Plating of small blind vias [multilayer PCBs]

Metallization of laminates with blind vias on the dielectric side was performed by electroless copper plating with subsequent copper electroplating. The vertical cross section of blind vias with diameters between 125 and 75 /spl mu/m were analyzed by reflective microscopy. Results indicate that ultrasonic vibration during the pretreatment processes of metallization enables complete electroless copper deposition of the inside wall of the small blind vias without any voids. Furthermore, the introduction of periodic pulse reversal current for the subsequent copper electroplating process resulted in high throwing power deposition. By employing these two protocols, it has been demonstrated that high throwing power deposition can be readily achieved for blind vias as small as 75 /spl mu/m in diameter with an aspect ratio of 3:1.