plated-copper thickness on the surface (Figure 1). Meanwhile, the copper filling of microvias re- placed many other filling technologies, such as plugging and capping realized by paste printing and overplating with copper (Figure 2). Both technologies—plugging and capping and cop- per-filled microvias—enable the so-called via- in-pad structure (Figure 3), which has the ad- vantage for PCB designers. The advantages of the via-in-pad designs are also useful for high- speed designs. Figure 1: Patented "SuperFilling" technology.