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I can set them to “inputs tri-stated with weak pull up” and then I don’t need to even connect them to the PCB. Is that correct?
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In this instance they need not be electrically connected. You're correct in that regard. However...
If I understand your post correctly you're proposing to remove PCB pads for device pads that are not used. Correct? In theory this is fine. However, I would anticipate you having difficulties assembling this. Without an associated pad for the MBGA ball to reflow to, I'd anticipate problems. What will this reflowed solder ball (from the package) do without a pad? Will it behave and solidify in situe or, without the expected reflow shape, will it end up shorting to another pin?
You may well find this is not an issue. Dropping a pad or two certainly wouldn't be an issue for traditional 'legged' devices and I suspect with larger pitch BGA devices you could well get away with this. Even if your unused input with pull-up does short to another pin - so what? As long as it only shorts to one other pin.
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keep the PCB to 2 layers and hopefully not need expensive laser-drilled microvias
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I strongly recommend you look to 4 layers for such a device. I've routed this package (although not MAX 10), on 6 layers, without the need for any micro-vias. You should be able to find a standard PCB technology that allows you to do all you need without the need to remove any pads.
Cheers,
Alex
Honored Contributor
