I’ve designed lot of ‘simple’ PCBs for hobby and proof-of-concept purposes, but never for (mass)manufacturing. In order to do so in the future, and further expanding my design skills and knowledge, I’m exploring the different package outline standards.
By now I learned there is no such thing as “one main standard for all packages”. Instead, there are multiple standards for multiple packages, set up by multiple organizations. ‘Most recognized’ are IPC and JEDEC standards.
But even within IPC there are multiple versions. IPC-7351B is the most recent from IPC (at the time of writing).
I learned* there is no such thing as a “standard” 0603 (1608 metric) package outline for example. Instead, a 0603 footprint (aka ‘land pattern’) depends on desired board density and the used soldering technique in manufacturing (wave or reflow).
This was quite a revelation to me as I previously assumed those generic packages were standardized in a way (because they are so common).
Anyway, I accepted this reality of chaotic standards and I understand I had to choose one standard for myself to work with. I choose IPC as it is by far the most used in the industry.
My CAD software (Autodesk Eagle) offers a very practical package generator which satisfies IPC norms. It generates a land pattern for - and 3D model of - a desired package which is IPC compliant.
However now I'm faced with a dilemma. I discovered not only a “standard 0603” does not exist (which I'll solve by sticking to one standard), but apparently even a “standard LQFP48”, for example, does not exist!
However, all three datasheets specify a slightly different land pattern for what I thought was the exact same LQFP48. The difference is subtle, and only affects the extension (length) of the pad and pad width (0,25 - 0,27 - 0,30 respectively), but it is there!
So what is the rule of thumb now? What would experienced PCB designers choose if these components were in the same design?
option 1: Using 3x a different land pattern for what is actually described as the same package outline.
option 2: Use the IPC-7351 compliant LQFP48* for all three.
*in IPC terms this would be: QFP50P900X900X160-48
Since the differences are so subtle, I know both options would probably turn out just fine but what is the general rule here? What is ‘good practice’?