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Page 53 of 93

54 PCB007 MAGAZINE I JULY 2023 Introduction In two previous columns, I explored several of the key competencies and processes required to successfully jump into IC substrates. In this edition, the key process of desmear will be explored. Desmear: Alkaline Permanganate and Plasma Methods ese processing steps require additional improvements over normal through-holes due to small diameter through-holes and blind vias. Getting process chemistries down into these small holes can be very difficult, especially if they have any trapped air bubbles. If baskets or racks are used in the vertical, there needs to be a way to "bump" the racks to dislodge the bub- bles. Installing vibration on the plating racks and frames is critical. Other important consid- erations include: • Equipment modifications requiring spray rinsing and flood processing for small diameter blind vias • Move toward direct metallization to elimi- nate gas bubble formation seen with con- ventional electroless copper (more on this in a future column) • Conveyorized processing as opposed to vertical immersion systems • Required online process monitoring; everything requires tighter control Consider processing tools that flip the con- ventional thinking upside down and instead Processes to Support IC Substrates and Advanced Packaging, Part 3 Trouble in Your Tank by Michael Carano, IPC CONSULTANT

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