Aspect Ratio is a technical term for the total board thickness divided by the minimum hole size before copper plating. PCB shops commonly enlarge the diameter of the drill hole by 0.004”-0.006” to reserve space for copper and finish, such as gold and solder, after drilling. For example, when the aspect ratio is 6 and the board thickness is 0.060”, the size of the hole before copper plating is 0.010”(0.060”/0.010”).

In most PCB shops, the maximum aspect ratio is under 7, but we can make it 20, as we have the latest technology to overcome the difficulty of getting the copper plating through the small holes completely at required copper thickness. This technology is considered crucial in building thick PCBs over 0.062” and high layer PCBs requiring 14 layers or more.