Blind via - trace to rectangular pad on 2 layer board


#1

Hi There,

Newbie to PCB Layout (mechanical engineering background), and my startup is using KiCAD for circuit design and layout. I would like to have a trace on the bottom copper layer connect to a rectangular, solid pad on the front copper layer, but I want to avoid putting a hole into the the rectangular pad.

Do you have any recommendations for doing a blind via for this? I thought making a footprint with a circular pad would work because you can select “bottom layer only” but it’s still a through hole which makes sense as indicated by the drop down (“through hole”). I’m thinking blind vias only work as thru-holes from copper layer to copper layer, so I might have to make this a 3 layer board but not use the middle copper layer - only use it to connect to for plating - but am not sure how tedious this is or how this affects the previous work.

Thanks!


#2

PCB are usually even layers, so 4 layers is next after 2
Talk to a PCB fab, and get a price on 2 layer vs 4 layer with blind vias

Why do you need to avoid a thru hole ?
Is that no-thru-hole rule across the whole PCB ?

A common way to avoid thru holes in one area, is to run tracks/copper to where they can be tolerated.
We have also used paste Vias on a 2 layer board, where we needed air-tight design.
(KiCad does not currently support Paste-Via, but you can use a 1 pin component as a workaround)


#3

hi akmark,
I’m no expert (fellow ME signing in) but I have a couple of comments. First, can you not put a typical via off to one side of the large copper pad, and bring a trace in under the soldermask? Blind vias cost money. Second, AFAIK typical board layer counts are always even numbers as a result of the manufacturing process. The thing you are describing goes beyond a blind via to a plug-plated or VIPPO via - they have different names, but a regular blind via does not get plated over. If you are worried about using a via in your rect. pad because of solder thieving, consider an epoxy filled via. Or, like I said above, just move the via out of the rect area defined with soldermask.


#4

Hey guys,

Appreciate the responses!

Basically, we have very little real estate to work with… I’m trying to maximize the size of the rectangular pad because it has to mate with a contact on another part. Extremely small parts, so I don’t want to reduce this surface area with the through hole via there… You make a good point with blind via expenses, so I think just moving the through-via out of the way and connecting with another trace is the way to go, especially if it’s standard practice.

I’m editing a file that has the through hole vias from which some boards were made, but we realized we needed blind vias (or each via moved to another location) so the manufacturer just made blind vias by editing the Gerber files I’m assuming. I don’t have his files but we now have parts with these blind vias, but I’m now revising the part and trying to replicate that change for the next iteration.

And I now realize boards have even layer counts typically and checked the layer setup options immediately after saying that. Oops.


#5

If they moved vias, you should be able to see where, by loading their modified Gerber files into KiCad’s GerbView
Then you can replicate that change more exactly.


#6

You will struggle to fine anyone who will make a 3 layer board. I f you can, you will have problems with board warping. Boards are made with a two layer core and then adding thinner layers in pairs on the outside. This balances the bending stresses


#7

Before you spend a lot on 4 layer boards or special vias that are being plated over you might want to check out micro-vias… they’re really tiny and should not interfere with your contact area.
Though, we have no idea what kind of sizes we’re talking about here for your pad really?!
Nor what the other contact thing looks like…


#8

This is very common. Imagine a power device with a big thermal slug or heat sink (like a SMT regulator). You define the copper pad to accommodate the slug. It’s an SMT pad so it’s only on one layer.

If you don’t want to put a hole in the pad, then draw a trace from it (start in the center of the pad), and right next to the edge of a pad, drop a via to the other layer, and continue drawing your trace to whatever.


#9

Sounds reasonable and this is what we ended up deciding to go with. Thanks for your input!


#10

Hi,
would like to know more about paste vias and where it suits most, and can you please tell about the workaround in kicad with images if possible.

Thanks.


#11

Same workaround as for via stitching. (But your pad will add mask and paste)


#12

Paste vias are simply vias with an associated PASTE entry, so they get solder paste during the paste screen process.

We use them for

  • Air-tight designs, where an O-ring was part of the PCB assembly
  • Better thermal conduction from one PCB side to the other.

last time I checked, kiCAD did not support a Paste-layer info on a via, but that likely not hard to fix.
Meantime, you can use a 1 pin component as a via.