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I am using KiCad and I am new in PCB design.

I want to use Fusion PCB service (SeeedStudio) for the boards. In their forum, they say that the minimum Via Drill size is 0.03 mm. But in SeeedStudio's site is written:

Drilling Hole(Mechanical) 0.3 - 6.35 mm

Finish Hole(Mechanical) 0.8 - 6.35 mm

And in tinyosshop's site it is written (just for comparing):

Minimum vias specifications: pad:20mil(0.5mm)/hole size:12mil(0.3mm)

I thought that the Via Diameter was equivalent to the Finish Hole and the via Drill Size was equivalent of the Drilling Hole, but I think I got it wrong. Then which are the parameters I should look at?

I was using 0.8 mm, as it was the biggest number, but I just realize that they are almost as the same size of the drill of a 100 mil header (it seems to big)

I'd appreciate if someone could help me understand this. Thanks.

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  • \$\begingroup\$ something is wrong with that spec, as the finished hole size must be smaller than the drilled size, as the finished hole size will be reduced by twice the thickness of the plating. \$\endgroup\$ – Peter Bennett Apr 21 '14 at 17:02
  • \$\begingroup\$ Unless drilled holes are strictly mechanical. \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 21 '14 at 17:10
  • \$\begingroup\$ I think that the drilling hole can or not be plated. So maybe you can do 0.3 mm holes in your project, but if you do, they can't be plated. If you decide to do a plated hole, than the minimum diameter would be 0.8 mm. Anyway, that was just the reasoning I created to try to make some sense out of it. =( \$\endgroup\$ – koike Apr 21 '14 at 17:17
  • \$\begingroup\$ @koike that's exactly wat I was thinking too. \$\endgroup\$ – Vladimir Cravero Apr 21 '14 at 18:12
  • \$\begingroup\$ 0.3 sounds reasonable, this is what most manufacturers use, and what I've used with seeedstudio before. Some offer 0.2 for an extra fee. \$\endgroup\$ – Simon Richter Sep 5 '16 at 18:26
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I would call SeeedStudio and talk to their manufacturing (or CAM) department. Different shops write their specs in different ways, and it's costly (in both time and money) to misinterpret what they're trying to say.

In the manufacturing process, first the hole is drilled, and then it is plated. The plating causes the finished hole size to be smaller than the drill size.

However, Advanced Circuits, for example, assumes that the hole size in your design documentation is what you would like your finished hole size to be. So, if your drill file has a 10-mil drill, what you get is a 10-mil finished hole. They automatically increase the drill size so that the finished hole size is what you specify.

(I am not affiliated with Advanced Circuits, but I have been very satisfied with their services)

So, give SeeedStudio a call (or an email) and see what they say :)

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The number in the forum, 0.03 mm, is a typo. You can see that they equated this to 12 mil (0.012 inch), indicating they really intended to write 0.3 mm.

0.3 mm is a reasonable minimum drill size when you need to minimize costs, but many shops offer down to 0.2 mm (8 mil) as a standard technology.

Also, the minimum drill size depends on the board thickness. If your board thickness is 2 or 2.5 mm (or more) you'll have a proportionally larger minimum drill size to maintain a minimum aspect ratio required to avoid drill breakage and for the plating bath to penetrate the via completely.

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