The rapid growth of the AI industry has sharply increased demand for AI servers, accelerator cards, and data centers, driving expansion of the AI hardware supply chain. PCBs are critical because they replace bulky cabling, enabling higher signal integrity and facilitating miniaturization. PCB fabrication involves numerous steps and materials, including copper traces, vias, pads, solder mask, openings, and surface finishes. Solder mask (photosensitive or thermosetting polymers) is applied to protect circuits, leaving only pads exposed; processes include coating, exposure, development, and curing. Developers use 1-2% Na₂CO₃ to remove unreacted mask monomers, while defective boards may be stripped with 3-5% NaOH. These streams produce high-COD (>10,000 mg/L) alkaline wastewater (developer/ink-removal mixed wastewater), requiring specific solid–liquid pre-treatment to remove dry film and residues.

MF/UF filtration technologies are now mature for such separations. Considering alkaline conditions, high COD, and cost, many manufacturers use polypropylene (PP) hollow fiber membranes in an outside-in filtration operation. Fouling forms on the fiber exterior, lowering flux and raising transmembrane pressure; routine outside-in forward flush and inside-out backwash restore performance. However, PP fibers are mechanically soft; pressure fluctuations could deform and enlarge pores, reducing filtration efficiency.

The capillary flow porometer quantifies membrane pore size by exploiting the interfacial tension difference between a low-surface-energy wetting liquid and a displacing fluid, using a pressure-scan protocol. In this study, the porometer was used to simulate the filtration of developer/ink-removal mixed wastewater and to investigate the effects of different cleaning conditions on membrane pore size and pore-size distribution, including forward (outside-in) wash pressure, reverse (inside-out) wash pressure, and wash duration. Concurrent water permeability tests were performed...