Aristotle said “The whole is greater than the sum of its parts.” Mathematically speaking, this would be nonsense. But fully functioning PCB assemblies are only possible because of the “sum of its parts”. If any “part” of the assembly, a component, design aspect, bare board, test or assembly process, were not optimum or correct, then the assembly would be less than the “whole”, or what it should be. A good PCB part library is integral to an efficient design process.
These footprints provide the basis for connecting or soldering a part to the circuit (wiring) board. Plated holes and SMT pads are interconnected per a netlist to create circuits. Documentation provides visual indicators and installation details of how each part should be assembled to the board.
Why is an accurate part library fundamental? One single part may be used multiple times across many board designs. If just one part were not designed well, every board design could be adversely affected. How can board assemblies be affected?
- Misplaced pads or pins of incorrect footprints can create assembly problems, and can require time consuming manual intervention to correct.
- Pin definition errors can prevent a circuit from functioning properly, and could lead to catastrophic failure.
- Poor documentation or part details can cause delays in delivery or improper circuit function.
- Less than optimum pad design can cause excess solder use or unreliable component soldering/mounting.
- Engineers and technicians may spend an large amount of time troubleshooting a circuit, delaying product introduction.
Obviously, there are other items that can affect board quality. But a poorly defined PCB library can cause unnecessary board revisions, increase assembly costs, and decrease reliability.
Therefore, a good PCB parts library is a fundamental element of successful board assembly. Valuable resources would not be used for long design cycles involving multiple board iterations. Costs can be better anticipated and controlled. On-time product release means greater market share. (Even social interactions can be more pleasant!)
Bottom line: Time and resources spent in ensuring an accurate parts library are well worth the effort.