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smallest via hole that can use a +/- 3 mils

Printed From: PCB Libraries Forum
Category: Training / Events
Forum Name: PCB Design Basics
Forum Description:
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=2497
Printed Date: 29 Oct 2025 at 11:05am


Topic: smallest via hole that can use a +/- 3 mils
Posted By: lsday
Subject: smallest via hole that can use a +/- 3 mils
Date Posted: 17 Jun 2019 at 8:16am
Can anyone answer this question please? what is smallest via hole that can use  +/- 3 mils tolerance?


Replies:
Posted By: Tom H
Date Posted: 17 Jun 2019 at 11:26am
0.20 mm (8 mils) However, there are high quality fabrication shops that say they can do 0.15 mm (6 mils). 

The big issue is the pad annular ring. 

The fab shop will add 3 - 4 mils to the finished hole size. 

Then you must consider drill drift and layer to layer tolerance of 3 mil. 

Then after the drill oversize and the layer to layer tolerance you still need to have 1 mil annular ring. 

IPC Class 3
Hole = 8 mil (0.20 mm)
Pad = 20 mil (0.50 mm)

IPC Class 2
Hole = 8 mil (0.20 mm)
Pad = 18 mil (0.45 mm)

The via hole tolerance would be +0, - the hole diameter



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