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86 PCB007 MAGAZINE I APRIL 2025 cause of PTH voids. e most effective desmear process available today is based on alkaline per- manganate. Although, with the development of new materials for the high frequency/low loss space and materials for improved longer-term reliability, adjustments in the desmear oper- ation may be warranted. is would include the use of plasma desmear or a combination of plasma and permanganate. I will elaborate on this subject in a future column. e use of alkaline permanganate for multi- layer circuit boards has had a dramatic effect on copper coverage and adhesion in the plated through-hole. However, this process, if not controlled, can be a major cause of voids. First, the process consists of four main chemical pro- cess steps: 1. A solvent conditioner designed to pene- trate the polymer matrix of the resin sys- tem and weaken the polymer-polymer bonds of the cross-linked chain. 2. e alkaline permanganate solution con- sisting of sodium or potassium permanga- nate and its corresponding hydroxide salt. 3. A neutralizer (possibly in combination with glass etch) for removing manganese residues. 4. Glass etch as a separate step to lightly roughen (frost) or more aggressively remove glass fibers that may be protruding into the hole due to etch-back. If any of these four steps is not controlled, it can lead to voids. If this is the case, even the most robust electroless copper processes will not be able to compensate. e effective alkaline permanganate process not only removes drill smear, but will micro- roughen the resin as shown in Figure 3. is texturing is oen referred to as the honey- combed appearance. is is desirable for two reasons: Figure 2: Horizontal section showing rough hole wall and voided areas.