Issue link: https://iconnect007.uberflip.com/i/1513227
50 PCB007 MAGAZINE I DECEMBER 2023 the degree of throwing power difficulty. e following examples compare two different board designs. For illustration, assume board one has thickness of 0.063" and a via diam- eter of 0.006", for an aspect ratio of approxi- mately 10:1. Board two is 0.125" thick with a via diameter of 0.012—approximately the same aspect ratio of the thinner board. However, it has been shown that the two will not perform equally. Not all aspect ratios are equal due to the L2 factor in the Ohmic resistance model (Figure 3). e thicker board will be more dif- ficult to achieve optimum throwing power vs. the thinner board of the same aspect ratio. To understand this a bit better, Figure 4 depicts a high aspect ratio via. Note the taper- ing of the plated copper from the surface to the center of the via. e condition shown in Figure 4 is known as "dog boning" for the tapered shape of the plated copper in the via. As the copper plat- ing becomes thinner in the via, the oppor- tunity for copper cracking becomes much greater. Mitigating the "dog boning" is critical to ensuring long term reliability. More about how to optimize throwing power in a future column. PCB007 Michael Carano brings over 40 years of electronics industry experience with special expertise in manufac- turing, performance chem- icals, metals, semiconduc- tors, medical devices, and advanced packaging. To read past columns, click here. Figure 4: Tapered plating leading to lower copper plating in the via.