Solving for EMC issues within the layout is as important as completing DRCs.
When it comes to design rule checks for PCB designs, some should be performed that are just as important as spacing rules. Strict adherence to basic PCB design rule checks, such as track to track, track to via, via to via, pad to track etc. – though necessary to avoid short circuits – only scratch the surface when trying to identify potential design flaws. I often see PCB designs that are completed based on this premise and wonder what else could be hiding in the design?
DRC rules covering the verification of min and max length of routed critical signals like clicks and strobes, as well as skew differences in multi-bit buses, are as important as metal spacing rules. If the minimal skew is not achieved, the PCB design will be scrapped just as easily as if shorts resulted in burning holes in the PCB during power-up.
Newer intelligent CAD output files reduce errors.
Manufacturing is all about taking data from the designer and delivering good working circuit boards. Well, it can be just data – as in full turnkey – or data plus some parts and or PCBs, as in a partial turnkey or a kitted job.
Regardless of whether parts and boards are sent, or if the EMS procures everything, your manufacturing partner needs good data, and a lot of it. That data are the difference between the working boards you want and need and a random jumble of expensive paperweights.
As an EMS, we need a bill of materials (BoM), the job specifications (which you give us by ordering and describing any special instructions on our website), and the CAD design files. Fab and assembly drawings are always a good idea, too. A little extra time spent on the files sent reduces risk, and that’s a very good thing.
Tips for avoiding EMI and simplifying debugging.
Power distribution on a PCB can come in a number of forms. The three most common methods are:
Route power and ground.
Use surface layer floods.
Use internal planes.
A user’s guide to clear communication of parts and intent.
A good portion of a quality build is simply the result of clear information. One of the more important pieces of information we deal with is the bill of materials, called “the BoM.”
The BoM is a list of all the components to be placed on the PCB. The file typically includes an index number, the number of times a specific component will be used on the board, the reference designator from the schematic, the component manufacturer, and the manufacturer’s part number.
If a specific component is used more than once – a common bypass capacitor, for example – it will still only take up one line in the BoM. One field in the BoM will list the number of times the component is used, and another field will list all the reference designators for that part number. In FIGURE 1, for example, line 5 in my BoM is a 0.1 microfarad, 10V capacitor.