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84 PCB007 MAGAZINE I APRIL 2025 Trouble in Your Tank by Michael Carano, IPC CONSULTANT Causes of Plating Voids, Pre-electroless Copper In the business of printed circuit fabrica- tion, yield-reducing and costly defects can eas- ily catch even the most seasoned engineers and production personnel off guard. In this month's column, I'll investigate copper plating voids with their genesis in the pre-plating pro- cess steps. Experienced engineers oen say that many process steps and variables will influence the success or failure of obtaining a continuous void-free copper deposit in the hole. Every- thing in the process is critical to the success of the overall metallization process. One of the obvious causes of voids, or at least inadequate copper coverage, is the result of poor drilling. Figure 1 shows rough hole walls and torn-out glass bundles. A closer look at this section shows a very poorly drilled hole wall, with glass bundles protruding from the resin, as well. is is a potential cause of voiding. e rough hole walls with broken glass fibers make metallization with electroless copper challeng- ing. e result is oen a plating void or a sig- nificant thinning of the metal deposit. Later, this may lead to the electroless copper being etched away by the micro-etching step prior to electrolytic copper plating. One should immediately investigate the drill- ing operation, looking at the following: • Drill bit quality: How many hits and what is the overall condition of the drill tool? • Spindle feeds and speeds: Is the drill tool punching its way through the stack? • Slow up feed causing the torn-out glass bundles: It should be 2x the infeed rate. • Check chip loads: Experiment with differ- ent chip loads to improve quality. • Stack height: How many PCBs are in the drill stack? Consider reducing number to improve quality. Figure 2 shows a horizontal section of a plated through-hole (PTH). Again, note the poor quality in the hole wall and its effect on the plating process. e desmear operation is another potential Figure 1: A rough hole wall, where glass fiber bundles were torn out exposing a deep gouge in the resin. Astonishingly, many feel the plating process should always compensate for such a travesty. A surface like the one shown here makes it very difficult to catalyze with the palladium-based activator from the electroless copper process.