Just Ask Happy: Stacked Microvia Reliability Issues

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We asked for you to send in your questions for Happy Holden, and you took us up on it! The questions you've posed run the gamut, covering technology, the worldwide fab market, and everything in between. Enjoy.

Q: Stacked microvias look good on paper, but they may have reliability problems. What are the best rules for designing stacked microvias to ensure a reliable PCB?

A: The current best practice is stacking no more than two layers, and then moving over for the next buried or blind via or stacking two layers there. The stacked vias should never be stacked on any buried vias.

An IPC committee is currently testing various stacked via configurations to have a comparison for reliability and testing coupons and design. Hopefully, they will also get at the root cause of why stacked microvias are failing at their interface.

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