https://jlcpcb.com/blog/what-is-pcb-via
https://jlcpcb.com/help/article/pcb-via-covering
https://jlcpcb.com/capabilities/pcb-capabilities
https://jlcpcb.com/blog/basic-design-of-solder-mask
Ordering
https://jlcpcb.com/help/article/How-to-export-Altium-PCB-to-gerber-files