The Basics of PCB Component Placement

There is a nice beginner's overview of component placement in the Feb 2010 edition of Printed Circuit Design and Fab magazing: Component Layout in Placement Process

Some interesting points:

• 75% of soldering defects are related to paste dispensing
• To deposit solderpaste on a large area it is better to use multiple smaller slots than one large slot.
• BGAs near a board’s edge are hard to rework because the thermal mass will be different on the side nearest the edge.

One thing missing from this overview: Even low-speed digital traces can be susceptible to noise from the outside world. It is not only important to keep clock lines clear of sensitive analog lines. It is important to keep digital lines, even “non-critical” ones with low edge rates and clock speeds, clear of places where noise from induced currents outside the board could corrupt the digital lines. A low-speed digital trace that veers across a mote and travels over a chassis ground plane is at risk of picking up noise from the outside world.