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.
For emergency respins, bureaucracy sometimes prohibits on-the-fly project completion, especially when colleagues refuse to revisit schematics.
Determining your optimum geometry, plus two methods for providing data to the fabricator.
Controlling impedance (resistance) is almost a given with today’s technology. One day we are adding a wireless option to a common object and calling it the Internet of Things. The next day we’re simply keeping up with the competition on processing the code. The trend is toward a greater percentage of the connections falling under the domain of impedance control.
Controlled impedance has two main branches: Single-ended transmission lines are the backbone of RF technology, while differential pairs do the heavy lifting for digital circuits. We’ll start with the single-ended lines. They have a start and an end point. The signal is sent one way on the transmission line, and the circuit is completed over the adjacent ground plane.
The main factor influencing impedance is the width of the trace relative to the thickness of the dielectric material between the trace and the ground plane – or planes – used as a reference. What is a reference? It is usually a metal plane with zero volts – “ground” but can have a few volts of its own, either positive or negative relative to what’s happening on the trace itself.