BGA Fanout 0.5 mm pitch

I was reading the section describing BGA fanout routing in the e-book.
There are some questions regarding via pads, drill size and trace width etc.

How do we define blind via ? Is that the via with one end open and the open end can be on top or bottom side of the PCB. Does this mean that blind via drilling start from either top or bottom and ends down to the inner layer and the inner layer can be any conductive layer, right ?

Buried via: Is this a via between two adjacent layers for example between L1 and L2 or between L7 and L8 OR Buried via can also be between L2 to L7 as well ?

How much it is expansive to have blind and buried via in the designs ? Which drill/pad size has optimum cost in blind and buried via ?

What is the aspect ratio in blind and buried via that we need to maintain ?

How do we define micro via and how it differs in definition and geometry than blind and buried via ?

Please explain how the 5 mil trace with 5 mil space can be routed in the BGA area. The geometry in the first post shows only 3 mil trace with 3 mil spacing is possible on the top layer in BGA area.

Yes, this is what it means. However it might turned out to be complicated and expensive.

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Yes to all. If you don’t plan properly, it may not be a good idea but in theory yes. You must work with your manufacturer to make sure this will be manufacturable with high yields.

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It will be more expensive as your fab house will take longer to build the board.

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A microvia can be a blind or buried via. This is a via with a hole diameter that is less than or equal to 0.15mm.

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This is way too complicated to explain in a post. And we would have to see your design. You could start by reading this article and I believe Robert Feranec has some good demos on his YouTube channel.

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So perhaps the answer is that with a 0.5mm pitch, you will need tech II or tech III, and you will need roughly a layer per row being fanned out in that direction?

Though I wouldn’t rule out that it just means “talk to us for a custom quote, because the rules are too complicated and/or changing to publish for generic designs.”