The two most common causes of delay in small volume manufacturing here at Screaming Circuits (and presumably, others like us) are component availability, and footprint mismatches.
We don’t substitute parts without your approval for a number of reasons. I’ve written about those reasons a few times before. (Here, here, and here.)
Incorrect footprints can lead to a host of headaches as well. (Read more here, here, and here.)
Until recently, I haven’t seen a lot of progress toward solving these problems for the hordes of engineers that don’t have big support departments at their disposal. In fact, with the proliferation of newer, and small, component packages, and evolution of the supply chain, it’s really gotten worse.
However, there are a couple of Knights in Shining Armor riding in to try and solve both problems. The Common Parts Library (CPL), created by Octopart, aims to create a list of components with the highest probability of being available and staying available (there are no guarantees where component supply is concerned).
The other exciting entrant is SnapEDA. SnapEDA has a massive, and growing, library of component footprints. I’ve used their footprints with good success for high pin-count devices, and other parts with complex packages. It can save a lot of time and give better confidence that all of the pins go to the right functions.
Map makers put fake roads in as copyright traps
These folks don’t do that. Nice.