Issue link: https://iconnect007.uberflip.com/i/1535414
12 PCB007 MAGAZINE I MAY 2025 › Risks: Over-etching can weaken cop- per traces or alter dielectric properties; under-etching results in poor adhesion and delamination. Defects will also result from contamination from the grit used, with through-holes especially vulnerable. › Prevention: Optimize blasting pressure, nozzle angle, and distance. Use a precise grit size for controlled material removal. Chemical Surface Preparation Chemical solutions remove oxidation, resin smear, and contaminants, improving surface properties for plating and adhesion. • Micro-etching (acid etching): Mild acidic solutions combined with surfactants, cor- rosion inhibitors such as hydrogen perox- ide or sodium nitrite, with solvents (iso- propanol and acetone) and water work together to create a micro-roughened cop- per surface before solder mask application or plating. › Risks: Over-etching thins copper traces and can cause open circuits; under-etch- ing leaves oxidation, leading to weak adhesion. › Prevention: Maintain strict control of chemical concentration and dwell time. Use inline thickness measurement tools to monitor copper reduction. • Desmearing (plasma or chemical): Removes resin smear from drilled vias before electroless copper plating. › Risks: Insufficient desmearing leaves resin residue, preventing plating adhe- sion; over-processing can damage dielec- tric material. › Prevention: Use multiple desmearing steps (plasma + chemical) for high-den- sity designs. Perform scanning electron microscopy (SEM) inspections of via walls. • Black oxide and alternative oxide treatment: Forms a micro-rough oxide layer on inner copper layers in multilayer PCBs, enhanc- ing resin adhesion. › Risks: Weak oxide layers lead to delami- nation under thermal cycling; over-oxi- dation reduces conductivity, impacting signal integrity. › Prevention: Optimize bath chemistry and exposure time. Conduct peel strength testing on sample panels. Advanced Surface Preparation Techniques Plasma Surface Treatment: Ionized gases clean and activate surfaces for better adhe- sion, particularly for PTFE, flex PCBs, and HDI circuits. › Risks: Insufficient plasma exposure leads to poor adhesion; overexposure alters surface chemistry, degrading material properties. › Prevention: Validate plasma power, expo- sure time, and gas composition. Conduct surface energy measurements (contact angle testing). • Silane coupling agents: Forms a chemi- cal bridge between copper and dielectric materials, improving adhesion for high- speed digital and RF PCBs. › Risks: Incorrect application leads to inconsistent adhesion, causing peeling or delamination. › Prevention: Apply silane in a controlled environment with precise concentration. Verify bonding quality with adhesion pull tests.