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64 PCB007 MAGAZINE I JUNE 2025 Particles blocking plating may become embedded in surrounding copper. eir nature can be determined using techniques like EDX (for inorganic particles) or FTIR (for organics). Eliminating gas bubble voids involves using agitation techniques such as bump and vibration, along with optimized panel spacing and paddle stroke. Electroplating-related Voids Acid copper plating baths generally produce fewer voids due to high efficiency, but improper practices like excessive current or ripple can lead to hydrogen evolution. Tin baths are less efficient and more prone to gas issues unless additives are used to suppress pitting. Air bubbles trapped in holes during bath immersion are a common problem. Solu- tions include using angled plating racks, pad- dle agitation, and air sparging. However, air sparging itself can introduce gas. Supersatu- ration from filter pumps can form bubbles, as can flaws on hole walls. Eductors are increas- ingly favored as a better alternative. Figure 3: Illustration of a rim void. Figure 4: Hole void due to broken tent Plating-related voids can arise from poor throwing power, poor current distribution, agitation faults, and filter or anode issues. Particulate contamination may indicate worn filters or damaged anode bags. Rim Voids and Their Causes Rim voids are metal coverage gaps near the surface of the board. Typically caused by photoresist entering the hole, they appear 50–75 microns from the board surface. e problem occurs when hot air in the hole dur- ing lamination cools, creating a pressure drop that pulls resist into the hole. See Figure 3. Contributing factors include: • Moisture in the hole prior to lamination • Small-diameter or high-aspect-ratio holes • Long intervals between lamination and development • Changes in photoresist formulation or lamination technique Drying the board adequately aer surface preparation is the most effective remedy. Tenting Process Defects In tent-and-etch processing, a punctured