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smallest via hole that can use a +/- 3 mils |
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lsday 
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Joined: 15 Dec 2014 Status: Offline Points: 24 |
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 Topic: smallest via hole that can use a +/- 3 milsPosted: 17 Jun 2019 at 8:16am |
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Can anyone answer this question please? what is smallest via hole that can use +/- 3 mils tolerance?
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Tom H
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Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716 |
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Posted: 17 Jun 2019 at 11:26am |
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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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