IPC International Community magazine an association member publication
Issue link: https://iconnect007.uberflip.com/i/1544975
30 I-CONNECT007 MAGAZINE I MAY 2026 pressures grow, more fabricators recognize direct metallization not just as an alternative process, but as a strategic enabler for future ready PCB manufacturing. Primary Metallization: The Foundation of PCB and IC Substrate Fabrication All multilayer PCBs and IC substrates rely on inner layer connections, typically created by buried through-holes, blind vias, or stacked microvias, to transmit electrical signals between layers. These vias are formed through mechanical or laser drill- ing. Primary metallization, commonly called "mak- ing holes conductive," prepares these non-conduc- tive hole walls for electroplating. The PCB industry currently utilizes two different processes for primary metallization: electroless copper and direct metallization. Electroless copper plating, the traditional primary metallization method, uses a chemical reducing agent (typically formaldehyde), along with multiple cleaning and plating baths, along with a palladium/ tin catalyst to deposit a thin, conductive copper layer on via hole walls before electroplating. While effective for conventional multilayer PCBs and some high-aspect-ratio through-holes, the process becomes increasingly difficult to control as feature sizes shrink and HDI complexity increas- es. The palladium-activated electroless copper interface introduces a distinct material boundary between deposited copper layers. Under re- peated thermal cycling, this interface can become a mechanical weak point, particularly in stacked microvias. Failures may manifest as voids, cracks, or intermittent electrical connections. In addition, electroless copper plating involves multiple chemical baths, tight process control windows, and ongoing bath maintenance. As feature sizes shrink, maintaining uniform deposi- tion becomes more challenging, increasing the risk of defects and scrap. With rising board complexity and cost, yield losses carry increasingly significant financial implications. The process also depends on palladium catalysts and other metal precursors, which are subject to price volatility and availability constraints. Further- more, electroless copper plating consumes sub- stantial water, energy, and hazardous chemicals. Aggressive sustainability targets and regulatory scrutiny around chemical handling, wastewater treatment, and worker safety continue to intensify globally, adding operational complexity and cost. These factors are prompting fabricators to evaluate whether legacy primary metallization ap- proaches remain optimal for the next generation of electronics manufacturing. Direct Metallization: Enabling High Density Designs Direct metallization is an attractive, technically robust alternative to electroless copper that offers reliable microvia performance, stable processing, and compatibility with today's high-density de- signs. Rather than chemically depositing a copper interface layer, the process applies a thin conduc- tive carbon- or graphite-based coating to via walls. After selectiving microetching the exposed copper surfaces, electrolytic copper plating proceeds, forming a direct copper-to-copper bond. Direct metallization delivers key reliability advan- tages over electroless copper for advanced HDI applications. By removing the electroless copper interface, the copper structure within microvias becomes more resistant to mechanical stress and thermal fatigue. These improvements have been consistently validated through industry standard tests, including via pull, IST, TCT, OM, CITC, and simulated reflow. Reliability is further enhanced by optimizing the " As stacked microvia architectures become more common, particularly in advanced packaging and IC substrate applications, this reliability margin becomes increasingly valuable."