Designer’s Notebook

John Burkhert

Why you should take the time to use the dimensioning tool.

One of the many hats worn by a board designer is that of draftsperson. Before settling into a position doing layout, I had a contract to create drawings on vellum – with a pencil! Before they turned me loose, the manager asked me to write my name and phone number on a piece of paper. That was all it took; get to work. Ever since seventh grade drafting class, my normal handwriting has been in all caps. We no longer need legible handwriting to land a job, but some of the things I learned at Cavro Scientific have stuck with me all these years.

Dimensions and tolerances. The electronic data alone are enough to fabricate a board most of the time. Whether it’s an omnibus file like IPC-2581 or a collection of Gerber and drill data, the hole size and locations are provided with the circuit pattern. Why take the time to use the dimensioning tool? Here’s why. Someone must inspect the PCB before it leaves the fabricator. Someone else inspects it on the way into the assembly factory. All the fab and assembly drawings are inspection documents.

Read more: I’m a PCB Designer. What Must I Know about Drafting?

John Burkhert

And why your library naming convention should be memorable.

As a designer who has put himself into the public eye, a lot of questions come my way. Several beginners have approached me with basic questions I can usually answer by sharing something I’ve already written. Sometimes I’ll end up writing a few paragraphs that eventually expand into a column to share with everyone. One gentleman, whom I will call Aakash, has leaned on me so many times I think he might be compiling a book. The messages pile up, as do the answers. Let’s get to one of those types of answers.

More than one person has asked about starting their first job going from the ground up. “How do I make all the parts I need for my first board?” The short answer is to build them one at a time. This is the internet age. This is the 21st Century. There must be a better way! It’s not that we’re impatient;  we just don’t have that kind of time. Software vendors know that, and the internet does too. The software installation comes with a bevy of common parts, but most boards go well beyond the generic SMD capacitors and resistors found in the default library.

Read more: Generating PCB Footprints for Your First Layout

John Burkhert

Lessons learned the hard way.

I still remember a day back in the late ’80s when an electrical engineer invited me into his office and showed me a CAD PCB layout on his monitor. How cool would it be to do that? Well, now I know. Pretty cool, but frustrating at times as well. Placing and routing are the meat and potatoes of PCB design. (If you don’t like “meat,” think of your own metaphor.) There are other things to do, but this is what holds it all together.

The basic framework is built around two disciplines: mechanical and electrical engineering. The two main features are the components and, of course, the board. An intelligent set of library parts is essential to getting the placement off to a good start. Over the years, schematic capture has shifted from the PCB designer’s hands to those of the EE.

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Read more: Place and Route: The Art of PCB Design

John Burkhert

Or why aspect ratio rules all.

The humble via comes in many flavors. By connecting one layer of a conductor pattern to another, vias have connected the world. My career has depended on them as part of the hardware I used to design for others to use. A foundational innovation in electronics brought plated through-holes to the masses. As a leap forward from wire-wrap technology, multilayer printed circuit boards put a “mainframe” in each of our pockets almost overnight.

From the first plated through-hole to the latest, the trend is to support higher-density interconnect. The key driver in plating holes is the aspect ratio, the hole’s width relative to its depth. For a through-hole, the depth is the thickness of the PCB. Most reputable fabricators can handle a 10:1 ratio, such that a common 0.062" board thickness will require a minimum finished hole size 0.006" (FIGURE 1).

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