IPC International Community magazine an association member publication
Issue link: https://iconnect007.uberflip.com/i/1542698
50 I-CONNECT007 MAGAZINE I JANUARY 2026 costs and reduce yields. I encourage designers to collaborate early and often with their fabricators to ensure their layouts are designed for manufactur- ability (DFM) by adhering to their specific capabili- ties and manufacturing processes. Key consider- ations include: • Uniform copper thickness: Layout-related variations in copper distribution can lead to localized differences in thickness and make it difficult to achieve uniform copper height across an entire production panel. • Impedance control and signal integrity: If the copper plating is uneven, it can disrupt impedance matching on high-frequency cir- cuits. This can lead to signal integrity issues and potential malfunctions in the finished electronic device. • Plating voids and pitting: UHDI boards have miniaturized features that demand design pre- cision, specifically microvias with high aspect ratios that make them susceptible to plat- ing voids, gaps, or pitting. These can prevent proper copper adhesion within these tiny holes and affect electrical continuity and reliability. The Process of Pattern Plating Most designers are unable to spend a lot of time on their favorite manufacturing partner's shop floor, and I believe it's helpful for designers to have a working knowledge of each step in the production process. This section breaks down the pattern plating process. C O N N ECT T H E D OT S Preparing the surface for pattern plating. We start with a pattern; we create the circuit board design by imaging and developing the pattern on photoresist, exposing all the traces and pads to the copper foil or plated copper below it. The next step is plating additional copper on top of the pattern. This builds copper thickness inside the holes, on the surface, along traces, and on pads. This process beefs up the thickness of the board's outer-layer copper features to create the current capacity specified in the design. It is important that channels created by the photoresist are deep enough to accommodate the required copper. If not, copper will plate over the top of the resist. This will create a mushroom effect at the top of the trace that can be harder to etch out from under- neath and result in overhanging copper that can break off, create a bridge, and cause shorts. Preparing Surfaces for Pattern Plating We ensure the copper surface is pristine so we can plate new copper on it. We use a surface treatment process called micro-etching and then run the board through a pattern plate pre-clean. We use a series of sulfuric acid rinses and micro-etches to remove any oxidation created during the imaging process, along with any impurities or oxidation on the surface. If residual developer solution or photoresist is present, the cleaning process should eliminate it and leave a clean copper surface. During this process, we are careful not to disturb the photore- sist or over-clean the surface where we may have etched the copper out of the holes. Avoiding Over-Cleaning The balancing act involves ensuring the deposit of electroless copper is thick enough to allow for the amount removed during the pre-plating pre-clean process. We utilize a statistical process control (SPC) tool, referred to as an etch rate coupon, to determine the amount of copper removed during the micro-etch process. That measurement quanti- fies the amount of copper removed. We can adjust the time in the bath and/or the temperature of the bath to target the desired amount of removal. However, etch rates are not necessarily constant. Etch rates are influenced by temperature, concen- tration, and copper loading. If you make a new