Issue link: https://iconnect007.uberflip.com/i/1361971
76 PCB007 MAGAZINE I APRIL 2021 ere are several possible causes for the con- dition shown in Figure 1: • Inadequate desmear • Overactive electroless copper process • Drill debris • Excess catalyst • Insufficient filtering of electroless copper solution • Instability ("dusting" in the bath) • Excessive solvent penetration • Poor rinsing or rinse water quality A more typical example of HWPA is depict- ed in Figure 3. e deposit pulled away from the hole wall but did not fracture or flake off. Nonetheless, this is a defect and must be rem- edied. e root cause of HWPA is very simi- lar to those that lead to flaking and blistering. I consider this at the very least a "process indi- cator." is means that the desmear and met- alization processes need attention. Of course, if the hole wall pull-away causes a violation of hole wall minimum diameter or leads to oth- er violations in hole diameter dimensional re- quirements, then this is, of course, a cause of concern and will result in non-conformance. So, one is dealing with the origin of the blis- ter or peeling deposit prior to electrolytic cop- per plating. Table 1 lists the most common causes for this type of defect. A precautionary note: Don't confuse HWPA with resin recession (Figure 3). Resin reces- sion is a material-related issue where the res- in has recessed or shrunk back away from the plating. is is evident generally aer thermal stress. According to the IPC-A600K, resin re- cession is permissible. Resin systems, for lack of a better term, will "shrink." Keep in mind that there is no substitute for process control. e operators should have a basic understanding of why certain process- Table 1: The most common causes for this type of defect. Figure 3: Example of resin recession.