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Thru-hole via, blind via or buried via ?

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cktay

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via stub blind

When do we need to use each via ? Why such a need ?
 

Hi,

Through hole via - When it is not a high speed design, through hole vias are used for an SMD pad to route in internal layer.

Blind via - If there are high speed signals, which cannot be routed in just external layers, blind via defined for less no. of layers is used, to avoid stub. For e.g. in a 20 layer board, for an SMD pad in top layer, fanout via is used to take trace in inner layer. If the trace is taken in layer 3, there will be unnecessary stub through the plating of the via from layer 3 to bottom. If it is high speed signal, this will be a concern. To avoid this, blind via till layer3 can be used.

Also, to have good aspect ratio, blind via is used. Aspect ratio is the ratio of the depth of a plated hole to its preplated diameter. So, instead of having through hole via, blind via can greatly improve aspect ratio.

Buried via - Buried via again is used to avoid stubs. If a via is defined only for few internal layers for layer switching of the route instead of through hole via, the stub in unused layers can be avoided.

But, blind and buried vias increase manufacturing costs.

Regards.
 

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