Replacing rivets with self-tapping screws seems a bad idea to me
It
is a bad idea. I sure was not suggesting it be done. I only mentioned them because I have seen them used before.
In fact, many case fans have been mounted using self-tapping screws.
I also note that most cases are made of steel and plastic, not aluminum. Aluminum is more expensive than steel which is why aluminum cases tend to cost much more than the equivalent steel cases. While aircraft grade aluminum (as often found in auto body panels and decent bicycles) can be very strong, nearly as strong as steel, it is much more expensive than steel.
the sheet metal is thin and the screw would wear out its own thread easily
Huh? Ummm, sorry but no! Not even.
Of course, I was assuming the use of the correct screw for the job, properly driven in.
I have to assume you are not aware that there are such things as self-tapping screws specifically designed for sheet metal. In fact, they are called,
Self-Tapping Sheet Metal Screws.
And while sheet metal, by definition, is thin (as a sheet), an undamaged, self-tapping "
sheet metal screw",
properly inserted will stay tight and secure in place. There is no way, once
properly inserted, it could "wear out".
The point was, and still is that self-tapping screws work by cutting threads (tapping) into the metal when driven in. If done properly (correct screw, correct initial screw hole, and no overtightening), they work great for the purpose of creating a
permanent mechanical (vs welding, for example) bond of two sheet metal surfaces. HOWEVER, the tapping process inevitably involves the removal of some metal filings, the "waste" products, being cut out of the thread grooves.
And the point was, you don't want those metal filings, even one very tiny metal filing, falling on to or in to your electronics.
