I have to use via to route small analog signals. If I want to minimize the effect of via on the signal, should I increase the annular ring size or hole size. Lets say the total via diameter is same in both cases.
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\$\begingroup\$ I'm not sure how you can increase the ring size without changing the via diameter. Can you give us a diagram? \$\endgroup\$– Greg d'EonCommented Mar 26, 2015 at 11:48
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\$\begingroup\$ Something relevant: you need to know your maximum ratio of hole to ring size as manufactures can not have thin annual rings. That is, if the hole is large, the ring might slip into the hole during drilling. \$\endgroup\$– NazarCommented Mar 26, 2015 at 11:53
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\$\begingroup\$ @Gregd'Eon: Via = annular ring + hole. I can use small annular ring with bigger hole or vice versa \$\endgroup\$– zudCommented Mar 26, 2015 at 11:59
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\$\begingroup\$ Oh - the "annular ring size" is the amount of the diameter that has copper on it. I see. I would have asked "should I increase or decrease the hole size?" \$\endgroup\$– Greg d'EonCommented Mar 26, 2015 at 12:07
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\$\begingroup\$ What problem are you trying to solve? \$\endgroup\$– Rolf OstergaardCommented Mar 26, 2015 at 12:10
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2 Answers
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Since you're dealing with low frequency (DC-audio) low level signals, you don't need to worry at all about the vias. Just pick a size that is not right up against the limits of what your PCB maker can handle so the connections are reliable, and leave extra clearance beyond the minimum.
The main layout worries with low frequency uV signals are thermoelectric voltages (if you need DC precision) and RF pickup (minimize loop size and keep things symmetric where that makes sense).
answered Mar 26, 2015 at 14:45
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\$\begingroup\$ enlarging the traces you will directly reduce possibles thermoelectric voltages \$\endgroup\$ Commented Mar 26, 2015 at 14:56
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To reduce the inductance of a via you should increase its copper diameter, not its hole. So, increase the annular ring size. Also, be careful while increasing it to not approach very much of other signals or you may experience crosstalk from (/to) other traces.
answered Mar 26, 2015 at 12:05
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\$\begingroup\$ As @Spehro said, inductance neither crosstalk will be a problem at this range of frequency. Just reduce the length of your crucial signal traces and probably it will be ok. If not, enlarge their width. \$\endgroup\$ Commented Mar 26, 2015 at 14:49
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\$\begingroup\$ The annular ring won't have much effect on the inductance- I think what you're looking for is the barrel thickness, as determined by (drill size - finished size). Annular ring is strictly defined as being (pad size - drill size), on a copper layer. You can request thicker barrel plating from some manufacturers, but it is typically a non-standard / custom spec item that will raise manufacturing costs in small volumes. \$\endgroup\$ Commented Jan 11, 2016 at 22:07