I have heard that stacking microvias on resin-filled buried vias can pose a reliability risk due to resin expansion at high temperatures, which can cause the copper cap to lift off the buried via, potentially causing an open. Here is one source that describes this risk:


http://pcb.iconnect007.media/index.php/article/66028/reid-on-reliability-lifted-pad-stacked-microvia-failure/66031/?skin=pcb


Nevertheless, this type of construction is plainly sanctioned in IPC-2226 (HDI Type III), so I wonder how serious this risk is, and/or if this is something the IPC-2226 Committee (D-41?) is planning to address.

Does anyone have any experience with or knowledge of this risk? How serious is the risk? Do you have internal rules/guidelines specifically to avoid this structure? (I'm referring only to stacked vias atop resin-filled buried vias; my understanding is that stacked, Cu-filled uvias are not a reliability risk. Correct assumption?)



Thanks in advance,
Todd MacFadden

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