Issue link: https://iconnect007.uberflip.com/i/636678
80 The PCB Magazine • February 2016 Panel vs. Pattern Plating Both methods of plating are being utilized in the industry. Panel plate creates greater uni- formity across the board; however, it is more de- manding on the planarizer to reduce the plated surface copper. Flash plating the electroless cop- per is not recommended as it tends to increase the aspect ratio of the hole. In most cases pattern plate is a pads-only pattern, referred to as a "dot" pattern. The pan- el after electroless metallization is imaged using photoimagable dry film resist. A half inch of non-imaged laminate copper is left exposed on all four sides. This edge is used for rack connec- tivity during electroplating. This copper edge has a thieving effect on the distribution of the copper thickness above the via. Vias or pads in the center of the panel will plate much thicker than their counterparts closer to the edge. Figure 6 shows that the current density at the different locations varies more than 2X between the vias along the edge versus the vias in the center of the panel; note that all the vias are filled in spite of the large variation in current density from via to via. All the variability in copper thickness above the via is removed during planarization. Periodic carbon treatment, to remove or- ganic contaminants leaching from the dry film, must be set up on a regular basis to ensure con- sistent performance from the electrolyte. Pre-treatment The pre-treatment is composed of the follow- ing steps: cleaner, micro-etch and acid pre-dip. Figure 7: IPC-6012D, filled via plating requirements. how to set up a suCCessful blind via hole fill dC plating proCess