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92 PCB007 MAGAZINE I AUGUST 2021 Article by Nagarajan Jayaraju, Derek Thoresen, Jimmy John, Joanna Dziewiszek, David West, Zukhra Niazimbetova and Chi Yen DUPONT Introduction Copper through-hole fill (THF) technology is a key breakthrough in sustaining the industry drive to increase wiring density and intercon- nect reliability while addressing the attendant challenges of thermal management and signal integrity at high frequencies. THF offers an el- egant solution to the current process of plug- ging through-holes with conductive paste. e latter process involves multiple steps that are hard to control, making it expensive and mak- ing the plug itself unreliable and prone to ther- mal failures (such as degassing) under opera- tion. THF, on the other hand, is a simple one- step electroplating process and, since copper is the filling material, it provides unmatched thermal performance. Filled mechanically drilled through-holes are also an attractive replacement for stacked- via structures, especially for high-speed high- frequency applications. is is preferred since the single-piece cylindrical geometry of these through-holes results in less scattering of high frequency signal compared to the compos- ite stacked-via structures with angled geom- etry and their susceptibility for misalignment during fabrication. Finally, THF can mitigate warpage of IC substrates during thermal pro- cessing by enabling fabrication of boards that are thicker but still have high interconnect density, as warpage rate and board thickness are inversely related. Extensive screening of various organic ad- ditive formulations was conducted to achieve both bridging and filling in the same formula- tion. Candidate formulation was further opti- mized in conjunction with waveform and flow adjustments, resulting in a novel PPR wave- forms process optimized for through-hole fill- ing application. e composition of the inor- ganics used was 225 g/L copper sulfate penta- hydrate, 40 g/L of sulfuric acid and 50 mg/L of Cl. e organic components in the bath are 10 ml/L THF Carrier, 0.4 ml/L THF Leveler and 0.5 ml/L THF Brightener. One Step/One Bath Copper Through-Hole Fill Pulse Plating Process Across Wide Range of Panel Dimensions

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