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28 PCB007 MAGAZINE I JUNE 2024 • Ceramic-filled materials can also introduce extra cost in fabrications. e ceramic can reduce the lifetime of a drill bit from 5,000 to 500 hits. • ere are concerns with hole wall qual- ity as fabricators move up the material technology curve. Most notably is rough drilled holes along with deep gouges (Figure 1). Drill quality or lack thereof (Figure 1) affects several aspects, including solderability, plating adhesion, and potentially component inser- tion. Regardless, the higher-performance materials are more difficult to drill. Hole wall roughness must be reckoned with. Monitor the number of hits each drill bit is subjected to. Be concerned that these higher- performance materials will cause the drill bit to wear out faster. In addition, adjusting spin- dle speeds and infeed rates must be considered to ensure good hole wall quality. Metallization As mentioned previously, these materials provide significant challenges to the fabrica- tor. e process step of providing a void-free, tightly adherent copper deposit to all surfaces (resin, glass, copper) is paramount in achiev- ing plated through-hole reliability. Any issue that compromises the copper plating unifor- mity and adhesion will lead to defects, includ- ing plating voids, hole wall pullaway, and inter- connect separation. Not a good thing. So, as these higher performance materi- als are more difficult to desmear and form any reasonable topography on the resin materi- als, adhesion of the plated copper is a concern. What should the fabricator do in this situa- tion? One option is to use an electroless cop- per process that deposits the copper at a slow and steady deposition rate. One may call this low-to-medium deposition electroless copper. e way the copper grain structure forms dur- ing the metallization process really does mat- ter. Low internal stress of the deposit is benefi- cial in improving adhesion to the various mate- rials that make up the circuit board. Slow and steady wins the race. Monitor the deposition rate of the copper. I prefer 1–1.5 microinches of electroless plating per minute. In this sce- nario, the copper deposit will be much more uniform and of lower stress. A second critical point is to not over-cata- lyze the surface with palladium. Excessive pal- ladium, while great for initiating the electroless copper, will lead to a spongy-looking deposit that will exhibit poor adhesion. Excessive pal- ladium acts as a barrier, preventing the plated copper from making intimate contact with the resin and copper surfaces. PCB007 Michael Carano brings over 40 years of electron- ics industry experience with special expertise in manufac- turing, performance chem- icals, metals, semiconduc- tors, medical devices, and advanced packaging. To read past columns, click here. Figure 1: Rough hole walls after drilling.