Greg gives some great tips for using parts libraries in EagleCAD, be they the original CADSoft libs or those provided by others. He writes:
My first recommendation is to not blindly trust library parts created by others. The problem is that I have found way too many errors in libraries created by others. You might think that since someone else has a working design using a part from the library, that the part must be right. While it is a good sign, the reality is they may have corrected an issue in their copy of the library, or worked around it somehow.
So I check any part I use for the first time from another source very carefully. It takes some time to do a thorough check, but it is far less time than you will loose if you have PCB’s built with errors.
I start a design by downloading the datasheets for parts I am going to use in my project. Usually near the top of the datasheet you will find pinout information, and near the bottom you will find the package dimensions and sometimes a recommended footprint.
The manufacturer’s recommended footprint is meant for volume production on automated machinery. I will take it as a starting point, but I usually increase the pad sizes for hand assembly, to give me more pad to touch with the soldering iron. This is especially true for SMT parts.
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