Spot Welds
Sppot welding aircraft structures (skins to stringers) was a process adopted in the 60's - 70's. The problem with it is that the joint has to be clean on assembly with no interface sealants etc. They are therefore more likely to corrode.
I work on Dassault F20's that have spot welded skins and believe me when I say the process isn't good. Not all the F20's were welded as Dassault even realised it was S**T after a while.
We have to NDT the welds on a regular basis etc. very time consuming and you normally finsd one or two corroded. Welds induce impurities.
A properly sealed and formed rivet is much better and easier to assemble in certain places.
With more and more composite structure these days even the rivets will be disapearing.