Issue link: https://iconnect007.uberflip.com/i/1513227
48 PCB007 MAGAZINE I DECEMBER 2023 Why does aspect ratio and overall board thickness matter? As shown in Figure 2, the thicker the panel, the larger the current density difference between the surface of the board and the hole. is is particularly critical in achiev- ing throwing power (TP), which is defined by the thickness of the plated copper in the cen- ter of the via divided by thickness of the plated copper on the surface. While there are numerous factors that affect throwing power, including cathodic current density, solution conductivity (sulfuric acid to copper ion concentration), and other addi- tives such as the chlo- ride ion, the aspect ratio is a significant contributor as well. is includes the over- all board thickness. As with any circuit board to be electrolytically plated, there is resis- tance to current flow into the hole vs. cur- rent flow on the sur- face. at is, there is a voltage drop as current flows from the surface through the hole. See an illustration of this in Figure 3. It is important to note that the board thick- ness effect is not a simple linear influence. In Figure 3, one can see that board thickness is shown as a squared number, which adds to Figure 1: Through-hole illustration showing aspect ratio of 60-mil thick board and 10-mil diameter via. Aspect ratio = 60/10 = 6:1. Figure 2: Measurement for throwing power. For example, assume 20.0 microns in center of hole and 25.0 microns on the surface, thus 20.0/25.0 = 80%. Figure 3: Ohmic resistance, Ohms law, E = IR.