Using Image Analysis Software to Measure Throwing Power or PCB Copper Plating Thickness Uniformity

Background

In the printed circuit board (PCB) manufacturing process, copper plating is applied to a layer of copper on the resin substrate. In the back-end process, the copper plating is further sliced during patterning. A uniform, design-specified thickness of copper plating prevents short circuits or disconnection of wiring and helps ensure the required performance and reliability of the final product. For this reason, it is important to measure the throwing power (expressed as a percentage, %), which represents the uniformity of the thickness of the copper plating.

Application

The throwing power (%) of a through-hole is obtained by measuring 11 points on the hole using magnified observation through a microscope. To prepare for this measurement, the substrate is first cut in such a way as to pass through the center of the through-hole. Next, it’s buried in resin. Finally, the surface is polished and etched. It is generally accepted that the measured throwing power should be approximately 80% or greater. Streamlining this series of processes has become an important goal of PCB manufacturing.

Solution

OLYMPUS Stream® image analysis software enables easy measurement of throwing power (%) and embeds the measurement information in the stored image. Even first-time users of the software can easily follow the guided steps to obtain inspection results. A precise cut along the center of a through hole requires technical skills and is time-consuming. However, OLYMPUS Stream software enables a correction of the measurement results based on the designed value of the through-hole diameter. In addition to through-holes, it is also possible to measure micro vias, filled vias, and through-hole filled vias.