Ultra-Uniform Copper Deposition in High Aspect Ratio Plated through Holes via Pulse-Reverse Plating

The uniformity and microstructure of the copper deposition in the high aspect ratio plated through holes (penetrating holes) are crucial for the performance of printed circuit board. We systematically investigated the effects of reverse pulse parameters in the period pulse reverse (PPR) plating on the uniformity and microstructure of the copper deposition, including reverse pulse frequency, reverse pulse duty cycle and reverse pulse current density. The Cu deposition behavior (throwing power) and its crystallographic characteristics, including grain size, crystallographic orientation, and grain boundary, were characterized by means of field-emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), and electron backscatter diffraction (EBSD). Our results clarify that the reverse pulse current density and duty ratio should be low to achieve the full filling and high uniformity of the through holes. The reverse pulse frequency of 1500 Hz would prevent the through holes to be fully filled. The copper electrodeposition in PTH prepared by double pulse electrodeposition has the good (111) surface texture and grain boundary distribution. This work demonstrated that the period pulse reverse (PPR) plating provides unique advantages in achieving the ultra-uniform copper deposition in the high aspect ratio plated through holes.