Like most trades, there are organizations that publish standards and processes that help govern and provide guidance. Electronics is no different. The IPC (Institute for Printed Circuits) (http://ipc.prg/) produces a series of standards documents. Here, we’ll focus on IPC-7351 – Generic Requirements for Surface Mount Design and Land Pattern Standard. It can be purchased from their website by clicking on this link. As far as trade publications go, it’s modestly priced at only $160 for non-members so it won’t break the bank.
Even with the modest price, it isn’t entirely necessary to purchase. Just like trace widths and the IPC-2221 standard, there’s a plethora of online calculators available. One source that I rather like are the ones provided by PCB Libraries. After signing-up they provide three really useful downloadable spreadsheets to handle this for you.
IPC-7351 – SMD Reference Calculator
IPC-7351 – Through-hole Reference Calculator
IPC-7351 Solder Joint Goal Tables
As a walk-through on how to use these, let’s use your standard 0402 resistor. Specifically, the AC0402FR-071KL.
The cells from the first collumn can be found in the datasheet linked above, while the cells highlighted in orange can be found in the Solder Joint Goal Table linked above from PCB Libraries. Highlighted in teal on the right are the resulting dimensions of the pads and their displacement.
These values applied to ECAD with an accurate 0402 resistor modeled from their datasheet produces the following:
