In nearly all standard footprints you can get from Kicad, SnapEDA, Ultralibrarian the soldermask opening is the exact same dimension( 1:1) as the pad opening.
IPC standard IPC-7351B snippet attached. Many tutorials/ recommend websites recommend to not follow this ipc standard and make the solder mask opening slightly larger than pad. Here's an example.
https://www.epectec.com/pcb/soldermask-design-basics.html
Unless it's a BGA package 1:1 is rarely used. In my opinion the IPC standard should be changed to add a "standard tolerance" ( between 0.05-0.1mm) for soldermask opening greater than pad.
IPC standard IPC-7351B snippet attached. Many tutorials/ recommend websites recommend to not follow this ipc standard and make the solder mask opening slightly larger than pad. Here's an example.
https://www.epectec.com/pcb/soldermask-design-basics.html
Unless it's a BGA package 1:1 is rarely used. In my opinion the IPC standard should be changed to add a "standard tolerance" ( between 0.05-0.1mm) for soldermask opening greater than pad.
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