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Electronics => PCB/EDA/CAD => Topic started by: stevenhoneyman on February 22, 2015, 06:25:10 pm

Title: Multilayer PCB vias - what am I looking at here?
Post by: stevenhoneyman on February 22, 2015, 06:25:10 pm
I'm working through deconstructing an 8 layer PCB and want to make sure I get this right before I make a few thousand mistakes |O

Attached is part of an image showing just underneath the outer layer of copper. For reference the 'large' hole is 1/16".
I see two types of via, small "dots" and hollow "circles". The dots only appear in layers 1&2, 7&8 but the circles can span all layers.

Reading wikipedia suggests to me that the dots are "microvias" but I'd like a second opinion!
Title: Re: Multilayer PCB vias - what am I looking at here?
Post by: mamalala on February 22, 2015, 07:29:20 pm
Regular via = going through the whole stack, from one side to the other

Blind via = going from one side to inside the stack, but not fully to the other side

Burried via = only inside the stack, never ending up at either side

Micro via = very small diameter, usually done by laser nowdays

Plugged via = where the hole is completely closed, "plugged"

Tented via = a via that is covered with the solder stop mask

So, it seems you have blind micro vias there.

Greetings,

Chris
Title: Re: Multilayer PCB vias - what am I looking at here?
Post by: free_electron on February 25, 2015, 05:24:52 am
They could still be buried micro vias. You need to peel of another layer.

There could even be stacked micro vias.

Looks like a smartphone or tablet board to me ..
Title: Re: Multilayer PCB vias - what am I looking at here?
Post by: stevenhoneyman on February 25, 2015, 05:45:47 pm
Quote from: free_electron on February 25, 2015, 05:24:52 am
They could still be buried micro vias. You need to peel of another layer.

There could even be stacked micro vias.

Looks like a smartphone or tablet board to me ..

Thanks mamalala; and you're absolutely right free_electron it was a smartphone.

It was just a practice run (1st attempt at this) so I've made little effort in tidying this up, but it turned out really well. The only mistake I know I made was I lost a few tracks at the very edges of the board - next time I'll put some scrap boards around the sides to keep it even.

I wish I knew of a 3d raster image exploded-layer-view program. I really don't want to have to vectorize this just to spin it around a bit!


Title: Re: Multilayer PCB vias - what am I looking at here?
Post by: Layoutguy on March 02, 2015, 04:09:21 am
I agree with the previous opinions.  The small dots look to be laser-drilled vias, probably plated closed.  If these vias extend from an external layer but stop at an internal layer, then they’re classified as blind vias.    The larger openings look to be thru vias.  Not sure why you’re deconstructing the board, but good luck. Smart phone layouts are usually obsolete and being revised before the product is released for distribution!