Auto BGA - 6 layer board - Layers used but not enabled

[marcbrooks991]

Currently creating a 6 layer board and have 5 BGA's that need I need to route via the BGA Auto Router.

I finished up editing the 1st BGA and went to start the auto-routing when it came up with the error "Layers # used  but not enabled".

The layers in question it was referring to were my 4 inner layers, currently labelled as Top_GND, Middle, Power & Bottom_GND.

I've already done polygons around my board area for each of the 6 layer but I haven't the foggiest clue on how I enable these layers so I don't get this error again?

Please note I intend to use blind/buried vias in this design, should this affect the outcome of the answer.

[jorge_garcia]

Hi @marcbrooks991,

I hope you're having a good day. Keep in mind, that when setting up the BGAs in the BGA autorouter you need to define what layers the nets can run on in the Edit BGA dialog. Did you do that?

If you are going to use blind and buried vias then you want to make sure that the microvias checkbox is checked.

Please let me know if there's anything else I can do for you.

Best Regards,

[marcbrooks991]

Hi Jorge,

By edit window I'm assuming you're meaning the below photo after you click edit button on any selected choice and choose between the 6 existing layers?

This I had done applying all pins to 4 different and respective layers. After clicking the okay button is when I was then presented with the warning message as stipulated in the 1st post.
The micro-via option was also checked by default.

[jorge_garcia]

Hi @marcbrooks991,

Thanks for posting the image, the looks good. Did you adjust your DRC to be able to process the BGAs? If your widths and clearances are too big there's just no way the BGA router could fanout the BGAs. You can test this by trying to manually fanout a couple of traces. If that fails then you know your DRC settings are too stringent to be able to fan the BGA out.

Let me know if there's anything else I can do for you.

Best Regards,

[marcbrooks991]

By default my clearance values are 6mil & my min width is also 6mil. with my min drill being 0.2mm and min micro via being 0.1mm what would you recommend I change width & clearance values to?

If I try to manually place a trace / via on 1 of the bga pins I get an error "Can't set via to layer '16' at (#.# #.#)"

[marcbrooks991]

I noticed in my DRC setup that the setup string hadn't been setup accordingly; however when I try to set it up. I feel like I'm doing something wrong.

The layer stackup I'm trying to create is:

1 - Signal

2 -GND
3 - Signal
14 - Power
15 - GND
16 - Signal

With the following via pairs:

Through: 1-6

Blind: 1-2, 1-3, 1-14, 3-16, 14-16, 15-16

The bare minimum I can get is everything bar either 1-14 or 3-16. If I try both then I get the following error - "Unexpected ':' " with the setup string of: ([[3:[2:14:1*2*3*14*15*16:15]:14]:3]) - this refers he the '14:1' If I try just the one on its own, it works and I get a setup string like this: ([2:[3:[1*2*3*14*15*16:3]:14]:15])

The problem for me is that I need both in the setup string, else how will I be able to connect  top signal-power (1-14) and middle signal-bot signal (3-16)?

Small idea came to head, but just want to confirm if right. Could I still get the intended result I want by removing the 1-14 & 3-16 and simply placing a buried via at 3-14?

Edit: on a side note I tried changing the min width to 0.2mm and clearance values to 0.1mm. Still get this same error of: Layer 2, 3, 14, 15 used but not enabled! Objects therein may collide with vias placed by the autorouter.

So wondering if I actually should just ignore this error as it seems no matter what I try it doesn't seem to solve this issue?