7.1 Aspect Ratio

Aspect ratio is the ratio of thickness of the board, and maximum drill diameter of the Plated Through Holes (PTH) that are used on the board. By traditional PCB fabrication methods, the aspect ratio must not be more than 1/10. This means the PTH diameter on the board must be 1/10 of the board thickness or more. When a smaller via hole is required, blind and buried via on PCB must be used. The drill hole is usually 3 mils wider than the required diameter, as the via plating process reduces the drill diameter by 3 mils.