If you searched through all component manufacturer's for a SOT23, you would end up with a list of 100 SOT23 packages with different dimensional data to the Terminal Lead and Package Body.
That is why component manufacture's assign a unique Case Code to every package.
Also, we use the mfr. recommended pattern sometimes and we have discovered that no 2 mfr.'s use the same pad size and spacing for their recommendations.
In the early 1990's component manufacturer's used the same EIA-PDP-100 or JEDEC dimensions and you could use the same footprint across all manufacturer's. Then in the late 1990's there was a major split from the standards where component manufacture's thought it was in their best interest to create Unique Package dimensions to differentiate their component package from the competition. This caused a lot of chaos in the electronics industry and I'm afraid to say that it's going to get much worse in the future. Component manufacturer's what a unique package and a unique footprint so that competitors packages will not have an optimum land pattern solder joint.
Single sourcing is what the component manufacturer's want. It's in the best interest of the stockholders, the company management and owners and employees to sell their components and boost their profits by locking you into buying their components that require a unique footprint pattern.
That's OK if you can purchase the component stock you need for your production line. As for PCB library footprints, they will be totally automated to instantly generate a custom pattern per the component dimensions and your personal User Preferences. The days of hording and maintaining a PCB library will be a thing of the past as most component dimensions will be readily available on the cloud and your Preferences will be customized for each PCB layout. So in the future you will collect and hoard component dimensions in FPX format and tweak your Preferences for each layout.
LEAP (Libraries Enhanced with Automated Preferences) is the future. All the component dimensions in the industry at your finger tips and pushing them through your personal Preferences will auto-generate a custom library for a specific PCB layout.
For all connectors and unique packages, the IPC-7351 rules do not apply. You should use the manufacturer recommended pattern for these packages, but still, all the custom Drafting Preferences for Legend, Assembly and Polarity markings still apply to these packages to create uniformity across every library part in your PCB layout.
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