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100 I-CONNECT007 MAGAZINE I AUGUST 2026 T RO U B L E I N YO U R TA N K 1. A solvent conditioner designed to penetrate the polymer matrix of the resin system and weaken the polymer-polymer bonds of the cross-linked chain. 2. The alkaline permanganate solution consists of sodium or potassium permanganate and its corresponding hydroxide salt. 3. A neutralizer (possibly in combination with glass etch) for removing manganese resi- dues. 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 etchback. If not controlled, any of these steps can lead to voids. If this is the case, even the most robust of electroless copper processes will not be able to compensate. In Figure 4, the microroughened epoxy resin has been properly prepped by the alkaline permanga- nate process. However, today's resin systems are far more complex than standard 140°C Tg epoxy, which remains one of the easiest materials to desmear. Modern resin systems require much tighter process control. These high-performance materials are highly cross-linked polymers that display very high Tgs and are more resistant to chemical treatments, including desmear. An effective alkaline perman- ganate process not only removes drill smear, but also microroughens the resin. This surface texture, often called a honeycombed appearance (Figure 4), is desirable for two reasons: The textured surface improves palladium catalyst adsorption, which supports electroless copper deposition and coverage. It also improves copper adhesion. This improves solderability by reducing or elimi- nating blowholes during wave soldering. Inad- equate texturing can increase the risk of voiding because reduced surface texture lowers catalyst adsorption. Electroless copper deposition requires sufficient catalyst on the hole wall to initiate and maintain uniform copper coverage. During trouble- shooting, consider the following: • Is the solvent conditioner, or swellant, pene- trating the resin matrix effectively, and is the solvent system compatible with the resin? Some higher Tg materials do not respond as standard FR-4 does. Because these resins are more highly cross-linked, the solvent may have difficulty penetrating and weakening the polymer bonds, reducing the permanganate solution's ability to remove resin and create the desired texture. • Verify the operating temperature of the alka- line permanganate solution, along with the hydroxide and permanganate concentrations. Figure 3: Poorly drilled plated through-hole with torn out glass and resin gouges.