Issue link: https://iconnect007.uberflip.com/i/1536435
34 PCB007 MAGAZINE I JUNE 2025 als, drilling parameters, stack heights, etc. In addition, the type of resin that makes up the circuit board, along with glass weave style and content, will play a role in drilling via quality. is will be the subject of a future column. First, Figure 2 depicts what can happen when the drilling operation is not in control. Note the gouges in the resin and the torn- out glass bundles. When a drilled hole such as this makes its way to the PTH pro- cess, the ability of the electroless cop- per or direct metallization chemis- tries to properly deposit in these drill gouges is compromised. Even if the PTH metallization is successful, sub- sequent electrodeposition of cop- per will yield areas where the copper thickness is too thin (thus violating copper thickness requirements), and potentially have a situation where the plated copper folds over. In the latter case, the copper cannot level due to the drill gouge. is leaves a very thin area and leads to the potential for a blow hole dur- ing assembly or an open in the PTH. is is precisely why many finished bare boards suc- cessfully pass in-circuit test only to exhibit some interrelated non-conforming defect aer assembly (Figure 3). Certainly, it is possible that there may be issues with the wave solder flux, but we can Figure 1: A five-head drilling machine. Figure 2: Rough hole walls due to less than optimum drilling.