Arduino vs 555 reliability

Considering how many die shrinks and process refinements the 555 has gone through, I would say poorer, and by quite a bit. Today's 555, or maybe even ones ten years old or more, are made to *just* meet all the published specifications, and *nothing* more. With low value, high volume parts like the 555, shaving fractions of a percent can save a lot of money in the long term. With a fairly young design, like a modern microcontroller, it pays to make them some amount better than the specs, because the fabs can always refine the chip later to shave those costs. As for metal film resistors - just the fact that they exist on the board makes them unreliable and yield killing. Old saying - the most reliable parts are the ones that are not there. -- Will