That which meets requirements, of stringent customers.
https://shop.ipc.org/ipc-j-std-001
https://shop.ipc.org/taxonomy/term/659

"J-STD-001 is recognized globally for its criteria on soldering processes and materials. Updated with participants from 18 countries providing input and expertise, this document brings the latest criteria along with new graphics to the industry for ease of use and comprehension. This is a must-have for those in the electronics industry with an interest in the process and acceptance criteria for..."