If a via is meant to carry current why not go for a solid copper
filled via than a plated via (which is hollow/nonconductive at the
Because a plated via hole is "good enough".
There are a number of processes needed to fabricate a bare PCB and each one takes money and time.
- Print onto laminate the areas to etch
- remove "black ink" used to protect traces
- Repeat for as many core as there is
- Repeat for as many foil layers as there is
- Drill PTH
- Plate (NOTE via size is finished so the fab will drill to larger and align to the plating thickness)
- Drill NPTH
Its a bit more than that, but generally that is the process. So while you are correct if via's are meant to carry current why not fill them with copper, its a bit more than that. Via's carry current but if the current you are carrying is uA (due to signals) or ~5A, then why are more process steps needed? If you need 10A put 2 0.3mm via's down. What more current? increase the diameter to trade off surface area and via size.
During the playing process could they fill the via completely? no and that why it isn't done. If they were to keep a PWB in the bath for longer, the thickness would build up and equally the via's would start to fill. At some point it would be completely filled wouldn't it? yes, but with what
- 100% copper
- fluid ?
And therein lies the problem. There is no way to guarantee the via's would be solid. If it started to tent before it was completed, when the PWB was populated there is a possibility that the contained fluid would pop. Even if there was no fluid there is no way to guarantee a full via so it isn't done.
However, you can fill the via's with epoxy and there are two types used
DuPont CB100 Tatsuto AE3030. These are silver coated copper particle’ filled epoxy matrix and thus help improve the electrical conductivity.
Peters PP2795 epoxy and San-Ei Kagaku PHP-900 epoxy. These are electrically non-conductive but are good thermally and are typically used to improve the thermal characteristic of thermal via's.
The downside? Cost and additional considerations with regards to CTE