Aligning signals to attain perfect synchronicity.
Clocks are essential gatekeepers of the digital domain. Setting the pace for all that follows the clock can be a single trace or a partnership of two traces that carry complementary signals. Either way, the function of a clock is to switch from high (a logical 1) to low (0) up and down continuously; on, off, on, off, all day long. Signals controlled by the clock switch only when activated by the code, meaning that other signals do not change their state with every cycle of the clock.
Communicating the design intent, clearly and concisely.
The CAD system can do a lot for you; then you’re on your own. Eyeballing the layers two or three at a time will help you find the hidden traps. A camera-ready board is just the beginning. Documenting the PCB requirements with dimensions and other details, including hole chart(s), stack up diagram(s), a list of intentional shorts, etc., puts the necessary guardrails around the fabrication and assembly.
Fabrication notes will change with the technology used for the PCB. The general thrust of this list of example notes is for a multilayer board targeted for consumer electronics with components on both sides and controlled impedance on inner- and outer layers.
Grounding and routing tips for sensitive parts.
Years ago, I set out to become a world-famous PCB designer. The journey, however, took much longer than that. Starting near the beginning, the second lesson I learned about electronics came on the first day on the job in electronics. I bet you’re wondering what I did in electronics on my first day.
My contribution was to put completed printed circuit board assemblies into pink bubble wrap bags. The bags were sealed with resealable ESD warning stickers and placed in individual boxes. Labels on the boxes had blanks for the information, which was copied from the board to the label. Completed sets of eight boxed boards were again boxed in a larger box, which was labeled with the content part numbers, revisions and so on.
As an aside, the next stop for the boxes was the shipping department and, finally, phone company offices around the country. Called offices, they were more of a precursor to today’s data centers. The build-out was a result of the US government forcing the phone company to break itself into regional businesses.
Why a tooling hole remains the answer for an end-to-end process.
Technology marches on and the result is a decreased margin for error. Even the language must adapt as mils give way to microns, because one thousandth of an inch is too coarse a measure for modern PCB geometry. As traces and spaces shrink to accommodate the latest chips, the onus is on fabricators and assemblers to achieve greater precision in all aspects of manufacturing.
Where does it end? Could Intel's new 2nm fab be the last stop? It seems so but I would not bet on it. Somewhere, somebody is working on angstrom class devices. Why not? Well, a single atom of copper comes in around 0.23nm, so Intel is depositing about eight or nine atoms of copper across the width of a connection. To quote Carl Sagan, “Billions and billions,” but we’re scaling down rather than up.