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JUNE 2025 I PCB007 MAGAZINE 63 IPC-based Defect Analysis Framework Karl recommended following a system- atic troubleshooting process akin to the IPC Troubleshooting Guide. is includes: • Starting with a clear defect description • Recognizing and categorizing the defect • Understanding the cause-and-effect chain leading to void formation • Walking through each processing step involved in via formation • Identifying distinctive void patterns and locations to trace root causes Drilling and Mechanical Considerations Hole void formation can begin at the drill- ing stage. Key concerns include the strength of the bond between copper and resin. A par- ticularly vulnerable area is the bond between the oxide bonder and the prepreg layer, which tends to be weaker than the bond between copper and the core dielectric. is can result in separation, oen observed as a "pink ring." Rough drilling, or rough drilling combined with pink ring conditions, can lead to defects such as wedge voids and blow holes. Wedge voids form at the bonder interface and may be concealed by electroplated copper. If moisture becomes trapped in these voids and later vaporizes during high-temperature processes like reflow, it can rupture the cop- per plating and create a blow hole. Desmear and Etchback Processes e desmear process is designed to remove resin smears from inner-layer cop- per using oxidative chemicals like perman- ganate. It usually follows a resin-swelling step and is succeeded by neutralization to remove residues. Glass fiber etchback typi- cally employs hydrofluoric acid. Two signif- icant issues can result from poor desmear: blow holes due to trapped liquids and hole wall pull-away caused by smear residue blocking copper-to-copper bonding. See Figure 1. Pre-electroless Catalysis Sequence is multi-step chemical process is prone to various failure modes that can result in hole voids. Problems may stem from incom- patibilities among the desmear, etchback, and electroless chemistries. Issues affect- ing palladium catalyst coverage include poor temperature control, improper catalyst con- centration, and inadequate dwell time. Voids on glass areas can result from insuffi- cient or excessive etching, weak catalyzation, or a sluggish electroless bath. Voids on resin areas may be due to incomplete neutraliza- tion, plasma residues, poor conditioning, or inadequate catalysis. Electroless Copper Metallization Defects Gas bubbles, solid particles, or organic films can interfere with plating and catalyst deposition. Entrapped gas bubbles—either from external sources (e.g., air entering the bath) or internal sources (e.g., hydrogen evo- lution during the electroless process)—can create symmetrical voids near the hole cen- ter. ese resemble plating pits, with sloped copper at the edges. Figure 2: Hole void caused by gas bubble